Patent Application
20150221987
1. Field of the Invention
The present invention relates to an electrolytic solution for a non-aqueous secondary battery and a non-aqueous electrolytic solution secondary battery.
2. Description of the Related Art
Portable electronic apparatuses are essential tools for today's social life or business. As these portable electronic apparatuses have been further developed and diversified, the performance of batteries as a power supply thereof has increasingly attracted attention. In order to satisfy the needs, it is necessary to decrease the size and weight and to increase the capacity in the power supply. In addition, the stability, reliability, and safety of the batteries are also required.
Among these batteries, a lithium secondary battery realizes a high operating voltage of 3 V to 4 V as compared to an aqueous solution battery having an operating voltage of about 1.2 V. In addition, the lithium secondary battery has superior lightweight properties. Further, the lithium secondary battery has no memory effect, which is a problem in a nickel-cadmium storage battery or a nickel-metal hydride storage battery, and can stably supply energy. Due to these characteristics, the lithium secondary battery is rapidly increasing in market share to be mainly used in a mobile phone or a laptop computer instead of other secondary batteries. Recently, the range of use of the lithium secondary battery has been widened to include an electric-assisted bicycle, an electric tool, a hybrid vehicle, an electric vehicle, a robot, a spaceship, and an airplane, and further development thereof is expected.
The battery capacity of the lithium secondary battery is also strongly desired to be improved, and the battery capacity of a commercially available product has been increasing. Hitherto, the battery capacity of the lithium secondary battery has been improved by measures, for example, an increase in the packing density of an active material, an increase in charging voltage to increase a positive electrode utilization rate, an increase in the graphitization degree of a negative electrode, or a decrease in the size of a separator or a current collector. However, an increase in capacity using the above-described method is approaching the limit. In particular, along with an increase in capacity, a safety countermeasure for obtaining a high level of flame retardancy has become important.
In order to improve flame retardancy, an electrolytic solution for a lithium secondary battery has been improved in various ways. Representative examples of the improvement include techniques in which an electrolytic solution contains cyclophosphazene or a phosphate compound (refer to WO2002/082575A, JP2011-108649A, and JP2012-134151A).
A phosphazene compound has an effect of imparting flame retardancy, and a technique of adding a phosphazene compound to an electrolytic solution is extremely useful to improve the safety and reliability of a lithium secondary battery. However, when the above-described strict requirements in the market are taken into consideration, further improvement of performance is urgently needed. The present inventors have focused on the development of a technique capable of further improving battery performance (cycle characteristics) while achieving a high level of flame retardancy.
The present invention has been made to provide an electrolytic solution for a non-aqueous secondary battery and a non-aqueous electrolytic solution secondary battery, capable of achieving both flame retardancy and battery performance (cycle characteristics) at a high level when the electrolytic solution containing a specific flame retardant is used.
The above-described problems are solved by the following means.
[1] An electrolytic solution for a non-aqueous secondary battery including an electrolyte, a phosphazene compound and an aprotic solvent, wherein 20 vol % to 90 vol % of the aprotic solvent is composed of a halogen-containing compound having a carbonyl group and a halogen atom.
[2] The electrolytic solution for a non-aqueous secondary battery according to [1],
wherein the ratio of the halogen-containing compound in the aprotic solvent is 40 vol % to 90 vol %.
[3] The electrolytic solution for a non-aqueous secondary battery according to [1] or [2],
wherein the halogen-containing compound is a compound represented by the following formula (H1) or (H2),
wherein X11, X12, X21, and X22 each independently represents CR18R19, an oxygen atom, NR20, or a sulfur atom; X11 may be a single bond; R11 to R16 and R21 to R24 each independently represents a hydrogen atom or a monovalent sub stituent; R18 to R20 each independently represents a hydrogen atom, a halogen atom, an alkyl group, or an aryl group; at least one of R11 to R16, X11, and X12 contains a halogen atom; at least one of R21 to R24, X21, and X22 contains a halogen atom; na represents an integer of 1 to 4; and in the case where na is 2 or more, R23 and R24 may be different from each other.
[4] The electrolytic solution for a non-aqueous secondary battery according to any one of [1] to [3],
wherein the halogen-containing compound is an ester compound, a carbonic ester compound, a ketone compound, or an amide compound.
[5] The electrolytic solution for a non-aqueous secondary battery according to any one of [1] to [4],
wherein the phosphazene compound is represented by the following formula (1),
wherein R1 to R6 each independently represents a monovalent substituent; n represents an integer of 1 or more; and in the case where n is 2 or more, R5 and R6 may be different from each other.
[6] The electrolytic solution for a non-aqueous secondary battery according to any one of [1] to [5],
wherein the aprotic solvent contains a compound represented by the following formula (4A), (4B), or (4C),
wherein R31 to R36 each independently represents a hydrogen atom, an alkyl group, an alkyl group having an ether chain, or an aryl group.
[7] The electrolytic solution for a non-aqueous secondary battery according to any one of [1] to [6],
wherein the electrolytic solution is used for a secondary battery including a positive electrode and a negative electrode, and
the positive electrode is an electrode containing manganese.
[8] The electrolytic solution for a non-aqueous secondary battery according to any one of [3] to [7],
wherein in the formula (H1), X11 and X12 each independently represents an oxygen atom, CR18R19, or NR20; R14 and R15 each independently represents a hydrogen atom or an alkyl group having 1 to 3 carbon atoms; and R11 and R16 each independently represents an alkyl group having 1 to 6 carbon atoms that may contain 1 to 6 fluorine atoms.
[9] The electrolytic solution for a non-aqueous secondary battery according to any one of [3] to [7],
wherein in the formula (H2), X21 and X22 each independently represents an oxygen atom, CR18R19, or NR20; and R21 to R24 each independently represents a hydrogen atom, a fluorine atom, or an alkyl group having 1 to 3 carbon atoms that may contain 1 to 6 fluorine atoms.
[10] The electrolytic solution for a non-aqueous secondary battery according to any one of [3] to [8],
wherein in the formula (H1), R11 and R16 each independently represents a perfluoroalkyl group.
[11] A secondary battery including:
the electrolytic solution according to any one of [1] to [10];
a positive electrode; and
a negative electrode.
[12] The secondary battery according to [11],
wherein an active material of the negative electrode is lithium titanate or graphite.
[13] The secondary battery according to [11] or [12],
wherein an active material of the positive electrode is lithium cobalt oxide or lithium nickel manganese cobalt oxide.
In this specification, when plural substituents or the number of substituents is defined at the same time, the substituents may be different from each other. In addition, adjacent substituents may be linked or condensed to form a ring.
By using an electrolytic solution for a non-aqueous secondary battery and a non-aqueous electrolytic solution secondary battery according to the present invention, both flame retardancy and battery performance (in particular cycle characteristics) can be achieved at a high level when the electrolytic solution containing a specific flame retardant is used.
The above-described and other characteristics and advantageous effects of the present invention will be clarified from the following description appropriately with reference to the accompanying drawings.
A specific flame retardant (phosphazene compound) is added to an electrolytic solution used in a non-aqueous electrolytic solution secondary battery according to the present invention, in which a specific amount of the solvent is composed of a specific compound containing halogen. As a result, according to the present invention, high flame retardancy can be maintained, and cycle characteristics can be improved. The reason is not completely clear but is presumed to be as follows. That is, it is considered that the permeability of an electrolytic solution through an electrode may be decreased by the addition of a flame retardant. On the other hand, it was found that, by selecting a phosphazene compound as a flame retardant and adopting a specific amount of a specific halogen-containing compound as a constituent element of a solvent, superior permeability through an electrode is realized, and cycle characteristics can be realized without deterioration of flame retardancy. Hereinafter, the present invention will be described in detail based on preferred embodiments thereof.
(Phosphazene Compound)
A phosphazene compound which is preferably adopted in the present invention refers to a group of compounds having a double bond which contain phosphorus and nitrogen as a constituent element. Among these compounds, a cyclophosphazene compound is preferable, and a compound represented by the following formula (1) is more preferable.
R1 to R6
In the formula, R1 to R6 each independently represents a monovalent substituent. The monovalent substituent is preferably an alkyl group, an aryl group, an alkoxy group, an aryloxy group, a specific nitrogen-containing group (described below) such as an amino group, or a halogen atom such as a fluorine atom, a chlorine atom, or a bromine atom. It is preferable that at least one of substituents of R1 to R6 is a fluorine atom. The alkyl group is preferably an alkyl group having preferably 1 to 8 carbon atoms, more preferably 1 to 6 carbon atoms, or still more preferably 1 to 4 carbon atoms that may be substituted. The aryl group is preferably an aryl group having preferably 6 to 12 carbon atoms or more preferably 6 to 8 carbon atoms that may be substituted. The alkoxy group is preferably an alkoxy group having preferably 1 to 8 carbon atoms, more preferably 1 to 6 carbon atoms, or still more preferably 1 to 4 carbon atoms that may be substituted. The aryloxy group is preferably an aryloxy group having preferably 6 to 12 carbon atoms or more preferably 6 to 8 carbon atoms that may be substituted. Other groups are each independently the specific nitrogen-containing group such as an amino group having 1 to 12 carbon atoms, a fluorine atom, or a chlorine atom.
