Electrolyte and secondary battery using same

Abstract

To provide: an electrolyte solution which enables a secondary battery comprising a silicon negative electrode to have a longer service life and to inhibit the resistance from increasing; and a secondary battery which uses the same.SOLUTION: The present invention provides an electrolyte solution used in a battery that is provided with an electrode comprising a negative electrode material that contains elemental silicon and elemental carbon. The electrolyte solution contains less than 10 mass% of a fluorinated ether represented by general formula (1): HCF2CF2-O-R (1), where R is a fluorinated alkyl group.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present disclosure relates to an electrolyte solution and a secondary battery using the same. [Background technology]

[0002] It has been reported that the use of fluorine ethers such as 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether as a solvent for the electrolyte of lithium-ion batteries improves the lifespan in the high voltage range (Non-patent prior art document 1). Specifically, lithium metal is used for the negative electrode and LiNi is used for the positive electrode. 0.5 Mn 1.5 It is disclosed that high voltage operating characteristics are improved by using O4 and mixing various fluorine ethers such as 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether with propylene carbonate as a solvent.

[0003] It has also been reported that the use of fluoroethylene carbonate as an additive for silicon negative electrodes improves their lifespan (Non-patent prior art document 2). [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Journal of the Electrochemical Society, 164 (1) A6412-A6416 (2017) [Non-Patent Document 2] Journal of the Electrochemical Society, 163 (8) A1705-A1716 (2016) Summary of the Invention [Problem to be solved by the invention]

[0005] An object of the present disclosure is to provide an electrolyte that enables an improvement in the life span and suppression of an increase in resistance of a secondary battery having a silicon negative electrode, and a secondary battery using the electrolyte. [Means for solving the problem]

[0006] The present disclosure relates to a negative electrode material containing silicon and carbon elements. layer have a negative electrode, and electrolyte a lithium ion secondary battery comprising the same And, The negative electrode material layer contains Si and / or SiOa (0 < a < 2) and a carbon compound, and the content of silicon-containing particles is 25 to 35% by mass with respect to the mass of the solid content in the negative electrode mixture, and the content of the carbon compound is 65 to 75% by mass with respect to the mass of the solid content in the negative electrode mixture, and the electrolytic solution is Contains less than 10% by mass of a fluorinated ether represented by the following general formula (1): such that the lower limit of LiF formed on the negative electrode is 3.0 μg / cm 2 , and the upper limit is 4.1 μg / cm 2 is Characterized by a lithium ion secondary battery It is. HCF2CF2-OR (1) (In the formula, R is a fluorinated alkyl group.)

[0007] The fluorinated ether represented by the above general formula (1) is preferably at least one fluorinated ether selected from the group consisting of fluorinated ethers represented by the following general formulae (2) to (4). HCF2CF2-O-CH2CF2CF2H (2) HCF2CF2-O-CH2CF2CF3(3) HCF2CF2-O-CH2CF3(4 ) Effect of the Invention

[0009] The present disclosure can provide an electrolyte solution that can improve the life span and suppress the increase in resistance of a secondary battery having a silicon negative electrode. In addition, a secondary battery using the electrolyte solution of the present disclosure has an improved battery life and suppresses the increase in resistance. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The present disclosure will be described in detail below. The electrolyte solution of the present disclosure is an electrolyte solution suitable for use in a battery having an electrode including a negative electrode material having a silicon element and a carbon element, and is characterized in that it contains less than 10 mass % of a fluorinated ether represented by the following general formula (1): HCF2CF2-OR (1) (In the formula, R is a fluorinated alkyl group.)

[0011] The present disclosure relates to electrolytes for use in secondary batteries that include silicon anodes as described above. The present disclosure relates to a method for producing a lithium ion secondary battery comprising the steps of: (1) adding a specific amount of the above-mentioned specific fluorinated ether as an additive to an electrolyte for the lithium ion secondary battery; (2) forming lithium fluoride (LiF) as a reduced coating on a silicon negative electrode; and (3) achieving a significant improvement in the battery's lifespan and suppression of an increase in resistance.

[0012] The lower limit of the LiF formed above is 3.0 μg / cm 2 is preferred, and 3.1 μg / cm 2 More preferably, 3.2 μg / cm 2 is particularly preferred. The upper limit is 4.1 μg / cm 2 is preferred, 3.9 μg / cm 2 If the amount of LiF formed on the negative electrode is too small, the improvement in life characteristics may not be sufficient, whereas if it is too large, the resistance tends to increase.

[0013] (Fluorinated Ethers) The electrolyte solution of the present disclosure contains less than 10 mass % of a fluorinated ether represented by the following general formula (1). HCF2CF2-OR (1) (In the formula, R is a fluorinated alkyl group.)

[0014] The above fluorinated alkyl group is preferably a fluorinated alkyl group having 1 to 10 carbon atoms, and more preferably a fluorinated alkyl group having 2 to 6 carbon atoms.

[0015] If the number of carbon atoms in the fluorinated alkyl group is too small, the boiling point tends to be low, and if the number of carbon atoms is too large, the viscosity tends to be high.

[0016] The fluorinated ether preferably has a fluorine content of 40 to 75% by mass. When the fluorine content is in this range, the balance between non-flammability and compatibility is particularly excellent. In addition, this is also preferable in terms of good oxidation resistance and safety. The lower limit of the fluorine content is more preferably 45% by mass, further preferably 50% by mass, and particularly preferably 55% by mass, and the upper limit is more preferably 70% by mass, and further preferably 69% by mass. The fluorine content of the fluorinated ether (I) is a value calculated based on the structural formula of the fluorinated ether (I) by {(number of fluorine atoms×19) / molecular weight of the fluorinated ether (I)}×100(%).

[0017] Examples of R include -CH2CF2CF3, -CF2CFHCF3, -CF2CF2CF2H, -CH2CF2CF2H, -CH2CH2CF2CF3, -CH2CF2CFHCF3, -CF2CF2CF2CF2H, -CH2CF2CF2CF2H, -CH2CH2CF2CF2H, -CH2CF(CF3)CF2H, -CF2CF2H, -CH2CF2H, -CH2CF3, -CF2CH3, and the like.

[0018] Specific examples of the fluorinated ether (I) include HCF2CF2-O-CH2CF2CF2H, HCF2CF2-O-CH2CF2CF3, HCF2CF2-O-CH2CF3, HCF2CF2-O-CF2CFHCF3, HCF2CF2-O-CF2CF2CF2H, HCF2CF2-O-CH2CH2CF2CF3, HCF2CF2-O-CH2CF2CFHCF3, HCF2CF2-O-CF2CF2CF2CF2H, HCF2CF2-O-CH2CF2CF2CF2H, HCF2CF2-O-CH2CH2CF2CF2H, HCF2CF2-O-CH2CF(CF3)CF2H, HCF2CF2-O-CF2CF2H, and HCF2CF2-O-CH2CF2H.

[0019] The fluorinated ether represented by the above general formula (1) is preferably at least one fluorinated ether selected from the group consisting of fluorinated ethers represented by the following general formulae (2) to (4).

[0020] HCF2CF2-O-CH2CF2CF2H (2) HCF2CF2-O-CH2CF2CF3(3) HCF2CF2-O-CH2CF3(4)

[0021] In particular, by including a fluorinated ether represented by any one of the above general formulas (2) to (4) in the electrolyte as an additive, lithium fluoride (LiF) is formed as a reduced coating on the silicon negative electrode, which is advantageous in terms of significantly improving the life span and suppressing an increase in resistance.

[0022] The content of the fluorinated ether in the electrolyte must be less than 10% by mass. By keeping the content within this range, the electrolyte can be used as a good electrolyte. That is, if the content is too high, the viscosity of the electrolyte increases and the ionic conductivity decreases, which shortens the life of the battery. The upper limit of the fluorinated ether content is preferably 9.0% by mass, and more preferably 5.0% by mass. The lower limit of the content of the fluorinated ether is preferably 0.001% by mass, and more preferably 0.01% by mass.

[0023] The electrolyte solution of the present disclosure preferably contains a solvent.

[0024] The solvent preferably contains at least one selected from the group consisting of carbonates and carboxylate esters.

[0025] The carbonate may be a cyclic carbonate or a chain carbonate.

[0026] The cyclic carbonate may be a non-fluorinated cyclic carbonate or a fluorinated cyclic carbonate.

[0027] The non-fluorinated cyclic carbonate may be a non-fluorinated saturated cyclic carbonate, preferably a non-fluorinated saturated alkylene carbonate having an alkylene group having 2 to 6 carbon atoms, more preferably a non-fluorinated saturated alkylene carbonate having an alkylene group having 2 to 4 carbon atoms.

[0028] Among these, the non-fluorinated saturated cyclic carbonate is preferably at least one selected from the group consisting of ethylene carbonate, propylene carbonate, cis-2,3-pentylene carbonate, cis-2,3-butylene carbonate, 2,3-pentylene carbonate, 2,3-butylene carbonate, 1,2-pentylene carbonate, 1,2-butylene carbonate, and butylene carbonate, in that it has a high dielectric constant and a suitable viscosity.

[0029] The non-fluorinated saturated cyclic carbonates may be used alone or as a mixture of two or more kinds in any combination and in any ratio.

[0030] When the non-fluorinated saturated cyclic carbonate is contained, the content of the non-fluorinated saturated cyclic carbonate is preferably 5 to 90 volume % relative to the solvent, more preferably 10 to 60 volume %, and even more preferably 15 to 50 volume %.

[0031] The fluorinated cyclic carbonate is a cyclic carbonate having a fluorine atom. The solvent containing the fluorinated cyclic carbonate can be suitably used even under high voltage. In this specification, the term "high voltage" refers to a voltage of 4.2 V or higher. The upper limit of the "high voltage" is preferably 4.9 V.

[0032] The fluorinated cyclic carbonate may be a fluorinated saturated cyclic carbonate or a fluorinated unsaturated cyclic carbonate.

[0033] The fluorinated saturated cyclic carbonate is a saturated cyclic carbonate having a fluorine atom, and specifically, is represented by the following general formula (A):

[0034] [ka] (In the formula, X 1 ~X 4 are the same or different and each represents -H, -CH3, -C2H5, -F, a fluorinated alkyl group which may have an ether bond, or a fluorinated alkoxy group which may have an ether bond. 1 ~X 4 At least one of the groups is -F, a fluorinated alkyl group which may have an ether bond, or a fluorinated alkoxy group which may have an ether bond. The fluorinated alkyl group is, for example, -CF3, -CF2H, -CH2F, etc.

[0035] When the electrolyte solution of the present disclosure contains the above-mentioned fluorinated saturated cyclic carbonate, the oxidation resistance of the electrolyte solution is improved and stable and excellent charge / discharge characteristics are obtained when the electrolyte solution is applied to a high-voltage lithium ion secondary battery or the like. In this specification, an "ether bond" is a bond represented by --O--.

[0036] Due to its excellent dielectric constant and oxidation resistance, X 1 ~X 4 It is preferable that one or two of these is -F, a fluorinated alkyl group which may have an ether bond, or a fluorinated alkoxy group which may have an ether bond.

[0037] It is expected that the viscosity at low temperatures will decrease, the flash point will increase, and the solubility of electrolyte salts will improve. 1 ~X 4 is preferably -H, -F, a fluorinated alkyl group (a), a fluorinated alkyl group having an ether bond (b), or a fluorinated alkoxy group (c).

[0038] The fluorinated alkyl group (a) is an alkyl group in which at least one hydrogen atom has been substituted with a fluorine atom. The fluorinated alkyl group (a) preferably has 1 to 20 carbon atoms, more preferably 1 to 17 carbon atoms, further preferably 1 to 7 carbon atoms, and particularly preferably 1 to 5 carbon atoms. If the number of carbon atoms is too large, there is a risk that the low-temperature characteristics and the solubility of the electrolyte salt may be reduced, whereas if the number of carbon atoms is too small, there may be a decrease in the solubility of the electrolyte salt, a decrease in discharge efficiency, and even an increase in viscosity.

[0039] Among the above fluorinated alkyl groups (a), those having a carbon number of 1 include CFH2-, CF2H-, and CF3-. In particular, CF2H- or CF3- is preferred in terms of high-temperature storage properties, and CF3- is most preferred.

[0040] Among the above-mentioned fluorinated alkyl groups (a), those having 2 or more carbon atoms include those represented by the following general formula (a-1): R 1 -R 2 - (a-1) (In the formula, R 1 R is an alkyl group having one or more carbon atoms which may have a fluorine atom; 2 is an alkylene group having 1 to 3 carbon atoms which may have a fluorine atom; provided that R 1 and R 2 At least one of which has a fluorine atom) is a preferred example from the viewpoint of good solubility of the electrolyte salt. In addition, R 1 and R 2 may further have atoms other than carbon atoms, hydrogen atoms and fluorine atoms.

[0041] R 1 R is an alkyl group having 1 or more carbon atoms which may have a fluorine atom. 1 R is preferably a linear or branched alkyl group having 1 to 16 carbon atoms. 1 The number of carbon atoms is more preferably 1 to 6, and further preferably 1 to 3.

[0042] R1 Specifically, the linear or branched alkyl group may be CH3-, CH3CH2-, CH3CH2CH2-, CH3CH2CH2CH2-,

[0043] [ka]

[0044] etc.

[0045] Also, R 1is a linear alkyl group having a fluorine atom, CF3-, CF3CH2-, CF3CF2-, CF3CH2CH2-, CF3CF2CH2-, CF3CF2CF2-, CF3CH2CF2-, CF3CH2CH2CH2-, CF3CF2CH2CH2-, CF3CF2CF2CH2-, CF3CF2CF2CH2-, CF3CF2CF2CH2-, CF3CF2CF2CH2-, CF3CF2CH2CF2-, CF3CF2CH2CF2-, CF3CF2CH2CH2-, CF3CF2CH2CH 2CH2-, CF3CH2CF2CH2CH2-, CF3CF2CF2CH2CH2-, CF3CF2CF2CF2CH2-, CF3CF2CH2CF2CH2-, CF3CF2CH2CH2CH2CH2-, CF3CF2C F2CF2CH2CH2-, CF3CF2CH2CF2CH2CH2-, HCF2-, HCF2CH2-, HCF2CF2-, HCF2CH2CH2-, HCF2CF2CH2-, HCF2CH2CF2-, HCF2CF2C H2CH2-, HCF2CH2CF2CH2-, HCF2CF2CF2CF2-, HCF2CF2CH2CH2CH2-, HCF2CH2CF2CH2CH2-, HCF2CF2CF2CF2CH2-, HCF2CF2CF2 CF2CH2CH2-, FCH2-, FCH2CH2-, FCH2CF2-, FCH2CF2CH2-, FCH2CF2CF2-, CH3CF2CH2-, CH3CF2CF2-, CH3CF2CH2CF2-, CH3CF2 Examples include CF2CF2-, CH3CH2CF2CF2-, CH3CF2CH2CF2CH2-, CH3CF2CF2CF2CH2-, CH3CF2CF2CH2CH2-, CH3CH2CF2CF2CH2-, CH3CF2CH2CF2CH2CH2-, CH3CF2CH2CF2CH2CH2-, CH3CF2CH2CF2CH2CH2-, HCFClCF2CH2-, HCF2CFClCH2-, HCF2CFClCF2CFClCH2-, HCFClCF2CFClCF2CH2-, and the like.

[0046] Also, R 1 is a branched alkyl group having a fluorine atom,

[0047] [ka]

[0048] [ka]

[0049] However, since the presence of branches such as CH3- or CF3- tends to increase viscosity, it is more preferable that the number of branches is small (one) or zero.

[0050] R 2 R is an alkylene group having 1 to 3 carbon atoms which may have a fluorine atom. 2 An example of the minimum structural unit constituting such a linear or branched alkylene group is shown below. 2 may consist of any one or a combination of these.

[0051] (i) Minimum linear structural unit: -CH2-, -CHF-, -CF2-, -CHCl-, -CFCl-, -CCl2-

[0052] (ii) Smallest branched structural unit:

[0053] [ka]

[0054] Among the above examples, it is preferable to use structural units that do not contain Cl, since they are more stable and do not undergo a deHCl reaction due to a base.

[0055] R 2 When it is linear, it is composed only of the above-mentioned linear minimum structural unit, and among them, -CH2-, -CH2CH2- or -CF2- is preferable. -CH2- or -CH2CH2- is more preferable because it can further improve the solubility of the electrolyte salt.

[0056] R 2When the branched chain is a branched chain, it contains at least one of the minimum branched chain structural units described above, and is represented by the general formula: -(CX a X b )-(X a is H, F, CH3 or CF3;X b is CH3 or CF3. However, X b If CF3, then X a is H or CH3) can be preferably exemplified. These can particularly further improve the solubility of the electrolyte salt.

[0057] Preferred fluorinated alkyl groups (a) include, for example, CF3CF2-, HCF2CF2-, H2CFCF2-, CH3CF2-, CF3CHF-, CH3CF2-, CF3CF2CF2-, HCF2CF2CF2-, H2CFCF2CF2-, CH3CF2CF2-,

[0058] [ka]

[0059] [ka]

[0060] etc.

[0061] The fluorinated alkyl group (b) having an ether bond is an alkyl group having an ether bond in which at least one hydrogen atom is substituted with a fluorine atom. The fluorinated alkyl group (b) having an ether bond preferably has 2 to 17 carbon atoms. If the number of carbon atoms is too large, the viscosity of the fluorinated saturated cyclic carbonate increases, and the number of fluorine-containing groups increases, which may result in a decrease in the solubility of the electrolyte salt due to a decrease in the dielectric constant, or a decrease in compatibility with other solvents. From this viewpoint, the number of carbon atoms of the fluorinated alkyl group (b) having an ether bond is more preferably 2 to 10, and even more preferably 2 to 7.

[0062] The alkylene group constituting the ether moiety of the fluorinated alkyl group (b) having an ether bond may be a linear or branched alkylene group. An example of the minimum structural unit constituting such a linear or branched alkylene group is shown below.

[0063] (i) Minimum linear structural unit: -CH2-, -CHF-, -CF2-, -CHCl-, -CFCl-, -CCl2-

[0064] (ii) Smallest branched structural unit:

[0065] [ka]

[0066] The alkylene group may be composed of these minimum structural units alone, or may be composed of a combination of linear (i) units, a combination of branched (ii) units, or a combination of linear (i) units and branched (ii) units. Preferred specific examples will be described later.

[0067] Among the above examples, it is preferable to use structural units that do not contain Cl, since they are more stable and do not undergo a deHCl reaction due to a base.

[0068] More preferred fluorinated alkyl groups having an ether bond (b) include those represented by the general formula (b-1): R 3 -(OR 4 ) n1 - (b-1) (In the formula, R 3 R is an alkyl group having 1 to 6 carbon atoms which may have a fluorine atom; 4 may have a fluorine atom, preferably an alkylene group having 1 to 4 carbon atoms; n1 is an integer of 1 to 3; provided that R 3 and R 4 At least one of the groups has a fluorine atom.

[0069] R 3 and R4 Examples of such a fluorinated alkyl group include those listed below, which can be appropriately combined to form the fluorinated alkyl group (b) having an ether bond represented by the above general formula (b-1), but are not limited to these.

[0070] (1)R 3 As the general formula: X c 3C-(R 5 ) n2 -(3 X c are the same or different and are either H or F;R 5 is preferably an alkylene group having 1 to 5 carbon atoms which may have a fluorine atom; n2 is preferably an alkyl group represented by 0 or 1).

[0071] If n2 is 0, R 3 Examples include CH3-, CF3-, HCF2-, and H2CF-.

[0072] A specific example when n2 is 1 is R 3As linear chains, CF3CH2-, CF3CF2-, CF3CH2CH2-, CF3CF2CH2-, CF3CF2CF2-, CF3CH2CF2-, CF3CH2CH2CH2-, CF3CF2CH2CH2-, CF3CF2CF2CH2-, CF3CF2CF2CH2-, CF3CF2CF2CH2-, CF3CF2CF2CF2-, CF3CF2CH2CF2-, CF3CH2CH2CH2CH2-, CF3CF2CH2CH2CH2-, C F3CH2CF2CH2CH2-, CF3CF2CF2CH2CH2-, CF3CF2CF2CF2CH2-, CF3CF2CH2CF2CH2-, CF3CF2CH2CH2CH2CH2-, CF3CF2CF 2CF2CH2CH2-, CF3CF2CH2CF2CH2CH2-, HCF2CH2-, HCF2CF2-, HCF2CH2CH2-, HCF2CF2CH2-, HCF2CH2CF2-, HCF2CF2CH 2CH2-, HCF2CH2CF2CH2-, HCF2CF2CF2CF2-, HCF2CF2CH2CH2CH2-, HCF2CH2CF2CH2CH2-, HCF2CF2CF2CF2CH2-, HCF2C F2CF2CF2CH2CH2-, FCH2CH2-, FCH2CF2-, FCH2CF2CH2-, CH3CF2-, CH3CH2-, CH3CF2CH2-, CH3CF2CF2-, CH3CH2CH2-, Examples include CH3CF2CH2CF2-, CH3CF2CF2CF2-, CH3CH2CF2CF2-, CH3CH2CH2CH2-, CH3CF2CH2CF2CH2-, CH3CF2CF2CF2CH2-, CH3CF2CF2CH2CH2-, CH3CF2CF2CH2CH2-, CH3CF2CH2CF2CH2CH2-, CH3CF2CH2CF2CH2CH2-, CH3CF2CH2CF2CH2CH2-, CH3CF2CH2CF2CH2CH2-, CH3CF2CH2CF2CH2CH2-, and the like.

[0073] n2 is 1 and R 3 As for branched chains,

[0074] [ka]

[0075] etc.

[0076] However, if the branch is CH3- or CF3-, the viscosity tends to be high, so R 3 However, a straight chain structure is more preferable.

[0077] (2) -(OR 4 ) n1 In the formula, n1 is an integer of 1 to 3, preferably 1 or 2. When n1=2 or 3, R 4 may be the same or different.

[0078] R 4 Preferred specific examples of the above include the following straight-chain or branched-chain copolymers:

[0079] Examples of linear alkyl groups include -CH2-, -CHF-, -CF2-, -CH2CH2-, -CF2CH2-, -CF2CF2-, -CH2CF2-, -CH2CH2CH2-, -CH2CH2CF2-, -CH2CF2CH2-, -CH2CF2CF2-, -CF2CH2CH2-, -CF2CF2CF2-, -CF2CH2CH2-, -CF2CF2CH2-, -CF2CH2CF2-, -CF2CF2CH2-, -CF2CF2CF2-, and the like.

[0080] As branched chains,

[0081] [ka]

[0082] etc.

[0083] The fluorinated alkoxy group (c) is an alkoxy group in which at least one hydrogen atom has been substituted with a fluorine atom. The fluorinated alkoxy group (c) preferably has 1 to 17 carbon atoms, and more preferably has 1 to 6 carbon atoms.

[0084] The fluorinated alkoxy group (c) may be represented by the general formula: X d 3C-(R 6 ) n3-O-(3 X d are the same or different and are either H or F;R 6 is preferably an alkylene group having 1 to 5 carbon atoms which may have a fluorine atom; n3 is 0 or 1; provided that three X d wherein any one of the groups contains a fluorine atom is particularly preferred.

[0085] Specific examples of the fluorinated alkoxy group (c) include R 1 Examples of the fluorinated alkoxy groups include those in which an oxygen atom is bonded to the terminal of the alkyl group exemplified as above.

[0086] The fluorine content of the fluorinated alkyl group (a), the fluorinated alkyl group having an ether bond (b), and the fluorinated alkoxy group (c) in the fluorinated saturated cyclic carbonate is preferably 10% by mass or more. If the fluorine content is too low, the effect of reducing viscosity at low temperatures and the effect of increasing the flash point may not be sufficiently obtained. From this viewpoint, the fluorine content is more preferably 12% by mass or more, and even more preferably 15% by mass or more. The upper limit is usually 76% by mass. The fluorine content of the fluorinated alkyl group (a), the fluorinated alkyl group having an ether bond (b), and the fluorinated alkoxy group (c) is a value calculated based on the structural formula of each group according to {(number of fluorine atoms × 19) / formula weight of each group} × 100(%).

[0087] From the viewpoint of obtaining good dielectric constant and oxidation resistance, the fluorine content of the entire fluorinated saturated cyclic carbonate is preferably 10% by mass or more, more preferably 15% by mass or more, and the upper limit is usually 76% by mass. The fluorine content of the above fluorinated saturated cyclic carbonate is a value calculated based on the structural formula of the fluorinated saturated cyclic carbonate by {(number of fluorine atoms×19) / molecular weight of fluorinated saturated cyclic carbonate}×100(%).

[0088] Specific examples of the fluorinated saturated cyclic carbonate include the following.

[0089] X 1 ~X 4 Specific examples of fluorinated saturated cyclic carbonates in which at least one of the groups is -F include:

[0090] [ka] These compounds have a high withstand voltage and good solubility of electrolyte salt.

[0091] In addition,

[0092] [ka]

[0093] etc. can also be used.

[0094] X 1 ~X 4 Specific examples of the fluorinated saturated cyclic carbonate in which at least one of the above is a fluorinated alkyl group (a) and the rest are all -H include:

[0095] [ka]

[0096] [ka]

[0097] [ka]

[0098] etc.

[0099] X 1 ~X 4Specific examples of the fluorinated saturated cyclic carbonate in which at least one of the above is a fluorinated alkyl group (b) having an ether bond or a fluorinated alkoxy group (c) and the rest are all -H include:

[0100] [ka]

[0101] [ka]

[0102] [ka]

[0103] [ka]

[0104] [ka]

[0105] [ka]

[0106] etc.

