Patent Application
20250006928
The disclosure relates to electrode active materials, electrodes, electrochemical devices, modules, and methods.
Current electric appliances demonstrate a tendency to have a reduced weight and a smaller size, which leads to development of electrochemical devices such as lithium-ion secondary batteries having a high energy density. Lithium-ion secondary batteries typically contain a lithium-containing metal oxide (e.g., lithium cobalt oxide) in the positive electrode and a carbon material (e.g., graphite) in the negative electrode, and are charged and discharged using lithium ions (Li+) as charge carriers.
Examples of electrochemical devices also include fluoride-ion batteries in which fluoride ions (F−) are used as charge carriers. Fluoride-ion batteries are characteristically high-voltage batteries. Commonly used fluoride-ion batteries are primary batteries containing graphite fluoride in the positive electrode and a lithium metal in the negative electrode. Use of fluoride-ion batteries as secondary batteries are now considered (see Patent Literature documents 1 and 2, for example).
The disclosure relates to an electrode active material containing a carbon material, wherein the electrode active material is configured such that: during discharge, a metal fluoride is generated; and during charge, a fluoride ion is desorbed from the metal fluoride and reacts with the carbon material to form a C—F bond.
The disclosure can provide an electrode active material, an electrode, an electrochemical device, a module, and a method, each utilizing a fluoride ion reaction to improve the charge-discharge cycle performance.
The disclosure will be specifically described hereinbelow.
The disclosure relates to an electrode active material (hereafter, also referred to as “first electrode active material of the disclosure”) containing a carbon material, wherein the electrode active material is configured such that: during discharge, a metal fluoride is generated; and during charge, a fluoride ion is desorbed from the metal fluoride and inserted into the carbon material.
The disclosure also relates to an electrode active material (hereafter, also referred to as “second electrode active material of the disclosure”) containing a carbon material and a metal fluoride in a discharged state; and a fluoride ion inserted into the carbon material in a charged state.
In a secondary battery utilizing a rocking chair-type reaction, where fluoride ions are exchanged between the positive electrode and the negative electrode, as disclosed in Patent Literature 2, the electrolyte solution needs to have a high fluoride ion concentration. Since a fluoride salt is typically hardly soluble, additives (anion receptor, cation receptor) are used in the secondary battery of Patent Literature 2 to increase the solubility of the fluoride ion, thereby promoting generation of fluoride ions. Still, the solubility of a fluoride salt is considered insufficient, leaving room for improvement in the cycle performance as a secondary battery.
In a secondary battery utilizing a rocking chair-type reaction, where fluoride ions are exchanged between the positive electrode and the negative electrode, an electrode material capable of occluding and desorbing fluoride ions needs to be used for both the positive electrode and the negative electrode. However, such an electrode material is limited, limiting the range of battery designs.
In the case of the first electrode active material of the disclosure, a metal fluoride is generated on the electrode during discharge. During charge, a reaction (conversion reaction) where fluoride ions are desorbed from the metal fluoride occurs, and then a reaction (insertion reaction) where the fluoride ions are inserted into the carbon material occurs. As a result, a C—F bond is formed between the carbon material and the fluoride ions, thereby generating carbon fluoride or the like. Occurrence of such an insertion reaction after a conversion reaction can improve the charge-discharge cycle performance, compared with that of the rocking chair-type secondary battery described above.
The second electrode active material of the disclosure is an electrode active material in which the above-described insertion reaction after the conversion reaction occurs and is described in different wording from the first electrode active material of the disclosure.
The first electrode active material of the disclosure and the second electrode active material of the disclosure are also collectively referred to as “electrode active material of the disclosure”.
As shown in Experiment 1 described later, the capacity was maintained to some extent after the 10th cycle at an operating voltage of 5 V. At an operating voltage of 4.8 V, however, the capacity was obtained little after the 10th cycle. This suggests that the above-described insertion reaction after the conversion reaction does not occur at a voltage of 4.8 V or lower.
In the examples of Patent Literature 1 where the operating voltage is 4.8 V, the above-described insertion reaction after the conversion reaction presumably does not occur as in the comparative example in Experiment 1.
In Example 2 of Patent Literature 2, an anion receptor and a cation receptor are used as additives.
As the anion receptor, boron-based compounds having any of the structures represented by AR1 to AR3 are shown. As shown in the comparative example of Experiment 2 described later, when any of these compounds are used as an electrolyte solution material, good cycle performance cannot be achieved even at an operating voltage of 5 V or higher. In the case of using the anion receptor, the anion receptor that coordinates to the fluoride ion of the fluoride salt promotes the formation of fluoride ions and the reaction between fluoride ions and active materials of both positive and negative electrodes preferentially proceeds, where the above-described insertion reaction after the conversion reaction at a single electrode presumably does not occur.
As the cation receptor, compounds such as crown ethers are shown. In the case of using any of such cation receptors, the cation receptor that coordinates to the metal ion of the fluoride salt promotes the formation of fluoride ions and the reaction between fluoride ions and active materials of both of the positive and negative electrodes preferentially proceeds, where the above-described insertion reaction after the conversion reaction at a single electrode presumably does not occur as in the case of using the anion receptor.
In Example 1 of Patent Literature 2, no anion receptor or cation receptor is used and the battery is charged to 5.2 V. As described in [0015] in Patent Literature 2, electrode active materials need to meet certain requirements for the reaction between fluoride ions and active materials of both of the positive and negative electrodes (rocking chair-type reaction using fluoride ions). Though the specific reason is not clear, the use of the electrode active material of the disclosure presumably causes a reaction of a different type from that of Patent Literature 2, i.e., an insertion reaction after a conversion reaction at a single electrode.
In the case of using the electrode active material of the disclosure, a metal fluoride is typically generated on the surface of the electrode containing the electrode active material of the disclosure. A metal source in the reaction for generating the metal fluoride is not limited, and may be an electrolyte salt or the other electrode.
Examples of the metal element contained in the metal fluoride include Li, Na, K, Rb, Cs, Ca, Mg, Al, Zn, La, Eu, Si, Ge, Sn, In, V, Cd, Cr, Fe, Ga, Ti, Nb, Mn, Yb, Zr, Sm, Ce, and Pb. Among these, the metal element may include at least one selected from the group consisting of Li, Na, K, Rb, Cs, Ca, Mg, Al, and Zn. Particularly preferred may be Li and/or Na, and most preferred may be Li. Specifically, the metal fluoride may be lithium fluoride.
The electrode active material of the disclosure may be any material that contains a carbon material and may cause the above-described insertion reaction after the conversion reaction, and may be a material configured such that a fluoride ion is desorbed from the metal fluoride during charge and reacts with the carbon material to generate carbon fluoride, i.e., a material where carbon fluoride is present in a charged state. In a discharged state, the amount of carbon fluoride is typically smaller than that in a charged state. In a discharged state, carbon fluoride may or may not be present. As a material satisfying such a condition, a carbon fluoride (may be graphite fluoride) can be used, for example.
A suitable example of the carbon fluoride (graphite fluoride) is a compound represented by CFx. x may be 0.3 to 0.9. The lower limit may be 0.4 and the upper limit may be 0.8.
The electrode active material of the disclosure may have a high fluorine concentration on the surface. This presumably promotes occurrence of the above-described insertion reaction after the conversion reaction.
The fluorine concentration on the surface can be measured by XPS with argon ion etching. The electrode active material of the disclosure may have a surface fluorine index I of 0.30 or lower, 0.20 or lower, or 0.10 or lower. The surface fluorine index I is a value represented by (peak intensity after 100 seconds)/(peak intensity after 0 seconds) in relation to the change over time of the peak assigned to CF2 in C1s with argon ion etching (10 mA, 0.5 kV), for example. The lower limit thereof may be, but not limited to, 0.01 or more. The peak assigned to CF2 moves within the range from 295 eV to 290 eV, depending on the type of the carbon material as a raw material and the degree of sputtering progress. The peak intensity of the peak assigned to CF2 herein is the peak top value when the peak top is distinct or the maximum value within the above range when the peak top is not distinct.
The fluorine concentration on the surface may be increased by any method. For example, it may be increased by adjustment of the conditions of the reaction between the carbon material as a raw material and fluorine gas in synthesis of the electrode active material, including a shorter reaction time (100 hours or shorter), a higher concentration of fluorine gas to be circulated (50% or higher), and a higher reaction temperature (300° C. or higher). These conditions may be employed alone or in combination.
The electrode active material of the disclosure may have a large specific surface area. This presumably promotes occurrence of the above-described insertion reaction after the conversion reaction. Since too large a specific surface area is likely to cause a side reaction, the specific surface area may fall within the following range.
The electrode active material of the disclosure may have a specific surface area of 100 m2/g or larger, 150 m2/g or larger, or 300 m2/g or larger, while 3000 m2/g or smaller, 2000 m2/g or smaller, 1000 m2/g or smaller, or 500 m2/g or smaller.
The specific surface area is a value obtained through analysis by the BET method based on nitrogen gas adsorption.
The specific surface area may be increased by any method. An exemplary method is the use of a carbon material with a large specific surface area, as a raw material, in synthesis of the electrode active material. Specifically, the carbon material as a raw material may have a specific surface area of 30 m2/g or larger, 100 m2/g or larger, or 200 m2/g or larger, while 3000 m2/g or smaller, 2000 m2/g or smaller, 1000 m2/g or smaller, or 500 m2/g or smaller.
When the electrode active material of the disclosure is a carbon fluoride represented by CFx, the specific surface area of the carbon fluoride tends to easily fall within the range described in the previous paragraph, provided that x is within the range described above.
Examples of the particle shape of the electrode active material of the disclosure include conventionally used ones such as a lumpy shape, a polyhedral shape, a spherical shape, an ellipsoidal shape, a plate shape, an acicular shape, a columnar shape, a fibrous shape, and a tubular shape. The primary particles may agglomerate to form secondary particles. The electrode active material particles in the fibrous or tubular shape have too large a specific surface area, which is likely to cause a side reaction other than the insertion reaction after the conversion reaction. The shape may be therefore not a fibrous or tubular shape, and may be a spherical shape.
The form of the electrode active material of the disclosure described in paragraphs [0026] to [0027] may be achieved in a state before charge and discharge (raw material state (state 1)) and/or in a state after being incorporated into a battery and subjected to charge-discharge cycles (state 2). More specifically, the form may be achieved either in state 1 or in state 2, or achieved both in state 1 and in state 2.
State 2 may be any of after charge, after discharge, during charge and discharge.
One type of the electrode active material of the disclosure may be used alone, or two or more types thereof may be used in combination.
The disclosure also relates to an electrode containing the electrode active material of the disclosure.
The electrode of the disclosure is suitably usable as a positive electrode.
The positive electrode includes a positive electrode active material layer containing a positive electrode active material and a current collector.
The positive electrode active material layer contains a positive electrode mixture containing a positive electrode active material.
The amount of the electrode active material of the disclosure may be 50 to 99.5% by mass of the positive electrode mixture. The lower limit of the amount may be 80% by mass and the upper limit may be 99% by mass. The amount of the electrode active material of the disclosure in the electrode active material layer may be 80% by mass or more, 82% by mass or more, or 84% by mass or more. The upper limit of the amount may be 99% by mass or less, or 98% by mass or less. Too small an amount of the electrode active material may lead to an insufficient electric capacity. In contrast, too large an amount thereof may lead to insufficient strength of the electrode. In order to achieve a high battery capacity, the amount may be 50 to 99.5% by mass, or 80 to 99% by mass, of the positive electrode mixture. The amount of the electrode active material of the disclosure in the positive electrode active material layer may be 80% by mass or more, 82% by mass or more, or 84% by mass or more. The upper limit of the amount may be 99% by mass or less, or 98% by mass or less. Too small an amount of the electrode active material may lead to an insufficient electric capacity. In contrast, too large an amount thereof may lead to insufficient strength of the positive electrode.
The positive electrode mixture may further contain a positive electrode active material other than the electrode active material of the disclosure.
Examples of the positive electrode active material include high-specific-surface-area materials that can provide an electric double layer capacity and materials that can electrochemically occlude and release lithium ions. Specific examples thereof include lithium-containing transition metal complex oxides, lithium-containing transition metal phosphoric acid compounds, sulfides (sulfur-based materials), and conductive polymers. Preferred among these may be lithium-containing transition metal complex oxides and lithium-containing transition metal phosphoric acid compounds. Particularly preferred may be a lithium-containing transition metal complex oxide that generates high voltage.
The positive electrode mixture may further contain a binder, a thickening agent, and a conductive material.
The binder may be any material that is safe against a solvent to be used in production of the electrode and the electrolyte solution. Examples thereof include resin polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, aromatic polyamide, chitosan, alginic acid, polyacrylic acid, polyimide, cellulose, and nitro cellulose; rubbery polymers such as SBR (styrene-butadiene rubber), isoprene rubber, butadiene rubber, fluoroelastomers, NBR (acrylonitrile-butadiene rubber), and ethylene-propylene rubber; styrene-butadiene-styrene block copolymers and hydrogenated products thereof; thermoplastic elastomeric polymers such as EPDM (ethylene-propylene-diene terpolymers), styrene-ethylene-butadiene-styrene copolymers, and styrene-isoprene-styrene block copolymers and hydrogenated products thereof; soft resin polymers such as syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymers, and propylene-α-olefin copolymers; fluoropolymers such as polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride copolymers, and tetrafluoroethylene-ethylene copolymers; and polymer compositions having ion conductivity of alkali metal ions (especially, lithium ions). One of these may be used alone or two or more thereof may be used in any combination at any ratio.
The amount of the binder, which is expressed as the proportion of the binder in the positive electrode active material layer, may be 0.1% by mass or more, 1% by mass or more, or 1.2% by mass or more. The proportion may be 50% by mass or less, 40% by mass or less, 30% by mass or less, or 10% by mass or less. Too low a proportion of the binder may fail to sufficiently hold the positive electrode active material and cause insufficient mechanical strength of the positive electrode, impairing the battery performance such as cycle characteristics. In contrast, too high a proportion thereof may cause reduction in battery capacity and conductivity.
Examples of the thickening agent include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, oxidized starch, monostarch phosphate, casein, polyvinylpyrrolidone, and salts thereof. One of these agents may be used alone or two or more thereof may be used in any combination at any ratio.
The proportion of the thickening agent relative to the active material may be 0.1% by mass or higher, 0.2% by mass or higher, or 0.3% by mass or higher, while 5% by mass or lower, 3% by mass or lower, or 2% by mass or lower. The thickening agent at a proportion lower than the above range may cause significantly poor easiness of application. The thickening agent at a proportion higher than the above range may cause a low proportion of the active material in the positive electrode active material layer, resulting in a low capacity of the battery and high resistance between the positive electrode active materials.
The conductive material may be any known conductive material. Specific examples thereof include metal materials such as copper, nickel, and gold, and carbon materials such as graphite, including natural graphite and artificial graphite, carbon black, including acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal black, and amorphous carbon, including needle coke, carbon nanotube, fullerene, and VGCF. One of these materials may be used alone or two or more thereof may be used in any combination at any ratio. The conductive material may be used in an amount of 0.01% by mass or more, 0.1% by mass or more, or 1% by mass or more, while 50% by mass or less, 30% by mass or less, or 15% by mass or less, in the positive electrode active material layer. The conductive material in an amount less than the above range may cause insufficient conductivity. In contrast, conductive material in an amount more than the above range may cause a low battery capacity.
The solvent for forming slurry may be any solvent that can dissolve or disperse therein the positive electrode active material, the conductive material, and the binder, as well as a thickening agent used as appropriate. The solvent may be either an aqueous solvent or an organic solvent. Examples of the aqueous solvent include water and solvent mixtures of an alcohol and water. Examples of the organic medium include aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, xylene, and methyl naphthalene; heterocyclic compounds such as quinoline and pyridine; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as methyl acetate and methyl acrylate; amines such as diethylene triamine and N,N-dimethylaminopropylamine; ethers such as diethyl ether, propylene oxide, and tetrahydrofuran (THF); amides such as N-methylpyrrolidone (NMP), N-butylpyrrolidone (NBP), 3-methoxy-N,N-dimethylpropionamide, dimethyl formamide, and dimethyl acetamide; and aprotic polar solvents such as hexamethyl phospharamide and dimethyl sulfoxide.
Examples of the material of the current collector for a positive electrode include metal materials such as aluminum, titanium, tantalum, stainless steel, and nickel, and alloys thereof; and carbon materials such as carbon cloth and carbon paper. Preferred may be any metal material, particularly aluminum or an alloy thereof.
In the case of a metal material, the current collector may be in the form of metal foil, metal cylinder, metal coil, metal plate, metal film, expanded metal, punched metal, metal foam, or the like. In the case of a carbon material, it may be in the form of carbon plate, carbon film, carbon cylinder, or the like. Preferred among these may be a metal film. The film may be in the form of mesh, as appropriate. The film may have any thickness, and the thickness may be 1 μm or greater, 3 μm or greater, or 5 μm or greater, while 1 mm or smaller, 100 μm or smaller, or 50 μm or smaller. The film having a thickness smaller than the above range may have insufficient strength as a current collector. In contrast, the film having a thickness greater than the above range may have poor handleability.
In order to reduce the electric contact resistance between the current collector and the positive electrode active material layer, the current collector also may have a conductive aid applied on the surface thereof. Examples of the conductive aid include carbon and noble metals such as gold, platinum, and silver.
The ratio between the thicknesses of the current collector and the positive electrode active material layer may be any value, and the ratio {(thickness of positive electrode active material layer on one side immediately before injection of electrolyte solution)/(thickness of current collector)} may be 20 or lower, 15 or lower, or 10 or lower. The ratio may be 0.5 or higher, 0.8 or higher, or 1 or higher. The current collector and the positive electrode active material layer showing a ratio higher than the above range may cause the current collector to generate heat due to Joule heating during high-current-density charge and discharge. The current collector and the positive electrode active material layer showing a ratio lower than the above range may cause an increased ratio by volume of the current collector to the positive electrode active material, reducing the battery capacity.
The positive electrode may be produced by a usual method. An example of the production method is a method in which the positive electrode active material is mixed with the aforementioned binder, thickening agent, conductive material, solvent, and other components to form a slurry-like positive electrode mixture, and then this mixture is applied to a current collector, dried, and pressed so as to be densified.
The densification may be achieved using a manual press or a roll press, for example. The density of the positive electrode active material layer may be 1.0 g/cm3 or higher, 1.3 g/cm3 or higher, or 1.5 g/cm3 or higher, while 5.0 g/cm3 or lower, 3.0 g/cm3 or lower, or 2.5 g/cm3 or lower. The positive electrode active material layer having a density higher than the above range may cause low permeability of the electrolyte solution toward the vicinity of the interface between the current collector and the active material, and poor charge and discharge characteristics particularly at a high current density, failing to provide high output. The positive electrode active material layer having a density lower than the above range may cause poor conductivity between the active materials and increase the battery resistance, failing to provide high output.
The disclosure also relates to an electrochemical device including the electrode of the disclosure.
The electrochemical device of the disclosure may include components such as a positive electrode, a negative electrode, an electrolyte, and a separator. Specifically, the electrochemical device of the disclosure may be a secondary battery including these components.
In a rocking chair-type secondary battery in which fluoride ions are exchanged between the positive electrode and the negative electrode, as disclosed in Patent Literature 2, both the positive electrode and the negative electrode react with fluoride ions during charge and discharge to form a bond with a fluoride ion. The fluoride ion concentration of the electrolyte solution therefore needs to be high. However, it is not easy to increase the fluoride ion concentration as a fluoride salt is hardly soluble.
In contrast, the electrochemical device of the disclosure can be a reserve-type secondary battery in which a reactant is stored in the electrolyte solution and reacts with another reactant in the vicinity of the electrode, because the electrochemical device of the disclosure utilizes the above-described insertion reaction after the conversion reaction at the electrode of the disclosure for charge and discharge. This enables sufficient charge and discharge without increasing the fluoride ion concentration of the electrolyte solution as in the case of the rocking chair-type secondary battery described above.
When the electrochemical device of the disclosure is provided as a reserve-type secondary battery, the counter electrode of the disclosure may be an electrode that forms no bond with a fluoride ion during charge and discharge. An electrode described later as a negative electrode is suitably usable as such an electrode.
A suitable configuration of the electrochemical device of the disclosure when it is provided as a reserve-type secondary battery is more specifically described hereinbelow.
The positive electrode in the electrochemical device of the disclosure may be the electrode of the disclosure described above.
The negative electrode includes a negative electrode active material layer containing a negative electrode active material and a current collector.
The negative electrode active material layer contains a negative electrode mixture containing a negative electrode active material.
A lithium storage material can be used as the negative electrode active material. More specifically, examples thereof include carbonaceous materials that can occlude and release lithium such as pyrolysates of organic matter under various pyrolysis conditions, artificial graphite, and natural graphite; metal oxide materials that can occlude and release lithium such as tin oxide and silicon oxide; lithium metals; various lithium alloys; and lithium-containing metal complex oxide materials. Two or more of these negative electrode active materials may be used in admixture with each other.
The carbonaceous material that can occlude and release lithium may be artificial graphite produced by high-temperature treatment of easily graphitizable pitch from various materials, purified natural graphite, or a material obtained by surface treatment on such graphite with pitch or other organic matter and then carbonization of the surface-treated graphite. In order to achieve a good balance between the initial irreversible capacity and the high-current-density charge and discharge characteristics, the carbonaceous material may be selected from carbonaceous materials obtained by heat-treating natural graphite, artificial graphite, artificial carbonaceous substances, or artificial graphite substances at 400° C. to 3200° C. once or more; carbonaceous materials which allow the negative electrode active material layer to include at least two or more carbonaceous matters having different crystallinities and/or have an interface between the carbonaceous matters having the different crystallinities; and carbonaceous materials which allow the negative electrode active material layer to have an interface between at least two or more carbonaceous matters having different orientations. One of these carbonaceous materials may be used alone or two or more thereof may be used in any combination at any ratio.
Examples of the carbonaceous materials obtained by heat-treating artificial carbonaceous substances or artificial graphite substances at 400° C. to 3200° C. once or more include coal-based coke, petroleum-based coke, coal-based pitch, petroleum-based pitch, and those prepared by oxidizing these pitches; needle coke, pitch coke, and carbon materials prepared by partially graphitizing these cokes; pyrolysates of organic matter such as furnace black, acetylene black, and pitch-based carbon fibers; carbonizable organic matter and carbides thereof; and solutions prepared by dissolving carbonizable organic matter in a low-molecular-weight organic solvent such as benzene, toluene, xylene, quinoline, or n-hexane, and carbides thereof.
The metal material (excluding lithium-titanium complex oxides) to be used as the negative electrode active material may be any compound that can occlude and release lithium, and examples thereof include simple lithium, simple metals and alloys that constitute lithium alloys, and oxides, carbides, nitrides, silicides, sulfides, and phosphides thereof. The simple metals and alloys constituting lithium alloys may be materials containing any of metal and semi-metal elements in Groups 13 and 14, or simple metal of aluminum, silicon, and tin (hereinafter, referred to as “specific metal elements”), and alloys and compounds containing any of these atoms. One of these materials may be used alone or two or more thereof may be used in any combination at any ratio.
Examples of the negative electrode active material containing at least one atom selected from the specific metal elements include simple metal of any one specific metal element, alloys of two or more specific metal elements, alloys of one or two or more specific metal elements and one or two or more other metal elements, compounds containing one or two or more specific metal elements, and composite compounds such as oxides, carbides, nitrides, silicides, sulfides, and phosphides of the compounds. Such a simple metal, alloy, or metal compound used as the negative electrode active material can lead to a high-capacity battery.
