Non-aqueous electrolyte solution

Abstract

A non-aqueous electrolyte solution characterized by including: a sulfonyl imide compound that is represented by general formula (1), LiN(RSO2)(FSO2) (where R is a fluorine atom, a C1-6 alkyl group, or a C1-6 fluoroalkyl group); and at least one nitrogen-containing compound selected from the group consisting of amide compounds having a C3-6 branched or linear alkyl group and nitrile compounds having a C3-6 branched or linear alkyl group, wherein the nitrogen-containing compound content relative to the sulfonyl imide compound is 10 ppm by mass to 6000 ppm by mass, inclusive.

Description

non-aqueous electrolyte

[0001] The present disclosure relates to non-aqueous electrolytes.

[0002] In order to improve the performance of secondary batteries such as lithium ion secondary batteries, various non-aqueous electrolyte solutions and materials thereof have been investigated. Based on the results of previous investigations, the present applicant has found that lithium bis(fluorosulfonyl)imide (LiN(FSO ２ ) ２ It has been found that a non-aqueous electrolyte containing a sulfonylimide compound such as methyl methyl acrylate improves the high-temperature durability and the battery performance such as charge-discharge cycle performance of a lithium ion secondary battery.

[0003] For example, in Patent Document 1, the present applicant has proposed a method for manufacturing a lithium nitride battery using LiN(FSO ２ ) ２ and at least one additive selected from the group consisting of a silicon atom-containing compound, a boron atom-containing compound, a carbon atom-containing compound, a sulfur atom-containing compound, and a phosphorus atom-containing compound. This sulfonylimide compound-containing nonaqueous electrolyte suppresses battery self-discharge by using a specific compound, and reduces charge transfer resistance (impedance) and battery direct current resistance (DCR), thereby improving battery performance.

[0004] International Publication No. 2022 / 239807

[0005] However, in a non-aqueous electrolyte solution containing a sulfonylimide compound, depending on the type of additive and its content, the resistance of a secondary battery containing the same may increase, and the battery performance may actually decrease, compared to a non-aqueous electrolyte solution containing no additive.

[0006] Here, in a secondary battery, three types of resistance affect the battery performance: the initial resistance when the battery is completed by charging and discharging under predetermined conditioning conditions after manufacture, the resistance associated with battery use, and the resistance after high-temperature storage. From the viewpoint of improving battery performance, it is desirable that all of these resistance values ​​be small.

[0007] Furthermore, if a non-aqueous electrolyte deteriorates during storage and its characteristics change, this will have a significant impact on battery performance. To improve battery performance, a non-aqueous electrolyte with excellent storage stability is desired.

[0008] The present disclosure has been made in view of the above points, and an object of the present disclosure is to achieve both storage stability and a reduction in the resistance of a secondary battery including a non-aqueous electrolyte solution containing a sulfonylimide compound.

[0009] As a result of extensive research to achieve the above object, the present inventors have found that by using a nitrogen-containing compound having a branched or linear alkyl group with a carbon number within a specific range as an additive to a non-aqueous electrolyte solution containing a sulfonylimide compound and specifying the content ratio of the nitrogen-containing compound, not only can all of the above three types of resistance of a secondary battery including this non-aqueous electrolyte solution be reduced, but also the storage stability of the non-aqueous electrolyte solution be improved.

[0010] The nonaqueous electrolyte of the present disclosure is a lithium nitrate-containing electrolyte represented by the general formula (1): LiN(RSO ２ ) (FSO ２ ) (R represents a fluorine atom, an alkyl group having 1 to 6 carbon atoms, or a fluoroalkyl group having 1 to 6 carbon atoms) ... (1) and at least one nitrogen-containing compound selected from the group consisting of amide compounds having a branched alkyl group of 3 to 6 carbon atoms and nitrile compounds having a branched alkyl group of 3 to 6 carbon atoms, wherein the content of the nitrogen-containing compound relative to the sulfonylimide compound is 10 ppm by mass or more and 6000 ppm by mass or less.

[0011] The nonaqueous electrolyte solution of the present disclosure is characterized in that it contains a sulfonylimide compound represented by the general formula (1) above and at least one nitrogen-containing compound selected from the group consisting of amide compounds having a linear alkyl group of 3 to 6 carbon atoms and nitrile compounds having a linear alkyl group of 3 to 6 carbon atoms, and the content of the nitrogen-containing compound relative to the sulfonylimide compound is 10 ppm by mass or more and 6000 ppm by mass or less.

[0012] The sulfonylimide compound represented by the general formula (1) is LiN(FSO ２ ) ２The nonaqueous electrolyte solution of the present disclosure may further contain another electrolyte, and in this case, the molar ratio of the sulfonylimide compound represented by general formula (1) above to the other electrolyte may be 1:25 or more and 2:1 or less.

[0013] According to the present disclosure, a non-aqueous electrolyte solution containing a sulfonylimide compound can achieve both storage stability and a reduction in the resistance of a secondary battery including the same.

[0014] The present embodiment will be described in detail below. The following description of the preferred embodiment is merely exemplary in nature and is in no way intended to limit the present invention, its applications, or its uses.

[0015] <Non-aqueous electrolyte> (Electrolyte salt) The non-aqueous electrolyte according to this embodiment contains an electrolyte salt represented by the general formula (1): [Chemical formula 1] LiN(RSO ２ ) (FSO ２ The non-aqueous electrolyte solution contains a sulfonylimide compound (1) as an essential component (fluorine-containing sulfonylimide salt) represented by the following formula:

[0016] In the general formula (1), R represents a fluorine atom, an alkyl group having 1 to 6 carbon atoms, or a fluoroalkyl group having 1 to 6 carbon atoms.

[0017] Examples of alkyl groups having 1 to 6 carbon atoms include methyl, ethyl, propyl, isopropyl, butyl, pentyl, and hexyl. Among alkyl groups having 1 to 6 carbon atoms, linear or branched alkyl groups having 1 to 6 carbon atoms are preferred, and linear alkyl groups having 1 to 6 carbon atoms are more preferred.

[0018] Examples of the fluoroalkyl group having 1 to 6 carbon atoms include alkyl groups having 1 to 6 carbon atoms in which some or all of the hydrogen atoms have been substituted with fluorine atoms. 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, and a pentafluoroethyl group. In particular, the fluoroalkyl group may be a perfluoroalkyl group.

[0019] The substituent R is preferably a fluorine atom or a perfluoroalkyl group (for example, a perfluoroalkyl group having 1 to 6 carbon atoms, such as a trifluoromethyl group, a pentafluoroethyl group, or a heptafluoropropyl group), more preferably a fluorine atom, a trifluoromethyl group, or a pentafluoroethyl group, still more preferably a fluorine atom or a trifluoromethyl group, and still more preferably a fluorine atom.