Among these, an alkyl group, an alkoxy group, a specific nitrogen-containing group, a fluorine atom, or a chlorine atom is preferable, and three or more fluorine atoms are more preferable.
The substituents are preferably composed of an alkoxy group, a specific nitrogen-containing group, and a fluorine atom, and are still more preferably composed of a specific nitrogen-containing group and a fluorine atom.
Among the substituents of R1 to R6, at least one is preferably —NRARB, —N═RC, or an azide group, and at least another one is preferably a halogen atom. Among these, it is preferable that all the substituents of R1 to R6 are composed of combinations of a halogen atom with a group or a combination (hereinafter, also referred to as “specific nitrogen-containing group”) selected from —NRARB, —N═RC, and an azide group. As the halogen atom, a fluorine atom is preferable. The number of the specific nitrogen-containing groups is not particularly limited, but is preferably 1 to 4, more preferably 1 to 3, still more preferably 1 or 2, and even still more preferably 1. Regarding a substitution site, it is preferable that one specific nitrogen-containing group is substituted with one phosphorus atom.
Among R1 to R6, adjacent substituents may be linked to form a ring containing a phosphorus atom. R1 to R6 may be the same as or different from one another. Particularly when a ring is formed, it is preferable that R1 and R2, R3 and R4, or R5 and R6 form the ring.
n
n represents an integer of 1 or more, preferably 1 to 3, more preferably 1 or 2, and still more preferably 1. When n represents an integer of 2 or more, plural R5's and R6's may be different from each other.
RA, RB
RA and RB each independently represents a hydrogen atom, an alkyl group, an aryl group, an alkenyl group, an alkynyl group, a heterocyclic group, a cyano group, a silyl group, or a substituent represented by the following formula (1A), (1B), (1C) or (1D).
RA and RB each independently represents preferably an alkyl group, an aryl group, or a substituent represented by the formula (1A) or (1D); more preferably an alkyl group having 1 to 6 carbon atoms, a fluorine-substituted alkyl group having 1 to 6 carbon atoms, an alkyl group having 1 to 6 carbon atoms that contains an ether group, an aryl group having 6 to 12 carbon atoms, or a substituent having 1 to 7 carbon atoms represented by the formula (1A); and still more preferably an alkyl group having 1 to 4 carbon atoms or a fluorine-substituted alkyl group having 1 to 4 carbon atoms. In this case, the total number of carbon atoms in the substituent is preferably 6 or less and more preferably 4 or less. RA and RB may be linked or condensed to form a ring containing a nitrogen atom. The alkyl group may be linear or branched. RA and RB may be the same as or different from each other.
R1A1, R1C1, R1D1, R1D2
In the formula, R1A1, R1C1, R1D1, and R1D2 each independently represents an alkyl group, an alkoxy group, an aryl group, an aryloxy group, a halogen atom, or an amino group. Preferable examples of the substituents are as follows. That is, R1A1, R1C1, R1D1, and R1D2 each independently represents preferably an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an aryl group having 6 to 12 carbon atoms, an aryloxy group having 6 to 12 carbon atoms, chlorine atoms, or a fluorine atom; and more preferably an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, a chlorine atom, or a fluorine atom. These substituents may be further substituted.* represents a direct bond.
R1B1, R1B2
R1B1 and RRB2 each independently represents a hydrogen atom, an alkyl group, an aryl group, an alkoxycarbonyl group, an aryloxycarbonyl group, an alkylsulfonyl group, an arylsulfonyl group, a silyl group, or a phosphonyl group. Preferable examples of the substituents are as follows. That is, R1B1 and R1B2 each independently represents preferably an alkyl group having 1 to 6 carbon atoms, an alkoxycarbonyl group having 1 to 7 carbon atoms, an aryl group having 6 to 12 carbon atoms, an aryloxycarbonyl group having 7 to 12 carbon atoms, an alkylsulfonyl group having 1 to 6 carbon atoms, an arylsulfonyl group having 6 to 12 carbon atoms, a silyl group having 1 to 6 carbon atoms, or a phosphonyl group having 1 to 12 carbon atoms; and more preferably an alkyl group having 1 to 6 carbon atoms, an alkoxycarbonyl group having 1 to 7 carbon atoms, an alkylsulfonyl group having 1 to 6 carbon atoms, a silyl group having 1 to 6 carbon atoms, or a phosphonyl group having 1 to 12 carbon atoms.
XA1, XD1, R1D3
In the formula, XA1 represents an oxygen atom or a sulfur atom.
XD1 represents an oxygen atom, a sulfur atom, or a nitrogen atom. When XD1 represents an oxygen atom or a sulfur atom, R1D3 is not present. When XD1 represents a nitrogen atom, R1D3 represents an alkyl group (having preferably 1 to 8 carbon atoms), an aryl group (having preferably 6 to 12 carbon atoms), a silyl group (having preferably 1 to 21 carbon atoms), or a phosphonyl group (having preferably 1 to 18 carbon atoms).
Rc
Rc represents a substituent represented by any one of the following formulae (C1) to (C6).
RX1, RX2, and RX3 each independently represents an alkyl group, an aryl group, an alkoxy group, an aryloxy group, an alkylthio group, an arylthio group, a heterocyclic group, a halogen atom, or a silyl group. RX1, RX2, and RX3 each independently represents preferably an alkyl group having 1 to 6 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an alkylthio group having 1 to 6 carbon atoms, a chlorine atom, a fluorine atom, or a silyl group having 1 to 15 carbon atoms. RY1 and RY2 each independently represents a halogen atom.
The kind and number of substituents of R1 to R6 are not particularly limited. However, from the viewpoint of securing flame retardancy while maintaining battery performance, it is preferable that two or more of all the substituents are fluorine atoms; and that the remaining substituents are the specific nitrogen-containing groups and alkoxy groups. It is more preferable that three or more of all the substituents are fluorine atoms. It is most preferable that four or more of all the substituents are fluorine atoms. Alternatively, from the same point as above, it is preferable that all the substituents of R1 to R6 are composed of a halogen atom (preferably a fluorine atom) and the specific nitrogen-containing group. It is preferable that 1 to 3 of all the substituents are the specific nitrogen-containing groups, it is more preferable that one or two of all the substituents are the specific nitrogen-containing groups, and it is still more preferable that one of all the substituents is the specific nitrogen-containing group.
It is preferable that the compound represented by the formula (1) is a compound represented by the following formula (2A) or (2B).
R21 to R28
In the formula, R21 to R28 have the same definition as that of R1 to R6 in the formula (1). R21 to R28 each independently represents preferably a halogen atom, an alkyl group, an aryl group, an alkoxy group, an aryloxy group, a thioalkyl group, a thioaryl group, or the specific nitrogen-containing group; more preferably an alkyl group having 1 to 6 carbon atoms, an aryl group having 6 to 12 carbon atoms, an alkoxy group having 1 to 6 carbon atoms, an aryloxy group having 6 to 12 carbon atoms, an alkylthio group having 1 to 6 carbon atoms, an arylthio group having 6 to 12 carbon atoms, a halogen atom (preferably, a chlorine atom or a fluorine atom), or the specific nitrogen-containing group; and still more preferably the specific nitrogen-containing group, a fluorine atom, an alkyl group having 1 to 6 carbon atoms, or an alkoxy group having 1 to 6 carbon atoms. The alkyl group and the aryl group may be substituted. The alkyl group may be linear or branched. Among the substituents of R21 to R28, at least one is preferably —NRARB, —N═RC, an azide group, or a combination (specific nitrogen-containing group), and at least another one is preferably a fluorine atom. It is more preferable that the substituents are compounds composed of the specific nitrogen-containing group and a fluorine atom. It is preferable that the number of the specific nitrogen-containing groups is 1 to 4, preferably 1 to 3, more preferably 1 or 2, and still more preferably 1; and that all the substituents other than the specific nitrogen-containing group are fluorine atoms.
Hereinafter, specific examples of the compound represented by the formula (1) will be shown below but are not intended to limit the present invention.
The compound represented by the formula (1) can be synthesized using an conventional method with reference to, for example, a method described in DE2139691B.