[0107] Among them, the fluorinated saturated cyclic carbonate is preferably any one of the following compounds:

[0108] [ka]

[0109] [ka]

[0110] Other examples of the fluorinated saturated cyclic carbonate include trans-4,5-difluoro-1,3-dioxolane-2-one, 5-(1,1-difluoroethyl)-4,4-difluoro-1,3-dioxolane-2-one, 4-methylene-1,3-dioxolane-2-one, 4-methyl-5-trifluoromethyl-1,3-dioxolane-2-one, 4-ethyl-5-fluoro-1,3-dioxolane-2-one, 4-ethyl-5,5-difluoro-1,3-dioxolane-2-one, and 4-ethyl-5,5-difluoro-1,3-dioxolane-2-one. Dioxolan-2-one, 4-ethyl-4,5-difluoro-1,3-dioxolan-2-one, 4-ethyl-4,5,5-trifluoro-1,3-dioxolan-2-one, 4,4-difluoro-5-methyl-1,3-dioxolan-2-one, 4-fluoro-5-methyl-1,3-dioxolan-2-one, 4-fluoro-5-trifluoromethyl-1,3-dioxolan-2-one, 4,4-difluoro-1,3-dioxolan-2-one and the like.

[0111] Of the above fluorinated saturated cyclic carbonates, fluoroethylene carbonate, difluoroethylene carbonate, trifluoromethylethylene carbonate (3,3,3-trifluoropropylene carbonate), and 2,2,3,3,3-pentafluoropropylethylene carbonate are more preferred.

[0112] The above-mentioned fluorinated unsaturated cyclic carbonate is a cyclic carbonate having an unsaturated bond and a fluorine atom, and is preferably a fluorinated ethylene carbonate derivative substituted with an aromatic ring or a substituent having a carbon-carbon double bond.Specific examples thereof include 4,4-difluoro-5-phenylethylene carbonate, 4,5-difluoro-4-phenylethylene carbonate, 4-fluoro-5-phenylethylene carbonate, 4-fluoro-5-vinylethylene carbonate, 4-fluoro-4-phenylethylene carbonate, 4,4-difluoro-4-vinylethylene carbonate, 4,4-difluoro-4-allylethylene carbonate, 4-fluoro-4-vinylethylene carbonate, 4-fluoro-4,5-diallylethylene carbonate, 4,5-difluoro-4-vinylethylene carbonate, 4,5-difluoro-4,5-divinylethylene carbonate, 4,5-difluoro-4,5-diallylethylene carbonate, etc.

[0113] The above fluorinated cyclic carbonates may be used alone or as a mixture of two or more kinds in any combination and in any ratio.

[0114] When the fluorinated cyclic carbonate is contained, the content of the fluorinated cyclic carbonate is preferably 5 to 90% by volume, more preferably 10 to 60% by volume, and even more preferably 15 to 45% by volume, relative to the solvent.

[0115] The chain carbonate may be a non-fluorinated chain carbonate or a fluorinated chain carbonate.

[0116] Examples of the non-fluorinated chain carbonate include hydrocarbon chain carbonates such as CH3OCOOCH3 (dimethyl carbonate: DMC), CH3CH2OCOOCH2CH3 (diethyl carbonate: DEC), CH3CH2OCOOCH3 (ethyl methyl carbonate: EMC), CH3OCOOCH2CH2CH3 (methyl propyl carbonate), methyl butyl carbonate, ethyl propyl carbonate, ethyl butyl carbonate, dipropyl carbonate, dibutyl carbonate, methyl isopropyl carbonate, methyl-2-phenylphenyl carbonate, phenyl-2-phenylphenyl carbonate, trans-2,3-pentylene carbonate, trans-2,3-butylene carbonate, and ethyl phenyl carbonate. Among these, at least one selected from the group consisting of ethyl methyl carbonate, diethyl carbonate, and dimethyl carbonate is preferable.

[0117] The non-fluorinated chain carbonates may be used alone or in any combination of two or more kinds in any ratio.

[0118] When the non-fluorinated chain carbonate is contained, the content of the non-fluorinated chain carbonate is preferably 10 to 90% by volume, more preferably 20 to 85% by volume, and further preferably 30 to 80% by volume, relative to the solvent.

[0119] The fluorinated chain carbonate is a chain carbonate having a fluorine atom. The solvent containing the fluorinated chain carbonate can be suitably used even under high voltage.

[0120] The fluorinated chain carbonate may be a fluorinated chain carbonate represented by the general formula (B): Rf 2 OCOOR 7 (B) (In the formula, Rf 2 is a fluorinated alkyl group having 1 to 7 carbon atoms, and R 7is an alkyl group having 1 to 7 carbon atoms which may contain a fluorine atom.

[0121] Rf 2 is a fluorinated alkyl group having 1 to 7 carbon atoms, and R 7 is an alkyl group having 1 to 7 carbon atoms which may contain a fluorine atom. The fluorinated alkyl group is an alkyl group in which at least one hydrogen atom is substituted with a fluorine atom. 7 When is an alkyl group containing a fluorine atom, it becomes a fluorinated alkyl group. Rf 2 and R 7 In terms of low viscosity, the carbon number of the alkyl group is preferably 1 to 7, and more preferably 1 or 2. If the number of carbon atoms is too large, there is a risk that the low-temperature characteristics and the solubility of the electrolyte salt may be reduced, whereas if the number of carbon atoms is too small, there may be a decrease in the solubility of the electrolyte salt, a decrease in discharge efficiency, and even an increase in viscosity.

[0122] Examples of the fluorinated alkyl group having one carbon atom include CFH2-, CF2H-, CF3-, etc. In particular, CFH2- or CF3- is preferred in terms of high-temperature storage properties.

[0123] The fluorinated alkyl group having two or more carbon atoms includes a group represented by the following general formula (d-1): R 1 -R 2 - (d-1) (In the formula, R 1 R is an alkyl group having one or more carbon atoms which may have a fluorine atom; 2 is an alkylene group having 1 to 3 carbon atoms which may have a fluorine atom; provided that R 1 and R 2 At least one of which has a fluorine atom) is a preferred example from the viewpoint of good solubility of the electrolyte salt. In addition, R 1 and R 2 may further have atoms other than carbon atoms, hydrogen atoms and fluorine atoms.

[0124] R 1 R is an alkyl group having 1 or more carbon atoms which may have a fluorine atom. 1 R is preferably a linear or branched alkyl group having 1 to 6 carbon atoms. 1 The number of carbon atoms is more preferably 1 to 3.

[0125] R 1 Specific examples of linear or branched alkyl groups include CH3-, CF3-, CH3CH2-, CH3CH2CH2-, CH3CH2CH2CH2-,

[0126] [ka]

[0127] etc.

[0128] Also, R 1is a linear alkyl group having a fluorine atom, CF3-, CF3CH2-, CF3CF2-, CF3CH2CH2-, CF3CF2CH2-, CF3CF2CF2-, CF3CH2CF2-, CF3CH2CH2CH2-, CF3CF2CH2CH2-, CF3CF2CF2CH2-, CF3CF2CF2CH2-, CF3CF2CF2CH2-, CF3CF2CF2CH2-, CF3CF2CH2CF2-, CF3CF2CH2CF2-, CF3CF2CH2CH2-, CF3CF2CH2CH 2CH2-, CF3CH2CF2CH2CH2-, CF3CF2CF2CH2CH2-, CF3CF2CF2CF2CH2-, CF3CF2CH2CF2CH2-, CF3CF2CH2CH2CH2CH2-, CF3CF2C F2CF2CH2CH2-, CF3CF2CH2CF2CH2CH2-, HCF2-, HCF2CH2-, HCF2CF2-, HCF2CH2CH2-, HCF2CF2CH2-, HCF2CH2CF2-, HCF2CF2C H2CH2-, HCF2CH2CF2CH2-, HCF2CF2CF2CF2-, HCF2CF2CH2CH2CH2-, HCF2CH2CF2CH2CH2-, HCF2CF2CF2CF2CH2-, HCF2CF2CF2 CF2CH2CH2-, FCH2-, FCH2CH2-, FCH2CF2-, FCH2CF2CH2-, FCH2CF2CF2-, CH3CF2CH2-, CH3CF2CF2-, CH3CF2CH2CF2-, CH3CF2 Examples include CF2CF2-, CH3CH2CF2CF2-, CH3CF2CH2CF2CH2-, CH3CF2CF2CF2CH2-, CH3CF2CF2CH2CH2-, CH3CH2CF2CF2CH2-, CH3CF2CH2CF2CH2CH2-, CH3CF2CH2CF2CH2CH2-, CH3CF2CH2CF2CH2CH2-, HCFClCF2CH2-, HCF2CFClCH2-, HCF2CFClCF2CFClCH2-, HCFClCF2CFClCF2CH2-, and the like.

[0129] Also, R 1 is a branched alkyl group having a fluorine atom,

[0130] [ka]

[0131] [ka]

[0132] However, since the presence of branches such as CH3- or CF3- tends to increase viscosity, it is more preferable that the number of branches is small (one) or zero.

[0133] R 2 R is an alkylene group having 1 to 3 carbon atoms which may have a fluorine atom. 2 An example of the minimum structural unit constituting such a linear or branched alkylene group is shown below. 2 may consist of any one or a combination of these.

[0134] (i) Minimum linear structural unit: -CH2-, -CHF-, -CF2-, -CHCl-, -CFCl-, -CCl2-

[0135] (ii) Smallest branched structural unit:

[0136] [ka]

[0137] Among the above examples, it is preferable to use structural units that do not contain Cl, since they are more stable and do not undergo a deHCl reaction due to a base.

[0138] R 2 When it is linear, it is composed only of the above-mentioned linear minimum structural unit, and among them, -CH2-, -CH2CH2- or -CF2- is preferable. -CH2- or -CH2CH2- is more preferable because it can further improve the solubility of the electrolyte salt.

[0139] R 2In the case where the branched chain is a branched chain, the branched chain contains at least one of the minimum structural units described above, and is represented by the general formula -(CX a X b )-(X a is H, F, CH3 or CF3;X b is CH3 or CF3. However, X b If CF3, then X a is H or CH3) can be preferably exemplified. These can particularly further improve the solubility of the electrolyte salt.

[0140] Specific examples of preferred fluorinated alkyl groups include CF3CF2-, HCF2CF2-, H2CFCF2-, CH3CF2-, CF3CH2-, CF3CF2CF2-, HCF2CF2CF2-, H2CFCF2CF2-, CH3CF2CF2-,

[0141] [ka]

[0142] [ka]

[0143] etc.

[0144] Among them, Rf 2 and R 7 As the fluorinated alkyl group, CF3-, CF3CF2-, (CF3)2CH-, CF3CH2-, C2F5CH2-, CF3CF2CH2-, HCF2CF2CH2-, CF3CFHCF2CH2-, CFH2-, and CF2H- are preferred, and CF3CH2-, CF3CF2CH2-, HCF2CF2CH2-, CFH2-, and CF2H- are more preferred from the viewpoints of high flame retardancy and good rate characteristics and oxidation resistance.

[0145] R 7 When R is an alkyl group that does not contain a fluorine atom, it is an alkyl group having 1 to 7 carbon atoms. 7In terms of low viscosity, the alkyl group preferably has 1 to 4 carbon atoms, and more preferably has 1 to 3 carbon atoms.

[0146] Examples of the alkyl group not containing a fluorine atom include CH3-, CH3CH2-, (CH3)2CH-, C3H7-, etc. Among these, CH3- and CH3CH2- are preferred from the viewpoints of low viscosity and good rate characteristics.

[0147] The fluorine content of the fluorinated chain carbonate is preferably 15 to 70% by mass. When the fluorine content is within the above range, compatibility with the solvent and solubility of the salt can be maintained. The fluorine content is more preferably 20% by mass or more, even more preferably 30% by mass or more, particularly preferably 35% by mass or more, more preferably 60% by mass or less, and even more preferably 50% by mass or less. In the present disclosure, the fluorine content is based on the structural formula of the fluorinated chain carbonate as follows: {(number of fluorine atoms x 19) / molecular weight of fluorinated chain carbonate} x 100(%) This value was calculated using the following formula.

[0148] The fluorinated chain carbonate is preferably any one of the following compounds, because it has a low viscosity.

[0149] [ka]

[0150] As the above-mentioned fluorinated chain carbonate, methyl 2,2,2-trifluoroethyl carbonate (F3CH2COC(=O)OCH3) is particularly preferable.

[0151] The above fluorinated chain carbonates may be used alone or as a mixture of two or more kinds in any combination and in any ratio.

[0152] When the fluorinated chain carbonate is contained, the content of the fluorinated chain carbonate is preferably 10 to 90% by volume, more preferably 20 to 85% by volume, and further preferably 30 to 80% by volume, relative to the solvent.

[0153] The carboxylate ester may be a cyclic carboxylate ester or a chain carboxylate ester.

[0154] The cyclic carboxylate may be a non-fluorinated cyclic carboxylate or a fluorinated cyclic carboxylate.

[0155] The non-fluorinated cyclic carboxylate may be a non-fluorinated saturated cyclic carboxylate, and is preferably a non-fluorinated saturated cyclic carboxylate having an alkylene group having 2 to 4 carbon atoms.

[0156] Specific examples of the non-fluorinated saturated cyclic carboxylic acid ester having an alkylene group having 2 to 4 carbon atoms include β-propiolactone, γ-butyrolactone, ε-caprolactone, δ-valerolactone, and α-methyl-γ-butyrolactone. Among these, γ-butyrolactone and δ-valerolactone are particularly preferred from the viewpoints of improving the degree of dissociation of lithium ions and improving load characteristics.

[0157] The non-fluorinated saturated cyclic carboxylic acid esters may be used alone or in any combination of two or more in any ratio.

[0158] When the non-fluorinated saturated cyclic carboxylic acid ester is contained, the content of the non-fluorinated saturated cyclic carboxylic acid ester relative to the solvent is preferably 0 to 90% by volume, more preferably 0.001 to 90% by volume, even more preferably 1 to 60% by volume, and particularly preferably 5 to 40% by volume.

[0159] The chain carboxylate may be a non-fluorinated chain carboxylate or a fluorinated chain carboxylate. When the solvent contains the chain carboxylate, the increase in resistance of the electrolyte solution after high-temperature storage can be further suppressed.

[0160] Examples of the non-fluorinated chain carboxylate ester include methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, butyl propionate, tert-butyl propionate, tert-butyl butyrate, sec-butyl propionate, sec-butyl butyrate, n-butyl butyrate, methyl pyrophosphate, ethyl pyrophosphate, tert-butyl formate, tert-butyl acetate, sec-butyl formate, sec-butyl acetate, n-hexyl pivalate, n-propyl formate, n-propyl butyl ester ... propyl acetate, n-butyl formate, n-butyl pivalate, n-octyl pivalate, ethyl 2-(dimethoxyphosphoryl)acetate, ethyl 2-(dimethylphosphoryl)acetate, ethyl 2-(diethoxyphosphoryl)acetate, ethyl 2-(diethylphosphoryl)acetate, isopropyl propionate, isopropyl acetate, ethyl formate, ethyl 2-propynyl oxalate, isopropyl formate, isopropyl butyrate, isobutyl formate, isobutyl propionate, isobutyl butyrate, and isobutyl acetate.

[0161] Of these, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, and butyl propionate are preferred, and ethyl propionate and propyl propionate are particularly preferred.

[0162] The non-fluorinated chain carboxylic acid esters may be used alone or in any combination of two or more in any ratio.

[0163] When the non-fluorinated chain carboxylate is contained, the content of the non-fluorinated chain carboxylate relative to the solvent is preferably 0 to 90% by volume, more preferably 0.001 to 90% by volume, further preferably 1 to 60% by volume, and particularly preferably 5 to 50% by volume.

[0164] The fluorinated chain carboxylate is a chain carboxylate having a fluorine atom. A solvent containing the fluorinated chain carboxylate can be suitably used even under high voltage.

[0165] The fluorinated chain carboxylate ester may be represented by the following general formula: R 31 COOR 32 (In the formula, R 31 and R 32 are each independently an alkyl group having 1 to 4 carbon atoms which may contain a fluorine atom, and R 31 and R 32 At least one of the groups contains a fluorine atom. Fluorinated chain carboxylates represented by the following formula (I) are preferred in terms of compatibility with other solvents and oxidation resistance.

[0166] R 31 and R 32Examples of the fluorinated alkyl groups include non-fluorinated alkyl groups such as a methyl group (-CH3), an ethyl group (-CH2CH3), a propyl group (-CH2CH2CH3), an isopropyl group (-CH(CH3)2), a normal butyl group (-CH2CH2CH2CH3), and a tertiary butyl group (-C(CH3)3); -CF3, -CF2H, -CFH2, -CF2CF3, -CF2CF2H, -CF2CFH2, -CH2CF3, -CH2CF2H, -CH2CFH2, -CF2CF2CF3, -CF2CF2CF2H, -CF2CF2CFH2, -CH2CF2CF3, -CH2CF 2CF2H, -CH2CF2CFH2, -CH2CH2CF3, -CH2CH2CF2H, -CH2CH2CFH2, -CF(CF3)2, -CF(CF2H)2, -CF(CFH2)2, -CH(CF3)2, -CH(CF2H)2, -CH(CFH2)2, -CF(OCH) 3)CF3, -CF2CF2CF2CF3, -CF2CF2CF2CF2H, -CF2CF2CF2CFH2, -CH2CF2CF2CF3, -CH2CF2CF2CF2H, -CH2CF2CF2CFH2, -CH2CH2CF2CF3, -CH2CH2CF2CF2H, -C H2CH2CF2CFH2, -CH2CH2CH2CF3, -CH2CH2CH2CF2H, -CH2CH2CH2CFH2, -CF(CF3)CF2CF3, -CF(CF2H)CF2CF3, -CF(CFH2)CF2CF3, -CF(CF3)CF2CF2H, -CF( CF3)CF2CFH2, -CF(CF3)CH2CF3, -CF(CF3)CH2CF2H, -CF(CF3)CH2CFH2, -CH(CF3)CF2CF3, -CH(CF2H)CF2CF3, -CH(CFH2)CF2CF3, -CH(CF3)CF2CF2H, -CH (CF3)CF2CFH2, -CH(CF3)CH2CF3, -CH(CF3)CH2CF2H, -CH(CF3)CH2CFH2, -CF2CF(CF3)CF3, -CF2CF(CF2H)CF3, -CF2CF(CFH2)CF3, -CF2CF(CF3)CF2H, - CF2CF(CF3)CFH2, -CH2CF(CF3)CF3, -CH2CF(CF2H)CF3, -CH2CF(CFH2)CF3, -CH2CF(CF3)CF2H, -CH2CF(CF3)CFH2, -CH2CH(CF3)CF3, -CH2CH(CF2H)CF3,Examples of the fluorinated alkyl groups include -CH2CH(CFH2)CF3, -CH2CH(CF3)CF2H, -CH2CH(CF3)CFH2, -CF2CH(CF3)CF3, -CF2CH(CF2H)CF3, -CF2CH(CFH2)CF3, -CF2CH(CF3)CF2H, -CF2CH(CF3)CFH2, -C(CF3)3, -C(CF2H)3, and -C(CFH2)3. Among these, methyl group, ethyl group, -CF3, -CF2H, -CF2CF3, -CH2CF3, -CH2CF2H, -CH2CFH2, -CH2CH2CF3, -CH2CF2CF3, -CH2CF2CF2H, and -CH2CF2CFH2 are particularly preferred in terms of compatibility with other solvents, viscosity, and oxidation resistance.

[0167] Specific examples of the fluorinated chain carboxylate ester include CF3CH2C(=O)OCH3 (methyl 3,3,3-trifluoropropionate), HCF2C(=O)OCH3 (methyl difluoroacetate), HCF2C(=O)OC2H5 (ethyl difluoroacetate), CF3C(=O)OCH2CH2CF3, CF3C(=O)OCH2C2F5, CF3C(=O)OCH2CF2CF2H (2,2,3,3-tetrafluoropropyl trifluoroacetate), CF3C(=O)OCH2CF3, CF3C(=O)OCH(CF3)2, ethyl pentafluorobutyrate, methyl pentafluoropropionate, ethyl pentafluoropropionate, methyl heptafluoroisobutyrate, isopropyl trifluorobutyrate, ethyl trifluoroacetate, tert-butyl trifluoroacetate, and n-butyl trifluoroacetate. , methyl tetrafluoro-2-(methoxy)propionate, 2,2-difluoroethyl acetate, 2,2,3,3-tetrafluoropropyl acetate, CH3C(=O)OCH2CF3 (2,2,2-trifluoroethyl acetate), 1H,1H-heptafluorobutyl acetate, methyl 4,4,4-trifluorobutyrate, ethyl 4,4,4-trifluorobutyrate, ethyl 3,3,3-trifluoropropionate, 3,3,3-trifluoropropyl 3,3,3-trifluoropropionate, ethyl 3-(trifluoromethyl)butyrate, methyl 2,3,3,3-tetrafluoropropionate, 2,2-difluorobutyl acetate, methyl 2,2,3,3-tetrafluoropropionate, 2-(trifluoromethyl)-3,3,3-trifluoropropionate, methyl heptafluorobutyrate, and the like can be exemplified by one or more of these. Among these, CF3CH2C(=O)OCH3, HCF2C(=O)OCH3, HCF2C(=O)OC2H5, CF3C(=O)OCH2C2F5, CF3C(=O)OCH2CF2CF2H, CF3C(=O)OCH2CF3, CF3C(=O)OCH(CF3)2, ethyl pentafluorobutyrate, methyl pentafluoropropionate, ethyl pentafluoropropionate, methyl heptafluoroisobutyrate, isopropyl trifluorobutyrate, ethyl trifluoroacetate, tert-butyl trifluoroacetate, n-butyl trifluoroacetate, methyl tetrafluoro-2-(methoxy)propionate, 2,2-difluoroethyl acetate, 2,2,3,3-tetrafluoropropyl acetate, CH3C(=O)OCH2CF3, 1H,1H-heptafluorobutyl acetate, methyl 4,4,4-trifluorobutyrate, Ethyl 4,4,4-trifluorobutyrate, ethyl 3,3,3-trifluoropropionate, 3,3,3-trifluoropropyl 3,3,3-trifluoropropionate, ethyl 3-(trifluoromethyl)butyrate, methyl 2,3,3,3-tetrafluoropropionate, 2,2-butyl difluoroacetate, methyl 2,2,3,3-tetrafluoropropionate, methyl 2-(trifluoromethyl)-3,3,3-trifluoropropionate, and methyl heptafluorobutyrate are preferred from the viewpoints of good compatibility with other solvents and rate characteristics, and CF3CH2C(=O)OCH3, HCF2C(=O)OCH3, HCF2C(=O)OC2H5, and CH3C(=O)OCH2CF3 are more preferred, and HCF2C(=O)OCH3, HCF2C(=O)OC2H5, and CH3C(=O)OCH2CF3 are particularly preferred.

[0168] The above fluorinated chain carboxylates may be used alone or in any combination of two or more in any ratio.

[0169] When the fluorinated chain carboxylate is contained, the content of the fluorinated chain carboxylate is preferably 10 to 90% by volume, more preferably 20 to 85% by volume, and even more preferably 30 to 80% by volume, relative to the solvent.

[0170] The solvent preferably contains at least one selected from the group consisting of the cyclic carbonate, the chain carbonate, and the chain carboxylate, and more preferably contains at least one selected from the group consisting of the cyclic carbonate, the chain carbonate, and the chain carboxylate. The cyclic carbonate is preferably a saturated cyclic carbonate. An electrolyte solution containing a solvent having the above composition can further improve the high-temperature storage characteristics and cycle characteristics of an electrochemical device.

[0171] When the solvent contains the cyclic carbonate and at least one selected from the group consisting of the chain carbonate and the chain carboxylate ester, the solvent preferably contains the cyclic carbonate and at least one selected from the group consisting of the chain carbonate and the chain carboxylate ester in a total amount of 10 to 100 volume %, more preferably 30 to 100 volume %, and even more preferably 50 to 100 volume %.

[0172] When the solvent contains the cyclic carbonate and at least one selected from the group consisting of the chain carbonate and the chain carboxylate ester, the volume ratio of the cyclic carbonate to the at least one selected from the group consisting of the chain carbonate and the chain carboxylate ester is preferably 5 / 95 to 95 / 5, more preferably 10 / 90 or more, even more preferably 15 / 85 or more, particularly preferably 20 / 80 or more, more preferably 90 / 10 or less, even more preferably 60 / 40 or less, and particularly preferably 50 / 50 or less.

[0173] The solvent also preferably contains at least one selected from the group consisting of the non-fluorinated saturated cyclic carbonate, the non-fluorinated chain carbonate, and the non-fluorinated chain carboxylate, and more preferably contains the non-fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the non-fluorinated chain carbonate and the non-fluorinated chain carboxylate. An electrolyte solution containing a solvent of the above composition can be suitably used in an electrochemical device used at a relatively low voltage.

[0174] When the solvent contains the non-fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the non-fluorinated chain carbonate and the non-fluorinated chain carboxylate ester, the solvent preferably contains the non-fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the non-fluorinated chain carbonate and the non-fluorinated chain carboxylate ester in a total amount of 5 to 100 volume %, more preferably 20 to 100 volume %, and even more preferably 30 to 100 volume %.

[0175] When the electrolytic solution contains the non-fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the non-fluorinated chain carbonate and the non-fluorinated chain carboxylic acid ester, the volume ratio of the non-fluorinated saturated cyclic carbonate to the at least one selected from the group consisting of the non-fluorinated chain carbonate and the non-fluorinated chain carboxylic acid ester is preferably 5 / 95 to 95 / 5, more preferably 10 / 90 or more, even more preferably 15 / 85 or more, particularly preferably 20 / 80 or more, more preferably 90 / 10 or less, even more preferably 60 / 40 or less, and particularly preferably 50 / 50 or less.

[0176] The solvent also preferably contains at least one selected from the group consisting of the fluorinated saturated cyclic carbonate, the fluorinated chain carbonate, and the fluorinated chain carboxylate, and more preferably contains the fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the fluorinated chain carbonate and the fluorinated chain carboxylate. An electrolyte solution containing a solvent of the above composition can be suitably used not only in electrochemical devices used at relatively low voltages, but also in electrochemical devices used at relatively high voltages.

[0177] When the solvent contains the fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the fluorinated chain carbonate and the fluorinated chain carboxylate ester, the solvent preferably contains 5 to 100 volume %, more preferably 10 to 100 volume %, and even more preferably 30 to 100 volume % of the fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the fluorinated chain carbonate and the fluorinated chain carboxylate ester.

