JP6712117B2 - Non-aqueous electrolyte and lithium-ion secondary battery including the same - Google Patents

Description

The present invention relates to a non-aqueous electrolyte solution and a lithium ion secondary battery including the same.

Lithium ion secondary batteries are used as power sources for smartphones and personal computers, and also as power sources for automobiles. Batteries used for these applications are being researched for the purpose of improving various characteristics such as higher output, higher energy density, and improved cycle characteristics and rate characteristics.

For example, as a technique for attempting to improve the characteristics of a lithium-ion secondary battery from the electrolyte surface, a technique using an acid anhydride as an additive for a non-aqueous electrolyte solution has been proposed. Patent Document 1 discloses a technique of suppressing deterioration of high-temperature storage characteristics by adding benzoic anhydride, phthalic anhydride, and maleic anhydride to an electrolyte of a non-aqueous electrolyte secondary battery. In 2, the use of a carboxylic acid anhydride such as succinic acid anhydride, glutaric acid anhydride or maleic acid anhydride in combination with a specific electrolyte salt improves the low temperature cycle characteristics of the battery and improves the chemical efficiency of the electrolyte solution. Techniques have been proposed to improve stability.

Japanese Patent No. 2697365 JP, 2013-16456, A

As described above, various studies have been made to improve the battery characteristics, but with the expansion of applications, batteries are required to have higher energy density. In order to increase the energy density of the battery, it is necessary to drive the battery under high voltage. However, when the battery is driven under a high voltage, there are problems that the electrolytic solution is decomposed at the positive electrode and the transition metal in the positive electrode active material is eluted to deteriorate the cycle characteristics and rate characteristics of the battery. Further, this problem becomes particularly noticeable when the lithium ion secondary battery is stored at a high temperature.

The present invention has been made by paying attention to the above circumstances, and an object thereof is to store capacity under high temperature (for example, 60° C. or higher) and then use under high voltage even if capacity, cycle characteristics and It is an object of the present invention to provide a non-aqueous electrolytic solution capable of suppressing deterioration of rate characteristics and a lithium ion secondary battery using the same.

The non-aqueous electrolyte solution of the present invention which can achieve the above-mentioned object is represented by the general formula (1): [N(XSO ₂ )(FSO ₂ )] ^- (in the general formula (1), X is a fluorine atom or carbon. Represents an alkyl group having 1 to 6 carbon atoms or a fluoroalkyl group having 1 to 6 carbon atoms),
Lithium cation,
It is characterized in that it contains an aromatic ring and an acid anhydride having at least one structure represented by —C(═O)—O—C(═O)— in the molecule.

The nonaqueous electrolytic solution contains, as an electrolyte salt, at least one compound selected from the group consisting of compounds represented by the following general formulas (7) and (8) and lithium hexafluoroarsenate. Is preferred.
LiPF _l (C _m F _2m+1 ) _6-l (0≦l≦6, 1≦m≦4) (7)
LiBF _n (C _o F _2o+1 ) _4-n (0≦n≦4, 1≦o≦4) (8)

The acid anhydride is preferably a compound having an aromatic ring having 6 to 10 carbon atoms, and the acid anhydride according to the present invention is -C(=O)-OC(=O)-. Compounds having a cyclic structure including the structures shown are preferred.

The present invention also includes a lithium ion secondary battery including the above non-aqueous electrolyte solution. The lithium-ion secondary battery of the present invention preferably has a rated charging voltage higher than 4.2V.

INDUSTRIAL APPLICABILITY The non-aqueous electrolyte solution of the present invention is effective in suppressing a decrease in capacity and rate characteristics of a lithium ion secondary battery after high temperature storage and in suppressing a decrease in capacity retention rate during high temperature cycles. Therefore, according to the non-aqueous electrolyte solution of the present invention, it is possible to provide a lithium ion secondary battery in which the deterioration of capacity, rate characteristics and cycle characteristics is suppressed.

1. Non-Aqueous Electrolyte Solution The non-aqueous electrolyte solution of the present invention is represented by the general formula (1): [N(XSO ₂ )(FSO ₂ )] ^- (in the general formula (1), X represents a fluorine atom and a carbon number of 1 to 1). An alkyl group having 6 or a fluoroalkyl group having 1 to 6 carbon atoms) (hereinafter referred to as a sulfonylimide anion (1)), a lithium cation, an aromatic ring in the molecule,- It is characterized in that it contains an acid anhydride having at least one structure represented by C(=O)-OC(=O)-.

The inventors of the present invention can use the non-aqueous electrolytic solution having the above-described configuration to decompose or decompose the electrolytic solution even if the battery is stored under a temperature environment of 60° C. or higher and then operated under a high voltage condition exceeding 4.2V. Elution of transition metal in the positive electrode active material is less likely to occur, and as a result, a lithium ion secondary battery in which deterioration of capacity and rate characteristics is suppressed can be obtained; and 4.2 V under a temperature condition of 45° C. or higher. The present invention has been completed by finding that the decomposition of the electrolytic solution and the elution of the transition metal in the positive electrode active material are less likely to occur even during the charge/discharge cycle at a charging voltage exceeding the limit, and the cycle performance is improved.

The non-aqueous electrolyte is a sulfonylimide anion (1), a lithium cation, an aromatic ring in the molecule, and an acid anhydride having a structure represented by -C(=O)-OC(=O)-. The present inventors consider the reason why the capacity and rate characteristics of the lithium-ion secondary battery can be improved by containing the following.

When the non-aqueous electrolyte contains the sulfonylimide anion (1) and the battery is stored at a high temperature and then driven under a high voltage condition of more than 4.2 V, the rate characteristic may be deteriorated. It is considered that this is because the sulfonylimide anion (1) enhances the activity of the positive electrode, and as a result, the electrolytic solution material is decomposed in the positive electrode and the decomposition products are deposited on the opposing separator and the negative electrode. However, the addition of a specific acid anhydride to the non-aqueous electrolyte containing the sulfonylimide anion (1) suppresses the deterioration of the rate characteristics. This is considered to be because the acid anhydride according to the present invention is present in the non-aqueous electrolytic solution, the electrolytic solution material is less likely to be decomposed, and the deposition of decomposition products on the negative electrode and the separator is suppressed. .. In addition, the compound containing the sulfonylimide anion (1) has an effect of suppressing the elution of the transition metal in the positive electrode active material, and exhibits a relatively high ionic conductivity. Therefore, as a result of the presence of the sulfonylimide anion (1) and the specific acid anhydride in the non-aqueous electrolyte, the respective effects act synergistically, and as a result, under relatively high voltage conditions after high temperature storage. It is presumed that deterioration of the battery can be suppressed even when used and the high battery characteristics can be maintained. The non-aqueous electrolyte solution of the present invention will be described below.