Moreover, a target product can also be obtained using a method of introducing the same amino group as that of the target product into hexachlorocyclotriphosphazen and then fluorinating the obtained compound using a fluorinating agent such as sodium fluoride or potassium fluoride. When chlorocyclotriphosphazene or fluorocyclotriphosphazene is aminated using the above-described method, the same amine as that of the target product can be used as a remover for an acid to be produced. The same synthesis can be performed by causing the same amine as that of the target product, an inorganic salt, or an organic salt to be present together. The inorganic salt is preferably an inorganic salt composed of an anion and a metal cation; and more preferably an inorganic salt composed of an anion selected from a hydroxide, a carbonate, a bicarbonate, and a fluoride and a metal cation selected from an alkali metal and an alkali earth metal. The metal cation is more preferably selected from sodium, potassium, magnesium, and calcium. Specifically, preferable examples of the inorganic salt include hydroxides such as sodium hydroxide and potassium hydroxide; carbonates such as potassium carbonate, sodium carbonate, and sodium bicarbonate; and fluorides such as sodium fluoride and potassium fluoride. Preferable examples of the organic salt include trialkylamines such as triethylamine, diisopropylethylamine, methylmorpholine, and 1,8-diazabicyclo[5.4.0]undec-7-ene; and aromatic bases such as pyridine and lutidine. As a solvent used during this synthesis, a commonly-used solvent can be used without any problems, and preferable examples thereof include ester solvents, ether solvents, nitrile solvents, and aliphatic solvents. Specifically, preferable examples of the solvent include ester solvents such as ethyl acetate and butyl acetate; ether solvents such as diethyl ether, tert-butyl methyl ether, and cyclopentyl methyl ether; nitrile solvents such as acetonitrile; and aliphatic solvents such as hexane and decane. Among these, ether solvents or nitrile solvents are preferable.
The content of the flame retardant in the electrolytic solution according to the present invention is not particularly limited, but is preferably 0.01 mol/L to 5 mol/L, more preferably 0.02 mol/L to 1 mol/L, and still more preferably 0.05 mol/L to 0.5 mol/L. By applying the flame retardant in the above-described range, a superior surfactant effect between a halogen-containing compound, an aprotic solvent, and an electrode surface described below is obtained, and both flame retardancy and battery characteristics such as rate characteristics can be achieved at an extremely high level. In terms of volume, the content of the flame retardant in the electrolytic solution is preferably 0.1 vol % to 50 vol % and more preferably 1 vol % to 30 vol %.
[Halogen-Containing Compound]
In the present invention, an aprotic solvent constituting the electrolytic solution is a specific solvent whose specific amount is composed of a halogen-containing compound having a carbonyl group and a halogen atom. The halogen-containing compound is not particularly limited as long as it has a carbonyl group and a halogen atom in the molecules thereof, and is preferably an ester compound (containing —COO—), a carbonic ester compound (containing —OCOO—), a ketone compound (containing —CR2—CO—CR2—; wherein R represents a hydrogen atom or a substituent), or an amide compound (containing —CONR—; wherein R represents a hydrogen atom or a substituent). The number of halogen atoms in the molecules is preferably 1 to 20 and more preferably 1 to 10. The halogen atom is preferably at least one selected from a chlorine atom, a fluorine atom, and a bromine atom and more preferably a fluorine atom. The number of carbonyl groups in the molecules is preferably 1 to 4 and more preferably 1. The number of carbon atoms in the halogen-containing compound is not particularly limited, but is preferably 2 to 13 and more preferably 3 to 9. The halogen-containing compound is preferably composed of a halogen atom, a carbonyl group, and an alkyl group (having preferably 1 to 12 carbon atoms) and optionally an alkenyl group (having preferably 2 to 12 carbon atoms) and is more preferably composed of a halogen atom, a carbonyl group, and an alkyl group.
The halogen-containing compound is preferably a compound represented by the following formula (H1) or (H2).
X11, X12, X21, and X22 each independently represents CR18R19, an oxygen atom, NR20, or a sulfur atom. X11 may be a single bond. R18 to R20 each independently represents a hydrogen atom, a halogen atom, an alkyl group, or an aryl group. The alkyl group represented by R18 to R20 is preferably an alkyl group having 1 to 8 carbon atoms and more preferably an alkyl group having 1 to 4 carbon atoms. The aryl group represented by R18 to R20 is preferably an aryl group having 6 to 20 carbon atoms and more preferably an aryl group having 6 to 14 carbon atoms. The alkyl group and the aryl group may have a substituent, and examples of this substituent include a substituent T described below. The substituent T is preferably an alkyl group or an aryl group that may have a halogen atom (preferably a fluorine atom). When the alkyl group or the aryl group has a halogen atom, the number of carbon atoms is not limited, but is preferably 1 to 3. X11, X12, X21, and X22 each independently represents preferably CR18R19, an oxygen atom, or NR20; and more preferably CR18R19 or an oxygen atom.
When the substituents have different definitions between the formula (H1) and (H2), and X12 in the formula (H1) each independently represents a single bond, an oxygen atom, CR18R19, or NR20. At this time, R18 to R20 each independently represents preferably a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. It is preferable that the alkyl group does not have a halogen atom (for example, a fluorine atom).
X21 and X22 in the formula (H2) each independently represents a single bond, an oxygen atom, C18R19, or NR20. At this time, R18 and R19 each independently represents a hydrogen atom, a halogen atom (preferably a fluorine atom), or an alkyl group having 1 to 6 carbon atoms that may have a halogen atom (preferably a fluorine atom). R20 represents preferably a hydrogen atom or an alkyl group having 1 to 6 carbon atoms. It is preferable that the alkyl group represented by R20 does not have a halogen atom (for example, a fluorine atom).
R11 to R16 and R21 to R24 each independently represents a hydrogen atom or a monovalent substituent; Examples of the substituent include a substituent T described below. R11 to R16 and R21 to R24 each independently represents preferably a hydrogen atom, a halogen atom (preferably a fluorine atom), or an alkyl group having 1 to 8 carbon atoms that may have a halogen atom (preferably a fluorine atom); and more preferably an alkyl group having 1 to 4 carbon atoms that may have a halogen atom (preferably a fluorine atom).
In the formula (H1), at least one of R11 to R16, X11, and X12 contains a halogen atom (or a fluorine atom). On the other hand, in the formula (H2), at least one of R21 to R24, X21, and X22 contains a halogen atom (or a fluorine atom). The preferable range of the number of halogen atoms in the molecules and the preferable kind of the halogen atom are the same as described above but will be described below separately depending on the formulae. In the formula (H1), the number of halogen atoms (preferably fluorine atoms) in the molecules is preferably 1 to 10 and more preferably 2 to 6. In the formula (H2), the number of halogen atoms (preferably fluorine atoms) in the molecules is preferably 1 to 8 and more preferably 1 to 5. The number of halogen atoms in each substituent is preferably 1 to 6 and more preferably 1 to 4.
Further, when the substituents are defined individually in the formula (H1), R11 and R16 each independently represents preferably an alkyl group having 1 to 8 carbon atoms that may have a halogen atom (preferably a fluorine atom); and more preferably an alkyl group having 1 to 4 carbon atoms that may have a halogen atom (preferably a fluorine atom). R11 and R16 each independently represents still more preferably a perfluoroalkyl group having carbon atoms in the above-described range.
R12 and R15 each independently represents a hydrogen atom, a halogen atom (preferably a fluorine atom), or an alkyl group having 1 to 4 carbon atoms that may have a halogen atom (preferably a fluorine atom).
In the formula (H2), R21 and R24 each independently represents a hydrogen atom, a halogen atom (preferably a fluorine atom), or an alkyl group having 1 to 4 carbon atoms that may have a halogen atom (preferably a fluorine atom).
na represents an integer of 1 to 4 and preferably an integer of 1 or 2. When na represents an integer of 2 or more, structural units defined therein may be different from each other.
The formula (H1) is preferably any one of the following formulae (H1a) to (H1d).
The formula (H2) is preferably any one of the following formulae (H2a) to (H2d).
In the formulae (H1a) to (H1d) and (H2a) to (H2d), R11 to R16, R18, R19, R21 to R24, and na have the same definitions those in the formulae (H1) and (H2).
Compounds represented by the formulae (H1a) to (H1d) and (H2a) to (H2d) have at least one halogen atom in the molecules thereof. The preferable number of halogen atoms is the same as those in formulae (H1) and (H2), respectively.
Specific examples of the halogen-containing compound will be shown below but are not intended to limit the present invention.