[0178] When the solvent contains the fluorinated saturated cyclic carbonate and at least one selected from the group consisting of the fluorinated chain carbonate and the fluorinated chain carboxylate ester, the volume ratio of the fluorinated saturated cyclic carbonate to the at least one selected from the group consisting of the fluorinated chain carbonate and the fluorinated chain carboxylate ester is preferably 5 / 95 to 95 / 5, more preferably 10 / 90 or more, even more preferably 15 / 85 or more, particularly preferably 20 / 80 or more, more preferably 90 / 10 or less, even more preferably 60 / 40 or less, and particularly preferably 50 / 50 or less.

[0179] Furthermore, an ionic liquid can also be used as the solvent. An "ionic liquid" is a liquid that is made up of ions that are a combination of organic cations and anions.

[0180] The organic cation is not particularly limited, but examples thereof include imidazolium ions such as dialkylimidazolium cations and trialkylimidazolium cations; tetraalkylammonium ions; alkylpyridinium ions; dialkylpyrrolidinium ions; and dialkylpiperidinium ions.

[0181] The anions that serve as counters to these organic cations are not particularly limited, but examples thereof that can be used include PF6 anion, PF3(C2F5)3 anion, PF3(CF3)3 anion, BF4 anion, BF2(CF3)2 anion, BF3(CF3) anion, bisoxalatoborate anion, P(C2O4)F2 anion, Tf (trifluoromethanesulfonyl) anion, Nf (nonafluorobutanesulfonyl) anion, bis(fluorosulfonyl)imide anion, bis(trifluoromethanesulfonyl)imide anion, bis(pentafluoroethanesulfonyl)imide anion, dicyanoamine anion, and halide anions.

[0182] The solvent is preferably a non-aqueous solvent, and the electrolyte solution of the present disclosure is preferably a non-aqueous electrolyte solution. The content of the solvent in the electrolytic solution is preferably 70 to 99.999% by mass, more preferably 80% by mass or more, and more preferably 92% by mass or less.

[0183] The electrolyte solution of the present disclosure may further contain a compound (5) represented by general formula (5).

[0184] General formula (5): [ka] (In the formula, A a+ is a metal ion, a hydrogen ion or an onium ion; a is an integer from 1 to 3, b is an integer from 1 to 3, p is b / a, n203 is an integer from 1 to 4, n201 is an integer from 0 to 8, n202 is 0 or 1, Z 201 is a transition metal, an element in group III, IV or V of the periodic table. X 201is O, S, an alkylene group having 1 to 10 carbon atoms, a halogenated alkylene group having 1 to 10 carbon atoms, an arylene group having 6 to 20 carbon atoms, or a halogenated arylene group having 6 to 20 carbon atoms (an alkylene group, a halogenated alkylene group, an arylene group, and a halogenated arylene group may have a substituent or a heteroatom in the structure, and when n202 is 1 and n203 is 2 to 4, n203 Xs 201 may be bonded to each other). L 201 is a halogen atom, a cyano group, an alkyl group having 1 to 10 carbon atoms, a halogenated alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 20 carbon atoms, a halogenated aryl group having 6 to 20 carbon atoms (an alkylene group, a halogenated alkylene group, an arylene group, and a halogenated arylene group may have a substituent or a heteroatom in the structure, and when n201 is 2 to 8, n201 L 201 may be bonded to each other to form a ring) or -Z 203 Y 203 . Y 201 , Y 202 and Z 203 are independently O, S, and NY 204 , a hydrocarbon group or a fluorinated hydrocarbon group. Y 203 and Y 204 are each independently H, F, an alkyl group having 1 to 10 carbon atoms, a halogenated alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 20 carbon atoms, or a halogenated aryl group having 6 to 20 carbon atoms (the alkyl group, halogenated alkyl group, aryl group, and halogenated aryl group may have a substituent or a heteroatom in the structure, and Y 203 Or Y 204 When a plurality of are present, they may be bonded to form a ring.

[0185] A a+Examples of the cations include a lithium ion, a sodium ion, a potassium ion, a magnesium ion, a calcium ion, a barium ion, a cesium ion, a silver ion, a zinc ion, a copper ion, a cobalt ion, an iron ion, a nickel ion, a manganese ion, a titanium ion, a lead ion, a chromium ion, a vanadium ion, a ruthenium ion, a yttrium ion, a lanthanoid ion, an actinoid ion, a tetrabutylammonium ion, a tetraethylammonium ion, a tetramethylammonium ion, a triethylmethylammonium ion, a triethylammonium ion, a pyridinium ion, an imidazolium ion, a hydrogen ion, a tetraethylphosphonium ion, a tetramethylphosphonium ion, a tetraphenylphosphonium ion, a triphenylsulfonium ion, and a triethylsulfonium ion.

[0186] When used for electrochemical devices, etc., A a+ is preferably a lithium ion, a sodium ion, a magnesium ion, a tetraalkylammonium ion, or a hydrogen ion, and particularly preferably a lithium ion. a+ The valence a of the cation is an integer of 1 to 3. If it is greater than 3, the crystal lattice energy becomes large, causing a problem that it becomes difficult to dissolve in a solvent. Therefore, when solubility is required, 1 is more preferable. The valence b of the anion is also an integer of 1 to 3, and 1 is particularly preferable. The constant p, which represents the ratio of the cation and anion, is inevitably determined by the ratio of the valences of the two, b / a.

[0187] Next, the ligand portion of the general formula (5) will be described. 201 The organic or inorganic moiety that is bound to the ligand is called a ligand.

[0188] Z 201 is preferably Al, B, V, Ti, Si, Zr, Ge, Sn, Cu, Y, Zn, Ga, Nb, Ta, Bi, P, As, Sc, Hf or Sb, and more preferably Al, B or P.

[0189] X 201 represents O, S, an alkylene group having 1 to 10 carbon atoms, a halogenated alkylene group having 1 to 10 carbon atoms, an arylene group having 6 to 20 carbon atoms, or a halogenated arylene group having 6 to 20 carbon atoms. These alkylene groups and arylene groups may have a substituent or a heteroatom in their structure. Specifically, instead of hydrogen on the alkylene group or arylene group, a halogen atom, a linear or cyclic alkyl group, an aryl group, an alkenyl group, an alkoxy group, an aryloxy group, a sulfonyl group, an amino group, a cyano group, a carbonyl group, an acyl group, an amide group, or a hydroxyl group may be substituted, or instead of carbon on the alkylene or arylene group, nitrogen, sulfur, or oxygen may be introduced. When n202 is 1 and n203 is 2 to 4, n203 X 201 may be bonded to each other. An example of such a ligand is ethylenediaminetetraacetic acid.

[0190] L 201 is a halogen atom, a cyano group, an alkyl group having 1 to 10 carbon atoms, a halogenated alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 20 carbon atoms, a halogenated aryl group having 6 to 20 carbon atoms, or -Z 203 Y 203 (Z 203 , Y 203 The alkyl group and the aryl group in this case are also represented by X 201 Similarly, the structure may have a substituent or a heteroatom, and when n201 is 2 to 8, n201 L 201 may be bonded to each other to form a ring. 201 As the anion, a fluorine atom or a cyano group is preferable. In the case of a fluorine atom, the solubility and dissociation degree of the salt of the anion compound are improved, and the ionic conductivity is improved accordingly. In addition, the oxidation resistance is improved, and thus the occurrence of side reactions can be suppressed.

[0191] Y 201 , Y 202 and Z 203 are independent of each other, O, S, NY 204represents a hydrocarbon group or a fluorinated hydrocarbon group. 201 and Y 202 is O, S or NY 204 It is preferable that Y is O, and more preferable that Y is O. 201 and Y 202 By Z 201 Because of the bonds with Z 201 and form a chelate structure. The effect of this chelate improves the heat resistance, chemical stability, and hydrolysis resistance of this compound. The constant n202 in this ligand is 0 or 1, and in particular, when it is 0, the chelate ring becomes a five-membered ring, which is preferable because the chelate effect is most pronounced and stability is increased. In this specification, a fluorinated hydrocarbon group is a group in which at least one hydrogen atom of a hydrocarbon group has been substituted with a fluorine atom.

[0192] Y 203 and Y 204 are each independently H, F, an alkyl group having 1 to 10 carbon atoms, a halogenated alkyl group having 1 to 10 carbon atoms, an aryl group having 6 to 20 carbon atoms, or a halogenated aryl group having 6 to 20 carbon atoms, and these alkyl and aryl groups may have a substituent or a heteroatom in their structure, and Y 203 Or Y 204 When a plurality of these are present, they may be bonded to form a ring.

[0193] Moreover, the constant n203 related to the number of ligands described above is an integer of 1 to 4, preferably 1 or 2, and more preferably 2. Moreover, the constant n201 related to the number of ligands described above is an integer of 0 to 8, preferably an integer of 0 to 4, and more preferably 0, 2, or 4. Furthermore, it is preferable that when n203 is 1, n201 is 2, and when n203 is 2, n201 is 0.

[0194] In the general formula (5), the alkyl group, halogenated alkyl group, aryl group, and halogenated aryl group include those having other functional groups such as a branch, a hydroxyl group, or an ether bond.

[0195] Compound (5) is represented by the general formula: [ka] (In the formula, A a+ , a, b, p, n201, Z 201 and L 201 is as described above), or a compound represented by the general formula: [ka] (In the formula, A a+ , a, b, p, n201, Z 201 and L 201 is as described above).

[0196] Compound (5) includes lithium oxalatoborate salts, and is represented by the following formula: [ka] Lithium bis(oxalato)borate (LIBOB), represented by the formula: [ka] Lithium difluorooxalatoborate (LIDFOB), represented by

[0197] Compound (5) also includes compounds represented by the following formula: [ka] Lithium difluorooxalatophosphanite (LIDFOP) represented by the following formula: [ka] Lithium tetrafluorooxalatophosphanite (LITFOP) represented by the following formula: [ka] Examples of the lithium bis(oxalato)difluorophosphanite include those represented by the following formula:

[0198] Other specific examples of dicarboxylic acid complex salts in which the complex central element is boron include lithium bis(malonato)borate, lithium difluoro(malonato)borate, lithium bis(methylmalonato)borate, lithium difluoro(methylmalonato)borate, lithium bis(dimethylmalonato)borate, and lithium difluoro(dimethylmalonato)borate.

[0199] Specific examples of dicarboxylic acid complex salts in which the complex central element is phosphorus include lithium tris(oxalato)phosphate, lithium tris(malonato)phosphate, lithium difluorobis(malonato)phosphate, lithium tetrafluoro(malonato)phosphate, lithium tris(methylmalonato)phosphate, lithium difluorobis(methylmalonato)phosphate, lithium tetrafluoro(methylmalonato)phosphate, lithium tris(dimethylmalonato)phosphate, lithium difluorobis(dimethylmalonato)phosphate, and lithium tetrafluoro(dimethylmalonato)phosphate.

[0200] Specific examples of dicarboxylic acid complex salts in which the central element of the complex is aluminum include LiAl(C2O4)2 and LiAlF2(C2O4).

[0201] Among these, lithium bis(oxalato)borate, lithium difluoro(oxalato)borate, lithium tris(oxalato)phosphate, lithium difluorobis(oxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate are more preferably used because of their ease of availability and their ability to contribute to the formation of a stable coating structure. The compound (5) is particularly preferably lithium bis(oxalato)borate.

[0202] The content of compound (5) is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, and is preferably 10% by mass or less, and more preferably 3% by mass or less, relative to the solvent, in order to obtain even more excellent cycle characteristics.

[0203] The electrolyte solution of the present disclosure preferably further contains an electrolyte salt (excluding compound (5)). As the electrolyte salt, any salt that can be used in an electrolyte solution can be used, such as an alkali metal salt, an ammonium salt, a metal salt other than an alkali metal salt (for example, a light metal salt other than an alkali metal salt), a liquid salt (ionic liquid), an inorganic polymer type salt, an organic polymer type salt, etc.

[0204] Examples of electrolyte salts for secondary battery electrolytes include the following compounds: MPF6, MBF4, MClO4, MAsF6, MB(C6H5)4, MCH3SO3, MCF3SO3, MAlCl4, M2SiF6, MCl, MBr. (In the formula, M is at least one metal selected from the group consisting of Li, Na, and K, preferably one metal selected from the group consisting of Li, Na, and K, more preferably Li or Na, and even more preferably Li.) By using these alkali metal salts, excellent battery capacity, cycle characteristics, storage characteristics, and the like can be obtained. Among them, at least one selected from MPF6, MBF4, MClO4, and MAsF6 is preferred, and MPF6 is more preferred. By using these alkali metal salts, the internal resistance is further reduced, and higher effects can be obtained.

[0205] The electrolyte salt of the secondary battery electrolyte is preferably a lithium salt. Any lithium salt can be used as the lithium salt, and specific examples include the following: LiPF6, LiBF4, LiClO4, LiAlF4, LiSbF6, LiTaF6, LiWF7, LiAsF6, LiAlCl4, LiI, LiBr, LiCl, LiB 10 Cl 10 Inorganic lithium salts such as Li2SiF6, Li2PFO3, and LiPO2F2; Lithium tungstates such as LiWOF5; Lithium carboxylates such as HCO2Li, CH3CO2Li, CH2FCO2Li, CHF2CO2Li, CF3CO2Li, CF3CH2CO2Li, CF3CF2CO2Li, CF3CF2CF2CO2Li, and CF3CF2CF2CF2CO2Li; Lithium salts having an S=O group, such as FSO3Li, CH3SO3Li, CH2FSO3Li, CHF2SO3Li, CF3SO3Li, CF3CF2SO3Li, CF3CF2CF2SO3Li, CF3CF2CF2CF2SO3Li, lithium methyl sulfate, lithium ethyl sulfate (C2H5OSO3Li), and lithium 2,2,2-trifluoroethyl sulfate; Lithium imide salts such as LiN(FCO)2, LiN(FCO)(FSO2), LiN(FSO2)2, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, lithium bisperfluoroethanesulfonylimide, lithium cyclic 1,2-perfluoroethanedisulfonylimide, lithium cyclic 1,3-perfluoropropanedisulfonylimide, lithium cyclic 1,2-ethanedisulfonylimide, lithium cyclic 1,3-propanedisulfonylimide, lithium cyclic 1,4-perfluorobutanedisulfonylimide, LiN(CF3SO2)(FSO2), LiN(CF3SO2)(C3F7SO2), LiN(CF3SO2)(C4F9SO2), and LiN(POF2)2; Lithium sulfamate compounds such as (CF3CH2)2NSO3Li, (CF3CH2)(CH3)NSO3Li, (CNCH2)2NSO3Li; Lithium methide salts such as LiC(FSO2)3, LiC(CF3SO2)3, LiC(C2F5SO2)3; Others, Formula: LiPF a (C n F 2n+1 ) 6-a(wherein a is an integer of 0 to 5, and n is an integer of 1 to 6) (e.g., fluorine-containing organic lithium salts such as LiPF3(C2F5)3, LiPF3(CF3)3, LiPF3(iso-C3F7)3, LiPF5(iso-C3F7), LiPF4(CF3)2, LiPF4(C2F5)2), LiPF4(CF3SO2)2, LiPF4(C2F5SO2)2, LiBF3CF3, LiBF3C2F5, LiBF3C3F7, LiBF2(CF3)2, LiBF2(C2F5)2, LiBF2(CF3SO2)2, and LiBF2(C2F5SO2)2, LiSCN, LiB(CN)4, LiB(C6H5)4, Li2(C2O4), LiP(C2O4)3, Li2B 12 F b H 12-b (b is an integer of 0 to 3), etc.

[0206] Among these, LiPF6, LiBF4, LiSbF6, LiTaF6, LiPO2F2, FSO3Li, CF3SO3Li, LiN(FSO2)2, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, lithium cyclic 1,2-perfluoroethane disulfonylimide, lithium cyclic 1,3-perfluoropropane disulfonylimide, LiC(FSO2)3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiBF3CF3, LiBF3C2F5, LiPF3(CF3)3, LiPF3(C2F5)3, and the like are particularly preferred because they have the effect of improving output characteristics, high-rate charge / discharge characteristics, high-temperature storage characteristics, cycle characteristics, and the like, and at least one lithium salt selected from the group consisting of LiPF6, LiN(FSO2)2, and LiBF4 is most preferred.

[0207] These electrolyte salts may be used alone or in combination of two or more. A preferred example of a combination of two or more is a combination of LiPF6 and LiBF4, or a combination of LiPF6 and LiPO2F2, C2H5OSO3Li or FSO3Li, which has the effect of improving high-temperature storage characteristics, load characteristics and cycle characteristics.

[0208] In this case, there is no limit to the amount of LiBF4, LiPO2F2, C2H5OSO3Li or FSO3Li blended relative to 100% by mass of the entire electrolyte solution, and it can be any amount as long as it does not significantly impair the effects of the present disclosure; however, relative to the electrolyte solution of the present disclosure, it is usually 0.01% by mass or more, preferably 0.1% by mass or more, and usually 30% by mass or less, preferably 20% by mass or less, more preferably 10% by mass or less, and even more preferably 5% by mass or less.

[0209] Another example is the combined use of an inorganic lithium salt and an organic lithium salt, which has the effect of suppressing deterioration due to high-temperature storage. As the organic lithium salt, CF3SO3Li, LiN(FSO2)2, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, LiN(C2F5SO2)2, lithium cyclic 1,2-perfluoroethane disulfonylimide, lithium cyclic 1,3-perfluoropropane disulfonylimide, LiC(FSO2)3, LiC(CF3SO2)3, LiC(C2F5SO2)3, LiBF3CF3, LiBF3C2F5, LiPF3(CF3)3, LiPF3(C2F5)3, etc. are preferred. In this case, the ratio of the organic lithium salt to the total 100% by mass of the electrolyte is preferably 0.1% by mass or more, particularly preferably 0.5% by mass or more, and preferably 30% by mass or less, particularly preferably 20% by mass or less.

[0210] The concentration of these electrolyte salts in the electrolyte is not particularly limited as long as it does not impair the effects of the present disclosure. In order to keep the electrical conductivity of the electrolyte in a good range and ensure good battery performance, the total molar concentration of lithium in the electrolyte is preferably 0.3 mol / L or more, more preferably 0.4 mol / L or more, even more preferably 0.5 mol / L or more, and is preferably 3 mol / L or less, more preferably 2.5 mol / L or less, even more preferably 2.0 mol / L or less.

[0211] If the total molar concentration of lithium is too low, the electrical conductivity of the electrolyte may be insufficient, whereas if the concentration is too high, the electrical conductivity may decrease due to increased viscosity, which may result in reduced battery performance.

[0212] The electrolyte solution of the present disclosure has the general formula (6): [ka] (In the formula, X 21 is a group containing at least H or C; n21 is an integer of 1 to 3; Y 21 and Z 21 are the same or different and contain at least H, C, O or F; n22 is 0 or 1; Y 21 and Z 21 may be bonded to each other to form a ring.) When the electrolyte solution contains compound (6), the capacity retention rate is more unlikely to decrease and the amount of gas generated is more unlikely to increase even when stored at high temperatures.

[0213] If n21 is 2 or 3, then 2 or 3 Xs 21 may be the same or different. Y 21 and Z 21 If there are multiple, there are multiple Y 21 and Z 21 may be the same or different.

[0214] X 21 As for -CY 21 Z 21 -(In the formula, Y 21 and Z 21 as above) or -CY 21 =CZ 21 -(In the formula, Y 21 and Z 21 is as defined above), is preferred.

[0215] Y 21 is preferably at least one selected from the group consisting of H-, F-, CH3-, CH3CH2-, CH3CH2CH2-, CF3-, CF3CF2-, CH2FCH2-, and CF3CF2CF2-. Z 21is preferably at least one selected from the group consisting of H-, F-, CH3-, CH3CH2-, CH3CH2CH2-, CF3-, CF3CF2-, CH2FCH2-, and CF3CF2CF2-.

[0216] Or Y 21 and Z 21 can be bonded to each other to form a carbocyclic or heterocyclic ring which may contain an unsaturated bond and which may have aromaticity. The number of carbon atoms in the ring is preferably 3 to 20.

[0217] Next, specific examples of compound (6) will be described. In the following examples, the term "analog" refers to an acid anhydride obtained by replacing a part of the structure of the exemplified acid anhydride with another structure within the scope of the present disclosure, and examples thereof include a dimer, trimer, tetramer, etc., consisting of a plurality of acid anhydrides, structural isomers such as those having the same number of carbon atoms in the substituent but having a branched chain, and those in which the substituent is bonded to the acid anhydride at a different site.

[0218] Specific examples of acid anhydrides forming a five-membered ring structure include succinic anhydride, methylsuccinic anhydride (4-methylsuccinic anhydride), dimethylsuccinic anhydride (4,4-dimethylsuccinic anhydride, 4,5-dimethylsuccinic anhydride, etc.), 4,4,5-trimethylsuccinic anhydride, 4,4,5,5-tetramethylsuccinic anhydride, 4-vinylsuccinic anhydride, 4,5-divinylsuccinic anhydride, phenylsuccinic anhydride (4-phenylsuccinic anhydride), 4,5-diphenylsuccinic anhydride, etc. Examples of maleic anhydride include 4,4-diphenylsuccinic anhydride, citraconic anhydride, maleic anhydride, methylmaleic anhydride (4-methylmaleic anhydride), 4,5-dimethylmaleic anhydride, phenylmaleic anhydride (4-phenylmaleic anhydride), 4,5-diphenylmaleic anhydride, itaconic anhydride, 5-methylitaconic anhydride, 5,5-dimethylitaconic anhydride, phthalic anhydride, 3,4,5,6-tetrahydrophthalic anhydride, and the like, and their analogs.

[0219] Specific examples of acid anhydrides forming a 6-membered ring structure include cyclohexanedicarboxylic anhydride (cyclohexane-1,2-dicarboxylic anhydride, etc.), 4-cyclohexene-1,2-dicarboxylic anhydride, glutaric anhydride, glutaconic anhydride, 2-phenylglutaric anhydride, and their analogs.

[0220] Other specific examples of acid anhydrides forming a cyclic structure include 5-norbornene-2,3-dicarboxylic anhydride, cyclopentanetetracarboxylic dianhydride, pyromellitic anhydride, diglycolic anhydride, and the like, and their analogues.

[0221] Specific examples of acid anhydrides which form a cyclic structure and are substituted with halogen atoms include monofluorosuccinic anhydride (4-fluorosuccinic anhydride, etc.), 4,4-difluorosuccinic anhydride, 4,5-difluorosuccinic anhydride, 4,4,5-trifluorosuccinic anhydride, trifluoromethylsuccinic anhydride, tetrafluorosuccinic anhydride (4,4,5,5-tetrafluorosuccinic anhydride), 4-fluoromaleic anhydride, 4,5-difluoromaleic anhydride, trifluoromethylmaleic anhydride, 5-fluoroitaconic anhydride, 5,5-difluoroitaconic anhydride, and analogs thereof.

[0222] Compound (6) may, among others, be glutaric anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, diglycolic anhydride, cyclohexanedicarboxylic anhydride, cyclopentanetetracarboxylic dianhydride, 4-cyclohexene-1,2-dicarboxylic anhydride, 3,4,5,6-tetrahydrophthalic anhydride, 5-norbornene-2,3-dicarboxylic anhydride, phenylsuccinic anhydride, 2-phenylglutaric anhydride, maleic anhydride, methylmaleic anhydride, trifluoromethyl anhydride, methylmaleic ... Preferred are maleic anhydride, phenylmaleic anhydride, succinic anhydride, methylsuccinic anhydride, dimethylsuccinic anhydride, trifluoromethylsuccinic anhydride, monofluorosuccinic anhydride, tetrafluorosuccinic anhydride, and the like, more preferred are maleic anhydride, methylmaleic anhydride, trifluoromethylmaleic anhydride, succinic anhydride, methylsuccinic anhydride, trifluoromethylsuccinic anhydride, and tetrafluorosuccinic anhydride, and even more preferred are maleic anhydride and succinic anhydride.

[0223] Compound (6) is represented by the general formula (7):

[0224] [ka] (In the formula, X 31 ~X 34 are the same or different and contain at least H, C, O or F), and a compound (7) represented by the general formula (8):

[0225] [ka] (In the formula, X 41 and X 42 are the same or different and contain at least H, C, O or F),

[0226] X 31 ~X 34are preferably at least one selected from the group consisting of an alkyl group, a fluorinated alkyl group, an alkenyl group, and a fluorinated alkenyl group, and X may be the same or different. 31 ~X 34 The carbon number of is preferably 1 to 10, and more preferably 1 to 3.

[0227] X 31 ~X 34 are the same or different, and are more preferably at least one selected from the group consisting of H-, F-, CH3-, CH3CH2-, CH3CH2CH2-, CF3-, CF3CF2-, CH2FCH2-, and CF3CF2CF2-.

[0228] X 41 and X 42 are preferably at least one selected from the group consisting of an alkyl group, a fluorinated alkyl group, an alkenyl group, and a fluorinated alkenyl group, and X may be the same or different. 41 and X 42 The carbon number of is preferably 1 to 10, and more preferably 1 to 3.

[0229] X 41 and X 42 are the same or different, and are more preferably at least one selected from the group consisting of H-, F-, CH3-, CH3CH2-, CH3CH2CH2-, CF3-, CF3CF2-, CH2FCH2-, and CF3CF2CF2-.

[0230] Compound (7) is preferably any one of the following compounds:

[0231] [ka]

[0232] Compound (8) is preferably any one of the following compounds:

[0233] [ka]

[0234] The electrolyte preferably contains 0.0001 to 15% by mass of compound (6) relative to the electrolyte, since the capacity retention rate is less likely to decrease and the amount of gas generated is less likely to increase even when stored at high temperatures. The content of compound (6) is more preferably 0.01 to 10% by mass, further preferably 0.1 to 5% by mass, and particularly preferably 0.1 to 3.0% by mass.

[0235] When the electrolyte contains both the compounds (7) and (8), even when stored at high temperatures, the capacity retention rate is less likely to decrease and the amount of gas generated is less likely to increase. Therefore, the electrolyte preferably contains 0.08 to 2.50 mass% of the compound (7) and 0.02 to 1.50 mass% of the compound (8), and more preferably contains 0.80 to 2.50 mass% of the compound (7) and 0.08 to 1.50 mass% of the compound (8).