Examples thereof further include compounds in which any of the above composite compounds are complexly bonded with several elements such as simple metals, alloys, and nonmetal elements. Specifically, in the case of silicon or tin, for example, an alloy of this element and a metal that does not serve as a negative electrode may be used. In the case of tin, for example, a composite compound including a combination of 5 or 6 elements, including tin, a metal (excluding silicon) that serves as a negative electrode, a metal that does not serve as a negative electrode, and a nonmetal element, may be used.
Specific examples thereof include simple Si, SiB4, SiB6, Mg2Si, Ni2Si, TiSi2, MoSi2, CoSi2, NiSi2, CaSi2, CrSi2, Cu6Si, FeSi2, MnSi2, NbSi2, TaSi2, VSi2, WSi2, ZnSi2, SiC, Si3N4, Si2N2O, SiOv (0<v≤2), LiSiO, simple tin, SnSiO3, LiSnO, Mg2Sn, and SnOw (0<w≤2).
Examples thereof further include composite materials of Si or Sn used as a first constitutional element, and second and third constitutional elements. The second constitutional element is at least one selected from the group consisting of cobalt, iron, magnesium, titanium, vanadium, chromium, manganese, nickel, copper, zinc, gallium, and zirconium, for example. The third constitutional element is at least one selected from the group consisting of boron, carbon, aluminum, and phosphorus, for example.
In order to achieve a high battery capacity and excellent battery characteristics, the metal material may be simple silicon or tin (which may contain trace impurities), SiOv (0<v≤2), SnOw (0≤w≤2), a Si—Co—C composite material, a Si—Ni—C composite material, a Sn—Co—C composite material, or a Sn—Ni—C composite material.
The lithium-containing metal complex oxide material to be used as the negative electrode active material may be any material that can occlude and release lithium. In order to achieve good high-current-density charge and discharge characteristics, materials containing titanium and lithium may be preferred, lithium-containing metal complex oxide materials containing titanium may be more preferred, and complex oxides of lithium and titanium (hereinafter, abbreviated as “lithium titanium complex oxides”) may be still more preferred. In other words, use of a spinel-structured lithium titanium complex oxide in the negative electrode active material for an electrolyte battery may be particularly preferred because this can markedly reduce the output resistance.
Preferred examples of the lithium titanium complex oxides may include compounds represented by the following formula:
LixTiyMzO4
wherein M is at least one element selected from the group consisting of Na, K, Co, Al, Fe, Ti, Mg, Cr, Ga, Cu, Zn, and Nb.
In order to achieve a good balance of the battery performance, particularly preferred among the above compositions may be those satisfying any of the following:
Particularly preferred representative composition of the compound may be Li4/3Ti4/3O4 corresponding to the composition (i), Li1Ti2O4 corresponding to the composition (ii), and Li4/5Ti11/5O4 corresponding to the composition (iii). Preferred examples of the structure satisfying Z≠0 may include Li4/3Ti4/3Al1/3O4.
The negative electrode active material may be a lithium storage material. It may include at least one selected from graphite, tin, silicon, silicon oxide, lithium, and a lithium-containing metal complex oxide, still more preferably at least one selected from graphite, tin, silicon, silicon oxide, and lithium.
The negative electrode mixture may further contain a binder, a thickening agent, and a conductive material.
Examples of the binder include the same binders as those mentioned for the positive electrode. The proportion of the binder may be 0.1% by mass or more, 0.5% by mass or more, or 0.6% by mass or more, while 20% by mass or less, 15% by mass or less, 10% by mass or less, or 8% by mass or less, relative to the negative electrode active material. The binder at a proportion relative to the negative electrode active material higher than the above range may lead to an increased proportion of the binder which fails to contribute to the battery capacity, causing a low battery capacity. The binder at a proportion lower than the above range may cause lowered strength of the negative electrode.
In particular, in the case of using a rubbery polymer typified by SBR as a main component, the proportion of the binder may be 0.1% by mass or more, 0.5% by mass or more, or 0.6% by mass or more, while 5% by mass or less, 3% by mass or less, or 2% by mass or less, relative to the negative electrode active material. In the case of using a fluoropolymer typified by polyvinylidene fluoride as a main component, the proportion of the binder may be 1% by mass or more, 2% by mass or more, or 3% by mass or more, while 15% by mass or less, 10% by mass or less, or 8% by mass or less, relative to the negative electrode active material.
Examples of the thickening agent include the same thickening agents as those mentioned for the positive electrode. The proportion of the thickening agent may be 0.1% by mass or more, 0.5% by mass or more, or 0.6% by mass or more, while 5% by mass or less, 3% by mass or less, or 2% by mass or less, relative to the negative electrode active material. The thickening agent at a proportion relative to the negative electrode active material lower than the above range may cause significantly poor easiness of application. The thickening agent at a proportion higher than the above range may cause a small proportion of the negative electrode active material in the negative electrode active material layer, resulting in a low capacity of the battery and high resistance between the negative electrode active materials.
Examples of the conductive material of the negative electrode include metal materials such as copper and nickel; and carbon materials such as graphite and carbon black.
The solvent for forming slurry may be any solvent that can dissolve or disperse the negative electrode active material and the binder, as well as a thickening agent and a conductive material used as appropriate. The solvent may be either an aqueous solvent or an organic solvent.
Examples of the aqueous solvent include water and alcohols. Examples of the organic solvent include N-methylpyrrolidone (NMP), N-butylpyrrolidone (NBP), 3-methoxy-N,N-dimethylpropionamide, dimethyl formamide, dimethyl acetamide, methyl ethyl ketone, cyclohexanone, methyl acetate, methyl acrylate, diethyl triamine, N,N-dimethyl aminopropyl amine, tetrahydrofuran (THF), toluene, acetone, diethyl ether, dimethyl acetamide, hexamethyl phospharamide, dimethyl sulfoxide, benzene, xylene, quinoline, pyridine, methyl naphthalene, and hexane.
Examples of the material of the current collector for a negative electrode include copper, nickel, and stainless steel. In order to easily process the material into a film and to minimize the cost, copper foil may be preferred.
The current collector may have a thickness of 1 μm or greater, or 5 μm or greater, while 100 μm or smaller, or 50 μm or smaller. Too thick a negative electrode current collector may cause an excessive reduction in capacity of the whole battery, while too thin a current collector may be difficult to handle.
The negative electrode may be produced by a usual method. An example of the production method is a method in which the negative electrode material is mixed with the aforementioned binder, thickening agent, conductive material, solvent, and other components to form a slurry-like mixture, and then this mixture is applied to a current collector, dried, and pressed so as to be densified. In the case of using an alloyed material, a thin film layer containing the above negative electrode active material (negative electrode active material layer) may be produced by vapor deposition, sputtering, plating, or the like.
The electrode formed from the negative electrode active material may have any structure. The negative electrode active material existing on the current collector may have a density of 1 g/cm−3 or higher, 1.2 g/cm−3 or higher, or 1.3 g/cm−3 or higher, while 2.2 g/cm−3 or lower, 2.1 g/cm−3 or lower, 2.0 g/cm−3 or lower, or 1.9 g/cm−3 or lower. The negative electrode active material existing on the current collector having a density higher than the above range may cause destruction of the negative electrode active material particles, resulting in a high initial irreversible capacity and poor high-current-density charge and discharge characteristics due to reduction in permeability of the electrolyte solution toward the vicinity of the interface between the current collector and the negative electrode active material. The negative electrode active material having a density below the above range may cause poor conductivity between the negative electrode active materials, high battery resistance, and a low capacity per unit volume.
The thickness of the negative electrode plate is a design matter in accordance with the positive electrode plate to be used, and may be any value. The thickness of the mixture layer excluding the thickness of the base metal foil may be 15 μm or greater, 20 μm or greater, or 30 μm or greater, while 300 μm or smaller, 280 μm or smaller, or 250 μm or smaller.
To a surface of the negative electrode plate may be attached a substance having a composition different from the negative electrode plate. Examples of the substance attached to the surface include oxides such as aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, and bismuth oxide; sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate; and carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate.
The electrolyte may be either an electrolyte solution containing a solvent and an electrolyte salt or a solid electrolyte.
The solvent may include at least one selected from the group consisting of a carbonate and a carboxylate.
Use of a fluoride of any of these as the solvent provides a fluorine electrolyte solution. Use of such a fluorine electrolyte solution in a fluoride ion battery characterized by high voltage allows maintenance of better cycle characteristics.
The carbonate may be either a cyclic carbonate or an acyclic carbonate.
The cyclic carbonate may be either a non-fluorinated cyclic carbonate or a fluorinated cyclic carbonate.
An example of the non-fluorinated cyclic carbonate is a non-fluorinated saturated cyclic carbonate. Preferred may be a non-fluorinated saturated alkylene carbonate containing a C2-C6 alkylene group, more preferred may be a non-fluorinated saturated alkylene carbonate containing a C2-C4 alkylene group.
In order to give high permittivity and suitable viscosity, the non-fluorinated saturated cyclic carbonate may include at least one selected from the group consisting of ethylene carbonate, propylene carbonate, cis-2,3-pentylene carbonate, cis-2,3-butylene carbonate, 2,3-pentylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 1,2-butylene carbonate, and butylene carbonate.
One non-fluorinated saturated cyclic carbonate may be used alone, or two or more thereof may be used in any combination at any ratio.
The non-fluorinated saturated cyclic carbonate, when contained, may be present in an amount of 5 to 90% by volume, 10 to 60% by volume, or 15 to 45% by volume, relative to the solvent.
The fluorinated cyclic carbonate is a cyclic carbonate containing a fluorine atom. A solvent containing a fluorinated cyclic carbonate can suitably be used at high voltage.
The term “high voltage” herein means a voltage of 4.2 V or higher. The upper limit of the “high voltage” is preferably 5.5 V, more preferably 5.4 V.
The fluorinated cyclic carbonate may be either a fluorinated saturated cyclic carbonate or a fluorinated unsaturated cyclic carbonate.
The fluorinated saturated cyclic carbonate is a saturated cyclic carbonate containing a fluorine atom. Specific examples thereof include a compound represented by the following formula (A):
wherein X1 to X4 are the same as or different from each other, and are each —H, —CH3, —C2H5, —F, a fluorinated alkyl group optionally containing an ether bond, or a fluorinated alkoxy group optionally containing an ether bond; at least one selected from X1 to X4 is —F, a fluorinated alkyl group optionally containing an ether bond, or a fluorinated alkoxy group optionally containing an ether bond. Examples of the fluorinated alkyl group include —CF3, —CF2H, and —CH2F.
The presence of the fluorinated saturated cyclic carbonate in the electrolyte solution when applied to a high-voltage fu, for example, can improve the oxidation resistance of the electrolyte solution, resulting in stable and excellent charge and discharge characteristics.
The term “ether bond” herein means a bond represented by —O—.
In order to give a good permittivity and oxidation resistance, one or two of X1 to X4 may be each —F, a fluorinated alkyl group optionally containing an ether bond, or a fluorinated alkoxy group optionally containing an ether bond.
In anticipation of a decrease in viscosity at low temperature, an increase in flash point, and improvement in solubility of an electrolyte salt, X1 to X4 may be each —H, —F, a fluorinated alkyl group (a), a fluorinated alkyl group (b) containing an ether bond, or a fluorinated alkoxy group (c).
The fluorinated alkyl group (a) is a group obtainable by replacing at least one hydrogen atom of an alkyl group by a fluorine atom. The fluorinated alkyl group (a) may have a carbon number of 1 to 20, 1 to 17, 1 to 7, or 1 to 5.
Too large a carbon number may cause poor low-temperature characteristics and low solubility of an electrolyte salt. Too small a carbon number may cause low solubility of an electrolyte salt, low discharge efficiency, and increased viscosity, for example.
Examples of the fluorinated alkyl group (a) having a carbon number of 1 include CFH2—, CF2H—, and CF3—. In order to give good high-temperature storage characteristics, particularly preferred may be CF2H— or CF3—. Most preferred may be CF3—.
In order to give good solubility of an electrolyte salt, preferred examples of the fluorinated alkyl group (a) having a carbon number of 2 or greater may include fluorinated alkyl groups represented by the following formula (a-1):
a1—Ra2— (a-1)
wherein Ra1 is an alkyl group having a carbon number of 1 or greater and optionally containing a fluorine atom; Ra2 is a C1-C3 alkylene group optionally containing a fluorine atom; and at least one of Ra1 or Ra2 contains a fluorine atom. Ra1 and Ra2 each may further contain an atom other than carbon, hydrogen, and fluorine atoms.
Ra1 is an alkyl group having a carbon number of 1 or greater and optionally containing a fluorine atom. Ra1 may be a C1-C16 linear or branched alkyl group. The carbon number of Ra1 may be 1 to 6, or 1 to 3.
Specifically, for example, CH3—, CH3CH2—, CH3CH2CH2—, CH3CH2CH2CH2—, and groups represented by the following formulas:
may be mentioned as linear or branched alkyl groups for Ra1.
Examples of Rai which is a linear alkyl group containing a fluorine atom include CF3—, CF3CH2—, CF3CF2—, CF3CH2CH2—, CF3CF2CH2—, CF3CF2CF2—, CF3CH2CF2—, CF3CH2CH2CH2—, CF3CF2CH2CH2—, CF3CH2CF2CH2—, CF3CF2CF2CH2—, CF3CF2CF2CF2—, CF3CF2CH2CF2—, CF3CH2CH2CH2CH2—, CF3CF2CH2CH2CH2—, CF3CH2CF2CH2CH2—, CF3CF2CF2CH2CH2—, CF3CF2CF2CF2CH2—, CF3CF2CH2CF2CH2—, CF3CF2CH2CH2CH2CH2—, CF3CF2CF2CF2CH2CH2—, CF3CF2CH2CF2CH2CH2—, HCF2—, HCF2CH2—, HCF2CF2—, HCF2CH2CH2—, HCF2CF2CH2—, HCF2CH2CF2—, HCF2CF2CH2CH2—, HCF2CH2CF2CH2—, HCF2CF2CF2CF2—, HCF2CF2CH2CH2CH2—, HCF2CH2CF2CH2CH2—, HCF2CF2CF2CF2CH2—, HCF2CF2CF2CF2CH2CH2—, FCH2—, FCH2CH2—, FCH2CF2—, FCH2CF2CH2—, FCH2CF2CF2—, CH3CF2CH2—, CH3CF2CF2—, CH3CF2CH2CF2—, CH3CF2CF2CF2—, CH3CH2CF2CF2—, CH3CF2CH2CF2CH2—, CH3CF2CF2CF2CH2—, CH3CF2CF2CH2CH2—, CH3CH2CF2CF2CH2—, CH3CF2CH2CF2CH2CH2—, CH3CF2CH2CF2CH2CH2—, HCFClCF2CH2—, HCF2CFClCH2—, HCF2CFClCF2CFClCH2—, and HCFClCF2CFClCF2CH2—.
Examples of Ra1 which is a branched alkyl group containing a fluorine atom include those represented by the following formulas.
The presence of a branch such as CH3— or CF3— may easily cause high viscosity. Thus, the number of such branches may be small (one) or zero.
Ra2 is a C1-C3 alkylene group optionally containing a fluorine atom. Ra2 may be either linear or branched. Examples of a minimum structural unit constituting such a linear or branched alkylene group are shown below. Ra2 is constituted by one or combination of these units.
(i) Linear minimum structural units
Preferred among these exemplified units may be Cl-free structural units because such units may not be dehydrochlorinated by a base, and thus may be more stable.
Ra2 which is a linear group consists of any of the above linear minimum structural units, and may be —CH2—, —CH2CH2—, or CF2—. In order to further improve the solubility of an electrolyte salt, —CH2— or —CH2CH2— may be more preferred.
Ra2 which is a branched group includes at least one of the above branched minimum structural units. A preferred example thereof may be a group represented by —(CXaXb)— (wherein Xa is H, F, CH3, or CF3; Xb is CH3 or CF3; when Xb is CF3, Xa is H or CH3). Such a group can much further improve the solubility of an electrolyte salt.
For example, CF3CF2—, HCF2CF2—, H2CFCF2—, CH3CF2—, CF3CHF—, CH3CF2—, CF3CF2CF2—, HCF2CF2CF2—, H2CFCF2CF2—, CH3CF2CF2—, and those represented by the following formulas:
may be mentioned as preferred examples of the fluorinated alkyl group (a).
The fluorinated alkyl group (b) containing an ether bond is a group obtainable by replacing at least one hydrogen atom of an alkyl group containing an ether bond by a fluorine atom. The fluorinated alkyl group (b) containing an ether bond may have a carbon number of 2 to 17. Too large a carbon number may cause high viscosity of the fluorinated saturated cyclic carbonate. This may also cause the presence of many fluorine-containing groups, resulting in poor solubility of an electrolyte salt due to reduction in permittivity, and poor miscibility with other solvents. Accordingly, the carbon number of the fluorinated alkyl group (b) containing an ether bond may be 2 to 10, or 2 to 7.
The alkylene group which constitutes the ether moiety of the fluorinated alkyl group (b) containing an ether bond is a linear or branched alkylene group. Examples of a minimum structural unit constituting such a linear or branched alkylene group are shown below.
The alkylene group may be constituted by one of these minimum structural units, or may be constituted by multiple linear units (i), by multiple branched units (ii), or by a combination of a linear unit (i) and a branched unit (ii). Preferred examples will be mentioned in detail later.
Preferred among these exemplified units may be Cl-free structural units because such units may not be dehydrochlorinated by a base, and thus may be more stable.
A still more preferred example of the fluorinated alkyl group (b) containing an ether bond may be a group represented by the following formula (b-1):
R3—(OR4)n1— (b-1)
wherein R3 may be a C1-C6 alkyl group optionally containing a fluorine atom; R4 may be a C1-C4 alkylene group optionally containing a fluorine atom; n1 is an integer of 1 to 3; and at least one of R3 or R4 contains a fluorine atom.
Examples of R3 and R4 include the following groups, and any appropriate combination of these groups can provide the fluorinated alkyl group (b) containing an ether bond represented by the formula (b-1). Still, the groups are not limited thereto.
(1) R3 may be an alkyl group represented by the formula: Xc3C—(R5)n2—, wherein three Xcs are the same as or different from each other, and are each H or F; R5 is a C1-C5 alkylene group optionally containing a fluorine atom; and n2 is 0 or 1.
When n2 is 0, R3 may be CH3—, CF3—, HCF2—, or H2CF—, for example.
When n2 is 1, specific examples of R3 which is a linear group include CF3CH2—, CF3CF2—, CF3CH2CH2—, CF3CF2CH2—, CF3CF2CF2—, CF3CH2CF2—, CF3CH2CH2CH2—, CF3CF2CH2CH2—, CF3CH2CF2CH2—, CF3CF2CF2CH2—, CF3CF2CF2CF2—, CF3CF2CH2CF2—, CF3CH2CH2CH2CH2—, CF3CF2CH2CH2CH2—, CF3CH2CF2CH2CH2—, CF3CF2CF2CH2CH2—, CF3CF2CF2CF2CH2—, CF3CF2CH2CF2CH2—, CF3CF2CH2CH2CH2CH2—, CF3CF2CF2CF2CH2CH2—, CF3CF2CH2CF2CH2CH2—, HCF2CH2—, HCF2CF2—, HCF2CH2CH2—, HCF2CF2CH2—, HCF2CH2CF2—, HCF2CF2CH2CH2—, HCF2CH2CF2CH2—, HCF2CF2CF2CF2—, HCF2CF2CH2CH2CH2—, HCF2CH2CF2CH2CH2—, HCF2CF2CF2CF2CH2—, HCF2CF2CF2CF2CH2CH2—, FCH2CH2—, FCH2CF2—, FCH2CF2CH2—, CH3CF2—, CH3CH2—, CH3CF2CH2—, CH3CF2CF2—, CH3CH2CH2—, CH3CF2CH2CF2—, CH3CF2CF2CF2—, CH3CH2CF2CF2—, CH3CH2CH2CH2—, CH3CF2CH2CF2CH2—, CH3CF2CF2CF2CH2—, CH3CF2CF2CH2CH2—, CH3CH2CF2CF2CH2—, CH3CF2CH2CF2CH2CH2—, CH3CH2CF2CF2CH2CH2—, and CH3CF2CH2CF2CH2CH2—.
When n2 is 1, those represented by the following formulas:
may be mentioned as examples of R3 which is a branched group.
The presence of a branch such as CH3— or CF3— may easily cause high viscosity. Thus, R3 may be a linear group.
(2) In —(OR4)n1— of the formula (b-1), n1 may be an integer of 1 to 3, or 1 or 2. When n1 is 2 or 3, R4s may be the same as or different from each other.
Preferred specific examples of R4 may include the following linear or branched groups.
Examples of the linear groups include —CH2—, —CHF—, —CF2—, —CH2CH2—, —CF2CH2—, —CF2CF2—, —CH2CF2—, —CH2CH2CH2—, —CH2CH2CF2—, —CH2CF2CH2—, —CH2CF2CF2—, —CF2CH2CH2—, —CF2CF2CH2—, —CF2CH2CF2—, and —CF2CF2CF2—.
Those represented by the following formulas:
may be mentioned as examples of the branched groups.
The fluorinated alkoxy group (c) is a group obtainable by replacing at least one hydrogen atom of an alkoxy group by a fluorine atom. The fluorinated alkoxy group (c) may have a carbon number of 1 to 17, or 1 to 6.
The fluorinated alkoxy group (c) may be a fluorinated alkoxy group represented by Xd3C—(R6)n3—O—, wherein three Xds are the same as or different from each other, and are each H or F; R6 is preferably a C1-C5 alkylene group optionally containing a fluorine atom; n3 is 0 or 1; and any of the three Xds contain a fluorine atom.
Specific examples of the fluorinated alkoxy group (c) include fluorinated alkoxy groups in which an oxygen atom binds to an end of an alkyl group mentioned as an example for R1 in the formula (a-1).
The fluorinated alkyl group (a), the fluorinated alkyl group (b) containing an ether bond, and the fluorinated alkoxy group (c) in the fluorinated saturated cyclic carbonate each may have a fluorine content of 10% by mass or more. Too less a fluorine content may cause a failure in sufficiently achieving an effect of reducing the viscosity at low temperature and an effect of increasing the flash point. Thus, the fluorine content may be 12% by mass or more, or 15% by mass or more. The upper limit thereof is usually 76% by mass.
The fluorine content of each of the fluorinated alkyl group (a), the fluorinated alkyl group (b) containing an ether bond, and the fluorinated alkoxy group (c) is a value calculated based on the corresponding structural formula by the following formula:
{(Number of fluorine atoms×19)/(Formula weight of group)}×100(%).
In order to give good permittivity and oxidation resistance, the fluorine content in the whole fluorinated saturated cyclic carbonate may be 10% by mass or more, or 15% by mass or more. The upper limit thereof is usually 76% by mass.
The fluorine content in the fluorinated saturated cyclic carbonate is a value calculated based on the structural formula of the fluorinated saturated cyclic carbonate by the following formula:
{(Number of fluorine atoms×19)/(Molecular weight of fluorinated saturated cyclic carbonate)}×100(%)
Specific examples of the fluorinated saturated cyclic carbonate include the following.
Specific examples of the fluorinated saturated cyclic carbonate in which at least one selected from X1 to X4 is —F include those represented by the following formulas.
These compounds have a high withstand voltage and give good solubility of an electrolyte salt.
Alternatively, those represented by the following formulas:
may also be used.
Those represented by the following formulas:
may be mentioned as specific examples of the fluorinated saturated cyclic carbonate in which at least one selected from X1 to X4 is a fluorinated alkyl group (a) and the others are —H.
Those represented by the following formulas:
may be mentioned as specific examples of the fluorinated saturated cyclic carbonate in which at least one selected from X1 to X4 is a fluorinated alkyl group (b) containing an ether bond or a fluorinated alkoxy group (c) and the others are —H.
