JP7749856B2 - Non-aqueous electrolytes and batteries - Google Patents

Description

The present invention relates to a non-aqueous electrolyte and a battery. More specifically, the present invention relates to a non-aqueous electrolyte that can be suitably used as a battery material for lithium-ion batteries and the like, and a battery constructed using the same.

In recent years, growing concern about environmental issues has led to a shift in energy resources away from fossil fuels such as oil and coal. This has led to an increase in the importance of batteries, and demand for them is expected to grow. Secondary batteries, which can be repeatedly charged and discharged, are increasingly being used in a variety of fields, including automobiles and aircraft, as well as in electronic devices such as mobile phones and laptops. Research and development is underway on various secondary batteries and the materials used in them. In particular, lithium-ion batteries, which offer large capacity and are lightweight, are the secondary batteries most expected to see increased use in the future, and are the batteries for which research and development is most actively underway.

In the research and development of such batteries, techniques for improving the performance of the electrolyte have been developed.
For example, Patent Document 1 discloses a nonaqueous electrolyte solution used in a nonaqueous electrolyte secondary battery including a negative electrode and a positive electrode capable of absorbing and releasing metal ions, and a nonaqueous electrolyte solution, the nonaqueous electrolyte solution containing a compound having a Si—Si bond and no aliphatic substituent having an unsaturated bond, and at least one compound selected from the group consisting of a carbonate ester having an unsaturated bond, a compound represented by a predetermined formula, a compound having an S═O group, a compound having an NCO group, a monofluorophosphate, a difluorophosphate, a fluorosulfonate, and an imide salt.
Patent Documents 2 to 4 also disclose electrolytes containing disilane compounds and secondary batteries containing the same.

International Publication No. 2012/105510 US Patent Application Publication No. 2018/0212281 JP 2016-051697 A JP 2011-124039 A

As mentioned above, various technologies for improving the performance of electrolytes have been reported, but nothing has been reported regarding the stability of electrolytes when stored in high-temperature environments. The inventors have discovered a new issue: when a non-aqueous electrolyte containing a sulfonylimide compound is stored in a high-temperature environment, the sulfonylimide compound decomposes. Furthermore, batteries using conventional electrolytes have the problem of increasing direct current resistance (DCR) when repeatedly charged.

The present invention has been made in consideration of the above-mentioned current situation, and aims to provide a non-aqueous electrolyte solution containing a sulfonylimide compound that has excellent storage stability in high-temperature environments and can suppress an increase in DCR in a battery.

The inventors conducted extensive research into non-aqueous electrolyte solutions containing sulfonylimide compounds and discovered that by combining a disilane compound of a specific structure with a non-aqueous electrolyte solution containing a sulfonylimide compound of a specific structure in a specific ratio, the non-aqueous electrolyte solution has excellent stability even when stored in a high-temperature environment and can suppress an increase in DCR in the battery. They then came to the conclusion that the above-mentioned problems could be successfully solved, leading to the present invention.

The present invention encompasses the following nonaqueous electrolytes and the like.
[1] The following formula (1):
M ¹ N(R ¹ SO ₂ )(R ² SO ₂ )(1)
(wherein ^M1 represents an alkali metal atom; ^R1 and ^R2 are the same or different and represent a fluorine atom, an alkyl group having 1 to 6 carbon atoms, or a fluoroalkyl group having 1 to 6 carbon atoms), with a sulfonylimide compound represented by the following formula (2);
(wherein R ³ to R ⁸ are the same or different and represent a hydrocarbon group having 1 to 14 carbon atoms which may have a heteroatom, a hydrogen atom, a hydroxyl group, or a halogen atom), and the concentration of the sulfonylimide compound is 0.1 mol/L or more.
[2] The nonaqueous electrolyte solution according to [1] above, wherein R ³ to R ⁸ in the formula (2) are the same or different and represent an alkyl group having 1 to 12 carbon atoms, an aryl group having 6 to 14 carbon atoms, an alkenyl group having 2 to 14 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, an aryloxy group having 6 to 14 carbon atoms, a hydrogen atom, or a halogen atom.
[3] The nonaqueous electrolyte solution according to [1] or [2] above, wherein R ³ to R ⁸ in the formula (2) are the same or different and represent an alkyl group having 1 to 12 carbon atoms, an aryl group having 6 to 14 carbon atoms, an alkenyl group having 2 to 14 carbon atoms, a hydrogen atom, or a halogen atom.
[4] The non-aqueous electrolyte solution according to any one of [1] to [3] above, wherein R ³ to R ⁸ in the formula (2) above are the same or different and each represent a methyl group, a hydrogen atom, or a halogen atom.
[5] The non-aqueous electrolyte solution according to any one of [1] to [4], wherein the content of the compound represented by formula (2) is 0.05% by mass or more and less than 5.0% by mass, relative to 100% by mass of the non-aqueous electrolyte solution.
[6] The nonaqueous electrolyte solution according to any one of the above [1 ^] to [5], further comprising at least one selected from the group consisting of M ² PF ₆ , M ² BF ₄ , M ² PO ₂ F _{2 and} M 2 FSO 3 (M ² represents an alkali metal atom).
[7] A battery comprising the nonaqueous electrolyte solution according to any one of [1] to [6] above.
[8] The battery comprises a lithium secondary battery represented by the following formula (3):
_{LiNixCoyMnzO2 ( 3 )}
(wherein x, y, and z are numbers satisfying x + y + z = 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1) and / or a positive electrode containing LiFePO _4. The battery according to [7] above.

The non-aqueous electrolyte of the present invention has the above-mentioned configuration, has excellent stability when stored in a high-temperature environment, and can suppress an increase in DCR in the battery, making it suitable for use as a battery material for lithium-ion batteries and the like.

The following describes in detail preferred embodiments of the present invention, but the present invention is not limited to the following description and can be modified and applied as appropriate within the scope of the present invention. Furthermore, a combination of two or more of the individual preferred embodiments of the present invention described below also falls under the category of preferred embodiments of the present invention.