[0236] The electrolyte solution of the present disclosure may contain at least one selected from the group consisting of nitrile compounds represented by the following general formulas (9a), (9b), and (9c). [ka] (In the formula, R a and R b each independently represents a hydrogen atom, a cyano group (CN), a halogen atom, an alkyl group, or an alkyl group in which at least a portion of the hydrogen atoms has been substituted with a halogen atom. n represents an integer of 1 to 10. [ka] (In the formula, R c represents a hydrogen atom, a halogen atom, an alkyl group, an alkyl group in which at least some of the hydrogen atoms are substituted with halogen atoms, or NC-R c1 -X c1 -(R c1 is an alkylene group, X c1 represents an oxygen atom or a sulfur atom. d and R eeach independently represents a hydrogen atom, a halogen atom, an alkyl group, or an alkyl group in which at least a portion of the hydrogen atoms has been substituted with a halogen atom; and m represents an integer of 1 to 10. [ka] (In the formula, R f , R g , R h and R i each independently represents a group containing a cyano group (CN), a hydrogen atom (H), a halogen atom, an alkyl group, or an alkyl group in which at least some of the hydrogen atoms have been substituted with halogen atoms. f , R g , R h and R i At least one of the groups is a group containing a cyano group. l represents an integer of 1 to 3. This can improve the high-temperature storage properties of the electrochemical device.The above nitrile compounds may be used alone or in any combination of two or more kinds in any ratio.

[0237] In the above general formula (9a), R a and R b are each independently a hydrogen atom, a cyano group (CN), a halogen atom, an alkyl group, or an alkyl group in which at least some of the hydrogen atoms have been substituted with halogen atoms. Examples of halogen atoms include a fluorine atom, a chlorine atom, a bromine atom, and an iodine atom, with a fluorine atom being preferred. The alkyl group preferably has a carbon number of 1 to 5. Specific examples of the alkyl group include a methyl group, an ethyl group, a propyl group, an isopropyl group, a butyl group, an isobutyl group, and a tert-butyl group. Examples of the alkyl group in which at least a portion of the hydrogen atoms have been substituted with halogen atoms include the above-mentioned alkyl groups in which at least a portion of the hydrogen atoms have been substituted with the above-mentioned halogen atoms. R a and R bWhen R is an alkyl group or an alkyl group in which at least some of the hydrogen atoms are substituted with halogen atoms, R a and R b may be bonded to each other to form a ring structure (for example, a cyclohexane ring). R a and R b is preferably a hydrogen atom or an alkyl group.

[0238] In the above general formula (9a), n is an integer of 1 to 10. When n is 2 or more, n R a may all be the same, or at least some may be different. b The same applies to the above. n is preferably an integer of 1 to 7, and more preferably an integer of 2 to 5.

[0239] As the nitrile compound represented by the above general formula (9a), dinitriles and tricarbonitriles are preferred. Specific examples of dinitriles include malononitrile, succinonitrile, glutaronitrile, adiponitrile, pimelonitrile, suberonitrile, azelanitrile, sebaconitrile, undecanedinitrile, dodecanedinitrile, methylmalononitrile, ethylmalononitrile, isopropylmalononitrile, tert-butylmalononitrile, methylsuccinonitrile, 2,2-dimethylsuccinonitrile, 2,3-dimethylsuccinonitrile, 2 ,3,3-Trimethylsuccinonitrile, 2,2,3,3-Tetramethylsuccinonitrile, 2,3-Diethyl-2,3-dimethylsuccinonitrile, 2,2-Diethyl-3,3-dimethylsuccinonitrile, Bicyclohexyl-1,1-dicarbonitrile, Bicyclohexyl-2,2-dicarbonitrile, Bicyclohexyl-3,3-dicarbonitrile, 2,5-Dimethyl-2,5-hexanedicarbonitrile, 2,3-Diisobutyl-2,3- Dimethylsuccinonitrile, 2,2-diisobutyl-3,3-dimethylsuccinonitrile, 2-methylglutaronitrile, 2,3-dimethylglutaronitrile, 2,4-dimethylglutaronitrile, 2,2,3,3-tetramethylglutaronitrile, 2,2,4,4-tetramethylglutaronitrile, 2,2,3,4-tetramethylglutaronitrile, 2,3,3,4-tetramethylglutaronitrile, 1,4-dicyanopentane, 2,6-dicyanopentane Examples include anoheptane, 2,7-dicyanooctane, 2,8-dicyanononane, 1,6-dicyanodecane, 1,2-dicyanobenzene, 1,3-dicyanobenzene, 1,4-dicyanobenzene, 3,3'-(ethylenedioxy)dipropionitrile, 3,3'-(ethylenedithio)dipropionitrile, 3,9-bis(2-cyanoethyl)-2,4,8,10-tetraoxaspiro[5,5]undecane, butanenitrile, phthalonitrile, etc. Among these, succinonitrile, glutaronitrile, and adiponitrile are particularly preferred. Specific examples of tricarbonitrile include pentanetricarbonitrile, propanetricarbonitrile, 1,3,5-hexanetricarbonitrile, 1,3,6-hexanetricarbonitrile, heptanetricarbonitrile, 1,2,3-propanetricarbonitrile, 1,3,5-pentanetricarbonitrile, cyclohexanetricarbonitrile, triscyanoethylamine, triscyanoethoxypropane, tricyanoethylene, tris(2-cyanoethyl)amine, and the like. Particularly preferred are 1,3,6-hexanetricarbonitrile and cyclohexanetricarbonitrile, and most preferred is cyclohexanetricarbonitrile.

[0240] In the above general formula (9b), R c represents a hydrogen atom, a halogen atom, an alkyl group, an alkyl group in which at least some of the hydrogen atoms are substituted with halogen atoms, or NC-R c1 -X c1 -(R c1 is an alkylene group, X c1 represents an oxygen atom or a sulfur atom; d and R e are each independently a hydrogen atom, a halogen atom, an alkyl group, or an alkyl group in which at least some of the hydrogen atoms have been substituted with halogen atoms. Examples of the halogen atom, the alkyl group, and the alkyl group in which at least a part of the hydrogen atoms has been substituted with a halogen atom include those exemplified for the above general formula (9a). Above NC-R c1 -X c1 -R in c1 is an alkylene group. The alkylene group is preferably an alkylene group having 1 to 3 carbon atoms. R c , R d and R e are preferably each independently a hydrogen atom, a halogen atom, an alkyl group, or an alkyl group in which at least a portion of the hydrogen atoms has been substituted with a halogen atom. R c , R d and R eAt least one of the above is preferably a halogen atom or a group in which at least a portion of the hydrogen atoms of an alkyl group have been substituted with halogen atoms, and more preferably a fluorine atom or a group in which at least a portion of the hydrogen atoms of an alkyl group have been substituted with fluorine atoms. R d and R e When R is an alkyl group or an alkyl group in which at least some of the hydrogen atoms are substituted with halogen atoms, R d and R e may be bonded to each other to form a ring structure (for example, a cyclohexane ring).

[0241] In the above general formula (9b), m is an integer of 1 to 10. When m is 2 or more, m R d may all be the same, or at least some may be different. e The same applies to m. m is preferably an integer of 2 to 7, and more preferably an integer of 2 to 5.

[0242] Examples of the nitrile compound represented by the general formula (9b) include acetonitrile, propionitrile, butyronitrile, isobutyronitrile, valeronitrile, isovaleronitrile, lauronitrile, 3-methoxypropionitrile, 2-methylbutyronitrile, trimethylacetonitrile, hexanenitrile, cyclopentanecarbonitrile, cyclohexanecarbonitrile, fluoroacetonitrile, difluoroacetonitrile, trifluoroacetonitrile, 2-fluoropropionitrile, 3-fluoropropionitrile, 2,2-difluoropropionitrile, 2,3-difluoropropionitrile, 3,3-difluoropropionitrile, 2,2,3-trifluoropropionitrile, 3,3,3-trifluoropropionitrile, 3,3'-oxydipropionitrile, 3,3'-thiodipropionitrile, pentafluoropropionitrile, methoxyacetonitrile, benzonitrile, etc. Among these, 3,3,3-trifluoropropionitrile is particularly preferred.

[0243] In the above general formula (9c), Rf , R g , R h and R i are each independently a group containing a cyano group (CN), a hydrogen atom, a halogen atom, an alkyl group, or an alkyl group in which at least some of the hydrogen atoms have been substituted with halogen atoms. Examples of the halogen atom, the alkyl group, and the alkyl group in which at least a part of the hydrogen atoms has been substituted with a halogen atom include those exemplified for the above general formula (9a). Examples of the group containing a cyano group include a cyano group and an alkyl group in which at least some of the hydrogen atoms are substituted with a cyano group. Examples of the alkyl group in this case include those exemplified for the above general formula (9a). R f , R g , R h and R i At least one of R is a group containing a cyano group. f , R g , R h and R i At least two of R are groups containing a cyano group, and more preferably, R h and R i R is a group containing a cyano group. h and R i When R is a group containing a cyano group, f and R g is preferably a hydrogen atom.

[0244] In the above general formula (9c), l is an integer of 1 to 3. When l is 2 or more, l R f may all be the same, or at least some may be different. g The same applies to l. An integer of 1 to 2 is preferable.

[0245] Examples of the nitrile compound represented by the above general formula (9c) include 3-hexenedinitrile, mucononitrile, maleonitrile, fumaronitrile, acrylonitrile, methacrylonitrile, crotononitrile, 3-methylcrotononitrile, 2-methyl-2-butenenitrile, 2-pentenenitrile, 2-methyl-2-pentenenitrile, 3-methyl-2-pentenenitrile, 2-hexenenitrile, and the like, of which 3-hexenedinitrile and mucononitrile are preferred, with 3-hexenedinitrile being particularly preferred.

[0246] The content of the nitrile compounds is preferably 0.2 to 7% by mass relative to the electrolytic solution. This can further improve the high-temperature storage characteristics and safety of the electrochemical device at high voltage. The lower limit of the total content of the nitrile compounds is more preferably 0.3% by mass, and even more preferably 0.5% by mass. The upper limit is more preferably 5% by mass, even more preferably 2% by mass, and particularly preferably 1.0% by mass.

[0247] The electrolyte solution of the present disclosure may contain a compound having an isocyanato group (hereinafter, may be abbreviated as "isocyanate"). The above-mentioned isocyanate is not particularly limited, and any isocyanate can be used. Examples of the isocyanate include monoisocyanates, diisocyanates, triisocyanates, etc.

[0248] Specific examples of monoisocyanates include isocyanatomethane, isocyanatoethane, 1-isocyanatopropane, 1-isocyanatobutane, 1-isocyanatopentane, 1-isocyanatohexane, 1-isocyanatoheptane, 1-isocyanatooctane, 1-isocyanatononane, 1-isocyanatodecane, isocyanatocyclohexane, methoxycarbonyl isocyanate, ethoxycarbonyl isocyanate, propoxycarbonyl isocyanate, butoxycarbonyl isocyanate, methoxysulfonyl isocyanate, ethoxysulfonyl isocyanate, propoxysulfonyl isocyanate, butoxysulfonyl isocyanate, fluorosulfonyl isocyanate, methyl isocyanate, butyl isocyanate, phenyl isocyanate, 2-isocyanatoethyl acrylate, 2-isocyanatoethyl methacrylate, and ethyl isocyanate.

[0249] Specific examples of diisocyanates include 1,4-diisocyanatobutane, 1,5-diisocyanatopentane, 1,6-diisocyanatohexane, 1,7-diisocyanatoheptane, 1,8-diisocyanatooctane, 1,9-diisocyanatononane, 1,10-diisocyanatodecane, 1,3-diisocyanatopropene, 1,4-diisocyanato-2-butene, 1,4-diisocyanato-2-fluorobutane, and 1,4-diisocyanato-2,3-difluorobutane. 1,5-diisocyanato-2-pentene, 1,5-diisocyanato-2-methylpentane, 1,6-diisocyanato-2-hexene, 1,6-diisocyanato-3-hexene, 1,6-diisocyanato-3-fluorohexane, 1,6-diisocyanato-3,4-difluorohexane, toluene diisocyanate, xylene diisocyanate, tolylene diisocyanate, 1,2-bis(isocyanatomethyl)cyclohexane, 1,3-bis(isocyanatomethyl)cyclohexane 1,4-bis(isocyanatomethyl)cyclohexane, 1,2-diisocyanatocyclohexane, 1,3-diisocyanatocyclohexane, 1,4-diisocyanatocyclohexane, dicyclohexylmethane-1,1'-diisocyanate, dicyclohexylmethane-2,2'-diisocyanate, dicyclohexylmethane-3,3'-diisocyanate, dicyclohexylmethane-4,4'-diisocyanate, isophorone diisocyanate bis(methyl isocyanate), bicyclo[2.2.1]heptane-2,5-diylbis(methyl isocyanate), bicyclo[2.2.1]heptane-2,6-diylbis(methyl isocyanate), 2,4,4-trimethylhexamethylene diisocyanate, 2,2,4-trimethylhexamethylene diisocyanate, hexamethylene diisocyanate, 1,4-phenylene diisocyanate, octamethylene diisocyanate, tetramethylene diisocyanate, and the like.

[0250] Specific examples of triisocyanates include 1,6,11-triisocyanatoundecane, 4-isocyanatomethyl-1,8-octamethylene diisocyanate, 1,3,5-triisocyanatomethylbenzene, 1,3,5-tris(6-isocyanatohex-1-yl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, and 4-(isocyanatomethyl)octamethylene diisocyanate.

[0251] Among these, 1,6-diisocyanatohexane, 1,3-bis(isocyanatomethyl)cyclohexane, 1,3,5-tris(6-isocyanatohex-1-yl)-1,3,5-triazine-2,4,6(1H,3H,5H)-trione, 2,4,4-trimethylhexamethylene diisocyanate, and 2,2,4-trimethylhexamethylene diisocyanate are preferred because they are easily available industrially and can keep the production costs of the electrolyte low, and also from a technical viewpoint, can contribute to the formation of a stable coating structure, and are therefore more preferably used.

[0252] The content of isocyanate is not particularly limited and may be any as long as it does not significantly impair the effects of the present disclosure, but is preferably 0.001% by mass or more and 1.0% by mass or less with respect to the electrolyte. When the content of isocyanate is above this lower limit, it is possible to bring about a sufficient effect of improving cycle characteristics to the non-aqueous electrolyte secondary battery. When the content is below this upper limit, it is possible to avoid an initial increase in resistance of the non-aqueous electrolyte secondary battery. The content of isocyanate is more preferably 0.01% by mass or more, even more preferably 0.1% by mass or more, particularly preferably 0.2% by mass or more, and more preferably 0.8% by mass or less, even more preferably 0.7% by mass or less, particularly preferably 0.6% by mass or less.

[0253] The electrolyte of the present disclosure may contain a cyclic sulfonate ester. The cyclic sulfonate ester is not particularly limited, and any cyclic sulfonate ester can be used. Examples of the cyclic sulfonate ester include saturated cyclic sulfonate esters, unsaturated cyclic sulfonate esters, saturated cyclic disulfonate esters, and unsaturated cyclic disulfonate esters.

[0254] Specific examples of saturated cyclic sulfonic acid esters include 1,3-propane sultone, 1-fluoro-1,3-propane sultone, 2-fluoro-1,3-propane sultone, 3-fluoro-1,3-propane sultone, 1-methyl-1,3-propane sultone, 2-methyl-1,3-propane sultone, 3-methyl-1,3-propane sultone, 1,3-butane sultone, 1,4-butane sultone, 1-fluoro-1,4-butane sultone, 2-fluoro-1,4-butane sultone, 3-fluoro-1,4-butane sultone, 4-fluoro-1,4-butane sultone, 1-methyl-1,4-butane sultone, 2-methyl-1,4-butane sultone, 3-methyl-1,4-butane sultone, 4-methyl-1,4-butane sultone, and 2,4-butane sultone.

[0255] Specific examples of the unsaturated cyclic sulfonic acid ester include 1-propene-1,3-sultone, 2-propene-1,3-sultone, 1-fluoro-1-propene-1,3-sultone, 2-fluoro-1-propene-1,3-sultone, 3-fluoro-1-propene-1,3-sultone, 1-fluoro-2-propene-1,3-sultone, 2-fluoro-2-propene-1,3-sultone, 3-fluoro-2-propene-1,3-sultone, 1-methyl-1-propene-1,3-sultone, 2-methyl-1-propene-1,3-sultone, 1-Butene-1,4-sultone, 2-Butene-1,4-sultone, 3-Butene-1,4-sultone, 1-Fluoro-1-butene-1,4-sultone, 2-Fluoro-1-butene-1,4-sultone, 3-Fluoro-1-butene-1,4-sultone, 4-Fluoro-1-butene-1,4-sultone, 5-Fluoro-1-butene-1,4-sultone, 6-Fluoro-1-butene-1,4-sultone, 7-Fluoro-1-butene-1,4-sultone, 8-Fluoro-1-butene-1,4-sultone, 9-Fluoro-1-butene-1,4-sultone, 10-Fluoro-1-butene-1,4-sultone, 11-Fluoro-1-butene-1,4-sultone, 12-Fluoro-1-butene-1,4-sultone, 13-Fluoro-1-butene-1,4-sultone, 14-Fluoro-1-butene-1,4-sultone, 15-Fluoro-1-butene-1,4-sultone, 16-Fluoro-1-butene-1,4-sultone, 17-Fluoro-1-butene-1,4-sultone, 18-Fluoro-1-butene-1,4-sultone, 19-Fluoro-1-butene-1,4-sultone, 20-Fluoro-1-butene-1,4-sultone, 21-Fluoro-1-butene-1,4-sultone, 22-Fluoro-1-butene-1,4-sultone, 23-Fluoro-1-butene-1,4-sultone, 24-Fluoro-1-butene-1,4-sult -sultone, 1-fluoro-2-butene-1,4-sultone, 2-fluoro-2-butene-1,4-sultone, 3-fluoro-2-butene-1,4-sultone, 4-fluoro-2-butene-1,4-sultone, 1,3-propene sultone, 1-fluoro-3-butene-1,4-sultone, 2-fluoro-3-butene-1,4-sultone, 3-fluoro-3-butene-1,4-sultone, 4-fluoro-3-butene-1,4-sultone, 1-methyl-1-butene-1,4-sultone, 2-methyl-1-butene Examples of such sultone include 1-methyl-1,4-sultone, 3-methyl-1-butene-1,4-sultone, 4-methyl-1-butene-1,4-sultone, 1-methyl-2-butene-1,4-sultone, 2-methyl-2-butene-1,4-sultone, 3-methyl-2-butene-1,4-sultone, 4-methyl-2-butene-1,4-sultone, 1-methyl-3-butene-1,4-sultone, 2-methyl-3-butene-1,4-sultone, 3-methyl-3-butene-1,4-sultone, and 4-methyl-3-butene-14-sultone.

[0256] Among them, 1,3-propane sultone, 1-fluoro-1,3-propane sultone, 2-fluoro-1,3-propane sultone, 3-fluoro-1,3-propane sultone, and 1-propene-1,3-sultone are more preferably used because they are easily available and can contribute to the formation of a stable coating structure. The content of the cyclic sulfonate is not particularly limited and can be any amount as long as it does not significantly impair the effects of the present disclosure, but is preferably 0.001% by mass or more and 3.0% by mass or less with respect to the electrolyte.

[0257] When the content of the cyclic sulfonate is equal to or more than this lower limit, the non-aqueous electrolyte secondary battery can be provided with a sufficient effect of improving cycle characteristics. When the content is equal to or less than this upper limit, the increase in the manufacturing cost of the non-aqueous electrolyte secondary battery can be avoided. The content of the cyclic sulfonate is more preferably 0.01% by mass or more, even more preferably 0.1% by mass or more, particularly preferably 0.2% by mass or more, and more preferably 2.5% by mass or less, even more preferably 2.0% by mass or less, particularly preferably 1.8% by mass or less.

[0258] The electrolyte solution of the present disclosure may further contain polyethylene oxide having a weight average molecular weight of 2000 to 4000 and having -OH, -OCOOH, or -COOH at its terminal. By containing such a compound, the stability of the electrode interface is improved, and the characteristics of the electrochemical device can be improved. Examples of the polyethylene oxide include polyethylene oxide monool, polyethylene oxide carboxylic acid, polyethylene oxide diol, polyethylene oxide dicarboxylic acid, polyethylene oxide triol, polyethylene oxide tricarboxylic acid, etc. These may be used alone or in combination of two or more kinds. Among these, a mixture of polyethylene oxide monol and polyethylene oxide diol, and a mixture of polyethylene carboxylic acid and polyethylene dicarboxylic acid are preferred in terms of improving the properties of the electrochemical device.

[0259] If the weight-average molecular weight of the polyethylene oxide is too small, it may be easily decomposed by oxidation. The weight average molecular weight can be measured in terms of polystyrene by gel permeation chromatography (GPC).

[0260] The content of the polyethylene oxide in the electrolyte is 1×10 -6 ~1×10 -2 If the content of polyethylene oxide is too high, the characteristics of the electrochemical device may be impaired. The content of the polyethylene oxide is 5×10 -6 It is more preferable that it is mol / kg or more.

[0261] The electrolyte solution of the present disclosure may further contain, as an additive, a fluorinated saturated cyclic carbonate, an unsaturated cyclic carbonate, an overcharge inhibitor, other known auxiliaries, etc. This can suppress deterioration of the characteristics of the electrochemical device.

[0262] The fluorinated saturated cyclic carbonate may be a compound represented by the above-mentioned general formula (A). Among them, fluoroethylene carbonate, difluoroethylene carbonate, monofluoromethylethylene carbonate, trifluoromethylethylene carbonate, and 2,2,3,3,3-pentafluoropropylethylene carbonate (4-(2,2,3,3,3-pentafluoro-propyl)-[1,3]dioxolan-2-one) are preferred. The fluorinated saturated cyclic carbonate may be used alone or in any combination and ratio of two or more.

[0263] The content of the fluorinated saturated cyclic carbonate is preferably 0.001 to 10% by mass, more preferably 0.01 to 5% by mass, and further preferably 0.1 to 3% by mass, relative to the electrolytic solution.

[0264] Examples of the unsaturated cyclic carbonate include vinylene carbonates, ethylene carbonates substituted with a substituent having an aromatic ring or a carbon-carbon double bond or a carbon-carbon triple bond, phenyl carbonates, vinyl carbonates, allyl carbonates, and catechol carbonates.

[0265] Examples of vinylene carbonates include vinylene carbonate, methyl vinylene carbonate, 4,5-dimethyl vinylene carbonate, phenyl vinylene carbonate, 4,5-diphenyl vinylene carbonate, vinyl vinylene carbonate, 4,5-divinyl vinylene carbonate, allyl vinylene carbonate, 4,5-diallyl vinylene carbonate, 4-fluoro vinylene carbonate, 4-fluoro-5-methyl vinylene carbonate, 4-fluoro-5-phenyl vinylene carbonate, 4-fluoro-5-vinyl vinylene carbonate, 4-allyl-5-fluoro vinylene carbonate, ethynyl ethylene carbonate, propargyl ethylene carbonate, methyl vinylene carbonate, and dimethyl vinylene carbonate.

[0266] Specific examples of ethylene carbonates substituted with a substituent having an aromatic ring or a carbon-carbon double bond or a carbon-carbon triple bond include vinyl ethylene carbonate, 4,5-divinyl ethylene carbonate, 4-methyl-5-vinyl ethylene carbonate, 4-allyl-5-vinyl ethylene carbonate, ethynyl ethylene carbonate, 4,5-diethynyl ethylene carbonate, 4-methyl-5-ethynyl ethylene carbonate, 4-vinyl-5-ethynyl ethylene carbonate, 4-allyl-5-ethynyl ethylene carbonate, Examples of the ethylene carbonate include 4-methyl-5-allylethylene carbonate, 4-methylene-1,3-dioxolan-2-one, 4,5-dimethylene-1,3-dioxolan-2-one, and 4-methyl-5-allylethylene carbonate.

[0267] Among these, preferred unsaturated cyclic carbonates are vinylene carbonate, methylvinylene carbonate, 4,5-dimethylvinylene carbonate, vinylvinylene carbonate, 4,5-vinylvinylene carbonate, allylvinylene carbonate, 4,5-diallylvinylene carbonate, vinylethylene carbonate, 4,5-divinylethylene carbonate, 4-methyl-5-vinylethylene carbonate, allylethylene carbonate, 4,5-diallylethylene carbonate, 4-methyl-5-allylethylene carbonate, 4-allyl-5-vinylethylene carbonate, ethynylethylene carbonate, 4,5-diethynylethylene carbonate, 4-methyl-5-ethynylethylene carbonate, and 4-vinyl-5-ethynylethylene carbonate. Furthermore, vinylene carbonate, vinyl ethylene carbonate, and ethynyl ethylene carbonate are particularly preferred since they form a more stable interface protective film, with vinylene carbonate being the most preferred.

[0268] The molecular weight of the unsaturated cyclic carbonate is not particularly limited, and may be any as long as it does not significantly impair the effects of the present disclosure. The molecular weight is preferably 50 or more and 250 or less. In this range, the solubility of the unsaturated cyclic carbonate in the electrolyte is easily ensured, and the effects of the present disclosure are easily fully exhibited. The molecular weight of the unsaturated cyclic carbonate is more preferably 80 or more, and more preferably 150 or less.

[0269] The method for producing the unsaturated cyclic carbonate is not particularly limited, and any known method can be selected for production.

[0270] The unsaturated cyclic carbonates may be used alone or as a mixture of two or more kinds in any combination and in any ratio.

[0271] The content of the unsaturated cyclic carbonate is not particularly limited, and may be any content as long as it does not significantly impair the effects of the present disclosure. The content of the unsaturated cyclic carbonate is preferably 0.001% by mass or more, more preferably 0.01% by mass or more, and even more preferably 0.1% by mass or more, based on 100% by mass of the electrolyte. The content is preferably 5% by mass or less, more preferably 4% by mass or less, and even more preferably 3% by mass or less. If it is within the above range, the electrochemical device using the electrolyte is likely to exhibit a sufficient cycle characteristic improvement effect, and it is also easy to avoid situations such as a decrease in high-temperature storage characteristics, an increase in gas generation, and a decrease in discharge capacity retention rate.

