Nonaqueous electrolyte and nonaqueous electrolyte secondary battery

Abstract

This nonaqueous electrolyte of the present disclosure is characterized by containing an amphoteric surfactant expressed with formula (I) presented below, where L1 represents an alkylene group having 2 to 5 carbon atoms, R1 to R3 each independently represent an organic functional group, and at least one of R1 to R3 is an organic functional group containing a carbonyl group.

Description

Non-aqueous electrolyte and non-aqueous electrolyte secondary battery

[0001] The present disclosure relates to a non-aqueous electrolyte and a non-aqueous electrolyte secondary battery.

[0002] In recent years, as a high-output and high-capacity secondary battery, a non-aqueous electrolyte secondary battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte, which performs charge and discharge by moving Li ions or the like between the positive electrode and the negative electrode, has been widely used. Patent Document 1 discloses a non-aqueous electrolyte containing an amphoteric surfactant for the purpose of improving the cycle characteristics of a battery.

[0003] International Publication No. 2016 / 027788

[0004] By the way, in a non-aqueous electrolyte secondary battery, the negative electrode expands during charging, and the gap between the electrode plates tends to decrease. As a result, the liquid circulation of the non-aqueous electrolyte deteriorates, and the cycle characteristics may deteriorate. In particular, with the change in the selection of the negative electrode material of non-aqueous electrolyte secondary batteries in recent years, the expansion of the negative electrode during charging has increased, and the above-mentioned deterioration of the liquid circulation has become more prominent.

[0005] The non-aqueous electrolyte according to one aspect of the present disclosure contains an amphoteric surfactant represented by the following formula (I), where L １ represents an alkylene group having 2 to 5 carbon atoms, and R １ to R ３ each independently represents an organic functional group, and at least one of R １ to R ３ is an organic functional group containing a carbonyl group.

[0006] Further, a non-aqueous electrolyte secondary battery according to one aspect of the present disclosure includes the above non-aqueous electrolyte, a positive electrode, and a negative electrode.

[0007] According to the non-aqueous electrolyte according to one aspect of the present disclosure, the liquid circulation of the non-aqueous electrolyte is improved, and the cycle characteristics can be improved.

[0008] It is an axial cross-sectional view of a non-aqueous electrolyte secondary battery which is an example of an embodiment.

[0009] Hereinafter, an example of an embodiment of a non-aqueous electrolyte secondary battery according to this disclosure will be described in detail with reference to the drawings. Note that configurations obtained by selectively combining the components of the multiple embodiments and modified examples described below are included within the scope of this disclosure.

[0010] In the following, a cylindrical battery in which a wound electrode body 14 is housed in a bottomed cylindrical outer casing 16 is given as an example of a non-aqueous electrolyte secondary battery, but the battery outer casing is not limited to a cylindrical shape. The non-aqueous electrolyte secondary battery according to this disclosure may be, for example, a prismatic battery with a prismatic outer casing, a coin-type battery with a coin-type outer casing, or a pouch-type battery with an outer casing made of a laminate sheet including a metal layer and a resin layer. Furthermore, the electrode body is not limited to a wound type, and may be a laminated electrode body in which a plurality of positive electrodes and a plurality of negative electrodes are alternately stacked with a separator in between. In addition, the design of the non-aqueous electrolyte secondary battery according to this disclosure is not limited to the example non-aqueous electrolyte secondary battery design, and known non-aqueous electrolyte secondary battery designs may be applied.

[0011] Figure 1 is an axial cross-sectional view of a cylindrical non-aqueous electrolyte secondary battery 10, which is an example of an embodiment. As shown in Figure 1, the non-aqueous electrolyte secondary battery 10 comprises a wound electrode body 14, a non-aqueous electrolyte, and an outer casing 16 that houses the electrode body 14 and the non-aqueous electrolyte. The electrode body 14 includes a positive electrode 11, a negative electrode 12, and a separator 13, and has a wound structure in which the positive electrode 11 and the negative electrode 12 are wound in a spiral shape via the separator 13. The outer casing 16 is a bottomed cylindrical metal container with one side open in the axial direction, and the opening of the outer casing 16 is closed by a sealing body 17. In the following, for convenience of explanation, the side of the battery with the sealing body 17 will be referred to as the top, and the bottom side of the outer casing 16 as the bottom.