1. Nonaqueous Electrolyte The nonaqueous electrolyte of the present invention contains a sulfonylimide compound represented by the above formula (1) (hereinafter also simply referred to as a sulfonylimide compound) and a disilane compound represented by the above formula (2) (hereinafter also simply referred to as a disilane compound), and the concentration of the sulfonylimide compound is 0.1 mol/L or more.
By using the disilane compound in a non-aqueous electrolyte containing a sulfonylimide compound in a predetermined proportion or more, decomposition of the sulfonylimide compound is suppressed even when the non-aqueous electrolyte is stored in a high-temperature environment, resulting in excellent storage stability and suppressing an increase in DCR in the battery. Furthermore, if decomposition of the sulfonylimide compound in the non-aqueous electrolyte progresses, problems such as an increase in DCR and a decrease in capacity retention rate at low temperatures may occur. However, a battery using such a non-aqueous electrolyte suppresses an increase in DCR at low temperatures and also exhibits an excellent capacity retention rate.

In the nonaqueous electrolyte, the concentration of the sulfonylimide compound is 0.1 mol/L or more, preferably 0.1 to 6.0 mol/L, more preferably 0.2 to 3.0 mol/L, even more preferably 0.4 to 2.0 mol/L, still more preferably 0.6 to 2.0 mol/L, and particularly preferably 0.8 to 2.0 mol/L.
The concentration of the sulfonylimide compound is preferably 0.1 to 6.0 mol/kg, more preferably 0.2 to 3.0 mol/kg, still more preferably 0.4 to 2.0 mol/kg, even more preferably 0.6 to 2.0 mol/kg, and particularly preferably 0.8 to 2.0 mol/kg.

The content of the disilane compound in the nonaqueous electrolyte is not particularly limited, but is preferably 0.05% by mass or more and less than 5.0% by mass, based on 100% by mass of the nonaqueous electrolyte. This more sufficiently reduces the increase in DCR in the battery under low-temperature conditions and further improves the DCR increase rate and capacity retention rate during repeated charging. The content of the disilane compound is more preferably 0.1 to 3.0% by mass, even more preferably 0.2 to 2.0% by mass, even more preferably 0.5 to 1.5% by mass, and particularly preferably 0.5 to 1.0% by mass.

The non-aqueous electrolyte contains the sulfonylimide compound as an alkali metal salt, but may contain an alkali metal salt other than the sulfonylimide compound.
The concentration of the alkali metal salt other than the sulfonylimide compound in the nonaqueous electrolyte is not particularly limited, but is preferably 0.1 to 1.5 mol/L, more preferably 0.2 to 1.0 mol/L, and even more preferably 0.2 to 0.6 mol/L.
The concentration of the alkali metal salt other than the sulfonylimide compound is preferably 0.1 to 1.5 mol/kg, more preferably 0.2 to 1.0 mol/kg, and even more preferably 0.2 to 0.6 mol/kg.

In the nonaqueous electrolyte, the total alkali metal concentration of the sulfonylimide compound and the alkali metal salt other than the sulfonylimide compound is preferably 0.8 to 6.0 mol/L, more preferably 1.0 to 3.0 mol/L, and even more preferably 1.2 to 2.0 mol/L.
The total alkali metal concentration of the sulfonylimide compound and the alkali metal salt other than the sulfonylimide compound is preferably 0.8 to 6.0 mol/kg, more preferably 1.0 to 3.0 mol/kg, and even more preferably 1.2 to 2.0 mol/kg.

The sulfonylimide compound is preferably present in an amount of 5 to 100 mol% relative to 100 mol% of the electrolyte (the sulfonylimide compound and other alkali metal salts) in the nonaqueous electrolyte. This allows the effects of the present invention to be more fully exhibited. It is more preferably present in an amount of 10 to 95 mol%, even more preferably 20 to 90 mol%, even more preferably 30 to 85 mol%, even more preferably 40 to 85 mol%, particularly preferably 50 to 85 mol%, and especially preferably 60 to 85 mol%. In one embodiment, the sulfonylimide compound may be present in an amount of 70 mol% or more, 80 mol% or more, or 90 mol% or more relative to 100 mol% of the electrolyte.

The nonaqueous electrolyte solution contains a nonaqueous solvent as a solvent, and may contain water at a rate of 10% or less. The water content is preferably 1% or less. This allows the effects of the present invention to be more fully exhibited. The water content is more preferably 1000 ppm or less, and even more preferably 100 ppm or less.
The water content can be measured using a Karl Fischer water content analyzer.

The proportion of non-aqueous solvent in the above-mentioned non-aqueous electrolyte solution is not particularly limited, but is preferably 100 to 5,000 parts by weight per 100 parts by weight of electrolyte (the above-mentioned sulfonylimide compound and other alkali metal salts), more preferably 150 to 2,500 parts by weight, and even more preferably 200 to 2,000 parts by weight.

The non-aqueous electrolyte may contain other components other than the sulfonylimide compound, the disilane compound, an alkali metal salt other than the sulfonylimide compound, and a solvent.
The content of the other components is not particularly limited, but is preferably 0 to 20% by mass, more preferably 0 to 10% by mass, and even more preferably 0 to 5% by mass, relative to 100% by mass of the nonaqueous electrolyte solution.

The essential components and optional components contained in the nonaqueous electrolyte solution of the present invention will be further described below.
<Sulfonylimide Compound>
The sulfonylimide compound is represented by the following formula (1):
M ¹ N(R ¹ SO ₂ )(R ² SO ₂ )(1)
(wherein ^M1 represents an alkali metal atom; ^R1 and ^R2 may be the same or different and represent a fluorine atom, an alkyl group having 1 to 6 carbon atoms, or a fluoroalkyl group having 1 to 6 carbon atoms).

The alkali metal for ^M1 includes lithium, sodium, potassium, rubidium, cesium, and francium. Preferred are lithium, sodium, and potassium, and more preferred is lithium.

