Patent Application
20230038509
The present invention relates to a lithium ion battery.
Conventionally, there has been proposed a battery in which a positive electrode lead connected to a positive electrode is covered with an insulating tape to improve insulation properties between the positive electrode lead and a negative electrode (see, for example, PATENT LITERATURE 1 to 3).
As shown in
PATENT LITERATURE 1: JP 2014-89856 A
PATENT LITERATURE 2: WO 2017/038010 A
PATENT LITERATURE 3: JP 2017-152372 A
When a foreign matter entering the inside of the battery penetrates through an insulating tape, and an internal short circuit occurs between a positive electrode lead and a negative electrode, the battery may generate heat. Therefore, conventionally, a filler such as alumina is added to the insulating tape to improve heat resistance of the insulating tape, thereby suppressing an increase in battery temperature at the time of internal short circuit.
However, in a lithium ion battery using an electrolyte including fluorine, there is a problem that a filler is eluted by hydrofluoric acid generated through a reaction between moisture that has entered the inside of the battery and fluorine, deteriorating high-temperature storage characteristics of the lithium ion battery.
An aspect of the present disclosure is a lithium ion battery including: a positive electrode; a negative electrode; a positive electrode lead connected to the positive electrode; an insulating tape covering the positive electrode lead; and an electrolyte, wherein the insulating tape has a substrate layer mainly containing organic material, and a filler layer provided on the substrate layer, the filler layer includes an oxide compound of an alkaline earth metal, and the electrolyte includes fluorine.
According to the present disclosure, in a lithium ion battery using an electrolyte including fluorine, it is possible to suppress an increase in battery temperature when a foreign matter penetrates an insulating tape to cause an internal short circuit, and to suppress a decrease in high-temperature storage characteristics.
Hereinafter, an example of a lithium ion battery according to an aspect of the present disclosure will be described. The drawings referred to in the following description of the embodiments are schematically illustrated, and dimensional ratios and the like of components drawn in the drawings may be different from those of actual components.
The electrode assembly 14 is not limited to a winding-type electrode assembly, and for example, other forms such as a layered type electrode assembly in which a positive electrode and a negative electrode are alternately layered with a separator interposed therebetween may be applied.
The battery case 15 accommodates the electrode assembly 14, the electrolyte, and the like, and comprises, for example, a bottomed cylindrical case body 16 having an opening, and a sealing assembly 17 sealing the opening of the case body 16. The battery case 15 desirably comprises a gasket 28 provided between the case body 16 and the sealing assembly 17, thereby ensuring the sealability inside the battery. The battery case 15 is not limited to one having a cylindrical shape, and may be, for example, a square battery case, a layered-type battery case, or the like.
The case body 16 has, for example, a projecting portion 22 supporting the sealing assembly 17, and a part of a side face of the case body 16 projects inward to form the projecting portion 22. The projecting portion 22 is preferably formed in an annular shape along the circumferential direction of the case body 16, and supports the sealing assembly 17 on the upper face thereof
The sealing assembly 17 has a structure in which a filter 23, a lower vent member 24, an insulator 25, an upper vent member 26, and a cap 27 are layered in this order from the electrode assembly 14 side. Each member constituting sealing assembly 17 has, for example, a disk shape or a ring shape, and each member except for the insulator 25 is electrically connected to each other. The lower vent member 24 and the upper vent member 26 are connected to each other at the central parts of respective members, and the insulator 25 is interposed between the peripheral parts of respective members. When the internal pressure increases due to heat generated by an internal short circuit or the like, the lower vent member 24 deforms so as to push up the upper vent member 26 toward the cap 27 and breaks, and the current path between the lower vent member 24 and the upper vent member 26 is cut off, for example. When the internal pressure further increases, the upper vent member 26 breaks, and the gas is discharged from an opening of the cap 27.
One end of the positive electrode lead 20 is connected to the positive electrode 11. In addition, the positive electrode lead 20 extends from the positive electrode 11 to the filter 23 through a through hole of the insulating plate 18, and the other end of the positive electrode lead 20 is connected to the lower face of the filter 23. As a result, the cap 27 electrically connected to the filter 23 serves as a positive electrode terminal. One end of the negative electrode lead 21 is connected to the negative electrode 12. The negative electrode lead 21 extends from the negative electrode 12 to the internal face of a bottom part of the case body 16 through the outside of the insulating plate 19, and the other end of the negative electrode lead 21 is connected to the internal face of the bottom part of the case body 16. As a result, the case body 16 serves as a negative electrode terminal.