In the present invention, the mixing amount of halogen-containing compound in the aprotic solvent is important and is preferably 20 vol % or greater, more preferably 30 vol % or greater, and still more preferably 40 vol % or greater. The upper limit of the mixing amount is 90 vol % or less, preferably 80 vol % or less, and more preferably 70 vol % or less. When the mixing amount is greater than the lower limit, both flame retardancy and cycle characteristics can be improved by the aprotic solvent containing the halogen-containing compound. It is preferable that the mixing amount is less than the upper limit because the solubility of an essential electrolyte salt is maintained, and the affinity of the electrolytic solution to a separator and an electrode surface can be improved.
[Aprotic Solvent]
The electrolytic solution according to the present invention contains an aprotic solvent containing a compound (hereinafter, also referred to as “halogen-free compound”) other than the halogen-containing compound. It is preferable that the halogen-free compound contains a compound represented by the following formula (4A), (4B), or (4C) or a combination thereof
R31 to R36
In the formula, R31 to R36 each independently represents a hydrogen atom, an alkyl group, an alkyl group having an ether chain, or an aryl group. Preferable examples of the alkyl group and the aryl group are as follows. That is, R31 to R36 each independently represents preferably a linear or branched alkyl group, a linear or branched aryl group, or a linear or branched alkyl group having an ether chain; and more preferably an alkyl group having 1 to 6 carbon atoms, an aryl group having 1 to 6 carbon atoms, or an alkyl group having 1 to 6 carbon atoms that contains an ether group. As described above, adjacent substituents may form a ring. In particular, substituents R31 and R32 or substituents R33 and R34 in the formula (4B) may form a ring. In addition, substituents R31 and R32, substituents R33 and R34, or substituents R35 and R36 in the formula (4C) may form a ring. The alkyl group or the aryl group represented by R31 to R36 may have a substituent but does not have a halogen atom.
In addition, when the aprotic solvent contains a compound represented by the formula (4A) and a compound selected from the group consisting of a compound represented by the formula (4B) and a compound represented by the formula (4C), a ratio (M4B/MAC) of the volume (M4B) of the compound represented by the formula (4B) to the total volume (MAC) of the compound represented by the formula (4A) and the compound represented by the formula (4C) is preferably 0.2 to 5 and more preferably 0.3 to L By adjusting this ratio to be the upper limit or less, the dielectric constant is sufficient, a significant increase in viscosity is prevented, a significant decrease in lithium ion conductivity is prevented, and superior battery characteristics can be maintained. On the other hand, by adjusting this ratio to be the lower limit or more, a significant decrease in dielectric constant is prevented, and superior battery characteristics can be realized.
The meaning of the compounds described in this specification include not only the compounds themselves but also salts and ions thereof. In addition, derivatives obtained by modifying a part of the compounds within a range where the desired effects are exhibited are also included.
The substituents (the same shall be applied to linking groups) which are not specified in this specification regarding whether to be substituted or unsubstituted may have an arbitrary substituent. The same shall be applied to the compounds which are not specified in this specification regarding whether to be substituted or unsubstituted.
Preferable examples of the substituent include a substituent T described below.
Examples of the substituent T are as follows: an alkyl group (preferably an alkyl group having 1 to 20 carbon atoms, for example, methyl, ethyl, isopropyl, t-butyl, pentyl, heptyl, 1-ethylpentyl, benzyl, 2-ethoxyethyl, or 1-carboxymethyl); an alkenyl group (preferably an alkenyl group having 2 to 20 carbon atoms, for example, vinyl, allyl, or oleyl); an alkynyl group (preferably an alkynyl group having 2 to 20 carbon atoms, for example, ethynyl, butadiynyl, or phenyl-ethynyl); a cycloalkyl group (preferably a cycloalkyl group having 3 to 20 carbon atoms, for example, cyclopropyl, cyclopentyl, cyclohexyl, or 4-methylcyclohexyl); an aryl group (preferably an aryl group having 6 to 26 carbon atoms, for example, phenyl, 1-naphthyl, 4-methoxyphenyl, 2-chlorophenyl, or 3-methylphenyl); a heterocyclic group (preferably a heterocyclic group having 2 to 20 carbon atoms and more preferably a 5-membered or 6-membered heterocyclic group having at least one oxygen atom, sulfur atom, or nitrogen atom, for example, 2-pyridyl, 4-pyridyl, 2-imidazolyl, 2-benzimidazolyl, 2-thiazolyl, or 2-oxazolyl); an alkoxy group (preferably an alkoxy group having 1 to 20 carbon atoms, for example, methoxy, ethoxy, isopropyloxy, or benzyloxy); an aryloxy group (preferably an aryloxy group having 6 to 26 carbon atoms, for example, phenoxy, 1-naphthyloxy, 3-methylphenoxy, or 4-methoxyphenoxy); an alkoxycarbonyl group (preferably, an alkoxycarbonyl group having 2 to 20 carbon atoms, for example, ethoxycarbonyl or 2-ethylhexyloxycarbonyl); an amino group (preferably an amino group having 0 to 20 carbon atoms, an alkylamino group, or an arylamino group, for example, amino, N,N-dimethylamino, N,N-diethylamino, N-ethylamino, or anilino); a sulfamoyl group (preferably a sulfamoyl group having 0 to 20 carbon atoms, for example, N,N-dimethylsulfamoyl or N-phenylsufamoyl); an acyl group (preferably an acyl group having 1 to 20 carbon atoms, for example, acetyl, propionyl, butyryl, or benzoyl); an acyloxy group (preferably an acyloxy group having 1 to 20 carbon atoms, for example, acetyloxy or benzoyloxy); a carbamoyl group (preferably a carbamoyl group having 1 to 20 carbon atoms, for example, N,N-dimethylcarbamoyl or N-phenylcarbamoyl); an acylamino group (preferably an acylamino group having 1 to 20 carbon atoms, for example, acetylamino or benzoylamino); a sulfonamide group (preferably a sulfonamide group having 0 to 20 carbon atoms, for example, methanesulfonamide, benzenesulfonamide, N-methylmethanesulfonamide, or N-ethylbenzenesulfonamide); an alkylthio group (preferably an alkylthio group having 1 to 20 carbon atoms, for example, methylthio, ethylthio, isopropylthio, or benzylthio); an arylthio group (preferably an arylthio group having 6 to 26 carbon atoms, for example, phenylthio, 1-naphthylthio, 3-methylphenylthio, or 4-methoxyphenylthio); an alkylsulfonyl or arylsulfonyl group (preferably an alkylsulfonyl or arylsulfonyl group having 1 to 20 carbon atoms, for example, methylsulfonyl, ethylsulfonyl, or benzenesulfonyl); a hydroxyl group; a cyano group; and a halogen atom (for example, a fluorine atom, a chlorine atom, a bromine atom, or an iodine atom). Among these, an alkyl group, an alkenyl group, an aryl group, a heterocyclic group, an alkoxy group, an aryloxy group, an alkoxycarbonyl group, an amino group, an acylamino group, a hydroxyl group, or a halogen atom is more preferable, and an alkyl group, an alkenyl group, a heterocyclic group, an alkoxy group, an alkoxycarbonyl group, an amino group, an acylamino group, or an hydroxyl group is still more preferable.
In addition, each exemplary group of the substituent T may be further substituted with the substituent T.
When a compound or a substituent, a linking group, or the like of the compound contains, for example, an alkyl group, an alkylene group, an alkenyl group, or an alkenylene group, these groups may be cyclic or chain, may be linear or branched, and may be substituted or unsubstituted as described above. In addition, when a compound or a substituent, a linking group, or the like of the compound contains, for example, an aryl group or a heterocyclic group, these groups may be monocyclic or polycyclic and may be substituted or unsubstituted as described above.
In this specification, technical features including the selection of a substituent or a linking group of a compound, a temperature, and a thickness can be combined with each other although the lists thereof are individually described.
(Electrolyte)
Examples of the electrolyte which can be used in the electrolytic solution according to the present invention include a metal ion or a salt thereof. A metal ion in Group I or Group II of the periodic table or a salt thereof is preferable. Specifically, the electrolyte can be appropriately selected according to the intended purpose of the electrolytic solution, and examples thereof include a lithium salt, a potassium salt, a sodium salt, a calcium salt, and a magnesium salt. Among these a lithium salt is preferable from the viewpoint of output. When the electrolytic solution according to the present invention is used for an electrolyte of a non-aqueous electrolytic solution for a lithium secondary battery, a lithium salt is preferably selected as a salt of a metal ion. The lithium salt is not particularly limited as long as it can be typically used for an electrolyte of a non-aqueous electrolytic solution for a lithium secondary battery. Preferable examples of the lithium salt are as follows.