Examples of the alkyl group having 1 to 6 carbon atoms in ^R1 include straight-chain alkyl groups such as methyl, ethyl, n-propyl, n-butyl, n-pentyl (amyl), and n-hexyl; branched-chain alkyl groups such as i-propyl, sec-butyl, i-butyl, t-butyl, 1-methylbutyl, 1-ethylpropyl, 2-methylbutyl, i-amyl, neopentyl, 1,2-dimethylpropyl, 1,1-dimethylpropyl, t-amyl, 1,3-dimethylbutyl, 3,3-dimethylbutyl, and 2-ethylbutyl; and cyclic alkyl groups such as cyclopropyl, cyclopropylmethyl, cyclobutyl, cyclobutylmethyl, cyclopentyl, and cyclohexyl. Of these, straight-chain alkyl groups are preferred.

The alkyl group in ^R1 and ^R2 preferably has 1 to 4 carbon atoms, more preferably 1 to 3 carbon atoms, and even more preferably 1 or 2 carbon atoms.

The fluoroalkyl group having 1 to 6 carbon atoms in ^R1 and ^R2 may be an alkyl group having 1 to 6 carbon atoms in which at least some of the hydrogen atoms bonded to the carbon atoms have been substituted with fluorine atoms. Specific examples of the alkyl group are as described above.
Examples of the fluoroalkyl group having 1 to 6 carbon atoms include a fluoromethyl group, a difluoromethyl group, a trifluoromethyl group, a fluoroethyl group, a difluoroethyl group, a trifluoroethyl group, a pentafluoroethyl group, a fluoropropyl group, a fluoropentyl group, and a fluorohexyl group.

The fluoroalkyl groups in R ¹ and R ² preferably have 1 to 4 carbon atoms, more preferably 1 to 3 carbon atoms, and even more preferably 1 or 2 carbon atoms.

^R1 and ^R2 are preferably a fluorine atom, a trifluoromethyl group, or a pentafluoroethyl group. A fluorine atom is more preferred, and it is preferable that at least one of ^R1 and ^R2 is a fluorine atom. An embodiment in which both ^R1 and ^R2 are fluorine atoms is one of the preferred embodiments of the present invention.

Examples of the sulfonylimide compound include lithium bis(fluorosulfonyl)imide (hereinafter also referred to as LiFSI), lithium (fluorosulfonyl)(trifluoromethylsulfonyl)imide, lithium bis(trifluoromethylsulfonyl)imide, lithium (fluorosulfonyl)(pentafluoroethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, potassium bis(fluorosulfonyl)imide, potassium (fluorosulfonyl)(trifluoromethylsulfonyl)imide, potassium bis(trifluoromethylsulfonyl)imide, sodium bis(fluorosulfonyl)imide, sodium (fluorosulfonyl)(trifluoromethylsulfonyl)imide, and sodium bis(trifluoromethylsulfonyl)imide.
Of these, lithium bis(fluorosulfonyl)imide, lithium (fluorosulfonyl)(trifluoromethylsulfonyl)imide, and lithium (fluorosulfonyl)(pentafluoroethylsulfonyl)imide are preferred, and lithium bis(fluorosulfonyl)imide is more preferred.

<Disilane Compounds>
The disilane compound is represented by the following formula (2):

(wherein R ³ to R ⁸ may be the same or different and represent a hydrocarbon group having 1 to 14 carbon atoms which may have a heteroatom, a hydrogen atom, a hydroxyl group, or a halogen atom).

Examples of the hydrocarbon group having 1 to 14 carbon atoms in R ³ to R ⁸ include an aliphatic alkyl group having 1 to 14 carbon atoms, an alicyclic alkyl group having 3 to 14 carbon atoms, an alkenyl group having 2 to 14 carbon atoms, an alkynyl group having 2 to 14 carbon atoms, and an aryl group having 6 to 14 carbon atoms.

Examples of the aliphatic alkyl group having 1 to 14 carbon atoms include methyl, ethyl, n-propyl, n-butyl, n-pentyl (amyl), n-hexyl, n-heptyl, n-octyl, n-nonyl, n-decyl, n-undecyl, n-dodecyl, n-tridecyl, n-tetradecyl, i-propyl, sec-butyl, i-butyl, t-butyl, 1-methylbutyl, 1-ethylpropyl, and 2-methylbutyl. Examples of such groups include an isopropyl group, an i-amyl group, a neopentyl group, a 1,2-dimethylpropyl group, a 1,1-dimethylpropyl group, a t-amyl group, a 1,3-dimethylbutyl group, a 3,3-dimethylbutyl group, a 2-ethylbutyl group, a 2-ethyl-2-methylpropyl group, a 1-methylheptyl group, a 2-ethylhexyl group, a 1,5-dimethylhexyl group, a t-octyl group, a branched nonyl group, a decyl group, an undecyl group, a dodecyl group, a tridecyl group, and a tetradecyl group.

Examples of the alicyclic alkyl group having 3 to 14 carbon atoms include a cyclopropyl group, a cyclopropylmethyl group, a cyclobutyl group, a cyclobutylmethyl group, a cyclopentyl group, a cyclohexyl group, a cyclohexylmethyl group, a cycloheptyl group, a cyclooctyl group, a cyclohexylpropyl group, a cyclododecyl group, a norbornyl group (C7), an adamantyl group (C10), and a cyclopentylethyl group.

Examples of the alkenyl group having 2 to 14 carbon atoms include a vinyl group, an allyl group, a 1-butenyl group, a 2-butenyl group, a pentenyl group, a hexenyl group, a heptenyl group, an octenyl group, a nonenyl group, a decenyl group, a dodecenyl group, and a tetradecenyl group.

Examples of the alkynyl group having 2 to 14 carbon atoms include ethynyl, 1-propynyl, 2-propynyl, butynyl, pentynyl, hexynyl, heptynyl, octynyl, nonynyl, decynyl, dodecynyl, and tetradecynyl groups.

Examples of the aryl group having 6 to 14 carbon atoms include a phenyl group, a naphthyl group, a benzyl group, a 1-phenylethyl group, a 2-phenylethyl group, a 3-phenylpropyl group, a 4-phenylbutyl group, a styryl group (Ph-CH=C- group), a cinnamyl group (Ph-CH=CHCH ₂ - group), etc. Preferred are a phenyl group and a benzyl group.