[0012] The positive electrode 11, negative electrode 12, and separator 13 constituting the electrode body 14 are all rectangular elongated bodies that are alternately stacked in the radial direction of the electrode body 14 by being wound in a spiral shape in the longitudinal direction. The separator 13 separates the positive electrode 11 and the negative electrode 12 from each other. Two separators 13 are arranged, for example, to sandwich the positive electrode 11. The electrode body 14 includes a positive electrode lead 20 connected to the positive electrode 11 by welding or the like, and a negative electrode lead 21 connected to the negative electrode 12 by welding or the like. In the electrode body 14, the longitudinal direction of the positive electrode 11 and the negative electrode 12 is the winding direction, and the short direction of the positive electrode 11 and the negative electrode 12 is the axial direction. That is, the end faces in the short direction of the positive electrode 11 and the negative electrode 12 form the axial end faces of the electrode body 14.

[0013] Insulating plates 18 and 19 are positioned above and below the electrode body 14, respectively. In the example shown in Figure 1, the positive electrode lead 20 extends through a through-hole in the insulating plate 18 towards the sealing body 17, and the negative electrode lead 21 extends outside the insulating plate 19 towards the bottom of the outer casing 16. The positive electrode lead 20 is connected to the lower surface of the internal terminal plate 23 of the sealing body 17 by welding or the like, and the cap 27, which is the top plate of the sealing body 17 and is electrically connected to the internal terminal plate 23, becomes the positive electrode terminal. The negative electrode lead 21 is connected to the bottom inner surface of the outer casing 16 by welding or the like, and the outer casing 16 becomes the negative electrode terminal.

[0014] A gasket 28 is provided between the outer casing 16 and the sealing body 17 to ensure airtightness inside the battery. The outer casing 16 has a grooved portion 22 formed on its side surface, which protrudes inward to support the sealing body 17. The grooved portion 22 is preferably formed in an annular shape along the circumferential direction of the outer casing 16, and its upper surface supports the sealing body 17. The sealing body 17 is fixed to the upper part of the outer casing 16 by the grooved portion 22 and the open end of the outer casing 16 which is crimped to the sealing body 17.

[0015] The sealing body 17 has a structure in which an internal terminal plate 23, a lower valve body 24, an insulating member 25, an upper valve body 26, and a cap 27 are laminated in this order from the side of the electrode body 14. Each member constituting the sealing body 17 has, for example, a disc shape or a ring shape, and each member except the insulating member 25 is electrically connected to each other. The lower valve body 24 and the upper valve body 26 are connected at their respective central portions, and the insulating member 25 is interposed between the peripheral portions of each. When the internal pressure of the battery rises due to abnormal heat generation, the lower valve body 24 is deformed and broken so as to push up the upper valve body 26 toward the cap 27 side, thereby cutting off the current path between the lower valve body 24 and the upper valve body 26. When the internal pressure further rises, the upper valve body 26 breaks, and gas is discharged from the opening of the cap 27.

[0016] Hereinafter, the positive electrode 11, the negative electrode 12, the separator 13, and the non-aqueous electrolyte that constitute the non-aqueous electrolyte secondary battery 10 will be described in detail, particularly the non-aqueous electrolyte.

[0017] [Positive Electrode] The positive electrode 11 is composed of, for example, a positive electrode current collector such as a metal foil, and a positive electrode mixture layer disposed on the positive electrode current collector. As the positive electrode current collector, a foil of a metal stable within the potential range of the positive electrode 11 such as aluminum, a film having the metal disposed on the surface layer, etc. can be used. The positive electrode mixture layer contains, for example, a positive electrode active material, a binder, a conductive agent, and the like. The positive electrode 11 can be manufactured, for example, by applying a positive electrode mixture slurry containing a positive electrode active material, a binder, a conductive agent, etc. onto the positive electrode current collector, drying to form a positive electrode mixture layer, and then rolling this positive electrode mixture layer.

[0018] Examples of the positive electrode active material include lithium transition metal composite oxides containing transition metal elements such as Co, Mn, and Ni. The lithium transition metal composite oxide is, for example, Li ｘ CoO ２ , Li ｘ NiO ２ , Li ｘ MnO ２ , Li ｘ Co ｙ Ni １－ｙ O ２ , Li ｘ Co ｙ M １－ｙ O ｚ , Li ｘ Ni １－ｙ Mｙ O ｚ Li ｘ Mn ２ O ４ Li ｘ Mn ２－ｙ M ｙ O ４ LiMPO ４ Li ２ MPO ４ F(M; at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, B, 0 < x ≤ 1.2, 0 < y ≤ 0.9, 2.0 ≤ z ≤ 2.3). These may be used individually or in combination of two or more types.