1-1. Sulfonylimide anion (1)
The sulfonylimide anion (1) according to the present invention is represented by the general formula (1): [N(XSO ₂ )(FSO ₂ )] ⁻ . In the general formula (1), X represents a fluorine atom, an alkyl group having 1 to 6 carbon atoms, or a fluoroalkyl group having 1 to 6 carbon atoms. The alkyl group having 1 to 6 carbon atoms is preferably a linear or branched alkyl group, and more preferably a linear alkyl group. Examples of the alkyl group having 1 to 6 carbon atoms include methyl group, ethyl group, propyl group, isopropyl group, butyl group, pentyl group and hexyl group. Examples of the fluoroalkyl group having 1 to 6 carbon atoms include those in which part or all of the hydrogen atoms of the alkyl group having 1 to 6 carbon atoms are substituted with fluorine atoms. Specific examples thereof include a fluoromethyl group, a difluoromethyl group, a trifluoromethyl group, a fluoroethyl group, a difluoroethyl group, a trifluoroethyl group and a pentafluoroethyl group. Among these, a fluorine atom, a trifluoromethyl group and a pentafluoroethyl group are preferable as X.

Specific examples of the sulfonylimide anion (1) include bis(fluorosulfonyl)imide anion, (fluorosulfonyl)(methylsulfonyl)imide anion, (fluorosulfonyl)(ethylsulfonyl)imide anion, (fluorosulfonyl)(trifluorosulfonyl) Examples thereof include fluoromethylsulfonyl)imide anion and (fluorosulfonyl)(pentafluoroethylsulfonyl)imide anion. Preferred is a bis(fluorosulfonyl)imide anion, (fluorosulfonyl)(trifluoromethylsulfonyl)imide anion, (fluorosulfonyl)(pentafluoroethylsulfonyl)imide anion, and more preferred is a bis(fluorosulfonyl)imide anion, ( Fluorosulfonyl)(trifluoromethylsulfonyl)imide anion.
The non-aqueous electrolytic solution of the present invention may contain one sulfonylimide anion (1) alone, or may contain two or more sulfonylimide anions (1).

In the non-aqueous electrolytic solution of the present invention, the sulfonylimide anion (1) is present in a dissociated state with the cation, but before being dispersed and dissolved in the non-aqueous electrolytic solution, it is in the state of a salt ionically bonded to the cation. Existing. The cation forming a salt with the sulfonylimide anion (1) according to the present invention is not particularly limited, and may be an inorganic cation or an organic cation. The sulfonylimide compound containing the sulfonylimide anion (1) can function as an electrolyte salt in the non-aqueous electrolytic solution of the present invention, and can also function as an additive for improving the performance of the battery. It is possible. That is, when the sulfonylimide compound containing the sulfonylimide anion (1) is, for example, a lithium salt, it can function as an electrolyte salt of an electrolytic solution for a lithium battery.

The inorganic cations include monovalent inorganic cations such as Li ⁺ , Na ⁺ , K ⁺ , Cs ⁺ , Pb ⁺ ; Mg ²⁺ , Ca ²⁺ , Zn ²⁺ , Pd ²⁺ , Sn ²⁺ , Hg ^2+. , Rh ²⁺ , Cu ²⁺ , Be ²⁺ , Sr ²⁺ , Ba ^{2+ and the} like; and trivalent inorganic cations such as Ga ³⁺ . Among these, alkali metal cations and alkaline earth metal cations are preferable, and Li ⁺ , Na ⁺ , Mg ²⁺ and Ca ²⁺ are more preferable because they have a small ionic radius and are easily used in batteries and the like, and Li ⁺ is particularly preferable.

Examples of the organic cation include general formula (3): L ⁺ —R _s (wherein, L represents C, Si, N, P, S or O, R is the same or different organic group, and is bonded to each other. S represents the number of Rs bonded to L and is 3 or 4. Note that s is a value determined by the valence of the element L and the number of double bonds directly bonded to L. An onium cation represented by) is suitable.

The “organic group” represented by R means a group having at least one hydrogen atom, fluorine atom, or carbon atom. The above-mentioned "group having at least one carbon atom" need only have at least one carbon atom, and may have another atom such as a halogen atom or a hetero atom, or a substituent. Good. Examples of the substituent include an amino group, an imino group, an amide group, a group having an ether bond, a group having a thioether bond, an ester group, a hydroxyl group, an alkoxy group, a carboxyl group, a carbamoyl group, a cyano group, a disulfide group, and a nitro group. Group, nitroso group, sulfonyl group and the like.

Examples of the onium cation represented by the general formula (3) include those represented by the following general formula.

(R in the formula is the same as in the general formula (3))

Among the six onium cations represented by the above general formula, those in which L is N, P, S or O are more preferable, and the onium cation in which L is N is more preferable. The onium cations may be used alone or in combination of two or more. Specific examples of the onium cation in which L is N include those represented by the following general formulas (4) to (6) as preferable onium cations.

General formula (4):

At least one of the 10 types of heterocyclic onium cations represented by.

Examples of the organic groups R ^{1 to} R ⁸ include the same groups as the organic group R exemplified in the general formula (3). More specifically, R ^{1 to} R ⁸ are a hydrogen atom, a fluorine atom or an organic group, and as the organic group, straight chain, branched chain or cyclic (provided that R ^{1 to} R ⁸ are bonded to each other to form a ring). C1-18 hydrocarbon group (excluding those having a carbon number of 1), or a C1-18 fluorocarbon group, and more preferably a C1-8 hydrocarbon group or a carbon number. 1 to 8 fluorocarbon groups. Further, the organic group may contain the substituents exemplified with respect to the general formula (3), a hetero atom such as N, O and S, and a halogen atom.

General formula (5):

(In the formula, R ^{1 to} R ¹² are the same as R ^{1 to} R ^{8 in} the general formula (4))
At least one of the three types of saturated ring onium cations represented by.