(L-1): inorganic lithium salts including: inorganic fluoride salts such as LiPF6, LiBF4, LiAsF6, and LiSbF6; perhalogenate salts such as LiClO4, LiBrO4, and LilO4; and inorganic chloride salts such as LiAlCl4.
(L-2): fluorine-containing organic lithium salts including: perfluoroalkanesulfonate salts such as LiCF3SO3; perfluoroalkanesulfonylimide salts such as LiN(CF3SO2)2, LiN(CF3CF2SO2)2, LiN(FSO2)2, and LiN(CF3SO2)(C4F9SO2); perfluoroalkanesulfonylmethide salts such as LiC(CF3SO2)3; fluoroalkyl fluorophosphates such as Li[PF5(CF2CF2CF3)], Li[PF4(CF2CF2CF3)2], Li[PF3(CF2CF2CF3)3], Li[PF5(CF2CF2CF2CF3)], Li[PF4(CF2CF2CF2CF3)2], and Li[PF3(CF2CF2CF2CF3)3].
(L-3): oxalato borates including: lithium bis(oxalato)borate and lithium difluoro(oxalato) borate.
Among these, LiPF6, LiBF4, LiAsF6, LiSbF6, LiClO4, Li(Rf1SO3), LiN(Rf1SO2)2, LiN(FSO2)2, and LiN(Rf1SO2)(Rf2SO2)2 are preferable, and lithium imide salts such as LiPF6, LiBF4, LiN(Rf1SO2)2, LiN(FSO2)2, and LiN(Rf1SO2)(Rf2SO2)2 are more preferable. Here, Rf1 and Rf2 each independently represents a perfluoroalkyl group.
Among these lithium salts used in the electrolytic solution, one kind may be used alone, or two or more kinds may be used in an arbitrary combination.
The content of the electrolyte (preferably an ion or a salt of a metal in Group I or Group II in the periodic table) in the electrolytic solution is adjusted such that a preferable concentration described in the following preparation method of the electrolytic solution is obtained. This concentration of the electrolyte can be appropriately selected according to the intended purpose of the electrolytic solution. In general, the concentration is preferably 10 mass % to 50 mass % and more preferably 15 mass % to 30 mass % with respect to the total mass of the electrolytic solution. When being evaluated as the ion concentration, the concentration of the electrolyte may be calculated in terms of a salt thereof with a metal which is preferably used.
(Other Components)
The electrolytic solution according to the present invention may contain at least one selected from a negative electrode film forming agent, a flame retardant, and an overcharge inhibitor. The content of each of these functional additives in the non-aqueous electrolytic solution is not particularly limited, but is preferably 0.001 mass % to 10 mass % with respect to the total mass of the non-aqueous electrolytic solution.
[Preparation Method of Electrolytic Solution and the Like]
The non-aqueous electrolytic solution can be prepared with a conventional method by dissolving the above-described respective components in the above-described solvent for a non-aqueous electrolytic solution, the components including the example in which a lithium salt is used as a salt of a metal ion.
In the present invention, “non-aqueous” represents substantially not containing water. The non-aqueous electrolytic solution may contain a small amount of water in a range where the effects of the present invention do not deteriorate. In consideration of obtaining superior characteristics, the content of water is preferably 200 ppm or lower (in terms of mass) and more preferably 100 ppm or lower. The lower limit is not particularly limited but, in practice, is 10 ppm or higher in consideration of unavoidable incorporation. The viscosity of the electrolytic solution according to the present invention is not particularly limited, but the viscosity at 25° C. is preferably 10 mPa·s to 0.1 mPa·s and more preferably 5 mPa·s to 0.5 mPa·s.
[Secondary Battery]
It is preferable that a non-aqueous electrolytic solution secondary battery according to the present invention contains the non-aqueous electrolytic solution. A lithium secondary battery according to a preferred embodiment of the present invention will be described with reference to
The lithium secondary battery 10 according to the embodiment includes: the above-described non-aqueous electrolytic solution 5 according to the present invention; a positive electrode C (including a positive electrode current collector 1 and a positive electrode active material layer 2) capable of storing and releasing lithium ions; and a negative electrode A (including a negative electrode current collector 3 and a negative electrode active material layer 4) capable of storing and releasing or dissolving or depositing lithium ions. In addition to these essential components, the lithium secondary battery 10 may further include, for example, a separator 9 that is disposed between the positive electrode and the negative electrode, a current collector terminal (not shown), and an outer case (not shown) in consideration of the intended use of the battery, the form of the potential, and the like. Optionally, a protective element may be mounted at least either inside or outside the battery. With such a structure, lithium ions in the electrolytic solution 5 are stored (a) and released (b), the battery can be charged (α) and discharged (β), and operating means 6 can operate and store electricity through a circuit wiring 7.
(Battery Shape)
The battery shape which is applied to the lithium secondary battery according to the embodiment is not particularly limited and may be, for example, a bottomed cylindrical shape, a bottomed square shape, a thin shape, a sheet shape, a paper shape, and a combination thereof. In addition, the battery shape may be a horseshoe shape or a comb shape in consideration of the form of a system or an apparatus to be incorporated. From the viewpoints of efficiently dissipating heat generated in the battery to the outside, the battery shape is preferably a square shape such as a bottomed square shape or a thin shape having at least one relatively flat surface with a large area.
In a bottomed cylindrical battery, the outer surface area relative to a power generating element to be charged is reduced. Therefore, the battery preferably has a design in which Joule's heat generated due to internal resistance during charging or discharging is efficiently dissipated to the outside. In addition, the battery preferably has a design in which the packing ratio of a material having high thermal conductivity is improved so as to decrease an internal temperature distribution. The bottomed cylindrical secondary battery will be described below with reference to
(Components Constituting Battery)
Referring to
(Electrode Mixture)
The electrode mixture is obtained by coating a current collector (electrode base material) with a dispersion of an active material, a conductive material, a binder, a filler, and the like and forming the coated material into a sheet shape. Typically, in a lithium battery, a positive electrode mixture including a positive electrode active material as an active material and a negative electrode mixture including a negative electrode active material as an active material are used. Next, the respective components in the dispersion (the mixture and the electrode composition) constituting the electrode mixture will be described.
Positive Electrode Active Material
In the electrode mixture for a secondary battery, a particulate positive electrode active material may be used. As the positive electrode active material, a transition metal oxide that can reversibly store and release lithium ions can be used, and a lithium-containing transition metal oxide is preferably used. Preferable examples of the lithium-containing transition metal oxide which can be used as the positive electrode active material include lithium-containing oxides containing Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Mo, and W. In addition, alkali metals other than lithium (elements in Group 1 (IA) and Group 2 (IIA) in the periodic table) and/or Al, Ga, In, Ge, Sn, Pb, Sb, Bi, Si, P, B, and the like may be mixed with the transition metal oxide. The mixing amount is preferably 0 mol % to 30 mol % with respect to the transition metal. When an oxide containing Ni and/or Co and/or Mn is used as the positive electrode active material, the effects of the present invention are significantly high.
Among the lithium-containing transition metal oxides which is preferably used as the positive electrode active material, a lithium-containing transition metal oxide which is synthesized by mixing a lithium compound and a transition metal compound (here, the transition metal refers to at least one selected from Ti, V, Cr, Mn, Fe, Co, Ni, Mo, and W) with each other such that a total molar ratio thereof is 0.3 to 2.2 is more preferable.
Further, as the lithium compound and the transition metal compound, a material containing LigM3O2 (wherein M3 represents one or more elements selected from Co, Ni, Fe, and Mn; and g represents 0 to 1.2) or a material having a spinel structure represented by LihM42O (wherein M4 represents Mn; and h represents 0 to 2) is more preferable. As M3 and M4, for example, Al, Ga, In, Ge, Sn, Pb, Sb, Bi, Si, P, or B may be added in addition to the transition metal. The mixing amount is preferably 0 mol % to 30 mol % with respect to the transition metal.
As the material containing LigM3O2 and the material having a spinel structure represented by LihM42O4, LigCoO2, LigNiO2, LigMnO2, LihMn2O4, LiNijMn1-jO2, LiCojNihMn1-j-hO2, LiMnhAl2-hO4, or LiMnhNi2-hO4, (wherein g represents 0.02 to 1.2; j represents 0.1 to 0.9; and h represents 0 to 2) is preferable; and LigCoO2, LihMn2O4, LiCojNihAl1-j-hO2, LiCojNihMn1-j-hO2, LiMnhAl2-hO4, or LiMnhNi2− is more preferable. From the viewpoints of high capacity and high output, an electrode containing Ni is still more preferable among the above-described electrodes. Here, the g value and h value are values before the start of charging and discharging and are values which are increased and decreased due to charging and discharging. Specific examples include LiCoO2, LiNi0.85Co0.01Al0.05O2, LiNi0.33Co0.33Mn0.33O2, LiMn1.8Al0.2O4, and LiMn1.5Ni0.5O4.