[0019] In terms of enabling higher capacity of non-aqueous electrolyte secondary batteries, the positive electrode active material is Li ｘ NiO ２ Li ｘ Co ｙ Ni １－ｙ O ２ Li ｘ Ni １－ｙ M ｙ O ｚ Preferably, it contains lithium nickel composite oxides such as (M; at least one of Na, Mg, Sc, Y, Mn, Fe, Co, Ni, Cu, Zn, Al, Cr, Pb, Sb, B, 0 < x ≤ 1.2, 0 < y ≤ 0.9, 2.0 ≤ z ≤ 2.3).

[0020] Examples of conductive agents included in the positive electrode mixture layer include carbon black (CB), acetylene black (AB), Ketjenblack, carbon nanotubes (CNT), graphene, and other carbon-based particles such as graphite. These may be used individually or in combination of two or more types.

[0021] Examples of binders included in the positive electrode mixture layer include fluorine-based resins such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF), polyimide resins, acrylic resins, polyolefin resins, and polyacrylonitrile (PAN). These may be used individually or in combination of two or more types.

[0022] [Negative Electrode] The negative electrode 12 comprises a negative electrode core and a negative electrode mixture layer formed on the surface of the negative electrode core. The negative electrode core can be made of a metal foil that is stable in the potential range of the negative electrode 12, such as copper or a copper alloy, or a film on which the metal is arranged on the surface. An example of a negative electrode core is a copper or copper alloy foil with a thickness of 5 μm or more and 15 μm or less. The negative electrode mixture layer contains a negative electrode active material and a binder, and is preferably formed on both sides of the negative electrode core. The thickness of the negative electrode mixture layer is, for example, 30 μm or more and 200 μm or less on one side of the negative electrode core. The negative electrode 12 can be manufactured by applying a negative electrode mixture slurry containing a negative electrode active material, a binder, etc., onto the negative electrode core, drying the coating, and then compressing it to form the negative electrode mixture layer on both sides of the negative electrode core.

[0023] The negative electrode mixture layer preferably contains a carbon material and a silicon-containing material as negative electrode active materials. Including a silicon-containing material can improve the battery capacity of the non-aqueous electrolyte secondary battery 10. Alternatively, the negative electrode mixture layer may use a material containing, for example, an element that alloys with Li, such as Sn, and at least one of a material containing that element, as the negative electrode active material.

[0024] The carbon material that functions as the negative electrode active material is, for example, at least one selected from the group consisting of natural graphite, artificial graphite, soft carbon, and hard carbon. In particular, it is preferable to use artificial graphite such as massive artificial graphite (MAG) or graphitized mesophase carbon microbeads (MCMB), natural graphite such as flake graphite, massive graphite, or earthy graphite, or a mixture thereof as the carbon material. The volume-based median diameter (D50) of the carbon material is, for example, 1 μm or more and 30 μm or less, preferably 5 μm or more and 25 μm or less.

[0025] The silicon-containing material can be any material containing Si, and examples include silicon alloys, silicon compounds, and Si-containing composite materials. Among these, Si-containing composite materials are preferred. The volume-based median diameter (D50) of the composite material is generally smaller than the volume-based median diameter (D50) of graphite. The volume-based median diameter (D50) of the composite material is, for example, 1 μm or more and 15 μm or less. Note that one type of silicon-containing material may be used alone, or two or more types may be used in combination.

[0026] From the viewpoint of increasing capacity, the content of silicon-containing material is preferably 5% by mass or more, more preferably 8% by mass or more, and even more preferably 10% by mass or more of the total mass of the negative electrode active material. Generally, silicon-containing material exhibits a larger volume change during charging and discharging compared to carbon material. Therefore, when silicon-containing material is included as the negative electrode active material, the flow of the non-aqueous electrolyte tends to worsen. Thus, when silicon-containing material is included as the negative electrode active material, the effects of this disclosure become more pronounced. The upper limit of the silicon-containing material content is, for example, 80% by mass of the total mass of the negative electrode active material.

[0027] A suitable silicon-containing material (composite material) is a composite particle comprising an ionic conductive phase, a Si phase dispersed within the ionic conductive phase, and a conductive layer covering the surface of the ionic conductive phase. The ionic conductive phase is, for example, at least one selected from the group consisting of a silicate phase, an amorphous carbon phase, a silicide phase, and a silicon oxide phase. The Si phase is formed by dispersing Si in the form of fine particles. The ionic conductive phase is a continuous phase composed of an aggregate of particles finer than those of the Si phase. The conductive layer is composed of a material with higher conductivity than the ionic conductive phase and forms a good conductive path in the negative electrode composite layer.