[0020] Specific examples of the sulfonylimide compound (1) include lithium bis(fluorosulfonyl)imide (LiN(FSO ２ ) ２ , LiFSI), lithium (fluorosulfonyl) (methylsulfonyl) imide, lithium (fluorosulfonyl) (ethylsulfonyl) imide, lithium (fluorosulfonyl) (trifluoromethylsulfonyl) imide, lithium (fluorosulfonyl) (pentafluoroethylsulfonyl) imide, lithium (fluorosulfonyl) (heptafluoropropylsulfonyl) imide, etc. The sulfonylimide compounds may be used alone or in combination of two or more. The sulfonylimide compound (1) may be a commercially available product, or may be one obtained by synthesis by a conventionally known method.

[0021] Among the sulfonylimide compounds (1), LiN(FSO ２ ) ２ , lithium(fluorosulfonyl)(trifluoromethylsulfonyl)imide and lithium(fluorosulfonyl)(pentafluoroethylsulfonyl)imide are preferred, LiN(FSO ２ ) ２ In other words, in the non-aqueous electrolyte, LiN(FSO ２ ) ２ Preferably, it contains:

[0022] The concentration (content, total content when two or more types are used) of the sulfonylimide compound (1) in the nonaqueous electrolyte is preferably 0.2 mol / L or more, more preferably 0.3 mol / L or more, and even more preferably 0.5 mol / L or more, from the viewpoint of improving battery performance (particularly reducing resistance). Furthermore, from the viewpoint of suppressing a decrease in battery performance due to an increase in the viscosity of the electrolyte, the concentration is preferably less than 2.1 mol / L, more preferably 2 mol / L or less, 1.9 mol / L or less, 1.8 mol / L or less, 1.7 mol / L or less, or 1.6 mol / L or less, and even more preferably 1.5 mol / L or less.

[0023] From the viewpoint of improving battery performance, the content of the sulfonylimide compound (1) in the non-aqueous electrolyte solution is preferably 10 mol% or more, more preferably 20 mol% or more, even more preferably 30 mol% or more, even more preferably 50 mol% or more, and even more preferably more than 50 mol% based on the total 100 mol% of the electrolyte salt contained in the non-aqueous electrolyte solution. The upper limit of the content is 100 mol%. That is, the electrolyte salt contained in the non-aqueous electrolyte solution may contain the sulfonylimide compound (1) alone.

[0024] The content of sulfonylimide compound (1) in the non-aqueous electrolyte is preferably 1% by mass or more, more preferably 3% by mass or more, and even more preferably 5% by mass or more, based on the total amount of the components contained in the non-aqueous electrolyte (100% by mass), from the viewpoint of improving battery performance. Furthermore, from the viewpoint of suppressing a decrease in battery performance due to an increase in the viscosity of the electrolyte, the content is preferably less than 30% by mass, more preferably 25% by mass or less, and even more preferably 20% by mass or less.

[0025] The electrolyte salt (lithium salt) may contain the sulfonylimide compound (1), but may also contain other electrolyte salts (electrolyte salts other than the sulfonylimide compound (1)). Examples of other electrolytes include imide salts and non-imide salts.

[0026] Examples of imide salts include fluorine-containing sulfonylimide salts other than sulfonylimide compound (1) (hereinafter referred to as "other sulfonylimide compounds"). Examples of other sulfonylimide compounds include non-lithium salts of the fluorine-containing sulfonylimides listed as sulfonylimide compound (1) (for example, salts in which lithium (ions) in sulfonylimide compound (1) are substituted with cations other than lithium ions). Examples of salts in which a cation other than lithium ions is substituted include alkali metal salts such as sodium salts, potassium salts, rubidium salts, and cesium salts; alkaline earth metal salts such as beryllium salts, magnesium salts, calcium salts, strontium salts, and barium salts; aluminum salts; ammonium salts; and phosphonium salts. The other sulfonylimide compounds may be used alone or in combination of two or more. Furthermore, commercially available products may be used as the other sulfonylimide compounds, or compounds synthesized by conventional methods may be used.

[0027] Examples of the non-imide salt include salts of non-imide anions and cations (lithium ions and the cations exemplified above). ａ (C ｍ F ２ｍ＋１ ) ６－ａ (a: 0≦a≦6, m: 1≦m≦4) (2) (hereinafter referred to as "fluorophosphate compound (2)"), a compound represented by the general formula (3): LiBF ｂ (C ｎ F ２ｎ+１ ) ４－ｂ (b: 0≦b≦4, n: 1≦n≦4) (3) (hereinafter referred to as "fluoroborate compound (3)"), lithium hexafluoroarsenate (LiAsF ６ ), LiSbF ６ , LiClO ４ , LiSCN, LiAlF ４ , C.F. ３ SO ３ Li, LiC [(CF ３ SO ２ ) ３ ], LiN(NO ２ ), LiN[(CN)２ Examples of the non-lithium salt include salts in which the lithium (ion) in these lithium salts is replaced with the cations listed above (for example, NaBF ４ , NaPF ６ , NaPF ３ (CF ３ ) ３ The non-imide salts may be used alone or in combination of two or more. In addition, the non-imide salts may be commercially available products or may be synthesized by a conventional method.

[0028] Among other electrolytes, non-imide salts are preferred from the viewpoints of ionic conductivity, cost, etc., and fluorophosphate compounds (2), fluoroboric acid compounds (3), and LiAsF ６ is preferred, and the fluorophosphate compound (2) is more preferred.

[0029] The fluorophosphate compound (2) is LiPF ６ , LiPF ３ (CF ３ ) ３ , LiPF ３ (C ２ F ５ ) ３ , LiPF ３ (C ３ F ７ ) ３ , LiPF ３ (C ４ F ９ ) ３ Among the fluorophosphate compounds (2), LiPF ６ and LiPF ３ (C ２ F ５ ) ３ is preferred, and LiPF ６ is more preferred.

[0030] The fluoroboric acid compound (3) is LiBF ４ , LiBF(CF ３ ) ３ , LiBF(C ２ F ５ ) ３ , LiBF(C３ F ７ ) ３ Among the fluoroboric acid compounds (3), LiBF ４ , and LiBF(CF ３ ) ３ is preferred, and LiBF ４ is more preferred.

[0031] These electrolyte salts (sulfonylimide compound (1), other electrolyte salts, etc.) may be present (contained) in the form of ions in the non-aqueous electrolyte solution.