General formula (6):

(In the formula, R ^{1 to} R ⁴ are the same as R ^{1 to} R ^{8 in} the general formula (4))
A chained onium cation represented by. For example, the chain onium cation represented by the general formula (6) includes tetramethylammonium, tetraethylammonium, tetrapropylammonium, tetrabutylammonium, tetraheptylammonium, tetrahexylammonium, tetraoctylammonium, triethylmethylammonium, methoxy. Ethyldiethylmethylammonium, trimethylphenylammonium, benzyltrimethylammonium, benzyltriethylammonium, benzyltributylammonium, dimethyldistearylammonium, diallyldimethylammonium, 2-methoxyethoxymethyltrimethylammonium, tetrakis(pentafluoroethyl)ammonium, N-methoxytrimethyl Quaternary ammoniums such as ammonium, N-ethoxytrimethylammonium and N-propoxytrimethylammonium; tertiary ammoniums such as trimethylammonium, triethylammonium, tributylammonium, diethylmethylammonium, dimethylethylammonium, dibutylmethylammonium; dimethyl. Secondary ammoniums such as ammonium, diethylammonium and dibutylammonium; primary ammoniums such as methylammonium, ethylammonium, butylammonium, hexylammonium and octylammonium; and ammonium ions represented by NH _4. ..

Among the onium cations represented by the general formulas (4) to (6), more preferable ones are the following general formulas;

(In the formula, R ^{1 to} R ¹² are the same as R ^{1 to} R ^{8 in} the general formula (4).)
At least one of the six types of onium cations represented by

Among the above six kinds of onium cations, chain quaternary ammonium such as tetraethylammonium, tetrabutylammonium and triethylmethylammonium; chain quaternary ammonium such as triethylammonium, tributylammonium, dibutylmethylammonium and dimethylethylammonium; Imidazolium such as 1-ethyl-3-methylimidazolium and 1,2,3-trimethylimidazolium; pyrrolidinium such as N,N-dimethylpyrrolidinium and N-ethyl-N-methylpyrrolidinium are easily available. It is more preferable because it exists. More preferred are quaternary ammonium and imidazolium. From the viewpoint of resistance to reduction, quaternary ammonium such as tetraethylammonium, tetrabutylammonium, and triethylmethylammonium, which are classified as the above chain onium cations, are more preferable.

The sulfonylimide compound (compound having the sulfonylimide anion (1)) that dissociates in the non-aqueous electrolyte to generate the sulfonylimide anion (1) may be a combination of the sulfonylimide anion (1) and the cation described above. For example, lithium bis(fluorosulfonyl)imide, lithium(fluorosulfonyl)(methylsulfonyl)imide, lithium(fluorosulfonyl)(ethylsulfonyl)imide, lithium(fluorosulfonyl)(trifluoromethylsulfonyl)imide, lithium (Fluorosulfonyl)(pentafluoroethylsulfonyl)imide and the like.

The sulfonylimide compounds may be used alone or in combination of two or more. As the sulfonylimide compound, a commercially available product may be used, or a compound synthesized by a conventionally known method may be used.

The concentration of the sulfonylimide anion (1) (sulfonylimide compound) in the non-aqueous electrolytic solution is preferably 0.01 mol/L or more, more preferably 0.1 mol/L or more, and further preferably 0.2 mol. /L or more, preferably 1.5 mol/L or less, more preferably 1.0 mol/L or less, and further preferably 0.8 mol/L or less. If the concentration of the sulfonylimide anion (1) in the non-aqueous electrolyte is too high, the viscosity of the non-aqueous electrolyte may increase and the ionic conductivity may decrease, or the sulfonylimide anion (1) may cause positive electrode current collection. Corrosion may occur in the body. On the other hand, if the concentration is too low, it may be difficult to obtain the effect of suppressing the elution of the positive electrode material and the effect of improving the ionic conductivity.

1-2. Electrolyte Salt The non-aqueous electrolyte solution of the present invention may contain an electrolyte salt different from the sulfonylimide compound. Examples of the electrolyte salt include trifluoromethanesulfonate ion (CF ₃ SO ₃ ⁻ ), fluorophosphate ion (PF ₆ ⁻ ), perchlorate ion (ClO ₄ ⁻ ), tetrafluoroborate ion (BF ₄ ⁻ ), and hexafluoro. Arsenate ion (AsF ₆ ⁻ ), tetracyanoborate ion ([B(CN) ₄ ] ⁻ ), tetrachloroaluminum ion (AlCl ₄ ⁻ ), tricyanomethide ion (C[(CN) ₃ ] ⁻ ), di Cyanamide ion (N[(CN) ₂ ] ^- ), tris(trifluoromethanesulfonyl)methide ion (C[(CF ₃ SO ₂ ) ₃ ] ^- ), hexafluoroantimonate ion (SbF ₆ ^- ) and dicyanotriazolate ion A conventionally known electrolyte salt such as an inorganic or organic cation salt having (DCTA) as an anion can be used. The inorganic cation and the organic cation include the same ones as the counter cation of the sulfonylimide anion (1).

Among the electrolyte salts, a compound (fluorophosphate) represented by the general formula (7): LiPF ₁ (C _m F _2m+1 ) _6-l (0≦l≦6, 1≦m≦4), generally equation _{(8): LiBF n (C} o F 2o + 1) 4-n (0 ≦ n ≦ 4,1 ≦ o ≦ 4) a compound represented by (fluoro borate) and hexafluoride arsenate lithium (LiAsF ₆ One or more lithium salts selected from the group consisting of By using these lithium salts together, corrosion of the positive electrode current collector due to the sulfonylimide anion (1) can be suppressed.

Examples of the compound represented by the general formula (7) (hereinafter sometimes referred to as lithium salt (7)) include LiPF ₆ , LiPF ₃ (CF ₃ ) ₃ , LiPF ₃ (C ₂ F ₅ ) ₃ and LiPF _{3. (C 3 F 7) 3,} LiPF 3 (C 4 F 9) 3 and the like as preferred. LiPF ₆ and LiPF ₃ (C ₂ F ₅ ) ₃ are more preferable, and LiPF ₆ is still more preferable.

Examples of the compound represented by the general formula (8) (hereinafter sometimes referred to as lithium salt (8)) include LiBF ₄ , LiBF(CF ₃ ) ₃ , LiBF(C ₂ F ₅ ) ₃ , LiBF(C ₃ F ₇ ) _{3 and the} like are mentioned as preferable ones, LiBF ₄ and LiBF(CF ₃ ) ₃ are more preferable, and LiBF ₄ is further preferable.

As the electrolyte salt, the above-exemplified compounds may be used alone or in combination of two or more. Preferred electrolyte salts are LiPF ₆ , LiPF ₃ (C ₂ F ₅ ) ₃ and LiBF(CF ₃ ) ₃ , more preferably LiPF ₆ and LiPF ₃ (C ₂ F ₅ ) ₃ and even more preferably LiPF 6. _{Is 6} . Particularly, LiPF ₆ is preferable from the viewpoint of ionic conductivity.