The alkyl group preferably has 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms, even more preferably 1 to 4 carbon atoms, and particularly preferably 1 or 2 carbon atoms.
The alkenyl group and alkynyl group preferably have 2 to 10 carbon atoms, more preferably 2 to 8 carbon atoms, even more preferably 2 to 4 carbon atoms, and particularly preferably 2 to 3 carbon atoms.
The aryl group preferably has 6 to 10 carbon atoms, more preferably 6 to 8 carbon atoms, and even more preferably 6 to 7 carbon atoms.
When the hydrocarbon group has a substituent, the number of carbon atoms included in the number of carbon atoms of the substituent is also included.

The hydrocarbon groups in R ³ to R ⁸ may contain heteroatoms, and examples of the heteroatoms include nitrogen atoms, sulfur atoms, oxygen atoms, phosphorus atoms, and halogen atoms.
The hydrocarbon groups in R ³ to R ⁸ may have a substituent having a hetero atom, and examples of the substituent having a hetero atom include a hydroxyl group, an ether group, an ester group, a carboxyl group, an acyl group, a sulfonic acid group, an amino group, and a phosphate group.

The substituent having a hetero atom is preferably an ether group, and the hydrocarbon group having a hetero atom is preferably an alkoxy group having 1 to 12 carbon atoms or an aryloxy group having 6 to 14 carbon atoms.
Examples of the alkoxy group include a methoxy group, an ethoxy group, and a propoxy group.
Examples of the aryloxy group include a phenyloxy group and a benzyloxy group.

Examples of the halogen atom in R ³ to R ⁸ include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

R ³ to R ⁸ are preferably an alkyl group having 1 to 12 carbon atoms, an aryl group having 6 to 14 carbon atoms, an alkenyl group having 2 to 14 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, an aryloxy group having 6 to 14 carbon atoms, a hydrogen atom, or a halogen atom, more preferably an alkyl group having 1 to 12 carbon atoms, an aryl group having 6 to 14 carbon atoms, an alkenyl group having 2 to 14 carbon atoms, a hydrogen atom, or a halogen atom, still more preferably an alkyl group having 1 to 12 carbon atoms, a hydrogen atom, or a halogen atom, and particularly preferably a methyl group, a hydrogen atom, or a halogen atom.

Specific examples of the above disilane compounds include tetramethyldisilane, tetraethyldisilane, tetrapropyldisilane, hexamethyldisilane, hexaethyldisilane, hexapropyldisilane, divinyltetramethyldisilane, hexaphenyldisilane, hexahydrodisilane, 1,1,2,2-tetramethyl-1,2-diphenyldisilane, 1,2-dimethyl-1,1,2,2-tetraphenyldisilane, 1,2-di(t-butyl)-1,1,2,2-tetramethyldisilane, 1,1,2,2-tetramethyl-1,2-dimethoxydisilane, 1,1,2,2-tetramethyl-1,2-diethoxydisilane, 1,1,2-trimethyl-1, Examples of the disilane include 2,2-trimethoxydisilane, 1,1,2-trimethyl-1,2,2-triethoxydisilane, 1,2-dimethyl-1,1,2,2-tetramethoxydisilane, 1,2-dimethyl-1,1,2,2-tetraethoxydisilane, 1,2-diallyl-1,1,2,2-tetramethyldisilane, 1,2-diallyl-1,1,2,2-tetraethyldisilane, 1,2-diallyl-1,1,2,2-tetrapropyldisilane, 1,2-diallyl-1,1,2,2-tetraphenyldisilane, hexahydrodisilane, 1,2-dichloro-1,1,2,2-tetramethyldisilane, and 1,1,2-trichloro-1,2,2-trimethyldisilane. Among these, tetramethyldisilane, hexamethyldisilane, and divinyltetramethyldisilane are preferred.

<Other alkali metal salts>
The other alkali metal salts are not particularly limited as long as they are alkali metal salts other than the above-mentioned sulfonylimide compounds, and examples thereof include alkali metal salts of fluorophosphates such as LiPF ₆ and LiPO ₂ F ₂ ; alkali metal salts of fluorosulfonic acids such as LiFSO ₃ ; alkali metal salts of trifluoromethanesulfonic acids such as LiCF ₃ SO ₃ ; alkali metal salts of perfluoroalkanesulfonylmethides such as LiC(CF ₃ SO ₂ ) ₃ ; fluorophosphates such as LiPF _a (C _m F _2m+1 ) _6-a (0≦a≦6, 1≦m≦2); alkali metal salts of perchlorates such as LiClO ₄ ; and LiBF _b (C _n F _2n+1 ) _4-b (0≦b≦4, 1≦n≦2); alkali metal salts of oxalatoborates such as LiBOB; cyanoborates such as lithium tetracyanoborate; alkali metal salts such as LiAsF ₆ , LiI, LiSbF ₆ , and the like.

The other alkali metal salt is preferably ^M2PF6 , ^M2BF4 , _M2PO2F2 , or _M2FSO3 ( ^M2 represents _an alkali metal atom) _, and _an embodiment including at least one selected from ^{the group consisting of M2PF6, M2BF4} _, ^M2PO2F2 _{, and} ^{M2FSO3 is} one of _the preferred embodiments of _the present invention. ^The other ^alkali metal salt is more preferably _M2PF6 ^.
Specific examples and preferred forms of the alkali metal atom are the same as those of the alkali metal atom in the sulfonylimide compound.

<Solvent>
The solvent in the non-aqueous electrolytic solution of the present invention is not particularly limited as long as it is non-aqueous and can dissolve the electrolyte (sulfonylimide compound and other alkali metal salts), the disilane compound, and other components described below. Examples of suitable solvents include chain carbonates such as dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate; cyclic carbonates such as ethylene carbonate, propylene carbonate, butylene carbonate, and chloroethylene carbonate; tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,1-dimethoxyethane, 1,2-dimethoxyethane, and 1,2-diethoxyethane. ethers such as 1,2-dibutoxyethane; lactones such as γ-butyrolactone, γ-valerolactone, and α-methyl-γ-butyrolactone; chain carboxylic acid esters such as methyl propionate and methyl butyrate; fluorinated cyclic carbonates such as fluoroethylene carbonate, 4,5-difluoroethylene carbonate, 4,4-difluoroethylene carbonate, tetrafluoroethylene carbonate, and 4-fluoro-5-methylethylene carbonate; and fluorinated chain carbonates such as trifluorodimethyl carbonate, trifluorodiethyl carbonate, and trifluoroethylmethyl carbonate. These nonaqueous solvents may be used in combination of two or more. Of these, chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethylmethyl carbonate are preferred.