[0032] The electrolyte salt composition may be an electrolyte salt having a simple salt composition of the sulfonylimide compound (1), or an electrolyte salt having a mixed salt composition containing the sulfonylimide compound (1) and another electrolyte. When an electrolyte salt having a mixed salt composition is used, an electrolyte salt having a mixed salt composition containing the sulfonylimide compound (1) and a fluorophosphate compound (2) is preferred, and LiN(FSO ２ ) ２ and LiPF ６ An electrolyte salt having a mixed salt composition containing the following is more preferred.

[0033] When an electrolyte salt having a mixed salt composition containing sulfonylimide compound (1) and other electrolytes is used, the concentration of the other electrolytes in the nonaqueous electrolyte (content, or the total content when two or more types are used in combination) is preferably 0.1 mol / L or more, more preferably 0.2 mol / L or more, even more preferably 0.5 mol / L or more, even more preferably 0.7 mol / L or more, and even more preferably 1 mol / L or more, from the viewpoint of improving battery performance. Furthermore, from the viewpoint of suppressing a decrease in battery performance due to an increase in the viscosity of the electrolyte, the concentration is preferably 5 mol / L or less, more preferably 3 mol / L or less, even more preferably 2 mol / L or less, and even more preferably 1.5 mol / L or less.

[0034] The total concentration of the electrolyte salts in the nonaqueous electrolyte solution is preferably 0.8 mol / L or more, more preferably 1 mol / L or more, and even more preferably 1.2 mol / L or more from the viewpoint of improving battery performance, and is preferably 5 mol / L or less, more preferably 3 mol / L or less, and even more preferably 2 mol / L or less from the viewpoint of suppressing a decrease in battery performance due to an increase in the viscosity of the electrolyte solution.

[0035] From the viewpoint of improving battery performance, it is preferable to increase the concentration of sulfonylimide compound (1). The molar ratio of sulfonylimide compound (1) to other electrolytes (the molar ratio of sulfonylimide compound (1) concentration to other electrolyte concentration) is preferably 1:25 or more, more preferably 1:10 or more, even more preferably 1:8 or more, even more preferably 1:5 or more, still more preferably 1:2 or more, and particularly preferably 1:1 or more, with the upper limit being preferably 25:1 or less, more preferably 10:1 or less, even more preferably 5:1 or less, and even more preferably 2:1 or less.

[0036] (Nitrogen-Containing Compound) The nonaqueous electrolyte according to the present embodiment contains, as an additive, at least one nitrogen-containing compound selected from the group consisting of amide compounds having a branched alkyl group of 3 to 6 carbon atoms and nitrile compounds having a branched alkyl group of 3 to 6 carbon atoms (hereinafter collectively referred to as "branched alkyl nitrogen-containing compound"), or at least one nitrogen-containing compound selected from the group consisting of amide compounds having a linear alkyl group of 3 to 6 carbon atoms and nitrile compounds having a linear alkyl group of 3 to 6 carbon atoms (hereinafter collectively referred to as "linear alkyl nitrogen-containing compound"). The "linear alkyl nitrogen-containing compound" is distinguished from the "branched alkyl nitrogen-containing compound" in that the linear alkyl group having 3 to 6 carbon atoms does not have a branched structure. The "branched alkyl nitrogen-containing compound" and the "linear alkyl nitrogen-containing compound" may be used alone or in combination of two or more types. The "branched alkyl nitrogen-containing compound" and the "linear alkyl nitrogen-containing compound" are collectively referred to as the "linear alkyl nitrogen-containing compound."

[0037] Examples of the amide compound having a branched alkyl group having 3 to 6 carbon atoms include isobutylamide (2-methylpropionamide) and N,N-dimethylisobutylamide.

[0038] Examples of nitrile compounds having a branched alkyl group having 3 to 6 carbon atoms include mononitrile compounds such as isobutyronitrile (isopropyl cyanide) and isovaleronitrile (isobutyl cyanide).

[0039] Among the branched alkyl nitrogen-containing compounds, isobutylamide and isobutyronitrile are preferred from the viewpoint of improving battery performance (particularly reducing resistance).

[0040] Examples of the amide compound having a linear alkyl group having 3 to 6 carbon atoms include n-butylamide and N,N-dimethylbutylamide.

[0041] Examples of nitrile compounds having a linear alkyl group having 3 to 6 carbon atoms include mononitrile compounds such as butyronitrile (propyl cyanide) and valeronitrile (butyl cyanide).

[0042] Among the linear alkyl nitrogen-containing compounds, n-butylamide and butyronitrile are preferred from the viewpoint of improving battery performance (particularly reducing resistance).

[0043] The content of the chain alkyl nitrogen-containing compound relative to the sulfonylimide compound (1) is 10 ppm by mass or more and 6000 ppm by mass or less. That is, in the nonaqueous electrolyte according to this embodiment, the quantitative ratio relationship between the sulfonylimide compound (1) and the chain alkyl nitrogen-containing compound is specified. This improves the storage stability of the nonaqueous electrolyte and reduces the resistance of a secondary battery equipped with this nonaqueous electrolyte. The content of the chain alkyl nitrogen-containing compound (the total when two or more types are used in combination) relative to the sulfonylimide compound (1) (the total when two or more types are used in combination) is 10 ppm by mass or more, preferably 20 ppm by mass or more, more preferably 100 ppm by mass or more, even more preferably 500 ppm by mass or more, and even more preferably 1000 ppm by mass or more. The upper limit of the content is 6000 ppm by mass or less, preferably 5000 ppm by mass or less, and more preferably 3000 ppm by mass or less.

[0044] The content of the chain alkyl nitrogen-containing compound in the nonaqueous electrolyte (the total content when two or more types are used in combination) is preferably 2 ppm by mass or more, more preferably 4 ppm by mass or more, even more preferably 50 ppm by mass or more, even more preferably 100 ppm by mass or more, and even more preferably 200 ppm by mass or more. The upper limit of the content is preferably 1200 ppm by mass or less, more preferably 1000 ppm by mass or less, and even more preferably 500 ppm by mass or less.