When the non-aqueous electrolyte solution of the present invention contains an electrolyte salt (lithium salt (7), (8) and/or LiAsF ₆ ), the amount of the electrolyte salt used is the lithium cation concentration in the non-aqueous electrolyte solution of the present invention. Especially as long as the sum total (the total of the lithium cation concentration derived from the electrolyte salt and the lithium cation concentration derived from the sulfonylimide compound containing the lithium cation) is within the range described below (preferably more than 1.1 mol/L and not more than the saturation concentration) There is no limitation.
However, if the concentration of the electrolyte salt is too high, the ionic conductivity may decrease due to an increase in viscosity, while if the concentration of the electrolyte salt is too low, corrosion of the positive electrode current collector due to the sulfonylimide compound may occur. There is. Therefore, it is preferable to use the electrolyte salt within a range where the ratio of the sulfonylimide compound to the electrolyte salt is 1:100 to 5:1 (sulfonylimide compound:electrolyte salt, molar ratio). It is more preferably 1:10 to 3:1 and even more preferably 1:2 to 2:1.

1-3. Lithium Cation The non-aqueous electrolytic solution of the present invention contains a lithium cation. The lithium cation may be derived from the sulfonylimide compound or may be derived from the above-mentioned electrolyte salt. The concentration of lithium cation contained in the non-aqueous electrolytic solution of the present invention is preferably more than 1.1 mol/L. The lithium cation concentration of the non-aqueous electrolytic solution of the present invention is more preferably 1.11 mol/L or more, still more preferably 1.2 mol/L or more, and further preferably 1.25 mol/L or more. If the lithium cation concentration is too high, the viscosity of the electrolytic solution may increase and the ionic conductivity may decrease. Therefore, it is preferably used at a saturation concentration or less. It is more preferably 2.0 mol/L or less, and further preferably 1.5 mol/L or less.

Here, the “concentration of lithium cations in the non-aqueous electrolytic solution” is a value based on the total amount of lithium cations contained in the non-aqueous electrolytic solution of the present invention, for example, an electrolyte salt having two or more kinds of lithium cations ( When the electrolyte salt (7), (8) and/or LiAsF ₆ ) is used, the total amount of lithium cations produced from the used electrolyte salt, and when the sulfonylimide compound contains a lithium cation, The value obtained based on the total amount of the lithium cations contained in the imide compound and the lithium cations contained in the electrolyte salt used together is the concentration of the lithium cations in the non-aqueous electrolytic solution. When the sulfonylimide compound does not contain a lithium cation, the total concentration of electrolyte salts (containing lithium cations) used in combination may be considered as the lithium cation concentration.

1-4. Acid Anhydride The non-aqueous electrolytic solution of the present invention contains an acid anhydride having at least one structure represented by —C(═O)—O—C(═O)— in the molecule. When such an acid anhydride is contained in the non-aqueous electrolytic solution, the acid anhydride is decomposed at the time of initial charging of the battery, and a film is formed on the positive electrode and the negative electrode, thereby suppressing decomposition of the electrolytic solution material. To be done. Further, the coating film suppresses the deposition of decomposition products on the negative electrode and the separator.

The acid anhydride according to the present invention has an aromatic ring. As the aromatic ring, for example, those having 6 to 20 carbon atoms are preferable. It is more preferably 6 to 12, and even more preferably 6 to 10. Specific examples of the aromatic ring include a benzene ring, a naphthalene ring, an anthracene ring, a pyrene ring and a perylene ring. A benzene ring and a naphthalene ring are preferable, and a benzene ring is more preferable. The acid anhydride of the present invention may contain one aromatic ring or two or more aromatic rings. An acid anhydride having one aromatic ring is preferable.

As the acid anhydride according to the present invention, for example, a dehydration condensation product obtained by a dehydration condensation reaction between carboxyl groups can be used. The dehydration condensate may be an intramolecular dehydration condensate (so-called anhydride) of a compound having two or more carboxyl groups in one molecule, and an intermolecular dehydration condensate between two molecules of compounds having a carboxyl group. May be

The acid anhydride according to the present invention is preferably a compound having an acid anhydride ring structure in which a “—C(═O)—O—C(═O)—” structure constitutes a part of the ring, and is preferably one molecule. A compound having 1 to 2 acid anhydride ring structures is preferable. Further, the acid anhydride according to the present invention is more preferably a compound having a structure in which an aromatic ring and an acid anhydride ring are condensed, for example, a dehydration condensation product of an aromatic polyvalent carboxylic acid.

The aromatic polycarboxylic acid may be a compound having two or more carboxylic acids bonded to an aromatic ring, and dehydration condensation of aromatic dicarboxylic acid compounds, aromatic tetracarboxylic acid compounds, aromatic hexacarboxylic acid compounds, etc. Things can be mentioned. A compound having one or two acid anhydride ring structures is preferable, and a dehydration condensation product of an aromatic dicarboxylic acid compound or an aromatic tetracarboxylic acid compound is preferable, and a dehydration condensation product of an aromatic dicarboxylic acid compound is more preferable. Is.

Examples of the acid anhydride according to the present invention include those represented by the following chemical formulas (2-1) to (2-12).

Among the above-exemplified acid anhydrides, from the viewpoint of more effectively suppressing deterioration of the characteristics of the battery during high temperature storage, a formula (intramolecular dehydration condensation product of a compound having two or more carboxyl groups in one molecule) ( The compounds represented by 2-1) to (2-10) are preferable, and more preferably the formulas (2-1), (2-2), (2-3), which have a 5-membered ring acid anhydride structure. It is a compound represented by (2-4), more preferably a compound represented by formula (2-1) or (2-2). The acid anhydrides may be used alone or in combination of two or more.

The concentration of the acid anhydride in the non-aqueous electrolytic solution of the present invention is based on the mass of the electrolytic solution before the addition of the acid anhydride (the total of the components other than the acid anhydride such as the electrolyte salt, the solvent and the additive is 100% by mass). Is preferably 0.001 mass% or more, more preferably 0.01 mass% or more, even more preferably 0.1 mass% or more, still more preferably 0.5 mass% or more, It is preferably 5% by mass or less, more preferably 3% by mass or less, and further preferably 2% by mass or less. Even if a large amount of acid anhydride is used, an effect commensurate with the amount used cannot be obtained, but rather, there is a possibility that the concentration of the electrolyte salt may be reduced or that the ionic conductivity may be reduced due to an increase in viscosity. If the concentration is too low, it may be difficult to obtain the intended effect of suppressing the decrease in battery capacity after high temperature storage.