<Other ingredients>
The other components in the non-aqueous electrolyte solution of the present invention are components other than the sulfonylimide compound, the disilane compound, the alkali metal salt other than the sulfonylimide compound, and the solvent, and are not particularly limited. Examples of the other components include carbonate compounds such as phenylethylene carbonate and erythritol carbonate; sulfonic acid esters such as 1,3-propane sultone, 1,4-butane sultone, 1,5-pentane sultone, 1,4-hexane sultone, 4,6-heptane sultone, methyl methanesulfonate, methyl benzenesulfonate, and methyl trifluoromethanesulfonate; sulfolane, 3-methylsulfolane, ethyl methyl sulfone, diphenyl sulfone, bis( sulfone compounds such as succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, diglycolic anhydride, cyclohexanedicarboxylic anhydride, cyclopentanetetracarboxylic dianhydride, phenylsuccinic anhydride, and the like; nitrogen-containing compounds such as 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl-2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone, N-methylsuccinimide, and the like; phosphates such as monofluorophosphates, difluorophosphates, and the like; hydrocarbon compounds such as heptane, octane, and cycloheptane, and the like.

2. Batteries The nonaqueous electrolyte solution of the present invention has the above-described structure and is highly stable when stored in a high-temperature environment, and therefore can be suitably used as a battery material for lithium-ion batteries and the like.
The present invention also relates to a battery comprising the nonaqueous electrolyte of the present invention.
The battery is preferably a battery including a positive electrode and a negative electrode, more preferably a battery in which a separator impregnated with the nonaqueous electrolyte solution of the present invention is provided between the positive electrode and the negative electrode, and even more preferably a battery in which these are housed in an exterior case.

The shape of the battery according to the present invention is not particularly limited, and any of the conventionally known battery shapes can be used, such as cylindrical, prismatic, laminated, coin, large, etc. Furthermore, when used as a high-voltage power source (several tens to several hundreds of volts) for installation in electric vehicles, hybrid electric vehicles, etc., it can also be made into a battery module consisting of individual batteries connected in series.

The above-mentioned battery is preferably an alkali metal battery, and an alkali metal battery comprising the nonaqueous electrolyte of the present invention also constitutes one aspect of the present invention. The above-mentioned battery is more preferably a secondary battery, and a configuration in which the above-mentioned battery is a lithium-ion secondary battery constitutes one preferred embodiment of the present invention.

The positive electrode constituting the above-mentioned battery is not particularly limited, but is typically a positive electrode active material composition containing a positive electrode active material, a conductive additive, a binder, a dispersion solvent, etc., supported on a positive electrode current collector and typically formed into a sheet.

Examples of methods for manufacturing positive electrodes include applying a positive electrode active material composition to a positive electrode current collector using a doctor blade method or immersing the positive electrode current collector in the positive electrode active material composition and then drying it; kneading and molding the positive electrode active material composition, drying the resulting sheet, and bonding it to a positive electrode current collector via a conductive adhesive, followed by pressing and drying; and applying or casting a positive electrode active material composition to which a liquid lubricant has been added onto a positive electrode current collector, forming it into the desired shape, removing the liquid lubricant, and then stretching it uniaxially or multiaxially.

The material for the positive electrode current collector is not particularly limited, and conductive metals such as aluminum, aluminum alloys, SUS (stainless steel), and titanium can be used. Among these, aluminum is preferred because it is easy to process into a thin film and is inexpensive.

The positive electrode active material may be any material capable of absorbing and releasing ions, and any known positive electrode active material may be used. Specifically, the materials include composite metal oxides ^{such as ternary oxides represented by M3CoO2, M3NiO2} _{, M3MnO2 ,} ^{M3NixCoyMnzO2} _, ^and _{M3NixCoyAlzO2 ( x} , y, and z are numbers that satisfy x+ _y + _z = ₁ , 0≦x≦ ₁ , 0≦y≦1, and 0≦z≦1), nickel manganese oxides represented by ^M3pNiqMn _{(2-q) O4} (0.9≦ _p ≦ _1.1 , 0<q<1), compounds with an olivine structure such as ^M3APO4 (A=Fe, Mn _, Ni, Co), and solid solution materials incorporating multiple transition metals (electrochemically inactive layered ^M32MnO3 and electrochemically active layered M32MnO3 _{) .} Examples of the positive electrode active material include a solid solution of ^M3MO (where M3 is a transition metal such as Co or Ni) ( ^M3 represents an alkali metal ion). These positive electrode active materials may be used alone or in combination.
The positive electrode active material may be a compound represented by the following formula (3):
_{LiNixCoyMnzO2 ( 3 )}
(wherein x, y, and z are numbers satisfying x + y + z = 1, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1) and/or _LiFePO4 are preferred. A battery configured with a positive electrode containing such a positive electrode active material is one of the preferred embodiments of the present invention.

Conductive additives include acetylene black, carbon black, graphite, metal powder materials, single-walled carbon nanotubes, multi-walled carbon nanotubes, vapor-grown carbon fibers, etc.

Examples of binders include fluorine-based resins such as polyvinylidene fluoride and polytetrafluoroethylene; synthetic rubbers such as styrene-butadiene rubber and nitrile butadiene rubber; polyamide-based resins such as polyamideimide; polyolefin-based resins such as polyethylene and polypropylene; poly(meth)acrylic resins; polyacrylic acid; cellulose-based resins such as carboxymethyl cellulose; and others. These binders may be used alone or in combination. Furthermore, these binders may be dissolved in a solvent or dispersed in a solvent when used.

The amount of conductive additive and binder can be adjusted appropriately taking into account the intended use of the battery (emphasis on output, emphasis on energy, etc.), ionic conductivity, etc.