[0045] (Additives) In addition to the chain alkyl nitrogen-containing compound, the non-aqueous electrolyte may contain additives for improving various properties of the lithium ion secondary battery. The additives may be added to the non-aqueous electrolyte or may be added during the preparation process of the non-aqueous electrolyte. Examples of additives include carboxylic acid anhydrides such as succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, diglycolic anhydride, cyclohexanedicarboxylic anhydride, cyclopentanetetracarboxylic dianhydride, and phenylsuccinic anhydride; ethylene sulfite, 1,3-propane sultone, 1,4-butane sultone, methyl methanesulfonate, busulfan, sulfolane, sulfolene, dimethyl sulfone, tetramethylthiuram monosulfide, and trimethylene glycol sulfate. Sulfur-containing compounds such as esters; nitrogen-containing compounds such as 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl-2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone, and N-methylsuccinimide; saturated hydrocarbon compounds such as heptane, octane, and cycloheptane; carbonate compounds such as vinylene carbonate, fluoroethylene carbonate (FEC), trifluoropropylene carbonate, phenylethylene carbonate, and erythritan carbonate; sulfamic acid (amidosulfuric acid, H ３ NSO ３ ); sulfamates (alkali metal salts such as lithium salts, sodium salts, potassium salts, etc.; alkaline earth metal salts such as calcium salts, strontium salts, barium salts, etc.; other metal salts such as manganese salts, copper salts, zinc salts, iron salts, cobalt salts, nickel salts, etc.; ammonium salts; guanidine salts, etc.); lithium fluorosulfonate (LiFSO ３ ), sodium fluorosulfonate (NaFSO ３ ), potassium fluorosulfonate (KFSO ３ ), magnesium fluorosulfonate (Mg(FSO ３ ) ２ fluorosulfonic acid compounds such as lithium monofluorophosphate (Li ２ P.O. ３ F), lithium difluorophosphate (LiPO ２ F ２and fluorooxalato compounds such as lithium salts having an oxalic acid skeleton, such as lithium bis(oxalato)borate (LiBOB), lithium difluorooxalatoborate (LiDFOB), lithium difluorooxalatophosphate (LIDFOP), lithium tetrafluorooxalatophosphate (LITFOP), lithium difluorobis(oxalato)phosphate (LiDFBOP), and lithium tris(oxalato)phosphate. These additives may be used alone or in combination of two or more.

[0046] The additive is preferably used in an amount of 0.1% by mass to 10% by mass, more preferably 0.2% by mass to 8% by mass, and even more preferably 0.3% by mass to 5% by mass, relative to 100% by mass of the total amount of the components contained in the non-aqueous electrolyte. If the amount of additive used is too small, it may be difficult to obtain the effects derived from the additive. On the other hand, even if a large amount of additive is used, it may be difficult to obtain effects commensurate with the amount added, and the viscosity of the non-aqueous electrolyte may increase, resulting in a decrease in conductivity.

[0047] (Electrolyte Solvent) The non-aqueous electrolyte may contain an electrolyte solvent. The electrolyte solvent is not particularly limited as long as it can dissolve and disperse the electrolyte salt. Examples of the electrolyte solvent include non-aqueous solvents, polymers used in place of electrolyte solvents, polymer gels, and other media, and any solvent generally used in batteries can be used.

[0048] The non-aqueous solvent is preferably a solvent having a high dielectric constant, a high solubility for the electrolyte, a boiling point of 60° C. or higher, and a wide electrochemical stability range. An organic solvent with a low water content is more preferable. Examples of such organic solvents include ether solvents such as ethylene glycol dimethyl ether, ethylene glycol diethyl ether, tetrahydrofuran, 2-methyltetrahydrofuran, 2,6-dimethyltetrahydrofuran, tetrahydropyran, crown ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, 1,4-dioxane, and 1,3-dioxolane; chain carbonate ester (carbonate) solvents such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), diphenyl carbonate, and methyl phenyl carbonate; saturated cyclic carbonate ester solvents such as ethylene carbonate (EC), propylene carbonate (PC), 2,3-dimethyl ethylene carbonate, 1,2-butylene carbonate, and erythritan carbonate; cyclic carbonate ester solvents having an unsaturated bond such as vinylene carbonate, methyl vinylene carbonate, ethyl vinylene carbonate, 2-vinyl ethylene carbonate, and phenyl ethylene carbonate; fluoroethylene carbonate, 4,5-difluoroethylene carbonate, and the like. fluorine-containing cyclic carbonate solvents such as methyl benzoate and trifluoropropylene carbonate; aromatic carboxylic acid ester solvents such as methyl benzoate and ethyl benzoate; lactone solvents such as γ-butyrolactone, γ-valerolactone and δ-valerolactone; phosphate ester solvents such as trimethyl phosphate, ethyl dimethyl phosphate, diethyl methyl phosphate and triethyl phosphate; nitrile solvents such as acetonitrile, propionitrile, methoxypropionitrile, glutaronitrile, adiponitrile and 2-methylglutaronitrile tolyl-based solvents; sulfur compound-based solvents such as dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, sulfolane, 3-methyl sulfolane, and 2,4-dimethyl sulfolane; aromatic nitrile-based solvents such as benzonitrile and tolunitrile; nitromethane, 1,3-dimethyl-2-imidazolidinone, 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone, and 3-methyl-2-oxazolidinone; and chain ester-based solvents such as ethyl acetate, butyl acetate, and propyl propionate.These solvents may be used alone or in combination of two or more.

[0049] Among the electrolyte solvents, carbonate solvents such as chain carbonate ester solvents and cyclic carbonate ester solvents, lactone solvents, ether solvents, and chain ester solvents are preferred, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, γ-butyrolactone, and γ-valerolactone are more preferred, and carbonate solvents such as dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, ethylene carbonate, and propylene carbonate are even more preferred.

[0050] When a polymer or polymer gel is used instead of the electrolyte solvent, the following methods may be employed: a method in which a solution of an electrolyte salt dissolved in a solvent is dropped onto a polymer formed into a film by a conventionally known method, thereby impregnating and supporting the electrolyte salt and non-aqueous solvent; a method in which a polymer and an electrolyte salt are melted and mixed at a temperature equal to or higher than the melting point of the polymer, and then a film is formed, which is then impregnated with a solvent (these are referred to as gel electrolytes); a method in which a non-aqueous electrolyte in which an electrolyte salt has been dissolved in an organic solvent is mixed with a polymer, which is then formed into a film by a casting method or a coating method, and the organic solvent is volatilized; a method in which a polymer and an electrolyte salt are melted at a temperature equal to or higher than the melting point of the polymer, mixed, and molded (true polymer electrolyte), etc.

[0051] Examples of polymers that can be used in place of the electrolyte solvent include polyether polymers such as polyethylene oxide (PEO), which is a homopolymer or copolymer of an epoxy compound (ethylene oxide, propylene oxide, butylene oxide, allyl glycidyl ether, etc.), polypropylene oxide, etc., methacrylic polymers such as polymethyl methacrylate (PMMA), nitrile polymers such as polyacrylonitrile (PAN), fluorine-based polymers such as polyvinylidene fluoride (PVdF) and polyvinylidene fluoride-hexafluoropropylene, and copolymers thereof. These polymers may be used alone or in combination of two or more.