[0028] An example of a suitable composite material containing Si is one having a sea-island structure in which fine Si particles are dispersed substantially uniformly in an amorphous silicon oxide phase, and the overall general formula is SiO ｘ These are composite particles represented by (0 < x ≤ 2). The main component of silicon oxide may be silicon dioxide. The oxygen content ratio (x) to Si is, for example, 0.5 ≤ x < 2.0, and preferably 0.8 ≤ x ≤ 1.5.

[0029] The binder in the negative electrode mixture layer may be a fluororesin, PAN, polyimide, acrylic resin, polyolefin, etc., similar to the positive electrode mixture layer, but styrene-butadiene rubber (SBR) is preferred. Furthermore, the negative electrode mixture layer preferably contains CMC or a salt thereof, polyacrylic acid (PAA) or a salt thereof, polyvinyl alcohol (PVA), etc. Among these, a combination of SBR and CMC or a salt thereof, PAA or a salt thereof is preferred. The negative electrode mixture layer may also contain a conductive agent such as carbon nanotubes (CNT).

[0030] [Separator] The separator 13 is made of a porous sheet having ion permeability and insulating properties. Specific examples of porous sheets include microporous thin films, woven fabrics, and nonwoven fabrics. Suitable materials for the separator 13 include polyethylene, polyolefins such as polypropylene, and cellulose. The separator 13 may have a single-layer structure or a multi-layer structure. In addition, a heat-resistant resin layer, such as aramid resin, may be formed on the surface of the separator 13.

[0031] A filler layer containing an inorganic filler may be formed at the interface between the separator 13 and at least one of the positive electrode 11 and the negative electrode 12. Examples of inorganic fillers include oxides containing metal elements such as Ti, Al, Si, and Mg, and phosphoric acid compounds. The filler layer can be formed by coating the surface of the positive electrode 11, the negative electrode 12, or the separator 13 with a slurry containing the filler.

[0032] [Non-aqueous electrolytes] Non-aqueous electrolytes are ionic conductive (e.g., lithium ion conductive). Non-aqueous electrolytes consist of a non-aqueous solvent and an electrolyte salt dissolved in the non-aqueous solvent. Examples of non-aqueous solvents include esters, ethers, nitriles such as acetonitrile, amides such as dimethylformamide, and mixed solvents of two or more of these. Non-aqueous solvents may contain halogen-substituted products in which at least some of the hydrogen atoms in the solvent are replaced with halogen atoms such as fluorine. Examples of halogen-substituted products include fluorinated cyclic carbonate esters such as fluoroethylene carbonate (FEC), fluorinated linear carbonate esters, and fluorinated linear carboxylic acid esters such as methyl fluoropropionate (FMP).

[0033] Examples of the above esters include cyclic carbonate esters such as ethylene carbonate (EC), propylene carbonate (PC), and butylene carbonate; linear carbonate 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 (GBL) and γ-valerolactone (GVL); and linear carboxylic acid esters such as methyl acetate, ethyl acetate, propyl acetate, methyl propionate (MP), and ethyl propionate (EP).

[0034] Examples of the above ethers include 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-butylene oxide, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-cineole, cyclic ethers such as crown ethers, 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, ethyl vinyl ether, butyl vinyl ether, and methylphenyl ether. Examples include chain ethers such as ethylphenyl ether, butylphenyl ether, pentylphenyl ether, methoxytoluene, benzyl ethyl ether, diphenyl ether, dibenzyl ether, o-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0035] The electrolyte salt is preferably a lithium salt. A suitable lithium salt is LiClO ４ LiBF ４ LiPF ６ LiAlCl ４ LiSbF ６ , LiSCN, LiCF ３ SO ３ LiCF ３ CO ２ LiAsF ６ LiB １０ Cl １０ Examples include lithium lower aliphatic carboxylates, LiCl, LiBr, LiI, phosphates, borates, and imide salts. Examples of phosphates include lithium difluorophosphate (LiPO4). ２ F ２Examples include lithium difluorobis(oxalato)phosphate (LiDFOBP), lithium tetrafluoro(oxalato)phosphate, etc. Examples of borates include lithium bis(oxalato)borate (LiBOB), lithium difluoro(oxalato)borate (LiDFOB), etc. Examples of imide salts include lithium bisfluorosulfonylimide (LiN(FSO)). ２ ) ２ ), bistrifluoromethanesulfonate lithium (LiN(CF ３ SO ２ ) ２ ), trifluoromethanesulfonic acid nonafluorobutanesulfonic acid lithium (LiN(CF ３ SO ２ ) (C ４ F ９ SO ２ )), bispentafluoroethanesulfonate lithium (LiN(C) ２ F ５ SO ２ ) ２ ) etc. are used. Of these, LiPF is used from the viewpoint of ionic conductivity, electrochemical stability, etc. ６ It is preferable to use the following. The concentration of the lithium salt may be, for example, 4 moles or less per liter of non-aqueous solvent, or 3 moles or less, preferably 1.8 moles or less, and more preferably 0.8 moles or more and 1.8 moles or less.

