Lithium-ion battery

Abstract

A lithium ion battery according to the present invention comprises a positive electrode, a negative electrode, a positive electrode lead that is connected to the positive electrode, an insulation tape that covers the positive electrode lead, and an electrolyte solution. The insulation tape comprises a base material layer that is mainly composed of an organic material, and a filler layer that is provided on the base material layer; the filler layer contains an oxide compound of an alkaline earth metal; and the electrolyte solution contains fluorine.

Description

[Technical Field]

[0001] The present invention relates to lithium-ion batteries. [Background technology]

[0002] Conventionally, batteries have been proposed in which the positive electrode lead connected to the positive electrode is covered with insulating tape to improve the insulation between the positive electrode lead and the negative electrode (see, for example, Patent Documents 1 to 3).

[0003] 4A and 4B are diagrams showing the configuration of the positive electrode of the lithium ion battery described in Patent Document 1, where FIG. 4A is a partial top view observed from one main surface side of the current collector, and FIG. 4B is a cross-sectional view taken along line L1-L1 in FIG. 4A.

[0004] 4A and 4B, insulating tape 44, which is disposed on one main surface of positive electrode current collector 40A, covers exposed surface 40a of positive electrode current collector in double-side uncoated portion 40b where positive electrode composite layer 40B is not formed, positive electrode lead 42 on exposed surface 40a of positive electrode current collector, and protective layer 46 interposed between the lower end portion of positive electrode lead 42 and exposed surface 40a of positive electrode current collector. By covering positive electrode lead 42 with insulating tape 44 in this way, it is possible to prevent an internal short circuit between the positive electrode lead and the negative electrode when, for example, the separator between the positive electrode and the negative electrode melts or tears in the event of a battery abnormality. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-89856 [Patent Document 2] International Publication No. 2017 / 038010 [Patent Document 3] Japanese Patent Application Publication No. 2017-152372 Summary of the Invention

[0006] If foreign matter that has entered the battery penetrates the insulating tape and causes an internal short circuit between the positive electrode lead and the negative electrode, the battery may become hot. To address this issue, a filler such as alumina has been added to the insulating tape to improve the heat resistance of the insulating tape and suppress the rise in battery temperature in the event of an internal short circuit.

[0007] However, in lithium-ion batteries that use an electrolyte containing fluorine, there is a problem in that the filler material is eluted by hydrofluoric acid produced by a reaction between water that has entered the battery and fluorine, which reduces the high-temperature storage characteristics of the lithium-ion battery.

[0008] One aspect of the present disclosure is a lithium-ion battery having 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 made of an organic material and a filler layer provided on the substrate layer, the filler layer contains an oxide compound of an alkaline earth metal, and the electrolyte contains fluorine.

[0009] According to the present disclosure, in a lithium-ion battery using an electrolyte solution containing fluorine, when a foreign object penetrates the insulating tape and an internal short circuit occurs, an increase in battery temperature can be suppressed and a deterioration in high-temperature storage characteristics can be suppressed. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a cross-sectional view of a lithium-ion battery according to an embodiment. [Figure 2A] FIG. 2A is a partial top view of the positive electrode observed from one main surface side. [Figure 2B] FIG. 2B is a cross-sectional view taken along line L1-L1 in FIG. 2A. [Figure 3] FIG. 2 is a partial cross-sectional view of an insulating tape used in the present embodiment. [Figure 4A] FIG. 1 is a diagram showing the configuration of a positive electrode of a lithium ion battery described in Patent Document 1. [Figure 4B] FIG. 1 is a diagram showing the configuration of a positive electrode of a lithium ion battery described in Patent Document 1. [Figure 5A] FIG. 5A is a partial top view of the positive electrode of Example 1 observed from one main surface side. [Figure 5B] FIG. 5B is a cross-sectional view taken along line L1-L1 in FIG. 5A. DETAILED DESCRIPTION OF THE INVENTION

[0011] An example of a lithium-ion battery according to one aspect of the present disclosure will be described below. The drawings referred to in the following description of the embodiment are schematic, and the dimensional ratios of the components depicted in the drawings may differ from those of the actual battery.

[0012] Fig. 1 is a cross-sectional view of a lithium-ion battery according to an embodiment. The lithium-ion battery 10 shown in Fig. 1 includes a wound electrode assembly 14 formed by winding a positive electrode 11 and a negative electrode 12 with a separator 13 interposed therebetween, an electrolyte, insulating plates 18 and 19 respectively disposed above and below the electrode assembly 14, a positive electrode lead 20 and a negative electrode lead 21, insulating tape covering the positive electrode lead 20, and a battery case 15.

[0013] The electrode body 14 is not limited to a wound type, and other forms may be applied, such as a stacked type in which positive electrodes and negative electrodes are alternately stacked with separators interposed therebetween.

[0014] The battery case 15 contains the electrode assembly 14, the electrolyte, and the like, and includes, for example, a cylindrical case body 16 with a bottom and an opening, and a sealing body 17 that seals the opening of the case body 16. The battery case 15 desirably includes a gasket 28 provided between the case body 16 and the sealing body 17, thereby ensuring airtightness of the interior of the battery. The battery case 15 is not limited to a cylindrical shape, and may be, for example, a rectangular or laminate type.

[0015] Case body 16 has, for example, a protruding portion 22, which is a portion of the side surface that protrudes inward and supports sealing body 17. Protruding portion 22 is preferably formed in an annular shape along the circumferential direction of case body 16, and supports sealing body 17 on its upper surface.