1-5. Solvent The non-aqueous electrolytic solution of the present invention may contain a solvent. The solvent that can be used in the non-aqueous electrolytic solution of the present invention is not particularly limited as long as it can dissolve and disperse an electrolyte salt (such as a sulfonylimide compound and the above-mentioned lithium salt), and for example, a cyclic carbonate described below. Any conventionally known solvent used for batteries, such as a non-aqueous solvent such as a solvent other than or a cyclic carbonate, a medium such as a polymer or a polymer gel used in place of the solvent, or the like can be used.

As the non-aqueous solvent, a solvent having a large dielectric constant, a high solubility of an electrolyte salt, a boiling point of 60° C. or higher, and a wide electrochemical stability range is suitable. More preferably, it is an organic solvent (non-aqueous solvent) having a low water content. As such an organic solvent, 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, Ethers such as 1,4-dioxane and 1,3-dioxolane; chain carbonates such as dimethyl carbonate, ethyl methyl carbonate (ethyl methyl carbonate), diethyl carbonate (diethyl carbonate), diphenyl carbonate, methyl phenyl carbonate; carbonic acid Saturated cyclic carbonates such as ethylene (ethylene carbonate), propylene carbonate (propylene carbonate), 2,3-dimethyl ethylene carbonate (2,3-butanediyl carbonate), 1,2-butylene carbonate and erythritan carbonate; vinylene carbonate, Methyl vinylene carbonate (MVC; 4-methyl-1,3-dioxole-2-one), ethyl vinylene carbonate (EVC; 4-ethyl-1,3-dioxole-2-one), 2-vinyl carbonate ethylene (4- Cyclic carbonic acid esters having unsaturated bonds such as vinyl-1,3-dioxolan-2-one) and phenylethylene carbonate (4-phenyl-1,3-dioxolan-2-one); fluoroethylene carbonate, 4,5 -Fluorine-containing cyclic carbonic acid esters such as difluoroethylene carbonate and trifluoropropylene carbonate; aromatic carboxylic acid esters such as methyl benzoate and ethyl benzoate; lactones such as γ-butyrolactone, γ-valerolactone and δ-valerolactone Phosphates such as trimethyl phosphate, ethyldimethyl phosphate, diethylmethyl phosphate, triethyl phosphate, etc.; acetonitrile, propionitrile, methoxypropionitrile, glutaronitrile, adiponitrile, 2-methylglutaronitrile, Nitriles such as valeronitrile, butyronitrile and isobutyronitrile; sulfur compounds such as dimethyl sulfone, ethylmethyl sulfone, diethyl sulfone, sulfolane, 3-methylsulfolane and 2,4-dimethylsulfolane; aromatics such as benzonitrile and tolunitrile Group nitriles; nitromethane, 1,3-dimethyl-2-imidazolidinone, 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone, 3-methyl-2-oxa Examples thereof include zolidinone.

Among these, carbonic acid esters (carbonate-based solvents) such as chain carbonic acid esters and cyclic carbonic acid esters, lactones and ethers are preferable, and dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, γ -Butyrolactone, γ-valerolactone and the like are more preferable, and carbonate solvents such as dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, ethylene carbonate and propylene carbonate are further preferable. The above non-aqueous solvents may be used alone or in combination of two or more.

When the above polymer or polymer gel is used instead of the solvent, the following method may be adopted. That is, a method in which a solution prepared by dissolving an electrolyte salt in the above-mentioned non-aqueous solvent is added dropwise to a polymer formed by a conventionally known method to impregnate and carry the electrolyte salt and the non-aqueous solvent; a temperature equal to or higher than the melting point of the polymer A method of melting and mixing a polymer and an electrolyte salt with, forming a film, and impregnating a non-aqueous solvent therein (above, gel electrolyte); a non-aqueous electrolyte solution and a polymer in which an electrolyte salt is previously dissolved in an organic solvent After mixing, a film is formed by a casting method or a coating method to evaporate the organic solvent; a method in which the polymer and the electrolyte salt are melted at a temperature equal to or higher than the melting point of the polymer, and the mixture is molded (intrinsic polymer electrolyte ); and the like.

The polymer used in place of the solvent is a polyether polymer such as polyethylene oxide (PEO) or polypropylene oxide, which is a homopolymer or copolymer of an epoxy compound (ethylene oxide, propylene oxide, butylene oxide, allyl glycidyl ether, etc.). , Methacrylic polymers such as polymethylmethacrylate (PMMA), nitrile polymers such as polyacrylonitrile (PAN), polyvinylidene fluoride (PVdF), fluoropolymers such as polyvinylidene fluoride-hexafluoropropylene, and copolymers thereof. Etc.

From the viewpoint of preventing decomposition of the solvent and suppressing deterioration of cycle characteristics (lifetime) when the non-aqueous electrolytic solution of the present invention is used in a lithium ion secondary battery, it is recommended to use a cyclic carbonate as the solvent. To be done. Examples of the cyclic carbonate include the above-mentioned saturated cyclic carbonate, cyclic carbonate having an unsaturated bond, and fluorine-containing cyclic carbonate. Among these, saturated cyclic carbonates are preferable from the viewpoint of cost, and ethylene carbonate and propylene carbonate are particularly preferable. The cyclic carbonate may be used alone or in combination of two or more kinds.

The cyclic carbonate is preferably used in such a range that the molar ratio (cyclic carbonate/Li ⁺ ) to all lithium cations contained in the non-aqueous electrolyte is 1 or more and 5 or less. When the cyclic carbonate is used within the above range, deterioration of cycle characteristics (lifetime) of the lithium ion secondary battery is further suppressed.

It is known that one cause of deterioration in cycle characteristics is decomposition of the solvent that constitutes the non-aqueous electrolyte. However, when the amount of cyclic carbonate used is within the above range with respect to lithium ions, deterioration of cycle characteristics can be further suppressed. By determining the amount of cyclic carbonate to be used according to the amount of lithium ions, the amount of cyclic carbonate (free cyclic carbonate) that is not solvated with lithium ions present in the non-aqueous electrolyte can be reduced. That is, since the amount of free cyclic carbonate that can participate in the decomposition reaction decreases, it is considered that the decomposition reaction of the solvent is less likely to occur and the deterioration of the cycle characteristics is suppressed.

If the molar ratio (cyclic carbonate/Li ⁺ ) is too large, the free cyclic carbonate excessively present in the non-aqueous electrolyte is oxidized and/or reductively decomposed, resulting in deterioration of cycle characteristics. On the other hand, if the molar ratio is too small, the amount of cyclic carbonate is too small, the effect derived from the cyclic carbonate (for example, the effect of forming a coating on the negative electrode, suppressing the decomposition of the non-aqueous electrolyte, etc.) is obtained. However, there is a possibility that the non-aqueous electrolyte may be drained due to consumption of the solvent (film formation, decomposition, etc.) due to repeated charging and discharging. Therefore, the cyclic carbonate is more preferably used in a molar ratio to the lithium ion (cyclic carbonate/Li ⁺ ) of 1 or more and 4 or less, more preferably 3 or less, further preferably 2.0 or less. It is particularly preferably 1.8 or less.