Hereinafter, the electrolyte will be described. The electrolyte includes a solvent and an electrolyte salt dissolved in the solvent. The electrolyte is an electrolyte including fluorine. Fluorine may be included in either the solvent or the electrolyte salt, or may be included in a component other than the solvent or the electrolyte salt constituting the electrolyte. Examples of the solvent including fluorine include fluorine-substituted products in which at least a part of hydrogen of esters, ethers, nitriles, amides such as dimethylformamide, and isocyanates such as hexamethylene diisocyanate is substituted with fluorine.
The fluorine-substituted product is preferably a fluorinated cyclic carbonic acid ester, a fluorinated chain carbonic acid ester, or a fluorinated chain carboxylic acid ester from the point of battery characteristics, and particularly preferably a fluorinated cyclic carbonic acid ester or a fluorinated chain carboxylic acid ester.
Preferred examples of the fluorinated cyclic carbonic acid ester include 4-fluoroethylene carbonate (FEC), 4,5-difluoroethylene carbonate, 4,4-difluoroethylene carbonate, 4,4,5-trifluoroethylene carbonate, and 4,4,5,5-tetrafluoroethylene carbonate.
Preferred examples of the fluorinated chain carboxylic acid ester include fluorinated ethyl propionate, fluorinated methyl acetate, fluorinated ethyl acetate, fluorinated propyl acetate, ethyl 2,2,2-trifluoroacetate, methyl 3,3,3-trifluoropropionate, and methyl pentafluoropropionate. These may be independently used, or two or more thereof may be used in combination.
The solvent may include a non-fluorine-based solvent including no fluorine. Examples of the non-fluorine-based solvent include cyclic carbonic acid esters such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate; chain carbonic acid esters such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, and methyl isopropyl carbonate; cyclic carboxylic acid esters such as γ-butyrolactone and γ-valerolactone; and chain carboxylic acid esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate.
Examples of the electrolyte salt include LiClO4, LiBF4, LiPF6, LiAlCl4, LiSbF6, LiSCN, LiCF3SO3, LiCF3CO2, LiAsF6, LiB10Cl10, lithium lower aliphatic carboxylate, LiCl, LiBr, LiILi (P(C2O4)F4), LiPF6-x(CnF2n+1)x (1<x<6, n is 1 or 2), chloroborane lithium, borates, and imide salts. Examples of the borates include Li [B(C2O4)2], Li[B(C2O4)F2], Li2B4O7, lithium bis(1,2-benzenediolate(2-)-O,O′)borate, lithium bis(2,3-naphthalenediolate(2-)-O,O′)borate, lithium bis(2,2′-biphenyldiolate(2-)-O,O′)borate, and lithium bis(5-fluoro-2-olate-1-benzenesulfonic acid-O,O′)borate. Examples of the imide salts include lithium bisfluorosulfonylimide (LiN(FsO2)2, hereinafter, also referred to as LiFSI), lithium imide bistrifluoromethanesulfonate (LiN(CF3SO2)2), lithium imide trifluoromethanesulfonate (LiN(CF3SO2)(C4F9SO2)), lithium imide bispentafluoroethanesulfonate (LiN(C2F5SO2)2), and LiN(C1F2I+1SO2)(CmF2m+1SO2) {l and m are an integer of 0 or more}. Among them, LiPF6, LiFSI (lithium bis(fluorosulfonyl)imide), LiBF4, LiSbF6, LiCF3SO3, LiCF3CO2, and LiAsF6 are preferable from the point of battery characteristics. These electrolyte salts may be independently used, or two or more thereof may be used in combination. The concentration of the electrolyte salt is, for example, preferably 0.5 to 3 mol/L, and more preferably 0.8 to 1.8 mol/L.
The electrolyte may include an additive. Examples of the additive include an unsaturated cyclic carbonic acid ester, an acid anhydride, a phenol compound, a benzene compound, a nitrile compound, an isocyanate compound, a sultone compound, and a sulfuric acid compound.
Examples of the unsaturated cyclic carbonic acid ester include vinylene carbonate, 4-methylvinylene carbonate, 4,5-dimethylvinylene carbonate, 4-ethylvinylene carbonate, 4,5-diethylvinylene carbonate, 4-propylvinylene carbonate, 4,5-dipropylvinylene carbonate, 4-phenylvinylene carbonate, 4,5-diphenylvinylene carbonate, vinylethylene carbonate, and divinylethylene carbonate. The unsaturated cyclic carbonic acid ester may be independently used, or two or more thereof may be used in combination. In the unsaturated cyclic carbonic acid ester, some of hydrogen atoms may be substituted with fluorine atoms.
The acid anhydride may be, for example, an anhydride in which a plurality of carboxylic acid molecules are condensed between molecules, but is preferably an acid anhydride of polycarboxylic acid. Examples of the acid anhydride of polycarboxylic acid include succinic anhydride, maleic anhydride, and phthalic anhydride.