[0016] The sealing body 17 has a structure in which a filter 23, a lower valve body 24, an insulator 25, an upper valve body 26, and a cap 27 are stacked in this order from the electrode body 14 side. Each component constituting the sealing body 17 has, for example, a disk or ring shape, and each component except for the insulator 25 is electrically connected to one another. The lower valve body 24 and the upper valve body 26 are connected to one another at their respective centers, with the insulator 25 interposed between their respective peripheral edges. If the internal pressure increases due to heat generation caused by an internal short circuit or the like, for example, the lower valve body 24 may deform and rupture, pushing the upper valve body 26 toward the cap 27, thereby interrupting the current path between the lower valve body 24 and the upper valve body 26. If the internal pressure further increases, the upper valve body 26 may rupture, and gas may be discharged from the opening of the cap 27.

[0017] One end of the positive electrode lead 20 is connected to the positive electrode 11. The positive electrode lead 20 extends from the positive electrode 11 through a through-hole in the insulating plate 18 to the filter 23, and the other end of the positive electrode lead 20 is connected to the underside of the filter 23. As a result, the cap 27 electrically connected to the filter 23 serves as the positive electrode terminal. The negative electrode lead 21 has one end connected to the negative electrode 12. The negative electrode lead 21 extends from the negative electrode 12 through the outside of the insulating plate 19 to the inner bottom surface of the case body 16, and the other end of the negative electrode lead 21 is connected to the inner bottom surface of the case body 16. As a result, the case body 16 serves as the negative electrode terminal.

[0018] The electrolyte solution will be described below. The electrolyte solution contains a solvent and an electrolyte salt dissolved in the solvent. The electrolyte solution is an electrolyte solution containing fluorine. Fluorine may be contained in either the solvent or the electrolyte salt, or may be contained in a component other than the solvent or the electrolyte salt that constitutes the electrolyte solution. Examples of fluorine-containing solvents include fluorine-substituted compounds in which at least a portion of the hydrogen atoms is substituted with fluorine, such as esters, ethers, nitriles, amides such as dimethylformamide, and isocyanates such as hexamethylene diisocyanate.

[0019] As the fluorine-substituted compound, fluorinated cyclic carbonates, fluorinated chain carbonates, and fluorinated chain carboxylates are preferred in terms of battery characteristics, with fluorinated cyclic carbonates and fluorinated chain carboxylates being particularly preferred.

[0020] Preferred fluorinated cyclic carbonates 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 fluorinated chain carboxylic acid esters include fluorinated ethyl propionate, fluorinated methyl acetate, fluorinated ethyl acetate, fluorinated propyl acetate, 2,2,2-trifluoroethyl acetate, methyl 3,3,3-trifluoropropionate, and methyl pentafluoropropionate. These may be used alone or in combination of two or more.

[0021] The solvent may contain a non-fluorine-based solvent that does not contain fluorine. Examples of the non-fluorine-based solvent include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate, chain carbonates 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.

[0022] Examples of electrolyte salts include LiClO4, LiBF4, LiPF6, LiAlCl4, LiSbF6, LiSCN, LiCF3SO3, LiCF3CO2, LiAsF6, LiB 10 Cl 10 , lower aliphatic lithium carboxylate, LiCl, LiBr, LiILi(P(C2O4)F4), LiPF 6-x (C n F 2n+1)x (where 1 < x < 6, n is 1 or 2), chloroborane lithium, borates, imide salts, etc. Examples of borates include Li[B(C2O4)2], Li[B(C2O4)F2], Li2B4O7, lithium bis(1,2-benzenediolate(2-)-O,O’), lithium bis(2,3-naphthalenediolate(2-)-O,O’), lithium bis(2,2’-biphenyldiolate(2-)-O,O’), lithium bis(5-fluoro-2-olate-1-benzenesulfonate-O,O’), etc. Examples of imide salts include lithium bis(fluorosulfonyl)imide (LiN(F S O2)2: hereinafter also referred to as LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF3SO2)2), lithium trifluoromethanesulfonate nonafluorobutanesulfonate imide (LiN(CF3SO2)(C4F9SO2)), lithium bis(pentafluoroethanesulfonyl)imide (LiN(C2F5SO2)2), LiN(C l F 2l+1 SO2)(C m F 2m+1 SO2){l,m are integers greater than or equal to 0}, etc. Among these, in terms of battery characteristics, LiPF6, LiFSI (lithium bis(fluorosulfonyl)imide), LiBF4, LiSbF6, LiCF3SO3, LiCF3CO2, LiAsF6 are preferred. The electrolyte salt may be used alone or in combination of multiple kinds. The concentration of the electrolyte salt is preferably, for example, 0.5 to 3 mol / L, and more preferably 0.8 to 1.8 mol / L.

[0023] The electrolytic solution may contain additives. Examples of additives include unsaturated cyclic carbonates, acid anhydrides, phenol compounds, benzene compounds, nitrile compounds, isocyanate compounds, sultone compounds, sulfuric acid compounds, etc.

[0024] Examples of unsaturated cyclic carbonates 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 carbonates may be used alone or in combination of two or more. The unsaturated cyclic carbonates may have some of their hydrogen atoms substituted with fluorine atoms.

[0025] The acid anhydride may be, for example, an anhydride formed by intermolecular condensation of a plurality of carboxylic acid molecules, but is preferably an acid anhydride of a polycarboxylic acid, such as succinic anhydride, maleic anhydride, or phthalic anhydride.