When manufacturing a positive electrode, solvents used in the positive electrode active material composition include N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, tetrahydrofuran, acetonitrile, acetone, ethanol, ethyl acetate, water, etc. These solvents may be used in combination. The amount of solvent used is not particularly limited and may be determined appropriately depending on the manufacturing method and materials used.

The negative electrode constituting the above-mentioned battery is not particularly limited, but is typically a negative electrode active material composition containing a negative electrode active material, a dispersion solvent, a binder, and optionally a conductive additive, etc., supported on a negative electrode current collector and typically formed into a sheet.

Conductive metals such as copper, iron, nickel, silver, and stainless steel (SUS) can be used as materials for the negative electrode current collector. Copper is preferred because it can be easily processed into a thin film.

The negative electrode active material can be any conventionally known negative electrode active material used in batteries, as long as it is capable of absorbing and releasing ions. Specifically, the following can be used: alkali metals, metal alloys such as alkali metal-aluminum alloys; graphite materials such as artificial graphite and natural graphite; mesophase sintered bodies made from coal or petroleum pitch; carbon materials such as non-graphitizable carbon; Si-based negative electrode materials such as Si, Si alloys, and SiO; and Sn-based negative electrode materials such as Sn alloys.

The negative electrode can be manufactured using the same method as the positive electrode. Furthermore, the conductive additives, binders, and solvents for dispersing materials used in manufacturing the negative electrode are the same as those used in manufacturing the positive electrode.

The separator is disposed to separate the positive electrode from the negative electrode.
The separator constituting the battery is not particularly limited, and any separator that is commonly used can be used.
Examples of the separator include a porous sheet made of a polymer capable of absorbing and retaining a non-aqueous electrolyte solution (e.g., a polyolefin-based microporous separator or a cellulose-based separator), a nonwoven fabric separator, a porous metal body, etc. Among these, a polyolefin-based microporous separator is preferred because it is chemically stable against organic solvents.

Examples of materials for the porous sheet include polyethylene, polypropylene, and laminates having a three-layer structure of polypropylene/polyethylene/polypropylene.

Examples of materials for the nonwoven fabric separator include cotton, rayon, acetate, nylon, polyester, polypropylene, polyethylene, polyimide, aramid, glass, etc., and the above-mentioned materials can be used alone or in combination depending on the mechanical strength required of the nonaqueous electrolyte layer.

The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples. Unless otherwise specified, "parts" means "parts by weight" and "%" means "% by mass."

The physical properties of the non-aqueous electrolyte and the battery characteristics were evaluated as follows.
(Evaluation of storage stability of non-aqueous electrolyte)
10 ml of the non-aqueous electrolyte solution was placed in a PFA (fluorine-based resin) container, the PFA container was sealed, wrapped in aluminum laminate zip, and stored for a desired period in a thermostatic chamber set at 60° C. After storage, the electrolyte solution was diluted 100 times with ultrapure water, and the sulfate ion (SO ₄ ²⁻ ) concentration was measured by ion chromatography as follows.
The storage stability was evaluated based on the relative amount of sulfate ions in the electrolyte solution to which no disilane compound was added, using the following formula (4), where the concentration of sulfate ions in the electrolyte solution to which no disilane compound was added was taken as 100.
Relative amount of sulfate ion (%)=sulfate ion concentration when disilane compound is included/sulfate ion concentration when disilane compound is not included×100 (4)
(Ion chromatography measurement)
The non-aqueous electrolyte was diluted 100 times with ultrapure water to prepare a measurement solution, and the concentration of sulfate ions (SO ₄ ²⁻ ) contained in the non-aqueous electrolyte was measured using an ion chromatography system ICS-3000 (manufactured by Nippon Dionex Co., Ltd.) under the following measurement conditions.
Measurement conditions: Separation mode: ion exchange; Eluent: 7 to 18 mM KOH aqueous solution; Detector: electrical conductivity detector; Column: anion analysis column Ion PAC AS-17C (manufactured by Nippon Dionex Co., Ltd.)

(DCR increase rate, capacity maintenance rate)
(i) DCR
The aged lithium-ion secondary battery (cell) was CCCV charged at 4.2 V and 1 C (30 mA) at room temperature. After 30 minutes, it was discharged at 0.2 C (6 mA) for 10 seconds, then left for 30 minutes, discharged at 1 C (30 mA) for 10 seconds, and then CC discharged at 3 C (90 mA) for 10 seconds after leaving for another 30 minutes. Each discharge current was plotted on the horizontal axis, and the difference (ΔV) in closed-circuit voltage between the start of discharge and 10 seconds after discharge at each discharge current was plotted on the vertical axis. The slope of the IV line was taken as the DCR of the cell.
(ii) Low-Temperature DCR
The aged cell was subjected to CCCV charging at 4.2 V and 1 C (30 mA) at room temperature. After setting the temperature of the thermostatic chamber to -10°C, the cell was discharged at 0.2 C (6 mA) for 10 seconds, then left for 30 minutes, discharged at 0.5 C (15 mA) for 10 seconds, and then left for another 30 minutes, after which it was CC discharged at 1 C (30 mA) for 10 seconds. The slope of the IV line was calculated in the same manner as for the DCR in (i) above, and this was used as the low-temperature DCR of the cell.
(iii) Cycle Charge/Discharge: After the DCR measurement in (i) above, the cell was CCCV charged at 4.2 V, 0.5 C (15 mA) at 45°C, followed by CC discharge at 2.75 V, 0.2 C (6 mA). Subsequently, CCCV charged at 4.2 V, 1 C (30 mA), followed by CC discharge at 2.75 V, 1 C (30 mA). This 1 C charge/discharge cycle was repeated a total of 500 times. The capacity retention rate at 500 cycles was calculated using the following formula (5):
Furthermore, the DCR of the cell after the cycle charge/discharge was measured again, and the DCR increase rate was calculated using the following formula (6).
Capacity retention rate (%)
= 500th 1C discharge capacity / 1st 1C discharge capacity × 100 (5)
DCR increase rate (%)
= DCR after cycle charge/discharge / DCR after aging × 100 (6)

(Preparation of Electrolyte Solutions: Examples 1-1 to 18-1, Comparative Examples 1-1 to 15-1)
Non-aqueous electrolyte solutions (hereinafter simply referred to as "electrolytes") with various salt concentrations were prepared by dissolving LiFSI (manufactured by Nippon Shokubai Co., Ltd.) and/or _LiPF6 (manufactured by Stella Chemifa Co., Ltd.) in a mixed solvent (manufactured by Kishida Chemical Co., Ltd.) with a composition of ethylene carbonate (EC):ethyl methyl carbonate (EMC) = 3:7 (volume ratio).
A disilane compound was further added to some of the electrolyte solutions to give the concentrations shown in Table 1 to prepare non-aqueous electrolyte solutions.

