Non-aqueous electrolyte and battery

Abstract

The purpose of the present invention is to provide a nonaqueous electrolyte that contains a sulfonylimide compound having excellent storage stability in a high-temperature environment. The present invention is a nonaqueous electrolyte characterized by containing a sulfonylimide compound represented by M1N(R1SO2)(R2SO2) (formula 1) (where M1 represents an alkali metal atom, R1 and R2 are the same or different, and represent a fluorine atom, a C1–6 alkyl group, or a C1–6 fluoroalkyl group), and a compound represented by formula (2) (where: R3 to R5 are the same or different, and represent a C1–14 hydrocarbon group, a hydrogen atom, or a halogen atom; and n represents an integer of 2–6).

Description

[Technical Field]

[0001] The present invention relates to a non-aqueous electrolyte and a battery, and more particularly 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. [Background technology]

[0002] 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, and this has led to an increase in the importance of batteries, with demand expected to grow accordingly. 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. Lithium-ion batteries, which offer high capacity and are lightweight, are particularly expected to see increased use in the future, and are the type of secondary battery that is most actively researched and developed.

[0003] 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 for a nonaqueous electrolyte secondary battery having a positive electrode and a negative electrode capable of absorbing and releasing metal ions, the nonaqueous electrolyte solution containing a compound represented by a predetermined formula together with an electrolyte and a nonaqueous solvent. Patent Document 2 discloses a non-aqueous organic electrolyte containing a lithium salt, a non-aqueous organic solvent, and a non-aqueous organic electrolyte additive, wherein the non-aqueous organic electrolyte additive is a mixture of non-aqueous organic electrolyte additives represented by predetermined formulas (I) to (III). Patent Document 3 discloses an electrolyte solution for a lithium ion secondary battery containing a lithium salt of sulfonimide and water, the electrolyte solution containing at least one anion selected from the group consisting of an anion generated by dissociation of an orthophosphate ion, a pyrophosphate ion, phosphorous acid, or a salt thereof, and an anion generated by dissociation of a phosphinic acid or a salt thereof. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-168443 [Patent Document 2] Chinese Patent No. 103972586 [Patent Document 3] U.S. Patent No. 11,069,922 Summary of the Invention [Problem to be solved by the invention]

[0005] As described above, although various techniques for improving the performance of an electrolyte solution have been reported, there is no description about the stability of the electrolyte solution when stored in a high-temperature environment. The present inventors have discovered a new problem that the sulfonylimide compound decomposes when a non-aqueous electrolyte solution containing the sulfonylimide compound is stored in a high-temperature environment.

[0006] The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a non-aqueous electrolyte solution containing a sulfonylimide compound that has excellent storage stability in a high-temperature environment. [Means for solving the problem]

[0007] The present inventors have conducted extensive research into non-aqueous electrolyte solutions containing sulfonylimide compounds and have found that by combining a sulfonylimide compound having a predetermined structure with a phosphate ester having a predetermined structure, the non-aqueous electrolyte solution has excellent stability even when stored in a high-temperature environment. This has led to the realization that the above-mentioned problems can be solved in an excellent manner, and has led to the present invention.

[0008] The present invention encompasses the following nonaqueous electrolytes and the like. [1] The following formula (1); M 1 N(R 1 SO2)(R 2 SO2)(1) (In the formula, M 1 represents an alkali metal atom. 1 and R 2 and 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, and a sulfonylimide compound represented by the following formula (2); [ka] (In the formula, R 3 ~R 5 are the same or different and represent a hydrocarbon group having 1 to 14 carbon atoms, a hydrogen atom, or a halogen atom, and n represents an integer of 2 to 6. [2] R in the above formula (2) 3 ~R 5 and are the same or different and are an alkyl group having 1 to 12 carbon atoms, an aryl 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 n in the formula (2) above is 2. [4] R in the above formula (2) 3 ~R 5 and are the same or different and are an aryl group having 6 to 14 carbon atoms. [5] The nonaqueous electrolyte solution according to any one of the above [1] to [4], which has a water concentration of 1000 ppm or less. [6] The nonaqueous electrolyte solution according to any one of the above [1] to [5], which has a water concentration of 100 ppm or less. [7] The non-aqueous electrolyte solution according to any one of [1] to [6] above, wherein the content of the compound represented by the formula (2) above 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. [8] Furthermore, M 2 PF6, M 2 BF4, M 2 PO2F2 and M 2 FSO3(M 2 represents an alkali metal atom.) The nonaqueous electrolyte solution according to any one of [1] to [7] above, which contains at least one selected from the group consisting of: [9] A battery comprising the nonaqueous electrolyte solution according to any one of [1] to [8] above.