[0052] The non-aqueous electrolyte solution thus constructed contains the sulfonylimide compound (1) and a branched alkyl nitrogen-containing compound or a linear alkyl nitrogen-containing compound (a chain alkyl nitrogen-containing compound) as essential components, and may optionally contain other components such as an electrolyte salt, an electrolyte solvent, various additives (other than the chain alkyl nitrogen-containing compound), etc. The non-aqueous electrolyte solution can be prepared, for example, by mixing these components in a predetermined composition ratio.

[0053] The nonaqueous electrolyte according to this embodiment is used, for example, in batteries (batteries having a charge / discharge mechanism), electricity storage (electrochemical) devices (or ion conductor materials constituting these), etc. Specifically, the electrolyte can be used as an electrolyte constituting, for example, primary batteries, secondary batteries (e.g., lithium (ion) secondary batteries), fuel cells, electrolytic capacitors, electric double layer capacitors, solar cells, electrochromic display elements, etc. Hereinafter, a description will be given taking batteries (particularly secondary batteries) as an example.

[0054] <Secondary Battery> The secondary battery includes a positive electrode, a negative electrode, and a nonaqueous electrolyte. By using the nonaqueous electrolyte according to this embodiment, the resistance of the secondary battery can be reduced, thereby improving battery performance. The positive electrode and the negative electrode are not particularly limited, and conventionally known secondary batteries (particularly lithium-ion secondary batteries) can be used. The secondary battery may also include a separator separating the positive electrode and the negative electrode. The separator is not particularly limited, and conventionally known separators can be used. The shape of the battery is not particularly limited, and any conventionally known battery shape can be used, such as a cylindrical, prismatic, laminated, coin, or large battery. Furthermore, when used as a high-voltage power source (several tens to several hundreds of volts) for installation in electric vehicles, hybrid electric vehicles, or the like, a battery module can be formed by connecting individual batteries in series.

[0055] As described above, the nonaqueous electrolyte according to this embodiment contains, as its constituent materials, a sulfonylimide compound (1) and a branched alkyl nitrogen-containing compound or a linear alkyl nitrogen-containing compound (a chain alkyl nitrogen-containing compound), and the quantitative ratio between the sulfonylimide compound (1) and the chain alkyl nitrogen-containing compound is specified such that the content of the chain alkyl nitrogen-containing compound relative to the sulfonylimide compound (1) is 10 ppm by mass or more and 6000 ppm by mass or less. Due to the above-described configuration, the nonaqueous electrolyte not only has excellent storage stability, but also reduces all three types of resistance when used in a secondary battery: initial resistance, resistance associated with battery use, and resistance after high-temperature storage.

[0056] The present disclosure will be described below based on examples. Note that the present disclosure is not limited to the following examples, and the following examples can be modified or changed based on the spirit of the present disclosure, and such modifications are not excluded from the scope of the present disclosure.

[0057] Example 1 Series Preparation of Nonaqueous Electrolyte A reference electrolyte (Comparative Example 1-1) was prepared by dissolving LiFSI (a sulfonylimide compound manufactured by Nippon Shokubai) as an electrolyte salt in a mixed solvent (EC / EMC = 30 / 70 (vol %)) containing ethylene carbonate (EC, commercially available) and ethyl methyl carbonate (EMC, commercially available) to a concentration of 1.2 mol / L. A branched alkyl nitrogen-containing compound or a linear alkyl nitrogen-containing compound (collectively referred to as "linear alkyl nitrogen-containing compound" in the table) shown in Table 1 was added to the reference electrolyte and dissolved therein to the content shown in Table 1 (the content of linear alkyl nitrogen-containing compound relative to LiFSI), to prepare "nitrogen-containing electrolytes" (each Example and Comparative Example 1-2 to 1-5). In Table 1 (and Tables 2 to 4 described below), "IBA" represents isobutylamide (commercially available), "IBN" represents isobutyronitrile (commercially available), "BA" represents n-butylamide (commercially available), and "BN" represents butyronitrile (commercially available). The content of LiFSI in the solution (nonaqueous electrolyte) dissolved in the above mixed solvent as the electrolyte solvent was approximately 18.4 mass%.

[0058] <Evaluation of non-aqueous electrolyte> (1) Evaluation of battery performance (1-1) Preparation of evaluation battery (positive electrode) LiFePO ４ (Commercially available product): acetylene black (manufactured by Denka, Denka Black): graphite (manufactured by Nippon Graphite, SP270): polyvinylidene fluoride (PVdF, #7208, commercially available product) were weighed in a mass ratio of 89:3:3:5 and dispersed in N-methyl-2-pyrrolidone (NMP, commercially available product) to prepare a slurry. The prepared slurry was coated on one side of a carbon-coated aluminum foil (coating weight 17.61 mg / cm). ２ After drying, the mixture was roll-pressed to prepare a positive electrode.

[0059] (Negative electrode) An aqueous slurry was prepared in a mass ratio of graphite (SMG, manufactured by Hitachi Chemical) / SFG15 (manufactured by Imerys) = 85 / 15: styrene butadiene rubber (SBR, commercially available): carboxymethyl cellulose (CMC, commercially available) = 97.4:1.5:1.1, and was coated on one side of a copper foil (coating weight 7.4 mg / cm ２ ) and dried, followed by roll pressing to prepare a negative electrode.

[0060] (Evaluation Battery) The resulting positive and negative electrodes were cut, and the polarity leads were ultrasonically welded. They were then placed facing each other with a 25 μm polyethylene (PE) separator, and sealed on three sides with a laminate exterior. The above electrolyte was poured into the unsealed side, vacuum sealed, and charged at a constant current of 3 mA at 25°C for 3 hours. The battery was then left at room temperature for 2 days, and one piece of the laminate exterior was cleaved and vacuum sealed again to degas the battery. After degassing, the battery was charged and discharged under the following conditioning condition 1 to complete the evaluation battery. (Conditioning Condition 1) 1st Cycle: Charge: 2.5 mA, constant current / constant voltage charge at 3.6 V, terminated at 0.25 mA ⇒ Discharge: Discharge at 5 mA, terminated at 2.0 V. 2nd cycle: Charge: 12.5mA, 3.6V constant current / constant voltage charge, terminated at 0.5mA ⇒ Discharge: 5mA discharge, terminated at 2.0V. 3rd cycle: Charge: 12.5mA, 3.6V constant current / constant voltage charge, terminated at 0.5mA ⇒ Discharge: 25mA discharge, terminated at 2.0V. 4th cycle: Charge: 12.5mA, 3.6V constant current / constant voltage charge, terminated at 0.5mA ⇒ Discharge: 50mA discharge, terminated at 2.0V.