In particular, the fluorinated saturated cyclic carbonate may be any of the following compounds.
Examples of the fluorinated saturated cyclic carbonate also include trans-4,5-difluoro-1,3-dioxolan-2-one, 5-(1,1-difluoroethyl)-4,4-difluoro-1,3-dioxolan-2-one, 4-methylene-1,3-dioxolan-2-one, 4-methyl-5-trifluoromethyl-1,3-dioxolan-2-one, 4-ethyl-5-fluoro-1,3-dioxolan-2-one, 4-ethyl-5,5-difluoro-1,3-dioxolan-2-one, 4-ethyl-4,5-difluoro-1,3-dioxolan-2-one, 4-ethyl-4,5,5-trifluoro-1,3-dioxolan-2-one, 4,4-difluoro-5-methyl-1,3-dioxolan-2-one, 4-fluoro-5-methyl-1,3-dioxolan-2-one, 4-fluoro-5-trifluoromethyl-1,3-dioxolan-2-one, and 4,4-difluoro-1,3-dioxolan-2-one.
More preferred among these as the fluorinated saturated cyclic carbonate may be fluoroethylene carbonate, difluoroethylene carbonate, trifluoromethylethylene carbonate, (3,3,3-trifluoropropylene carbonate), and 2,2,3,3,3-pentafluoropropylethylene carbonate.
The fluorinated unsaturated cyclic carbonate is a cyclic carbonate containing an unsaturated bond and a fluorine atom, and may be a fluorinated ethylene carbonate derivative substituted with a substituent containing an aromatic ring or a carbon-carbon double bond. Specific examples thereof include 4,4-difluoro-5-phenyl ethylene carbonate, 4,5-difluoro-4-phenyl ethylene carbonate, 4-fluoro-5-phenyl ethylene carbonate, 4-fluoro-5-vinyl ethylene carbonate, 4-fluoro-4-phenyl ethylene carbonate, 4,4-difluoro-4-vinyl ethylene carbonate, 4,4-difluoro-4-allyl ethylene carbonate, 4-fluoro-4-vinyl ethylene carbonate, 4-fluoro-4,5-diallyl ethylene carbonate, 4,5-difluoro-4-vinyl ethylene carbonate, 4,5-difluoro-4,5-divinyl ethylene carbonate, and 4,5-difluoro-4,5-diallyl ethylene carbonate.
One fluorinated cyclic carbonate may be used alone or two or more thereof may be used in any combination at any ratio.
The fluorinated cyclic carbonate, when contained, may be present in an amount of 0.5 to 90% by volume, 5 to 60% by volume, or 10 to 40% by volume, relative to the solvent.
The acyclic carbonate may be either a non-fluorinated acyclic carbonate or a fluorinated acyclic carbonate.
Examples of the non-fluorinated acyclic carbonate include hydrocarbon-based acyclic carbonates such as CH3OCOOCH3 (dimethyl carbonate, DMC), CH3CH2OCOOCH2CH3 (diethyl carbonate, DEC), CH3CH2OCOOCH3 (ethyl methyl carbonate, EMC), CH3OCOOCH2CH2CH3 (methyl propyl carbonate), methyl butyl carbonate, ethyl propyl carbonate, ethyl butyl carbonate, dipropyl carbonate, dibutyl carbonate, methyl isopropyl carbonate, methyl-2-phenyl phenyl carbonate, phenyl-2-phenyl phenyl carbonate, trans-2,3-pentylene carbonate, trans-2,3-butylene carbonate, and ethyl phenyl carbonate. Preferred among these may be at least one selected from the group consisting of ethyl methyl carbonate, diethyl carbonate, and dimethyl carbonate.
One non-fluorinated acyclic carbonate may be used alone or two or more thereof may be used in any combination at any ratio.
The non-fluorinated acyclic carbonate, when contained, may be present in an amount of 10 to 90% by volume, 40 to 85% by volume, or 50 to 80% by volume, relative to the solvent.
The fluorinated acyclic carbonate is an acyclic carbonate containing a fluorine atom. A solvent containing a fluorinated acyclic carbonate can suitably be used at high voltage.
An example of the fluorinated acyclic carbonate is a compound represented by the following formula (B):
Rf2OCOOR7 (B)
wherein Rf2 is a C1-C7 fluorinated alkyl group; and R7 is a C1-C7 alkyl group optionally containing a fluorine atom.
Rf2 is a C1-C7 fluorinated alkyl group and R7 is a C1-C7 alkyl group optionally containing a fluorine atom.
The fluorinated alkyl group is a group obtainable by replacing at least one hydrogen atom of an alkyl group by a fluorine atom. When R7 is an alkyl group containing a fluorine atom, it is a fluorinated alkyl group.
In order to give low viscosity, Rf2 and R7 each may have a carbon number of 1 to 7, or 1 to 2.
Too large a carbon number may cause poor low-temperature characteristics and low solubility of an electrolyte salt. Too small a carbon number may cause low solubility of an electrolyte salt, low discharge efficiency, and increased viscosity, for example.
Examples of the fluorinated alkyl group having a carbon number of 1 include CFH2—, CF2H—, and CF3—. In order to give high-temperature storage characteristics, particularly preferred may be CFH2— or CF3—.
In order to give good solubility of an electrolyte salt, preferred examples of the fluorinated alkyl group having a carbon number of 2 or greater may include fluorinated alkyl groups represented by the following formula (d-1):
Rd1—Rd2— (d-1)
wherein Rd1 is an alkyl group having a carbon number of 1 or greater and optionally containing a fluorine atom; Rd2 is a C1-C3 alkylene group optionally containing a fluorine atom; and at least one of Rd1 or Rd2 contains a fluorine atom.
Rd1 and Rd2 each may further contain an atom other than carbon, hydrogen, and fluorine atoms.
Rd1 is an alkyl group having a carbon number of 1 or greater and optionally containing a fluorine atom. Rd1 may be a C1-C6 linear or branched alkyl group. The carbon number of Rd1 may be 1 to 3.
Specifically, for example, CH3—, CF3—, CH3CH2—, CH3CH2CH2—, CH3CH2CH2CH2—, and groups represented by the following formulas:
may be mentioned as linear or branched alkyl groups for Rd1.
Examples of Rd1 which is a linear alkyl group containing a fluorine atom include CF3—, CF3CH2—, CF3CF2—, CF3CH2CH2—, CF3CF2CH2—, CF3CF2CF2—, CF3CH2CF2—, CF3CH2CH2CH2—, CF3CF2CH2CH2—, Use Gap Code CF3CH2CF2CH2—, CF3CF2CF2CH2—, CF3CF2CF2CF2—, CF3CF2CH2CF2—, CF3CH2CH2CH2CH2—, CF3CF2CH2CH2CH2—, CF3CH2CF2CH2CH2—, CF3CF2CF2CH2CH2—, CF3CF2CF2CF2CH2—, CF3CF2CH2CF2CH2—, CF3CF2CH2CH2CH2CH2—, CF3CF2CF2CF2CH2CH2—, CF3CF2CH2CF2CH2CH2—, HCF2—, HCF2CH2—, HCF2CF2—, HCF2CH2CH2—, HCF2CF2CH2—, HCF2CH2CF2—, HCF2CF2CH2CH2—, HCF2CH2CF2CH2—, HCF2CF2CF2CF2—, HCF2CF2CH2CH2CH2—, HCF2CH2CF2CH2CH2—, HCF2CF2CF2CF2CH2—, HCF2CF2CF2CF2CH2CH2—, FCH2—, FCH2CH2—, FCH2CF2—, FCH2CF2CH2—, FCH2CF2CF2—, CH3CF2CH2—, CH3CF2CF2—, CH3CF2CH2CF2—, CH3CF2CF2CF2—, CH3CH2CF2CF2—, CH3CF2CH2CF2CH2—, CH3CF2CF2CF2CH2—, CH3CF2CF2CH2CH2—, CH3CH2CF2CF2CH2—, CH3CF2CH2CF2CH2CH2—, CH3CF2CH2CF2CH2CH2—, HCFClCF2CH2—, HCF2CFClCH2—, HCF2CFClCF2CFClCH2—, and HCFClCF2CFClCF2CH2—.
Examples of Rd1 which is a branched alkyl group containing a fluorine atom include those represented by the following formulas.
The presence of a branch such as CH3— or CF3— may easily cause high viscosity. Thus, the number of such branches may be small (one) or zero.
Rd2 is a C1-C3 alkylene group optionally containing a fluorine atom. Rd2 may be either linear or branched. Examples of a minimum structural unit constituting such a linear or branched alkylene group are shown below. Rd2 is constituted by one or combination of these units.
Preferred among these exemplified units may be Cl-free structural units because such units may not be dehydrochlorinated by a base, and thus may be more stable.
Rd2 which is a linear group consists of any of the above linear minimum structural units, and may be —CH2—, —CH2CH2—, or —CF2—. In order to further improve the solubility of an electrolyte salt, —CH2— or —CH2CH2— may be more preferred.
Rd2 which is a branched group includes at least one of the above branched minimum structural units. A preferred example thereof may be a group represented by —(CXaXb)— (wherein Xa is H, F, CH3, or CF3; Xb is CH3 or CF3; when Xb is CF3, Xa is H or CH3). Such a group can much further improve the solubility of an electrolyte salt.
For example, CF3CF2—, HCF2CF2—, H2CFCF2—, CH3CF2—, CF3CH2—, CF3CF2CF2—, HCF2CF2CF2—, H2CFCF2CF2—, CH3CF2CF2—, and those represented by the following formulas:
may be specifically mentioned as preferred examples of the fluorinated alkyl group.
The fluorinated alkyl group for Rf2 and R7 may be CF3—, CF3CF2—, (CF3)2CH—, CF3CH2—, C2F5CH2—, CF3CF2CH2—, HCF2CF2CH2—, CF3CFHCF2CH2—, CFH2—, and CF2H—. In order to give high incombustibility and good rate characteristics and oxidation resistance, more preferred may be CF3CH2—, CF3CF2CH2—, HCF2CF2CH2—, CFH2—, and CF2H—.
R7, when it is an alkyl group free from a fluorine atom, is a C1-C7 alkyl group. In order to give low viscosity, R7 may have a carbon number of 1 to 4, or 1 to 3.
Examples of the alkyl group free from a fluorine atom include CH3—, CH3CH2—, (CH3)2CH—, and C3H7—. In order to give low viscosity and good rate characteristics, preferred may be CH3— and CH3CH2—.
The fluorinated acyclic carbonate may have a fluorine content of 15 to 70% by mass. The fluorinated acyclic carbonate having a fluorine content within the above range can maintain the miscibility with a solvent and the solubility of a salt. The fluorine content may be 20% by mass or more, 30% by mass or more, or 35% by mass or more, while 60% by mass or less, or 50% by mass or less.
In the disclosure, the fluorine content is a value calculated based on the structural formula of the fluorinated acyclic carbonate by the following formula:
{(Number of fluorine atoms×19)/(Molecular weight of fluorinated acyclic carbonate)}×100(%).
In order to give low viscosity, the fluorinated acyclic carbonate may be any of the following compounds.
The fluorinated acyclic carbonate may be methyl 2,2,2-trifluoroethyl carbonate (F3CH2COC(═O)OCH3).
One fluorinated acyclic carbonate may be used alone, or two or more thereof may be used in any combination at any ratio.
The fluorinated acyclic carbonate, when contained, may be present in an amount of 10 to 90% by volume, 40 to 85% by volume, or 50 to 80% by volume, relative to the solvent.
The carboxylate may be either a cyclic carboxylate or an acyclic carboxylate.
The cyclic carboxylate may be either a non-fluorinated cyclic carboxylate or a fluorinated cyclic carboxylate.
Examples of the non-fluorinated cyclic carboxylate include a non-fluorinated saturated cyclic carboxylate, and preferred may be a non-fluorinated saturated cyclic carboxylate containing a C2-C4 alkylene group.
Specific examples of the non-fluorinated saturated cyclic carboxylate containing a C2-C4 alkylene group include β-propiolactone, γ-butyrolactone, ε-caprolactone, δ-valerolactone, and α-methyl-γ-butyrolactone. In order to improve the degree of dissociation of lithium ions and to improve the load characteristics, particularly preferred among these may be γ-butyrolactone and δ-valerolactone.
One non-fluorinated saturated cyclic carboxylate may be used alone or two or more thereof may be used in any combination at any ratio.
The non-fluorinated saturated cyclic carboxylate, when contained, may be present in an amount of 0 to 90% by volume, 0.001 to 90% by volume, 1 to 60% by volume, or 5 to 40% by volume, relative to the solvent.
The acyclic carboxylate may be either a non-fluorinated acyclic carboxylate or a fluorinated acyclic carboxylate. The solvent containing the acyclic carboxylate enables further reduction of an increase in resistance after high-temperature storage of the electrolyte solution.
Examples of the non-fluorinated acyclic carboxylate include methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, tert-butyl propionate, tert-butyl butyrate, sec-butyl propionate, sec-butyl butyrate, n-butyl butyrate, methyl pyrophosphate, ethyl pyrophosphate, tert-butyl formate, tert-butyl acetate, sec-butyl formate, sec-butyl acetate, n-hexyl pivalate, n-propyl formate, n-propyl acetate, n-butyl formate, n-butyl pivalate, n-octyl pivalate, ethyl 2-(dimethoxyphosphoryl)acetate, ethyl 2-(dimethylphosphoryl)acetate, ethyl 2-(diethoxyphosphoryl)acetate, ethyl 2-(diethylphosphoryl)acetate, isopropyl propionate, isopropyl acetate, ethyl formate, ethyl 2-propynyl oxalate, isopropyl formate, isopropyl butyrate, isobutyl formate, isobutyl propionate, isobutyl butyrate, and isobutyl acetate.
Preferred among these may be butyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate, particularly preferred may be ethyl propionate and propyl propionate.
One non-fluorinated acyclic carboxylate may be used alone or two or more thereof may be used in any combination at any ratio.
The non-fluorinated acyclic carboxylate, when contained, may be present in an amount of 0 to 90% by volume, 0.001 to 90% by volume, 1 to 60% by volume, or 5 to 40% by volume, relative to the solvent.
The fluorinated acyclic carboxylate is an acyclic carboxylate containing a fluorine atom. A solvent containing a fluorinated acyclic carboxylate can be suitably used at high voltage.
In order to achieve good miscibility with other solvents and to give good oxidation resistance, preferred examples of the fluorinated acyclic carboxylate may include a fluorinated acyclic carboxylate represented by the following formula: R31COOR32 (wherein R31 and R32 are each independently a C1-C4 alkyl group optionally containing a fluorine atom, and at least one of R31 or R32 contains a fluorine atom).
Examples of R31 and R32 include non-fluorinated alkyl groups such as a methyl group (—CH3), an ethyl group (—CH2CH3), a propyl group (—CH2CH2CH3), an isopropyl group (—CH(CH3)2), a normal butyl group (—CH2CH2CH2CH3), and a tertiary butyl group (—C(CH3)3); and fluorinated alkyl groups such as —CF3, —CF2H, —CFH2, —CF2CF3, —CF2CF2H, —CF2CFH2, —CH2CF3, —CH2CF2H, —CH2CFH2, —CF2CF2CF3, —CF2CF2CF2H, —CF2CF2CFH2, —CH2CF2CF3, —CH2CF2CF2H, —CH2CF2CFH2, —CH2CH2CF3, —CH2CH2CF2H, —CH2CH2CFH2, —CF(CF3)2, —CF(CF2H)2, —CF(CFH2)2, —CH(CF3)2, —CH(CF2H)2, —CH(CFH2)2, —CF(OCH3)CF3, —CF2CF2CF2CF3, —CF2CF2CF2CF2H, —CF2CF2CF2CFH2, —CH2CF2CF2CF3, —CH2CF2CF2CF2H, —CH2CF2CF2CFH2, —CH2CH2CF2CF3, —CH2CH2CF2CF2H, —CH2CH2CF2CFH2, —CH2CH2CH2CF3, —CH2CH2CH2CF2H, —CH2CH2CH2CFH2, —CF(CF3)CF2CF3, —CF(CF2H)CF2CF3, —CF(CFH2)CF2CF3, —CF(CF3)CF2CF2H, —CF(CF3)CF2CFH2, —CF(CF3) CH2CF3, —CF(CF3) CH2CF2H, —CF(CF3) CH2CFH2, —CH(CF3)CF2CF3, —CH(CF2H)CF2CF3, —CH(CFH2)CF2CF3, —CH(CF3)CF2CF2H, —CH(CF3)CF2CFH2, —CH(CF3) CH2CF3, —CH(CF3) CH2CF2H, —CH(CF3) CH2CFH2, —CF2CF(CF3)CF3, —CF2CF(CF2H)CF3, —CF2CF(CFH2)CF3, —CF2CF(CF3)CF2H, —CF2CF(CF3)CFH2, —CH2CF(CF3)CF3, —CH2CF(CF2H)CF3, —CH2CF(CFH2)CF3, —CH2CF(CF3)CF2H, —CH2CF(CF3)CFH2, —CH2CH(CF3)CF3, —CH2CH(CF2H)CF3, —CH2CH(CFH2)CF3, —CH2CH(CF3)CF2H, —CH2CH(CF3)CFH2, —CF2CH(CF3)CF3, —CF2CH(CF2H)CF3, —CF2CH(CFH2)CF3, —CF2CH(CF3)CF2H, —CF2CH(CF3)CFH2, —C(CF3)3, —C(CF2H)3, and —C(CFH2)3. In order to improve the miscibility with other solvents, viscosity, and oxidation resistance, particularly preferred among these may be a methyl group, an ethyl group, —CF3, —CF2H, —CF2CF3, —CH2CF3, —CH2CF2H, —CH2CFH2, —CH2CH2CF3, —CH2CF2CF3, —CH2CF2CF2H, and —CH2CF2CFH2.
Specific examples of the fluorinated acyclic carboxylate include one or two or more of CF3CH2C(═O)OCH3 (methyl 3,3,3-trifluoropropionate), HCF2C(═O)OCH3 (methyl difluoroacetate), HCF2C(═O)OC2H5 (ethyl difluoroacetate), CF3C(=O)OCH2CH2CF3, CF3C(=O)OCH2C2F5, CF3C(=O)OCH2CF2CF2H (2,2,3,3-tetrafluoropropyl trifluoroacetate), CF3C(=O)OCH2CF3, CF3C(=O)OCH(CF3)2, ethyl pentafluorobutyrate, methyl pentafluoropropionate, ethyl pentafluoropropionate, methyl heptafluoroisobutyrate, isopropyl trifluorobutyrate, ethyl trifluoroacetate, tert-butyl trifluoroacetate, n-butyl trifluoroacetate, methyl tetrafluoro-2-(methoxy)propionate, 2,2-difluoroethyl acetate, 2,2,3,3-tetrafluoropropyl acetate, CH3C(═O)OCH2CF3 (2,2,2-trifluoroethyl acetate), 1H,1H-heptafluorobutyl acetate, methyl 4,4,4-trifluorobutyrate, ethyl 4,4,4-trifluorobutyrate, ethyl 3,3,3-trifluoropropionate, 3,3,3-trifluoropropyl 3,3,3-trifluoropropionate, ethyl 3-(trifluoromethyl)butyrate, methyl 2,3,3,3-tetrafluoropropionate, butyl 2,2-difluoroacetate, methyl 2,2,3,3-tetrafluoropropionate, methyl 2-(trifluoromethyl)-3,3,3-trifluoropropionate, and methyl heptafluorobutyrate.
In order to achieve good miscibility with other solvents and good rate characteristics, preferred among these may be CF3CH2C(=O)OCH3, HCF2C(=O)OCH3, HCF2C(=O)OC2H5, CF3C(=O)OCH2C2F5, CF3C(=O)OCH2CF2CF2H, CF3C(=O)OCH2CF3, CF3C(=O)OCH(CF3)2, ethyl pentafluorobutyrate, methyl pentafluoropropionate, ethyl pentafluoropropionate, methyl heptafluoroisobutyrate, isopropyl trifluorobutyrate, ethyl trifluoroacetate, tert-butyl trifluoroacetate, n-butyl trifluoroacetate, methyl tetrafluoro-2-(methoxy)propionate, 2,2-difluoroethyl acetate, 2,2,3,3-tetrafluoropropyl acetate, CH3C(═O)OCH2CF3, 1H, 1H-heptafluorobutyl acetate, methyl 4,4,4-trifluorobutyrate, ethyl 4,4,4-trifluorobutyrate, ethyl 3,3,3-trifluoropropionate, 3,3,3-trifluoropropyl 3,3,3-trifluoropropionate, ethyl 3-(trifluoromethyl)butyrate, methyl 2,3,3,3-tetrafluoropropionate, butyl 2,2-difluoroacetate, methyl 2,2,3,3-tetrafluoropropionate, methyl 2-(trifluoromethyl)-3,3,3-trifluoropropionate, and methyl heptafluorobutyrate, more preferred may be CF3CH2C(═O)OCH3, HCF2C(=O)OCH3, HCF2C(=O)OC2H5, and CH3C(=O)OCH2CF3, and particularly preferred may be HCF2C(═O)OCH3, HCF2C(═O)OC2H5, and CH3C(=O)OCH2CF3.
One fluorinated acyclic carboxylate may be used alone or two or more thereof may be used in any combination at any ratio.
The fluorinated acyclic carboxylate, when contained, may be present in an amount of 10 to 90% by volume, 40 to 85% by volume, or 50 to 80% by volume, relative to the solvent.
The solvent may contain at least one selected from the group consisting of the cyclic carbonate, the acyclic carbonate, and the acyclic carboxylate, and may contain the cyclic carbonate and at least one selected from the group consisting of the acyclic carbonate and the acyclic carboxylate. The cyclic carbonate may be a saturated cyclic carbonate.
An electrolyte solution containing a solvent of such a composition allows an electrochemical device to have further improved high-temperature storage characteristics and cycle characteristics.
For the solvent containing the cyclic carbonate and at least one selected from the group consisting of the acyclic carbonate and the acyclic carboxylate, the total amount of the cyclic carbonate and at least one selected from the group consisting of the acyclic carbonate and the acyclic carboxylate may be 10 to 100% by volume, 30 to 100% by volume, or 50 to 100% by volume.
For the solvent containing the cyclic carbonate and at least one selected from the group consisting of the acyclic carbonate and the acyclic carboxylate, the cyclic carbonate and at least one selected from the group consisting of the acyclic carbonate and the acyclic carboxylate may give a volume ratio of 5/95 to 95/5, 10/90 or more, 15/85 or more, or 20/80 or more, while 90/10 or less, 60/40 or less, or 50/50 or less.
The solvent also may contain at least one selected from the group consisting of the non-fluorinated saturated cyclic carbonate, the non-fluorinated acyclic carbonate, and the non-fluorinated acyclic carboxylate, may contain the non-fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the non-fluorinated acyclic carbonate and the non-fluorinated acyclic carboxylate. An electrolyte solution containing a solvent of such a composition can suitably be used for electrochemical devices used at relatively low voltage.
For the solvent containing the non-fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the non-fluorinated acyclic carbonate and the non-fluorinated acyclic carboxylate, the total amount of the non-fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the non-fluorinated acyclic carbonate and the non-fluorinated acyclic carboxylate may be 5 to 100% by volume, 20 to 100% by volume, or 30 to 100% by volume.
For the electrolyte solution containing the non-fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the non-fluorinated acyclic carbonate and the non-fluorinated acyclic carboxylate, the non-fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the non-fluorinated acyclic carbonate and the non-fluorinated acyclic carboxylate may give a volume ratio of 5/95 to 95/5, 10/90 or more, 15/85 or more, or 20/80 or more, while 90/10 or less, 60/40 or less, or 50/50 or less.