[0272] As the unsaturated cyclic carbonate, in addition to the above-mentioned non-fluorinated unsaturated cyclic carbonates, fluorinated unsaturated cyclic carbonates can also be suitably used. The fluorinated unsaturated cyclic carbonate is a cyclic carbonate having an unsaturated bond and a fluorine atom. The number of fluorine atoms in the fluorinated unsaturated cyclic carbonate is not particularly limited as long as it is 1 or more. Among them, the number of fluorine atoms is usually 6 or less, preferably 4 or less, and most preferably 1 or 2.

[0273] Examples of the fluorinated unsaturated cyclic carbonate include fluorinated vinylene carbonate derivatives and fluorinated ethylene carbonate derivatives substituted with a substituent having an aromatic ring or a carbon-carbon double bond.

[0274] Examples of the fluorinated vinylene carbonate derivatives include 4-fluorovinylene carbonate, 4-fluoro-5-methylvinylene carbonate, 4-fluoro-5-phenylvinylene carbonate, 4-allyl-5-fluorovinylene carbonate, and 4-fluoro-5-vinylvinylene carbonate.

[0275] Examples of fluorinated ethylene carbonate derivatives substituted with a substituent having an aromatic ring or a carbon-carbon double bond include 4-fluoro-4-vinylethylene carbonate, 4-fluoro-4-allylethylene carbonate, 4-fluoro-5-vinylethylene carbonate, 4-fluoro-5-allylethylene carbonate, 4,4-difluoro-4-vinylethylene carbonate, 4,4-difluoro-4-allylethylene carbonate, 4,5-difluoro-4-vinylethylene carbonate, 4,5-difluoro-4-arylethylene carbonate, and 4,5-difluoro-4-arylethylene carbonate. Examples of such fluoroalkyl ethylene carbonates include 4-fluoro-4,5-divinylethylene carbonate, 4-fluoro-4,5-diallylethylene carbonate, 4,5-difluoro-4,5-divinylethylene carbonate, 4,5-difluoro-4,5-diallylethylene carbonate, 4-fluoro-4-phenylethylene carbonate, 4-fluoro-5-phenylethylene carbonate, 4,4-difluoro-5-phenylethylene carbonate, and 4,5-difluoro-4-phenylethylene carbonate.

[0276] Among them, examples of fluorinated unsaturated cyclic carbonates include 4-fluorovinylene carbonate, 4-fluoro-5-methylvinylene carbonate, 4-fluoro-5-vinylvinylene carbonate, 4-allyl-5-fluorovinylene carbonate, 4-fluoro-4-vinylethylene carbonate, 4-fluoro-4-allylethylene carbonate, 4-fluoro-5-vinylethylene carbonate, 4-fluoro-5-allylethylene carbonate, and 4,4-difluoro-4-vinylethylene carbonate. Carbonate, 4,4-difluoro-4-allylethylene carbonate, 4,5-difluoro-4-vinylethylene carbonate, 4,5-difluoro-4-allylethylene carbonate, 4-fluoro-4,5-divinylethylene carbonate, 4-fluoro-4,5-diallylethylene carbonate, 4,5-difluoro-4,5-divinylethylene carbonate, and 4,5-difluoro-4,5-diallylethylene carbonate are more preferably used since they form stable interface protective coatings.

[0277] The molecular weight of the fluorinated unsaturated cyclic carbonate is not particularly limited, and may be any as long as it does not significantly impair the effects of the present disclosure. The molecular weight is preferably 50 or more and 500 or less. Within this range, the solubility of the fluorinated unsaturated cyclic carbonate in the electrolyte is easily ensured.

[0278] The method for producing the fluorinated unsaturated cyclic carbonate is not particularly limited, and any known method can be selected for production. The molecular weight is more preferably 100 or more, and more preferably 200 or less.

[0279] The fluorinated unsaturated cyclic carbonate may be used alone or in any combination and ratio of two or more. The content of the fluorinated unsaturated cyclic carbonate is not particularly limited and may be any as long as it does not significantly impair the effects of the present disclosure. The content of the fluorinated unsaturated cyclic carbonate is usually, in 100 mass% of the electrolyte, preferably 0.001 mass% or more, more preferably 0.01 mass% or more, and even more preferably 0.1 mass% or more, and is also preferably 5 mass% or less, more preferably 4 mass% or less, and even more preferably 3 mass% or less. Within this range, the electrochemical device using the electrolyte is likely to exhibit a sufficient cycle characteristic improvement effect, and it is also easy to avoid situations such as a decrease in high-temperature storage characteristics, an increase in gas generation, and a decrease in discharge capacity retention rate.

[0280] The electrolyte solution of the present disclosure may contain a compound having a triple bond. There are no particular limitations on the type of compound as long as the compound has one or more triple bonds in the molecule. Specific examples of the compound having a triple bond include the following compounds. Hydrocarbon compounds such as 1-pentyne, 2-pentyne, 1-hexyne, 2-hexyne, 3-hexyne, 1-heptyne, 2-heptyne, 3-heptyne, 1-octyne, 2-octyne, 3-octyne, 4-octyne, 1-nonyne, 2-nonyne, 3-nonyne, 4-nonyne, 1-dodecyne, 2-dodecyne, 3-dodecyne, 4-dodecyne, 5-dodecyne, phenylacetylene, 1-phenyl-1-propyne, 1-phenyl-2-propyne, 1-phenyl-1-butyne, 4-phenyl-1-butyne, 4-phenyl-1-butyne, 1-phenyl-1-pentyne, 5-phenyl-1-pentyne, 1-phenyl-1-hexyne, 6-phenyl-1-hexyne, diphenylacetylene, 4-ethynyltoluene, and dicyclohexylacetylene;

[0281] 2-propynyl methyl carbonate, 2-propynyl ethyl carbonate, 2-propynyl propyl carbonate, 2-propynyl butyl carbonate, 2-propynyl phenyl carbonate, 2-propynyl cyclohexyl carbonate, di-2-propynyl carbonate, 1-methyl-2-propynyl methyl carbonate, 1,1-dimethyl-2-propynyl methyl carbonate, 2-butynyl methyl carbonate, 3-butynyl methyl carbonate, 2-pentynyl methyl carbonate monocarbonates such as 2-butyne-1,4-diol dimethyl dicarbonate, 2-butyne-1,4-diol diethyl dicarbonate, 2-butyne-1,4-diol dipropyl dicarbonate, 2-butyne-1,4-diol dibutyl dicarbonate, 2-butyne-1,4-diol diphenyl dicarbonate, 2-butyne-1,4-diol dicyclohexyl dicarbonate, and other dicarbonates;

[0282] 2-Propynyl acetate, 2-Propynyl propionate, 2-Propynyl butyrate, 2-Propynyl benzoate, 2-Propynyl cyclohexylcarboxylate, 1,1-Dimethyl-2-propynyl acetate, 1,1-Dimethyl-2-propynyl propionate, 1,1-Dimethyl-2-propynyl butyrate, 1,1-Dimethyl-2-propynyl benzoate, 1,1-Dimethyl-2-propynyl cyclohexylcarboxylate, 2-Butynyl acetate, 3-Butynyl acetate, 2-Pentynyl acetate, 3-Pentynyl acetate, 4-Pentynyl acetate, Methyl acrylate, Ethyl acrylate, propyl acrylate, vinyl acrylate, 2-propenyl acrylate, 2-butenyl acrylate, 3-butenyl acrylate, methyl methacrylate, ethyl methacrylate, propyl methacrylate, vinyl methacrylate, 2-propenyl methacrylate, 2-butenyl methacrylate, 3-butenyl methacrylate, methyl 2-propynoate, ethyl 2-propynoate, propyl 2-propynoate, vinyl 2-propynoate, 2-propenyl 2-propynoate, 2-butenyl 2-propynoate, 3-butenyl 2-propynoate, 2 -Methyl butynoate, Ethyl 2-butynoate, Propyl 2-butynoate, Vinyl 2-butynoate, 2-propenyl 2-butynoate, 2-butenyl 2-butynoate, 3-butenyl 2-butynoate, Methyl 3-butynoate, Ethyl 3-butynoate, Propyl 3-butynoate, Vinyl 3-butynoate, 2-propenyl 3-butynoate, 2-butenyl 3-butynoate, 3-butenyl 3-butynoate, Methyl 2-pentynoate, Ethyl 2-pentynoate, Propyl 2-pentynoate, Vinyl 2-pentynoate, 2-propenyl 2-pentynoate, 2-butenyl 2-pentynoate , monocarboxylic acid esters such as 3-butenyl 2-pentynoate, methyl 3-pentynoate, ethyl 3-pentynoate, propyl 3-pentynoate, vinyl 3-pentynoate, 2-propenyl 3-pentynoate, 2-butenyl 3-pentynoate, 3-butenyl 3-pentynoate, methyl 4-pentynoate, ethyl 4-pentynoate, propyl 4-pentynoate, vinyl 4-pentynoate, 2-propenyl 4-pentynoate, 2-butenyl 4-pentynoate, 3-butenyl 4-pentynoate, fumaric acid esters, methyl trimethylacetate, ethyl trimethylacetate;

[0283] Dicarboxylic acid esters such as 2-butyne-1,4-diol diacetate, 2-butyne-1,4-diol dipropionate, 2-butyne-1,4-diol dibutyrate, 2-butyne-1,4-diol dibenzoate, 2-butyne-1,4-diol dicyclohexanecarboxylate, hexahydrobenzo[1,3,2]dioxathiolan-2-oxide (1,2-cyclohexanediol, 2,2-dioxido-1,2-oxathiolan-4-yl acetate, 2,2-dioxido-1,2-oxathiolan-4-yl acetate, etc.;

[0284] oxalic acid diesters such as methyl 2-propynyl oxalate, ethyl 2-propynyl oxalate, propyl 2-propynyl oxalate, 2-propynyl vinyl oxalate, allyl 2-propynyl oxalate, di-2-propynyl oxalate, 2-butynyl methyl oxalate, 2-butynyl ethyl oxalate, 2-butynyl propyl oxalate, 2-butynyl vinyl oxalate, allyl 2-butynyl oxalate, di-2-butynyl oxalate, 3-butynyl methyl oxalate, 3-butynyl ethyl oxalate, 3-butynyl propyl oxalate, 3-butynyl vinyl oxalate, allyl 3-butynyl oxalate, and di-3-butynyl oxalate;

[0285] Phosphine oxides such as methyl(2-propynyl)(vinyl)phosphine oxide, divinyl(2-propynyl)phosphine oxide, di(2-propynyl)(vinyl)phosphine oxide, di(2-propenyl)2(-propynyl)phosphine oxide, di(2-propynyl)(2-propenyl)phosphine oxide, di(3-butenyl)(2-propynyl)phosphine oxide, and di(2-propynyl)(3-butenyl)phosphine oxide;

[0286] 2-propynyl methyl(2-propenyl)phosphinate, 2-propynyl 2-butenyl(methyl)phosphinate, 2-propynyl di(2-propenyl)phosphinate, 2-propynyl di(3-butenyl)phosphinate, 1,1-dimethyl-2-propynyl methyl(2-propenyl)phosphinate, 1,1-dimethyl-2-propynyl 2-butenyl(methyl)phosphinate, 1,1-dimethyl-2-propynyl di(2-propenyl)phosphinate, and phosphinic acid esters such as 1,1-dimethyl-2-propynyl di(3-butenyl)phosphinate, 2-propenyl methyl(2-propynyl)phosphinate, 3-butenyl methyl(2-propynyl)phosphinate, 2-propenyl di(2-propynyl)phosphinate, 3-butenyl di(2-propynyl)phosphinate, 2-propenyl 2-propynyl(2-propenyl)phosphinate, and 3-butenyl 2-propynyl(2-propenyl)phosphinate;

[0287] 2-propenylphosphonic acid methyl 2-propynyl, 2-butenylphosphonic acid methyl (2-propynyl), 2-propenylphosphonic acid (2-propynyl) (2-propenyl), 3-butenylphosphonic acid (3-butenyl) (2-propynyl), 2-propenylphosphonic acid (1,1-dimethyl-2-propynyl) (methyl), 2-butenylphosphonic acid (1,1-dimethyl-2-propynyl) (methyl), 2-propenylphosphonic acid (1,1-dimethyl-2-propynyl) (2-propenyl), and 3-butenylphosphonic acid (3-butenyl) (1,1-dimethyl-2-propynyl), methyl phosphonic acid esters such as ethylphosphonic acid (2-propynyl) (2-propenyl), methylphosphonic acid (3-butenyl) (2-propynyl), methylphosphonic acid (1,1-dimethyl-2-propynyl) (2-propenyl), methylphosphonic acid (3-butenyl) (1,1-dimethyl-2-propynyl), ethylphosphonic acid (2-propynyl) (2-propenyl), ethylphosphonic acid (3-butenyl) (2-propynyl), ethylphosphonic acid (1,1-dimethyl-2-propynyl) (2-propenyl), and ethylphosphonic acid (3-butenyl) (1,1-dimethyl-2-propynyl);

[0288] phosphate esters such as (methyl)(2-propenyl)(2-propynyl) phosphate, (ethyl)(2-propenyl)(2-propynyl) phosphate, (2-butenyl)(methyl)(2-propynyl) phosphate, (2-butenyl)(ethyl)(2-propynyl) phosphate, (1,1-dimethyl-2-propynyl)(methyl)(2-propenyl) phosphate, (1,1-dimethyl-2-propynyl)(ethyl)(2-propenyl) phosphate, (2-butenyl)(1,1-dimethyl-2-propynyl)(methyl) phosphate, and (2-butenyl)(ethyl)(1,1-dimethyl-2-propynyl) phosphate;

[0289] Among these, compounds having an alkynyloxy group are preferred because they form a more stable negative electrode coating in the electrolyte.

[0290] Furthermore, compounds such as 2-propynyl methyl carbonate, di-2-propynyl carbonate, 2-butyne-1,4-diol dimethyl dicarbonate, 2-propynyl acetate, 2-butyne-1,4-diol diacetate, methyl 2-propynyl oxalate, and di-2-propynyl oxalate are particularly preferred in terms of improving storage properties.

[0291] The compound having a triple bond may be used alone or in any combination and ratio of two or more. The amount of the compound having a triple bond relative to the entire electrolyte solution of the present disclosure is not limited, and is optional as long as it does not significantly impair the effects of the present disclosure. The compound is usually contained in the electrolyte solution of the present disclosure at a concentration of 0.01% by mass or more, preferably 0.05% by mass or more, more preferably 0.1% by mass or more, and usually 5% by mass or less, preferably 3% by mass or less, more preferably 1% by mass or less. When the above range is satisfied, the effects of output characteristics, load characteristics, cycle characteristics, high-temperature storage characteristics, etc. are further improved.

[0292] In the electrolyte solution of the present disclosure, an overcharge inhibitor can be used to effectively prevent the battery from exploding or catching fire when an electrochemical device using the electrolyte solution is in a state of overcharging or the like.

[0293] Examples of the overcharge inhibitor include unsubstituted or alkyl group-substituted terphenyl derivatives such as biphenyl, o-terphenyl, m-terphenyl, and p-terphenyl, partial hydrogenation products of unsubstituted or alkyl group-substituted terphenyl derivatives, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether, dibenzofuran, diphenylcyclohexane, 1,1,3-trimethyl-3-phenylindane, cyclopentylbenzene, cyclohexylbenzene, cumene, 1,3-diisopropylbenzene, 1,4-diisopropylbenzene, t-butylbenzene, t-amylbenzene, t-hexylbenzene, and anisole; aromatic compounds such as 2-fluorobiphenyl, 4-fluorobiphenyl, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene, o-cyclohexylfluorobenzene, p-cyclohexylfluorobenzene, and the like. Examples of the aromatic compounds include partially fluorinated compounds of the above aromatic compounds such as xylfluorobenzene, fluorotoluene, and benzotrifluoride; fluorine-containing anisole compounds such as 2,4-difluoroanisole, 2,5-difluoroanisole, 1,6-difluoroanisole, 2,6-difluoroanisole, and 3,5-difluoroanisole; aromatic acetates such as 3-propylphenyl acetate, 2-ethylphenyl acetate, benzylphenyl acetate, methylphenyl acetate, benzyl acetate, and phenethylphenyl acetate; aromatic carbonates such as diphenyl carbonate and methylphenyl carbonate, toluene derivatives such as toluene and xylene, and biphenyl derivatives substituted with an alkyl group or unsubstituted such as 2-methylbiphenyl, 3-methylbiphenyl, 4-methylbiphenyl, and o-cyclohexylbiphenyl. Among these, aromatic compounds such as biphenyl, alkylbiphenyls, terphenyls, partially hydrogenated terphenyls, cyclohexylbenzene, t-butylbenzene, t-amylbenzene, diphenyl ether and dibenzofuran, diphenylcyclohexane, 1,1,3-trimethyl-3-phenylindane, 3-propylphenyl acetate, 2-ethylphenyl acetate, benzylphenyl acetate, methylphenyl acetate, benzyl acetate, diphenyl carbonate and methylphenyl carbonate are preferred.These may be used alone or in combination of two or more. When two or more are used in combination, it is particularly preferable to use a combination of cyclohexylbenzene with t-butylbenzene or t-amylbenzene, or a combination of at least one selected from aromatic compounds not containing oxygen, such as biphenyl, alkylbiphenyl, terphenyl, partially hydrogenated terphenyl, cyclohexylbenzene, t-butylbenzene, and t-amylbenzene, and at least one selected from aromatic compounds containing oxygen, such as diphenyl ether and dibenzofuran, in terms of the balance between overcharge prevention properties and high-temperature storage properties.

[0294] The electrolyte used in the present disclosure may contain a carboxylic acid anhydride (excluding compound (6)). A compound represented by the following general formula (10) is preferred. The method for producing the carboxylic acid anhydride is not particularly limited, and any known method can be selected to produce the carboxylic acid anhydride.

[0295] General formula (10): [ka] (In general formula (10), R 61 , R 62 each independently represents a hydrocarbon group having 1 to 15 carbon atoms which may have a substituent.

[0296] R 61 , R 62 is not particularly limited in type, so long as it is a monovalent hydrocarbon group. For example, it may be an aliphatic hydrocarbon group or an aromatic hydrocarbon group, or it may be a group in which an aliphatic hydrocarbon group and an aromatic hydrocarbon group are bonded together. The aliphatic hydrocarbon group may be a saturated hydrocarbon group or may contain an unsaturated bond (carbon-carbon double bond or carbon-carbon triple bond). Furthermore, the aliphatic hydrocarbon group may be chain-like or cyclic, and if it is chain-like, it may be linear or branched. Furthermore, it may be a group in which a chain-like group and a cyclic group are bonded together. In addition, R 61 and R 62 may be the same as or different from each other.

[0297] Also, R 61 , R 62 When the hydrocarbon group has a substituent, the type of the substituent is not particularly limited as long as it is not contrary to the spirit of the present disclosure, and examples thereof include halogen atoms such as fluorine atom, chlorine atom, bromine atom, iodine atom, etc., preferably fluorine atom. Alternatively, examples of the substituent other than halogen atom include substituents having functional groups such as ester group, cyano group, carbonyl group, ether group, etc., preferably cyano group, carbonyl group. 61 , R 62 The hydrocarbon group may have only one of these substituents or may have two or more of these substituents. When the hydrocarbon group has two or more substituents, the substituents may be the same or different from each other.

[0298] R 61 , R 62 The number of carbon atoms in each of the hydrocarbon groups in R is usually 1 or more and usually 15 or less, preferably 12 or less, more preferably 10 or less, and even more preferably 9 or less. 1 and R 2 When R is bonded to each other to form a divalent hydrocarbon group, the carbon number of the divalent hydrocarbon group is usually 1 or more and usually 15 or less, preferably 13 or less, more preferably 10 or less, and further preferably 8 or less. 61 , R 62 If the hydrocarbon group has a substituent containing a carbon atom, the substituent is also included in R 61 , R 62 It is preferable that the total number of carbon atoms falls within the above range.

[0299] Next, specific examples of the acid anhydride represented by the above general formula (10) will be described. In the following examples, the term "analog" refers to an acid anhydride obtained by replacing a part of the structure of the exemplified acid anhydride with another structure within the scope of the present disclosure, and examples thereof include a dimer, trimer, tetramer, etc. consisting of a plurality of acid anhydrides, structural isomers such as those having the same number of carbon atoms in the substituent but having a branched chain, and those having a substituent bonded to the acid anhydride at different positions.

[0300] First, R 61 , R 62 Specific examples of acid anhydrides in which are the same are shown below.

[0301] R 61 , R 62 Specific examples of acid anhydrides in which is a chain alkyl group include acetic anhydride, propionic anhydride, butanoic anhydride, 2-methylpropionic anhydride, 2,2-dimethylpropionic anhydride, 2-methylbutanoic anhydride, 3-methylbutanoic anhydride, 2,2-dimethylbutanoic anhydride, 2,3-dimethylbutanoic anhydride, 3,3-dimethylbutanoic anhydride, 2,2,3-trimethylbutanoic anhydride, 2,3,3-trimethylbutanoic anhydride, 2,2,3,3-tetramethylbutanoic anhydride, 2-ethylbutanoic anhydride, and the like, and analogs thereof.

[0302] R 61 , R 62 Specific examples of acid anhydrides in which is a cyclic alkyl group include cyclopropanecarboxylic anhydride, cyclopentanecarboxylic anhydride, cyclohexanecarboxylic anhydride, and the like, and their analogues.

[0303] R 61 , R 62 Specific examples of acid anhydrides in which is an alkenyl group include acrylic anhydride, 2-methylacrylic anhydride, 3-methylacrylic anhydride, 2,3-dimethylacrylic anhydride, 3,3-dimethylacrylic anhydride, 2,3,3-trimethylacrylic anhydride, 2-phenylacrylic anhydride, 3-phenylacrylic anhydride, 2,3-diphenylacrylic anhydride, 3,3-diphenylacrylic anhydride, 3-butenoic anhydride, 2-methyl-3-butenoic anhydride, 2,2-dimethyl-3-butenoic anhydride, 3-methyl-3-enoic anhydride, 2-methyl-3-methyl-3-butenoic anhydride, 2,2-dimethyl-3-methyl-3-butenoic anhydride, 3-pentenoic anhydride, 4-pentenoic anhydride, 2-cyclopentenecarboxylic anhydride, 3-cyclopentenecarboxylic anhydride, 4-cyclopentenecarboxylic anhydride, and the like, and analogs thereof.

[0304] R 61 , R 62 Specific examples of acid anhydrides in which is an alkynyl group include propynoic anhydride, 3-phenylpropynoic anhydride, 2-butynoic anhydride, 2-pentynoic anhydride, 3-butynoic anhydride, 3-pentynoic anhydride, 4-pentynoic anhydride, and analogs thereof.

[0305] R 61 , R 62 Specific examples of acid anhydrides in which is an aryl group include benzoic anhydride, 4-methylbenzoic anhydride, 4-ethylbenzoic anhydride, 4-tert-butylbenzoic anhydride, 2-methylbenzoic anhydride, 2,4,6-trimethylbenzoic anhydride, 1-naphthalenecarboxylic anhydride, 2-naphthalenecarboxylic anhydride, and analogs thereof.

[0306] Also, R 61 , R 62 As examples of acid anhydrides in which halogen atoms are substituted, examples of acid anhydrides in which fluorine atoms are mainly substituted are given below, but acid anhydrides obtained by substituting some or all of these fluorine atoms with chlorine atoms, bromine atoms, or iodine atoms are also included in the exemplified compounds.

[0307] R 61 , R 62 Examples of acid anhydrides in which is a chain alkyl group substituted with a halogen atom include fluoroacetic anhydride, difluoroacetic anhydride, trifluoroacetic anhydride, 2-fluoropropionic anhydride, 2,2-difluoropropionic anhydride, 2,3-difluoropropionic anhydride, 2,2,3-trifluoropropionic anhydride, 2,3,3-trifluoropropionic anhydride, 2,2,3,3-tetrapropionic anhydride, 2,3,3,3-tetrapropionic anhydride, 3-fluoropropionic anhydride, 3,3-difluoropropionic anhydride, 3,3,3-trifluoropropionic anhydride, perfluoropropionic anhydride, and the like, and analogs thereof.

[0308] R61 , R 62 Examples of acid anhydrides in which is a cyclic alkyl group substituted with a halogen atom include 2-fluorocyclopentanecarboxylic anhydride, 3-fluorocyclopentanecarboxylic anhydride, 4-fluorocyclopentanecarboxylic anhydride, and the like, and their analogs.

[0309] R 61 , R 62 Examples of acid anhydrides in which is an alkenyl group substituted with a halogen atom include 2-fluoroacrylic anhydride, 3-fluoroacrylic anhydride, 2,3-difluoroacrylic anhydride, 3,3-difluoroacrylic anhydride, 2,3,3-trifluoroacrylic anhydride, 2-(trifluoromethyl)acrylic anhydride, 3-(trifluoromethyl)acrylic anhydride, 2,3-bis(trifluoromethyl)acrylic anhydride, 2,3,3-tris(trifluoromethyl)acrylic anhydride, 2-(4-fluoroacrylic anhydride, 2,3-difluoro ... Examples of the fluorophenyl acrylic anhydride include 3-(4-fluorophenyl)acrylic anhydride, 2,3-bis(4-fluorophenyl)acrylic anhydride, 3,3-bis(4-fluorophenyl)acrylic anhydride, 2-fluoro-3-butenoic anhydride, 2,2-difluoro-3-butenoic anhydride, 3-fluoro-2-butenoic anhydride, 4-fluoro-3-butenoic anhydride, 3,4-difluoro-3-butenoic anhydride, 3,3,4-trifluoro-3-butenoic anhydride, and the like, and their analogs.