[0061] (1-2) Evaluation of Characteristics of Evaluation Battery Using the evaluation battery obtained in (1-1) above, the reduction rates of DCR (direct current resistance) and impedance (charge transfer resistance) were evaluated by the following method. The results are shown in Table 1.

[0062] <DCR Decrease Rate> (Initial DCR) Using a charge / discharge tester, the evaluation battery was charged at a constant current and constant voltage of 25 mA (1 C), 3.6 V, and 0.5 mA termination, until it reached a fully charged state. From the fully charged state, the DCR (DCR before cycle testing) was measured at 25°C. For DCR measurement, the battery was waited 30 minutes after full charge completion, and then discharged at 5 mA (0.2 C) for 10 seconds. Subsequently, after waiting 30 minutes, the battery was discharged at 25 mA (1 C) for 10 seconds. Finally, after waiting 30 minutes, the battery was discharged at 75 mA (3 C) for 10 seconds. An IV line was created from the relationship between the difference in voltage immediately before and 10 seconds after the start of discharge at each discharge current and the current, and the slope of the line was calculated as the DCR (initial DCR). The reduction rate of the initial DCR was calculated using an evaluation battery having the same positive electrode active material as a comparison battery according to the following formula (1): [Formula 1] Reduction rate of initial DCR (%) = (initial DCR of "nitrogen-containing electrolyte") / (initial DCR of "reference electrolyte") × 100 (1) A smaller reduction rate of the initial DCR means a greater reduction in the initial DCR of the battery.

[0063] (DCR after 200 cycle test) - After measuring the initial DCR, the battery was subjected to 200 cycles of a 45°C cycle test. The cycle conditions were: charge: 3.6 V, 25 mA (1 C), terminated at 0.5 mA (0.05 C), and rested for 10 minutes; discharge: 25 mA (1 C), terminated at 2.0 V, and rested for 10 minutes. After the cycle test, the "DCR after 200 cycle test" was measured and calculated at 25°C in the same manner as above. - The rate of decrease in DCR after 200 cycle test was calculated in the same manner as above, except that in formula (1), "initial DCR" was replaced with "DCR after 200 cycle test." A smaller rate of decrease in DCR after 200 cycle test indicates a greater decrease in DCR with battery use.

[0064] (DCR after 28 days at 60°C (after high-temperature storage)) - The battery after initial DCR measurement was fully charged in the same manner as above, stored at 60°C for 28 days, and then left to stand at 25°C for 4 hours, and then the "DCR after 28 days at 60°C" was measured and calculated at 25°C in the same manner as above. - The rate of decrease in DCR after 28 days at 60°C was calculated in the same manner as above, except that in formula (1) "initial DCR" was changed to "DCR after 28 days at 60°C". A smaller rate of decrease in DCR after 28 days at 60°C means that the DCR of the battery after high-temperature storage is more reduced.

[0065] <Impedance Decrease Rate> (Initial Impedance) The evaluation battery was fully charged using the same method as above. Subsequently, the evaluation battery was subjected to impedance measurement at frequencies from 1 GHz to 1 mHz at 25°C using an impedance analyzer (manufactured by Bio Logic, product number: VSP-300). The real axis resistance (interface resistance) was calculated from the frequency at which the arc of the obtained measured value diverged. The frequency at which the arc diverged refers to the frequency at which the imaginary axis value reached a minimum between 1 kHz and 0.001 Hz. Specifically, the real axis resistance at which the imaginary axis resistance became zero was defined as the bulk resistance, and the value obtained by subtracting the bulk resistance from the real axis resistance at which the imaginary axis resistance was maximized in the low-frequency region below 1 kHz was defined as the "initial impedance." The initial impedance decrease rate was calculated in the same manner as in the above formula (1), except that "initial DCR" was replaced with "initial impedance." A smaller decrease rate of initial impedance indicates a greater decrease in the initial impedance of the battery.

[0066] (Impedance after 200 cycle test) After the initial impedance measurement, the battery was subjected to 200 cycles of a 45°C cycle test in the same manner as above. After the cycle test, the "impedance after 200 cycle test" was measured at 25°C in the same manner as above. The rate of decrease in impedance after 200 cycle test was calculated in the same manner as above, except that in formula (1), "initial DCR" was changed to "impedance after 200 cycle test." A smaller rate of decrease (%) in impedance after 200 cycle test indicates a greater decrease in impedance with battery use.

[0067]

[0068] (1) Summary of Battery Performance Evaluations - From Table 1, it was confirmed that in a nonaqueous electrolyte solution containing LiFSI (sulfonylimide compound (1)) alone (including an electrolyte salt having a simple salt composition of sulfonylimide compound (1)), a secondary battery including a "nitrogen-containing electrolyte solution" (each Example) containing IBA or IBN (branched alkyl nitrogen-containing compound) or BA or BN (linear alkyl nitrogen-containing compound) in an amount of 10 ppm by mass or more and 6000 ppm by mass or less relative to LiFSI exhibited reduced resistance in all three types of resistance: initial resistance, resistance associated with battery use, and resistance after high-temperature storage, compared to a secondary battery including a "reference electrolyte solution" (Comparative Example 1-1) that did not contain a linear alkyl nitrogen-containing compound. - On the other hand, it was confirmed that a secondary battery including a "nitrogen-containing electrolyte" (Comparative Examples 1-2 to 1-5) in which the content of the linear alkyl nitrogen-containing compound relative to LiFSI exceeded 6000 ppm by mass exhibited increased resistance in all three types of resistance compared to a secondary battery including a "reference electrolyte." Therefore, it was found that in a "nitrogen-containing electrolyte" containing an electrolyte salt having a simple salt composition containing only LiFSI, both the "branched alkyl nitrogen-containing compound" and the "linear alkyl nitrogen-containing compound" have the effect of reducing the resistance of a secondary battery.

[0069] (2) Evaluation of storage stability Each of the nonaqueous electrolyte solutions prepared in the above <Preparation of nonaqueous electrolyte solutions> shown in Table 2 was stored in a sealed container made of PFA (fluororesin) at 45°C for one month. After that, the sulfate ions (SO ４ ２－ The concentrations of these compounds were measured by ion chromatography as follows. The results are shown in Table 2.