The solvent may contain at least one selected from the group consisting of the fluorinated saturated cyclic carbonate, the fluorinated acyclic carbonate, and the fluorinated acyclic carboxylate, and may contain the fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the fluorinated acyclic carbonate and the fluorinated acyclic carboxylate. An electrolyte solution containing a solvent of such a composition can suitably be used for not only electrochemical devices used at relatively low voltage but also electrochemical devices used at relatively high voltage.
For the solvent containing the fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the fluorinated acyclic carbonate and the fluorinated acyclic carboxylate, the total amount of the fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the fluorinated acyclic carbonate and the fluorinated acyclic carboxylate may be 5 to 100% by volume, 10 to 100% by volume, or 30 to 100% by volume.
For the solvent containing the fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the fluorinated acyclic carbonate and the fluorinated acyclic carboxylate, the fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the fluorinated acyclic carbonate and the fluorinated acyclic carboxylate may give a volume ratio of 5/95 to 95/5, 10/90 or more, 15/85 or more, or 20/80 or more, while 90/10 or less, 60/40 or less, or 50/50 or less.
The solvent used may be an ionic liquid. The “ionic liquid” means a liquid containing an ion that is a combination of an organic cation and an anion.
Examples of the organic cation include, but are not limited to, imidazolium ions such as dialkyl imidazolium cations and trialkyl imidazolium cations; tetraalkyl ammonium ions; alkyl pyridinium ions; dialkyl pyrrolidinium ions; and dialkyl piperidinium ions.
Examples of the anion to be used as a counterion of any of these organic cations include, but are not limited to, a PF6 anion, a PF3(C2F5)3 anion, a PF3(CF3)3 anion, a BF4 anion, a BF2(CF3)2 anion, a BF3(CF3) anion, a bis(oxalato)boric acid anion, a P(C2O4)F2 anion, a Tf (trifluoromethanesulfonyl) anion, a Nf (nonafluorobutanesulfonyl) anion, a bis(fluorosulfonyl)imide anion, a bis(trifluoromethanesulfonyl)imide anion, a bis(pentafluoroethanesulfonyl)imide anion, a dicyanoamine anion, and halide anions.
The solvent may be a non-aqueous solvent and the electrolyte solution may be a non-aqueous electrolyte solution.
The solvent may be present in an amount of 70 to 99.999% by mass, or 80% by mass or more, while 92% by mass or less, of the electrolyte solution.
The electrolyte solution may further contain a compound (5) represented by the following formula (5).
In the formula, Aa+ is a metal ion, a hydrogen ion, or an onium ion; a is an integer of 1 to 3; b is an integer of 1 to 3; p is b/a; n203 is an integer of 1 to 4; n201 is an integer of 0 to 8; n202 is 0 or 1; and Z201 is a transition metal or an element of group III, IV, or V of the periodic table.
X201 is O, S, a C1-C10 alkylene group, a C1-C10 halogenated alkylene group, a C6-C20 arylene group, or a C6-C20 halogenated arylene group (the alkylene, halogenated alkylene, arylene, and halogenated arylene groups may have a substituent or a hetero atom in the structure, and when n202 is 1 and n203 is 2 to 4, n203 X201s may be bonded to each other).
L201 is a halogen atom, a cyano group, a C1-C10 alkyl group, a C1-C10 halogenated alkyl group, a C6-C20 aryl group, a C6-C20 halogenated aryl group (the alkylene, halogenated alkylene, arylene, and halogenated arylene groups may have a substituent or a hetero atom in the structure, and when n201 is 2 to 8, n201 L201s may be bonded to form a ring), or —Z203Y203.
Y201, Y202, and Z203 are each independently 0, S, NY204, a hydrocarbon group, or a fluorinated hydrocarbon group. Y203 and Y204 are each independently H, F, a C1-C10 alkyl group, a C1-C10 halogenated alkyl group, a C6-C20 aryl group, or a C6-C20 halogenated aryl group (the alkyl, halogenated alkyl, aryl, and halogenated aryl groups may have a substituent or a hetero atom in the structure, and when multiple Y203s or Y204s are present, they may be bonded to form a ring).
Examples of Aa+ include a lithium ion, a sodium ion, a potassium ion, a magnesium ion, a calcium ion, a barium ion, a cesium ion, a silver ion, a zinc ion, a copper ion, a cobalt ion, an iron ion, a nickel ion, a manganese ion, a titanium ion, a lead ion, a chromium ion, a vanadium ion, a ruthenium ion, a yttrium ion, a lanthanoid ion, an actinoid ion, a tetrabutylammonium ion, a tetraethylammonium ion, a tetramethylammonium ion, a triethylmethylammonium ion, a triethylammonium ion, a pyridinium ion, an imidazolium ion, a hydrogen ion, a tetraethylphosphonium ion, a tetramethylphosphonium ion, a tetraphenylphosphonium ion, a triphenylsulfonium ion, and a triethylsulfonium ion.
For applications such as electrochemical devices, Aa+ may be a lithium ion, a sodium ion, a magnesium ion, a tetraalkylammonium ion, or a hydrogen ion, or a lithium ion. The valence a of an Aa+ cation is an integer of 1 to 3. When the valence a is larger than 3, the crystal lattice energy becomes larger, which makes it difficult to dissolve the electrolyte solution of the disclosure in a solvent. The valence may be therefore 1 when the solubility is required. The valence b of an anion may be similarly an integer of 1 to 3, or 1. The constant p which represents a ratio between the cation and the anion is necessarily determined by the ratio b/a of their valence values.
Next, a ligand portion of the formula (5) is described. Herein, the organic or inorganic moiety bonded to Z201 in the formula (5) is referred to as a ligand.
Z201 may be Al, B, V, Ti, Si, Zr, Ge, Sn, Cu, Y, Zn, Ga, Nb, Ta, Bi, P, As, Sc, Hf, or Sb, or Al, B, or P.
X201 represents 0, S, a C1-C10 alkylene group, a C1-C10 halogenated alkylene group, a C6-C20 arylene group, or a C6-C20 halogenated arylene group. These alkylene and arylene groups may have a substituent or a hetero atom in the structure. Specifically, they may have a halogen atom or a linear or cyclic alkyl group, an aryl group, an alkenyl group, an alkoxy group, an aryloxy group, a sulfonyl group, an amino group, a cyano group, a carbonyl group, an acyl group, an amide group, or a hydroxy group as a substituent in place of hydrogen on the alkylene or arylene group. They also may have a structure where nitrogen, sulfur, or oxygen is introduced in place of carbon on the alkylene or arylene group. When n202 is 1 and n203 is 2 to 4, n203 X201s may be bonded to each other. Examples of such a structure include ligands such as ethylenediaminetetraacetic acid.
L201 represents a halogen atom, a cyano group, a C1-C10 alkyl group, a C1-C10 halogenated alkyl group, a C6-C20 aryl group, a C6-C20 halogenated aryl group, or —Z203Y203 (Z203 and Y203 are described later). As in the case of X201, the alkyl and aryl groups here may have a substituent or a hetero atom in the structure, and when n201 is 2 to 8, n201 L201s may be bonded to form a ring. L201 may be a fluorine atom or a cyano group. When L201 is a fluorine atom, solubility and dissociation of anionic compound salts are increased, which in turn favorably increases ionic conductivity. In addition, oxidation resistance is improved to reduce or inhibit occurrence of side reactions.
Y201, Y202, and Z203 each independently represent O, S, NY204, a hydrocarbon group, or a fluorinated hydrocarbon group. Y201 and Y202 each may be O, S, or NY204, or O. The compound (5) is characterized in that a bond of Y201 with Z201 and a bond of Y202 with Z201 are present within the same ligand and such ligands form a chelate structure with Z201. Owing to this chelate, the compound has higher heat resistance, higher chemical stability, and higher hydrolysis resistance. The constant n202 in this ligand is 0 or 1. When the constant n202 is 0, in particular, the chelate ring is a 5-membered ring, which favorably allows strongest exertion of the chelate effect to increase the stability.
The fluorinated hydrocarbon group herein is a group obtainable by replacing at least one hydrogen atom of a hydrocarbon group with a fluorine atom.
Y203 and Y204 are each independently H, F, a C1-C10 alkyl group, a C1-C10 halogenated alkyl group, a C6-C20 aryl group, or a C6-C20 halogenated aryl group. These alkyl and aryl groups may have a substituent or a hetero atom in the structure. When multiple Y203s or Y204s are present, they may be bonded to form a ring.
The constant n203 related to the number of ligands described above may be an integer of 1 to 4, 1 or 2, or 2. The constant n201 related to the number of ligands described above may be an integer of 0 to 8, an integer of 0 to 4, or 0, 2, or 4. n201 may be 2 when n203 is 1 and n201 may be 0 when n203 is 2.
In the formula (5), the alkyl, halogenated alkyl, aryl, and halogenated aryl groups may be those with a different functional group such as a branch, a hydroxy group, or an ether bond.
The compound (5) may be a compound represented by the following formula:
(wherein Aa+, a, b, p, n201, Z201, and L201 are as described above), or a compound represented by the following formula:
(wherein Aa+, a, b, p, n201, Z201, and L201 are as described above).
Examples of the compound (5) include lithium (oxalate)borate salts including lithium bis(oxalate)borate (LIBOB) represented by the following formula:
lithium difluorooxalatoborate (LiDFOB) represented by the following formula:
lithium difluorooxaratophosphanite (LiDFOP) represented by the following formula: [Chem. 36]
lithium tetrafluorooxalatophosphanite (LiTFOP) represented by the following formula:
and lithium bis(oxalato)difluorophosphanite represented by the following formula:
Examples of the compound (5) also include dicarboxylic acid complex salts in which the complex center element is boron, such as lithium bis(malonato)borate, lithium difluoro(malonato)borate, lithium bis(methylmalonato)borate, lithium difluoro(methylmalonato)borate, lithium bis(dimethylmalonato)borate, and lithium difluoro(dimethylmalonato)borate.
Examples of the compound (5) also include dicarboxylic acid complex salts in which the complex center element is phosphorus, such as lithium tris(oxalato)phosphate, lithium tris(malonato)phosphate, lithium difluorobis(malonato)phosphate, lithium tetrafluoro(malonato)phosphate, lithium tris(methylmalonato)phosphate, lithium difluorobis(methylmalonato)phosphate, lithium tetrafluoro(methylmalonato)phosphate, lithium tris(dimethylmalonato)phosphate, lithium difluorobis(dimethylmalonato)phosphate, and lithium tetrafluoro(dimethylmalonato)phosphate.
Examples of the compound (5) also include dicarboxylic acid complex salts in which the complex center element is aluminum, such as LiAl(C2O4)2 and LiAlF2(C2O4).
In order to enable easy availability and contribute to formation of a stable film-shaped structure, more preferred among these may be lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium tris(oxalato)phosphate, lithium difluorobis(oxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate.
The compound (5) may be lithium bis(oxalato)borate.
In order to give much better cycle characteristics, the compound (5) may be in an amount of 0.001% by mass or more, or 0.01% by mass or more, while 10% by mass or less, or 3% by mass or less, relative to the solvent.
Examples of the electrolyte salt used include lithium salts, ammonium salts, and metal salts, as well as any of those to be used for electrolyte solutions such as liquid salts (ionic liquids), inorganic polymer salts, and organic polymer salts.
The electrolyte salt of the electrolyte solution for a secondary battery may be a lithium salt.
Any lithium salt may be used. Specific examples thereof include the following: inorganic lithium salts such as LiPF6, LiBF4, LiClO4, LiAlF4, LiSbF6, LiTaF6, LiWF7, LiAsF6, LiAlCl4, LiI, LiBr, LiCl, LiB10Cl10, Li2SiF6, Li2PFO3, and LiPO2F2;
In order to achieve an effect of improving properties such as output characteristics, high-rate charge and discharge characteristics, high-temperature storage characteristics, and cycle characteristics, particularly preferred among these may be LiPF6, LiBF4, LiSbF6, LiTaF6, LiPO2F2, FSO3Li, CF3SO3Li, LiN(FSO2)2, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, lithium cyclic 1,2-perfluoroethanedisulfonyl imide, lithium cyclic 1,3-perfluoropropanedisulfonyl imide, LiC(FSO2)3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiBF3CF3, LiBF3C2F5, LiPF3(CF3)3, LiPF3(C2F5)3, and the like. Most preferred may be at least one lithium salt selected from the group consisting of LiPF6, LiN(FSO2)2, and LiBF4.
One of these electrolyte salts may be used alone or two or more thereof may be used in any combination. In combination use of two or more thereof, preferred examples thereof may include a combination of LiPF6 and LiBF4 and a combination of LiPF6 and LiPO2F2, C2H5OSO3Li, or FSO3Li, each of which have an effect of improving the high-temperature storage characteristics, the load characteristics, and the cycle characteristics.
In this case, LiBF4, LiPO2F2, C2H5OSO3Li, or FSO3Li may be present in any amount that does not significantly impair the effects of the disclosure in 100% by mass of the whole electrolyte solution. The amount thereof is 0.01% by mass or more, or 0.1% by mass or more, while the upper limit thereof is 30% by mass or less, 20% by mass or less, 10% by mass or less, or 5% by mass or less, relative to the electrolyte solution.
In another example, an inorganic lithium salt and an organic lithium salt are used in combination. Such a combination has an effect of reducing deterioration due to high-temperature storage. The organic lithium salt may be CF3SO3Li, LiN(FSO2)2, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, lithium cyclic 1,2-perfluoroethanedisulfonyl imide, lithium cyclic 1,3-perfluoropropanedisulfonyl imide, LiC(FSO2)3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiBF3CF3, LiBF3C2F5, LiPF3(CF3)3, LiPF3(C2F5)3, or the like. In this case, the proportion of the organic lithium salt may be 0.1% by mass or more, or 0.5% by mass or more, while 30% by mass or less, or 10% by mass or less, of 100% by mass of the whole electrolyte solution.
The electrolyte salt in the electrolyte solution may have any concentration that does not impair the effects of the disclosure. In order to make the electric conductivity of the electrolyte solution within a favorable range and to ensure good battery performance, the lithium in the electrolyte solution may have a total mole concentration of 0.3 mol/L or higher, 0.4 mol/L or higher, or 0.5 mol/L or higher, while 5.0 mol/L or lower, 3.0 mol/L or lower, or 2.0 mol/L or lower.
Too low a total mole concentration of lithium may cause insufficient electric conductivity of the electrolyte solution, while too high a concentration may cause an increase in viscosity and then reduction in electric conductivity, impairing the battery performance.
The electrolyte solution may further contain a compound (2) represented by the following formula (2):
(wherein X21 is a group containing at least H or C; n21 is an integer of 1 to 3; Y21 and Z21 are the same as or different from each other, and are each a group containing at least H, C, O, or F; n22 is 0 or 1; and Y21 and Z21 optionally bind to each other to form a ring). The electrolyte solution containing the compound (2) can cause less reduction in capacity retention and can cause a less increase in amount of gas generated even when stored at high temperature.
When n21 is 2 or 3, the two or three X21s may be the same as or different from each other.
When multiple Y21s and multiple Z21s are present, the multiple Y21s may be the same as or different from each other and the multiple Z21s may be the same as or different from each other.
X21 may be a group represented by —CY21Z21— (wherein Y21 and Z21 are defined as described above) or a group represented by —CY21═CZ21— (wherein Y21 and Z21 are defined as described above).
Y21 may include at least one selected from the group consisting of H—, F—, CH3—, CH3CH2—, CH3CH2CH2—, CF3—, CF3CF2—, CH2FCH2—, and CF3CF2CF2—.
Z21 may include at least one selected from the group consisting of H—, F—, CH3—, CH3CH2—, CH3CH2CH2—, CF3—, CF3CF2—, CH2FCH2—, and CF3CF2CF2—.
Alternatively, Y21 and Z21 may bind to each other to form a carbon ring or a heterocycle that may contain an unsaturated bond and may have aromaticity. The ring may have a carbon number of 3 to 20.
Next, specific examples of the compound (2) are described. In the following examples, the term “analog” means an acid anhydride obtainable by replacing part of the structure of an acid anhydride mentioned as an example by another structure within the scope of the disclosure. Examples thereof include dimers, trimers, and tetramers each composed of a plurality of acid anhydrides, those having respective substituents which are structural isomers having the same carbon number but having different branch structures, and those having the same substituent but at different sites in an acid anhydride.
Specific examples of an acid anhydride having a 5-membered cyclic structure include succinic anhydride, methylsuccinic anhydride (4-methylsuccinic anhydride), dimethylsuccinic anhydride (e.g., 4,4-dimethylsuccinic anhydride, 4,5-dimethylsuccinic anhydride), 4,4,5-trimethylsuccinic anhydride, 4,4,5,5-tetramethylsuccinic anhydride, 4-vinylsuccinic anhydride, 4,5-divinylsuccinic anhydride, phenylsuccinic anhydride (4-phenylsuccinic anhydride), 4,5-diphenylsuccinic anhydride, 4,4-diphenylsuccinic anhydride, citraconic anhydride, maleic anhydride, methylmaleic anhydride (4-methylmaleic anhydride), 4,5-dimethylmaleic anhydride, phenylmaleic anhydride (4-phenylmaleic anhydride), 4,5-diphenylmaleic anhydride, itaconic anhydride, 5-methylitaconic anhydride, 5,5-dimethylitaconic anhydride, phthalic anhydride, and 3,4,5,6-tetrahydrophthalic anhydride, and analogs thereof.
Specific examples of an acid anhydride having a 6-membered cyclic structure include cyclohexanedicarboxylic anhydride (e.g., cyclohexane-1,2-dicarboxylic anhydride), 4-cyclohexene-1,2-dicarboxylic anhydride, glutaric anhydride, glutaconic anhydride, and 2-phenylglutaric anhydride, and analogs thereof.
Specific examples of an acid anhydride having a different cyclic structure include 5-norbornene-2,3-dicarboxylic anhydride, cyclopentanetetracarboxylic dianhydride, pyromellitic anhydride, and diglycolic anhydride, and analogs thereof.
Specific examples of an acid anhydride having a cyclic structure and substituted with a halogen atom include monofluorosuccinic anhydride (e.g., 4-fluorosuccinic anhydride), 4,4-difluorosuccinic anhydride, 4,5-difluorosuccinic anhydride, 4,4,5-trifluorosuccinic anhydride, trifluoromethylsuccinic anhydride, tetrafluorosuccinic anhydride (4,4,5,5-tetrafluorosuccinic anhydride), 4-fluoromaleic anhydride, 4,5-difluoromaleic anhydride, trifluoromethylmaleic anhydride, 5-fluoroitaconic anhydride, and 5,5-difluoroitaconic anhydride, and analogs thereof.
Preferred among these as the compound (2) may be glutaric anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, diglycolic anhydride, cyclohexanedicarboxylic anhydride, cyclopentanetetracarboxylic dianhydride, 4-cyclohexene-1,2-dicarboxylic anhydride, 3,4,5,6-tetrahydrophthalic anhydride, 5-norbornene-2,3-dicarboxylic anhydride, phenylsuccinic anhydride, 2-phenylglutaric anhydride, maleic anhydride, methylmaleic anhydride, trifluoromethylmaleic anhydride, phenylmaleic anhydride, succinic anhydride, methylsuccinic anhydride, dimethylsuccinic anhydride, trifluoromethylsuccinic anhydride, monofluorosuccinic anhydride, and tetrafluorosuccinic anhydride. More preferred may be maleic anhydride, methylmaleic anhydride, trifluoromethylmaleic anhydride, succinic anhydride, methylsuccinic anhydride, trifluoromethylsuccinic anhydride, and tetrafluorosuccinic anhydride, and still more preferred may be maleic anhydride and succinic anhydride.
The compound (2) may include at least one selected from the group consisting of: a compound (3) represented by the following formula (3):
(wherein X31 to X34 are the same as or different from each other, and are each a group containing at least H, C, O, or F); and a compound (4) represented by the following formula (4):
(wherein X41 and X42 are the same as or different from each other, and are each a group containing at least H, C, O, or F).
X31 to X34 are the same as or different from each other, and may include at least one selected from the group consisting of an alkyl group, a fluorinated alkyl group, an alkenyl group, and a fluorinated alkenyl group. X31 to X34 each may have a carbon number of 1 to 10, or 1 to 3.
X31 to X34 are the same as or different from each other, and may include at least one selected from the group consisting of H—, F—, CH3—, CH3CH2—, CH3CH2CH2—, CF3—, CF3CF2—, CH2FCH2—, and CF3CF2CF2—.
X41 and X42 are the same as or different from each other, and may include at least one selected from the group consisting of an alkyl group, a fluorinated alkyl group, an alkenyl group, and a fluorinated alkenyl group. X41 and X42 each may have a carbon number of 1 to 10, or 1 to 3.
X41 and X42 are the same as or different from each other, and may include at least one selected from the group consisting of H—, F—, CH3—, CH3CH2—, CH3CH2CH2—, CF3—, CF3CF2—, CH2FCH2—, and CF3CF2CF2—.
The compound (3) may be any of the following compounds.
The compound (4) may be any of the following compounds.
In order to cause less reduction in capacity retention and a less increase in amount of gas generated even when stored at high temperature, the electrolyte solution may contain 0.0001 to 15% by mass of the compound (2) relative to the electrolyte solution. The amount of the compound (2) may be 0.01 to 10% by mass, 0.1 to 3% by mass, or 0.1 to 1.0% by mass.
In order to cause less reduction in capacity retention and a less increase in amount of gas generated even when stored at high temperature, the electrolyte solution, when containing both the compounds (3) and (4), may contain 0.08 to 2.50% by mass of the compound (3) and 0.02 to 1.50% by mass of the compound (4), or 0.80 to 2.50% by mass of the compound (3) and 0.08 to 1.50% by mass of the compound (4), relative to the electrolyte solution.
The electrolyte solution may contain at least one selected from the group consisting of nitrile compounds represented by the following formulas (1a), (1b), and (1c):
(wherein Ra and Rb are each independently a hydrogen atom, a cyano group (CN), a halogen atom, an alkyl group, or a group obtainable by replacing at least one hydrogen atom of an alkyl group by a halogen atom; and n is an integer of 1 to 10);
(wherein Rc is a hydrogen atom, a halogen atom, an alkyl group, a group obtainable by replacing at least one hydrogen atom of an alkyl group by a halogen atom, or a group represented by NC—Rc1—Xc1— (wherein Rc1 is an alkylene group, Xc1 is an oxygen atom or a sulfur atom); Rd and Re are each independently a hydrogen atom, a halogen atom, an alkyl group, or a group obtainable by replacing at least one hydrogen atom of an alkyl group by a halogen atom; and m is an integer of 1 to 10);
(wherein Rf, Rg, Rh, and Ri are each independently a group containing a cyano group (CN), a hydrogen atom (H), a halogen atom, an alkyl group, or a group obtainable by replacing at least one hydrogen atom of an alkyl group by a halogen atom; at least one selected from the group consisting of Rf, Rg, Rh, and Ri is a group containing a cyano group; and 1 is an integer of 1 to 3).
This can improve the high-temperature storage characteristics of an electrochemical device. One nitrile compound may be used alone, or two or more thereof may be used in any combination at any ratio.
In the formula (1a), Ra and Rb are each independently a hydrogen atom, a cyano group (CN), a halogen atom, an alkyl group, or a group obtainable by replacing at least one hydrogen atom of an alkyl group by a halogen atom.
Examples of the halogen atom include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. Preferred among these may be a fluorine atom.
The alkyl group may be a C1-C5 alkyl group. Specific examples of the alkyl group include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, and a tert-butyl group.