The molar ratio of the cyclic carbonate to the lithium cation (cyclic carbonate/Li ⁺ ) may be calculated based on the specific gravity and molar mass of the cyclic carbonate. For example, in the case of ethylene carbonate, the specific gravity may be 1.321 and the molar mass may be 88.06.

Even when the cyclic carbonate is used, the non-aqueous electrolytic solution may contain a solvent (other solvent) other than the cyclic carbonate. Examples of the other solvent include the above-mentioned non-aqueous solvents (other than cyclic carbonate). Among the above non-aqueous solvents, chain carbonic acid esters, aliphatic carboxylic acid esters, lactones and ethers are preferable, and dimethyl carbonate, ethylmethyl carbonate, diethyl carbonate, γ-butyrolactone, γ-valerolactone and the like are more preferable. .. The other solvent may be used alone or in combination of two or more.

In this case, the amount of the other solvent used is preferably 50% by volume or more, more preferably 55% by volume or more, further preferably 60% by volume, based on 100% by volume of the total amount of the cyclic carbonate and the other solvent. % Or more, preferably 99% by volume or less, more preferably 95% by volume or less, and further preferably 90% by volume or less.

1-6. Other Components The non-aqueous electrolytic solution according to the present invention may contain an additive for the purpose of improving various characteristics of the lithium ion secondary battery.
As the additive, acetic anhydride, propionic anhydride, butyric anhydride, crotonic anhydride, succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, diglycolic acid, cyclohexanedicarboxylic acid. Carboxylic acid anhydrides such as acid anhydrides and cyclopentanetetracarboxylic acid dianhydrides; ethylene sulfite, 1,3-propane sultone, 1,4-butane sultone, methyl methanesulfonate, busulfan, sulfolane, sulfolene, dimethyl sulfone, Sulfur-containing compounds such as tetramethylthiuram monosulfide and trimethylene glycol sulfate; 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl-2-oxazolidinone, 1,3-dimethyl-2-imidazo Examples thereof include nitrogen-containing compounds such as ridinone and N-methylsuccinimide; phosphates such as monofluorophosphate and difluorophosphate; saturated hydrocarbon compounds such as heptane, octane and cycloheptane.

The additive is preferably used in the range of 0.1% by mass or more and 10% by mass or less in 100% by mass of the non-aqueous electrolyte solution of the present invention (more preferably 0.2% by mass or more and 8% by mass or less, More preferably 0.3 mass% or more and 5 mass% or less). When the amount of the additive used is too small, it may be difficult to obtain the effect derived from the additive, on the other hand, even if a large amount of other additives is used, it is difficult to obtain the effect corresponding to the added amount, and There is a risk that the viscosity of the non-aqueous electrolytic solution will increase and the conductivity will decrease.
In addition, 100 mass% of non-aqueous electrolytes means the sum total of all the components contained in non-aqueous electrolytes, such as the above-mentioned sulfonyl imide compound, electrolyte salt, solvent, and the additive used suitably.

2. Lithium-ion secondary battery The lithium-ion secondary battery of the present invention is a positive electrode containing a positive electrode active material capable of storing and releasing lithium ions, a negative electrode containing a negative electrode active material capable of storing and releasing lithium ions, And a non-aqueous electrolyte. More specifically, a separator is provided between the positive electrode and the negative electrode, and the nonaqueous electrolytic solution is contained in the outer case together with the positive electrode, the negative electrode, etc. in a state of being impregnated in the separator. The lithium ion secondary battery of the present invention comprises the above-mentioned non-aqueous electrolyte solution of the present invention.

2-1. Positive Electrode The positive electrode is obtained by supporting a positive electrode mixture containing a positive electrode active material, a conductive auxiliary agent, a binder and the like on a positive electrode current collector, and is usually formed into a sheet shape.

The method for producing the positive electrode is not particularly limited. For example, (i) a positive electrode active material composition obtained by dissolving or dispersing a positive electrode mixture in a dispersion solvent is applied to a positive electrode current collector by a doctor blade method or the like. A method in which the current collector is dipped in the positive electrode active material composition and then dried; (ii) a sheet obtained by kneading and molding the positive electrode active material composition and drying is joined to the positive electrode current collector via a conductive adhesive. Then, the positive electrode active material composition containing a liquid lubricant is applied or cast onto a positive electrode current collector to form a desired shape, and then the liquid lubricant is removed. Then, a method of uniaxially or polyaxially stretching; and the like. Moreover, you may pressurize the positive electrode mixture layer after drying as needed. This increases the adhesive strength with the positive electrode current collector and also increases the electrode density.

The material used for the positive electrode current collector, the positive electrode active material, the conductive auxiliary agent, the binder, and the solvent used in the positive electrode active material composition (a solvent that disperses or dissolves the positive electrode mixture) is not particularly limited and may be any conventionally known one. Materials can be used, and for example, each material described in JP-A-2014-13704 can be used.

The amount of the positive electrode active material used is preferably 75 parts by mass or more and 99 parts by mass or less with respect to 100 parts by mass of the positive electrode mixture, more preferably 85 parts by mass or more, and further preferably 90 parts by mass or more. Yes, more preferably 98 parts by mass or less, and further preferably 97 parts by mass or less.

When the conductive auxiliary agent is used, the content of the conductive auxiliary agent in the positive electrode mixture is preferably 0.1% by mass to 10% by mass with respect to 100% by mass of the positive electrode mixture (more Preferably 0.5% by mass to 10% by mass, more preferably 1% by mass to 10% by mass). If the amount of the conductive additive is too small, the conductivity may be extremely deteriorated, and the load characteristics and the discharge capacity may be deteriorated. On the other hand, if the amount is too large, the bulk density of the positive electrode mixture layer becomes high, and the content of the binder needs to be further increased, which is not preferable.

When a binder is used, the content of the binder in the positive electrode mixture is preferably 0.1% by mass to 10% by mass with respect to 100% by mass of the positive electrode mixture (more preferably 0.5% by mass). % To 9% by mass, more preferably 1% to 8% by mass). If the amount of the binder is too small, good adhesion cannot be obtained, and the positive electrode active material and the conductive additive may be detached from the current collector. On the other hand, if the amount is too large, the internal resistance may increase and the battery characteristics may be adversely affected.
The compounding amounts of the conduction aid and the binder can be appropriately adjusted in consideration of the purpose of use of the battery (emphasis on output, emphasis on energy, etc.), ionic conductivity and the like.