[10] The battery has the following formula (3); LiNi x Co y Mn z O2(3) (wherein x, y, and z are numbers satisfying x+y+z=1, 0≦x≦1, 0≦y≦1, and 0≦z≦1) and / or a positive electrode containing LiFePO4. The battery according to [9] above. [Effects of the Invention]

[0009] The nonaqueous electrolyte solution of the present invention has the above-mentioned constitution and is excellent in stability when stored in a high-temperature environment, and therefore can be suitably used as a battery material for lithium-ion batteries and the like. DETAILED DESCRIPTION OF THE INVENTION

[0010] Preferred embodiments of the present invention will be specifically described below, but the present invention is not limited to the following description and can be appropriately modified and applied within the scope of the present invention. Note that combinations of two or more of the individual preferred embodiments of the present invention described below also fall within the scope of preferred embodiments of the present invention.

[0011] 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 phosphate ester represented by the above formula (2) (hereinafter also simply referred to as a phosphate ester). By combining the sulfonylimide compound with the phosphate ester, decomposition of the sulfonylimide compound is suppressed even when the nonaqueous electrolyte is stored in a high-temperature environment, resulting in excellent storage stability. If decomposition of the sulfonylimide compound progresses, battery characteristics may deteriorate due to an increase in direct current resistance (DCR) during repeated charging, a decrease in capacity retention, an increase in initial interface resistance, etc. However, a battery using such a nonaqueous electrolyte has reduced interface resistance and is excellent in DCR increase rate and capacity retention rate.

[0012] In the non-aqueous electrolyte, the concentration of the sulfonylimide compound is not particularly limited, but is preferably 0.1 to 6.0 mol / L. This allows the effects of the present invention to be more fully exhibited. The concentration is more preferably 0.2 to 3.0 mol / L, even more preferably 0.4 to 2.0 mol / L, even more preferably 0.6 to 2.0 mol / L, and particularly preferably 0.8 to 2.0 mol / L.

[0013] The concentration of the sulfonylimide compound is preferably 0.1 to 6.0 mol / kg, more preferably 0.2 to 3.0 mol / kg, even more preferably 0.4 to 2.0 mol / kg, still more preferably 0.6 to 2.0 mol / kg, and particularly preferably 0.8 to 2.0 mol / kg.

[0014] The content of the phosphate ester in the non-aqueous 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 non-aqueous electrolyte. This not only provides the excellent storage stability of the non-aqueous electrolyte, but also further reduces the interfacial resistance in the battery, thereby further improving the DCR increase rate and capacity retention rate. The content of the phosphate ester 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. do.

[0015] 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.

[0016] 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.

[0017] 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. The amount is more preferably 10 to 95 mol %, even more preferably 20 to 90 mol %, even more preferably 30 to 85 mol %, still more preferably 40 to 85 mol %, particularly preferably 50 to 85 mol %, and especially more 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.

[0018] 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.

[0019] The proportion of the non-aqueous solvent in the non-aqueous electrolytic solution is not particularly limited, but is preferably 100 to 5000 parts by mass, more preferably 150 to 2500 parts by mass, and even more preferably 200 to 2000 parts by mass, per 100 parts by mass of the electrolyte (the sulfonylimide compound and other alkali metal salts).

[0020] The non-aqueous electrolyte may contain other components other than the sulfonylimide compound, the phosphate ester, an alkali metal salt other than the sulfonylimide compound, and a solvent. The content of 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 non-aqueous electrolyte.

[0021] The essential components and optional components contained in the nonaqueous electrolyte solution of the present invention will be further described below. <Sulfonylimide compounds> The sulfonylimide compound is represented by the following formula (1): M 1 N(R 1 SO2)(R 2 SO2)(1) (In the formula, M 1 represents an alkali metal atom. 1 and R 2 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.

[0022] The above M 1 The alkali metal in the formula (I) includes lithium, sodium, potassium, rubidium, cesium, and francium. Preferred are lithium, sodium, and potassium, and more preferred is lithium.

[0023] Above R 1 Examples of the alkyl group having 1 to 6 carbon atoms in the formula (I) include linear alkyl groups such as methyl, ethyl, n-propyl, n-butyl, n-pentyl (amyl), and n-hexyl; branched 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, linear alkyl groups are preferred.

[0024] Above R 1 and R 2 The alkyl group preferably has 1 to 4 carbon atoms, more preferably 1 to 3 carbon atoms, and even more preferably 1 to 2 carbon atoms.