As the transition metal of the lithium-containing transition metal phosphate compound, for example, V, Ti, Cr, Mn, Fe, Co, Ni, or Cu is preferable, and specific examples thereof include iron phosphates such as LiFePO4, Li3Fe2(PO4)3, and LiFeP2O7; cobalt phosphates such as LiCoPO4; and compounds in which a portion of transition metal atoms which are a major component of the lithium transition metal phosphate compound is substituted with another metal such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Nb, or Si.
In the present invention, as the positive electrode active material, a material having a charging region of 4.25 V or higher is preferably used. Specifically, a lithium-containing transition metal oxide having a lithium storage-release potential peak of 4.25 V or higher against lithium is preferable. At this time, the charge-discharge potential peak can be specified by preparing a thin film electrode of the positive electrode active material using a sol-gel method or a sputtering method and performing electrochemical measurement (cyclic voltammetry) thereon.
Examples of the positive electrode active material having the specific charging region are as follows.
(i) LiNixMnyCozO2 (x>0.2, y>0.2, x+y+z=1) representative example:
LiNi1/3Mn1/3Co1/3O2 (also referred to as LiNi0.33Mn0.33Co0.33O2) LiNi1/2Mn1/2O2 (also referred to as LiNi0.5Mn0.5Co0.33O2)
(ii) LiNixMnyO4 (x>0.2, y>0.7, x+y=1)
representative example:
LiNi1/4Mn3/4O2 (also referred to as LiNi0.5Mn1.5O4)
(iii) LiNixCoyAlzO2 (x>0.7, y>0.1, 0.1>z>0.05, x+y+z=1)
representative example:
As the positive electrode active material having the specific charging region, the following compounds can be used.
In the non-aqueous electrolytic solution secondary battery according to the present invention, a particulate positive electrode active material may be used. The average particle size of the positive electrode active material to be used is not particularly limited but is preferably 0.1 μm to 50 μm. The specific surface area is not particularly limited but is preferably 0.01 m2/g to 50 m2/g when measured using the BET method. In addition, when 5 g of the positive electrode active material is dissolved in 100 ml of distilled water, the pH of the supernatant liquid is preferably 7 to 12.
In order for the positive electrode active material to have a predetermined particle size, a commonly-used pulverizer or classifier can be used. For example, a mortar, a ball mill, a vibration ball mill, a vibration mill, a satellite ball mill, a planetary ball mill, a swirling air flow jet mill, or a sieve is used. The positive electrode active material obtained using the calcination method may be used after being washed with water, an acidic aqueous solution, an alkaline aqueous solution, or an organic solvent.
The mixing amount of the positive electrode active material is not particularly limited, but the mixing amount in the dispersion (mixture) constituting the electrode mixture is preferably 60 mass % to 98 mass % and more preferably 70 mass % to 95 mass % with respect to 100 mass % of the solid components.
Negative Electrode Active Material
The negative electrode active material is not particularly limited as long as it can reversibly store and release lithium ions, and examples thereof include carbonaceous materials; metal oxides such as tin oxide and silicon oxide; metal composite oxides; lithium and lithium alloys such as a lithium-aluminum alloy; and metals capable of forming an alloy with lithium, such as Sn and Si.
Among these, one kind may be used alone, or two or more kinds may be used in an arbitrary combination at an arbitrary ratio. Among these, carbonaceous material or lithium metal composite oxides are preferably used from the viewpoint of safety.
In addition, the metal composite oxide is not particularly limited as long as it can store and release lithium, but it is preferable that the metal composite oxide contains titanium and/or lithium as a constituent element from the viewpoint of high current density charging-discharging characteristics.
The carbonaceous material which is used as the negative electrode active material is a material substantially containing carbon. Examples of the carbonaceous material include petroleum pitch, natural graphite, artificial graphite such as vapor-grown graphite, and carbonaceous materials obtained by firing various synthetic resins such as PAN resins and furfuryl alcohol resins. Further, other examples of the carbonaceous material include various carbon fibers such as PAN-based carbon fibers, cellulose-based carbon fibers, pitch-based carbon fibers, vapor-grown carbon fibers, dehydrated PVA-based carbon fibers, lignin carbon fibers, vitreous carbon fibers, activated carbon fibers; mesophase microspheres; graphite whiskers; and tabular graphite.
These carbonaceous materials can be classified into non-graphitizable carbonaceous materials and graphitizable carbonaceous materials based on the graphitization degree. In addition, it is preferable that the carbonaceous material has the lattice spacing, density, and crystallite size described in JP1987-22066A (JPS62-22066A), JP1990-6856A (JPH2-6856A), and JP1991-45473A (JPH3-45473A). The carbonaceous material is not necessarily a single material and, for example, may be a mixture of natural graphite and artificial graphite described in JP1993-90844A (JPH5-90844A) or graphite having a coating layer described in JP1994-4516A (JPH6-4516A).
The metal oxide and the metal composite oxide, which are negative electrode active materials used in the non-aqueous electrolytic solution secondary battery, are not particularly limited as long as at least one thereof is included. The metal oxide and the metal composite oxide are more preferably amorphous oxides. Further, chalcogenides which are reaction products between metal elements and elements in Group 16 of the periodic table are preferably used. “Amorphous” described herein represents an oxide having a broad scattering band with a peak in a range of 20° to 40° in terms of 2θ when measured by an X-ray diffraction method using CuKα rays, and the oxide may have a crystal diffraction line. The highest intensity in a crystal diffraction line observed in a range of 40° to 70° in terms of 20 is preferably 100 times or less and more preferably 5 times or less relative to the intensity of a diffraction peak line in a broad scattering band observed in a range of 20° to 40° in terms of 20, and it is still more preferable that the oxide does not have a crystal diffraction line.
In a group of compounds consisting of the amorphous oxides and the chalcogenides, amorphous oxides and chalcogenides of metalloid elements are more preferable, and oxides and chalcogenides formed of a single element or a combination of two or more elements selected from elements in Groups 13 (IIIB) to 15 (VB) of the periodic table, Al, Ga, Si, Sn, Ge, Pb, Sb, and Bi are still more preferable. Specifically, preferable examples of the amorphous oxides and chalcogenides include Ga2O3, SiO, GeO, SnO, SnO2, PbO, PbO2, Pb2O3, Pb2O4, Pb3O4, Sb2O3, Sb2O4, Sb2O5, Bi2O3, Bi2O4, SnSiO3, GeS, SnS, SnS2, PbS, PbS2, Sb2S3, Sb2S5, and SnSiS3. In addition, composite oxides of these examples with lithium oxide, for example, Li2SnO2 may be used.
In the non-aqueous electrolytic solution secondary battery, the average particle size of the negative electrode active material to be used is preferably 0.1 μm to 60 μm. In order to obtain the predetermined particle size, a well-known pulverizer or classifier is used. For example, a mortar, a ball mill, a sand mill, a vibration ball mill, a satellite ball mill, a planetary ball mill, a swirling air flow jet mill, or a sieve is preferably used. During the pulverization, wet pulverization of causing water or an organic solvent such as methanol to coexist with the negative electrode active material can be optionally performed. In order to obtain a desired particle size, it is possible to perform classification. A classification method is not particularly limited, and a method using, for example, a sieve or an air classifier can be optionally used. The classification can be used using a dry method or a wet method.
The chemical formula of the compound obtained using the calcination method can be obtained by using inductively coupled plasma (ICP) optical emission spectroscopy as a measurement method, or can be calculated from a mass difference of the powder before and after calcination as a short-cut method.
Preferable examples of the negative electrode active material which can be used in combination with the amorphous oxide as a negative electrode active material containing Sn, Si, or Ge as a major component include carbon materials that can store and release lithium ions or lithium metal; lithium; lithium alloys; and metals that can form an alloy with lithium.
In the present invention, lithium titanate, more specifically, lithium titanium oxide (Li[Li1/3Ti5/3]O4) can be preferably used as the negative electrode active material.
The mixing amount of the negative electrode active material in the dispersion (mixture) constituting the electrode mixture is not particularly limited, but is preferably 60 mass % to 98 mass % and more preferably 70 mass % to 95 mass % with respect to 100 mass % of the solid components.