[0026] Examples of the phenolic compound include phenol and hydroxytoluene.

[0027] Examples of benzene compounds include fluorobenzene, hexafluorobenzene, and cyclohexylbenzene (CHB).

[0028] Examples of the nitrile compound include adiponitrile, pimelonitrile, propionitrile, and succinonitrile.

[0029] Examples of the isocyanate compound include methyl isocyanate (MIC), diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), and bisisocyanate methylcyclohexane (BIMCH).

[0030] Examples of the sultone compound include propane sultone and propene sultone.

[0031] Examples of the sulfate compound include ethylene sulfate, ethylene sulfite, dimethyl sulfate, and lithium fluorosulfate.

[0032] Among the above additives, vinylene carbonate is preferred in terms of battery characteristics.

[0033] In terms of battery characteristics, the electrolyte preferably contains a difluorophosphate, and particularly preferably contains lithium difluorophosphate (LiPF2O2).

[0034] The insulating tape of this embodiment that covers the positive electrode 11 and the positive electrode lead 20 will be described below.

[0035] Fig. 2A is a partial top view observed from one main surface side of the positive electrode, and Fig. 2B is a cross-sectional view taken along line L1-L1 in Fig. 2A. In Fig. 2A, in order to clarify the configuration of the positive electrode 11, the insulating tape (reference numeral 30) covering the positive electrode lead 20 is shown in a see-through view by a dashed line.

[0036] The positive electrode 11 includes a positive electrode current collector 32 and a positive electrode active material layer 34 formed on the positive electrode current collector 32. The positive electrode current collector 32 may be a foil of a metal such as aluminum that is stable within the potential range of the positive electrode, or a film having such a metal disposed on its surface. The positive electrode active material layer 34 contains a positive electrode active material. In addition to the positive electrode active material, the positive electrode active material layer 34 preferably contains a conductive material and a binder.

[0037] Examples of positive electrode active materials include Li composite oxides containing lithium (Li) and transition metal elements such as cobalt (Co), manganese (Mn), and nickel (Ni). The Li composite oxides may contain additional elements other than Co, Mn, and Ni, such as 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).

[0038] The positive electrode active material preferably contains a Li composite oxide having a Co content of 20% or less in order to suppress deterioration of high-temperature storage characteristics. In order to suppress deterioration of high-temperature storage characteristics, a lower Co content is preferable, and a Co content of 10% or less is more preferable. Here, the Co content refers to the molar ratio relative to the total amount of metals excluding Li in the Li composite oxide. For example, a Co content of 20% or less means that the Co content in the Li composite oxide is 0.2 or less in terms of the molar ratio relative to the total amount of metals excluding Li. The lower limit of the Co content is preferably 5% or more in order to suppress deterioration of the charge-discharge cycle characteristics of a lithium-ion battery. That is, in order to suppress deterioration of high-temperature storage characteristics and charge-discharge cycle characteristics, the positive electrode active material preferably contains a Li composite oxide having a Co content of 5% to 20% and more preferably a Li composite oxide having a Co content of 5% to 10%. The positive electrode active material is not limited to a Li composite oxide having a Co content of more than 20%, and may contain Co 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 relative to 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 relative to the total amount of the positive electrode active material.

[0039] Examples of the conductive material contained in the positive electrode active material layer 34 include carbon powders such as carbon black, acetylene black, ketjen black, and graphite. These may be used alone or in combination of two or more.

[0040] Examples of binders contained in the positive electrode active material layer 34 include fluorine-based polymers and rubber-based polymers. For example, examples of fluorine-based polymers include polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVdF), and modified versions of these, and examples of rubber-based polymers include ethylene-propylene-isoprene copolymers and ethylene-propylene-butadiene copolymers. These may be used alone or in combination of two or more.

[0041] The positive electrode current collector 32 has an exposed portion 32a where the positive electrode active material layer 34 is not formed. The exposed portion 32a shown in Figures 2A and 2B is formed on both one principal surface side and the other principal surface side of the positive electrode current collector 32. The exposed portion 32a may be formed anywhere on the positive electrode current collector 32, but is generally formed on the longitudinal center side of the positive electrode current collector 32.

[0042] The positive electrode lead 20 has one end 20a connected to the exposed portion 32a of the positive electrode current collector 32, and an extending portion 20b extending outward from the peripheral edge portion 32b of the positive electrode current collector 32. The positive electrode lead 20 also has the other end located further forward than the extending portion 20b, and as described above, the other end is connected to the filter 23 of the sealing body 17. The method for connecting the one end 20a of the positive electrode lead 20 to the exposed portion 32a of the positive electrode current collector 32 is not particularly limited as long as the electrical connection between the positive electrode lead 20 and the positive electrode current collector 32 is ensured, and examples thereof include ultrasonic welding.

[0043] The material of the positive electrode lead 20 is not particularly limited and may be a metal such as aluminum or titanium.