An example of the group obtainable by replacing at least one hydrogen atom of an alkyl group by a halogen atom is a group obtainable by replacing at least one hydrogen atom of the aforementioned alkyl group by the aforementioned halogen atom.
When Ra and Rb are alkyl groups or groups each obtainable by replacing at least one hydrogen atom of an alkyl group by a halogen atom, Ra and Rb may bind to each other to form a cyclic structure (e.g., a cyclohexane ring).
Ra and Rb may be each a hydrogen atom or an alkyl group.
In the formula (1a), n is an integer of 1 to 10. When n is 2 or greater, all of n Ras may be the same as each other, or at least part of them may be different from the others. The same applies to Rb. In the formula, n may be an integer of 1 to 7, or an integer of 2 to 5.
Preferred as the nitrile compound represented by the formula (1a) may be dinitriles and tricarbonitriles.
Specific examples of the dinitriles include malononitrile, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelanitrile, sebaconitrile, undecanedinitrile, dodecanedinitrile, methylmalononitrile, ethylmalononitrile, isopropylmalononitrile, tert-butylmalononitrile, methylsuccinonitrile, 2,2-dimethylsuccinonitrile, 2,3-dimethylsuccinonitrile, 2,3,3-trimethylsuccinonitrile, 2,2,3,3-tetramethylsuccinonitrile, 2,3-diethyl-2,3-dimethylsuccinonitrile, 2,2-diethyl-3,3-dimethylsuccinonitrile, bicyclohexyl-1,1-dicarbonitrile, bicyclohexyl-2,2-dicarbonitrile, bicyclohexyl-3,3-dicarbonitrile, 2,5-dimethyl-2,5-hexanedicarbonitrile, 2,3-diisobutyl-2,3-dimethylsuccinonitrile, 2,2-diisobutyl-3,3-dimethylsuccinonitrile, 2-methylglutaronitrile, 2,3-dimethylglutaronitrile, 2,4-dimethylglutaronitrile, 2,2,3,3-tetramethylglutaronitrile, 2,2,4,4-tetramethylglutaronitrile, 2,2,3,4-tetramethylglutaronitrile, 2,3,3,4-tetramethylglutaronitrile, 1,4-dicyanopentane, 2,6-dicyanoheptane, 2,7-dicyanooctane, 2,8-dicyanononane, 1,6-dicyanodecane, 1,2-dicyanobenzene, 1,3-dicyanobenzene, 1,4-dicyanobenzene, 3,3′-(ethylenedioxy)dipropionitrile, 3,3′-(ethylenedithio)dipropionitrile, 3,9-bis(2-cyanoethyl)-2,4,8,10-tetraoxaspiro[5,5]undecane, butanenitrile, and phthalonitrile. Particularly preferred among these may be succinonitrile, glutaronitrile, and adiponitrile.
Specific examples of the tricarbonitriles include pentanetricarbonitrile, propanetricarbonitrile, 1,3,5-hexanetricarbonitrile, 1,3,6-hexanetricarbonitrile, heptanetricarbonitrile, 1,2,3-propanetricarbonitrile, 1,3,5-pentanetricarbonitrile, cyclohexanetricarbonitrile, triscyanoethylamine, triscyanoethoxypropane, tricyanoethylene, and tris(2-cyanoethyl)amine. Particularly preferred may be 1,3,6-hexanetricarbonitrile and cyclohexanetricarbonitrile, and most preferred may be cyclohexanetricarbonitrile.
In the formula (1b), Rc is a hydrogen atom, a halogen atom, an alkyl group, a group obtainable by replacing at least one hydrogen atom of an alkyl group by a halogen atom, or a group represented by NC—Rc1—Xc1-(wherein Rc1 is an alkylene group; and Xc1 is an oxygen atom or a sulfur atom); Rd and Re are each independently a hydrogen atom, a halogen atom, an alkyl group, or a group obtainable by replacing at least one hydrogen atom of an alkyl group by a halogen atom.
Examples of the halogen atom, the alkyl group, and the group obtainable by replacing at least one hydrogen atom of an alkyl group by a halogen atom include those mentioned as examples thereof for the formula (1a).
Rc1 in NC—Rc1—Xc1— is an alkylene group. The alkylene group may be a C1-C3 alkylene group.
Rc, Rd, and Re may be each independently a hydrogen atom, a halogen atom, an alkyl group, or a group obtainable by replacing at least one hydrogen atom of an alkyl group by a halogen atom.
At least one selected from Rc, Rd, and Re may be a halogen atom or a group obtainable by replacing at least one hydrogen atom of an alkyl group by a halogen atom, or a fluorine atom or a group obtainable by replacing at least one hydrogen atom of an alkyl group by a fluorine atom.
When Rd and Re are each an alkyl group or a group obtainable by replacing at least one hydrogen atom of an alkyl group by a halogen atom, Rd and Re may bind to each other to form a cyclic structure (e.g., a cyclohexane ring).
In the formula (1b), m is an integer of 1 to 10. When m is 2 or greater, all of m Rds may be the same as each other, or at least part of them may be different from the others. The same applies to Re. In the formula, m may be an integer of 2 to 7, or an integer of 2 to 5.
Examples of the nitrile compound represented by the formula (1b) include acetonitrile, propionitrile, butyronitrile, isobutyronitrile, valeronitrile, isovaleronitrile, lauronitrile, 3-methoxypropionitrile, 2-methylbutyronitrile, trimethylacetonitrile, hexanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, fluoroacetonitrile, difluoroacetonitrile, trifluoroacetonitrile, 2-fluoropropionitrile, 3-fluoropropionitrile, 2,2-difluoropropionitrile, 2,3-difluoropropionitrile, 3,3-difluoropropionitrile, 2,2,3-trifluoropropionitrile, 3,3,3-trifluoropropionitrile, 3,3′-oxydipropionitrile, 3,3′-thiodipropionitrile, pentafluoropropionitrile, methoxyacetonitrile, and benzonitrile. Particularly preferred among these may be 3,3,3-trifluoropropionitrile.
In the formula (1c), Rf, Rg, Rh, and Ri are each independently a group containing a cyano group (CN), a hydrogen atom, a halogen atom, an alkyl group, or a group obtainable by replacing at least one hydrogen atom of an alkyl group by a halogen atom.
Examples of the halogen atom, the alkyl group, and the group obtainable by replacing at least one hydrogen atom of an alkyl group by a halogen atom include those mentioned as examples thereof for the formula (1a).
Examples of the group containing a cyano group include a cyano group and a group obtainable by replacing at least one hydrogen atom of an alkyl group by a cyano group. Examples of the alkyl group in this case include those mentioned as examples for the formula (1a).
At least one selected from Rf, Rg, Rh, and Ri is a group containing a cyano group. At least two selected from Rf, Rg, Rh, and Ri may be each a group containing a cyano group. Rh and Ri may be each a group containing a cyano group. When Rh and Ri are each a group containing a cyano group, Rf and Rg may be hydrogen atoms.
In the formula (1c), 1 is an integer of 1 to 3. When 1 is 2 or greater, all of 1 Rfs may be the same as each other, or at least part of them may be different from the others. The same applies to Rg. In the formula, 1 may be an integer of 1 or 2.
Examples of the nitrile compound represented by the formula (1c) include 3-hexenedinitrile, mucononitrile, maleonitrile, fumaronitrile, acrylonitrile, methacrylonitrile, crotononitrile, 3-methylcrotononitrile, 2-methyl-2-butenenitrile, 2-pentenenitrile, 2-methyl-2-pentenenitrile, 3-methyl-2-pentenenitrile, and 2-hexenenitrile. Preferred may be 3-hexenedinitrile and mucononitrile, or may be 3-hexenedinitrile.
The nitrile compounds may be present in an amount of 0.2 to 7% by mass relative to the electrolyte solution. This can further improve the high-temperature storage characteristics and safety of an electrochemical device at high voltage. The lower limit of the total amount of the nitrile compounds may be 0.3% by mass, or 0.5% by mass. The upper limit thereof may be 5% by mass, 2% by mass, or 0.5% by mass.
The electrolyte solution may contain a compound containing an isocyanate group (hereinafter, also abbreviated as “isocyanate”). The isocyanate used may be any isocyanate. Examples of the isocyanate include monoisocyanates, diisocyanates, and triisocyanates.
Specific examples of the monoisocyanate include isocyanatomethane, isocyanatoethane, 1-isocyanatopropane, 1-isocyanatobutane, 1-isocyanatopentane, 1-isocyanatohexane, 1-isocyanatoheptane, 1-isocyanatooctane, 1-isocyanatononane, 1-isocyanatodecane, isocyanatocyclohexane, methoxycarbonyl isocyanate, ethoxycarbonyl isocyanate, propoxycarbonyl isocyanate, butoxycarbonyl isocyanate, methoxysulfonyl isocyanate, ethoxysulfonyl isocyanate, propoxysulfonyl isocyanate, butoxysulfonyl isocyanate, fluorosulfonyl isocyanate, methyl isocyanate, butyl isocyanate, phenyl isocyanate, 2-isocyanatoethyl acrylate, 2-isocyanatoethyl methacrylate, and ethyl isocyanate.
Specific examples of the diisocyanates include 1,4-diisocyanatobutane, 1,5-diisocyanatopentane, 1,6-diisocyanatohexane, 1,7-diisocyanatoheptane, 1,8-diisocyanatooctane, 1,9-diisocyanatononane, 1,10-diisocyanatodecane, 1,3-diisocyanatopropene, 1,4-diisocyanato-2-butene, 1,4-diisocyanato-2-fluorobutane, 1,4-diisocyanato-2,3-difluorobutane, 1,5-diisocyanato-2-pentene, 1,5-diisocyanato-2-methylpentane, 1,6-diisocyanato-2-hexene, 1,6-diisocyanato-3-hexene, 1,6-diisocyanato-3-fluorohexane, 1,6-diisocyanato-3,4-difluorohexane, toluene diisocyanate, xylene diisocyanate, tolylene diisocyanate, 1,2-bis(isocyanatomethyl)cyclohexane, 1,3-bis(isocyanatomethyl)cyclohexane, 1,4-bis(isocyanatomethyl)cyclohexane, 1,2-diisocyanatocyclohexane, 1,3-diisocyanatocyclohexane, 1,4-diisocyanatocyclohexane, dicyclohexylmethane-1,1′-diisocyanate, dicyclohexylmethane-2,2′-diisocyanate, dicyclohexylmethane-3,3′-diisocyanate, dicyclohexylmethane-4,4′-diisocyanate, isophorone diisocyanate, bicyclo[2.2.1]heptane-2,5-diylbis(methyl=isocyanate), bicyclo[2.2.1]heptane-2,6-diylbis(methyl=isocyanate), 2,4,4-trimethylhexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, hexamethylene diisocyanate, 1,4-phenylene diisocyanate, octamethylene diisocyanate, and tetramethylene diisocyanate.
Specific examples of the triisocyanates include 1,6,11-triisocyanatoundecane, 4-isocyanatomethyl-1,8-octamethylene diisocyanate, 1,3,5-triisocyanatomethylbenzene, 1,3,5-tris(6-isocyanatohex-1-yl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, and 4-(isocyanatomethyl)octamethylene=diisocyanate.
In order to enable industrially easy availability and cause low cost in production of an electrolyte solution, preferred among these may be 1,6-diisocyanatohexane, 1,3-bis(isocyanatomethyl)cyclohexane, 1,3,5-tris(6-isocyanatohex-1-yl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 2,4,4-trimethylhexamethylene diisocyanate, and 2,2,4-trimethylhexamethylene diisocyanate. From the technical viewpoint, they can contribute to formation of a stable film-shaped structure and can therefore more suitably be used.
The isocyanate may be present in any amount that does not significantly impair the effects of the disclosure. The amount may be, but not limited to, 0.001% by mass or more and 1.0% by mass or less relative to the electrolyte solution. The isocyanate in an amount of not smaller than this lower limit can give a sufficient effect of improving the cycle characteristics to a non-aqueous electrolyte secondary battery. The isocyanate in an amount of not larger than this upper limit can eliminate an initial increase in resistance of a non-aqueous electrolyte secondary battery. The amount of the isocyanate may be 0.01% by mass or more, 0.1% by mass or more, or 0.2% by mass or more, while 0.8% by mass or less, 0.7% by mass or less, or 0.6% by mass or less.
The electrolyte solution may contain a cyclic sulfonate. The cyclic sulfonate may be any cyclic sulfonate. Examples of the cyclic sulfonate include a saturated cyclic sulfonate, an unsaturated cyclic sulfonate, a saturated cyclic disulfonate, and an unsaturated cyclic disulfonate.
Specific examples of the saturated cyclic sulfonate include 1,3-propanesultone, 1-fluoro-1,3-propanesultone, 2-fluoro-1,3-propanesultone, 3-fluoro-1,3-propanesultone, 1-methyl-1,3-propanesultone, 2-methyl-1,3-propanesultone, 3-methyl-1,3-propanesultone, 1,3-butanesultone, 1,4-butanesultone, 1-fluoro-1,4-butanesultone, 2-fluoro-1,4-butanesultone, 3-fluoro-1,4-butanesultone, 4-fluoro-1,4-butanesultone, 1-methyl-1,4-butanesultone, 2-methyl-1,4-butanesultone, 3-methyl-1,4-butanesultone, 4-methyl-1,4-butanesultone, and 2,4-butanesultone.
Specific examples of the unsaturated cyclic sulfonate include 1-propene-1,3-sultone, 2-propene-1,3-sultone, 1-fluoro-1-propene-1,3-sultone, 2-fluoro-1-propene-1,3-sultone, 3-fluoro-1-propene-1,3-sultone, 1-fluoro-2-propene-1,3-sultone, 2-fluoro-2-propene-1,3-sultone, 3-fluoro-2-propene-1,3-sultone, 1-methyl-1-propene-1,3-sultone, 2-methyl-1-propene-1,3-sultone, 3-methyl-1-propene-1,3-sultone, 1-methyl-2-propene-1,3-sultone, 2-methyl-2-propene-1,3-sultone, 3-methyl-2-propene-1,3-sultone, 1-butene-1,4-sultone, 2-butene-1,4-sultone, 3-butene-1,4-sultone, 1-fluoro-1-butene-1,4-sultone, 2-fluoro-1-butene-1,4-sultone, 3-fluoro-1-butene-1,4-sultone, 4-fluoro-1-butene-1,4-sultone, 1-fluoro-2-butene-1,4-sultone, 2-fluoro-2-butene-1,4-sultone, 3-fluoro-2-butene-1,4-sultone, 4-fluoro-2-butene-1,4-sultone, 1,3-propenesultone, 1-fluoro-3-butene-1,4-sultone, 2-fluoro-3-butene-1,4-sultone, 3-fluoro-3-butene-1,4-sultone, 4-fluoro-3-butene-1,4-sultone, 1-methyl-1-butene-1,4-sultone, 2-methyl-1-butene-1,4-sultone, 3-methyl-1-butene-1,4-sultone, 4-methyl-1-butene-1,4-sultone, 1-methyl-2-butene-1,4-sultone, 2-methyl-2-butene-1,4-sultone, 3-methyl-2-butene-1,4-sultone, 4-methyl-2-butene-1,4-sultone, 1-methyl-3-butene-1,4-sultone, 2-methyl-3-butene-1,4-sultone, 3-methyl-3-butene-1,4-sultone, and 4-methyl-3-butene-1,4-sultone.
In order to enable easy availability and contribute to formation of a stable film-shaped structure, more preferred among these may be 1,3-propanesultone, 1-fluoro-1,3-propanesultone, 2-fluoro-1,3-propanesultone, 3-fluoro-1,3-propanesultone, and 1-propene-1,3-sultone. The cyclic sulfonate may be in any amount that does not significantly impair the effects of the disclosure. The amount may be, but not limited to, 0.001% by mass or more and 3.0% by mass or less relative to the electrolyte solution.
The cyclic sulfonate in an amount of not smaller than this lower limit can give a sufficient effect of improving the cycle characteristics to a non-aqueous electrolyte secondary battery. The cyclic sulfonate in an amount of not larger than this upper limit can eliminate an increase in the cost of producing a non-aqueous electrolyte secondary battery. The amount of the cyclic sulfonate may be 0.01% by mass or more, 0.1% by mass or more, or 0.2% by mass or more, while 2.5% by mass or less, 2.0% by mass or less, or 1.8% by mass or less.
The electrolyte solution may further contain a polyethylene oxide that has a weight average molecular weight of 2000 to 4000 and has —OH, —OCOOH, or —COOH at an end.
The presence of such a compound can improve the stability at the interfaces with the respective electrodes, improving the characteristics of an electrochemical device.
Examples of the polyethylene oxide include polyethylene oxide monool, polyethylene oxide carboxylic acid, polyethylene oxide diol, polyethylene oxide dicarboxylic acid, polyethylene oxide triol, and polyethylene oxide tricarboxylic acid. One of these may be used alone or two or more thereof may be used in any combination.
In order to give better characteristics of an electrochemical device, preferred may be a mixture of polyethylene oxide monool and polyethylene oxide diol and a mixture of polyethylene carboxylic acid and polyethylene dicarboxylic acid.
The polyethylene oxide having too small a weight average molecular weight may be easily oxidatively decomposed. The weight average molecular weight may be 3000 to 4000.
The weight average molecular weight can be determined by gel permeation chromatography (GPC) in polystyrene equivalent.
The polyethylene oxide may be present in an amount of 1×10−6 to 1×10−2 mol/kg in the electrolyte solution. Too large an amount of the polyethylene oxide may cause poor characteristics of an electrochemical device.
The amount of the polyethylene oxide may be 5×10−6 mol/kg or more.
The electrolyte solution may further contain as an additive any of other components such as a fluorinated saturated cyclic carbonate, an unsaturated cyclic carbonate, an overcharge inhibitor, and a known different aid. This can reduce impairment of the characteristics of an electrochemical device.
Examples of the fluorinated saturated cyclic carbonate include compounds represented by the aforementioned formula (A). Preferred among these may be fluoroethylene carbonate, difluoroethylene carbonate, monofluoromethyl ethylene carbonate, trifluoromethyl ethylene carbonate, 2,2,3,3,3-pentafluoropropylethylene carbonate, and (4-(2,2,3,3,3-pentafluoro-propyl)-[1,3]dioxolan-2-one). One fluorinated saturated cyclic carbonate may be used alone, or two or more thereof may be used in any combination at any ratio.
The fluorinated saturated cyclic carbonate may be present in an amount of 0.001 to 10% by mass, 0.01 to 5% by mass, or 0.1 to 3% by mass, relative to the electrolyte solution.
Examples of the unsaturated cyclic carbonate include vinylene carbonate compounds, ethylene carbonate compounds substituted with a substituent that contains an aromatic ring, a carbon-carbon double bond, or a carbon-carbon triple bond, phenyl carbonate compounds, vinyl carbonate compounds, allyl carbonate compounds, and catechol carbonate compounds.
Examples of the vinylene carbonate compounds include vinylene carbonate, methylvinylene carbonate, 4,5-dimethylvinylene carbonate, phenylvinylene carbonate, 4,5-diphenylvinylene carbonate, vinylvinylene carbonate, 4,5-divinylvinylene carbonate, allylvinylene carbonate, 4,5-diallylvinylene carbonate, 4-fluorovinylene carbonate, 4-fluoro-5-methylvinylene carbonate, 4-fluoro-5-phenylvinylene carbonate, 4-fluoro-5-vinylvinylene carbonate, 4-allyl-5-fluorovinylene carbonate, ethynylethylene carbonate, propargylethylene carbonate, methylvinylene carbonate, and dimethylvinylene carbonate.
Specific examples of the ethylene carbonate compounds substituted with a substituent that contains an aromatic ring, a carbon-carbon double bond, or a carbon-carbon triple bond include vinylethylene carbonate, 4,5-divinylethylene carbonate, 4-methyl-5-vinylethylene carbonate, 4-allyl-5-vinylethylene carbonate, ethynylethylene carbonate, 4,5-diethynylethylene carbonate, 4-methyl-5-ethynylethylene carbonate, 4-vinyl-5-ethynylethylene carbonate, 4-allyl-5-ethynylethylene carbonate, phenylethylene carbonate, 4,5-diphenylethylene carbonate, 4-phenyl-5-vinylethylene carbonate, 4-allyl-5-phenylethylene carbonate, allylethylene carbonate, 4,5-diallylethylene carbonate, 4-methyl-5-allylethylene carbonate, 4-methylene-1,3-dioxolan-2-one, 4,5-dimethylene-1,3-dioxolan-2-one, and 4-methyl-5-allylethylene carbonate.
The unsaturated cyclic carbonate may be vinylene carbonate, methylvinylene carbonate, 4,5-dimethylvinylene carbonate, vinylvinylene carbonate, 4,5-vinylvinylene carbonate, allylvinylene carbonate, 4,5-diallylvinylene carbonate, vinylethylene carbonate, 4,5-divinylethylene carbonate, 4-methyl-5-vinylethylene carbonate, allylethylene carbonate, 4,5-diallylethylene carbonate, 4-methyl-5-allylethylene carbonate, 4-allyl-5-vinylethylene carbonate, ethynylethylene carbonate, 4,5-diethynylethylene carbonate, 4-methyl-5-ethynylethylene carbonate, and 4-vinyl-5-ethynylethylene carbonate. In order to form a more stable interface protecting film, particularly preferred may be vinylene carbonate, vinylethylene carbonate, and ethynylethylene carbonate, and most preferred may be vinylene carbonate.
The unsaturated cyclic carbonate may have any molecular weight that does not significantly impair the effects of the disclosure. The molecular weight may be 50 or higher and 250 or lower. The unsaturated cyclic carbonate having a molecular weight within this range can easily ensure its solubility in the electrolyte solution and can easily lead to sufficient achievement of the effects of the disclosure. The molecular weight of the unsaturated cyclic carbonate may be 80 or higher and 150 or lower.
The unsaturated cyclic carbonate may be produced by any production method, and may be produced by a known method selected as appropriate.
One unsaturated cyclic carbonate may be used alone or two or more thereof may be used in any combination at any ratio.
The unsaturated cyclic carbonate may be present in any amount that does not significantly impair the effects of the disclosure. The amount of the unsaturated cyclic carbonate may be 0.001% by mass or more, 0.01% by mass or more, or 0.1% by mass or more, of 100% by mass of the electrolyte solution. The amount may be 5% by mass or less, 4% by mass or less, or 3% by mass or less. The unsaturated cyclic carbonate in an amount within the above range allows an electrochemical device containing the electrolyte solution to easily exhibit a sufficient effect of improving the cycle characteristics, and can easily avoid a situation with impaired high-temperature storage characteristics, generation of a large amount of gas, and a reduced discharge capacity retention.
In addition to the aforementioned non-fluorinated unsaturated cyclic carbonates, a fluorinated unsaturated cyclic carbonate may also suitably be used as an unsaturated cyclic carbonate.
The fluorinated unsaturated cyclic carbonate is a cyclic carbonate containing an unsaturated bond and a fluorine atom. The number of fluorine atoms in the fluorinated unsaturated cyclic carbonate may be any number that is 1 or greater. The number of fluorine atoms may be 6 or smaller, 4 or smaller, or 1 or 2.
Examples of the fluorinated unsaturated cyclic carbonate include fluorinated vinylene carbonate derivatives and fluorinated ethylene carbonate derivatives substituted with a substituent that contains an aromatic ring or a carbon-carbon double bond.
Examples of the fluorinated vinylene carbonate derivatives include 4-fluorovinylene carbonate, 4-fluoro-5-methylvinylene carbonate, 4-fluoro-5-phenylvinylene carbonate, 4-allyl-5-fluorovinylene carbonate, and 4-fluoro-5-vinylvinylene carbonate.