[0070] [Ion Chromatography Measurement] Each non-aqueous electrolyte solution was diluted 100 times with ultrapure water (over 18.2 Ω cm) to prepare a measurement solution. The concentration of sulfate ions contained in each non-aqueous electrolyte solution was measured using an ion chromatography system ICS-3000 (manufactured by Nippon Dionex Co., Ltd.). The measurement conditions were as follows: (Measurement conditions for ion chromatography measurement) Separation mode: ion exchange Eluent: 4.5 mM Na ２ CO ３ / 0.5mM NaHCO ３ Aqueous solution. Detector: Electrical conductivity detector. Column: Anion analysis column Ion PAC AS-23 (manufactured by Nippon Dionex Co., Ltd.).

[0071]

[0072] (2) Summary of Evaluation of Storage Stability) Table 2 shows that, in nonaqueous electrolytes containing only LiFSI (sulfonylimide compound (1)), the "nitrogen-containing electrolytes" (each Example) containing 10 ppm by mass or more and 6,000 ppm by mass or less of a branched alkyl nitrogen-containing compound relative to LiFSI had lower sulfate ion concentrations (amount of decomposition products of LiFSI) after storage at 45°C for one month compared to the "reference electrolyte" (Comparative Example 1-1) that did not contain a chain alkyl nitrogen-containing compound. Therefore, it was confirmed that the "nitrogen-containing electrolytes" suppressed decomposition of LiFSI and had better storage stability compared to the "reference electrolyte." On the other hand, even though they were "nitrogen-containing electrolytes," the electrolytes (Comparative Examples 1-2 and 1-3) in which the content of chain alkyl nitrogen-containing compounds relative to LiFSI exceeded 6,000 ppm by mass showed a higher sulfate ion concentration after one month of storage at 45°C than the "reference electrolyte," demonstrating that decomposition of LiFSI had progressed and the storage stability was poor.

[0073] Example 2 Series Preparation of Non-Aqueous Electrolyte A non-aqueous electrolyte solution was prepared by dissolving LiPF as an electrolyte salt in a mixed solvent (EC / EMC=30 / 70 (vol%)) containing ethylene carbonate (EC, commercially available product) and ethyl methyl carbonate (EMC, commercially available product). ６A reference electrolyte (Comparative Example 2-1) was prepared by dissolving LiFSI (a commercially available product) and LiFSI (a sulfonylimide compound manufactured by Nippon Shokubai) at a concentration of 0.6 mol / L. The chain alkyl nitrogen-containing compound shown in Table 3 or 4 was added to the reference electrolyte and dissolved in the amount shown in Table 3 or 4 (the content of the chain alkyl nitrogen-containing compound relative to LiFSI), to prepare a "nitrogen-containing electrolyte" (each Example and Comparative Example 2-2 to 2-7). The content of LiFSI in the solution (nonaqueous electrolyte) dissolved in the above mixed solvent as the electrolyte solvent was approximately 9.2% by mass.

[0074] <Evaluation of non-aqueous electrolyte> (1) Evaluation of battery performance (1-1) Preparation of evaluation battery (positive electrode) LiNi was used as a ternary positive electrode active material. ０．５ Co ０．２ Mn ０．３ O ２ (NCM523, manufactured by Beijing Toben Co., Ltd.): acetylene black (manufactured by Denka, Denka Black): graphite (manufactured by Nippon Graphite, SP270): polyvinylidene fluoride (PVdF, #1120, commercially available product) were weighed in a mass ratio of 100:3:3:3 and dispersed in N-methyl-2-pyrrolidone (NMP, commercially available product) to prepare a slurry. The prepared slurry was coated on one side of an aluminum foil (coating weight 19.5 mg / cm). ２ After drying, the mixture was roll-pressed to prepare a positive electrode.

[0075] (Negative electrode) An aqueous slurry containing graphite (O-MAC, Osaka Gas Chemicals) / SFG15 (Imerys) = 85 / 15: carbon fiber (VGCF, Showa Denko K.K.): styrene butadiene rubber (SBR, commercially available): carboxymethyl cellulose (CMC, commercially available) = 100:2:1:1 in mass ratio was prepared, and coated on one side of a copper foil (coating weight 9.8 mg / cm ２ ) and dried, followed by roll pressing to prepare a negative electrode.

[0076] (Evaluation Battery) An evaluation battery was completed in the same manner as in Example 1 series, except that it was charged and discharged under the following conditioning condition 2. (Conditioning Condition 2) 1st cycle: Charge: 3 mA, constant current / constant voltage charge at 4.2 V, terminated at 0.3 mA ⇒ Discharge: 6 mA discharge, terminated at 2.75 V. 2nd cycle: Charge: 15 mA, constant current / constant voltage charge at 4.2 V, terminated at 0.6 mA ⇒ Discharge: 6 mA discharge, terminated at 2.75 V. 3rd cycle: Charge: 15 mA, constant current / constant voltage charge at 4.2 V, terminated at 0.6 mA ⇒ Discharge: 30 mA discharge, terminated at 2.75 V. 4th cycle: Charge: 15 mA, constant current / constant voltage charge at 4.2 V, terminated at 0.6 mA ⇒ Discharge: 60 mA discharge, terminated at 2.75 V.

[0077] (1-2) Evaluation of Characteristics of Evaluation Battery Using the evaluation battery obtained in (1-1) above, the reduction rates of DCR (direct current resistance) and impedance (charge transfer resistance) were evaluated by the following method. The results are shown in Table 3.

[0078] <DCR Decrease Rate> (Initial DCR) Using a charge / discharge tester, the test battery was charged at a constant current and constant voltage of 30 mA (1 C), 4.2 V, and a 0.6 mA cutoff to a fully charged state. The DCR (DCR before cycle testing) was measured at 25°C from the fully charged state. For DCR measurement, the battery was waited 30 minutes after full charge and then discharged at 6 mA (0.2 C) for 10 seconds. After waiting 30 minutes, the battery was discharged at 30 mA (1 C) for 10 seconds. Finally, after waiting 30 minutes, the battery was discharged at 90 mA (3 C) for 10 seconds. An IV line was created based on the relationship between the difference in voltage immediately before and 10 seconds after discharge at each discharge current and the current, and the slope of the line was calculated as the DCR (initial DCR). The initial DCR decrease rate was calculated in the same manner as in Example 1 series.

[0079] (DCR after 200 cycle test) - After the initial DCR measurement, the battery was subjected to 200 cycles of 45°C cycle test. The cycle conditions were: charge: 4.2 V, 30 mA (1 C), terminated at 0.6 mA (0.05 C), 10-minute rest ⇒ discharge: 30 mA (1 C), terminated at 2.75 V, 10-minute rest. After the cycle test, the "DCR after 200 cycle test" was measured and calculated at 25°C in the same manner as above. - The DCR reduction rate after 200 cycle test was calculated in the same manner as in Example 1 series.