[0044] The insulating tape 30 shown in FIGS. 2A and 2B covers one end 20a of the positive electrode lead 20. That is, the insulating tape 30 covers the positive electrode lead 20 located on the exposed portion 32a of the positive electrode current collector 32. However, the position of the positive electrode lead 20 covered with the insulating tape 30 is not limited to the one end 20a of the positive electrode lead 20. For example, the insulating tape 30 may cover the extending portion 20b of the positive electrode lead 20 or the other end of the positive electrode lead 20, which is the connection portion with the sealing body 17. An internal short circuit between the positive electrode lead 20 and the negative electrode 12 is likely to occur mainly between the one end 20a of the positive electrode lead 20 and the negative electrode 12 or between the extending portion 20b of the positive electrode lead 20 and the negative electrode 12. Therefore, it is preferable that the insulating tape 30 cover at least one of the one end 20a and the extending portion 20b of the positive electrode lead 20, and it is particularly preferable that the insulating tape 30 cover the one end 20a of the positive electrode lead 20. When covering one end 20a of the positive electrode lead 20 with the insulating tape 30, it is sufficient to cover only a portion of the one end 20a of the positive electrode lead 20 with the insulating tape 30, but it is preferable to cover the entire one end 20a in order to effectively suppress the occurrence of an internal short circuit, etc. Similarly, when covering the extended portion 20b of the positive electrode lead 20 with the insulating tape 30, it is sufficient to cover only a portion of the extended portion 20b with the insulating tape 30, but it is preferable to cover the entire extended portion 20b. When covering a portion or the entire extended portion 20b of the positive electrode lead 20 with the insulating tape 30, it is preferable to wrap the insulating tape 30 around the extended portion 20b to cover the entire outer periphery of the extended portion 20b.

[0045] 2A and 2B, the insulating tape 30 may cover one end 20a of the positive electrode lead 20 and also cover the exposed portion 32a of the positive electrode current collector 32. When covering the exposed portion 32a with the insulating tape 30, it is sufficient to cover only a portion of the exposed portion 32a with the insulating tape 30. However, it is preferable to cover the entire exposed portion 32a in order to effectively prevent internal short circuits. Although FIGS. 2A and 2B show a space (distance) between the insulating tape 30 and the exposed portion 32a, it is preferable that the insulating tape 30 be adhered to the exposed portion 32a. As shown in FIGS. 2A and 2B, the insulating tape 30 may be disposed on the positive electrode active material layer 34, protruding from the exposed portion 32a.

[0046] The configuration of the insulating tape 30 will be described below.

[0047] Fig. 3 is a partial cross-sectional view of the insulating tape used in this embodiment. As shown in Fig. 3, the insulating tape 30 has a filler layer 30a and a base layer 30b. The filler layer 30a of the insulating tape 30 is disposed on the positive electrode lead 20 side. That is, the insulating tape 30 shown in Fig. 3 has a layered structure in which the filler layer 30a and the base layer 30b are layered in this order from the positive electrode lead 20 side.

[0048] The base layer 30b is not particularly limited as long as it is a layer primarily made of an organic material. Here, "primarily made of an organic material" means that the organic material accounts for the largest proportion of the materials constituting the base layer 30b. In terms of the strength of the insulating tape 30, the organic material content is preferably 80% by mass or more, and more preferably 90% by mass or more, of the total mass of the base layer 30b. In terms of the flexibility and strength of the insulating tape 30, the organic material is preferably a polymer material. Examples of the organic material include cellulose derivatives (e.g., cellulose ether, cellulose ester, etc.), polyvinyl chloride, polyolefins (e.g., polyethylene, polypropylene, etc.), polystyrene, polyesters (e.g., polyethylene terephthalate, etc.), polyimide, polyamide, polyamideimide, polycarbonate, and polyphenylene sulfide. Among these, polyimide and wholly aromatic polyamide (aramid) are preferred, with polyimide being particularly preferred. These materials may be used alone or in combination of two or more. The base layer 30b may also have a laminated structure including a first resin layer and a second resin layer, such as a laminated structure including a first resin layer including polyimide and a second resin layer including a resin other than polyimide. When the base layer 30b includes polyimide, the polyimide content is preferably 80% by mass or more, and more preferably 90% by mass or more.

[0049] Polyimide is a general term for polymers containing imide bonds in their repeating units, but it usually refers to aromatic polyimides in which aromatic compounds are directly linked by imide bonds. Aromatic polyimides have a conjugated structure in which imide bonds are interposed between aromatic rings, resulting in a rigid and strong molecular structure. The type of polyimide is not particularly limited, and may be a wholly aromatic polyimide such as polypyromellitimide, a semi-aromatic polyimide such as polyetherimide, or a thermosetting polyimide obtained by reacting bismaleimide with an aromatic diamine.

[0050] The thickness of the base material layer 30b is arbitrary, but in terms of the strength of the insulating tape 30, it is preferably, for example, 5 μm or more and 30 μm or less, and more preferably 10 μm or more and 30 μm or less.

[0051] Although the base layer 30b is not limited to containing a filler such as an inorganic material, it is preferable to contain as little filler as possible in terms of the flexibility of the insulating tape 30 and the like.

[0052] The filler layer 30a contains an alkaline earth metal oxide compound. Providing the filler layer 30a containing an alkaline earth metal oxide compound improves the heat resistance of the insulating tape 30. For example, even if a foreign object penetrates the insulating tape 30, causing an internal short circuit between the positive electrode lead 20 and the negative electrode 12 and resulting in battery heat generation, melting or decomposition of the insulating tape 30 is suppressed. As a result, the expansion or continuation of the short circuit is suppressed, and the increase in battery temperature is suppressed. Furthermore, alkaline earth metal oxide compounds are less soluble in hydrofluoric acid than fillers such as alumina and silica contained in conventional filler layers. Therefore, even if hydrofluoric acid is generated in a lithium-ion battery using a fluorine-containing electrolyte, the hydrofluoric acid suppresses the elution of the alkaline earth metal oxide compound in the filler layer 30a. As a result, compared to when a filler layer containing a conventional filler material (e.g., alumina or silica) is used, the diffusion of impurities originating from the filler layer within the lithium-ion battery is suppressed, thereby suppressing deterioration of the high-temperature storage characteristics of the lithium-ion battery. The high-temperature storage characteristics refer to the degree of capacity loss after a charged lithium-ion battery is stored for a predetermined period in a high-temperature environment.