[0036] The non-aqueous electrolyte contains an amphoteric surfactant represented by the following formula (I) (hereinafter sometimes simply referred to as "amphoteric surfactant"). In the formula, L １ R represents an alkylene group with 2 to 5 carbon atoms, and R1 to R3 each independently represent an organic functional group. １ ~R ３ At least one of them is an organic functional group containing a carbonyl group.

[0037] Amphoteric surfactants are surfactants that contain both a cationic and anionic portion in their molecule. Therefore, when a battery is charged, the ends of the surfactant bind to the surface of the active material, and the ionic components of the electrolyte salt are attracted to the cationic and anionic surfactants on the surface of the active material. As a result, even if the gap between the electrode plates decreases during charging, the non-aqueous electrolyte is supplied to the electrode plate surface, improving the circulation of the non-aqueous electrolyte.

[0038] Furthermore, amphoteric surfactants are as shown in formula (I), where R １ ~R ３ If at least one of the components is an organic functional group containing a carbonyl group, the fluidity of the non-aqueous electrolyte can be further improved. This is presumed to be because the polarity of the carbonyl group improves the wettability of the electrode surface. Furthermore, if the amphoteric surfactant contains a sulfonate as shown in formula (I), the ionic components of the electrolyte salt are more easily attracted to the electrode surface, further improving the fluidity of the non-aqueous electrolyte. Note that the carbonyl group in the amphoteric surfactant is not decomposed and is maintained even after the non-aqueous electrolyte secondary battery 10 is manufactured. In other words, if an amphoteric surfactant containing a carbonyl group is added during the manufacture of the non-aqueous electrolyte, the amphoteric surfactant will still contain a carbonyl group in the final non-aqueous electrolyte secondary battery 10.

[0039] In the formula, R １ ~R ３ Preferably, at least one of these is an organic functional group containing an ester bond or an amide bond. In this case, the ionic components of the electrolyte salt are more easily attracted to the electrode surface, and the flow of the non-aqueous electrolyte is further improved.

[0040] Examples of amphoteric surfactants represented by formula (I) include 3-[[2-(acryloyloxy)ethyl]dimethylammonio]propane-1-sulfonic acid, 3-[(3-acrylamidopropyl)dimethylammonio]propane-1-sulfonic acid, 3-[(3-methacrylamidopropyl)dimethylammonio]propane-1-sulfonic acid, 4-[[2-(methacryloyloxy)ethyl]dimethylammonio]butane-1-sulfonic acid, 3-[[2-(methacryloyloxy)ethyl]dimethylammonio]propane-1-sulfonic acid, and bis[2-(methacryloyloxy)ethyl](methyl)ammonio]propane-1-sulfonic acid. These may be used individually or in combination of two or more types.

[0041] The content of the amphoteric surfactant relative to the total mass of the nonaqueous electrolyte other than the amphoteric surfactant is preferably 1.0% by mass or less, more preferably 0.8% by mass or less, and even more preferably 0.6% by mass or less. By setting the content of the amphoteric surfactant to 1.0% by mass or less, it becomes easier to achieve higher capacity and lower resistance in batteries. The lower limit of the content of the amphoteric surfactant is, for example, 0.01% by mass relative to the total mass of the nonaqueous electrolyte. Therefore, the content of the amphoteric surfactant relative to the total mass of the nonaqueous electrolyte other than the amphoteric surfactant is preferably 0.01% by mass or more and 1.0% by mass or less, more preferably 0.01% by mass or more and 0.8% by mass or less, and even more preferably 0.01% by mass or more and 0.6% by mass or less.