[0080] (DCR after 28 days at 60°C (after high-temperature storage)) After the initial DCR measurement, the battery was fully charged in the same manner as above, stored at 60°C for 28 days, and then left to stand at 25°C for 4 hours, after which the "DCR after 28 days at 60°C" was measured and calculated at 25°C in the same manner as in Example 1. The rate of decrease in DCR after 28 days at 60°C was calculated in the same manner as in Example 1.

[0081] <Impedance Reduction Rate> (Initial Impedance) The test battery was fully charged in the same manner as above. Subsequently, the impedance of this test battery was measured in the same manner as in Example 1 series to determine the "initial impedance." The initial impedance reduction rate was calculated in the same manner as in Example 1 series.

[0082] (Impedance after 200 cycle test) After the initial impedance measurement, the battery was subjected to 200 cycles of a 45° C. cycle test in the same manner as in Example 1 series, and the "impedance after 200 cycle test" was measured at 25° C. The reduction rate of the impedance after 200 cycle test was calculated in the same manner as in Example 1 series.

[0083]

[0084] ((1) Summary of Battery Performance Evaluation) From Table 3, LiFSI (sulfonylimide compound (1)) and LiPF ６In a non-aqueous electrolyte containing an electrolyte salt of a mixed salt composition including (another electrolyte), a "nitrogen-containing electrolyte" (each Example) containing 10 ppm by mass or more and 6000 ppm by mass or less of IBA or IBN (branched alkyl nitrogen-containing compound) or BA or BN (linear alkyl nitrogen-containing compound) relative to LiFSI was confirmed to reduce all three types of resistance: initial resistance, resistance associated with battery use, and resistance after high-temperature storage, compared to a secondary battery containing a "reference electrolyte" (Comparative Example 2-1) that does not contain a linear alkyl nitrogen-containing compound. On the other hand, it was confirmed that even in the case of a "nitrogen-containing electrolyte," electrolytes in which the content of the linear alkyl nitrogen-containing compound relative to LiFSI exceeds 6000 ppm by mass (Comparative Examples 2-2, 2-3, 2-5, and 2-6) increased all three types of resistance compared to a secondary battery containing a "reference electrolyte." Therefore, LiFSI and LiPF ６ It was found that the "nitrogen-containing electrolyte solution" containing an electrolyte salt of a mixed salt composition including (another electrolyte) also has the effect of reducing the resistance of a secondary battery, similar to the "nitrogen-containing electrolyte solution" containing an electrolyte salt of a simple salt composition including LiFSI alone.

[0085] (2) Evaluation of storage stability Each of the nonaqueous electrolyte solutions prepared in the above <Preparation of nonaqueous electrolyte solutions> shown in Table 4 was stored in a sealed PFA container at 45°C for one month. After that, the sulfate ions (SO ４ ２－ The concentrations of ) were measured in the same manner as in Example 1. The results are shown in Table 4.

[0086]

[0087] ((2) Summary of Evaluation of Storage Stability) From Table 4, LiFSI (sulfonylimide compound (1)) and LiPF ６In nonaqueous electrolytes containing electrolyte salts of mixed salt compositions containing (other electrolytes), the "nitrogen-containing electrolytes" (each Example) containing 10 ppm by mass or more and 6000 ppm by mass or less of a branched alkyl nitrogen-containing compound or a linear alkyl nitrogen-containing compound relative to LiFSI were confirmed to have lower sulfate ion concentrations (amount of decomposition products of LiFSI) after one month of storage at 45°C than the "reference electrolyte" (Comparative Example 2-1) that did not contain a linear alkyl nitrogen-containing compound. Therefore, it was confirmed that the "nitrogen-containing electrolytes" suppressed LiFSI decomposition and had better storage stability than the "reference electrolyte." Meanwhile, even for "nitrogen-containing electrolytes," electrolytes (Comparative Examples 2-4 and 2-7) containing more than 6000 ppm by mass of a linear alkyl nitrogen-containing compound relative to LiFSI showed higher sulfate ion concentrations after one month of storage at 45°C than the "reference electrolyte," demonstrating advanced LiFSI decomposition and inferior storage stability. Therefore, LiFSI and LiPF ６ It was found that "nitrogen-containing electrolytes" containing electrolyte salts of mixed salt compositions including (other electrolytes) also have the same effect of excellent storage stability as "nitrogen-containing electrolytes" containing electrolyte salts of simple salt compositions containing LiFSI alone. Furthermore, taking these results into consideration, it is predicted that the effect of excellent storage stability will also be obtained when the branched alkyl nitrogen-containing compound is replaced with a linear alkyl nitrogen-containing compound in the "nitrogen-containing electrolytes" (Table 2) containing electrolyte salts of simple salt compositions containing LiFSI alone.

Claims

1. a sulfonylimide compound represented by general formula (1) and at least one nitrogen-containing compound selected from the group consisting of an amide compound having a branched alkyl group with 3 to 6 carbon atoms and a nitrile compound having a branched alkyl group with 3 to 6 carbon atoms, The nonaqueous electrolyte solution is characterized in that the content of the nitrogen-containing compound relative to the sulfonylimide compound is 10 ppm by mass or more and 6000 ppm by mass or less. LiN (RSO ２ ) (FSO ２ ) (R represents a fluorine atom, an alkyl group having 1 to 6 carbon atoms, or a fluoroalkyl group having 1 to 6 carbon atoms) ... (1)

2. a sulfonylimide compound represented by general formula (1) and at least one nitrogen-containing compound selected from the group consisting of an amide compound having a linear alkyl group with 3 to 6 carbon atoms and a nitrile compound having a linear alkyl group with 3 to 6 carbon atoms, The nonaqueous electrolyte solution is characterized in that the content of the nitrogen-containing compound relative to the sulfonylimide compound is 10 ppm by mass or more and 6000 ppm by mass or less. LiN (RSO ２ ) (FSO ２ ) (R represents a fluorine atom, an alkyl group having 1 to 6 carbon atoms, or a fluoroalkyl group having 1 to 6 carbon atoms) ... (1)

3. The sulfonylimide compound represented by the general formula (1) is LiN(FSO ２ ) ２ 3. The nonaqueous electrolyte solution according to claim 1, comprising:

4. 3. The nonaqueous electrolyte solution according to claim 1, further comprising another electrolyte.

5. 5. The nonaqueous electrolyte solution according to claim 4, wherein the molar ratio of the sulfonylimide compound represented by the general formula (1) to the other electrolyte is 1:25 or more and 2:1 or less.