[0025] Above R 1 and R 2 The fluoroalkyl group having 1 to 6 carbon atoms may be an alkyl group having 1 to 6 carbon atoms in which at least some of the hydrogen atoms bonded to 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.

[0026] Above R 1 and R 2 The fluoroalkyl group preferably has 1 to 4 carbon atoms, more preferably 1 to 3 carbon atoms, and even more preferably 1 to 2 carbon atoms.

[0027] Above R 1 and R 2 is preferably a fluorine atom, a trifluoromethyl group, or a pentafluoroethyl group, more preferably a fluorine atom, and 1 and R 2 It is preferable that at least one of R is a fluorine atom. 1 and R 2 An embodiment in which both of are fluorine atoms is one of the preferred embodiments of the present invention.

[0028] 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, sodium bis(trifluoromethylsulfonyl)imide, and the like. 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.

[0029] <Phosphate ester> The phosphate ester is represented by the following formula (2):

[0030] [ka]

[0031] (In the formula, R 3 ~R 5 are the same or different and represent a hydrocarbon group having 1 to 14 carbon atoms, a hydrogen atom, or a halogen atom, and n represents an integer of 2 to 6.

[0032] Above R 3 ~R 5 Examples of the hydrocarbon group having 1 to 14 carbon atoms 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.

[0033] Examples of the aliphatic alkyl group having 1 to 14 carbon atoms include a methyl group, an ethyl group, an n-propyl group, an n-butyl group, an n-pentyl group (an amyl group), an n-hexyl group, an n-heptyl group, an n-octyl group, an n-nonyl group, an n-decyl group, an n-undecyl group, an n-dodecyl group, an n-tridecyl group, an n-tetradecyl group, an i-propyl group, a sec-butyl group, an i-butyl group, a t-butyl group, a 1-methylbutyl group, a 1-ethylpropyl group, a 2-methylbutyl group, an 1-ethylpropyl group, an 1 ... Examples of such groups include an aryl 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.

[0034] 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.

[0035] 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.

[0036] Examples of the alkynyl group having 2 to 14 carbon atoms include an ethynyl group, a 1-propynyl group, a 2-propynyl group, a butynyl group, a pentynyl group, a hexynyl group, a heptynyl group, an octynyl group, a nonynyl group, a decynyl group, a dodecynyl group, and a tetradecynyl group.

[0037] 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=CHCH2- group), etc. Preferred are a phenyl group and a benzyl group.

[0038] The alkyl group preferably has 1 to 10 carbon atoms, more preferably 1 to 8 carbon atoms, and even more preferably 1 to 4 carbon atoms. The alkenyl group and alkynyl group preferably have 2 to 10 carbon atoms, more preferably 2 to 8 carbon atoms, and even more preferably 2 to 4 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.

[0039] Above R 3 ~R 5 Examples of the halogen atom in include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom.

[0040] Above R 3 ~R 5 is preferably an alkyl group having 1 to 14 carbon atoms or an aryl group having 6 to 14 carbon atoms, and more preferably an aryl group having 6 to 14 carbon atoms.

[0041] Specific examples of the phosphate ester include tetramethyl pyrophosphate, tetraethyl pyrophosphate, tetrapropyl pyrophosphate, tetrabutyl pyrophosphate, tetravinyl pyrophosphate, tetraallyl pyrophosphate, tetraphenyl pyrophosphate, tetrabenzyl pyrophosphate, etc. Among these, tetraethyl pyrophosphate, tetraphenyl pyrophosphate, and tetrabenzyl pyrophosphate are preferred, tetraphenyl pyrophosphate and tetrabenzyl pyrophosphate are more preferred, and tetrabenzyl pyrophosphate is particularly preferred.

[0042] <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 LiPF6 and LiPO2F2; alkali metal salts of fluorosulfonic acids such as LiFSO3; alkali metal salts of trifluoromethanesulfonic acids such as LiCF3SO3; alkali metal salts of perfluoroalkanesulfonylmethides such as LiC(CF3SO2)3; LiPF a (C m F 2m+1 ) 6-a Fluorophosphates such as (0≦a≦6, 1≦m≦2); alkali metal perchlorates such as LiClO4; LiBF b (C n F 2n+1 ) 4-b (0≦b≦4, 1≦n≦2) and other fluoroborates; alkali metal salts of oxalatoborates such as LiBOB; cyanoborates such as lithium tetracyanoborate; and alkali metal salts such as LiAsF6, LiI, and LiSbF6.