2-2. Negative Electrode The negative electrode is obtained by supporting a negative electrode mixture containing a negative electrode active material, a binder and, if necessary, a conductive auxiliary agent on a negative electrode current collector, and is usually formed into a sheet shape.
As the method for producing the negative electrode, the same method as the method for producing the positive electrode can be adopted. Further, as the conductive auxiliary agent, the binder, and the solvent for dispersing the material, which are used at the time of manufacturing the negative electrode, those similar to those used for the positive electrode are used.

A conventionally known negative electrode active material can be used as the material of the negative electrode current collector and the negative electrode active material, and for example, each material described in JP-A-2014-13704 can be used.

2-3. Separator The separator is arranged so as to separate the positive electrode and the negative electrode. The separator is not particularly limited, and any conventionally known separator can be used in the present invention. For example, each material described in JP-A-2014-13704 can be used.

2-4. Battery exterior material A battery element equipped with a positive electrode, negative electrode, separator, non-aqueous electrolyte, etc. is housed in the battery exterior material to protect the battery element from external impacts, environmental degradation, etc. when using a lithium ion secondary battery. It In the present invention, the material of the battery exterior material is not particularly limited, and any conventionally known exterior material can be used.

The shape of the lithium ion secondary battery according to the present invention is not particularly limited, and any shape conventionally known as the shape of the lithium ion secondary battery, such as a cylindrical shape, a prismatic shape, a laminate type, a coin type, or a large size, may be used. You can When used as a high-voltage power supply (several tens V to several hundreds V) for mounting on an electric vehicle, a hybrid electric vehicle, etc., a battery module configured by connecting individual batteries in series can also be used. ..

The rated charging voltage of the lithium ion secondary battery of the present invention is not particularly limited, but it is preferably more than 4.2V. The effects of the present invention are particularly remarkable when used at a voltage exceeding 4.2V. It is more preferably 4.3 V or higher, and further preferably 4.35 V or higher. The higher the rated charging voltage is, the higher the energy density can be, but if it is too high, it may be difficult to ensure safety. Therefore, the rated charging voltage is preferably 4.6 V or less. More preferably, it is 4.5 V or less.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited by the following examples as well as the present invention, and may be appropriately modified within a range compatible with the gist of the preceding and the following. Of course, it is possible to carry out, and all of them are included in the technical scope of the present invention.

1. Preparation of Non-Aqueous Electrolyte Solution Lithium hexafluorophosphate (LiPF ₆ , manufactured by Kishida Chemical Co., Ltd.) was added to a non-aqueous solvent prepared by mixing ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 3:7. , Electrolyte salt) were dissolved to prepare a non-aqueous electrolyte solution 1 having a LiPF ₆ concentration of 1.2 mol/L.

As a compound having a sulfonylimide anion (1) and generating the sulfonylimide anion (1) in a non-aqueous electrolyte, lithium bis(fluorosulfonyl)imide (hereinafter sometimes referred to as LiFSI), lithium (fluorosulfonyl) ) (Trifluoromethylsulfonyl)imide (hereinafter sometimes referred to as LiFTI), phthalic anhydride (manufactured by Wako Pure Chemical Industries, Ltd.), and pyromellitic dianhydride (manufactured by Tokyo Chemical Industry Co., Ltd.) as acid anhydrides. However, except that the concentrations of lithium hexafluorophosphate, the compound having the sulfonylimide anion (1) and the acid anhydride in the non-aqueous electrolyte solution were changed as shown in Table 1, Nonaqueous electrolyte solutions 2 to 9 were prepared in the same manner.

2. Production of Laminated Lithium Ion Secondary Battery 2-1. Preparation of Positive Electrode Sheet A positive electrode active material (LiCoO ₂ ), a conductive auxiliary agent 1 (acetylene black, AB), a conductive auxiliary agent 2 (graphite), and a binder (polyvinylidene fluoride, PVdF) were added in a ratio of 93:2:2:3. The positive electrode mixture slurry mixed in a mass ratio and dispersed in N-methylpyrrolidone was applied onto an aluminum foil (positive electrode current collector), dried, and compressed to prepare a positive electrode sheet 1.

2-2. Manufacture of Negative Electrode Sheet As a negative electrode active material, artificial graphite, a conductive auxiliary agent (vapor phase carbon fiber, “VGCF (registered trademark)”, manufactured by Showa Denko KK), and a binder (polyvinylidene fluoride, PVdF) were used at 95.7. : 0.5: 3.8 in a mass ratio and mixed with N-methyl-2-pyrrolidone to prepare a slurry-like solution. The charge capacity of the positive electrode at 4.3 V or 4.4 V charge was calculated, and the negative electrode mixture slurry was changed to copper foil (negative electrode current collector) so that the lithium ion storable capacity of the negative electrode/positive electrode charge capacity=1.15. ) Was coated on the above, dried and compressed to prepare two types of negative electrode sheets 1 and 2.

2-3. Preparation of Laminated Lithium Ion Secondary Battery Opposed to the positive electrode sheet 1 prepared above and the negative electrode sheet selected so that the rated charging voltage of the laminated lithium ion secondary battery when combined with the positive electrode sheet is 4.3V. And a polyethylene separator (16 μm) was sandwiched between them. A laminate of a positive electrode sheet, a separator and a negative electrode sheet was sandwiched between two aluminum laminate films, the inside of the aluminum laminate film was filled with the non-aqueous electrolyte solution 1, and the aluminum laminate film was sealed in a vacuum state.

The non-aqueous electrolyte was changed as shown in Table 1, and the negative electrode sheet was changed so that the rated charging voltage of the laminated lithium-ion secondary battery when combined with the positive electrode sheet was 4.3 V or 4.4 V. Laminated lithium ion secondary batteries 2 to 14 were manufactured in the same manner as above except for the above. Table 1 shows the configuration of each battery. The batteries used in Experimental Examples 1 to 14 correspond to laminate type lithium ion secondary batteries 1 to 14, respectively.

3. Battery evaluation 3-1. Measurement of 0.2C recovery capacity and rate characteristic after storage (1C/0.2C) Using a charge/discharge tester (ACD-01, manufactured by Asuka Electronics Co., Ltd.), temperature of 25° C. Below, the laminate type lithium ion secondary battery 1 was charged under predetermined charge conditions (0.5 C, 4.3 V or 4.4 V, constant current constant voltage mode, 0.02 C end), and then the discharge rate was 0. Discharged at 2C until the voltage was 2.75V. The discharge capacity at this time was the initial 0.2C capacity.
After recharging the battery under the same conditions, the battery was discharged at a discharge rate of 1 C until the voltage reached 2.75 V, and the 1 C discharge capacity was measured.