Conductive Material
Any electron conductive materials can be used as the conductive material as long as they do not cause a chemical change in a constructed secondary battery, and a well-known conductive material can be arbitrarily used. Typically, one kind or a mixture of two or more kinds can be used among the following conductive materials including: natural graphite (for example, scale-like graphite, flaky graphite, or amorphous graphite), artificial graphite, carbon black, acetylene black, Ketjen black, carbon fibers, metal powders (for example, copper, nickel, aluminum, or silver (described in JP1988-10148A (JPS63-10148A) and JP1988-554A (JPS63-554A), metal fibers, and polyphenylene derivatives (described in JP1984-20A (JPS59-20A) and JP1984-971A (JPS59-971A). Among these, a combination of graphite and acetylene black is more preferable. The addition amount of the conductive material in the dispersion (mixture) constituting the electrode mixture is preferably 0.1 mass % to 50 mass % and more preferably 0.5 mass % to 30 mass % with respect to 100 mass % of the solid components. The addition amount of carbon or graphite in the dispersion is more preferably 0.5 mass % to 15 mass %
Binder
Examples of the binder include polysaccharides, thermoplastic resins, and polymers having rubber elasticity. Preferable examples of the binder include emulsions (latexes) or suspensions of starch, carboxymethyl cellulose, cellulose, diacetyl cellulose, methyl cellulose, hydroxyethyl cellulose, hydroxypropyl cellulose, sodium alginate, polyacrylic acid, sodium polyacrylate, water-soluble polymers (for example, polyvinyl phenol, polyvinyl methyl ether, polyvinyl alcohol, polyvinyl pyrrolidone, polyacrylonitrile, polyacrylamide, polyhydroxy (meth)acrylate, and a styrene-maleic acid copolymer), polyvinyl chloride, polytetrafluoroethylene, polyvinylidene fluoride, a tetrafluoroethylene-hexafluoropropylene copolymer, a vinylidene fluoride-tetrafluoroethylene-hexafluoropropylene copolymer, polyethylene, polypropylene, an ethylene-propylene-diene terpolymer (EPDM), a sulfonated EPDM, a polyvinyl acetal resin, (meth)acyrylic acid ester copolymers containing a (meth)acyrylic acid ester (for example, methyl methacrylate and 2-ethylhexyl acrylate), a (meth)acrylic acid ester-acrylonitrile copolymer, a polyvinyl ester copolymer containing a vinyl ester (for example, vinyl acetate), a styrene-butadiene copolymer, an acrylonitrile-butadiene copolymer, polybutadiene, a neoprene rubber, a fluorine rubber, poly(ethylene oxide), a polyester polyurethane resin, a polyether polyurethane resin, a polycarbonate polyurethane resin, a polyester resin, a phenolic resin, and an epoxy resin. More preferable examples of the binder include a polyacrylic acid ester latex, carboxymethyl cellulose, polytetrafluoroethylene, and polyvinylidene fluoride.
As the binder, one kind can be used alone, or a mixture of two or more kinds can be used. When the addition amount of the binder is excessively small, the holding force and cohesive force of the electrode mixture are weakened. When the addition amount of the binder is excessively great, the electrode volume increases, and thus the capacity per unit volume or unit mass of the electrode is decreased. Due to the above-described reasons, the addition amount of the binder in the dispersion (mixture) constituting the electrode mixture is preferably 1 mass % to 30 mass % and more preferably 2 mass % to 10 mass % with respect to 100 mass % of the solid components.
Filler
The electrode mixture may contain a filler. As a material forming the filler, any fibrous materials can be used as long as they do not cause a chemical change in the secondary battery according to the present invention. Typically, fibrous fillers formed from olefin polymers such as polypropylene and polyethylene, and materials such as glass and carbon are used. The addition amount of the filler is not particularly limited, but the addition amount in the dispersion (mixture) constituting the electrode mixture is preferably 0 mass % to 30 mass % with respect to 100 mass % of the solid components.
Current Collector
As the current collectors of the positive and negative electrodes, an electron conductor that does not cause a chemical change in the non-aqueous electrolytic solution secondary battery according to the present invention is used. As the current collector of the positive electrode, aluminum, stainless steel, nickel, titanium, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, or silver is preferable. Among these, aluminum or an aluminum alloy is more preferable.
As the current collector of the negative electrode, aluminum, copper, stainless steel, nickel, or titanium is preferable, and aluminum copper, or a copper alloy is more preferable.
Regarding the shape of the current collector, a film sheet-shaped current collector is usually used, but a net-shaped material, a material formed by punching, a lath material, a porous material, a foam, a material obtained by molding a group of fibers, and the like can also be used. The thickness of the current collector is not particularly limited but is preferably 1 μm to 500 μm. In addition, it is also preferable that the surface of the current collector is made to be uneven through a surface treatment.
The electrode mixture of the lithium secondary battery is formed of components which are appropriately selected from these materials.
(Separator)
The separator which can be used in the present invention is not particularly limited as long as it is formed of a material that electronically insulates the positive electrode and the negative electrode and has mechanical strength, ion permeability, and oxidation-reduction resistance at a contact surface between the positive electrode and the negative electrode. As such a material, for example, a porous polymer material, an inorganic material, an organic-inorganic hybrid material, or a glass fiber is used. In order to secure safety, it is preferable that the separator has a shutdown function, that is, a function of interrupting the current by blocking pores at 80° C. or higher to increase resistance. The blocking temperature is preferably 90° C. to 180° C.
The shape of the pores of the separator is typically circular or elliptical, and the size thereof is 0.05 μm to 30 μm and preferably 0.1 μm to 20 μm. Further, the shape of the pores may be rod-like or indefinite as in a case where a separator is prepared using a drawing method or a phase separation method. An occupancy ratio of the pores, that is, a porosity is 20% to 90% and preferably 35% to 80%.
As the polymer material, a single material such as cellulose non-woven fabric, polyethylene, or polypropylene may be used alone, and a composite material of two or more kinds may be used. A laminate of two or more microporous films having different pore sizes, porosities, and pore blocking temperatures is preferable.
As the inorganic material, an oxide such as alumina or silicon dioxide, a nitride such as aluminum nitride or silicon nitride, or a sulfate such as barium sulfate or calcium sulfate is used, and the shape thereof is particulate or fibrous. The form of the inorganic material may be a thin film-shaped material such as a non-woven fabric, a woven fabric, or a microporous film. As the thin film-shaped material, a material having a pore size of 0.01 μm to 1 μm and a thickness of 5 μm to 50 μm is preferably used. In addition to the above-described independent thin film-shaped material, a separator in which a composite porous layer containing particles of the above-described inorganic material is formed on a surface layer of the positive electrode and/or the negative electrode using a binder formed of a resin can be used. For example, a porous layer containing alumina particles having a 90% particle size of less than 1 μm is formed on both surfaces of the positive electrode using a binder formed of a fluororesin.
(Preparation of Non-Aqueous Electrolyte Secondary Battery)
As described above, the lithium secondary battery may have any shape such as a sheet shape, a square shape, or a cylindrical shape. In many cases, the current collectors are coated with the mixture (dispersion) containing the positive electrode active material and the negative electrode active material, are dried, and are compressed to be used.
Hereinafter, the configuration and preparation method of the bottomed cylindrical lithium secondary battery 100 will be described as an example with reference to
First, the negative electrode active material and various additives including the binder, the filler, and the like which are optionally used are dissolved in an organic solvent to obtain a mixture. As a result, a slurry or paste negative electrode mixture is prepared. The entire region of both surfaces of a metal core as a current collector is uniformly coated with the obtained negative electrode mixture. Next, the organic solvent is removed, and a negative electrode active material layer is formed. Further, the laminate (mixture) of the current collector and the negative electrode active material layer is rolled using a roll press machine. As a result, a negative electrode sheet (electrode sheet) having a predetermined thickness is prepared. At this time, conventional methods can be used as the coating method of the respective materials, the drying method of the coated material, and the forming method of the positive and negative electrodes.
In the embodiment, the cylindrical battery has been described as an example, but the present invention is not limited thereto. For example, after the positive and negative electrode sheets (mixtures) prepared using the above-described method are superimposed with the separator interposed therebetween, the laminate may be processed into a sheet-shaped battery as it is. Alternatively, the laminate may be folded and inserted into a square can so as to electrically connect the can and the sheet to each other, and then an electrolyte is injected thereto, and an opening is sealed using the sealing plate, thereby forming a square battery.
In all the embodiments, a safety valve can be used as the sealing plate for sealing the opening. In addition, as a sealing component, various well-known safety elements of the related art may be provided in addition to the safety valve. For example, as an overcurrent preventing element, for example, a fuse, a bimetal, or a PTC element is preferably used.
In addition, in addition to the safety valve, as a countermeasure against an increase in the internal pressure of the battery can, a method of forming a slit in the battery can, a gasket cracking method, or a sealing plate cracking method, or a method of disconnecting a lead plate can be used. In addition, a protective circuit into which an overcharge or overdischarge preventing mechanism is embedded is provided to a charger or is separately connected to a charger.