[0042] The presence or absence of amphoteric surfactants in nonaqueous electrolytes, as well as their molecular weight, can be measured using various NMR (e.g., 1H-NMR, 13C-NMR) or various MS (e.g., ESI-MS).

[0043] Non-aqueous electrolytes may further contain additives. Examples of additives include unsaturated carbonate esters, acid anhydrides, phenol compounds, benzene compounds, nitrile compounds, isocyanate compounds, sultone compounds, sulfuric acid compounds, borate ester compounds, phosphate ester compounds, and phosphite ester compounds.

[0044] Examples of unsaturated cyclic carbonate esters 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. Unsaturated cyclic carbonate esters may be used individually or in combination of two or more. Some hydrogen atoms in the unsaturated cyclic carbonate esters may be substituted with fluorine atoms. The acid anhydride may be an anhydride formed by the intermolecular condensation of multiple carboxylic acid molecules, but it is preferable that it be an acid anhydride of a polycarboxylic acid. Examples of polycarboxylic acid acid anhydrides include succinic anhydride, maleic anhydride, and phthalic anhydride.

[0045] Examples of phenolic compounds include phenol and hydroxytoluene. Examples of benzene compounds include fluorobenzene, hexafluorobenzene, and cyclohexylbenzene (CHB).

[0046] Examples of nitrile compounds include adiponitrile, pimelonitrile, propionitrile, and succinonitrile. Examples of isocyanate compounds include methyl isocyanate (MIC), diphenylmethane diisocyanate (MDI), hexamethylene diisocyanate (HDI), toluene diisocyanate (TDI), isophorone diisocyanate (IPDI), and bisisocyanate methylcyclohexane (BIMCH). Examples of sultone compounds include propanesultone and propensultone. Examples of sulfate compounds include ethylene sulfate, ethylene sulfite, dimethyl sulfate, and lithium fluorosulfate. Examples of borate ester compounds include trimethylborate and tris(trimethylsilyl)borate. Examples of phosphate ester compounds include trimethylphosphate and tris(trimethylsilyl)phosphate. Examples of phosphite ester compounds include trimethylphosphite and tris(trimethylsilyl)phosphite.

[0047] The present disclosure will be further illustrated below with reference to examples and comparative examples, but the present disclosure is not limited to the following examples.

[0048] <Example 1> [Fabrication of the positive electrode] As the positive electrode active material, LiNi ０．８２ Mn ０．１８ O ２ A lithium transition metal composite oxide represented by [formula] was used. A positive electrode mixture layer slurry was prepared by mixing 100 parts by mass of the above positive electrode active material, 0.75 parts by mass of acetylene black, 0.4 parts by mass of carbon nanotubes, and 0.9 parts by mass of polyvinylidene fluoride. Next, the positive electrode mixture layer slurry was applied to aluminum foil and the coating was dried. After rolling the coating using a roller, it was cut to a predetermined electrode size having a 20 mm square positive electrode mixture layer, and a positive electrode was fabricated in which the positive electrode mixture layer was formed on one side of the positive electrode current collector.

[0049] [Fabrication of the negative electrode] As the negative electrode active material, silicon-containing material SiO, graphite, lithium salt of polyacrylic acid, sodium salt of carboxymethylcellulose, carbon nanotubes, and a dispersion of styrene-butadiene copolymer were mixed in a solid content mass ratio of 7.8:100:0.52:0.85:0.02:1.23, and an appropriate amount of water was added to prepare the negative electrode mixture layer slurry. Next, the negative electrode mixture layer slurry was applied to a negative electrode current collector made of copper foil, and the coating was dried. Then, the coating was rolled using a roller, cut to a predetermined electrode size, and a negative electrode was fabricated in which the negative electrode mixture layer was formed on one side of the negative electrode current collector.

[0050] [Preparation of Non-Aqueous Electrolyte] Ethylene carbonate (EC), fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC), and dimethyl carbonate (DMC) were mixed in a volume ratio of 10:10:5:75. Lithium hexafluoride phosphate (LiPF) was added to this mixed solvent. ６ The solution was dissolved to a concentration of 1.35 mol / liter. The prepared electrolyte was measured into an iBoy using a pipette, and the surfactant represented by the following formula (II) (bis[2-(methacryloyloxy)ethyl](methyl)ammonio]propane-1-sulfonic acid) was measured out with a teaspoon and added to the electrolyte at a concentration of 0.05% by mass. The lid of the iBoy was then closed and shaken to mix and prepare a non-aqueous electrolyte.