[0310] R 61 , R 62 Examples of acid anhydrides in which is an alkynyl group substituted with a halogen atom include 3-fluoro-2-propynoic anhydride, 3-(4-fluorophenyl)-2-propynoic anhydride, 3-(2,3,4,5,6-pentafluorophenyl)-2-propynoic anhydride, 4-fluoro-2-butynoic anhydride, 4,4-difluoro-2-butynoic anhydride, 4,4,4-trifluoro-2-butynoic anhydride, and the like, and analogs thereof.

[0311] R 61 , R 62Examples of acid anhydrides in which is an aryl group substituted with a halogen atom include 4-fluorobenzoic anhydride, 2,3,4,5,6-pentafluorobenzoic anhydride, 4-trifluoromethylbenzoic anhydride, and the like, and analogs thereof.

[0312] R 61 , R 62 Examples of acid anhydrides having a substituent having a functional group such as an ester, a nitrile, a ketone, or an ether include methoxyformic anhydride, ethoxyformic anhydride, methyloxalic anhydride, ethyloxalic anhydride, 2-cyanoacetic anhydride, 2-oxopropionic anhydride, 3-oxobutanoic anhydride, 4-acetylbenzoic anhydride, methoxyacetic anhydride, 4-methoxybenzoic anhydride, and the like, and their analogs.

[0313] Next, R 61 , R 62 Specific examples of acid anhydrides having different groups are given below.

[0314] R 61 , R 62 Although all combinations of the above-mentioned examples and their analogues are possible, representative examples are given below.

[0315] Examples of combinations of chain alkyl groups include acetic acid propionic anhydride, acetic acid butanoic anhydride, butanoic acid propionic anhydride, and acetic acid 2-methylpropionic anhydride.

[0316] Examples of the combination of a chain alkyl group and a cyclic alkyl group include acetic acid cyclopentanoic anhydride, acetic acid cyclohexanoic anhydride, and cyclopentanoic acid propionic anhydride.

[0317] Examples of the combination of a chain alkyl group and an alkenyl group include acetic acid acrylic anhydride, acetic acid 3-methylacrylic anhydride, acetic acid 3-butenoic anhydride, and acrylic acid propionic anhydride.

[0318] Examples of combinations of a chain alkyl group and an alkynyl group include acetic acid propynoic anhydride, acetic acid 2-butynoic anhydride, acetic acid 3-butynoic anhydride, acetic acid 3-phenylpropynoic anhydride, and propionic acid propynoic anhydride.

[0319] Examples of the combination of a chain alkyl group and an aryl group include acetic acid benzoic anhydride, acetic acid 4-methylbenzoic anhydride, acetic acid 1-naphthalenecarboxylic anhydride, and benzoic acid propionic anhydride.

[0320] Examples of combinations of a chain alkyl group and a hydrocarbon group having a functional group include acetic acid fluoroacetic anhydride, acetic acid trifluoroacetic anhydride, acetic acid 4-fluorobenzoic anhydride, fluoroacetic acid propionic anhydride, acetic acid alkyl oxalic anhydride, acetic acid 2-cyanoacetic anhydride, acetic acid 2-oxopropionic anhydride, acetic acid methoxyacetic anhydride, and methoxyacetic acid propionic anhydride.

[0321] Examples of combinations of cyclic alkyl groups include cyclopentanoic acid and cyclohexanoic acid anhydride.

[0322] Examples of combinations of a cyclic alkyl group and an alkenyl group include acrylic acid cyclopentanoic acid anhydride, 3-methylacrylic acid cyclopentanoic acid anhydride, 3-butenoic acid cyclopentanoic acid anhydride, and acrylic acid cyclohexanoic acid anhydride.

[0323] Examples of combinations of a cyclic alkyl group and an alkynyl group include propynoic acid cyclopentanoic acid anhydride, 2-butynoic acid cyclopentanoic acid anhydride, and propynoic acid cyclohexanoic acid anhydride.

[0324] Examples of the combination of a cyclic alkyl group and an aryl group include benzoic acid cyclopentanoic acid anhydride, 4-methylbenzoic acid cyclopentanoic acid anhydride, and benzoic acid cyclohexanoic acid anhydride.

[0325] Examples of combinations of a cyclic alkyl group and a hydrocarbon group having a functional group include cyclopentanoic fluoroacetic anhydride, cyclopentanoic trifluoroacetic anhydride, cyclopentanoic 2-cyanoacetic anhydride, cyclopentanoic methoxyacetic anhydride, and cyclohexanoic fluoroacetic anhydride.

[0326] Examples of combinations of alkenyl groups include acrylic acid 2-methylacrylic anhydride, acrylic acid 3-methylacrylic anhydride, acrylic acid 3-butenoic anhydride, and 2-methylacrylic acid 3-methylacrylic anhydride.

[0327] Examples of combinations of an alkenyl group and an alkynyl group include acrylic acid propynoic anhydride, acrylic acid 2-butynoic anhydride, and 2-methylacrylic acid propynoic anhydride.

[0328] Examples of combinations of an alkenyl group and an aryl group include acrylic acid benzoic acid anhydride, acrylic acid 4-methylbenzoic acid anhydride, and 2-methylacrylic acid benzoic acid anhydride.

[0329] Examples of combinations of an alkenyl group and a hydrocarbon group having a functional group include acrylic acid fluoroacetic anhydride, acrylic acid trifluoroacetic anhydride, acrylic acid 2-cyanoacetic anhydride, acrylic acid methoxyacetic anhydride, and 2-methylacrylic acid fluoroacetic anhydride.

[0330] Examples of combinations of alkynyl groups include propynoic acid 2-butynoic acid anhydride, propynoic acid 3-butynoic acid anhydride, and 2-butynoic acid 3-butynoic acid anhydride.

[0331] Examples of the combination of an alkynyl group and an aryl group include benzoic acid propynoic acid anhydride, 4-methylbenzoic acid propynoic acid anhydride, and benzoic acid 2-butynoic acid anhydride.

[0332] Examples of combinations of an alkynyl group and a hydrocarbon group having a functional group include propynoic acid fluoroacetic anhydride, propynoic acid trifluoroacetic anhydride, propynoic acid 2-cyanoacetic anhydride, propynoic acid methoxyacetic anhydride, and 2-butynoic acid fluoroacetic anhydride.

[0333] Examples of combinations of aryl groups include benzoic acid 4-methylbenzoic acid anhydride, benzoic acid 1-naphthalenecarboxylic acid anhydride, and 4-methylbenzoic acid 1-naphthalenecarboxylic acid anhydride.

[0334] Examples of combinations of an aryl group and a hydrocarbon group having a functional group include benzoic acid fluoroacetic anhydride, benzoic acid trifluoroacetic anhydride, benzoic acid 2-cyanoacetic anhydride, benzoic acid methoxyacetic anhydride, and 4-methylbenzoic acid fluoroacetic anhydride.

[0335] Examples of combinations of hydrocarbon groups having functional groups include fluoroacetic acid trifluoroacetic anhydride, fluoroacetic acid 2-cyanoacetic anhydride, fluoroacetic acid methoxyacetic anhydride, and trifluoroacetic acid 2-cyanoacetic anhydride.

[0336] Among the acid anhydrides forming the chain structure, preferred are acetic anhydride, propionic anhydride, 2-methylpropionic anhydride, cyclopentanecarboxylic anhydride, cyclohexanecarboxylic anhydride, etc., acrylic anhydride, 2-methylacrylic anhydride, 3-methylacrylic anhydride, 2,3-dimethylacrylic anhydride, 3,3-dimethylacrylic anhydride, 3-butenoic anhydride, 2-methyl-3-butenoic anhydride, propynoic anhydride, 2-butynoic anhydride, benzoic anhydride, 2-methylbenzoic anhydride, 4-methylbenzoic anhydride, 4-tert-butylbenzoic anhydride, trifluoroacetic anhydride, 3,3,3-trifluoroacetic anhydride, 4-tert-butylbenzoic ... Examples of the fluoropropionic anhydride include 2-(trifluoromethyl)acrylic anhydride, 2-(4-fluorophenyl)acrylic anhydride, 4-fluorobenzoic anhydride, 2,3,4,5,6-pentafluorobenzoic anhydride, methoxyformic anhydride, and ethoxyformic anhydride, and more preferably, acrylic anhydride, 2-methylacrylic anhydride, 3-methylacrylic anhydride, benzoic anhydride, 2-methylbenzoic anhydride, 4-methylbenzoic anhydride, 4-tert-butylbenzoic anhydride, 4-fluorobenzoic anhydride, 2,3,4,5,6-pentafluorobenzoic anhydride, methoxyformic anhydride, and ethoxyformic anhydride.

[0337] These compounds are preferred from the viewpoint of being able to appropriately form bonds with the lithium oxalate to form a coating having excellent durability, thereby improving the charge / discharge rate characteristics, input / output characteristics, and impedance characteristics, particularly after a durability test.

[0338] The molecular weight of the carboxylic acid anhydride is not limited and may be any value as long as it does not significantly impair the effects of the present disclosure, but is usually at least 90, preferably at least 95, and usually at most 300, preferably at most 200. When the molecular weight of the carboxylic acid anhydride is within the above range, an increase in the viscosity of the electrolyte can be suppressed, and the film density can be optimized, thereby appropriately improving durability.

[0339] The method for producing the carboxylic acid anhydride is not particularly limited, and any known method can be selected for production. The nonaqueous electrolyte solution of the present disclosure may contain any one of the above-described carboxylic acid anhydrides alone, or may contain two or more of them in any combination and ratio.

[0340] In addition, the content of the carboxylic acid anhydride in the electrolyte solution of the present disclosure is not particularly limited, and may be any content as long as it does not significantly impair the effects of the present disclosure, but it is desirable to include the carboxylic acid anhydride in the electrolyte solution of the present disclosure at a concentration of usually 0.01% by mass or more, preferably 0.1% by mass or more, and usually 5% by mass or less, preferably 3% by mass or less. When the content of the carboxylic acid anhydride is within the above range, the effect of improving cycle characteristics is easily exhibited, and the reactivity is suitable, so that the battery characteristics are easily improved.

[0341] Other known auxiliary agents can be used in the electrolyte solution of the present disclosure, such as hydrocarbon compounds such as pentane, heptane, octane, nonane, decane, cycloheptane, benzene, furan, naphthalene, 2-phenylbicyclohexyl, cyclohexane, 2,4,8,10-tetraoxaspiro[5.5]undecane, and 3,9-divinyl-2,4,8,10-tetraoxaspiro[5.5]undecane; Fluorine-containing aromatic compounds such as fluorobenzene, difluorobenzene, hexafluorobenzene, benzotrifluoride, monofluorobenzene, 1-fluoro-2-cyclohexylbenzene, 1-fluoro-4-tert-butylbenzene, 1-fluoro-3-cyclohexylbenzene, 1-fluoro-2-cyclohexylbenzene, and fluorinated biphenyls; Carbonate compounds such as erythritan carbonate, spiro-bis-dimethylene carbonate, and methoxyethyl-methyl carbonate; Ether compounds such as dioxolane, dioxane, 2,5,8,11-tetraoxadodecane, 2,5,8,11,14-pentaoxapentadecane, ethoxymethoxyethane, trimethoxymethane, glyme, and ethyl monoglyme; Ketone compounds such as dimethyl ketone, diethyl ketone, and 3-pentanone; Acid anhydrides such as 2-allyl succinic anhydride; Ester compounds such as dimethyl oxalate, diethyl oxalate, ethyl methyl oxalate, di(2-propynyl) oxalate, methyl 2-propynyl oxalate, dimethyl succinate, di(2-propynyl) glutarate, methyl formate, ethyl formate, 2-propynyl formate, 2-butyne-1,4-diyl diformate, 2-propynyl methacrylate, and dimethyl malonate; Amide compounds such as acetamide, N-methylformamide, N,N-dimethylformamide, and N,N-dimethylacetamide; Ethylene sulfate, vinylene sulfate, ethylene sulfite, methyl fluorosulfonate, ethyl fluorosulfonate, methyl methanesulfonate, ethyl methanesulfonate, busulfan, sulfolene, diphenyl sulfone, N,N-dimethylmethanesulfonamide, N,N-diethylmethanesulfonamide, methyl vinylsulfonate, ethyl vinylsulfonate, allyl vinylsulfonate, propargyl vinylsulfonate, methyl allylsulfonate, ethyl allylsulfonate, allyl allylsulfonate, propargyl allylsulfonate, 1,2-bis(vinylsulfonyloxy)ethane, propanedisulfonic anhydride, sulfobutyric anhydride, sulfobenzoic anhydride, sulfopropionic anhydride, ethanedisulfonic anhydride, methylenemethanedisulfonate, 2-propynyl methanesulfonate, pentenesulfite, pentafluorophenylmethanesulfonate, propylene sulfate, propylene sulfite, propane 2-propynyl vinylsulfonate, bis(2-vinylsulfonylethyl)ether, 5-vinyl-hexahydro-1,3,2-benzodioxathiol-2-oxide, 2-propynyl 2-(methanesulfonyloxy)propionate, 5,5-dimethyl-1,2-oxathiolan-4-one 2,2-dioxy sulfur-containing compounds such as 3-sulfo-propionic anhydride, trimethylenemethane disulfonate, 2-methyltetrahydrofuran, trimethylenemethane disulfonate, tetramethylene sulfoxide, dimethylenemethane disulfonate, difluoroethyl methyl sulfone, divinyl sulfone, 1,2-bis(vinylsulfonyl)ethane, ethylenebismethylsulfonate, ethylenebisethylsulfonate, ethylene sulfate, and thiophene 1-oxide; 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, nitromethane, nitroethane, and ethylenediamine; Trimethyl phosphite, Triethyl phosphite, Triphenyl phosphite, Trimethyl phosphate, Triethyl phosphate, Triphenyl phosphate, Dimethyl methylphosphonate, Diethyl ethylphosphonate, Dimethyl vinylphosphonate, Diethyl vinylphosphonate, Ethyl diethylphosphonoacetate, Methyl dimethylphosphinate, Ethyl diethylphosphinate, Trimethylphosphine oxide, Triethylphosphine oxide, Bis(2,2-difluoroethyl) 2,2,2-trifluoroethyl phosphate, Bis(2,2,3,3-tetrafluoropropyl) phosphate, 2-Trifluoroethyl, bis(2,2,2-trifluoroethyl)methyl phosphate, bis(2,2,2-trifluoroethyl)ethyl phosphate, bis(2,2,2-trifluoroethyl) 2,2-difluoroethyl phosphate, bis(2,2,2-trifluoroethyl) 2,2,3,3-tetrafluoropropyl phosphate, tributyl phosphate, tris(2,2,2-trifluoroethyl) phosphate, tris(1,1,1,3,3,3-hexafluoropropan-2-yl) phosphate, trioctyl phosphate, 2-phenylphenyl dimethyl phosphate, 2-phenylphenyl phosphate diethyl, (2,2,2-trifluoroethyl)(2,2,3,3-tetrafluoropropyl)methyl phosphate, methyl 2-(dimethoxyphosphoryl)acetate, methyl 2-(dimethylphosphoryl)acetate, methyl 2-(diethoxyphosphoryl)acetate, methyl 2-(diethylphosphoryl)acetate, methyl methylenebisphosphonate, ethyl methylenebisphosphonate, methyl ethylenebisphosphonate, ethyl ethylenebisphosphonate, methyl butylenebisphosphonate, ethyl butylenebisphosphonate, 2-propynyl 2-(dimethoxy) phosphorus-containing compounds such as diphosphoryl, 2-propynyl 2-(dimethylphosphoryl) acetate, 2-propynyl 2-(diethoxyphosphoryl) acetate, 2-propynyl 2-(diethylphosphoryl) acetate, tris(trimethylsilyl) phosphate, tris(triethylsilyl) phosphate, tris(t-butyldimethylsilyl) phosphate, tris(trimethoxysilyl) phosphate, tris(trimethylsilyl) phosphite, tris(triethylsilyl) phosphite, tris(t-butyldimethylsilyl) phosphite, tris(trimethoxysilyl) phosphite, and trimethylsilyl polyphosphate; Boron-containing compounds such as tris(trimethylsilyl) borate and tris(trimethoxysilyl) borate; silane compounds such as dimethoxyaluminoxytrimethoxysilane, diethoxyaluminoxytriethoxysilane, dipropoxyaluminoxytriethoxysilane, dibutoxyaluminoxytrimethoxysilane, dibutoxyaluminoxytriethoxysilane, titanium tetrakis(trimethylsiloxide), titanium tetrakis(triethylsiloxide), and tetramethylsilane; These may be used alone or in combination of two or more. By adding these auxiliary agents, it is possible to improve the capacity retention characteristics and cycle characteristics after high-temperature storage. Of the other auxiliaries, phosphorus-containing compounds are preferred, with tris(trimethylsilyl) phosphate and (tristrimethylsilyl) phosphite being preferred.

[0342] The amount of the other auxiliary agent is not particularly limited and may be any amount as long as it does not significantly impair the effects of the present disclosure. The amount of the other auxiliary agent is preferably 0.01% by mass or more and 5% by mass or less in 100% by mass of the electrolyte. Within this range, the effect of the other auxiliary agent is easily exerted, and it is easy to avoid a situation in which the battery characteristics such as high-load discharge characteristics are deteriorated. The amount of the other auxiliary agent is more preferably 0.1% by mass or more, even more preferably 0.2% by mass or more, and more preferably 3% by mass or less, even more preferably 1% by mass or less.

[0343] The electrolyte solution of the present disclosure may further contain, as additives, such as an ether compound other than the fluorinated ether represented by the above general formula (1), a cyclic or chain carboxylic acid ester, a nitrogen-containing compound, a boron-containing compound, an organic silicon-containing compound, a flame retardant (flame retardant) agent, a surfactant, a high dielectric additive, an agent for improving cycle characteristics and rate characteristics, a sulfone-based compound, etc., within a range that does not impair the effects of the present disclosure.

[0344] As the ether compound, a chain ether having 2 to 10 carbon atoms and a cyclic ether having 3 to 6 carbon atoms are preferred. Examples of chain ethers having 2 to 10 carbon atoms include dimethyl ether, diethyl ether, di-n-butyl ether, dimethoxymethane, methoxyethoxymethane, diethoxymethane, dimethoxyethane, methoxyethoxyethane, diethoxyethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, diethylene glycol, diethylene glycol dimethyl ether, pentaethylene glycol, triethylene glycol dimethyl ether, triethylene glycol, tetraethylene glycol, tetraethylene glycol dimethyl ether, and diisopropyl ether.

[0345] The ether compound may contain a fluorinated ether other than the fluorinated ether represented by the formula (1) above. Such fluorinated ethers include those represented by the following general formula (I): Rf 4 -O-Rf 5 (I) (In the formula, Rf 4 and Rf 5 are the same or different and are an alkyl group having 1 to 10 carbon atoms or a fluorinated alkyl group having 1 to 10 carbon atoms. 3 and Rf 4 At least one of the above is a fluorinated alkyl group, excluding the fluorinated ether represented by the above formula (1). Examples of the fluorinated ether (I) include the fluorinated ether represented by the following formula: By including the fluorinated ether (I), the flame retardancy of the electrolyte is improved, and the stability and safety at high temperatures and high voltages are also improved.

[0346] In the above general formula (I), Rf 4 and Rf 5 At least one of Rf may be a fluorinated alkyl group having 1 to 10 carbon atoms. From the viewpoint of further improving the flame retardancy of the electrolyte and the stability and safety at high temperatures and high voltages, 3 and Rf 4 are preferably fluorinated alkyl groups having 1 to 10 carbon atoms. 3and Rf 4 may be the same or different from each other. Among them, Rf 4 and Rf 5 are the same or different, and Rf 4 is a fluorinated alkyl group having 3 to 6 carbon atoms, and Rf 5 It is more preferable that the group is a fluorinated alkyl group having 2 to 6 carbon atoms.

[0347] Rf 4 and Rf 5 If the total number of carbon atoms is too small, the boiling point of the fluorinated ether will be too low, and Rf 4 or Rf 5 If the number of carbon atoms in Rf is too large, the solubility of the electrolyte salt decreases, the compatibility with other solvents begins to be adversely affected, and the viscosity increases, reducing the rate characteristics. 4 The carbon number is 3 or 4, Rf 5 When the carbon number is 2 or 3, it is advantageous in that the boiling point and rate characteristics are excellent.

[0348] The fluorinated ether (I) preferably has a fluorine content of 40 to 75% by mass. When the fluorine content is in this range, the balance between non-flammability and compatibility is particularly excellent. In addition, this is also preferable in terms of good oxidation resistance and safety. The lower limit of the fluorine content is more preferably 45% by mass, further preferably 50% by mass, and particularly preferably 55% by mass, and the upper limit is more preferably 70% by mass, and further preferably 66% by mass. The fluorine content of the fluorinated ether (I) is a value calculated based on the structural formula of the fluorinated ether (I) by {(number of fluorine atoms×19) / molecular weight of the fluorinated ether (I)}×100(%).

[0349] Rf 4Examples of Rf include CF3CF2CH2-, CF3CFHCF2-, HCF2CF2CF2-, HCF2CF2CH2-, CF3CF2CH2CH2-, CF3CFHCF2CH2-, HCF2CF2CF2CF2-, HCF2CF2CF2CH2-, HCF2CF2CH2CH2-, and HCF2CF(CF3)CH2-. 5 Examples of such groups include -CH2CF2CF3, -CF2CFHCF3, -CF2CF2CF2H, -CH2CF2CF2H, -CH2CH2CF2CF3, -CH2CF2CFHCF3, -CF2CF2CF2CF2H, -CH2CF2CF2CF2H, -CH2CH2CF2CF2H, -CH2CF(CF3)CF2H, -CF2CF2H, -CH2CF2H, -CF2CH3, and the like.

[0350] Specific examples of the fluorinated ether (I) include HCF2CF2CH2OCF2CFHCF3, CF3CF2CH2OCF2CFHCF3, and C6F 13 OCH3, C6F 13 OC2H5, C8F 17 OCH3, C8F 17 Examples include OC2H5, CF3CFHCF2CH(CH3)OCF2CFHCF3, HCF2CF2OCH(C2H5)2, HCF2CF2OC4H9, HCF2CF2OCH2CH(C2H5)2, and HCF2CF2OCH2CH(CH3)2.

[0351] Among these, those containing HCF2- or CF3CFH- at one or both ends have excellent polarizability and can give fluorinated ethers (I) with high boiling points. The boiling point of the fluorinated ether (I) is preferably 67 to 120° C., more preferably 80° C. or higher, and further preferably 90° C. or higher.

[0352] Examples of such fluorinated ethers (I) include one or more of CF3CH2OCF2CFHCF3, CF3CF2CH2OCF2CFHCF3, HCF2CF2CH2OCF2CFHCF3, HCF2CF2CH2OCH2CF2CF2H, CF3CFHCF2CH2OCF2CFHCF3, and the like. Among these, at least one selected from the group consisting of HCF2CF2CH2OCF2CFHCF3 (boiling point 106°C) and CF3CF2CH2OCF2CFHCF3 (boiling point 82°C) is preferred, as it has the advantages of a high boiling point, compatibility with other solvents, and good solubility of electrolyte salts, and HCF2CF2CH2OCF2CFHCF3 (boiling point 106°C) is more preferred.

[0353] Examples of cyclic ethers having 3 to 6 carbon atoms include 1,2-dioxane, 1,3-dioxane, 2-methyl-1,3-dioxane, 4-methyl-1,3-dioxane, 1,4-dioxane, methaneformaldehyde, 2-methyl-1,3-dioxolane, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 2-(trifluoroethyl)dioxolane, 2,2-bis(trifluoromethyl)-1,3-dioxolane, and fluorinated compounds thereof.

[0354] Among these, as the ether compounds, dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol-n-propyl ether, ethylene glycol di-n-butyl ether, diethylene glycol dimethyl ether, and crown ether are preferred in that they have a high solvation ability for lithium ions and improve the degree of ion dissociation, and dimethoxymethane, diethoxymethane, and ethoxymethoxymethane are particularly preferred because they have a low viscosity and provide high ionic conductivity.

[0355] Examples of the cyclic carboxylate ester include those having a total carbon atom number in the structural formula of 3 to 12. Specific examples include gamma-butyrolactone, gamma-valerolactone, gamma-caprolactone, epsilon-caprolactone, 3-methyl-γ-butyrolactone, etc. Among them, gamma-butyrolactone is particularly preferred from the viewpoint of improving the characteristics of electrochemical devices due to the improvement in the degree of dissociation of lithium ions.

[0356] The amount of the cyclic carboxylate ester as an additive is usually preferably 0.1% by mass or more, more preferably 1% by mass or more, based on 100% by mass of the solvent. Within this range, the electrical conductivity of the electrolyte is improved, and the large-current discharge characteristics of the electrochemical device are easily improved. In addition, the amount of the cyclic carboxylate ester is preferably 10% by mass or less, more preferably 5% by mass or less. By setting the upper limit in this way, the viscosity of the electrolyte is kept in an appropriate range, a decrease in electrical conductivity is avoided, an increase in the negative electrode resistance is suppressed, and the large-current discharge characteristics of the electrochemical device are easily kept in a good range.

[0357] As the cyclic carboxylate, a fluorinated cyclic carboxylate (fluorine-containing lactone) can also be suitably used. Examples of the fluorine-containing lactone include those represented by the following formula (C):

[0358] [ka]

[0359] (In the formula, X 15 ~X 20 are the same or different and are each -H, -F, -Cl, -CH3, or a fluorinated alkyl group; provided that X 15 ~X 20 at least one of which is a fluorinated alkyl group Examples of fluorine-containing lactones include those represented by the following formula:

[0360] X 15 ~X 20Examples of the fluorinated alkyl group in include -CFH2, -CF2H, -CF3, -CH2CF3, -CF2CF3, -CH2CF2CF3, -CF(CF3)2, and the like. Of these, -CH2CF3 and -CH2CF2CF3 are preferred because of their high oxidation resistance and safety-improving effect.

[0361] X 15 ~X 20 is a fluorinated alkyl group, -H, -F, -Cl, -CH3 or a fluorinated alkyl group is X 15 ~X 20 The substitution may be at only one position or at multiple positions, preferably 1 to 3 positions, more preferably 1 to 2 positions, from the viewpoint of good solubility of the electrolyte salt.