As the can or the lead plate, an electrically conductive metal or alloy can be used. For example, a metal such as iron, nickel, titanium, chromium, molybdenum, copper or aluminum or an alloy thereof is preferably used.
As a welding method of a cap, a can, a sheet, or a lead plate, a well-known method (for example, DC or AC electric welding, laser welding, or ultrasonic welding) can be used. As a sealing agent for sealing the opening, a well-known compound of the related art such as asphalt or a mixture can be used.
[Use of Non-Aqueous Electrolytic Solution Secondary Battery]
The non-aqueous electrolytic solution secondary battery according to the present invention is superior in cycle characteristics and is applied to various uses.
The application embodiment is not particularly limited, and examples of an electronic apparatus to which the non-aqueous electrolytic solution secondary battery is applied include a laptop computer, a pen-input PC, a mobile PC, an electronic book player, a mobile phone, a cord-less phone system, a pager, a handy terminal, a portable fax, a portable copying machine, a portable printer, a headphone stereo set, a video camera, a liquid crystal television, a handy cleaner, a portable CD player, a mini disc player, an electric shaver, a transceiver, an electronic organizer, an electronic calculator, a portable tape recorder, a radio player, a backup power supply and a memory card. In addition, examples of an electronic apparatus for consumer use include an automobile, an electromotive vehicle, a motor, a lighting device, a toy, a game device, a load conditioner, a timepiece, a strobe, a camera, and a medical device (for example, a pacemaker, a hearing aid, or a shoulder massager). Further, the non-aqueous electrolytic solution secondary battery can be used as various batteries for use in military or aerospace applications. In addition, the non-aqueous electrolytic solution secondary battery can be used in combination with a solar battery.
A metal ion which is used for transporting an electron in the secondary battery is not particularly limited, and it is preferable that a metal ion in Group I or Group II in the periodic table is used. Among these, for example, a lithium ion, a sodium ion, a magnesium ion, a calcium ion, or an aluminum ion is preferably used. Regarding a secondary battery using a lithium ion, general technical features can refer to various documents and publications such as Patent Documents which are described above at the beginning of this specification. Regarding a secondary battery using a sodium ion, for example, general technical features can refer to Journal of Electrochemical Society; and Electrochemical Science and Technology United States, 1980, Vol. 127, pp. 2097 to 2099. Regarding a secondary battery using a magnesium ion, for example, general technical features can refer to Nature pp. 407, 724 to 727 (2000). Regarding a secondary battery using a calcium ion, for example, general technical features can refer to J. Electrochem. Soc. Vol. 138, 3536 (1991). It is preferable that he present invention is applied to a lithium ion secondary battery because the lithium ion secondary battery is widely used. Even when the present invention is applied to other batteries, the desired effects can be exhibited, and the present invention is not limited to a lithium ion secondary battery.
Hereinafter, examples of the present invention will be described, but the present invention is not limited to these examples.
A halogen-containing compound shown in Table 1 was added in an addition amount shown in Table 1 to an electrolytic solution containing 1 M LiPF6 ethylene carbonate and diethyl carbonate at a volume ratio of 1:2. As a result, an electrolytic solution for a test was prepared.
Preparation of 2032-Type Coin Battery
A positive electrode was prepared using an electrode mixture including: 85 mass % of lithium cobalt oxide (LiCoO2) as an active material; 7 mass % of carbon black as a conductive auxiliary agent; and 8 mass % of PVDF (polyvinyl fluoride) as a binder. A negative electrode was prepared using an electrode mixture including: 92 mass % of Gr (natural graphite) as an active material; and 8 mass % of PVDF (polyvinyl fluoride) as a binder. A separator was formed of polypropylene, and the thickness thereof was 25 μm. Using the positive and negative electrodes and the separator, a 2032-type coin battery was prepared for each electrolytic solution for a test and was evaluated for the following items. The results are shown in Table 1.
<Flame Retardancy Test>
Referring to the UL-94 HB (horizontal burning) test, an evaluation was performed in the following test system. A glass filter paper (ADVANTEC GA-100) having a width of 13 mm and a length of 110 mm was cut, and 1.7 ml of the prepared electrolytic solution was uniformly dropped on the glass filter paper. After the electrolytic solution was sufficiently impregnated into the glass filter paper, the remaining electrolytic solution was wiped off, and the glass filter paper was horizontally suspended. The glass filter paper was ignited for 10 seconds at a position where a tip end of the glass filter paper was in contact with inner flame in a butane gas burner in which the entire flame length was adjusted to 2 cm. Next, after being released from the flame, the condition of the glass filter paper was evaluated.
AA . . . A level where the glass filter was not burned or the flame was removed immediately
A . . . The flame was observed for a while after the ignition, but the flame was removed before extending to the entire filter paper
B . . . A level where a combustion preventing effect was observed; however, the glass filter paper was burned, and the flame was not removed
C . . . A level where a combustion preventing effect was not observed
<Wettability>
Evaluation of Wettability
The contact angle of each of the prepared electrolytic solutions with the positive electrode prepared as described above was measured using a contact angle meter Drop Master 700 (manufactured by Kyowa Interface Science Co., Ltd.). The evaluation criteria are as follows.
A: When the contact angle was less than a contact angle value of an electrolytic solution not containing a phosphazene compound and a halogen-containing compound
B: When the contact angles were equal to each other
C: When the contact angle was greater than the contact angle of an electrolytic solution not containing a phosphazene compound and a halogen-containing compound
<Cycle Characteristics>
In a thermostatic chamber at 30° C., the 2032-type battery prepared using the above-described method was charged to a battery voltage of 4.3 V at a constant current of 1.0 mA at 0.5 C. Next, the battery was charged to a current value of 0.12 mA at a constant voltage of 4.3 V or was charged for two hours. Next, the battery was discharged to a battery voltage of 2.7 V at a constant current of 2.0 mA at 1C. The above-described processes were set as one cycle. This cycle was repeated, and the number of cycles was measured until the discharge capacity (mAh) was 75% or lower of the discharge capacity of the first cycle. The evaluation results were classified into the following categories.
A: 120 cycles or more
110 cycles to 119 cycles
B: 100 cycles to 109 cycles
C: 90 cycles to 99 cycles
D: 89 cycles or less
<Notes in Table>
Vol % (1): Volume content with respect to 100% of the electrolytic solution
Vol % (2): Volume content with respect to 100% of the aprotic solvent
Gr: Graphite
LCO: Lithium cobalt oxide (LiCoO2)
Electrolytic solution of C14: Corresponding to the electrolytic solution of Example 1 disclosed in JP2012-134151A)
EC: Ethylene carbonate
FEC: Fluoroethylene carbonate
EMC: Ethyl methyl carbonate
FE: Fluoroalkyl ether (CF2H—CF2—CH2—O—CF2—CF2H)
It can be seen from the above results that the electrolytic solution for a non-aqueous secondary battery and the non-aqueous electrolytic solution secondary battery according to the present invention can achieve both flame retardancy and battery performance (cycle characteristics) at a high level in a system containing a phosphazene compound as a flame retardant.
The evaluation tests of the respective items were performed by the same procedure as that of Example 1 and Comparative Example 1, except that the positive electrode active material was changed. The results are shown in Table 2 below.
<Notes in Table> Notes other than those shown in Table 1
LNMCO: Lithium nickel manganese cobalt oxide (LiNip3Mn1/3Co1/3O2)
It can be seen from the above results of Table 2 that the electrolytic solution containing a phosphazene compound and a halogen-containing compound according to the formula of the present invention has high affinity to the high-potential positive electrode (LNMCO) and can significantly improve performance.
The evaluation was performed by the same procedure as that of Test No. 101, except that the phosphazene compound and the halogen-containing compound to be used were changed as shown below. As a result, it was verified that good results were obtained in all the electrolytic solutions.
The present invention has been described using the embodiments. However, unless specified otherwise, any of the details of the above description is not intended to limit the present invention and can be construed in a broad sense within a range not departing from the concept and scope of the present invention disclosed in the accompanying claims.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2012-226051 | Oct 2012 | JP | national |
This application is a Continuation of PCT International Application No. PCT/JP2013/077129 filed on Oct. 4, 2013, which claims priority under 35 U.S.C §119(a) to Japanese Patent Application No. 2012-226051 filed on Oct. 11, 2012. Each of the above application(s) is hereby expressly incorporated by reference, in its entirety, into the present application.
| Number | Date | Country | |
|---|---|---|---|
| Parent | PCT/JP2013/077129 | Oct 2013 | US |
| Child | 14683287 | US |