Examples of the phenol compound include phenol and hydroxytoluene.
Examples of the benzene compound include fluorobenzene, hexafluorobenzene, and cyclohexylbenzene (CHB).
Examples of the nitrile compound include adiponitrile, pimelonitrile, propionitrile, and succinonitrile.
Examples of the isocyanate compound include methyl isocyanate (MIC), diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), and bisisocyanatemethylcyclohexane (BIMCH).
Examples of the sultone compound include propane sultone and propene sultone.
Examples of the sulfuric acid compound include ethylene sulfate, ethylene sulfite, dimethyl sulfate, and lithium fluorosulfate.
Among the above additives, vinylene carbonate is preferable from the point of battery characteristics.
The electrolyte preferably includes a difluorophosphoric acid salt from the point of battery characteristics, and particularly preferably includes lithium difluorophosphate (LiPF2O2).
Hereinafter, the insulating tape of the present embodiment covering the positive electrode 11 and the positive electrode lead 20 will be described.
The positive electrode 11 comprises a positive electrode current collector 32 and a positive electrode active material layer 34 formed on the positive electrode current collector 32. Foil of a metal such as aluminum which is stable within the potential range of the positive electrode, a film in which the metal is disposed on a surface layer thereof, or the like is used for the positive electrode current collector 32. The positive electrode active material layer 34 includes a positive electrode active material. The positive electrode active material layer 34 preferably includes a conductive agent and a binder in addition to the positive electrode active material.
Examples of the positive electrode active material include Li composite oxides including lithium (Li) and a transition metal element such as cobalt (Co), manganese (Mn), and nickel (Ni). The Li composite oxide may include other additive elements other than Co, Mn, and Ni, and may include, for example, aluminum (Al), zirconium (Zr), boron (B), magnesium (Mg), scandium (Sc), yttrium (Y), titanium (Ti), iron (Fe), copper (Cu), zinc (Zn), chromium (Cr), lead (Pb), tin (Sn), sodium (Na), potassium (K), barium (Ba), strontium (Sr), calcium (Ca), tungsten (W), molybdenum (Mo), niobium (Nb), and silicon
(Si).
The positive electrode active material preferably includes a Li composite oxide having a Co content of 20% or less from the point of suppressing deterioration of high-temperature storage characteristics. From the point of suppressing deterioration of high-temperature storage characteristics, a lower Co content is preferable, and the Co content is more preferably 10% or less. Here, the Co content means a molar ratio of Co to the total amount of metals excluding Li in the Li composite oxide. For example, the Co content of 20% or less means that the Co content in the Li composite oxide is 0.2 or less in terms of a molar ratio with respect to the total amount of metals excluding Li. The lower limit of the
Co content is preferably 5% or more from the point of, for example, suppressing deterioration of charge-discharge cycle characteristics of the lithium ion battery. That is, from the point of, for example, suppressing deterioration of high-temperature storage characteristics and charge-discharge cycle characteristics, the positive electrode active material preferably includes a Li composite oxide having a Co content of 5% or more and 20% or less, more preferably includes a Li composite oxide having a Co content of 5% or more and 10% or less. The positive electrode active material is not limited to one including a Li composite oxide having a Co content of more than 20%, and may be included as long as the effects of the present disclosure are not impaired. For example, the content of the Li composite oxide having a Co content of more than 20% is preferably 10 mass % or less based on the total amount of the positive electrode active material, and the content of the Li composite oxide having a Co content of 20% or less is preferably 90 mass % or more based on the total amount of the positive electrode active material.
Examples of the conductive agent included in the positive electrode active material layer 34 include carbon powders and the like of carbon black, acetylene black, Ketjen black, graphite, and the like. These may be independently used, or two or more thereof may be used in combination.
Examples of the binder included in the positive electrode active material layer 34 include fluoropolymers and rubber polymers. Examples of the fluoropolymer include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and modified products thereof. Examples of the rubber polymer include ethylene-propylene-isoprene copolymers and ethylene-propylene-butadiene copolymers. These may be independently used, or two or more thereof may be used in combination.
The positive electrode current collector 32 has an exposed part 32a where the positive electrode active material layer 34 is not formed. The exposed part 32a shown in
The positive electrode lead 20 comprises one end part 20a connected to the exposed part 32a of the positive electrode current collector 32 and an extending part 20b extending to the outside of a peripheral part 32b of the positive electrode current collector 32. The positive electrode lead 20 has the other end part on the tip side from the extending part 20b, and the other end part is connected to the filter 23 of the sealing assembly 17 as described above. A method for connecting the one end part 20a of the positive electrode lead 20 and the exposed part 32a of the positive electrode current collector 32 is not particularly limited as long as electrical connection between the positive electrode lead 20 and the positive electrode current collector 32 is secured, and examples thereof include ultrasonic welding.