[0043] Other alkali metal salts are preferably M 2 PF6, M 2 BF4, M 2 PO2F2 or M 2 FSO3(M 2 represents an alkali metal atom.) and M 2 PF6, M 2 BF4, M 2 PO2F2 and M 2 The embodiment containing at least one selected from the group consisting of FSO3 is one of the preferred embodiments of the present invention. 2 It is PF6. Specific examples and preferred forms of the alkali metal atom are the same as those of the alkali metal atom in the sulfonylimide compound.

[0044] <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 phosphate ester, 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. Examples of suitable non-aqueous solvents include ethers 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 non-aqueous solvents may be used in combination of two or more. Among these, chain carbonates such as dimethyl carbonate, diethyl carbonate, and ethylmethyl carbonate are preferred.

[0045] <Other ingredients> The other components in the non-aqueous electrolyte solution of the present invention are components other than the sulfonylimide compound, the phosphate ester, 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 and difluorophosphates; and hydrocarbon compounds such as heptane, octane, and cycloheptane.

[0046] 2.Battery The nonaqueous electrolyte solution of the present invention has the above-mentioned constitution and is excellent in stability 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.

[0047] The shape of the battery according to the present invention is not particularly limited, and any of the conventionally known shapes of batteries 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., the battery can also be made into a battery module consisting of individual batteries connected in series.

[0048] The battery is preferably an alkali metal battery, and an alkali metal battery comprising the nonaqueous electrolyte solution of the present invention also constitutes one aspect of the present invention. The battery is more preferably a secondary battery, and a preferred embodiment of the present invention is one in which the battery is a lithium ion secondary battery.

[0049] The positive electrode constituting the battery is not particularly limited, but is 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 is usually formed into a sheet shape.

[0050] Examples of methods for producing a positive electrode include a method in which a positive electrode active material composition is applied to a positive electrode current collector by a doctor blade method or the like, or the positive electrode current collector is immersed in a positive electrode active material composition and then dried; a method in which a sheet obtained by kneading and molding a positive electrode active material composition and drying it is bonded to a positive electrode current collector via a conductive adhesive, followed by pressing and drying; and a method in which a positive electrode active material composition to which a liquid lubricant has been added is applied or cast onto a positive electrode current collector, molded into a desired shape, the liquid lubricant is removed, and then the composition is stretched in uniaxial or multiaxial directions.

[0051] The material for the positive electrode current collector is not particularly limited, and may be, for example, a conductive metal such as aluminum, an aluminum alloy, SUS (stainless steel), titanium, etc. Among these, aluminum is preferred from the viewpoints of ease of processing into a thin film and low cost.

[0052] 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. 3 CoO2, M3 NiO₂, M 3 MnO₂, M 3 Ni x Co y Mn z O₂ or M 3 Ni x Co y Al z Composite metal oxides such as ternary system oxides represented by O₂ (where x, y, z are numbers satisfying x + y + z = 1, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1), M 3 p Ni q Mn (2-q) Nickel manganate represented by O₄ (0.9 ≤ p ≤ 1.1, 0 < q < 1), M 3 Compounds having an olivine structure such as APO₄ (A = Fe, Mn, Ni, Co), solid solution materials incorporating a plurality of transition metals (electrochemically inert layered M 3 2MnO₃ and electrochemically active layered M 3 Solid solution with M”O ([M” is a transition metal such as Co, Ni]) (M 3 represents an alkali metal ion)) etc. can be exemplified as the positive electrode active material. These positive electrode active materials may be used alone or in combination of a plurality of them. As the positive electrode active material, the following formula (3); LiNi x Co y Mn z O₂(3) (In the formula, x, y, z are numbers satisfying x + y + z = 1, 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, 0 ≤ z ≤ 1.) The composite metal oxide represented by and / or LiFePO₄ is preferable. A battery configured with a positive electrode containing such a positive electrode active material is one of the preferred embodiments of the present invention.

[0053] Examples of the conductive assistant include acetylene black, carbon black, graphite, metal powder materials, single-walled carbon nanotubes, multi-walled carbon nanotubes, vapor-phase carbon fibers, etc.

[0054] 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; and cellulose-based resins such as carboxymethyl cellulose. These binders may be used alone or in combination. These binders may be dissolved in a solvent or dispersed in a solvent when used.

[0055] The amounts of the conductive additive and binder to be blended can be adjusted appropriately in consideration of the intended use of the battery (emphasis on output, emphasis on energy, etc.), ion conductivity, and the like.