[0053] Examples of alkaline earth metal oxide compounds include alkaline earth metal oxides, alkaline earth metal sulfates, alkaline earth metal nitrates, and alkaline earth metal carbonates. Among these, alkaline earth metal sulfates and alkaline earth metal nitrates are preferred, with alkaline earth metal sulfates being particularly preferred, in terms of 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 preferred. These compounds may be used alone or in combination of two or more.

[0054] The filler layer 30a preferably contains an adhesive material, for example, to ensure adhesion between the insulating tape 30 and the positive electrode lead 20. Examples of adhesive materials include acrylic resin, natural rubber, synthetic rubber, silicone, epoxy resin, melamine resin, and phenolic resin. These may be used alone or in combination of two or more. In addition to the resin material, the adhesive material may contain additives such as a tackifier, a crosslinking agent, an antiaging agent, a coloring agent, an antioxidant, a chain transfer agent, a plasticizer, a softener, a surfactant, and an antistatic agent, as well as a solvent, as needed.

[0055] The content of the alkaline earth metal oxide compound in the filler layer 30a is, for example, preferably in the range of 3% to 80% by mass, and more preferably in the range of 20% to 70% by mass. The content of the adhesive material in the filler layer 30a is, for example, preferably in the range of 20% to 97% by mass, and more preferably in the range of 30% to 80% by mass. The filler layer 30a may contain a conventional filler such as alumina or silica. However, if the content of the conventional filler is too high, the effect of suppressing the 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% by mass or less, and more preferably 1% by mass or less.

[0056] The thickness of the filler layer 30a is arbitrary, but in terms of effectively suppressing melting or decomposition of the insulating tape 30, it is preferably in the range of 1 μm to 25 μm, and more preferably in the range of 5 μm to 20 μm.

[0057] The thickness of the insulating tape 30 is not particularly limited, but is preferably in the range of 10 to 55 μm. If the thickness of the insulating tape 30 is less than 10 μm, it is likely to break due to foreign matter that gets mixed in the battery. If the thickness of the insulating tape 30 is more than 55 μm, it may be necessary to reduce the volume of other components in order to fit the electrode assembly 14 into a case body 16 of a given size.

[0058] A modified example of the insulating tape 30 of this embodiment will be described. The insulating tape 30 of this embodiment may have a filler layer 30a containing an alkaline earth metal oxide compound provided on both sides of a base layer 30b mainly made of an organic material. Furthermore, the insulating tape 30 of this embodiment may have the filler layer 30a containing an alkaline earth metal oxide compound disposed on the side opposite the positive electrode lead 20, across the base layer 30b mainly made of an organic material. That is, the insulating tape 30 may have a layered structure in which the base layer 30b mainly made of an organic material and the filler layer 30a containing an alkaline earth metal oxide compound are layered in this order from the positive electrode lead 20 side. Furthermore, the insulating tape 30 of this embodiment may have a separate adhesive layer containing an adhesive material. That is, the insulating tape 30 may have a laminated structure in which, from the positive electrode lead 20 side, an adhesive layer containing an adhesive material, a filler layer 30a containing an oxide compound of an alkaline earth metal, and a base layer 30b mainly made of an organic material are laminated in this order, or a laminated structure in which, from the positive electrode lead 20 side, an adhesive layer containing an adhesive material, a base layer 30b mainly made of an organic material, and a filler layer 30a containing an oxide compound of an alkaline earth metal are laminated in this order.

[0059] The insulating tape 30 of this embodiment may not only cover the positive electrode lead 20, but also cover a location where an internal short circuit of the battery may occur. For example, the negative electrode 12 usually has an exposed portion of the negative electrode current collector formed thereon, similar to the positive electrode 11, and one end of the negative electrode lead 21 is connected to this exposed portion. However, if the exposed portion of the negative electrode lead 21 or the negative electrode current collector is a location where an internal short circuit of the battery may occur, the exposed portion of the negative electrode lead 21 or the negative electrode current collector may be covered with the insulating tape 30 of this embodiment.

[0060] The negative electrode 12 and the separator 13 will be described below.

[0061] The negative electrode 12 includes a negative electrode current collector and a negative electrode active material layer formed on the negative electrode current collector. The negative electrode current collector can be a foil of a metal such as copper that is stable within the potential range of the negative electrode, or a film with such a metal disposed on its surface. The negative electrode active material layer contains a negative electrode active material. In addition to the negative electrode active material, the negative electrode active material layer preferably contains a thickener and a binder.

[0062] As the negative electrode active material, a carbon material capable of absorbing and releasing lithium ions can be used, and in addition to graphite, non-graphitizable carbon, graphitizable carbon, fibrous carbon, coke, carbon black, etc. Furthermore, as a non-carbon-based material, silicon, tin, and alloys and oxides mainly containing these can be used.

[0063] As in the case of the positive electrode, PTFE or the like can be used as the binder, but styrene-butadiene copolymer (SBR) or its modified form may also be used. Carboxymethyl cellulose (CMC) or the like can be used as the thickener.