[0362] The substitution position of the fluorinated alkyl group is not particularly limited. However, X 17 and / or X 18 But especially X 17 Or X 18 is preferably a fluorinated alkyl group, particularly -CH2CF3 or -CH2CF2CF3. X other than a fluorinated alkyl group is preferably 15 ~X 20 is -H, -F, -Cl or CH3, and is preferably -H in view of good solubility of the electrolyte salt.

[0363] As the fluorine-containing lactone, in addition to those represented by the above formula, for example, those represented by the following formula (D):

[0364] [ka]

[0365] (In the formula, either A or B is CX 226 X 227 (X 226 and X 227are the same or different, and each is -H, -F, -Cl, -CF3, -CH3, or an alkylene group in which a hydrogen atom may be replaced by a halogen atom and which may contain a heteroatom in the chain), and the other is an oxygen atom; Rf 12 X is a fluorinated alkyl group or a fluorinated alkoxy group which may have an ether bond; 221 and X 222 are the same or different, and each is -H, -F, -Cl, -CF3 or CH3; X 223 ~X 225 are the same or different, and each is -H, -F, -Cl, or an alkyl group in which a hydrogen atom may be replaced by a halogen atom and which may contain a heteroatom in the chain; n=0 or 1) Also included are fluorine-containing lactones represented by the following formula:

[0366] The fluorine-containing lactone represented by formula (D) includes a fluorine-containing lactone represented by the following formula (E):

[0367] [ka]

[0368] (In the formula, A, B, Rf 12 , X 221 , X 222 and X 223 is the same as formula (D). A five-membered ring structure represented by the following formula (F):

[0369] [ka]

[0370] (In the formula, Rf 12 , X 221 , X 222 , X 223 , X 226 and X 227 is the same as formula (D). and a fluorine-containing lactone represented by the following formula (G):

[0371] [ka]

[0372] (In the formula, Rf 12 , X 221 , X 222 , X 223 , X 226 and X 227 is the same as formula (D). There is a fluorine-containing lactone represented by the formula:

[0373] Among these, the electrolyte solution of the present disclosure has excellent properties such as a high dielectric constant and a high withstand voltage, and the electrolyte salt has good solubility and a good reduction in internal resistance, so that the electrolyte solution of the present disclosure has improved properties.

[0374] [ka] etc. By incorporating a fluorinated cyclic carboxylate, effects such as improved ion conductivity, improved safety, and improved stability at high temperatures can be obtained.

[0375] Examples of the chain carboxylate ester include those having a total carbon number in the structural formula of 3 to 7. Specific examples include methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, n-propyl propionate, isobutyl propionate, n-butyl propionate, methyl butyrate, isobutyl propionate, t-butyl propionate, methyl butyrate, ethyl butyrate, n-propyl butyrate, isopropyl butyrate, methyl isobutyrate, ethyl isobutyrate, n-propyl isobutyrate, and isopropyl isobutyrate.

[0376] Among these, methyl acetate, ethyl acetate, n-propyl acetate, n-butyl acetate, methyl propionate, ethyl propionate, n-propyl propionate, isopropyl propionate, methyl butyrate, ethyl butyrate, etc. are preferred from the viewpoint of improving ionic conductivity due to a decrease in viscosity.

[0377] Examples of the nitrogen-containing compound include nitriles, fluorine-containing nitriles, carboxylic acid amides, fluorine-containing carboxylic acid amides, sulfonic acid amides, fluorine-containing sulfonic acid amides, acetamides, and formamides. In addition, 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl-2-oxaziridinone, 1,3-dimethyl-2-imidazolidinone, and N-methylsuccinimide can also be used. However, the nitrile compounds represented by the general formulas (1a), (1b), and (1c) are not included in the nitrogen-containing compound.

[0378] Examples of the boron-containing compound include borate esters such as trimethyl borate and triethyl borate, borate ethers, and alkyl borates.

[0379] Examples of the organic silicon-containing compound include (CH3)4-Si, (CH3)3-Si-Si(CH3)3, and silicone oil.

[0380] Examples of the flame retardant (fire retardant) agent include phosphate esters and phosphazene compounds. Examples of the phosphate esters include fluorine-containing alkyl phosphate esters, non-fluorine-containing alkyl phosphate esters, aryl phosphate esters, etc. Among these, fluorine-containing alkyl phosphate esters are preferred because they can exert a flame retardant effect in a small amount.

[0381] Examples of the phosphazene compound include methoxypentafluorocyclotriphosphazene, phenoxypentafluorocyclotriphosphazene, dimethylaminopentafluorocyclotriphosphazene, diethylaminopentafluorocyclotriphosphazene, ethoxypentafluorocyclotriphosphazene, and ethoxyheptafluorocyclotetraphosphazene.

[0382] Specific examples of the fluorine-containing alkyl phosphate ester include the fluorine-containing dialkyl phosphate ester described in JP-A-11-233141, the cyclic alkyl phosphate ester described in JP-A-11-283669, and the fluorine-containing trialkyl phosphate ester.

[0383] As the above-mentioned non-flammable (flame retardant) agent, (CH3O)3P=O, (CF3CH2O)3P=O, (HCF2CH2O)3P=O, (CF3CF2CH2)3P=O, (HCF2CF2CH2)3P=O, and the like are preferred.

[0384] The surfactant may be any of a cationic surfactant, an anionic surfactant, a nonionic surfactant, and an amphoteric surfactant. From the viewpoint of improving cycle characteristics and rate characteristics, it is preferable that the surfactant contains a fluorine atom.

[0385] Examples of such a surfactant containing a fluorine atom include a surfactant represented by the following formula (30): Rf 6 COO - M + (30) (In the formula, Rf 6 is a fluorine-containing alkyl group having 3 to 10 carbon atoms which may contain an ether bond; M + Li + , Na + , K + or NHR'3 + (R' may be the same or different, and each is H or an alkyl group having 1 to 3 carbon atoms) or a fluorine-containing carboxylate represented by the following formula (40): Rf 7SO3 - M + (40) (In the formula, Rf 7 is a fluorine-containing alkyl group having 3 to 10 carbon atoms which may contain an ether bond; M + Li + , Na + , K + or NHR'3 + (R' may be the same or different, and each is H or an alkyl group having 1 to 3 carbon atoms) Preferred is a fluorine-containing sulfonate represented by the following formula:

[0386] The content of the surfactant in the electrolyte is preferably 0.01 to 2% by mass, since the surface tension of the electrolyte can be reduced without deteriorating the charge-discharge cycle characteristics.

[0387] Examples of the high dielectric additive include sulfolane, methylsulfolane, γ-butyrolactone, and γ-valerolactone.

[0388] Examples of the cycle characteristic and rate characteristic improver include methyl acetate, ethyl acetate, tetrahydrofuran, 1,4-dioxane, and the like.

[0389] Furthermore, the electrolyte solution of the present disclosure may be further combined with a polymer material to form a gel-like (plasticized) gel electrolyte solution.

[0390] Examples of such polymeric materials include conventionally known polyethylene oxide, polypropylene oxide, and modified products thereof (JP Patent Publication Nos. 8-222270 and 2002-100405); polyacrylate polymers, polyacrylonitrile, fluororesins such as polyvinylidene fluoride and vinylidene fluoride-hexafluoropropylene copolymers (JP Patent Publication Nos. 4-506726, 8-507407, and 10-294131); and complexes of such fluororesins and hydrocarbon resins (JP Patent Publication Nos. 11-35765 and 11-86630). In particular, it is desirable to use polyvinylidene fluoride and vinylidene fluoride-hexafluoropropylene copolymers as polymeric materials for gel electrolytes.

[0391] In addition, the electrolyte solution of the present disclosure may also contain the ion-conductive compound described in Japanese Patent Application No. 2004-301934.

[0392] The ion-conducting compound has the formula (101): A-(D)-B (101) [Wherein, D represents the formula (201): -(D1) n -(FAE) m -(AE) p -(Y) q - (201) (Wherein, D1 is a compound represented by the formula (10a):

[0393] [ka]

[0394] (In the formula, Rf represents a fluorine-containing ether group which may have a crosslinkable functional group; R 10 is a group or bond connecting Rf to the main chain) an ether unit having a fluorine-containing ether group in a side chain, represented by the formula: The FAE can be calculated by the formula (10b):

[0395] [ka]

[0396] (In the formula, Rfa represents a hydrogen atom or a fluorinated alkyl group which may have a crosslinkable functional group; R 11 is a group or bond that connects Rfa to the main chain) an ether unit having a fluorinated alkyl group on the side chain, represented by the formula: AE is represented by the formula (10c):

[0397] [ka]

[0398] (In the formula, R 13 represents a hydrogen atom, an alkyl group which may have a crosslinkable functional group, an aliphatic cyclic hydrocarbon group which may have a crosslinkable functional group, or an aromatic hydrocarbon group which may have a crosslinkable functional group; R 12 is R 13 and the group or bond that connects the main chain) Ether units denoted by; Y is represented by the formulas (10d-1) to (10d-3):

[0399] [ka]

[0400] A unit that contains at least one of the following: n is an integer from 0 to 200; m is an integer from 0 to 200; p is an integer from 0 to 10,000; q is an integer from 1 to 100; provided that n+m is not 0, and the bonding order of D1, FAE, AE, and Y is not specified); A and B are the same or different and each represent a hydrogen atom, an alkyl group which may contain a fluorine atom and / or a crosslinkable functional group, a phenyl group which may contain a fluorine atom and / or a crosslinkable functional group, a -COOH group, -OR (R is a hydrogen atom or an alkyl group which may contain a fluorine atom and / or a crosslinkable functional group), an ester group or a carbonate group (however, when the terminal of D is an oxygen atom, it is not a -COOH group, -OR, an ester group or a carbonate group) The compound is an amorphous fluorine-containing polyether compound having a fluorine-containing group in the side chain represented by the formula:

[0401] The electrolyte solution of the present disclosure may contain a sulfone-based compound. As the sulfone-based compound, cyclic sulfones having 3 to 6 carbon atoms and chain sulfones having 2 to 6 carbon atoms are preferred. The number of sulfonyl groups in one molecule is preferably 1 or 2.

[0402] Examples of cyclic sulfones include monosulfone compounds such as trimethylene sulfones, tetramethylene sulfones, and hexamethylene sulfones; and disulfone compounds such as trimethylene disulfones, tetramethylene disulfones, and hexamethylene disulfones. Among these, from the viewpoint of dielectric constant and viscosity, tetramethylene sulfones, tetramethylene disulfones, hexamethylene sulfones, and hexamethylene disulfones are more preferred, and tetramethylene sulfones (sulfolanes) are particularly preferred.

[0403] The sulfolane is preferably sulfolane and / or a sulfolane derivative (hereinafter, sulfolane may be abbreviated as "sulfolane") The sulfolane derivative is preferably one in which one or more hydrogen atoms bonded to the carbon atom constituting the sulfolane ring are substituted with a fluorine atom or an alkyl group.

[0404] Among these, 2-methylsulfolane, 3-methylsulfolane, 2-fluorosulfolane, 3-fluorosulfolane, 2,2-difluorosulfolane, 2,3-difluorosulfolane, 2,4-difluorosulfolane, 2,5-difluorosulfolane, 3,4-difluorosulfolane, 2-fluoro-3-methylsulfolane, 2-fluoro-2-methylsulfolane, 3-fluoro-3-methylsulfolane, 3-fluoro-2-methylsulfolane, 4-fluoro-3-methylsulfolane, 4-fluoro-2-methylsulfolane, 5-fluoro-3-methylsulfolane , 5-fluoro-2-methylsulfolane, 2-fluoromethylsulfolane, 3-fluoromethylsulfolane, 2-difluoromethylsulfolane, 3-difluoromethylsulfolane, 2-trifluoromethylsulfolane, 3-trifluoromethylsulfolane, 2-fluoro-3-(trifluoromethyl)sulfolane, 3-fluoro-3-(trifluoromethyl)sulfolane, 4-fluoro-3-(trifluoromethyl)sulfolane, 3-sulfolene, 5-fluoro-3-(trifluoromethyl)sulfolane, and the like are preferred in terms of high ionic conductivity and high input / output.

[0405] Examples of the chain sulfone include dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, n-propyl methyl sulfone, n-propyl ethyl sulfone, di-n-propyl sulfone, isopropyl methyl sulfone, isopropyl ethyl sulfone, diisopropyl sulfone, n-butyl methyl sulfone, n-butyl ethyl sulfone, t-butyl methyl sulfone, t-butyl ethyl sulfone, monofluoromethyl methyl sulfone, difluoromethyl methyl sulfone, trifluoromethyl methyl sulfone, monofluoroethyl methyl sulfone, difluoroethyl methyl sulfone, trifluoroethyl methyl sulfone, pentafluoroethyl methyl sulfone, ethyl monofluoromethyl sulfone, ethyl difluoromethyl sulfone, ethyl trifluoromethyl sulfone, and perfluoroethyl methyl sulfone. Examples of such sulfones include ethyl trifluoroethyl sulfone, ethyl pentafluoroethyl sulfone, di(trifluoroethyl)sulfone, perfluorodiethyl sulfone, fluoromethyl-n-propyl sulfone, difluoromethyl-n-propyl sulfone, trifluoromethyl-n-propyl sulfone, fluoromethyl isopropyl sulfone, difluoromethyl isopropyl sulfone, trifluoromethyl isopropyl sulfone, trifluoroethyl-n-propyl sulfone, trifluoroethyl isopropyl sulfone, pentafluoroethyl-n-propyl sulfone, pentafluoroethyl isopropyl sulfone, trifluoroethyl-n-butyl sulfone, trifluoroethyl-t-butyl sulfone, pentafluoroethyl-n-butyl sulfone, and pentafluoroethyl-t-butyl sulfone.

[0406] Among these, dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, n-propyl methyl sulfone, isopropyl methyl sulfone, n-butyl methyl sulfone, t-butyl methyl sulfone, monofluoromethyl methyl sulfone, difluoromethyl methyl sulfone, trifluoromethyl methyl sulfone, monofluoroethyl methyl sulfone, difluoroethyl methyl sulfone, trifluoroethyl methyl sulfone, pentafluoroethyl methyl sulfone, ethyl monofluoromethyl sulfone, ethyl difluoromethyl sulfone, ethyl trifluoromethyl sulfone, ethyl trifluoroethyl sulfone, ethyl pentafluoroethyl sulfone, trifluoromethyl-n-propyl sulfone, trifluoromethyl isopropyl sulfone, trifluoroethyl-n-butyl sulfone, trifluoroethyl-t-butyl sulfone, trifluoromethyl-n-butyl sulfone, trifluoromethyl-t-butyl sulfone, and the like are preferred in terms of high ionic conductivity and high input / output.

[0407] The content of the sulfone-based compound is not particularly limited and may be any content as long as it does not significantly impair the effects of the present disclosure, but is usually 0.3% by volume or more, preferably 0.5% by volume or more, more preferably 1% by volume or more, and is usually 40% by volume or less, preferably 35% by volume or less, more preferably 30% by volume or less, in 100% by volume of the solvent. If the content of the sulfone-based compound is within the above range, it is easy to obtain an effect of improving durability such as cycle characteristics and storage characteristics, and the viscosity of the nonaqueous electrolyte can be set to an appropriate range, the decrease in electrical conductivity can be avoided, and the input / output characteristics and charge / discharge rate characteristics of the nonaqueous electrolyte secondary battery can be set to an appropriate range.

[0408] From the viewpoint of improving output characteristics, the electrolyte solution of the present disclosure also preferably contains, as an additive, at least one compound (11) selected from the group consisting of lithium fluorophosphate salts (excluding LiPF6) and lithium salts having an S=O group. When compound (11) is used as an additive, it is preferable to use a compound other than compound (11) as the above-mentioned electrolyte salt.

[0409] Examples of the lithium fluorophosphate salts include lithium monofluorophosphate (LiPO3F) and lithium difluorophosphate (LiPO2F2). Examples of the lithium salts having the S=O group include lithium monofluorosulfonate (FSO3Li), lithium methylsulfate (CH3OSO3Li), lithium ethylsulfate (C2H5OSO3Li), and lithium 2,2,2-trifluoroethylsulfate. Of these, the compound (11) is preferably LiPO2F2, FSO3Li, or C2H5OSO3Li.

[0410] The content of compound (11) in the electrolyte is preferably 0.001 to 20 mass%, more preferably 0.01 to 15 mass%, further preferably 0.1 to 10 mass%, and particularly preferably 0.1 to 7 mass%.

[0411] The electrolyte solution of the present disclosure may further contain other additives as necessary, such as metal oxides and glass.

[0412] The electrolyte solution of the present disclosure preferably contains 5 to 200 ppm of hydrogen fluoride (HF). By containing HF, the film formation of the above-mentioned additives can be promoted. If the HF content is too low, the film forming ability on the negative electrode decreases, and the characteristics of the electrochemical device tend to deteriorate. If the HF content is too high, the oxidation resistance of the electrolyte solution tends to decrease due to the influence of HF. Even if the electrolyte solution of the present disclosure contains HF within the above range, it does not decrease the high-temperature storage recovery capacity rate of the electrochemical device. The HF content is more preferably 10 ppm or more, and even more preferably 20 ppm or more. The HF content is more preferably 100 ppm or less, and even more preferably 80 ppm or less, and particularly preferably 50 ppm or less. The HF content can be measured by neutralization titration.

[0413] The electrolytic solution of the present disclosure may be prepared by any method using the above-described components.

[0414] The electrolytic solution of the present disclosure has the characteristic of suppressing the electrodeposition of alkali metals and can be suitably applied to a secondary battery including an electrode having a negative electrode material containing a silicon element and a carbon element. A secondary battery including such a negative electrode, a positive electrode, and the electrolytic solution of the present disclosure is also one of the present disclosures.

[0415] <Negative electrode> In the present disclosure, it is preferable that the negative electrode includes a negative electrode material layer and a current collector. In the present disclosure, the negative electrode material contains a silicon element and a carbon element. In particular, it preferably contains Si and / or SiOa (0 < a < 2) and a carbon compound. In the present disclosure, the "negative electrode material" means a material that contributes to conductivity and refers to a negative electrode active material and / or a conductive assistant, which will be described in detail below.

[0416] (Negative electrode active material) The negative electrode active material used in the present disclosure preferably contains silicon as a constituent element. By using a material containing silicon as a constituent element, a high-capacity battery can be manufactured.

[0417] Examples of the particles containing silicon include silicon particles (Si), silicon oxide particles represented by the general formula SiOa (0 < a < 2), particles having a structure in which fine particles of silicon are dispersed in a silicon-based compound, or a mixture thereof (hereinafter, these may be collectively referred to as "particles containing silicon"). By using these, a negative electrode mixture for a lithium-ion secondary battery with higher initial charge-discharge efficiency, higher capacity, and excellent cycle characteristics can be obtained. Among them, at least one selected from the group consisting of Si and SiOa (0 < a < 2) is preferable.

[0418] Silicon oxide in the present disclosure is a general term for amorphous silicon oxides. The silicon oxide before disproportionation is represented by the general formula SiOa (0 < a < 2). a is preferably 0.5 ≦ a ≦ 1.6, more preferably 0.8 ≦ a < 1.6, and even more preferably 0.8 ≦ a < 1.3. This silicon oxide can be obtained, for example, by cooling and depositing monosilicon oxide gas generated by heating a mixture of silicon dioxide and metallic silicon.

[0419] Particles having a structure in which silicon fine particles are dispersed in a silicon-based compound can be obtained, for example, by firing a mixture of silicon fine particles and a silicon-based compound, or by subjecting silicon oxide particles before disproportionation represented by the general formula SiOa to heat treatment at a temperature of 400 °C or higher, preferably 800 to 1100 °C, in an inert non-oxidizing atmosphere such as argon to perform a disproportionation reaction. In particular, the material obtained by the latter method is suitable because the microcrystals of silicon are uniformly dispersed. By the disproportionation reaction as described above, the size of the silicon nanoparticles can be made 1 to 100 nm. It should be noted that the silicon oxide in the particles having a structure in which silicon nanoparticles are dispersed in silicon oxide is preferably silicon dioxide. It should be noted that it can be confirmed by a transmission electron microscope that silicon nanoparticles (crystals) are dispersed in amorphous silicon oxide.

[0420] The physical properties of the particles containing silicon can be appropriately selected according to the target composite particles. For example, the average particle size is preferably 0.1 to 50 μm, more preferably 0.2 μm or more, and even more preferably 0.5 μm or more for the lower limit. The upper limit is more preferably 30 μm or less, and even more preferably 20 μm or less. The average particle size in the present invention is represented by the weight average particle size in the particle size distribution measurement by the laser diffraction method.

[0421] The BET specific surface area of the particles containing silicon is preferably 0.5 to 100 m 2 / g, more preferably 1 to 20 m 2 / g. If the BET specific surface area is 0.5 m 2 / g or more, there is no risk that the adhesiveness when applied to the electrode will decrease and the battery characteristics will deteriorate. Also 100 m 2If it is below / g, the ratio of silicon dioxide on the particle surface increases, and there is no risk of a decrease in battery capacity when used as a negative electrode material for a lithium ion secondary battery.

[0422] Also, conductivity may be imparted by carbon coating or the like on the above-mentioned silicon-containing particles so as to improve battery characteristics. As a method for imparting conductivity, there are methods such as mixing with conductive particles such as graphite (graphite), a method of coating the surface of the above-mentioned silicon-containing particles with a carbon film, and a method of combining both. The method of coating with a carbon film is preferable, and as the coating method, the method of chemical vapor deposition (CVD) is more preferable.

[0423] Also, as the negative electrode active material, a carbon compound such as graphite powder may be used together with Si and / or SiOa (0 < a < 2). Examples of carbon compounds include natural graphite, artificial carbonaceous substances, artificial graphitic substances, carbonaceous substances {for example, natural graphite, coal-based coke, petroleum-based coke, coal-based pitch, petroleum-based pitch, or these pitches that have been oxidized, needle coke, pitch coke, and carbon materials obtained by partially graphitizing these pitches, furnace black, acetylene black, ketjen black, pitch-based carbon fibers, and other organic pyrolysis products; carbonizable organic substances (for example, coal tar pitch ranging from soft pitch to hard pitch, or coal-based heavy oils such as carbonized liquefied oil, atmospheric residual oil, vacuum residual oil, straight-run heavy oils, cracked petroleum heavy oils such as ethylene tar that are by-produced during the thermal decomposition of crude oil, naphtha, and the like; aromatic hydrocarbons such as acenaphthylene, decacyclene, anthracene, and phenanthrene; N-ring compounds such as phenazine and acridine; S-ring compounds such as thiophene and bithiophene; biphene, biphenyls, and the like; Examples of the carbonaceous materials include polyphenylenes such as polyphenylenes (e.g., polyvinyl, terphenyl, etc.), polyvinyl chloride, polyvinyl alcohol, polyvinyl butyral, insolubilized products of these, nitrogen-containing organic polymers such as polyacrylonitrile, polypyrrole, etc., sulfur-containing organic polymers such as polythiophene, polystyrene, etc., natural polymers such as polysaccharides represented by cellulose, lignin, mannan, polygalacturonic acid, chitosan, and saccharose, thermoplastic resins such as polyphenylene sulfide, polyphenylene oxide, etc., thermosetting resins such as furfuryl alcohol resin, phenol-formaldehyde resin, and imide resin), and carbonized products thereof, or solutions in which carbonizable organic substances are dissolved in low-molecular organic solvents such as benzene, toluene, xylene, quinoline, and n-hexane, and carbonized products thereof, which have been heat-treated at least once in the range of 400 to 3200°C.

[0424] For example, the carbon compound has an average particle size of preferably 1 to 100 μm, more preferably 3 μm or more as the lower limit, and even more preferably 5 μm or more as the upper limit. It is more preferably 80 μm or less, and even more preferably 20 μm or less as the upper limit. Note that the average particle size in the present disclosure is represented by the weight average particle size in particle size distribution measurement by laser diffraction method.

[0425] The BET specific surface area of ​​carbon compounds is 0.1 to 50 m 2 / g is preferable, and 1 to 20 m 2 / g is more preferable. If the BET specific surface area is 0.1 m 2 / g or more, there is no risk that the adhesiveness when applied to the electrode will decrease and the battery characteristics will deteriorate. Also, if it is 50 m 2 / g or less, there is no risk that the battery capacity will decrease when used as the negative electrode material for a lithium-ion secondary battery.

[0426] The mass ratio of the silicon-containing particles to the carbon compound is preferably 1 / 99 to 99 / 1, more preferably 5 / 95 to 95 / 5, and even more preferably 10 / 90 to 90 / 10.

[0427] The mass ratio of the above Si and / or SiOa (0 < a < 2) to the carbon compound is preferably 1 / 99 to 99 / 1, more preferably 5 / 95 to 95 / 5, and even more preferably 10 / 90 to 90 / 10.

[0428] The content of the negative electrode active material in the negative electrode material layer is preferably 80.0 to 99.9% by mass, more preferably 90.0 to 99.0% by mass, based on the mass of the solid content in the negative electrode binder.

[0429] The content of the silicon-containing particles in the negative electrode material layer is preferably 20 to 40% by mass, more preferably 25 to 35% by mass, based on the mass of the solid content in the negative electrode binder. The content of the carbon compound in the negative electrode material layer is preferably 40 to 60% by mass, more preferably 65 to 75% by mass, based on the mass of the solid content in the negative electrode binder.

[0430] (Conductive aid) The negative electrode material layer may further contain a conductive aid. In particular, when the negative electrode active material does not contain a carbon compound, it is preferable to include a conductive aid. Any known conductive material can be used as the conductive assistant. Specific examples include metal materials such as copper and nickel, graphite such as natural graphite and artificial graphite, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black, and carbon compounds such as needle coke, carbon nanotubes, fullerene, and amorphous carbon such as VGCF. These may be used alone or in any combination and ratio of two or more.

[0431] The conductive assistant preferably has an average particle size of 0.05 to 100 μm, more preferably a lower limit of 0.1 μm or more, and even more preferably 0.15 μm or more. The upper limit is more preferably 10 μm or less, and even more preferably 5 μm or less. The average particle size in the present invention is represented by the weight average particle size measured by a particle size distribution measurement using a laser diffraction method.