Using a charge/discharge tester (ACD-01, manufactured by Asuka Electronics Co., Ltd.), the laminate type lithium ion secondary battery was set under a predetermined charging condition (1C, 4.3V or 4.4V) under an environment of a temperature of 25°C. , Constant current/constant voltage mode, 3 hours termination) and then stored in a thermostat set at 80° C. for 3 days.
The laminated lithium-ion secondary battery after storage was placed in an environment of a temperature of 25° C. for 24 hours, then discharged at a temperature of 25° C. and a discharge rate of 1 C to a voltage of 2.75 V to measure the discharge capacity (1 C Remaining capacity).

Next, after constant-current constant-voltage charging at 0.02C termination at 1C until the rated charging voltage (4.3V or 4.4V) was reached, constant-current discharging at 0.2C was performed up to 2.75V. The capacity at this time was defined as a 0.2 C recovery capacity after standing. From the values of the initial 0.2C capacity and the 0.2C recovery capacity after standing, the 0.2C recovery capacity (%) was calculated from the following formula. The results are shown in Table 1.
0.2C recovery capacity (%)=(0.2C capacity after leaving/initial 0.2C capacity)×100

Furthermore, constant-current constant-voltage charging was performed at 1C until the rated charging voltage (4.3V or 4.4V) was reached, and then constant-current discharging was performed at 1C to 2.75V. The capacity at this time was set to 1C capacity after standing. Table 1 shows the ratio of 1 C capacity after standing to 0.2 C capacity after standing as rate characteristics after storage.
Rate characteristic after storage (%) = (1C capacity after standing/0.2C capacity after standing) x 100

3-2. ICP emission spectroscopic analysis of negative electrode (Co detection amount)
The negative electrode after the high temperature storage test was analyzed using an ICP emission spectroscopic analyzer (manufactured by Shimadzu Corporation). After washing the negative electrode after the high-temperature storage test with 50 ml of ethyl methyl carbonate, the negative electrode active material was peeled off, dissolved in 1 g of nitric acid, and diluted with pure water 15 times to prepare a measurement sample, and ICP emission Spectroscopic analysis was performed. Table 1 shows values indexed with the amount of Co detected in the negative electrode of Experimental Example 3 being 100.

3-3. Measurement of capacity retention rate Using a charge/discharge tester (ACD-01, manufactured by Asuka Electronics Co., Ltd.), at a temperature of 45°C, 4.3V or 4.4V constant-current constant-voltage constant-current charging was performed at a charging rate of 1C. The amount of discharge is 0.02C, the discharge is performed at a discharge rate of 1C until the voltage becomes 2.75V, and a cycle characteristic test is performed with a charge/discharge pause time of 10 minutes at each charge/discharge. The capacity retention rate was calculated. The results are shown in Table 1.
Capacity retention rate (%)=(discharge capacity at 200 cycles/discharge capacity at 1 cycle)×100

From the comparison of the batteries 1, 3, 6 and 11 shown in Table 1, although the battery characteristics are slightly improved by the addition of the acid anhydride (comparison between the batteries 1 and 3 and the batteries 6 and 11), the improvement effect is It can be seen that it deteriorates with increasing temperature (comparison between batteries 1 and 6). Further, from the comparison of Batteries 3, 4, 10 to 12, the battery characteristics were rather deteriorated by adding only the compound having the sulfonylimide anion (1) (Batteries 3 and 4, Battery 11 and Battery 10 or 12). It is understood that the deterioration of the battery characteristics is further promoted by the increase of the voltage (comparison between batteries 4 and 12).
On the other hand, when the sulfonylimide anion (1) and the acid anhydride are contained in the electrolytic solution (Batteries 2, 5, 8, 13), they have better battery characteristics than the batteries 3 and 11. It was From these results, it is possible to suppress the deterioration of the battery characteristics by using the compound having the sulfonylimide anion (1) and the acid anhydride together, and to suppress the deterioration of the battery characteristics due to the increase of the voltage. The synergistic effect that cannot be obtained with can be confirmed. Also, the same effect was confirmed when pyromellitic dianhydride was used as the acid anhydride (Batteries 7, 9, 14).

Furthermore, when the non-aqueous electrolyte solution contains the sulfonylimide anion (1) (Batteries 2, 5, 8, 9, 13, 14), it is more negative in the negative electrode than batteries 1, 6, and 7 that do not contain this. The amount of Co detected was greatly reduced, and the elution of the transition metal contained in the positive electrode was suppressed.

From these results, when the non-aqueous electrolyte contains the sulfonylimide anion (1) and an acid anhydride, the effect of suppressing the deterioration of the battery capacity and rate characteristics derived from the acid anhydride and the sulfonylimide anion (1 )-Derived positive electrode elution suppressing effect and the relatively high ionic conductivity of the sulfonylimide compound act synergistically, and as a result, even if the battery is used under relatively high voltage conditions after high temperature storage, It is considered that deterioration was suppressed and high battery characteristics could be maintained.

Claims (3)

A non-aqueous electrolyte used in a lithium-ion secondary battery,
Formula (1): [N (XSO 2) (FSO 2)] - ( In the general formula (1), X is a fluorine atom, an alkyl group or a fluoroalkyl group having 1 to 6 carbon atoms having 1 to 6 carbon atoms And an anion represented by
Lithium cation,
And an aromatic ring having 6 to 10 carbon atoms in the molecule, -C (= O) -O- C (= O) - with an acid anhydride having a cyclic structure containing a structure represented by,
A non-aqueous solvent,
LiPF ₆ ,
Including,
The non-aqueous solvent is an ether; a chain carbonic acid ester; a saturated cyclic carbonic acid ester containing no fluorine; a cyclic carbonic acid ester having an unsaturated bond; an aromatic carboxylic acid ester; a lactone; a phosphoric acid ester; Nitriles; sulfur compounds; aromatic nitriles; and nitromethane, 1,3-dimethyl-2-imidazolidinone, 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone, A non-aqueous electrolyte solution, which is at least one selected from the group consisting of 3-methyl-2-oxazolidinone . A lithium-ion secondary battery comprising the non-aqueous electrolyte solution according to claim 1. The lithium-ion secondary battery according to claim 2, wherein the rated charging voltage is more than 4.2V.