[0056] When producing a positive electrode, examples of solvents used in the positive electrode active material composition include N-methylpyrrolidone, dimethylformamide, dimethylacetamide, methyl ethyl ketone, tetrahydrofuran, acetonitrile, acetone, ethanol, ethyl acetate, and water. These solvents may be used in combination. The amount of solvent used is not particularly limited and may be determined appropriately depending on the production method and materials used.

[0057] The negative electrode constituting the battery is not particularly limited, but is a negative electrode active material composition containing a negative electrode active material, a dispersion solvent, a binder, and, if necessary, a conductive additive, etc., supported on a negative electrode current collector, and is usually formed into a sheet shape.

[0058] The material of the negative electrode current collector can be a conductive metal such as copper, iron, nickel, silver, stainless steel (SUS), etc. Copper is preferred from the viewpoint of ease of processing into a thin film.

[0059] The negative electrode active material may be any conventionally known negative electrode active material used in batteries, as long as it is capable of absorbing and releasing ions. Specifically, examples of the negative electrode active material include 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.

[0060] The negative electrode can be manufactured by the same method as the positive electrode, and the conductive additive, binder, and material dispersion solvent used in manufacturing the negative electrode are also the same as those used in manufacturing the positive electrode.

[0061] 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.

[0062] Examples of the material for the porous sheet include polyethylene, polypropylene, and a laminate having a three-layer structure of polypropylene / polyethylene / polypropylene.

[0063] Examples of materials for the nonwoven fabric separator include cotton, rayon, acetate, nylon, polyester, polypropylene, polyethylene, polyimide, aramid, and glass. Depending on the mechanical strength required of the nonaqueous electrolyte layer, the above-exemplified materials can be used alone or in combination. [Example]

[0064] The present invention will be described 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."

[0065] The physical properties of the non-aqueous electrolyte and the battery characteristics were evaluated as follows. (Measurement of water content of non-aqueous electrolyte) The water content of the non-aqueous electrolyte was measured using a Karl Fischer moisture content analyzer AQ-2000 (manufactured by Hiranuma Sangyo Co., Ltd.) and using Aqualite RS-A (manufactured by Hiranuma Sangyo Co., Ltd.) as the generating liquid and Aqualite CN (manufactured by Hiranuma Sangyo Co., Ltd.) as the counter electrode liquid.

[0066] (Evaluation of storage stability of non-aqueous electrolyte) 10 ml of non-aqueous electrolyte was placed in a PFA (fluorine-based resin) container, the PFA container was sealed, wrapped in aluminum laminate zip, and stored in a thermostatic chamber set at 60°C for a given period of time. After storage, the electrolyte was diluted 100 times with ultrapure water and subjected to ion chromatography as follows to measure sulfate ions (SO4 2- The storage stability was evaluated based on the sulfate ion concentration relative to the sulfate ion concentration in the electrolyte solution containing no added phosphate ester, which was set at 100. (Ion chromatography measurement) The non-aqueous electrolyte was diluted 100 times with ultrapure water to prepare a measurement solution, and the sulfate ions (SO4 2- ) concentration was measured. Measurement conditions Separation mode: Ion exchange Eluent: 7-18mM KOH aqueous solution Detector: Electrical conductivity detector Column: Anion analysis column Ion PAC AS-17C (manufactured by Nippon Dionex Co., Ltd.)

[0067] (Evaluation of interface resistance) The aged lithium-ion secondary battery (cell) was CC-charged at room temperature for 30 minutes at 1C (30mA). The cell was then transferred to a -30°C thermostatic chamber and fully regulated. Then, impedance measurements were performed using an impedance analyzer (Bio Logic, product number: VSP-300) at frequencies from 1GHz to 1mHz. The interfacial resistance was calculated from the frequency at which the arcs of the measured values ​​diverged. The frequency at which the arcs diverged was the frequency at which the imaginary axis value reached a minimum between 10Hz and 0.001Hz.