The stability of the obtained non-aqueous electrolyte solution was evaluated after storage at 60°C for 3 months. The results are shown in Table 1.

(Fabrication of Lithium-ion Secondary Battery 1: Examples 1-2 to 13-2, Comparative Examples 1-2 to 14-2)
(i) Preparation of positive electrode (NMC111) A ternary positive electrode active material, LiNi _1/3 Co _1/3 Mn _1/3 O ₂ (manufactured by Umicore), acetylene black (AB, manufactured by Denka Co., Ltd., product name: Denka Black (registered trademark)), graphite (manufactured by Nippon Graphite Industries Co., Ltd., product number: SP270), and polyvinylidene fluoride (PVdF, manufactured by Kureha Corporation, product number: KF1120) were dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode mixture slurry (positive electrode active material: AB: graphite: PVdF = 93:2:2:3 (mass ratio of solids)). Next, the obtained positive electrode mixture slurry was applied to one side of an aluminum foil (positive electrode current collector, manufactured by Nippon Foil Co., Ltd., thickness 15 μm) using an applicator so that the coating weight after drying would be 19.4 mg/ ^cm² , and the resultant was dried on a hot plate at 110°C for 10 minutes. It was then further dried in a vacuum drying furnace at 110°C for 12 hours. Thereafter, the resultant was pressure-molded using a roll press to a density of 3.1 g/ ^cm³ , thereby obtaining a sheet-shaped positive electrode (thickness 83 μm).

(ii) Preparation of negative electrode As the negative electrode active material, graphite (natural graphite), styrene-butadiene rubber (SBR, binder), and carboxymethyl cellulose (CMC, binder) were dispersed in ultrapure water to prepare a negative electrode mixture slurry (negative electrode active material: SBR: CMC = 97.3: 1.5: 1.2 (solid mass ratio)). Subsequently, the obtained negative electrode mixture slurry was applied to a copper foil (negative electrode current collector, manufactured by Fukuda Metal Foil and Powder Co., Ltd., thickness 15 μm) with an applicator to a single-sided coating weight of 9.8 mg / cm ² after drying, and then dried on a hot plate at 80 ° C. for 10 minutes. Further, the mixture was dried for 12 hours in a vacuum drying oven at 100 ° C. Then, the negative electrode was pressure-molded using a roll press to a density of 1.3 g / cm ³ , thereby obtaining a sheet-shaped negative electrode (thickness 113 μm).

(iii) Fabrication of Lithium-Ion Secondary Batteries The positive and negative electrodes obtained in (i) and (ii) above were cut, and the polarity leads were ultrasonically welded. The positive and negative electrodes were placed opposite each other via a 25 μm polyethylene (PE) separator, and the three sides were sealed with a laminate exterior to fabricate unfilled batteries. Subsequently, 700 μL of each electrolyte solution shown in Table 2 was added to one of the unsealed sides of the unfilled battery. After the electrolyte solution was injected, the battery was vacuum sealed to fabricate a 4.2 V, 30 mAh capacity lithium-ion secondary battery (cell).

(iv) Cell Aging Process Using a charge-discharge tester (manufactured by Asuka Electronics Co., Ltd., product number: ACD-01, the same applies hereinafter), the cell obtained in (iii) above was aged. Specifically, the cell was charged at a constant current (CC) of 0.1 C (3 mA) for 3 hours at room temperature (25°C, the same applies hereinafter), and then left at room temperature for 48 hours. After leaving the cell, the excess laminate was cleaved and the cell was vacuum-sealed to degas the cell. Furthermore, the cell was charged at a constant current/constant voltage (CCCV) of 4.2 V and 0.5 C (15 mA) at room temperature, and then CC discharged at 2.75 V and 0.2 C (6 mA). After the same CCCV charging, the cells were discharged at 2.75 V, 1 C (30 mA), and then discharged at 2.75 V, 2 C (60 mA), followed by a final CC discharge at 2.75 V, 0.2 C (6 mA). This was the aging process for the cells.

Using the obtained lithium ion secondary battery 1, the DCR increase rate, capacity retention rate, and low-temperature DCR were measured, and the results are shown in Table 2.

(Fabrication of lithium ion secondary battery 2: Examples 6-3, 11-3, 13-3, 16-2 to 18-2, Comparative Examples 3-3, 4-3, 7-3, 8-3, 10-3, 11-3, 14-3, 15-2)
(i) Preparation of Positive Electrode (LFP) LiFePO ₄ , an iron phosphate-based positive electrode active material, acetylene black as a conductive additive, and polyvinylidene fluoride (PVdF, manufactured by Kureha Corporation, product number: KF1120) as a binder were dispersed in N-methyl-2-pyrrolidone (NMP) to prepare a positive electrode mixture slurry (positive electrode active material: AB: PVdF = 87:8:5 (solid content mass ratio)). Subsequently, the obtained positive electrode mixture slurry was applied to one side of an aluminum foil (positive electrode current collector, manufactured by Nippon Foil Co., Ltd., thickness 15 μm) with an applicator so that the coating weight after drying was 20.0 mg/cm ² , and then dried on a hot plate at 110 ° C. for 10 minutes. Further, it was dried for 12 hours in a vacuum drying oven at 110 ° C. Thereafter, the mixture was press-molded using a roll press until the density reached 1.6 g/cm ³ , thereby obtaining a sheet-shaped positive electrode (thickness: 129 μm).