[0064] Although not shown in the drawings, the negative electrode current collector has an exposed portion on which no negative electrode active material layer is formed, similar to the previously described positive electrode current collector 32. The exposed portion of the negative electrode current collector may be formed anywhere on the negative electrode current collector, but is generally formed on the longitudinal end side of the negative electrode current collector. Similarly to the previously described positive electrode lead 20, the negative electrode lead 21 has one end connected to the exposed portion of the negative electrode current collector and an extension extending from the one end to the outside of the peripheral edge of the negative electrode current collector. The negative electrode lead 21 also has another end located further forward than the extension, and the other end is connected to the inner bottom surface of the case body 16. The material of the negative electrode lead 21 is not particularly limited, and may be a metal such as nickel or titanium.

[0065] At least one of one end, an extending portion, and the other end of the negative electrode lead 21 may be covered with insulating tape 30. In addition, the exposed portion of the negative electrode current collector may also be covered with insulating tape 30.

[0066] The separator 13 may be, for example, a porous sheet having ion permeability and insulating properties. Specific examples of porous sheets include a microporous thin film, a woven fabric, and a nonwoven fabric. Suitable materials for the separator 13 include olefin-based resins such as polyethylene and polypropylene, and cellulose. The separator 13 may be a laminate having a cellulose fiber layer and a thermoplastic resin fiber layer such as an olefin-based resin. Alternatively, the separator 13 may be a multilayer separator including a polyethylene layer and a polypropylene layer, and a separator whose surface is coated with a material such as an aramid-based resin or ceramic may be used.

[0067] <Example> The present disclosure will be further described below with reference to examples, but the present disclosure is not limited to these examples.

[0068] Example 1 [Preparation of positive electrode] LiNi, the positive electrode active material 0.77 Co 0.20 Al 0.03 A positive electrode composite slurry was prepared by mixing 100 parts by mass of O2, 1.0 part by mass of acetylene black (a conductive material), 0.9 parts by mass of polyvinylidene fluoride (a binder), and an appropriate amount of NMP. The resulting positive electrode composite slurry was applied to both sides of a 15 μm-thick aluminum foil serving as a positive electrode current collector, dried, and then rolled to produce a strip-shaped positive electrode. FIG. 5A is a partial top view of one main surface of the positive electrode of Example 1, and FIG. 5B is a cross-sectional view taken along line L1-L1 in FIG. 5A. As shown in FIGS. 5A and 5B, an exposed portion 32a of the aluminum foil was provided on both sides of the outermost end in the longitudinal direction of the positive electrode 11, exposing the positive electrode current collector 32 from one end to the other in the width direction. The width of the exposed portion 32a was 60 mm. One end of the positive electrode lead 20 was placed on the exposed portion 32a of the positive electrode current collector 32 at a position 3 mm from the outermost peripheral edge, and the one end was welded to the exposed portion 32a.

[0069] An insulating tape was applied so as to cover the entire surface of one end of the positive electrode lead and the exposed portion of the positive electrode current collector. The insulating tape used had a 25 μm thick polyimide substrate layer and a 7 μm thick filler layer. The polyimide was synthesized by reacting pyromellitic anhydride with diaminodiphenyl ether. The filler layer was a mixture of 50 parts by mass of an acrylic adhesive material mainly composed of acrylic resin and 50 parts by mass of Ba(NO3)2 particles as a filler.

[0070] [Preparation of negative electrode] A negative electrode composite slurry was prepared by mixing 100 parts by weight of flake-shaped artificial graphite with an average particle size of approximately 20 μm (negative electrode active material), 1 part by weight of styrene butadiene rubber (binder), 1 part by weight of carboxymethyl cellulose (thickener), and water. The resulting negative electrode composite slurry was uniformly applied to both sides of an 8 μm-thick copper foil serving as a negative electrode current collector, dried, and rolled to produce a strip-shaped negative electrode. However, exposed portions were provided on both sides of the end of the winding of the negative electrode. One end of a negative electrode lead was placed on the exposed portion of the negative electrode current collector, and one end was welded to the exposed portion.

[0071] [Preparation of electrolyte] An electrolyte solution was prepared by dissolving LiPF6 in a mixed solvent of DMC, EMC, and 4-fluoroethylene carbonate (volume ratio 40:40:20) to a concentration of 1.0 mol / L.

[0072] [Battery construction] The positive and negative electrodes were stacked with a separator interposed therebetween and wound to form an electrode assembly. Insulating plates were placed above and below the electrode assembly, and the assembly was then housed in an iron case body with a nickel-plated inner surface. The negative electrode lead protruding from the electrode assembly was welded to the bottom of the battery case, and the positive electrode lead protruding from the electrode assembly was welded to the inner surface of a sealing body with a gasket attached to its periphery. After pouring a nonaqueous electrolyte into the case body, the opening of the case body was sealed with the sealing body, and the open edge of the case body was crimped to the periphery of the sealing body via the gasket, producing a cylindrical lithium-ion battery.

[0073] <Example 2> As the positive electrode active material, LiNi 0.77 Co 0.20 Al 0.03 A lithium-ion battery was fabricated in the same manner as in Example 1, except that O2 was used and a mixture of 50 parts by mass of an acrylic adhesive material containing acrylic resin as the main component and 50 parts by mass of BaSO4 particles as a filler was used as the filler layer of the insulating tape.