[0068] (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 left for another 30 minutes, after which it was CC discharged at 3 C (90 mA) for 10 seconds. The discharge current was plotted on the horizontal axis, and the difference in closed-circuit voltage (ΔV) 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) Cycle charge / discharge After DCR measurement, the cell was subjected to CCCV charging 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). Next, CCCV charging at 4.2 V, 1 C (30 mA) was performed, 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 at 500 cycles was calculated using the following formula (4): 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 (5). Capacity retention rate (%) = 500th 1C discharge capacity / 1st 1C discharge capacity × 100 (4) DCR increase rate (%) = DCR after cycle charging / discharging / DCR after aging × 100 (5)

[0069] (Preparation of Electrolyte Solutions: Examples 1 to 33, Comparative Examples 1 to 33) Non-aqueous electrolyte solutions (hereinafter simply referred to as "electrolytes") with various salt concentrations were prepared by dissolving an electrolyte salt having a simple salt composition containing only LiFSI (manufactured by Nippon Shokubai Co., Ltd.), an electrolyte salt having a mixed salt composition containing LiFSI and LiPF6 (manufactured by Stella Chemifa Corporation), or an electrolyte salt having a simple salt composition containing only LiPF6 in a mixed solvent (manufactured by Kishida Chemical Co., Ltd.) having an ethylene carbonate (EC):ethyl methyl carbonate (EMC) = 3:7 (volume ratio). To some of the electrolyte solutions, phosphate ester was further added to obtain the concentrations shown in Tables 1 and 2 to prepare nonaqueous electrolyte solutions. In addition, ultrapure water (over 18.2 Ω cm) was added to each of the prepared electrolyte solutions to prepare nonaqueous electrolyte solutions with the water contents shown in Tables 1 to 4. The phosphate esters used in the preparation of the non-aqueous electrolyte solution are as follows: TBP: tribenzyl phosphate TEPP: tetraethyl pyrophosphate TPPP: tetraphenyl pyrophosphate TBPP: Tetrabenzyl pyrophosphate

[0070] The water content of the obtained non-aqueous electrolyte solution was measured, and the stability of the electrolyte solution was evaluated after storage for 3 months and 6 months at 60° C. The results are shown in Tables 1 to 4.

[0071] (Fabrication of lithium-ion secondary battery 1) (i) Preparation of the positive electrode (NMC111) LiNi, a ternary positive electrode active material 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (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 composite slurry (positive electrode active material: AB: graphite: PVdF = 93:2:2:3 (solid mass ratio)). Subsequently, the obtained positive electrode composite slurry was applied to an aluminum foil (positive electrode current collector, manufactured by Nippon Foil Co., Ltd., thickness 15 μm) so that the coating weight after drying was 19.4 mg / cm.2 The mixture was coated on one side with an applicator so that the density was 3.1 g / cm , and then dried on a hot plate at 110°C for 10 minutes. It was then dried in a vacuum drying oven at 110°C for 12 hours. The density was then adjusted to 3.1 g / cm using a roll press. 3 The mixture was pressed into a sheet-like positive electrode (thickness: 83 μm) by molding until the sheet reached the desired thickness.

[0072] (ii) Preparation of the negative electrode Graphite (natural graphite), styrene-butadiene rubber (SBR, binder), and carboxymethyl cellulose (CMC, binder) were dispersed in ultrapure water to prepare a negative electrode composite slurry (negative electrode active material: SBR: CMC = 97.3: 1.5: 1.2 (solid mass ratio)). The resulting negative electrode composite slurry was then applied to a copper foil (negative electrode current collector, manufactured by Fukuda Metal Foil & Powder Co., Ltd., thickness 15 μm) so that the coating weight after drying was 9.8 mg / cm. 2 The mixture was coated on one side with an applicator so that the density was 1.3 g / cm , and then dried on a hot plate at 80°C for 10 minutes. It was then dried in a vacuum drying oven at 100°C for 12 hours. The mixture was then pressed with a roll press to a density of 1.3 g / cm . 3 The mixture was pressed and molded until a sheet-like negative electrode (thickness: 113 μm) was obtained.

[0073] (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 with a 25 μm polyethylene (PE) separator interposed therebetween, and the three sides were sealed with a laminate exterior to produce a non-filled battery. Subsequently, 700 μL of each electrolyte solution of the Examples or Comparative Examples was added to one of the unsealed sides of the non-filled battery. After the electrolyte solution was poured, the battery was vacuum sealed to produce a 4.2 V, 30 mAh lithium-ion secondary battery (cell) 1.

[0074] (iv) Cell aging process The cell obtained in (iii) above was aged using a charge-discharge tester (ASKA Electronics Co., Ltd., product number: ACD-01, hereinafter the same). Specifically, the cell was charged at 0.1 C (3 mA) for 3 hours at room temperature (25°C, hereinafter the same) 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. The cell was then charged at 4.2 V, 0.5 C (15 mA) at room temperature, followed by CC discharge at 2.75 V, 0.2 C (6 mA). After the same CCCV charge, the cell was CC discharged at 2.75 V, 1 C (30 mA). After the same CCCV charge, the cell was CC discharged at 2.75 V, 2 C (60 mA), and finally CC discharged at 2.75 V, 0.2 C (6 mA). This constituted the cell aging process.