Material for the positive electrode lead 20 is not particularly limited, and may be a metal such as aluminum or titanium.
The insulating tape 30 shown in
However, the position of the positive electrode lead 20 covered with the insulating tape 30 is not limited to the one end part 20a of the positive electrode lead 20, and may be, for example, the extending part 20b of the positive electrode lead 20 or the other end part of the positive electrode lead 20 which is a part connected to the sealing assembly 17. The internal short circuit occurring between the positive electrode lead 20 and the negative electrode 12 is likely to occur mainly between the one end part 20a of the positive electrode lead 20 and the negative electrode 12 or between the extending part 20b of the positive electrode lead 20 and the negative electrode 12. Therefore, the insulating tape 30 preferably covers at least one of the one end part 20a and the extending part 20b of the positive electrode lead 20, and particularly preferably covers the one end part 20a of the positive electrode lead 20. When the one end part 20a of the positive electrode lead 20 is covered with the insulating tape 30, a part of the one end part 20a of the positive electrode lead 20 may be covered with the insulating tape 30, but it is preferable to cover the entire one end part 20a from the point of, for example, effectively suppressing the occurrence of the internal short circuit. Incidentally, when the extending part 20b of the positive electrode lead 20 is covered with the insulating tape 30, the insulating tape 30 may cover a part of the extending part 20b, but preferably covers the entirety of the extending part 20b. When a part or the entirety of the extending part 20b of the positive electrode lead 20 is covered with the insulating tape 30, the insulating tape 30 is preferably wound around the extending part 20b to cover the entirety of the outer periphery of the extending part 20b.
As shown in
Hereinafter, the configuration of the insulating tape 30 will be described.
The substrate layer 30b is not particularly limited as long as it is a layer mainly containing organic material. Here, the phrase “mainly containing organic material” means that the proportion of the organic material is the highest among materials constituting substrate layer 30b. The content of the organic material is, for example, preferably 80 mass % or more, and more preferably 90 mass % or more, based on the total mass of the substrate layer 30b, from the point of the strength and the like of the insulating tape 30. The organic material is preferably polymer material from the point of, for example, flexibility and strength of the insulating tape 30. Examples thereof include cellulose derivatives (for example, cellulose ether and cellulose ester), polyvinyl chloride, polyolefin (for example, polyethylene and polypropylene), polystyrene, polyester (for example, polyethylene terephthalate), polyimide, polyamide, polyamideimide, polycarbonate, and polyphenylene sulfide. Among them, polyimide and wholly aromatic polyamide (aramid) are preferable, and polyimide is particularly preferable. These may be independently used, or two or more thereof may be used in combination. The substrate layer 30b may have a layered structure having a first resin layer and a second resin layer, and examples thereof include a layered structure having a first resin layer including polyimide and a second resin layer including a resin other than polyimide. When the substrate layer 30b includes polyimide, the content of polyimide is preferably 80 mass % or more, and more preferably 90 mass % or more.
Polyimide is a collective term for polymers including an imide bond in a repeating unit, and usually means an aromatic polyimide in which an aromatic compound directly binds through an imide bond. The aromatic polyimide has a conjugate structure in which an imide bond intervenes between aromatic rings, and therefore is rigid and has a strong molecular structure. The type of the polyimide is not particularly limited, and may be a wholly aromatic polyimide such as polypyrromellitimide, a semi-aromatic polyimide such as polyetherimide, or a thermosetting polyimide obtained by reacting bismaleimide with aromatic diamine.
The thickness of the substrate layer 30b is arbitrary, but is, for example, preferably 5 pm or more and 30 μm or less, and more preferably 10 μm or more and 30 μm or less, from the point of, for example, the strength of the insulating tape 30.
Incidentally, the substrate layer 30b is not limited to one including a filler such as inorganic material, but it is preferable that the substrate layer 30b does not include a filler as much as possible from the point of, for example, flexibility of the insulating tape 30.