Examples of the fluorinated ethylene carbonate derivatives substituted with a substituent that contains an aromatic ring or a carbon-carbon double bond include 4-fluoro-4-vinylethylene carbonate, 4-fluoro-4-allylethylene carbonate, 4-fluoro-5-vinylethylene carbonate, 4-fluoro-5-allylethylene carbonate, 4,4-difluoro-4-vinylethylene carbonate, 4,4-difluoro-4-allylethylene carbonate, 4,5-difluoro-4-vinylethylene carbonate, 4,5-difluoro-4-allylethylene carbonate, 4-fluoro-4,5-divinylethylene carbonate, 4-fluoro-4,5-diallylethylene carbonate, 4,5-difluoro-4,5-divinylethylene carbonate, 4,5-difluoro-4,5-diallylethylene carbonate, 4-fluoro-4-phenylethylene carbonate, 4-fluoro-5-phenylethylene carbonate, 4,4-difluoro-5-phenylethylene carbonate, and 4,5-difluoro-4-phenylethylene carbonate.
In order to form a stable interface protecting film, more suitably used as the fluorinated unsaturated cyclic carbonate are 4-fluorovinylene carbonate, 4-fluoro-5-methylvinylene carbonate, 4-fluoro-5-vinylvinylene carbonate, 4-allyl-5-fluorovinylene carbonate, 4-fluoro-4-vinylethylene carbonate, 4-fluoro-4-allylethylene carbonate, 4-fluoro-5-vinylethylene carbonate, 4-fluoro-5-allylethylene carbonate, 4,4-difluoro-4-vinylethylene carbonate, 4,4-difluoro-4-allylethylene carbonate, 4,5-difluoro-4-vinylethylene carbonate, 4,5-difluoro-4-allylethylene carbonate, 4-fluoro-4,5-divinylethylene carbonate, 4-fluoro-4,5-diallylethylene carbonate, 4,5-difluoro-4,5-divinylethylene carbonate, and 4,5-difluoro-4,5-diallylethylene carbonate.
The fluorinated unsaturated cyclic carbonate may have any molecular weight that does not significantly impair the effects of the disclosure. The molecular weight may be 50 or higher and 500 or lower. The fluorinated unsaturated cyclic carbonate having a molecular weight within this range can easily ensure the solubility of the fluorinated unsaturated cyclic carbonate in the electrolyte solution.
The fluorinated unsaturated cyclic carbonate may be produced by any method, and may be produced by any known method selected as appropriate. The molecular weight may be 100 or higher and 200 or lower.
One fluorinated unsaturated cyclic carbonate may be used alone or two or more thereof may be used in any combination at any ratio. The fluorinated unsaturated cyclic carbonate may be contained in any amount that does not significantly impair the effects of the disclosure. The amount of the fluorinated unsaturated cyclic carbonate may be 0.001% by mass or more, 0.01% by mass or more, or 0.1% by mass or more, while 5% by mass or less, 4% by mass or less, or 3% by mass or less, of 100% by mass of the electrolyte solution. The fluorinated unsaturated cyclic carbonate in an amount within this range allows an electrochemical device containing the electrolyte solution to exhibit an effect of sufficiently improving the cycle characteristics and can easily avoid a situation with reduced high-temperature storage characteristics, generation of a large amount of gas, and a reduced discharge capacity retention.
The electrolyte solution may contain a compound containing a triple bond. This compound may be of any type as long as it contains one or more triple bonds in the molecule.
Specific examples of the compound containing a triple bond include the following compounds:
In order to more stably form a negative electrode film in the electrolyte solution, preferred among these may be compounds containing an alkynyloxy group.
In order to improve the storage characteristics, particularly preferred may be compounds such as 2-propynylmethyl carbonate, di-2-propynyl carbonate, 2-butyne-1,4-diol dimethyl dicarbonate, 2-propynyl acetate, 2-butyne-1,4-diol diacetate, methyl 2-propynyl oxalate, and di-2-propynyl oxalate.
One compound containing a triple bond may be used alone or two or more thereof may be used in any combination at any ratio. The compound containing a triple bond may be present in any amount that does not significantly impair the effects of the disclosure relative to the whole electrolyte solution. The compound may be contained at a concentration of 0.01% by mass or more, 0.05% by mass or more, or 0.1% by mass or more, while 5% by mass or less, 3% by mass or less, or 1% by mass or less, relative to the electrolyte solution of the disclosure. The compound satisfying the above range can further improve the effects such as output characteristics, load characteristics, cycle characteristics, and high-temperature storage characteristics.
In order to effectively reduce burst or combustion of a battery in case of overcharge, for example, of an electrochemical device containing the electrolyte solution, the electrolyte solution may contain an overcharge inhibitor.
Examples of the overcharge inhibitor include aromatic compounds, including unsubstituted or alkyl-substituted terphenyl derivatives such as biphenyl, o-terphenyl, m-terphenyl, and p-terphenyl, partially hydrogenated products of unsubstituted or alkyl-substituted terphenyl derivatives, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, dibenzofuran, diphenyl cyclohexane, 1,1,3-trimethyl-3-phenylindan, cyclopentylbenzene, cyclohexylbenzene, cumene, 1,3-diisopropylbenzene, 1,4-diisopropylbenzene, t-butylbenzene, t-amylbenzene, t-hexylbenzene, and anisole; partially fluorinated products of the aromatic compounds such as 2-fluorobiphenyl, 4-fluorobiphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene, fluorotoluene, and benzotrifluoride; fluorine-containing anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, 1,6-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole; aromatic acetates such as 3-propylphenyl acetate, 2-ethylphenyl acetate, benzylphenyl acetate, methylphenyl acetate, benzyl acetate, and phenethylphenyl acetate; aromatic carbonates such as diphenyl carbonate and methylphenyl carbonate, toluene derivatives such as toluene and xylene, and unsubstituted or alkyl-substituted biphenyl derivatives such as 2-methylbiphenyl, 3-methylbiphenyl, 4-methylbiphenyl, and o-cyclohexylbiphenyl. Preferred among these may be aromatic compounds such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, and dibenzofuran, diphenyl cyclohexane, 1,1,3-trimethyl-3-phenylindan, 3-propylphenyl acetate, 2-ethylphenyl acetate, benzylphenyl acetate, methylphenyl acetate, benzyl acetate, diphenyl carbonate, and methylphenyl carbonate. One of these compounds may be used alone or two or more thereof may be used in any combination. In order to achieve good balance between the overcharge inhibiting characteristics and the high-temperature storage characteristics with a combination use of two or more thereof, preferred may be a combination of cyclohexylbenzene and t-butylbenzene or t-amylbenzene, or a combination of at least one oxygen-free aromatic compound selected from the group consisting of biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, and the like and at least one oxygen-containing aromatic compound selected from the group consisting of diphenyl ether, dibenzofuran, and the like.
The electrolyte solution used in the disclosure may contain a carboxylic anhydride other than the compound (2). The carboxylic anhydride may be a compound represented by the following formula (6). The carboxylic anhydride may be produced by any method which may be selected from known methods as appropriate.
In the formula (6), R61 and R62 are each independently a hydrocarbon group having a carbon number of 1 or greater and 15 or smaller and optionally containing a substituent.
R61 and R62 each may be any monovalent hydrocarbon group. For example, each of them may be either an aliphatic hydrocarbon group or an aromatic hydrocarbon group, or may be a bond of an aliphatic hydrocarbon group and an aromatic hydrocarbon group. The aliphatic hydrocarbon group may be a saturated hydrocarbon group and may contain an unsaturated bond (carbon-carbon double bond or carbon-carbon triple bond). The aliphatic hydrocarbon group may be either acyclic or cyclic. In the case of an acyclic group, it may be either linear or branched. The group may be a bond of an acyclic group and a cyclic group. R61 and R62 may be the same as or different from each other.
When the hydrocarbon group for R61 and R62 contains a substituent, the substituent may be of any type as long as it is not beyond the scope of the disclosure. Examples thereof include halogen atoms such as a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom. Preferred may be a fluorine atom. Examples of the substituent other than the halogen atoms include substituents containing a functional group such as an ester group, a cyano group, a carbonyl group, or an ether group. Preferred may be a cyano group and a carbonyl group. The hydrocarbon group for R61 and R62 may contain only one of these substituents or may contain two or more thereof. When two or more substituents are contained, these substituents may be the same as or different from each other.
The hydrocarbon group for R61 and R62 may have a carbon number of 1 or greater, while 15 or smaller, 12 or smaller, 10 or smaller, or 9 or smaller. When R61 and R62 bind to each other to form a divalent hydrocarbon group, the divalent hydrocarbon group may have a carbon number of 1 or greater, while 15 or smaller, 13 or smaller, 10 or smaller, or 8 or smaller. When the hydrocarbon group for R61 and R62 contains a substituent that contains a carbon atom, the carbon number of the whole R61 or R62 including the substituent may satisfy the above range.
Next, specific examples of the acid anhydride represented by the formula (6) are described. In the following examples, the term “analog” means an acid anhydride obtainable by replacing part of the structure of an acid anhydride mentioned as an example by another structure within the scope of the disclosure. Examples thereof include dimers, trimers, and tetramers each composed of a plurality of acid anhydrides, those having respective substituents which are structural isomers having the same carbon number but having different branch structures, and those having the same substituent but at different sites in an acid anhydride.
First, specific examples of an acid anhydride in which R61 and R62 are the same as each other are described.
Specific examples of an acid anhydride in which R61 and R62 are acyclic alkyl groups include acetic anhydride, propionic anhydride, butanoic anhydride, 2-methylpropionic anhydride, 2,2-dimethylpropionic anhydride, 2-methylbutanoic anhydride, 3-methylbutanoic anhydride, 2,2-dimethylbutanoic anhydride, 2,3-dimethylbutanoic anhydride, 3,3-dimethylbutanoic anhydride, 2,2,3-trimethylbutanoic anhydride, 2,3,3-trimethylbutanoic anhydride, 2,2,3,3-tetramethylbutanoic anhydride, and 2-ethylbutanoic anhydride, and analogs thereof.
Specific examples of an acid anhydride in which R61 and R62 are cyclic alkyl groups include cyclopropanecarboxylic anhydride, cyclopentanecarboxylic anhydride, and cyclohexanecarboxylic anhydride, and analogs thereof.
Specific examples of an acid anhydride in which R61 and R62 are alkenyl groups include acrylic anhydride, 2-methylacrylic anhydride, 3-methylacrylic anhydride, 2,3-dimethylacrylic anhydride, 3,3-dimethylacrylic anhydride, 2,3,3-trimethylacrylic anhydride, 2-phenylacrylic anhydride, 3-phenylacrylic anhydride, 2,3-diphenylacrylic anhydride, 3,3-diphenylacrylic anhydride, 3-butenoic anhydride, 2-methyl-3-butenoic anhydride, 2,2-dimethyl-3-butenoic anhydride, 3-methyl-3-butenoic anhydride, 2-methyl-3-methyl-3-butenoic anhydride, 2,2-dimethyl-3-methyl-3-butenoic anhydride, 3-pentenoic anhydride, 4-pentenoic anhydride, 2-cyclopentenecarboxylic anhydride, 3-cyclopentenecarboxylic anhydride, and 4-cyclopentenecarboxylic anhydride, and analogs thereof.
Specific examples of an acid anhydride in which R61 and R62 are alkynyl groups include propynoic anhydride, 3-phenylpropynoic anhydride, 2-butynoic anhydride, 2-penthynoic anhydride, 3-butynoic anhydride, 3-penthynoic anhydride, and 4-penthynoic anhydride, and analogs thereof.
Specific examples of an acid anhydride in which R61 and R62 are aryl groups include benzoic anhydride, 4-methylbenzoic anhydride, 4-ethylbenzoic anhydride, 4-tert-butylbenzoic anhydride, 2-methylbenzoic anhydride, 2,4,6-trimethylbenzoic anhydride, 1-naphthalenecarboxylic anhydride, and 2-naphthalenecarboxylic anhydride, and analogs thereof.
Examples of an acid anhydride substituted with a fluorine atom are mainly listed below as examples of the acid anhydride in which R61 and R62 are substituted with a halogen atom. Acid anhydrides obtainable by replacing any or all of the fluorine atoms thereof with a chlorine atom, a bromine atom, or an iodine atom are also included in the exemplary compounds.
Examples of an acid anhydride in which R61 and R62 are halogen-substituted acyclic alkyl groups include fluoroacetic anhydride, difluoroacetic anhydride, trifluoroacetic anhydride, 2-fluoropropionic anhydride, 2,2-difluoropropionic anhydride, 2,3-difluoropropionic anhydride, 2,2,3-trifluoropropionic anhydride, 2,3,3-trifluoropropionic anhydride, 2,2,3,3-tetrapropionic anhydride, 2,3,3,3-tetrapropionic anhydride, 3-fluoropropionic anhydride, 3,3-difluoropropionic anhydride, 3,3,3-trifluoropropionic anhydride, and perfluoropropionic anhydride, and analogs thereof.
Examples of an acid anhydride in which R61 and R62 are halogen-substituted cyclic alkyl groups include 2-fluorocyclopentanecarboxylic anhydride, 3-fluorocyclopentanecarboxylic anhydride, and 4-fluorocyclopentanecarboxylic anhydride, and analogs thereof.
Examples of an acid anhydride in which R61 and R62 are halogen-substituted alkenyl groups include 2-fluoroacrylic anhydride, 3-fluoroacrylic anhydride, 2,3-difluoroacrylic anhydride, 3,3-difluoroacrylic anhydride, 2,3,3-trifluoroacrylic anhydride, 2-(trifluoromethyl)acrylic anhydride, 3-(trifluoromethyl)acrylic anhydride, 2,3-bis(trifluoromethyl)acrylic anhydride, 2,3,3-tris(trifluoromethyl)acrylic anhydride, 2-(4-fluorophenyl)acrylic anhydride, 3-(4-fluorophenyl)acrylic anhydride, 2,3-bis(4-fluorophenyl)acrylic anhydride, 3,3-bis(4-fluorophenyl)acrylic anhydride, 2-fluoro-3-butenoic anhydride, 2,2-difluoro-3-butenoic anhydride, 3-fluoro-2-butenoic anhydride, 4-fluoro-3-butenoic anhydride, 3,4-difluoro-3-butenoic anhydride, and 3,3,4-trifluoro-3-butenoic anhydride, and analogs thereof.
Examples of an acid anhydride in which R61 and R62 are halogen-substituted alkynyl groups include 3-fluoro-2-propynoic anhydride, 3-(4-fluorophenyl)-2-propynoic anhydride, 3-(2,3,4,5,6-pentafluorophenyl)-2-propynoic anhydride, 4-fluoro-2-butynoic anhydride, 4,4-difluoro-2-butynoic anhydride, and 4,4,4-trifluoro-2-butynoic anhydride, and analogs thereof.
Examples of an acid anhydride in which R61 and R62 are halogen-substituted aryl groups include 4-fluorobenzoic anhydride, 2,3,4,5,6-pentafluorobenzoic anhydride, and 4-trifluoromethylbenzoic anhydride, and analogs thereof.
Examples of an acid anhydride in which R61 and R62 each contain a substituent containing a functional group such as an ester, a nitrile, a ketone, an ether, or the like include methoxyformic anhydride, ethoxyformic anhydride, methyloxalic anhydride, ethyloxalic anhydride, 2-cyanoacetic anhydride, 2-oxopropionic anhydride, 3-oxobutanoic anhydride, 4-acetylbenzoic anhydride, methoxyacetic anhydride, and 4-methoxybenzoic anhydride, and analogs thereof.
Then, specific examples of an acid anhydride in which R61 and R62 are different from each other are described below.
R61 and R62 may be in any combination of those mentioned as examples above and analogs thereof. The following gives representative examples.
Examples of a combination of acyclic alkyl groups include acetic propionic anhydride, acetic butanoic anhydride, butanoic propionic anhydride, and acetic 2-methylpropionic anhydride.
Examples of a combination of an acyclic alkyl group and a cyclic alkyl group include acetic cyclopentanoic anhydride, acetic cyclohexanoic anhydride, and cyclopentanoic propionic anhydride.
Examples of a combination of an acyclic alkyl group and an alkenyl group include acetic acrylic anhydride, acetic 3-methylacrylic anhydride, acetic 3-butenoic anhydride, and acrylic propionic anhydride.
Examples of a combination of an acyclic alkyl group and an alkynyl group include acetic propynoic anhydride, acetic 2-butynoic anhydride, acetic 3-butynoic anhydride, acetic 3-phenyl propynoic anhydride, and propionic propynoic anhydride.
Examples of a combination of an acyclic alkyl group and an aryl group include acetic benzoic anhydride, acetic 4-methylbenzoic anhydride, acetic 1-naphthalenecarboxylic anhydride, and benzoic propionic anhydride.
Examples of a combination of an acyclic alkyl group and a hydrocarbon group containing a functional group include acetic fluoroacetic anhydride, acetic trifluoroacetic anhydride, acetic 4-fluorobenzoic anhydride, fluoroacetic propionic anhydride, acetic alkyloxalic anhydride, acetic 2-cyanoacetic anhydride, acetic 2-oxopropionic anhydride, acetic methoxyacetic anhydride, and methoxyacetic propionic anhydride.
Examples of a combination of cyclic alkyl groups include cyclopentanoic cyclohexanoic anhydride.
Examples of a combination of a cyclic alkyl group and an alkenyl group include acrylic cyclopentanoic anhydride, 3-methylacrylic cyclopentanoic anhydride, 3-butenoic cyclopentanoic anhydride, and acrylic cyclohexanoic anhydride.
Examples of a combination of a cyclic alkyl group and an alkynyl group include propynoic cyclopentanoic anhydride, 2-butynoic cyclopentanoic anhydride, and propynoic cyclohexanoic anhydride.
Examples of a combination of a cyclic alkyl group and an aryl group include benzoic cyclopentanoic anhydride, 4-methylbenzoic cyclopentanoic anhydride, and benzoic cyclohexanoic anhydride.
Examples of a combination of a cyclic alkyl group and a hydrocarbon group containing a functional group include fluoroacetic cyclopentanoic anhydride, cyclopentanoic trifluoroacetic anhydride, cyclopentanoic 2-cyanoacetic anhydride, cyclopentanoic methoxyacetic anhydride, and cyclohexanoic fluoroacetic anhydride.
Examples of a combination of alkenyl groups include acrylic 2-methylacrylic anhydride, acrylic 3-methylacrylic anhydride, acrylic 3-butenoic anhydride, and 2-methylacrylic 3-methylacrylic anhydride.
Examples of a combination of an alkenyl group and an alkynyl group include acrylic propynoic anhydride, acrylic 2-butynoic anhydride, and 2-methylacrylic propynoic anhydride.
Examples of a combination of an alkenyl group and an aryl group include acrylic benzoic anhydride, acrylic 4-methylbenzoic anhydride, and 2-methylacrylic benzoic anhydride.
Examples of a combination of an alkenyl group and a hydrocarbon group containing a functional group include acrylic fluoroacetic anhydride, acrylic trifluoroacetic anhydride, acrylic 2-cyanoacetic anhydride, acrylic methoxyacetic anhydride, and 2-methylacrylic fluoroacetic anhydride.
Examples of a combination of alkynyl groups include propynoic 2-butynoic anhydride, propynoic 3-butynoic anhydride, and 2-butynoic 3-butynoic anhydride.
Examples of a combination of an alkynyl group and an aryl group include benzoic propynoic anhydride, 4-methylbenzoic propynoic anhydride, and benzoic 2-butynoic anhydride.
Examples of a combination of an alkynyl group and a hydrocarbon group containing a functional group include propynoic fluoroacetic anhydride, propynoic trifluoroacetic anhydride, propynoic 2-cyanoacetic anhydride, propynoic methoxyacetic anhydride, and 2-butynoic fluoroacetic anhydride.
Examples of a combination of aryl groups include benzoic 4-methylbenzoic anhydride, benzoic 1-naphthalenecarboxylic anhydride, and 4-methylbenzoic 1-naphthalenecarboxylic anhydride.
Examples of a combination of an aryl group and a hydrocarbon group containing a functional group include benzoic fluoroacetic anhydride, benzoic trifluoroacetic anhydride, benzoic 2-cyanoacetic anhydride, benzoic methoxyacetic anhydride, and 4-methylbenzoic fluoroacetic anhydride.
Examples of a combination of hydrocarbon groups each containing a functional group include fluoroacetic trifluoroacetic anhydride, fluoroacetic 2-cyanoacetic anhydride, fluoroacetic methoxyacetic anhydride, and trifluoroacetic 2-cyanoacetic anhydride.
Preferred among the acid anhydrides having an acyclic structure may be acetic anhydride, propionic anhydride, 2-methylpropionic anhydride, cyclopentanecarboxylic anhydride, cyclohexanecarboxylic anhydride, acrylic anhydride, 2-methylacrylic anhydride, 3-methylacrylic anhydride, 2,3-dimethylacrylic anhydride, 3,3-dimethylacrylic anhydride, 3-butenoic anhydride, 2-methyl-3-butenoic anhydride, propynoic anhydride, 2-butynoic anhydride, benzoic anhydride, 2-methylbenzoic anhydride, 4-methylbenzoic anhydride, 4-tert-butylbenzoic anhydride, trifluoroacetic anhydride, 3,3,3-trifluoropropionic anhydride, 2-(trifluoromethyl)acrylic anhydride, 2-(4-fluorophenyl)acrylic anhydride, 4-fluorobenzoic anhydride, 2,3,4,5,6-pentafluorobenzoic anhydride, methoxyformic anhydride, and ethoxyformic anhydride. More preferred may be acrylic anhydride, 2-methylacrylic anhydride, 3-methylacrylic anhydride, benzoic anhydride, 2-methylbenzoic anhydride, 4-methylbenzoic anhydride, 4-tert-butylbenzoic anhydride, 4-fluorobenzoic anhydride, 2,3,4,5,6-pentafluorobenzoic anhydride, methoxyformic anhydride, and ethoxyformic anhydride.
These compounds may be preferred because they can appropriately form a bond with lithium oxalate to provide a film having excellent durability, thereby improving especially the charge and discharge rate characteristics after a durability test, input and output characteristics, and impedance characteristics.
The carboxylic anhydride may have any molecular weight that does not significantly impair the effects of the disclosure. The molecular weight may be 90 or higher, or 95 or higher, while 300 or lower, or 200 or lower. The carboxylic anhydride having a molecular weight within the above range can reduce an increase in viscosity of an electrolyte solution and can give a reasonable film density, appropriately improving the durability.
The carboxylic anhydride may be formed by any production method which may be selected from known methods. One of the carboxylic anhydrides described above alone may be contained in the non-aqueous electrolyte solution, or two or more thereof may be contained in any combination at any ratio.
The carboxylic anhydride may be contained in any amount that does not significantly impair the effects of the disclosure relative to the electrolyte solution. The carboxylic anhydride may be contained at a concentration of 0.01% by mass or more, or 0.1% by mass or more, while 5% by mass or less, or 3% by mass or less, relative to the electrolyte solution. The carboxylic anhydride in an amount within the above range can easily achieve an effect of improving the cycle characteristics and have good reactivity, easily improving the battery characteristics.
The electrolyte solution may further contain a known different aid. Examples of the different aid include hydrocarbon compounds such as pentane, heptane, octane, nonane, decane, cycloheptane, benzene, furan, naphthalene, 2-phenyl bicyclohexyl, cyclohexane, 2,4,8,10-tetraoxaspiro[5.5]undecane, and 3,9-divinyl-2,4,8,10-tetraoxaspiro[5.5]undecane;
One of these compounds may be used alone or two or more thereof may be used in any combination. These aids can improve the capacity retention characteristics and the cycle characteristics after high-temperature storage.