[0075] (Fabrication of lithium ion secondary battery 2) (i) Preparation of the positive electrode (LFP) A cathode mixture slurry (cathode active material: AB: graphite powder: PVdF = 89:3:3:5 (solid mass ratio)) was prepared by dispersing LiFePO4, an iron phosphate cathode active material, acetylene black and graphite powder (manufactured by Nippon Graphite Industries Co., Ltd., product number SP270) as conductive additives, and polyvinylidene fluoride (PVdF, manufactured by Kureha Corporation, product number KF1120) as a binder in N-methyl-2-pyrrolidone (NMP). The resulting cathode mixture slurry was then applied to a carbon-coated aluminum foil (cathode current collector, manufactured by Nippon Graphite Industries Co., Ltd., thickness 20 μm) so that the coating weight after drying was 17.6 mg / cm. 2 The mixture was coated on one side with an applicator so that the density was 1.6 g / cm , and then dried on a hot plate at 110°C for 10 minutes. It was then dried in a vacuum drying oven at 110°C for 12 hours. The resulting mixture was then pressed with a roll press to a density of 1.6 g / cm . 3 The mixture was press-molded until a sheet-like positive electrode (thickness: 111 μm) was obtained.

[0076] (ii) Preparation of the negative electrode Graphite (natural graphite) as the negative electrode active material, fibrous graphite as the conductive additive, and styrene-butadiene rubber (SBR, binder) and carboxymethyl cellulose (CMC, binder) as binders were dispersed in ultrapure water to prepare a negative electrode composite slurry (negative electrode active material: fibrous graphite: SBR: CMC = 96:2:1:1 (solid mass ratio)). The resulting negative electrode composite slurry was then applied to a copper foil (negative electrode current collector, manufactured by Fukuda Metal Foil & Powder Co., Ltd., thickness 15 μm) so that the coating weight after drying was 8.0 mg / cm. 2 The mixture was coated on one side with an applicator so that the density was 1.2 g / cm , and then dried on a hot plate at 80°C for 10 minutes. It was then dried in a vacuum drying oven at 100°C for 12 hours. The mixture was then pressed with a roll press to a density of 1.2 g / cm . 3 The mixture was pressed until a sheet-like negative electrode (thickness: 65 μm) was obtained.

[0077] (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 with a 25 μm polyethylene (PE) separator interposed therebetween, and the three sides were sealed with a laminate exterior to produce a non-filled battery. Subsequently, 700 μL of each electrolyte solution of the Examples or Comparative Examples was added to one of the unsealed sides of the non-filled battery. After the electrolyte solution was poured into the non-filled battery, the battery was vacuum sealed to produce a 3.6 V, 21 mAh capacity lithium-ion secondary battery (cell) 2.

[0078] (iv) Cell aging process The cell obtained in (iii) above was aged using a charge-discharge tester. Specifically, it was charged at 0.1 C (2.1 mA) for 3 hours at room temperature (25°C, hereinafter the same) and then left at room temperature for 48 hours. After leaving it, the excess laminate was cleaved and the cell was vacuum-sealed to degas it. It was then charged at 3.6 V and 0.1 C (2.1 mA) at room temperature, followed by CC discharge at 2.0 V and 0.2 C (4.2 mA). It was also charged at 3.6 V and 0.5 C (10.5 mA) and then CC discharged at 2.00 V and 1 C (21 mA). After the same CCCV charge, it was CC discharged at 2.00 V and 2 C (42 mA), and finally CC discharged at 2.0 V and 0.2 C (4.2 mA). This constituted the cell aging process.

[0079] The resulting lithium ion secondary batteries 1 and 2 were used to measure the interface resistance, DCR increase rate, and capacity retention rate. The results are shown in Tables 1 to 4.

[0080] [Table 1]

[0081] [Table 2]

[0082] [Table 3]

[0083] [Table 4]

[0084] Tables 1 to 4 reveal that adding the phosphate ester represented by the formula (2) to a non-aqueous electrolyte solution containing the sulfonylimide compound represented by the formula (1) above provides excellent stability when stored in a high-temperature environment.