The filler layer 30a includes an oxide compound of an alkaline earth metal. By providing the filler layer 30a including an oxide compound of an alkaline earth metal, heat resistance of the insulating tape 30 can be improved. For example, even if a foreign matter penetrates the insulating tape 30 to cause an internal short circuit between the positive electrode lead 20 and the negative electrode 12, and as a result, the battery generates heat, melting or decomposition of the insulating tape 30 can be suppressed. As a result, expansion of the short-circuit part or continuation of the short circuit is suppressed, and an increase in battery temperature is suppressed. In addition, the oxide compound of an alkaline earth metal is less soluble in hydrofluoric acid than fillers such as alumina and silica included in conventional filler layers. Therefore, even when hydrofluoric acid is generated in a lithium ion battery using an electrolyte including fluorine, elution of an oxide compound of an alkaline earth metal in the filler layer 30a is suppressed by the hydrofluoric acid. As a result, diffusion of impurities derived from the filler layer into the lithium ion battery is suppressed, so that deterioration of the high-temperature storage characteristics of the lithium ion battery is suppressed as compared with the case of using a filler layer including a conventional filler (alumina, silica, or the like). The high-temperature storage characteristics mean the degree of capacity decrease after the lithium ion battery in a charged state is stored for a predetermined period under a high-temperature environment.
Examples of the oxide compound of an alkaline earth metal include an oxide of an alkaline earth metal, a sulfate of an alkaline earth metal, a nitrate of an alkaline earth metal, and a carbonate of an alkaline earth metal. Among them, a sulfate of an alkaline earth metal and a nitrate of an alkaline earth metal are preferable, and a sulfate of an alkaline earth metal is particularly preferable from the point of, for example, effectively suppressing deterioration of high-temperature storage characteristics. Specifically, beryllium nitrate, magnesium nitrate, calcium nitrate, strontium nitrate, barium nitrate, beryllium sulfate, magnesium sulfate, calcium sulfate, strontium sulfate, barium sulfate and the like are preferable. These may be independently used, or two or more thereof may be used in combination.
The filler layer 30a preferably includes an adhesive from the point of, for example, securing adhesiveness between the insulating tape 30 and the positive electrode lead 20. Examples of the adhesive include acrylic resin, natural rubber, synthetic rubber, silicone, epoxy resin, melamine resin, and phenol resin. These may be independently used, or two or more thereof may be used in combination. The adhesive may include an additive material such as a tackifier, a crosslinking agent, an antiaging agent, a colorant, an antioxidant, a chain transfer agent, a plasticizer, a softener, a surfactant, and an antistatic agent, and a solvent in addition to the resin material as necessary.
The content of the oxide compound of an alkaline earth metal in the filler layer 30a is, for example, preferably in a range of 3 mass % to 80 mass %, and more preferably in a range of 20 mass % to 70 mass %. In addition, the content of the adhesive in the filler layer 30a is, for example, preferably in a range of 20 mass % to 97 mass %, and more preferably in a range of 30 mass % to 80 mass %. In addition, the filler layer 30a may include a conventional filler such as alumina or silica, but when the content of the conventional filler increases, the effect of suppressing deterioration of the high-temperature storage characteristics of the lithium ion battery may not be sufficiently obtained. Therefore, the content of the conventional filler in the filler layer 30a is preferably 5 mass % or less, and preferably 1 mass % or less.
The thickness of the filler layer 30a is arbitrary, but is, for example, preferably in a range of 1 μm to 25 μm, and more preferably in a range of 5 μm to 20 μm, from the point of, for example, effectively suppressing melting or decomposition of the insulating tape 30.
The thickness of the insulating tape 30 is not particularly limited, but is preferably in a range of 10 to 55 μm, for example. When the thickness of the insulating tape 30 is less than 10 μm, the insulating tape 30 is easily broken by a foreign matter entering the inside of the battery. When the thickness of the insulating tape 30 exceeds 55 μm, the volume of another component is required to be reduced so as to accommodate the electrode assembly 14 in the case body 16 having a predetermined size.
A modification of the insulating tape 30 of the present embodiment will be described. In the insulating tape 30 of the present embodiment, the filler layer 30a including an oxide compound of an alkaline earth metal may be provided on both sides of the substrate layer 30b mainly containing organic material. The insulating tape 30 of the present embodiment may be disposed on the positive electrode lead 20 such that the filler layer 30a including an oxide compound of an alkaline earth metal is disposed on a side opposite to the positive electrode lead 20 with the substrate layer 30b mainly containing organic material interposed between the filler layer 30a and the positive electrode lead 20. That is, the insulating tape 30 may have a layered structure in which the substrate layer 30b mainly containing organic material and the filler layer 30a including an oxide compound of an alkaline earth metal are layered in this order from the positive electrode lead 20 side. In addition, the insulating tape 30 of the present embodiment may further have an adhesive layer including an adhesive. That is, the insulating tape 30 may have a layered structure in which the adhesive layer including an adhesive, the filler layer 30a including an oxide compound of an alkaline earth metal, and the substrate layer 30b mainly containing organic material are layered in this order from the positive electrode lead 20 side, a layered structure in which the adhesive layer including an adhesive, the substrate layer 30b mainly containing organic material, and the filler layer 30a including an oxide compound of an alkaline earth metal are layered in this order from the positive electrode lead 20 side, or the like.