Preferred among these as the different aid may be phosphorus-containing compounds, and preferred may be tris(trimethylsilyl) phosphate and tris(trimethylsilyl) phosphite.
The different aid may be present in any amount that does not significantly impair the effects of the disclosure. The amount of the different aid may be 0.01% by mass or more and 5% by mass or less of 100% by mass of the electrolyte solution. The different aid in an amount within this range can easily sufficiently exhibit the effects thereof and can easily avoid a situation with impairment of battery characteristics such as high-load discharge characteristics. The amount of the different aid may be 0.1% by mass or more, or 0.2% by mass or more, while 3% by mass or less, or 1% by mass or less.
The electrolyte solution may further contain as an additive any of a cyclic carboxylate, an acyclic carboxylate, an ether compound, a nitrogen-containing compound, a boron-containing compound, an organosilicon-containing compound, a fireproof agent (flame retardant), a surfactant, an additive for increasing the permittivity, an improver for cycle characteristics and rate characteristics, and a sulfone-based compound to the extent that the effects of the disclosure are not impaired.
Examples of the cyclic carboxylate include those having a carbon number of 3 to 12 in total in the structural formula. Specific examples thereof include gamma-butyrolactone, gamma-valerolactone, gamma-caprolactone, epsilon-caprolactone, and 3-methyl-y-butyrolactone. In order to improve the characteristics of an electrochemical device owing to improvement in the degree of dissociation of lithium ions, particularly preferred may be gamma-butyrolactone.
In general, the cyclic carboxylate as an additive may be present in an amount of 0.1% by mass or more, or 1% by mass or more, of 100% by mass of the solvent. The cyclic carboxylate in an amount within this range can easily improve the electric conductivity of the electrolyte solution, improving the large-current discharge characteristics of an electrochemical device. The amount of the cyclic carboxylate may be 10% by mass or less, or 5% by mass or less. Such an upper limit may allow the electrolyte solution to have a viscosity within an appropriate range, may make it possible to avoid a reduction in the electric conductivity, may reduce an increase in the resistance of the negative electrode, and may allow an electrochemical device to have large-current discharge characteristics within a favorable range.
The cyclic carboxylate to be suitably used may also be a fluorinated cyclic carboxylate (fluorine-containing lactone). Examples of the fluorine-containing lactone include fluorine-containing lactones represented by the following formula (C):
wherein X15 to X20 are the same as or different from each other, and are each —H, —F, —Cl, —CH3, or a fluorinated alkyl group; and at least one selected from X15 to X20 is a fluorinated alkyl group.
Examples of the fluorinated alkyl group for X15 to X20 include —CFH2, —CF2H, —CF3, —CH2CF3, —CF2CF3, —CH2CF2CF3, and —CF(CF3)2. In order to achieve high oxidation resistance and an effect of improving the safety, —CH2CF3 and —CH2CF2CF3 may be preferred.
Only one of X15 to X20 or a plurality thereof may be replaced by —H, —F, —Cl, —CH3, or a fluorinated alkyl group as long as at least one selected from X15 to X20 is a fluorinated alkyl group. In order to give good solubility of an electrolyte salt, the number of substituents may be 1 to 3, or 1 or 2.
The substitution of the fluorinated alkyl group may be at any of the above sites. In order to give a good synthesizing yield, the substitution site may be X17 and/or X11. In particular, X17 or X18 may be a fluorinated alkyl group, especially —CH2CF3 or —CH2CF2CF3. The substituent for X15 to X20 other than the fluorinated alkyl group is —H, —F, —Cl, or CH3. In order to give good solubility of an electrolyte salt, —H may be preferred.
In addition to those represented by the above formula, the fluorine-containing lactone may also be a fluorine-containing lactone represented by the following formula (D):
wherein one of A or B is CX226X227 (where X226 and X227 are the same as or different from each other, and are each —H, —F, —Cl, —CF3, —CH3, or an alkylene group in which a hydrogen atom is optionally replaced by a halogen atom and which optionally contains a hetero atom in the chain) and the other is an oxygen atom; Rf12 is a fluorinated alkyl group optionally containing an ether bond or a fluorinated alkoxy group; X221 and X222 are the same as or different from each other, and are each —H, —F, —Cl, —CF3, or CH3; X223 to X225 are the same as or different from each other, and are each —H, —F, —Cl, or an alkyl group in which a hydrogen atom is optionally replaced by a halogen atom and which optionally contains a hetero atom in the chain; and n=0 or 1.
A preferred example of the fluorine-containing lactone represented by the formula (D) may be a 5-membered ring structure represented by the following formula (E):
(wherein A, B, Rf12, X221, X222, and X223 are defined as in the formula (D)) because it can be easily synthesized and can have good chemical stability. Further, in relation to the combination of A and B, fluorine-containing lactones represented by the following formula (F):
(wherein Rf12, X221, X222, X223, X226, and X227 are defined as in the formula (D)) and fluorine-containing lactones represented by the following formula (G):
(wherein Rf12, X221, X222, X223, X226, and X227 are defined as in the formula (D)) may be mentioned.
In order to particularly give excellent characteristics such as high permittivity and high withstand voltage, and to improve the characteristics of the electrolyte solution in the disclosure, for example, to give good solubility of an electrolyte salt and to reduce the internal resistance well, those represented by the following formulas:
may be mentioned.
The presence of a fluorinated cyclic carboxylate can lead to, for example, effects of improving the ion conductivity, improving the safety, and improving the stability at high temperature.
Examples of the acyclic carboxylate include those having a carbon number of 3 to 7 in total in the structural formula thereof. Specific examples thereof include methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, n-propyl propionate, isobutyl propionate, n-butyl propionate, methyl butyrate, isobutyl propionate, t-butyl propionate, methyl butyrate, ethyl butyrate, n-propyl butyrate, isopropyl butyrate, methyl isobutyrate, ethyl isobutyrate, n-propyl isobutyrate, and isopropyl isobutyrate.
In order to improve the ion conductivity owing to viscosity reduction, preferred among these may be methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate, methyl propionate, ethyl propionate, n-propyl propionate, isopropyl propionate, methyl butyrate, and ethyl butyrate.
The ether compound may be a C2-C10 acyclic ether or a C3-C6 cyclic ether.
Examples of the C2-C10 acyclic ether include dimethyl ether, diethyl ether, di-n-butyl ether, dimethoxymethane, methoxyethoxymethane, diethoxymethane, dimethoxyethane, methoxyethoxyethane, diethoxyethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, diethylene glycol, diethylene glycol dimethyl ether, pentaethylene glycol, triethylene glycol dimethyl ether, triethylene glycol, tetraethylene glycol, tetraethylene glycol dimethyl ether, and diisopropyl ether.
Further, the ether compound may also suitably be a fluorinated ether.
An example of the fluorinated ether is a fluorinated ether (I) represented by the following formula (I):
Rf3—O—Rf4 (I)
(wherein Rf3 and Rf4 are the same as or different from each other, and are each a C1-C10 alkyl group or a C1-C10 fluorinated alkyl group; and at least one selected from the group consisting Rf3 and Rf4 is a fluorinated alkyl group).
The presence of the fluorinated ether (I) allows the electrolyte solution to have improved incombustibility as well as improved stability and safety at high temperature under high voltage.
In the formula (I), at least one of Rf3 or Rf4 is a C1-C10 fluorinated alkyl group. In order to allow the electrolyte solution to have further improved incombustibility and further improved stability and safety at high temperature under high voltage, both Rf3 and Rf4 may be C1-C10 fluorinated alkyl groups. In this case, Rf3 and Rf4 may be the same as or different from each other.
Rf3 and Rf4 may be the same as or different from each other, and Rf3 may be a C3-C6 fluorinated alkyl group and Rf4 may be a C2-C6 fluorinated alkyl group.
If the sum of the carbon numbers of Rf3 and Rf4 is too small, the fluorinated ether may have too low a boiling point. Too large a carbon number of Rf3 or Rf4 may cause low solubility of an electrolyte salt, may start to adversely affect the miscibility with other solvents, and may cause high viscosity, resulting in poor rate characteristics. In order to achieve an excellent boiling point and rate characteristics, advantageously, the carbon number of Rf3 is 3 or 4 and the carbon number of Rf4 is 2 or 3.
The fluorinated ether (I) may have a fluorine content of 40 to 75% by mass. The fluorinated ether (I) having a fluorine content within this range may lead to particularly excellent balance between the non-flammability and the miscibility. The above range may be preferred for good oxidation resistance and safety.
The lower limit of the fluorine content may be 45% by mass, 50% by mass, or 55% by mass. The upper limit thereof may be 70% by mass, or 66% by mass.
The fluorine content of the fluorinated ether (I) is a value calculated based on the structural formula of the fluorinated ether (I) by the following formula:
{(Number of fluorine atoms×19)/(Molecular weight of fluorinated ether (I))}×100(%).
Examples of Rf3 include HCF2CF2—, CF3CF2CH2—, CF3CFHCF2—, HCF2CF2CF2—, HCF2CF2CH2—, CF3CF2CH2CH2—, CF3CFHCF2CH2—, HCF2CF2CF2CF2—, HCF2CF2CF2CH2—, HCF2CF2CH2CH2—, and HCF2CF(CF3)CH2—. Examples of Rf4 include —CH2CF2CF3, —CF2CFHCF3, —CF2CF2CF2H, —CH2CF2CF2H, —CH2CH2CF2CF3, —CH2CF2CFHCF3, —CF2CF2CF2CF2H, —CH2CF2CF2CF2H, —CH2CH2CF2CF2H, —CH2CF(CF3)CF2H, —CF2CF2H, —CH2CF2H, and —CF2CH3.
Specific examples of the fluorinated ether (I) include HCF2CF2OCH2CF2CF2H, HCF2CF2CH2OCF2CF2H, CF3CF2CH2OCF2CF2H, HCF2CF2CH2OCF2CFHCF3, CF3CF2CH2OCF2CFHCF3, C6F13OCH3, C6F13OC2H5, C8F17OCH3, C8F17OC2H5, CF3CFHCF2CH(CH3)OCF2CFHCF3, HCF2CF2OCH(C2H5)2, HCF2CF2OC4H9, HCF2CF2OCH2CH(C2H5)2, and HCF2CF2OCH2CH(CH3)2.
In particular, those having HCF2— or CF3CFH— at one or each end can provide a fluorinated ether (I) having excellent polarizability and a high boiling point. Those having HCF2-at each end may be particularly preferred. The boiling point of the fluorinated ether (I) may be 67° C. to 120° C., 80° C. or higher, or 90° C. or higher.
Such a fluorinated ether (I) may include one or two or more of HCF2CF2OCH2CF2CF2H, CF3CH2OCF2CFHCF3, CF3CF2CH2OCF2CFHCF3, HCF2CF2CH2OCF2CFHCF3, HCF2CF2CH2OCH2CF2CF2H, CF3CFHCF2CH2OCF2CFHCF3, HCF2CF2CH2OCF2CF2H, CF3CF2CH2OCF2CF2H, and the like.
Advantageously, in order to achieve a high boiling point and good miscibility with other solvents and to give good solubility of an electrolyte salt, the fluorinated ether (I) may include at least one selected from the group consisting of HCF2CF2OCH2CF2CF2H, HCF2CF2CH2OCF2CFHCF3 (boiling point: 106° C.), CF3CF2CH2OCF2CFHCF3 (boiling point: 82° C.), HCF2CF2CH2OCF2CF2H (boiling point: 92° C.), and CF3CF2CH2OCF2CF2H (boiling point: 68° C.), at least one selected from the group consisting of HCF2CF2OCH2CF2CF2H, HCF2CF2CH2OCF2CFHCF3 (boiling point: 106° C.), and HCF2CF2CH2OCF2CF2H (boiling point: 92° C.), or HCF2CF2OCH2CF2CF2H.
Examples of the C3-C6 cyclic ether include 1,2-dioxane, 1,3-dioxane, 2-methyl-1,3-dioxane, 4-methyl-1,3-dioxane, 1,4-dioxane, metaformaldehyde, 2-methyl-1,3-dioxolane, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 2-(trifluoroethyl)dioxolane, 2,2,-bis(trifluoromethyl)-1,3-dioxolane, and fluorinated compounds thereof. In order to achieve a high ability to solvate with lithium ions and improve the degree of ion dissociation, preferred may be dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol n-propyl ether, ethylene glycol di-n-butyl ether, diethylene glycol dimethyl ether, and crown ethers. In order to achieve low viscosity and to give a high ion conductivity, particularly preferred may be dimethoxymethane, diethoxymethane, and ethoxymethoxymethane.
Examples of the nitrogen-containing compound include nitrile, fluorine-containing nitrile, carboxylic acid amide, fluorine-containing carboxylic acid amide, sulfonic acid amide, fluorine-containing sulfonic acid amide, acetamide, and formamide. Also, 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl-2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone, and N-methylsuccinimide may be used. The nitrile compounds represented by the formulas (1a), (1b), and (1c) are not included in the above nitrogen-containing compounds.
Examples of the boron-containing compound include borates such as trimethyl borate and triethyl borate, boric acid ethers, and alkyl borates.
Examples of the organosilicon-containing compound include (CH3)4—Si, (CH3)3—Si—Si(CH3)3, and silicone oil.
Examples of the fireproof agent (flame retardant) include organophosphates and phosphazene-based compounds. Examples of the organophosphates include fluorine-containing alkyl phosphates, non-fluorine-containing alkyl phosphates, and aryl phosphates. In order to achieve a flame retardant effect even in a small amount, fluorine-containing alkyl phosphates may be particularly preferred.
Examples of the phosphazene-based compounds include methoxypentafluorocyclotriphosphazene, phenoxypentafluorocyclotriphosphazene, dimethylaminopentafluorocyclotriphosphazene, diethylaminopentafluorocyclotriphosphazene, ethoxypentafluorocyclotriphosphazene, and ethoxyheptafluorocyclotetraphosphazene.
Specific examples of the fluorine-containing alkyl phosphates include fluorine-containing dialkyl phosphates disclosed in JP H11-233141 A, cyclic alkyl phosphates disclosed in JP H11-283669 A, and fluorine-containing trialkyl phosphates.
Examples of the fireproof agent (flame retardant) may include (CH3O)3P═O, (CF3CH2O)3P═O, (HCF2CH2O)3P═O, (CF3CF2CH2)3P=O, and (HCF2CF2CH2)3P═O.
The surfactant may be any of cationic surfactants, anionic surfactants, nonionic surfactants, and amphoteric surfactants. In order to give good cycle characteristics and rate characteristics, the surfactant may be one containing a fluorine atom.
Examples of such a surfactant containing a fluorine atom may include fluorine-containing carboxylic acid salts represented by the following formula (30):
Rf5COO−M+ (30)
(wherein Rf5 is a C3-C10 fluorine-containing alkyl group optionally containing an ether bond; M+ is Li+, Na+, K+, or NHR′3+, wherein R's are the same as or different from each other, and are each H or a C1-C3 alkyl group), and fluorine-containing sulfonic acid salts represented by the following formula (40):
Rf6SO3−M+ (40)
(wherein Rf6 is a C3-C10 fluorine-containing alkyl group optionally containing an ether bond; M+ is Li+, Na+, K+, or NHR′3+, wherein R's are the same as or different from each other, and are each H or a C1-C3 alkyl group).
In order to reduce the surface tension of the electrolyte solution without impairing the charge and discharge cycle characteristics, the surfactant may be present in an amount of 0.01 to 2% by mass of the electrolyte solution.
Examples of the additive for increasing the permittivity include sulfolane, methylsulfolane, y-butyrolactone, and y-valerolactone.
Examples of the improver for cycle characteristics and rate characteristics include methyl acetate, ethyl acetate, tetrahydrofuran, and 1,4-dioxane.
The electrolyte solution may be combined with a polymer material and thereby formed into a gel-like (plasticized), gel electrolyte solution.
Examples of such a polymer material include conventionally known polyethylene oxide and polypropylene oxide, and modified products thereof (see JP H08-222270 A, JP 2002-100405 A); polyacrylate-based polymers, polyacrylonitrile, and fluororesins such as polyvinylidene fluoride and vinylidene fluoride-hexafluoropropylene copolymers (see JP H04-506726 T, JP H08-507407 T, JP H10-294131 A); and composites of any of these fluororesins and any hydrocarbon resin (see JP H11-35765 A, JP H11-86630 A). In particular, polyvinylidene fluoride or a vinylidene fluoride-hexafluoropropylene copolymer may be used as a polymer material for a gel electrolyte.
The electrolyte solution may also contain an ion conductive compound disclosed in Japanese Patent Application No. 2004-301934.
This ion conductive compound is an amorphous fluorine-containing polyether compound having a fluorine-containing group at a side chain and is represented by the following formula (101):
A-(D)-B (101)
wherein D is represented by the following formula (201):
-(D1)n-(FAE)m-(AE)p-(Y)q— (201)
[wherein D1 is an ether unit containing a fluorine-containing ether group at a side chain and is represented by the following formula (2a):
(wherein Rf is a fluorine-containing ether group optionally containing a crosslinkable functional group; and R10 is a group or a bond that links Rf and the main chain);
(wherein Rfa is a hydrogen atom or a fluorinated alkyl group optionally containing a crosslinkable functional group; and R11 is a group or a bond that links Rfa and the main chain);
(wherein R13 is a hydrogen atom, an alkyl group optionally containing a crosslinkable functional group, an aliphatic cyclic hydrocarbon group optionally containing a crosslinkable functional group, or an aromatic hydrocarbon group optionally containing a crosslinkable functional group; and R12 is a group or a bond that links R13 and the main chain);
Y is a unit containing at least one selected from the following formulas (2d-1) to (2d-3):
The electrolyte solution may contain a sulfone-based compound. Preferred as the sulfone-based compound may be a C3-C6 cyclic sulfone and a C2-C6 acyclic sulfone. The number of sulfonyl groups in one molecule may be 1 or 2.
Examples of the cyclic sulfone include monosulfone compounds such as trimethylene sulfones, tetramethylene sulfones, and hexamethylene sulfones; disulfone compounds such as trimethylene disulfones, tetramethylene disulfones, and hexamethylene disulfones. In order to give good permittivity and viscosity, more preferred among these may be tetramethylene sulfones, tetramethylene disulfones, hexamethylene sulfones, and hexamethylene disulfones, particularly preferred may be tetramethylene sulfones (sulfolanes).
The sulfolanes may be sulfolane and/or sulfolane derivatives (hereinafter, also abbreviated as “sulfolanes” including sulfolane). The sulfolane derivatives may be those in which one or more hydrogen atoms binding to any carbon atom constituting the sulfolane ring is replaced by a fluorine atom or an alkyl group.
In order to achieve high ion conductivity and high input and output, preferred among these may be 2-methylsulfolane, 3-methylsulfolane, 2-fluorosulfolane, 3-fluorosulfolane, 2,2-difluorosulfolane, 2,3-difluorosulfolane, 2,4-difluorosulfolane, 2,5-difluorosulfolane, 3,4-difluorosulfolane, 2-fluoro-3-methylsulfolane, 2-fluoro-2-methylsulfolane, 3-fluoro-3-methylsulfolane, 3-fluoro-2-methylsulfolane, 4-fluoro-3-methylsulfolane, 4-fluoro-2-methylsulfolane, 5-fluoro-3-methylsulfolane, 5-fluoro-2-methylsulfolane, 2-fluoromethylsulfolane, 3-fluoromethylsulfolane, 2-difluoromethylsulfolane, 3-difluoromethylsulfolane, 2-trifluoromethylsulfolane, 3-trifluoromethylsulfolane, 2-fluoro-3-(trifluoromethyl)sulfolane, 3-fluoro-3-(trifluoromethyl)sulfolane, 4-fluoro-3-(trifluoromethyl)sulfolane, 3-sulfolene, 5-fluoro-3-(trifluoromethyl)sulfolane, and the like.
Examples of the acyclic sulfone include dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, n-propyl methyl sulfone, n-propyl ethyl sulfone, di-n-propyl sulfone, isopropyl methyl sulfone, isopropyl ethyl sulfone, diisopropyl sulfone, n-butyl methyl sulfone, n-butyl ethyl sulfone, t-butyl methyl sulfone, t-butyl ethyl sulfone, monofluoromethyl methyl sulfone, difluoromethyl methyl sulfone, trifluoromethyl methyl sulfone, monofluoroethyl methyl sulfone, difluoroethyl methyl sulfone, trifluoroethyl methyl sulfone, pentafluoroethyl methyl sulfone, ethyl monofluoromethyl sulfone, ethyl difluoromethyl sulfone, ethyl trifluoromethyl sulfone, perfluoroethyl methyl sulfone, ethyl trifluoroethyl sulfone, ethyl pentafluoroethyl sulfone, di(trifluoroethyl)sulfone, perfluorodiethyl sulfone, fluoromethyl-n-propyl sulfone, difluoromethyl-n-propyl sulfone, trifluoromethyl-n-propyl sulfone, fluoromethyl isopropyl sulfone, difluoromethyl isopropyl sulfone, trifluoromethyl isopropyl sulfone, trifluoroethyl-n-propyl sulfone, trifluoroethyl isopropyl sulfone, pentafluoroethyl-n-propyl sulfone, pentafluoroethyl isopropyl sulfone, trifluoroethyl-n-butyl sulfone, trifluoroethyl-t-butyl sulfone, pentafluoroethyl-n-butyl sulfone, and pentafluoroethyl-t-butyl sulfone.
In order to achieve high ion conductivity and high input and output, preferred among these may be dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, n-propyl methyl sulfone, isopropyl methyl sulfone, n-butyl methyl sulfone, t-butyl methyl sulfone, monofluoromethyl methyl sulfone, difluoromethyl methyl sulfone, trifluoromethyl methyl sulfone, monofluoroethyl methyl sulfone, difluoroethyl methyl sulfone, trifluoroethyl methyl sulfone, pentafluoroethyl methyl sulfone, ethyl monofluoromethyl sulfone, ethyl difluoromethyl sulfone, ethyl trifluoromethyl sulfone, ethyl trifluoroethyl sulfone, ethyl pentafluoroethyl sulfone, trifluoromethyl-n-propyl sulfone, trifluoromethyl isopropyl sulfone, trifluoroethyl-n-butyl sulfone, trifluoroethyl-t-butyl sulfone, trifluoromethyl-n-butyl sulfone, trifluoromethyl-t-butyl sulfone, and the like.
The sulfone-based compound may be present in any amount that does not significantly impair the effects of the disclosure. The amount may be 0.3% by volume or more, 0.5% by volume or more, or 1% by volume or more, while 40% by volume or less, 35% by volume or less, or 30% by volume or less, in 100% by volume of the solvent. The sulfone-based compound in an amount within the above range can easily achieve an effect of improving the cycle characteristics and the durability such as storage characteristics, can lead to an appropriate range of the viscosity of a non-aqueous electrolyte solution, can eliminate a reduction in electric conductivity, and can lead to appropriate ranges of the input and output characteristics and charge and discharge rate characteristics of a non-aqueous electrolyte secondary battery.
In order to improve the output characteristics, the electrolyte solution may contain as an additive a compound (7) that includes at least one selected from the group consisting of lithium fluorophosphate salts (other than LiPF6) and lithium salts containing a S=O group.
When the compound (7) is used as an additive, the above-described electrolyte salt may be a compound other than the compound (7).
Examples of the lithium fluorophosphate salts include lithium monofluorophosphate (LiPO3F) and lithium difluorophosphate (LiPO2F2).
Examples of the lithium salts containing a S═O group include lithium monofluorosulfonate (FSO3Li), lithium methyl sulfate (CH3OSO3Li), lithium ethyl sulfate (C2H5OSO3Li), and lithium 2,2,2-trifluoroethyl sulfate.