[0051] [Preparation of Test Cells] Positive electrode leads and negative electrode leads were attached to the positive electrode and negative electrode, respectively, and an electrode body was fabricated by stacking the positive electrode and negative electrode with a separator in between. An aramid-coated separator was used. The fabricated electrode body was inserted into an outer casing made of aluminum laminate sheet, the prepared non-aqueous electrolyte was injected, and the opening of the outer casing was sealed to fabricate a test cell (laminate cell).

[0052] [Evaluation of Capacity Retention Rate] Under an ambient temperature of 25°C, the test cell was charged with a constant current at 0.3C to 4.4V, and then charged with a constant voltage at 4.4V to 0.02C. Afterward, it was discharged with a constant current at 0.5C to 2.85V. This charge-discharge cycle was considered one cycle, and 50 cycles were performed. The capacity retention rate of the test cell in the charge-discharge cycle was calculated using the following formula: Capacity Retention Rate [%] = (Discharge Capacity at Cycle 50 / Discharge Capacity at Cycle 1) × 100

[0053] <Example 2> In the preparation of the non-aqueous electrolyte, the amount of surfactant added was 0.4% by mass relative to the electrolyte, but otherwise, a test cell was prepared and evaluated in the same manner as in Example 1.

[0054] <Example 3> In the preparation of the non-aqueous electrolyte, the amount of surfactant added was 0.6% by mass relative to the electrolyte, but otherwise, a test cell was prepared and evaluated in the same manner as in Example 1.

[0055] <Example 4> In the preparation of the non-aqueous electrolyte, a surfactant represented by the following formula (III) (3-[[2-(acryloyloxy)ethyl]dimethylammonio]propane-1-sulfonic acid) was used as the surfactant, but the test cell was prepared and evaluated in the same manner as in Example 3.

[0056] <Example 5> In the preparation of the non-aqueous electrolyte, a surfactant represented by the following formula (IV) (3-[(3-acrylamidopropyl)dimethylammonio]propane-1-sulfonic acid) was used as the surfactant, but the test cell was prepared and evaluated in the same manner as in Example 3.

[0057] <Example 6> In the preparation of the non-aqueous electrolyte, a surfactant represented by the following formula (V) (3-[(3-methacrylamidopropyl)dimethylammonio]propane-1-sulfonic acid) was used as the surfactant, but the test cell was prepared and evaluated in the same manner as in Example 3.

[0058] <Example 7> In the preparation of the non-aqueous electrolyte, a test cell was prepared and evaluated in the same manner as in Example 3, except that the surfactant used was 4-[[2-(methacryloyloxy)ethyl]dimethylammonio]butane-1-sulfonic acid] represented by the following formula (VI).

[0059] <Example 8> In the preparation of the non-aqueous electrolyte, a test cell was prepared and evaluated in the same manner as in Example 3, except that the surfactant used was represented by the following formula (VII) (3-[[2-(methacryloyloxy)ethyl]dimethylammonio]propane-1-sulfonic acid).

[0060] <Comparative Example 1> In the preparation of the non-aqueous electrolyte, a test cell was prepared and evaluated in the same manner as in Example 1, except that no surfactant was added.

[0061] <Comparative Example 2> In the preparation of the non-aqueous electrolyte, a test cell was prepared and evaluated in the same manner as in Example 3, except that a surfactant represented by the following formula (VIII) was used as the surfactant.

[0062] Table 1 shows the evaluation results of the volume retention rate of the test cells for each example and comparative example.

[0063]

[0064] As shown in Table 1, the volume retention rates of the test cells in Examples 1 to 3 were higher than those of the test cell in Comparative Example 1, which did not contain an amphoteric surfactant. Furthermore, the volume retention rates of the test cells in Examples 1 to 3 were higher than those of the test cell in Comparative Example 2, which contained an amphoteric surfactant without a carbonyl group. This suggests that the inclusion of an amphoteric surfactant having both a carbonyl group and a sulfonate in the nonaqueous electrolyte improves the fluid flow of the nonaqueous electrolyte and enhances its cycle characteristics. Similarly, when the volume retention rates of the test cells in Examples 4 to 8 were evaluated, it was confirmed that they were higher than those of the test cells in Comparative Examples 1 and 2.