The insulating tape 30 of the present embodiment may cover not only the positive electrode lead 20 but also a portion where an internal short circuit of the battery may occur.
For example, in the negative electrode 12, an exposed part of the negative electrode current collector is usually formed, and one end of the negative electrode lead 21 is connected onto the exposed part, similarly to the positive electrode 11. The negative electrode lead 21 and the exposed part of the negative electrode current collector may be covered with the insulating tape 30 of the present embodiment when the negative electrode lead 21 and the exposed part of the negative electrode current collector are a portion where an internal short circuit of the battery occurs.
Hereinafter, the negative electrode 12 and the separator 13 will be described.
The negative electrode 12 comprises a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector. Foil of a metal which is stable within the potential range of the negative electrode, such as copper, a film in which the metal is disposed on a surface layer thereof, or the like can be used for the negative electrode current collector. The negative electrode active material layer includes a negative electrode active material. The negative electrode active material layer preferably includes a thickener and a binder in addition to the negative electrode active material.
Carbon material capable of storing and releasing lithium ions can be used as the negative electrode active material, and hardly graphitizable carbon, easily graphitizable carbon, fibrous carbon, coke, carbon black, and the like can be used in addition to graphite. Furthermore, silicon, tin, and alloys or oxides mainly containing these can be used as the non-carbon-based material.
As the binder, PTFE or the like can be used as in the case of the positive electrode, but a styrene-butadiene copolymer (SBR) or a modified product thereof, or the like may be used. As the thickener, carboxymethyl cellulose (CMC) or the like can be used.
Although not shown in the drawings, the negative electrode current collector has an exposed part where the negative electrode active material layer is not formed, similarly to the positive electrode current collector 32 described above. The exposed part of the negative electrode current collector may be formed at any position of the negative electrode current collector, but is usually formed on an end part in the longitudinal direction of the negative electrode current collector. Similarly to the positive electrode lead 20 described above, the negative electrode lead 21 comprises one end part connected to the exposed part of the negative electrode current collector and an extending part extending from the one end part to the outside of the peripheral part of the negative electrode current collector. The negative electrode lead 21 has the other end part on the tip side from the extending part, and the other end part is connected to the internal face of the bottom part of the case body 16. Material for the negative electrode lead 21 is not particularly limited, and may be a metal such as nickel or titanium.
At least one of the one end part, the extending part, and the other end part of the negative electrode lead 21 may be covered with the insulating tape 30. The exposed part of the negative electrode current collector may also be covered with the insulating tape 30.
A porous sheet having ion permeability and insulation properties is used as the separator 13, for example. Specific examples of the porous sheet include a fine porous thin film, a woven fabric, and a nonwoven fabric. As material of the separator 13, olefin-based resin such as polyethylene or polypropylene, cellulose, or the like is suitable. The separator 13 may be a layered body having a cellulose fiber layer and a fiber layer of thermoplastic resin such as olefin-based resin. In addition, the separator 13 may be a multilayer separator having a polyethylene layer and a polypropylene layer, and a separator having a surface coated with a material such as aramid-based resin or ceramic may be used.
Hereinafter, the present disclosure will be further described with reference to examples, but the present disclosure is not limited to these examples.
[Production of Positive Electrode]
A positive electrode mixture slurry was prepared by mixing 100 parts by mass of LiNi0.77Co0.20Al0.03O2 as a positive electrode active material, 1.0 parts by mass of acetylene black as a conductive agent, 0.9 parts by mass of polyvinylidene fluoride as a binder, and an appropriate amount of NMP. The obtained positive electrode mixture slurry was applied to both sides of aluminum foil having a thickness of 15 μm to be a positive electrode current collector, followed by drying and rolling to produce a strip-shaped positive electrode.
An insulating tape was attached so as to cover the entirety of the surface of the one end part of the positive electrode lead and the exposed part of the positive electrode current collector. The insulating tape used is an insulating tape having a substrate layer made of polyimide and having a thickness of 25 μm and a filler layer having a thickness of 7 μm. The polyimide is synthesized by a reaction of pyromellitic anhydride and diaminodiphenyl ether. As the filler layer, a mixture of 50 parts by mass of an acrylic adhesive containing acrylic resin as a main component and 50 parts by mass of Ba(NO3)2 particles as a filler was used.
[Production of Negative Electrode]
A negative electrode mixture slurry was prepared by mixing 100 parts by mass of scaly artificial graphite having an average particle diameter of about 20 μm as a negative electrode active material, 1 part by mass of styrene butadiene rubber as a binder, 1 part by mass of carboxymethyl cellulose as a thickener, and water. The obtained negative electrode mixture slurry was uniformly applied to both sides of copper foil having a thickness of 8 μm to be a negative electrode current collector, followed by drying and rolling to produce a strip-shaped negative electrode. Provided that exposed parts were provided on both sides of the end part of the negative electrode at the winding end side. One end part of the negative electrode lead was disposed on the exposed part of the negative electrode current collector, and the one end part was welded to the exposed part.