[0074] Example 3 As the positive electrode active material, LiNi 0.67 Co 0.30 Al 0.03 A lithium-ion battery was fabricated in the same manner as in Example 1, except that O2 was used and a mixture of 20 parts by mass of an acrylic adhesive material containing acrylic resin as the main component and 80 parts by mass of BaSO4 particles as a filler was used as the filler layer of the insulating tape.

[0075] Example 4 As the positive electrode active material, LiNi 0.67 Co 0.30 Al 0.03 A lithium-ion battery was fabricated in the same manner as in Example 1, except that O2 was used and a mixture of 97 parts by mass of an acrylic adhesive material whose main component was acrylic resin and 3 parts by mass of BaSO4 particles as a filler was used as the filler layer of the insulating tape.

[0076] <Example 5> As the positive electrode active material, LiNi 0.92 Co 0.05 Al 0.03 A lithium-ion battery was fabricated in the same manner as in Example 1, except that O2 was used, a mixture of 50 parts by mass of an acrylic adhesive mainly composed of acrylic resin and 50 parts by mass of SrSO4 particles as a filler was used as the filler layer of the insulating tape, and 2% by mass of vinylene carbonate was added to the electrolyte.

[0077] Example 6 As the positive electrode active material, LiNi 0.92 Co 0.05 Al 0.03A lithium-ion battery was fabricated in the same manner as in Example 1, except that O2 was used, a mixture of 50 parts by mass of an acrylic adhesive mainly composed of acrylic resin and 50 parts by mass of BaSO4 particles as a filler was used as the filler layer of the insulating tape, and 2% by mass of vinylene carbonate was added to the electrolyte.

[0078] Example 7 As the positive electrode active material, LiNi 0.77 Co 0.20 Al 0.03 A lithium-ion battery was fabricated in the same manner as in Example 1, except that O2 was used, a mixture of 50 parts by mass of an acrylic adhesive mainly composed of acrylic resin and 50 parts by mass of BaSO4 particles as a filler was used as the filler layer of the insulating tape, and 2% by mass of vinylene carbonate was added to the electrolyte.

[0079] Example 8 As the positive electrode active material, LiNi 0.87 Co 0.10 Al 0.03 A lithium-ion battery was fabricated in the same manner as in Example 1, except that O2 was used, a mixture of 50 parts by mass of an acrylic adhesive mainly composed of acrylic resin and 50 parts by mass of BaSO4 particles as a filler was used as the filler layer of the insulating tape, and 2% by mass of vinylene carbonate was added to the electrolyte.

[0080] Example 9 As the positive electrode active material, LiNi 0.92 Co 0.05 Al 0.03 A lithium-ion battery was fabricated in the same manner as in Example 1, except that O2 was used, a mixture of 50 parts by mass of an acrylic adhesive mainly composed of acrylic resin and 50 parts by mass of BaSO4 particles as a filler was used as the filler layer of the insulating tape, and 0.1% by mass of vinylene carbonate was added to the electrolyte.

[0081] Example 10 As the positive electrode active material, LiNi 0.92 Co 0.05 Al 0.03A lithium-ion battery was fabricated in the same manner as in Example 1, except that O2 was used, a mixture of 50 parts by mass of an acrylic adhesive mainly composed of acrylic resin and 50 parts by mass of BaSO4 particles as a filler was used as the filler layer of the insulating tape, and 10% by mass of vinylene carbonate was added to the electrolyte.

[0082] <Comparative Example 1> As the positive electrode active material, LiNi 0.67 Co 0.30 Al 0.03 A lithium ion battery was fabricated in the same manner as in Example 1, except that O2 was used and an insulating tape containing no filler was used.

[0083] <Comparative Example 2> As the positive electrode active material, LiNi 0.67 Co 0.30 Al 0.03 A lithium-ion battery was fabricated in the same manner as in Example 1, except that O2 was used and a mixture of 50 parts by mass of an acrylic adhesive material containing acrylic resin as the main component and 50 parts by mass of SiO2 particles as a filler was used as the filler layer of the insulating tape.

[0084] <Comparative Example 3> As the positive electrode active material, LiNi 0.67 Co 0.30 Al 0.03 A lithium-ion battery was fabricated in the same manner as in Example 1, except that O2 was used, and a mixture of 50 parts by mass of an acrylic adhesive material containing acrylic resin as the main component and 50 parts by mass of Al2O3 particles as a filler was used as the filler layer of the insulating tape.

[0085] [Forced internal short circuit test] A forced internal short circuit test was conducted on the batteries of each example and comparative example in accordance with JIS C 8714. However, a severe test was conducted using nickel pieces (0.5 mm high, 0.2 mm wide, 3 mm on each side, L-shaped (90° angle)) larger than standard-sized nickel pieces. The nickel pieces were placed between the insulating tape and the separator so that they penetrated the insulating tape. Specifically, the nickel pieces were placed on the insulating tape at the center of the positive electrode current collector in the width direction and 5 mm from the edge of the positive electrode active material layer. Then, a forced internal short circuit test was conducted, and the temperature rise on the side of the battery was measured with a thermocouple. The measured battery temperatures were evaluated according to the following criteria, and the results are shown in Table 1.