[0065] The present disclosure will be further described by the following embodiments. Configuration 1: It contains an amphoteric surfactant represented by the following formula (I), where L １ represents an alkylene group having 2 to 5 carbon atoms, and R １ to R ３ each independently represents an organic functional group, and at least one of R １ to R ３ is an organic functional group containing a carbonyl group, a non-aqueous electrolyte. Configuration 2: The above R １ to R ３The non-aqueous electrolyte according to configuration 1, wherein at least one of the components is an organic functional group containing an ester bond or an amide bond. Configuration 3: The non-aqueous electrolyte according to configuration 1 or 2, wherein the amphoteric surfactant comprises at least one selected from the group consisting of 3-[[2-(acryloyloxy)ethyl]dimethylammonio]propane-1-sulfonic acid, 3-[(3-acrylamidopropyl)dimethylammonio]propane-1-sulfonic acid, 3-[(3-methacryloyloxy)ethyl]dimethylammonio]propane-1-sulfonic acid, and bis[2-(methacryloyloxy)ethyl](methyl)ammonio]propane-1-sulfonic acid. Configuration 4: A non-aqueous electrolyte according to any one of Configurations 1 to 3, wherein the content of the amphoteric surfactant relative to the total mass of the non-aqueous electrolyte other than the amphoteric surfactant is 1.0% by mass or less. Configuration 5: A non-aqueous electrolyte according to Configuration 2, wherein the content of the amphoteric surfactant relative to the total mass of the non-aqueous electrolyte other than the amphoteric surfactant is 1.0% by mass or less. Configuration 6: A non-aqueous electrolyte according to Configuration 3, wherein the content of the amphoteric surfactant relative to the total mass of the non-aqueous electrolyte other than the amphoteric surfactant is 1.0% by mass or less. Configuration 7: A non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte according to any one of Configurations 1 to 6, a positive electrode, and a negative electrode. Configuration 8: A non-aqueous electrolyte secondary battery according to Configuration 7, wherein the negative electrode comprises a negative electrode core and a negative electrode mixture layer containing a negative electrode active material disposed on the negative electrode core, and the negative electrode active material contains a silicon-containing material.

[0066] 10 Non-aqueous electrolyte secondary battery, 11 Positive electrode, 12 Negative electrode, 13 Separator, 14 Electrode body, 16 Outer casing, 17 Sealing body, 18, 19 Insulating plate, 20 Positive electrode lead, 21 Negative electrode lead, 22 Grooved section, 23 Internal terminal plate, 24 Lower valve body, 25 Insulating member, 26 Upper valve body, 27 Cap, 28 Gasket.

Claims

1. Contains an amphoteric surfactant represented by the following formula (I), where L １ R represents an alkylene group with 2 to 5 carbon atoms. １ ~R ３ Each of these independently represents an organic functional group, R １ ~R ３ A non-aqueous electrolyte in which at least one of the organic functional groups is a carbonyl group.

2. The aforementioned R １ ~R ３ The non-aqueous electrolyte according to claim 1, wherein at least one of the is an organic functional group comprising an ester bond or an amide bond.

3. The non-aqueous electrolyte according to claim 1, wherein the amphoteric surfactant comprises at least one selected from the group consisting of 3-[[2-(acryloyloxy)ethyl]dimethylammonio]propane-1-sulfonic acid, 3-[(3-acrylamidopropyl)dimethylammonio]propane-1-sulfonic acid, 3-[(3-methacrylamidopropyl)dimethylammonio]propane-1-sulfonic acid, 4-[[2-(methacryloyloxy)ethyl]dimethylammonio]butane-1-sulfonic acid, 3-[[2-(methacryloyloxy)ethyl]dimethylammonio]propane-1-sulfonic acid, and bis[2-(methacryloyloxy)ethyl](methyl)ammonio]propane-1-sulfonic acid.

4. The nonaqueous electrolyte according to claim 1, wherein the content of the amphoteric surfactant relative to the total mass of the nonaqueous electrolyte other than the amphoteric surfactant is 1.0% by mass or less.

5. The nonaqueous electrolyte according to claim 2, wherein the content of the amphoteric surfactant relative to the total mass of the nonaqueous electrolyte other than the amphoteric surfactant is 1.0% by mass or less.

6. The nonaqueous electrolyte according to claim 3, wherein the content of the amphoteric surfactant relative to the total mass of the nonaqueous electrolyte other than the amphoteric surfactant is 1.0% by mass or less.

7. A non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte according to any one of claims 1 to 6, a positive electrode, and a negative electrode.

8. The non-aqueous electrolyte secondary battery according to claim 7, wherein the negative electrode comprises a negative electrode core and a negative electrode mixture layer containing a negative electrode active material disposed on the negative electrode core, and the negative electrode active material contains a silicon-containing material.

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