[Preparation of Electrolyte]
LiPF6 was dissolved in a mixed solvent of DMC, EMC, and 4-fluoroethylene carbonate (volume ratio 40:40:20) so as to have a concentration of 1.0 mol/L to prepare an electrolyte.
[Production of Battery]
The positive electrode and the negative electrode were layered with the separator interposed therebetween and wound to form an electrode assembly. Insulating plates were disposed above and below the electrode assembly, and the electrode assembly was accommodated in an iron case body whose internal surface was plated with nickel. The negative electrode lead projecting from the electrode assembly and the bottom face of the battery case were welded, and the positive electrode lead projecting from the electrode assembly and the internal face of the sealing assembly provided with a gasket at the peripheral part thereof were welded. After the non-aqueous electrolyte was injected into the case body, the opening of the case body was closed with a sealing assembly, and the end part of the opening of the case body was crimped with the peripheral part of the sealing assembly via the gasket to produce a cylindrical lithium ion battery.
A lithium ion battery was produced in the same manner as in Example 1 except that LiNi0.77Co0.20Al0.03O2 was used as the positive electrode active material, and a mixture of 50 parts by mass of an acrylic adhesive containing acrylic resin as a main component and 50 parts by mass of BaSO4 particles as the filler was used as the filler layer of the insulating tape.
A lithium ion battery was produced in the same manner as in Example 1 except that LiNi0.67Co0.30Al0.03O2 was used as the positive electrode active material, and a mixture of 20 parts by mass of an acrylic adhesive material containing acrylic resin as a main component and 80 parts by mass of BaSO4 particles as the filler was used as the filler layer of the insulating tape.
A lithium ion battery was produced in the same manner as in Example 1 except that LiNi0.67Co0.30Al0.03O2 was used as the positive electrode active material, and a mixture of 97 parts by mass of an acrylic adhesive containing acrylic resin as a main component and 3 parts by mass of BaSO4 particles as the filler was used as the filler layer of the insulating tape.
A lithium ion battery was produced in the same manner as in Example 1 except that LiNi0.92Co0.05Al0.03O2 was used as the positive electrode active material, a mixture of 50 parts by mass of an acrylic adhesive containing acrylic resin as a main component and 50 parts by mass of SrSO4 particles as the filler was used as the filler layer of the insulating tape, and 2 mass % of vinylene carbonate was added to the electrolyte.
A lithium ion battery was produced in the same manner as in Example 1 except that LiNi0.92Co0.05Al0.03O2 was used as the positive electrode active material, a mixture of 50 parts by mass of an acrylic adhesive containing acrylic resin as a main component and 50 parts by mass of BaSO4 particles as the filler was used as the filler layer of the insulating tape, and 2 mass % of vinylene carbonate was added to the electrolyte.
A lithium ion battery was produced in the same manner as in Example 1 except that LiNi0.77Co0.20Al0.03O2 was used as the positive electrode active material, a mixture of 50 parts by mass of an acrylic adhesive containing acrylic resin as a main component and 50 parts by mass of BaSO4 particles as the filler was used as the filler layer of the insulating tape, and 2 mass % of vinylene carbonate was added to the electrolyte.
A lithium ion battery was produced in the same manner as in Example 1 except that LiNi0.87Co0.10Al0.03O2 was used as the positive electrode active material, a mixture of 50 parts by mass of an acrylic adhesive containing acrylic resin as a main component and 50 parts by mass of BaSO4 particles as the filler was used as the filler layer of the insulating tape, and 2 mass % of vinylene carbonate was added to the electrolyte.
A lithium ion battery was produced in the same manner as in Example 1 except that LiNi0.92Co0.05Al0.03O2 was used as the positive electrode active material, a mixture of 50 parts by mass of an acrylic adhesive containing acrylic resin as a main component and 50 parts by mass of BaSO4 particles as the filler was used as the filler layer of the insulating tape, and 0.1 mass % of vinylene carbonate was added to the electrolyte.
A lithium ion battery was produced in the same manner as in Example 1 except that LiNi0.92Co0.05Al0.03O2 was used as the positive electrode active material, a mixture of 50 parts by mass of an acrylic adhesive containing acrylic resin as a main component and 50 parts by mass of BaSO4 particles as the filler was used as the filler layer of the insulating tape, and 10 mass % of vinylene carbonate was added to the electrolyte.