Preferred among these as the compound (7) may be LiPO2F2, FSO3Li, and C2H5OSO3Li.
The compound (7) may be present in an amount of 0.001 to 20% by mass, 0.01 to 15% by mass, 0.1 to 10% by mass, or 0.1 to 7% by mass, relative to the electrolyte solution.
The electrolyte solution may further contain a different additive, if necessary. Examples of the different additive include metal oxides and glass.
The electrolyte solution may contain 1 to 1000 ppm of hydrogen fluoride (HF). The presence of HF can promote formation of a film of the aforementioned additive. Too small an amount of HF tends to impair the ability to form a film on the negative electrode, impairing the characteristics of an electrochemical device. Too large an amount of HF tends to impair the oxidation resistance of the electrolyte solution due to the influence by HF. The electrolyte solution, even when containing HF in an amount within the above range, causes no reduction in capacity recovery of an electrochemical device after high-temperature storage.
The amount of HF may be 5 ppm or more, 10 ppm or more, or 20 ppm or more. The amount of HF may be 200 ppm or less, 100 ppm or less, 80 ppm or less, or 50 ppm or less. The amount of HF can be determined by neutralization titration.
The electrolyte solution may contain a fluorine-containing compound. This allows the electrochemical device of the disclosure to be suitably used at high voltage.
The fluorine-containing compound may include at least one selected from the group consisting of a fluorinated carbonate, a fluorinated carboxylate, and a fluorinated ether.
Examples of a usable fluorinated carbonate include a fluorinated cyclic carbonate and a fluorinated acyclic carbonate, which are mentioned in the description of the solvent.
Examples of a usable fluorinated carboxylate include a fluorinated cyclic carboxylate mentioned in the description of the solvent and additives and a fluorinated acyclic carboxylate mentioned in the description of the solvent.
The fluorinated ether used may be, for example, the fluorinated ether (I) mentioned in the description of additives.
The electrolyte solution may be prepared by any method using the aforementioned components.
The solid electrolyte may be a sulfide-based solid electrolyte or an oxide-based solid electrolyte. In particular, when a sulfide-based solid electrolyte is used, the solid-state secondary battery mixture is advantageously flexible.
The sulfide-based solid electrolyte is not limited. The sulfide-based solid electrolyte used may be any one selected from Li2S—P2S5, Li2S—P2S3, Li2S—P2S3-P2S5, Li2S—SiS2, LiI—Li2S—SiS2, LiI—Li2S—P2S5, LiI—Li2S—P20s, LiI—Li3PO4—P2S5, LiI—Li2S—SiS2—P2S5, Li2S—SiS2—Li4SiO4, Li2S—SiS2—Li3PO4, Li3PS4—Li4GeS4, Li3.4P0.6Si0.4S4, Li3.25P0.25Ge0.76S4, Li4-xGe1-xPxS4 (X=0.6 to 0.8), Li4+yGe1-yGayS4 (y=0.2 to 0.3), LiPSCl, LiCl, Li7-x-2yPS6-x-yClx (0.8≤x≤1.7, 0<y≤−0.25x+0.5), or a mixture of two or more thereof.
The sulfide-based solid electrolyte may contain lithium. Sulfide-based solid electrolytes containing lithium may be used in solid-state batteries in which lithium ions are used as carriers, and may be particularly preferred in that they provide electrochemical devices having high energy density.
The oxide-based solid electrolyte may be a compound that contains an oxygen atom (O), has conductivity of metal ions belonging to Group 1 or Group 2 of the periodic table, and has electronic insulating properties.
Specific examples of the compound include LixaLayaTiO3 (xa=0.3 to 0.7, ya=0.3 to 0.7) (LLT), LixbLaybZrzbMbbmbOnb (wherein Mbb includes at least one element selected from Al, Mg, Ca, Sr, V, Nb, Ta, Ti, Ge, In, and Sn; xb satisfies 5≤xb≤10; yb satisfies 1≤yb≤4; zb satisfies 1≤zb≤4; mb satisfies 0≤mb≤2; and nb satisfies 5≤nb≤20), LixcBycMcczcOnc (wherein Mcc includes at least one element selected from C, S, Al, Si, Ga, Ge, In, and Sn; xc satisfies 0≤xc≤5; yc satisfies 0≤yc≤1; zc satisfies 0≤zc≤1; and nc satisfies 0≤nc≤6), Lixd (Al,Ga)yd(Ti, Ge)zdSiadPmdOnd (1≤xd≤3, 0≤yd≤2, 0≤zd≤2, 0≤ad≤2, 1≤md≤7, and 3≤nd≤15), Li(3-2xe)MeexeDeeO (wherein xe is a number of 0 or greater and 0.1 or smaller, Mee is a divalent metal atom, Dee is a halogen atom or a combination of two or more halogen atoms), LixfSiyfOzf (1≤xf≤5, 0<yf≤3, and 1≤zf≤10), LixgSygOzg (1≤xg≤3, 0<yg≤2, and 1≤zg≤10), Li3BO3—Li2SO4, Li2O—B2O3—P2O5, Li2O—SiO2, Li6BaLa2Ta2O12, Li3PO(4-3/2w)Nw (w<1), Li3.5Zn0.25GeO4 having a lithium super ionic conductor (LISICON) crystal structure, La0.51Li0.34TiO2.94 having a perovskite crystal structure, La0.55Li0.35TiO3, LiTi2P3O12 having a natrium super ionic conductor (NASICON) crystal structure, Li1+xh+yh(Al,Ga)xh(Ti,Ge)2-xhSiyhP3-yhOi2 (0≤xh≤1 and 0≤yh≤1), and Li7La3Zr2O12 (LLZ) having a garnet crystal structure. Ceramic materials in which element substitution is performed for LLZ are also known. Examples include LLZ-based ceramic materials in which element substitution using at least one of magnesium (Mg) and A (A includes at least one element selected from the group consisting of calcium (Ca), strontium (Sr), and barium (Ba)) is performed for LLZ. Phosphorus compounds containing Li, P and O are also desirable. Examples include lithium phosphate (Li3PO4), LiPON in which one or more oxygen atoms in lithium phosphate are replaced with nitrogen, and LiPOD1 (wherein D1 includes at least one selected from Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr, Nb, Mo, Ru, Ag, Ta, W, Pt, Au, and the like). LiA1ON (wherein Al includes at least one selected from Si, B, Ge, Al, C, Ga, and the like) can also be preferably used. Specific examples include Li2O—Al2O3—SiO2—P2O5—TiO2—GeO2 and Li2O—Al2O3—SiO2—P2O5—TiO2.
The oxide-based solid electrolyte may contain lithium. Oxide-based solid electrolytes containing lithium are used in solid-state batteries in which lithium ions are used as carriers, and may be particularly preferred in that they provide electrochemical devices having high energy density.
The oxide-based solid electrolyte may be an oxide having a crystal structure. Oxides having a crystal structure may be particularly preferred in terms of good Li ion conductivity. The oxide having a crystal structure may be of perovskite type (La0.51Li0.34TiO2.94 etc.), NASICON type (Li1.3Al0.3Ti1.7(PO4)3 etc.), or garnet type (Li7La3Zr2O12 (LLZ) etc.). Preferred among these may be the NASICON type.
The volume average particle size of the oxide-based solid electrolyte is not limited. Still, the volume average particle size may be 0.01 μm or greater, or 0.03 μm or greater. The upper limit may be 100 μm or smaller, or 50 μm or smaller. The average particle size of the oxide-based solid electrolyte particles is measured by the following procedure. A 1% by mass dispersion of the oxide-based solid electrolyte particles is prepared by dilution with water (or heptane in the case of a substance unstable in water) in a 20-mL sample bottle. The diluted dispersion sample is irradiated with 1-kHz ultrasonic waves for 10 minutes, and immediately thereafter used for the test. Data was acquired from this dispersion sample 50 times using a quartz cell for measurement at a temperature of 25° C. with a laser diffraction/scattering particle size distribution analyzer LA-920 (HORIBA), and the volume average particle size was determined. For other detailed conditions and the like, JIS Z8828:2013 “Particle size analysis—Dynamic light scattering” is referred as necessary. Five samples are prepared for each level and the average value is used.
The separator may be formed from any known material and may have any known shape. The separator may be in the form of a porous sheet or a nonwoven fabric which is formed from a material such as resin, glass fiber, or inorganic matter and which is excellent in liquid retention.
Examples of the material of a resin or glass-fiber separator include polyolefins such as polyethylene and polypropylene, aromatic polyamide, polytetrafluoroethylene, polyether sulfone, and glass filters. One of these materials may be used alone or two or more thereof may be used in any combination at any ratio, for example, in the form of a polypropylene/polyethylene bilayer film or a polypropylene/polyethylene/polypropylene trilayer film. In order to achieve good permeability of the electrolyte solution and a good shut-down effect, the separator may be a porous sheet or a nonwoven fabric formed from a polyolefin such as polyethylene or polypropylene.
The separator may have any thickness, and the thickness may be 1 μm or greater, 5 μm or greater, or 8 μm or greater, while 50 μm or smaller, 40 un or smaller, or 30 un or smaller. The separator thinner than the above range may have poor insulation and mechanical strength. The separator thicker than the above range may cause not only poor battery performance such as poor rate characteristics but also a low energy density of the whole electrolyte battery.
The separator which is a porous one such as a porous sheet or a nonwoven fabric may have any porosity. The porosity may be 20% or higher, 35% or higher, or 45% or higher, while 90% or lower, 85% or lower, or 75% or lower. The separator having a porosity lower than the above range tends to have high film resistance, causing poor rate characteristics. The separator having a porosity higher than the above range tends to have low mechanical strength, causing poor insulation.
The separator may also have any average pore size. The average pore size may be 0.5 μm or smaller, or 0.2 μm or smaller, while 0.05 μm or larger. The separator having an average pore size larger than the above range may easily cause short circuits. The separator having an average pore size smaller than the above range may have high film resistance, causing poor rate characteristics.
Examples of the inorganic matter include oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates such as barium sulfate and calcium sulfate, each in the form of particles or fibers.
The separator is in the form of a thin film such as a nonwoven fabric, a woven fabric, or a microporous film. The thin film favorably has a pore size of 0.01 to 1 μm and a thickness of 5 to 50 μm. Instead of the above separate thin film, the separator may have a structure in which a composite porous layer containing particles of the above inorganic matter is disposed on a surface of one or each of the positive and negative electrodes using a resin binder. For example, alumina particles having a 90% particle size of smaller than 1 μm may be applied to the respective surfaces of the positive electrode with fluororesin used as a binder to form a porous layer.
The electrode group may be either a laminate structure including the above positive and negative electrode plates with the above separator in between, or a wound structure including the above positive and negative electrode plates in spiral with the above separator in between. The proportion of the volume of the electrode group in the battery internal volume (hereinafter, referred to as an electrode group proportion) may be 40% or higher, or 50% or higher, while 90% or lower, or 80% or lower.
The electrode group proportion lower than the above range may cause a low battery capacity. The electrode group proportion higher than the above range may cause small void space in the battery. Thus, if the battery temperature rises to high temperature and thereby the components swell and the liquid fraction of the electrolyte solution exhibits high vapor pressure to raise the internal pressure, the battery characteristics such as charge and discharge repeatability and high-temperature storageability may be impaired and a gas-releasing valve for releasing the internal pressure toward the outside may be actuated.
The current collecting structure may be any structure. In order to more effectively improve the high-current-density charge and discharge performance by the electrolyte solution, the current collecting structure may be a structure which reduces the resistances at wiring portions and jointing portions. With such reduction in internal resistance, the effects achievable with the electrolyte solution can be particularly favorably exerted.
In an electrode group having the laminate structure, the metal core portions of the respective electrode layers may be bundled and welded to a terminal. If an electrode has a large area, the internal resistance is high. Thus, multiple terminals may be disposed in the electrode so as to reduce the resistance. In an electrode group having the wound structure, multiple lead structures may be disposed on each of the positive electrode and the negative electrode and bundled to a terminal. This can reduce the internal resistance.
The external case may be made of any material that is stable to an electrolyte solution to be used. Specific examples thereof include metals such as nickel-plated steel plates, stainless steel, aluminum and aluminum alloys, and magnesium alloys, and a layered film (laminate film) of resin and aluminum foil. In order to reduce the weight, a metal such as aluminum or an aluminum alloy or a laminate film is favorably used.
An external case made of metal may have a sealed-up structure formed by welding the metal by laser welding, resistance welding, or ultrasonic welding, or a caulking structure using the metal with a resin gasket in between. An external case made of a laminate film may have a sealed-up structure formed by hot-melting resin layers. In order to improve the sealability, a resin which is different from the resin of the laminate film may be disposed between the resin layers. Especially, in the case of forming a sealed-up structure by hot-melting the resin layers with current collecting terminals in between, metal and resin are to be bonded. Thus, the resin to be disposed between the resin layers is favorably a resin having a polar group or a modified resin having a polar group introduced therein.
The electrochemical device of the disclosure may have any shape, such as a cylindrical shape, a square shape, a laminate shape, a coin shape, or a large-size shape. The shapes and the structures of the positive electrode, the negative electrode, and the separator may be changed in accordance with the shape of the battery.
The disclosure also relates to a module including the electrochemical device of the disclosure.
The electrochemical device of the disclosure may be used at a voltage of 4.9 V or higher, or at 5.0 V or higher. This allows for the sufficient development of the above-described insertion reaction after the conversion reaction. The upper limit of the voltage may be 5.5 V, or 5.4 V.
The disclosure also relates to a method of using the electrochemical device of the disclosure at a voltage of 4.9 V or higher (preferable at 5.0 V or higher). The upper limit of the voltage may be 5.5 V, or 5.4 V.
The embodiments have been described above, and it will be understood that various changes in form or detail can be made without departing from the gist and scope of the claims.
The disclosure relates to an electrode active material containing a carbon material, wherein the electrode active material is configured such that: during discharge, a metal fluoride is generated; and during charge, a fluoride ion is desorbed from the metal fluoride and reacts with the carbon material to form a C—F bond.
The disclosure also relates to an electrode active material containing: a carbon material and a metal fluoride in a discharged state; and a C—F bond in a charged state.
In the electrode active material, carbon fluoride may be present in a charged state.
The electrode active material may have a surface fluorine index I of 0.30 or lower, the surface fluorine index being a value represented by (peak intensity after 100 seconds)/(peak intensity after 0 seconds), where each peak intensity is an intensity of a peak assigned to CF2 in C1s and is measured by X-ray photoelectron spectroscopy with argon ion etching at 10 mA and 0.5 kV.
The disclosure also relates to an electrode containing the electrode active material.
The electrode may serve as a positive electrode.
The disclosure also relates to an electrochemical device including the electrode.
The electrochemical device may further include, as a counter electrode to the electrode, an electrode that forms no bond with a fluoride ion during charge and discharge.
The electrochemical device may further contain an electrolyte solution that contains a fluorine-containing compound.
In the electrochemical device, the electrode may be used as a positive electrode.
In the electrochemical device, a lithium storage material may be used as a negative electrode.
The lithium storage material may include at least one selected from graphite, tin, silicon, silicon oxide, and lithium.
The electrochemical device may be used at a voltage of 4.9 V or higher.
The disclosure also relates to a module including the electrochemical device.
The disclosure also relates to a method of using the electrochemical device at a voltage of 4.9 V or higher.
The disclosure is described with reference to examples, but the disclosure is not intended to be limited by these examples.
Carbon fluoride (CFx) used in the below experiment was analyzed by the following method.
The carbon fluoride was subjected to X-ray photoelectron spectroscopy (XPS) under the following conditions, and the surface fluorine index I was calculated.
The specific surface area of the carbon fluoride was measured using an automatic specific surface area analyzer (BELSORP-mini, from Bel Japan, Inc.). Specifically, the adsorption isotherm was measured by a nitrogen gas adsorption method at a liquid nitrogen temperature, and analyzed by the BET method. Thus, the specific surface area was determined. As a pretreatment of the sample, vacuum deaeration was performed at 100° C. for 10 hours using Belprep vac-II (from Bel Japan, Inc.)
LiBF4 was added to a mixture of propylene carbonate which is a high-permittivity solvent and ethyl methyl carbonate which is a low-viscosity solvent (volume ratio=1:1) such that the concentration of LiBF4 was 1.0 mol/L, whereby a non-aqueous electrolyte solution was prepared.
First, 80% by mass of CF0.45 (I: 0.21, specific surface area: 111 m2/g) serving as a positive electrode active material, 10% by mass of acetylene black serving as a conductive material, and 10% by mass of polyvinylidene fluoride (PVdF) serving as a binding agent were mixed in a N-methylpyrrolidone solvent to form slurry. The resulting positive electrode mixture slurry was uniformly applied onto an aluminum current collector and dried to form a positive electrode active material layer (50 μm in thickness). The workpiece was compression molded using a roll press, whereby a positive electrode laminate was produced. The positive electrode laminate was punched out to the size of 1.3 mm in diameter using a punching machine, whereby a circular positive electrode was produced.
Separately, a lithium metal foil with a thickness of 0.1 mm was punched out to the size of 1.6 mm in diameter using a punching machine, whereby a circular negative electrode was produced.
The above circular positive and negative electrodes were placed to face each other with a 20-μm-thick porous polyethylene film (separator) in between. The electrolyte solution prepared above was injected thereinto and the electrolyte solution was made to sufficiently permeate into the components such as the separator. The workpiece was then sealed, pre-charged, and aged, whereby a coin-type secondary battery was produced.
The resulting coin-type secondary battery was subjected to charge and discharge at a current density of 50 mA/g. After the 10th cycle, the discharge capacity was measured. For the operating voltage, the upper limit voltage (charging voltage) was set to 5.0 V (Example 1) or 4.8 V (Comparative Example 1) and the lower limit voltage was set to 1.5 V. The results are shown in Table 1.
The positive electrode was analyzed by X-ray photoelectron spectroscopy (XPS) before charge and discharge, after the initial discharge, after recharge to 5.0 V, and after recharge to 5.3 V. The same conditions used for XPS on carbon fluoride were employed. The results are shown in
As shown in
Image observation of the positive electrode using an electron microscope was performed after the initial discharge, after recharge to 5.0 V, and after re-discharge. The results are shown in
As shown in
The sample used in the image observation and the positive electrode before charge and discharge were subjected to analysis by x-ray diffraction (XRD) under the following conditions. The results are shown in
As shown in
Though peaks assigned to impurities derived from the electrolyte component were observed, (a) generation of LiF, (b) disappearance of LiF, and (c) re-generation of LiF were confirmed from the XRD patterns of
The solvents were mixed in accordance with the composition shown in Table 2. To the resulting solvent mixture was added a lithium salt such that the lithium salt concentration was 1.2 mol/L, whereby a non-aqueous electrolyte solution was prepared.
First, CF0.5 (I: 0.13, specific surface area: 263 m2/g), carbon black, and polyvinylidene fluoride were mixed at a mass ratio of 85/10/5 and then dispersed in N-methylpyrrolidone to form slurry, whereby a positive electrode mixture slurry was prepared. The resulting positive electrode mixture slurry was uniformly applied onto an aluminum current collector and dried to form a positive electrode active material layer (50 μm in thickness). The workpiece was compression molded using a roll press, whereby a positive electrode laminate was produced. The positive electrode laminate was punched out to the size of 1.3 mm in diameter using a punching machine, whereby a circular positive electrode was produced.
Separately, a lithium metal foil (0.1 mm in thickness) coated with various materials was punched out to the size of 1.6 mm in diameter using a punching machine, whereby a circular negative electrode was produced.
The above circular positive and negative electrodes were placed to face each other with a 20-pim-thick porous polyethylene film (separator) in between. The electrolyte solution prepared above was injected thereinto and the electrolyte solution was made to sufficiently permeate into the components such as the separator. The workpiece was then sealed, pre-charged, and aged, whereby a coin-type secondary battery was produced.
The capacity retention of the resulting coin-type secondary battery was determined as follows. The results are shown in Table 2.
Capacity retention (%)=(Discharge capacity after 100th cycle (mAh))/(Discharge capacity after 3rd cycle (mAh))×100
The secondary battery after the evaluation of initial discharge capacity was charged at 25° C. and a current of 100 mA/g up to half the initial discharge capacity. The battery was kept at 25° C. and discharged at 200 mA/g, and the voltage at the 10th second was measured. The resistance was calculated from the voltage drop during discharge, which was taken as the IV resistance. The results are shown in Table 2.
LiFSI was added to a mixture of monofluoroethylene carbonate which is a high-permittivity solvent, ethyl methyl carbonate which is a low-viscosity solvent, and F4:(HCF2CF2OCH2CF2CF2H) (volume ratio=3:4:3) such that the concentration of LiFSI was 1.0 mol/L, whereby a non-aqueous electrolyte solution was prepared.
First, 80% by mass of CF0.8 (I: 0.09, specific surface area: 370 m2/g) serving as a positive electrode active material, 10% by mass of acetylene black serving as a conductive material, and 10% by mass of polyvinylidene fluoride (PVdF) serving as a binding agent were mixed in a N-methylpyrrolidone solvent to form slurry. The resulting positive electrode mixture slurry was uniformly applied onto an aluminum current collector and dried to form a positive electrode active material layer (50 μm in thickness). The workpiece was compression molded using a roll press, whereby a positive electrode laminate was produced. The positive electrode laminate was punched out to the size of 1.3 mm in diameter using a punching machine, whereby a circular positive electrode was produced.
The active materials Anode 1, 2, and 4 were each mixed with graphite at a ratio by weight of 10:90, to which styrene-butadiene rubber dispersed in distilled water was added such that the solid content was set to 6% by mass. The mixture was mixed using a disperser to form slurry. The resulting slurry was uniformly applied onto a negative electrode current collector (10-μm-thick copper foil) and dried, whereby a negative electrode mixture layer was formed. Then, the workpiece was compression molded using a roll press, and punched out to the size of 1.6 mm in diameter using a punching machine, whereby a circular negative electrode was produced. Anode 3 was processed as in Experiment 1.
The above circular positive and negative electrodes were placed to face each other with a 20-μm-thick porous polyethylene film (separator) in between. The electrolyte solution prepared above was injected thereinto and the electrolyte solution was made to sufficiently permeate into the components such as the separator. The workpiece was then sealed, pre-charged, and aged, whereby a coin-type secondary battery was produced.
The capacity retention of the resulting coin-type secondary battery was determined as follows. The results are shown in Table 3.
Capacity retention (%)=(Discharge capacity after 20th cycle (mAh))/(Discharge capacity after 3rd cycle (mAh))×100
Li2S—SiS2 which is a solid electrolyte was sandwiched between positive and negative electrodes which had been produced under the same conditions as in Experiment 1, whereby a cell was structured.
The capacity retention of the resulting coin-type secondary battery was determined as follows. The results are shown in Table 4.
Capacity retention (%)=(Discharge capacity after 5th cycle (mAh))/(Discharge capacity after 2nd cycle (mAh))×100
The capacity retention in the 5th cycle of the battery of Example 1 in Experiment 1 was calculated under the same test conditions.
Capacity retention (%)=(Discharge capacity after 5th cycle (mAh))/(Discharge capacity after 2nd cycle (mAh))×100
The evaluation was performed as in Example 18, except that the positive electrode active material used was CF0.5 (I: 0.13, specific surface area: 263 m2/g). (Example 20)
The evaluation was performed as in Example 18, except that the positive electrode active material used was CF0.6 (I: 0.09, specific surface area: 311 m2/g). (Example 21)
Although the disclosure has been described with respect to only a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that various other embodiments may be devised without departing from the scope of the present disclosure. Accordingly, the scope of the invention should be limited only by the attached claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2022-032708 | Mar 2022 | JP | national |
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2023/007354 | Feb 2023 | WO |
| Child | 18819277 | US |