[0085] (Consideration) (Storage stability of electrolyte) Compared with electrolytes that do not contain the phosphate ester represented by formula (2) (e.g., electrolyte 48), electrolytes containing the phosphate esters (e.g., electrolytes 2, 6, 10, 18, 21, 24, 30, 33, and 36) contained fewer sulfate ions, suppressing electrolyte decomposition. This trend remained unchanged regardless of the type or amount of compound added, as long as the phosphate esters satisfied formula (2). However, electrolytes containing TBP, a monomer of the phosphate ester (e.g., electrolytes 14, 27, and 39), showed almost no reduction in sulfate ions. Therefore, it is speculated that the condensed phosphate structure in the phosphate esters is an important factor in the development of this effect.

[0086] (NMC111 series) (Evaluation of interface resistance) When the phosphate ester represented by the above formula (2) was added to the TBP monomer, which does not satisfy the requirements of the above formula (2), the interfacial resistance was low and the impedance was reduced. As with the storage stability of the electrolyte, this tendency remains the same regardless of the type or amount of compound added, as long as the phosphate ester satisfies the formula (2).

[0087] (Capacity retention rate during cycle charging and discharging) When the phosphate ester represented by the above formula (2) was added to the TBP monomer, which does not satisfy the requirements of the above formula (2), the capacity retention rate was high and the battery life was improved. As with the storage stability of the electrolyte, this tendency remains the same regardless of the type or amount of compound added, as long as the phosphate ester satisfies the formula (2).

[0088] (DCR increase rate) When the phosphate ester represented by the formula (2) was added to the TBP monomer, which does not satisfy the requirements of the formula (2), the DCR increase rate was small and the increase in resistance during cycle charging and discharging was suppressed. Similar to the storage stability of the electrolyte, this tendency remains the same regardless of the type or amount of compound added, as long as the phosphate ester satisfies the formula (2).

[0089] (LFP series) (Evaluation of interface resistance) The addition of the phosphate ester represented by the above formula (2) resulted in a low interfacial resistance and reduced impedance. This tendency remained the same even when the amount of phosphate ester added was changed, just like the storage stability of the electrolyte solution.

[0090] (Capacity retention rate during cycle charging and discharging) The addition of the phosphate ester represented by the above formula (2) resulted in a high capacity retention rate and improved battery life. This tendency was the same even when the amount of phosphate ester added was changed, as was the case with the storage stability of the electrolyte solution.

[0091] (DCR increase rate) The addition of the phosphate ester represented by the above formula (2) resulted in a small increase in DCR and suppressed the increase in resistance during cycle charging and discharging. This tendency remained the same even when the amount of phosphate ester added was changed, just like the storage stability of the electrolyte solution.

[0092] (summary) From the above results, it was confirmed that the storage stability of the electrolyte solution was improved by adding the phosphate ester represented by the above formula (2) to the electrolyte solution containing LiFSI. Furthermore, it was confirmed that the battery performance of the lithium ion secondary battery using this electrolyte solution was improved in terms of reduced interfacial resistance, improved capacity retention during cycle charging and discharging, and reduced DCR increase rate.

Claims

1. The following formula (1): M １ N(R １ SO ２ )(R ２ SO ２ )(1) (In the formula, M １ represents an alkali metal atom. １ and R ２ and 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, 【Chemical 1】 (In the formula, R ３ ~R ５ are the same or different and represent a hydrocarbon group having 1 to 14 carbon atoms, a hydrogen atom, or a halogen atom; and n represents an integer of 2 to 6.

2. R in the formula (2) ３ ~R ５ and are the same or different and are an alkyl group having 1 to 12 carbon atoms, an aryl group having 6 to 14 carbon atoms, a hydrogen atom, or a halogen atom.

3. 3. The nonaqueous electrolyte solution according to claim 1, wherein n in the formula (2) is 2.

4. R in the formula (2) ３ ~R ５ and are the same or different and are aryl groups having 6 to 14 carbon atoms.

5. 3. The nonaqueous electrolyte according to claim 1, wherein the water concentration is 1000 ppm or less.

6. 3. The nonaqueous electrolyte according to claim 1, wherein the water concentration is 100 ppm or less.

7. 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.

8. Furthermore, M ２ PF ６ , M ２ BF ４ , M ２ P.O. ２ F ２ and M ２ FSO ３ (M ２ 3. The nonaqueous electrolyte solution according to claim 1, further comprising at least one selected from the group consisting of:

9. A battery comprising the nonaqueous electrolyte solution according to claim 1 or 2.

10. The battery has the following formula (3): L)) ｘ Co ｙ Mn ｚ O ２ (3) (wherein x, y, and z are numbers satisfying x+y+z=1, 0≦x≦1, 0≦y≦1, and 0≦z≦1) and / or LiFePO ４ 10. The battery of claim 9, comprising a positive electrode comprising:

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