[0086] 〇: Battery temperature is below 40℃ △: Battery temperature is between 40℃ and 100℃ ×: Battery temperature is 100°C or higher [High temperature storage test] The lithium-ion batteries of each example and comparative example were charged to 4.2 V at a constant current of 1 C under conditions of 25°C, and then constant-voltage charged at 4.2 V until the current value reached 0.05 C, completing the charge (this charge is referred to as Charge A). After a 10-minute pause, they were discharged at a constant current of 1 C until the voltage reached 2.5 V (this discharge is referred to as Discharge A), and this discharge capacity was recorded as the pre-storage capacity. After a 10-minute pause, only Charge A was performed and the batteries were stored at 60°C for 20 days. After storage, the batteries were cooled to room temperature, and only Discharge A was performed. After a 10-minute pause, Charge A was performed, and then Discharge A was performed again. The discharge capacity at this time was recorded as the recovery capacity. The capacity recovery rate after high-temperature storage was calculated using the following formula. The results are shown in Table 1. Note that a higher capacity recovery rate after high-temperature storage indicates that the deterioration of high-temperature storage characteristics was suppressed.

[0087] Capacity recovery rate after high-temperature storage (%) = (recovered capacity / capacity before storage) x 100

[0088] [Table 1]

[0089] All of Examples 1 to 10 and Comparative Examples 1 to 3 were lithium-ion batteries using a fluorine-containing electrolyte. However, Examples 1 to 10, which used an alkaline earth metal oxide compound in the filler layer of the insulating tape, showed a more suppressed increase in battery temperature during a forced internal short circuit test than Comparative Example 1, in which the insulating tape did not have a filler layer. Furthermore, Examples 1 to 10 also showed a more suppressed decrease in capacity recovery rate after high-temperature storage than Comparative Example 2, in which SiO2 particles were used in the filler layer of the insulating tape, and Comparative Example 3, in which Al2O3 particles were used in the filler layer of the insulating tape. Furthermore, as can be seen from a comparison between Examples 1 and 2, the increase in battery temperature during a forced internal short circuit test was more suppressed when the content of the alkaline earth metal oxide compound in the filler layer was increased, while the decrease in the capacity recovery rate after high-temperature storage was more suppressed when the content of the alkaline earth metal oxide compound in the filler layer was decreased. Furthermore, as can be seen from a comparison between Examples 2 and 7, the addition of vinylene carbonate further suppressed the decrease in capacity recovery rate after high-temperature storage. Furthermore, the results of Examples 6, 9, and 10 indicate that the content of vinylene carbonate in the electrolyte is preferably in the range of 0.1% by mass to 10% by mass. Furthermore, as can be seen from a comparison between Examples 2 and 3 and a comparison between Examples 6, 7, and 8, a decrease in the Co content in the positive electrode active material further suppresses the decrease in the capacity recovery rate after high-temperature storage. Furthermore, the results of the Examples indicate that the filler used in the filler layer may be an oxide compound of an alkaline earth metal. [Explanation of symbols]

[0090] 10. Lithium-ion battery 11 Positive electrode 12 Negative electrode 13 Separator 14 Electrode body 15 Battery case 16 Case body 17 Sealing body 18,19 Insulating plate 20 Positive lead 20a One end 20b Extension 21 Negative lead 22 Overhang 23 Filters 24 Lower valve body 25 Insulators 26 Superior valve 27 Cap 28 Gasket 30 Electrical Tape 30a Filler layer 30b Base material layer 32 Positive electrode current collector 32a Exposed part 32b Periphery 34 Cathode active material layer

Claims

1. A lithium ion battery having 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, The insulating tape has a base layer mainly made of an organic material and a filler layer provided on the base layer, the filler layer comprises an oxide compound of an alkaline earth metal; the electrolyte contains fluorine, the alkaline earth metal oxide compound includes at least one of beryllium nitrate, magnesium nitrate, calcium nitrate, strontium nitrate, barium nitrate, beryllium sulfate, and strontium sulfate; a content of the alkaline earth metal oxide compound in the filler layer being 3% by mass or more and 80% by mass or less;

2. the electrolyte solution contains vinylene carbonate; 2. The lithium ion battery according to claim 1, wherein the content of the vinylene carbonate in the electrolyte solution is 0.1% by mass or more and 10% by mass or less.

3. 3. The lithium ion battery according to claim 1, wherein the alkaline earth metal oxide compound includes at least one of barium nitrate and strontium sulfate.

4. The lithium ion battery according to any one of claims 1 to 3, wherein the positive electrode contains a Li composite oxide having a Co content of 20% or less.

5. The electrolyte solution is lithium difluorophosphate (LiPO ２ F ２ 5. The lithium ion battery according to claim 1, comprising:

6. The solvent of the electrolyte solution includes at least one selected from the group consisting of 4-fluoroethylene carbonate, 4,5-difluoroethylene carbonate, 4,4-difluoroethylene carbonate, 4,4,5-trifluoroethylene carbonate, 4,4,5,5-tetrafluoroethylene carbonate, fluorinated ethyl propionate, fluorinated methyl acetate, fluorinated ethyl acetate, fluorinated propyl acetate, 2,2,2-ethyl trifluoroacetate, 3,3,3-methyl trifluoropropionate, and methyl pentafluoropropionate. The lithium ion battery according to any one of claims 1 to 5.

7. The electrolyte is LiPF ６ , LiFSI (lithium bis(fluorosulfonyl)imide), LiBF ４ , LiSbF ６ , LiCF ３ SO ３ , LiCF ３ CO ２ , LiAsF ６ The lithium ion battery according to any one of claims 1 to 6, comprising at least one selected from the group consisting of:

Images