(ii) Preparation of negative electrode Graphite (natural graphite) as a negative electrode active material, fibrous graphite as a conductive aid, styrene-butadiene rubber (SBR, binder) and carboxymethyl cellulose (CMC, binder) as binders were dispersed in ultrapure water to prepare a negative electrode mixture slurry (negative electrode active material: fibrous graphite: SBR: CMC = 96: 2: 1: 1 (solid mass ratio)). Subsequently, the obtained negative electrode mixture slurry was applied to a copper foil (negative electrode current collector, manufactured by Fukuda Metal Foil and Powder Co., Ltd., thickness 15 μm) with an applicator to a single-sided coating weight of 8.7 mg / cm ² after drying, and dried on a hot plate at 80 ° C. for 10 minutes. Further, it was dried for 12 hours in a vacuum drying oven at 100 ° C. Then, it was pressure-molded using a roll press to a density of 1.2 g / cm ³ , thereby obtaining a sheet-shaped negative electrode (thickness 73 μm).

(iii) Fabrication of Lithium-Ion Secondary Battery The resulting positive and negative electrodes were cut, and the polarity leads were ultrasonically welded. The positive and negative electrodes were placed opposite each other via a 25 μm polyethylene (PE) separator, and the three sides were sealed with a laminate exterior to fabricate a non-filled battery. Subsequently, 700 μL of each electrolyte solution shown in Table 3 was added to one of the unsealed sides of the non-filled battery. After the electrolyte solution was injected, the battery was vacuum sealed to fabricate a 3.6 V, 21 mAh capacity lithium-ion secondary battery (cell) 2.

(iv) Cell Aging Process: The cell obtained in (iii) above was aged using a charge/discharge tester. Specifically, the cell was charged at 0.1 C (2.1 mA) for 3 hours at room temperature (25 ° C, the same applies below) and then left at room temperature for 48 hours. After leaving the cell, the excess laminate was cleaved and vacuum sealed to degas the cell. Furthermore, the cell was charged at 3.6 V, 0.1 C (2.1 mA) at room temperature using constant current constant voltage (CCCV), followed by CC discharge at 2.0 V, 0.2 C (4.2 mA). In addition, after CCCV charging at 3.6 V, 0.5 C (10.5 mA), CC discharging was performed at 2.00 V, 1 C (21 mA), and after similar CCCV charging, CC discharging was performed at 2.00 V, 2 C (42 mA), and finally CC discharging was performed at 2.0 V, 0.2 C (4.2 mA). This was the cell aging process.

Using the obtained lithium ion secondary battery 2, the DCR increase rate, capacity retention rate, and low-temperature DCR were measured, and the results are shown in Table 3.

From Tables 1 to 3, it was revealed that by adding the disilane compound represented by the formula (2) to a non-aqueous electrolyte containing a sulfonylimide compound represented by the formula (1) at a concentration of 0.1 mol/L or more, the electrolyte exhibited excellent stability when stored in a high-temperature environment and could suppress an increase in DCR. In particular, in Comparative Examples 2-2 and 4-2, when the concentration of the sulfonylimide compound represented by the formula (1) was 0.05 mol/L, the increase in DCR was not suppressed even when the disilane compound represented by the formula (2) was added. In contrast, in Examples 1-2 and 4-2, when the concentration of the sulfonylimide compound represented by the formula (1) was 0.1 mol/L or more, the increase in DCR was effectively suppressed by adding the disilane compound. From the above, it was revealed that the present invention has technical significance in that the concentration of the sulfonylimide compound represented by the formula (1) was 0.1 mol/L or more and the disilane compound represented by the formula (2) was used.

Claims (8)

The following formula (1):
M ¹ N(R ¹ SO ₂ )(R ² SO ₂ )(1)
(wherein ^M1 represents an alkali metal atom; ^R1 and ^R2 are the same or different and represent a fluorine atom, an alkyl group having 1 to 6 carbon atoms, or a fluoroalkyl group having 1 to 6 carbon atoms), with a sulfonylimide compound represented by the following formula (2);
(wherein R ³ to R ⁸ are the same or different and represent a hydrocarbon group having 1 to 14 carbon atoms which may have a heteroatom, a hydrogen atom, a hydroxyl group, or a halogen atom),
The non-aqueous electrolyte solution is characterized in that the concentration of the sulfonylimide compound is 0.1 mol/L or more. The nonaqueous electrolyte solution according to claim 1, characterized in that R ³ to R ⁸ in the formula (2) are the same or different and represent an alkyl group having 1 to 12 carbon atoms, an aryl group having 6 to 14 carbon atoms, an alkenyl group having 2 to 14 carbon atoms, an alkoxy group having 1 to 12 carbon atoms, an aryloxy group having 6 to 14 carbon atoms, a hydrogen atom, or a halogen atom. The nonaqueous electrolyte solution according to claim 1 or 2, characterized in that R ³ to R ⁸ in the formula (2) are the same or different and represent an alkyl group having 1 to 12 carbon atoms, an aryl group having 6 to 14 carbon atoms, an alkenyl group having 2 to 14 carbon atoms, a hydrogen atom, or a halogen atom. 3. The nonaqueous electrolyte solution according to claim 1, wherein R ³ to R ⁸ in the formula (2) are the same or different and each represent a methyl group, a hydrogen atom, or a halogen atom. 3. The non-aqueous electrolyte solution according to claim 1, wherein the content of the compound represented by formula (2) is 0.05% by mass or more and less than 5.0% by mass, relative to 100% by mass of the non-aqueous electrolyte solution. _3. ^The _nonaqueous electrolyte _solution according to claim 1, further comprising at least one selected from the group consisting _of ^M2PF6 , ^M2BF4 , _M2PO2F2 and ^M2FSO3 ( ^M2 represents an alkali metal atom). A battery comprising the nonaqueous electrolyte solution according to claim 1 or 2 . The battery has the following formula (3):
_{LiNixCoyMnzO2 ( 3 )}
(wherein x, y, and z are numbers satisfying x + y + z = 1, 0 ≦ x ≦ 1, 0 ≦ y ≦ 1, 0 ≦ z ≦ 1), and/or a positive electrode containing _LiFePO4 .