A lithium ion battery was produced in the same manner as in Example 1 except that LiNi0.67Co0.30Al0.03O2 was used as the positive electrode active material and an insulating tape including no filler was used.
A lithium ion battery was produced in the same manner as in Example 1 except that LiNi0.67Co0.30Al0.03O2 was used as the positive electrode active material, and a mixture of 50 parts by mass of an acrylic adhesive containing acrylic resin as a main component and 50 parts by mass of SiO2 particles as the filler was used as the filler layer of the insulating tape.
A lithium ion battery was produced in the same manner as in Example 1 except that LiNi0.67Co0.30Al0.03O2 was used as the positive electrode active material, and a mixture of 50 parts by mass of an acrylic adhesive material containing acrylic resin as a main component and 50 parts by mass of Al2O3 particles as the filler was used as the filler layer of the insulating tape.
[Forced Internal Short Circuit Test]
A forced internal short circuit test of the batteries of Examples and Comparative Examples was performed in accordance with JIS C 8714. Note that a severe test was performed using a nickel small piece (height: 0.5 mm, width: 0.2 mm, L-shape with a side of 3 mm (angle: 90°)) having a size larger than that of a nickel small piece with a standard size. The nickel small piece was disposed between the insulating tape and the separator such that the small piece penetrated the insulating tape. Specifically, the nickel small piece was disposed on the insulating tape at the central part in the width direction of the positive electrode current collector and at a position 5 mm from the end part of the positive electrode active material layer. Then, a forced internal short circuit test was performed, and an increase in temperature on the side face of the battery was measured with a thermocouple. The measured battery temperature was evaluated according to the following criteria, and the results thereof are shown in Table 1.
∘: Battery temperature is lower than 40° C.
Δ: Battery temperature is 40° C. or higher and lower than 100° C.
×: Battery temperature is 100° C. or higher
[High Temperature Storage Test]
The lithium ion battery of each of Examples and Comparative Examples was charged to 4.2 V at a constant current of 1C under the condition of 25° C., and then charged at a constant voltage of 4.2 V until the current value reached 0.05C to complete the charge (this charge is referred to as charge A). After 10 minutes of quiescence, the battery was discharged at a constant current of 1C until the voltage reached 2.5 V (this discharge is referred to as discharge A), and the discharge capacity at that time was defined as a capacity before storage. After 10 minutes of quiescence, only the charge A was performed, and the battery was stored at 60° C. for 20 days. After the storage, the temperature was lowered to room temperature, and only the discharge A was performed. After 10 minutes of quiescence, the charge A was performed, after 10 minutes of quiescence, the discharge A was performed, and the discharge capacity at that time was defined as a recovered capacity. Then, the capacity recovery rate after high-temperature storage was determined from the following equation. The results thereof are shown in Table 1. Note that a higher value of the capacity recovery rate after high-temperature storage indicates that deterioration of high-temperature storage characteristics is suppressed.
Capacity recovery rate after high-temperature storage (%)=(recovered capacity/capacity before storage)×100
All of the batteries of Examples 1 to 10 and Comparative Examples 1 to 3 were lithium ion batteries using an electrolyte including fluorine. In Examples 1 to 10 in which an oxide compound of an alkaline earth metal was used for the filler layer of the insulating tape, an increase in battery temperature in the forced internal short circuit test was suppressed as compared with Comparative Example 1 in which the filler layer was not provided in the insulating tape, and a decrease in capacity recovery rate after high-temperature storage was suppressed as compared with Comparative Example 2 in which SiO2 particles were used for the filler layer of the insulating tape and Comparative Example 3 in which Al2O3 particles were used for the filler layer of the insulating tape. In addition, as can be seen from the comparison between Examples 1 and 2, when the content of the oxide compound of an alkaline earth metal in the filler layer increases, an increase in battery temperature in the forced internal short circuit test is further suppressed, and when the content of the oxide compound of an alkaline earth metal in the filler layer decreases, a decrease in capacity recovery rate after high-temperature storage is further suppressed. In addition, as can be seen from the comparison between Examples 2 and 7, by adding vinylene carbonate, a decrease in capacity recovery rate after high-temperature storage is further suppressed. From the results of Examples 6, 9, and 10, the content of vinylene carbonate in the electrolyte is preferably in a range of 0.1 mass % or more and 10 mass % or less. As can be seen from the comparison between Examples 2 and 3 and the comparison between Examples 6, 7, and 8, when the Co content in the positive electrode active material decreases, a decrease in capacity recovery rate after high-temperature storage is further suppressed. From the results of Examples, the filler used for the filler layer may be an oxide compound of an alkaline earth metal.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2019-235642 | Dec 2019 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2020/038955 | 10/15/2020 | WO |