[0432] The BET specific surface area of ​​the conductive additive is 0.1 to 1000 m 2 / g is preferable, and 0.5 to 500m 2 / g is more preferred.

[0433] As described above, the carbon compound can be used both as an active material and as a conductive assistant.

[0434] The conductive assistant is used in such a way that it is contained in the negative electrode material layer in an amount of usually 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 1% by mass or more, and usually 50% by mass or less, preferably 30% by mass or less, more preferably 15% by mass or less. If the content is lower than this range, the conductivity may be insufficient. Conversely, if the content is higher than this range, the battery capacity may decrease.

[0435] (Binding agent) The negative electrode material layer preferably contains a binder. The binder preferably contains a fluorine-containing copolymer containing vinylidene fluoride (VdF) units and monomer units other than VdF. The other monomer may be a fluorinated monomer or a non-fluorinated monomer.

[0436] Examples of fluorinated monomers (excluding VdF) include tetrafluoroethylene (TFE), vinyl fluoride, trifluoroethylene, chlorotrifluoroethylene (CTFE), fluoroalkyl vinyl ethers, hexafluoropropylene (HFP), (perfluoroalkyl)ethylenes, 2,3,3,3-tetrafluoropropene, and trans-1,3,3,3-tetrafluoropropene.

[0437] The fluoroalkyl vinyl ether is preferably a fluoroalkyl vinyl ether having a fluoroalkyl group having 1 to 5 carbon atoms, and more preferably at least one selected from the group consisting of perfluoro(methyl vinyl ether) (PMVE), perfluoro(ethyl vinyl ether) and perfluoro(propyl vinyl ether).

[0438] The fluorinated monomer is preferably at least one selected from the group consisting of TFE, CTFE, 2,3,3,3-tetrafluoropropene, HFP, and fluoroalkyl vinyl ether, more preferably at least one selected from the group consisting of TFE and HFP, and particularly preferably TFE.

[0439] The fluorinated monomers (except for VdF) may or may not have a polar group.

[0440] Examples of the non-fluorinated monomer include non-fluorinated monomers that do not have a polar group, such as ethylene and propylene, and non-fluorinated monomers that have a polar group (hereinafter sometimes referred to as polar group-containing monomers).

[0441] When a non-fluorinated monomer having a polar group is used, the polar group is introduced into the fluorine-containing copolymer, and this results in even better adhesion between the coating layer and the metal foil. The polar group is preferably at least one selected from the group consisting of a carbonyl group-containing group, an epoxy group, a hydroxy group, a sulfonic acid group, a sulfate group, a phosphoric acid group, an amino group, an amide group, and an alkoxy group, more preferably at least one selected from the group consisting of a carbonyl group-containing group, an epoxy group, and a hydroxy group, and even more preferably a carbonyl group-containing group. The hydroxy group does not include a hydroxy group constituting a part of the carbonyl group-containing group. The amino group is a monovalent functional group formed by removing hydrogen from ammonia, a primary amine, or a secondary amine.

[0442] The carbonyl-containing group is a functional group having a carbonyl group (-C(=O)-). The carbonyl-containing group is preferably a group represented by the general formula -COOR (R represents a hydrogen atom, an alkyl group, or a hydroxyalkyl group) or a carboxylic acid anhydride group, and more preferably a group represented by the general formula -COOR. The number of carbon atoms in the alkyl group and the hydroxyalkyl group is preferably 1 to 16, more preferably 1 to 6, and even more preferably 1 to 3. Specific examples of the group represented by the general formula -COOR include -COOCH2CH2OH, -COOCH2CH(CH3)OH, -COOCH(CH3)CH2OH, -COOH, -COOCH3, and -COOC2H5. When the group represented by the general formula: -COOR is -COOH or contains -COOH, the -COOH may be a carboxylate such as a metal carboxylate or an ammonium carboxylate.

[0443] In addition, the carbonyl group-containing group is General formula:-X-COOR (X is an atomic group having a main chain composed of 1 to 20 atoms and a molecular weight of 500 or less, and R represents a hydrogen atom, an alkyl group, or a hydroxyalkyl group). The number of carbon atoms in the alkyl group and the hydroxyalkyl group is preferably 1 to 16, more preferably 1 to 6, and further preferably 1 to 3.

[0444] The amide group is preferably a group represented by the general formula: -CO-NRR' (R and R' independently represent a hydrogen atom or a substituted or unsubstituted alkyl group), or a bond represented by the general formula: -CO-NR"- (R" represents a hydrogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted phenyl group).

[0445] Examples of the polar group-containing monomer include hydroxyalkyl (meth)acrylates such as hydroxyethyl acrylate and 2-hydroxypropyl acrylate; alkylidene malonic acid esters such as dimethyl methylidene malonate; vinyl carboxyalkyl ethers such as vinyl carboxymethyl ether and vinyl carboxyethyl ether; carboxyalkyl (meth)acrylates such as 2-carboxyethyl acrylate and 2-carboxyethyl methacrylate; (meth)acryloyloxyalkyl dicarboxylate esters such as acryloyloxyethyl succinate, acryloyloxypropyl succinate, methacryloyloxyethyl succinate, acryloyloxyethyl phthalate, and methacryloyloxyethyl phthalate; monoesters of unsaturated dibasic acids such as monomethyl maleate, monoethyl maleate, monomethyl citraconic acid, and monoethyl citraconic acid; [ka] (In the formula, R 11 ~R 13 R independently represents a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms. 14 represents a single bond or a hydrocarbon group having 1 to 8 carbon atoms. 1 represents an inorganic cation and / or an organic cation. The monomer represented by (50); unsaturated dibasic acids such as maleic acid, maleic anhydride, citraconic acid, and citraconic anhydride;

[0446] The polar group-containing monomer unit which the fluorine-containing copolymer may contain is preferably a unit based on a monomer (50) represented by the general formula (50).

[0447] In the general formula (50), Y1 represents an inorganic cation and / or an organic cation. Examples of the inorganic cation include cations such as H, Li, Na, K, Mg, Ca, Al, and Fe. Examples of the organic cation include NH4, NH3R, and the like. 15 , NH2R 15 2. NHR 15 3. NR 15 4(R 15 each independently represents an alkyl group having 1 to 4 carbon atoms.) and other cations are included. Y1 is preferably H, Li, Na, K, Mg, Ca, Al, or NH4, more preferably H, Li, Na, K, Mg, Al, or NH4, further preferably H, Li, Al, or NH4, and particularly preferably H. For convenience, specific examples of inorganic cations and organic cations are described without the symbols and valences.

[0448] In the general formula (50), R 11 ~R 13 R independently represents a hydrogen atom or a hydrocarbon group having 1 to 8 carbon atoms. The above hydrocarbon group is a monovalent hydrocarbon group. The above hydrocarbon group preferably has 4 or less carbon atoms. Examples of the above hydrocarbon group include alkyl groups, alkenyl groups, alkynyl groups, etc. having the above carbon numbers, and a methyl group or an ethyl group is preferred. 11 and R 12 are preferably independently a hydrogen atom, a methyl group or an ethyl group, and R 13 is preferably a hydrogen atom or a methyl group.

[0449] In the general formula (50), R 14represents a single bond or a hydrocarbon group having 1 to 8 carbon atoms. The above hydrocarbon group is a divalent hydrocarbon group. The above hydrocarbon group preferably has 4 or less carbon atoms. Examples of the above hydrocarbon group include alkylene groups and alkenylene groups having the above carbon numbers, and among these, at least one selected from the group consisting of a methylene group, an ethylene group, an ethylidene group, a propylidene group and an isopropylidene group is preferable, and a methylene group is more preferable.

[0450] The monomer (50) is preferably at least one selected from the group consisting of (meth)acrylic acid and its salts, vinylacetic acid (3-butenoic acid) and its salts, 3-pentenoic acid and its salts, 4-pentenoic acid and its salts, 3-hexenoic acid and its salts, 4-heptenoic acid and its salts, and 5-hexenoic acid and its salts.

[0451] The other monomer is preferably at least one selected from the group consisting of TFE, CTFE, (meth)acrylic acid, 2,3,3,3-tetrafluoropropene, HFP, and fluoroalkyl vinyl ether. (Meth)acrylic acid includes acrylic acid and methacrylic acid.

[0452] The content of other monomer units in the fluorine-containing copolymer is preferably 0.0001 to 50.0 mol %, more preferably 0.01 mol % or more, even more preferably 0.10 mol % or more, more preferably 45.0 mol % or less, even more preferably 40.0 mol % or less, and particularly preferably 35.0 mol % or less, based on the total monomer units.

[0453] The content of VdF units in the fluorine-containing copolymer is 50.0 to 99.9999 mol%, more preferably 55.0 mol% or more, even more preferably 60.0 mol% or more, particularly preferably 65.0 mol% or more, more preferably 99.99 mol% or less, and even more preferably 99.90 mol% or less, based on the total monomer units.

[0454] When the fluorinated copolymer contains a fluorinated monomer unit as another monomer unit, the content of the fluorinated monomer unit is preferably 0.0001 to 50.0 mol%, more preferably 2.0 mol% or more, even more preferably 3.0 mol% or more, particularly preferably 4.0 mol% or more, more preferably 45.0 mol% or less, even more preferably 40.0 mol% or less, particularly preferably 35.0 mol% or less, based on the total monomer units.

[0455] When the fluorine-containing copolymer contains fluorinated monomer units as other monomer units, the content of VdF units in the fluorine-containing copolymer is 50.0 to 99.999 mol%, more preferably 55.0 mol% or more, still more preferably 60.0 mol% or more, particularly preferably 65.0 mol% or more, more preferably 98.0 mol% or less, still more preferably 97.0 mol% or less, particularly preferably 96.0 mol% or less, based on the total monomer units.

[0456] When the fluorinated copolymer contains non-fluorinated monomer units such as a polar group-containing monomer as other monomer units, the content of the non-fluorinated monomer units is preferably 0.0001 to 50.0 mol %, more preferably 0.01 mol % or more, still more preferably 0.10 mol % or more, more preferably 5.0 mol % or less, still more preferably 3.0 mol % or less, and particularly preferably 1.5 mol % or less, based on the total monomer units.

[0457] When the fluorine-containing copolymer contains non-fluorinated monomer units as other monomer units, the content of VdF units in the fluorine-containing copolymer is preferably 50.0 to 99.999 mol%, more preferably 95.0 mol% or more, even more preferably 97.0 mol% or more, particularly preferably 98.5 mol% or more, more preferably 99.99 mol% or less, and even more preferably 99.90 mol% or less, based on the total monomer units.

[0458] In the present disclosure, the composition of the fluorine-containing copolymer can be measured, for example, by 19F-NMR measurement. When the fluorine-containing copolymer contains a polar group-containing monomer unit as another monomer unit, the content of the polar group-containing monomer unit can be measured, for example, by acid-base titration of the acid group when the polar group is an acid group such as a carboxylic acid.

[0459] The weight average molecular weight (polystyrene equivalent) of the fluorine-containing copolymer is preferably 10,000 to 3,000,000, more preferably 30,000 or more, even more preferably 50,000 or more, particularly preferably 200,000 or more, more preferably 2,400,000 or less, even more preferably 2,200,000 or less, particularly preferably 2,000,000 or less. The weight average molecular weight can be measured by gel permeation chromatography (GPC) using dimethylformamide as a solvent.

[0460] The number average molecular weight (polystyrene equivalent) of the fluorine-containing copolymer is preferably 7000 to 1,500,000, more preferably 21,000 or more, further preferably 35,000 or more, more preferably 1,400,000 or less, further preferably 1,200,000 or less, particularly preferably 1,100,000 or less. The number average molecular weight can be measured by gel permeation chromatography (GPC) using dimethylformamide as a solvent.

[0461] Examples of the fluorine-containing copolymer include VdF / (meth)acrylic acid copolymer, VdF / TFE copolymer, VdF / HFP copolymer, VdF / fluoroalkyl vinyl ether copolymer, VdF / TFE / HFP copolymer, VdF / 2,3,3,3-tetrafluoro propene copolymer, VdF / TFE / 2,3,3,3-tetrafluoropropene copolymer, VdF / TFE / (meth)acrylic acid copolymer, VdF / HFP / (meth)acrylic acid copolymer, VdF / CTFE copolymer, VdF / TFE / 4-pentenoic acid copolymer, VdF / TFE / 3-butenoic acid copolymer, VdF / TFE / HFP / (meth)acrylic acid copolymer, VdF / TFE / HFP / 4-pentenoic acid copolymer, VdF / TFE / HFP / 3-butenoic acid copolymer, VdF / TFE / 2-carboxyethyl acrylate copolymer, VdF / TFE / HFP / 2-carboxyethyl acrylate copolymer, VdF / TFE / acryloyloxyethyl succinic acid copolymer, VdF / TFE / HFP / acryloyloxyethyl succinic acid copolymer, and the like.

[0462] As the fluorine-containing copolymer, at least one selected from the group consisting of VdF / TFE copolymer, VdF / CTFE copolymer, VdF / (meth)acrylic acid copolymer, VdF / 2,3,3,3-tetrafluoropropene copolymer, VdF / HFP copolymer and VdF / fluoroalkyl vinyl ether copolymer is preferable.

[0463] The VdF / TFE copolymer contains VdF units and TFE units. By using the VdF / TFE copolymer as the copolymer, the negative electrode mixture can be formed very easily, and the negative electrode mixture having excellent slurry stability can be obtained, and a coating layer having excellent flexibility can be formed. The content of the VdF units is preferably 50.0 to 95.0 mol%, more preferably 55.0 mol% or more, even more preferably 60.0 mol% or more, more preferably 92.0 mol% or less, and even more preferably 89.0 mol% or less, based on the total monomer units of the VdF / TFE copolymer. The content of the TFE units is preferably 50.0 to 5.0 mol%, more preferably 45.0 mol% or less, even more preferably 40.0 mol% or less, more preferably 8.0 mol% or more, and even more preferably 11.0 mol% or more, based on the total monomer units of the VdF / TFE copolymer.

[0464] The VdF / TFE copolymer may contain units based on monomers copolymerizable with VdF and TFE (excluding VdF and TFE) in addition to VdF units and TFE units. From the viewpoint of electrolyte swelling resistance, the content of units based on monomers copolymerizable with VdF and TFE is preferably 3.0 mol % or less based on the total monomer units of the VdF / TFE copolymer.

[0465] The monomer copolymerizable with VdF and TFE includes the above-mentioned fluorinated monomer, the above-mentioned non-fluorinated monomer, etc. Among them, the monomer copolymerizable with VdF and TFE is preferably at least one selected from the group consisting of fluorinated monomers and polar group-containing monomers, and more preferably at least one selected from the group consisting of HFP, 2,3,3,3-tetrafluoropropene, and monomer (4).

[0466] The weight average molecular weight (in terms of polystyrene) of the VdF / TFE copolymer is preferably 50,000 to 2,000,000, more preferably 80,000 to 1,700,000, and further preferably 100,000 to 1,500,000.

[0467] The number average molecular weight (in terms of polystyrene) of the VdF / TFE copolymer is 35,000 to 1,400,000, more preferably 40,000 to 1,300,000, and further preferably 50,000 to 1,200,000.

[0468] The VdF / CTFE copolymer contains VdF units and CTFE units. By using the VdF / CTFE copolymer as the copolymer, the negative electrode mixture can be formed very easily, and a coating layer that adheres very strongly to the metal foil can be formed. The content of the VdF units is preferably 80.0 to 98.0 mol%, more preferably 85.0 mol% or more, even more preferably 90.0 mol% or more, more preferably 97.5 mol% or less, and even more preferably 97.0 mol% or less, based on the total monomer units of the VdF / CTFE copolymer. The content of the CTFE units is preferably 20.0 to 2.0 mol%, more preferably 15.0 mol% or less, even more preferably 10.0 mol% or less, more preferably 2.5 mol% or more, and even more preferably 3.0 mol% or more, based on the total monomer units of the VdF / CTFE copolymer.

[0469] The VdF / CTFE copolymer may contain, in addition to the VdF units and CTFE units, units based on monomers copolymerizable with VdF and CTFE (excluding VdF and CTFE). From the viewpoint of electrolyte swelling resistance, the content of units based on monomers copolymerizable with VdF and CTFE is preferably 3.0 mol % or less based on the total monomer units of the VdF / CTFE copolymer.

[0470] Examples of the monomer copolymerizable with VdF and CTFE include the above-mentioned fluorinated monomers and the above-mentioned non-fluorinated monomers. Among them, the monomer copolymerizable with VdF and CTFE is preferably at least one selected from the group consisting of fluorinated monomers and polar group-containing monomers, more preferably at least one selected from the group consisting of TFE, HFP, 2,3,3,3-tetrafluoropropene, and monomer (4), and even more preferably TFE.

[0471] The weight average molecular weight (in terms of polystyrene) of the VdF / CTFE copolymer is preferably 50,000 to 2,000,000, more preferably 80,000 to 1,700,000, and further preferably 100,000 to 1,500,000.

[0472] The number average molecular weight (in terms of polystyrene) of the VdF / CTFE copolymer is preferably 35,000 to 1,400,000, more preferably 40,000 to 1,300,000, and further preferably 50,000 to 1,200,000.

[0473] The VdF / (meth)acrylic acid copolymer contains VdF units and (meth)acrylic acid units. By using the VdF / (meth)acrylic acid copolymer as the copolymer, it is possible to very easily form a negative electrode mixture and to form a coating layer that adheres very firmly to the metal foil. The content of the (meth)acrylic acid units is preferably 0.0001 to 5.0 mol%, more preferably 0.01 to 3.0 mol%, and even more preferably 0.10 to 1.5 mol% based on the total monomer units.

[0474] The content of VdF units in the VdF / (meth)acrylic acid copolymer is preferably 95.0 to 99.9999 mol %, more preferably 97.0 to 99.99 mol %, and even more preferably 98.5 to 99.90 mol %, based on the total monomer units.

[0475] The weight average molecular weight (polystyrene equivalent) of the VdF / (meth)acrylic acid copolymer is preferably 50,000 to 3,000,000, more preferably 80,000 or more, even more preferably 100,000 or more, particularly preferably 200,000 or more, more preferably 2,400,000 or less, even more preferably 2,200,000 or less, and particularly preferably 2,000,000 or less.

[0476] The number average molecular weight (polystyrene equivalent) of the VdF / (meth)acrylic acid copolymer is preferably 20,000 to 1,500,000, more preferably 40,000 or more, even more preferably 70,000 or more, particularly preferably 140,000 or more, more preferably 1,400,000 or less, even more preferably 1,200,000 or less, and particularly preferably 1,100,000 or less.

[0477] The VdF / 2,3,3,3-tetrafluoropropene copolymer contains VdF units and 2,3,3,3-tetrafluoropropene units. By using the VdF / 2,3,3,3-tetrafluoropropene copolymer as the copolymer, it is possible to form a negative electrode mixture very easily and to form a coating layer with excellent flexibility and conductivity. The content of the VdF units is preferably 50.0 to 98.0 mol%, more preferably 55.0 mol% or more, even more preferably 60.0 mol% or more, particularly preferably 65.0 mol% or more, more preferably 97.0 mol% or less, and even more preferably 96.0 mol% or less, based on the total monomer units of the VdF / 2,3,3,3-tetrafluoropropene copolymer. The content of 2,3,3,3-tetrafluoropropene units is preferably 2.0 to 50.0 mol %, more preferably 3.0 mol % or more, even more preferably 4.0 mol % or more, more preferably 45.0 mol % or less, even more preferably 40.0 mol % or less, and particularly preferably 35.0 mol % or less, based on the total monomer units of the VdF / TFE copolymer.

[0478] The VdF / 2,3,3,3-tetrafluoropropene copolymer may contain units based on monomers copolymerizable with VdF and 2,3,3,3-tetrafluoropropene (excluding VdF and 2,3,3,3-tetrafluoropropene) in addition to VdF units and 2,3,3,3-tetrafluoropropene units. From the viewpoint of electrolyte swelling resistance, the content of units based on monomers copolymerizable with VdF and 2,3,3,3-tetrafluoropropene is preferably 3.0 mol% or less based on the total monomer units of the VdF / 2,3,3,3-tetrafluoropropene copolymer.

[0479] Examples of the monomer that can be copolymerized with VdF and 2,3,3,3-tetrafluoropropene include the above-mentioned fluorinated monomers and the above-mentioned non-fluorinated monomers. Among them, the monomer that can be copolymerized with VdF and 2,3,3,3-tetrafluoropropene is preferably at least one selected from the group consisting of fluorinated monomers and polar group-containing monomers, and more preferably at least one selected from the group consisting of TFE, HFP, and monomer (50).

[0480] The weight average molecular weight (polystyrene equivalent) of the VdF / 2,3,3,3-tetrafluoropropene copolymer is preferably 10,000 to 2,000,000, more preferably 30,000 to 1,700,000, and further preferably 5,000 to 1,500,000.

[0481] The number average molecular weight (polystyrene equivalent) of the VdF / 2,3,3,3-tetrafluoropropene copolymer is preferably 7,000 to 1,400,000, more preferably 21,000 to 1,300,000, and further preferably 35,000 to 1,200,000.

[0482] The VdF / HFP copolymer contains VdF units and HFP units. By using the VdF / HFP copolymer as the copolymer, the negative electrode mixture can be formed very easily, and a coating layer that adheres very firmly to the metal foil can be formed. The content of the VdF units is preferably 80.0 to 98.0 mol%, more preferably 83.0 mol% or more, even more preferably 85.0 mol% or more, more preferably 97.0 mol% or less, and even more preferably 96.0 mol% or less, based on the total monomer units of the VdF / HFP copolymer. The content of the HFP units is preferably 20.0 to 2.0 mol%, more preferably 17.0 mol% or less, even more preferably 15.0 mol% or less, more preferably 3.0 mol% or more, and even more preferably 4.0 mol% or more, based on the total monomer units of the VdF / HFP copolymer.

[0483] The VdF / HFP copolymer may contain, in addition to VdF units and HFP units, units based on monomers copolymerizable with VdF and HFP (excluding VdF and HFP). From the viewpoint of electrolyte swelling resistance, the content of units based on monomers copolymerizable with VdF and HFP is preferably 3.0 mol % or less based on the total monomer units of the VdF / HFP copolymer.

[0484] Examples of the monomer copolymerizable with VdF and HFP include the above-mentioned fluorinated monomers and the above-mentioned non-fluorinated monomers. Among them, the monomer copolymerizable with VdF and HFP is preferably at least one selected from the group consisting of fluorinated monomers and polar group-containing monomers, more preferably at least one selected from the group consisting of TFE, 2,3,3,3-tetrafluoropropene, and monomer (50), and further preferably monomer (50).

[0485] The weight average molecular weight (in terms of polystyrene) of the VdF / HFP copolymer is preferably 50,000 to 2,000,000, more preferably 80,000 to 1,700,000, and further preferably 100,000 to 1,500,000.

[0486] The number average molecular weight (in terms of polystyrene) of the VdF / HFP copolymer is preferably 35,000 to 1,400,000, more preferably 40,000 to 1,300,000, and further preferably 50,000 to 1,200,000.

[0487] The VdF / fluoroalkyl vinyl ether copolymer contains VdF units and fluoroalkyl vinyl ether units. The content of the VdF units is preferably 80.0 to 98.0 mol%, more preferably 83.0 mol% or more, even more preferably 85.0 mol% or more, more preferably 97.0 mol% or less, and even more preferably 96.0 mol% or less, based on the total monomer units of the VdF / fluoroalkyl vinyl ether copolymer. The content of the fluoroalkyl vinyl ether units is preferably 20.0 to 2.0 mol%, more preferably 17.0 mol% or less, even more preferably 15.0 mol% or less, more preferably 3.0 mol% or more, and even more preferably 4.0 mol% or more, based on the total monomer units of the VdF / fluoroalkyl vinyl ether copolymer.

[0488] The VdF / fluoroalkyl vinyl ether copolymer may contain, in addition to the VdF unit and the fluoroalkyl vinyl ether unit, a unit based on a monomer copolymerizable with VdF and the fluoroalkyl vinyl ether (excluding VdF and the fluoroalkyl vinyl ether). From the viewpoint of resistance to electrolyte swelling, the content of the unit based on the monomer copolymerizable with VdF and the fluoroalkyl vinyl ether is preferably 3.0 mol% or less based on the total monomer units of the VdF / fluoroalkyl vinyl ether copolymer.

[0489] Examples of the monomer copolymerizable with VdF and fluoroalkyl vinyl ether include the above-mentioned fluorinated monomers and the above-mentioned non-fluorinated monomers. Among them, the monomer copolymerizable with VdF and fluoroalkyl vinyl ether is preferably at least one selected from the group consisting of fluorinated monomers and polar group-containing monomers, more preferably at least one selected from the group consisting of TFE, 2,3,3,3-tetrafluoropropene, and monomer (4), and further preferably monomer (50).

[0490] The weight average molecular weight (polystyrene equivalent) of the VdF / fluoroalkyl vinyl ether copolymer is preferably 50,000 to 2,000,000, more preferably 8,000 to 1,700,000, and even more preferably 100,000 to 1,500,000.

[0491] The number average molecular weight (polystyrene equivalent) of the VdF / fluoroalkyl vinyl ether copolymer is preferably 35,000 to 1,400,000, more preferably 40,000 to 1,300,000, and even more preferably 50,000 to 1,200,000.

[0492] It is also preferable that the binder further contains polyvinylidene fluoride (PVdF). PVdF is a polymer containing VdF units and is a polymer different from the above-mentioned fluorine-containing copolymer. PVdF may be a VdF homopolymer consisting of only VdF units, or may be a polymer containing VdF units and units based on a monomer copolymerizable with VdF.

[0493] In the above PVdF, the monomer copolymerizable with VdF is preferably a monomer other than tetrafluoroethylene (TFE), that is, PVdF preferably does not contain a TFE unit.

[0494] In the above PVdF, examples of the monomer copolymerizable with VdF include fluorinated monomers and non-fluorinated monomers, with fluorinated monomers being preferred. Examples of the above fluorinated monomers include vinyl fluoride, trifluoroethylene, chlorotrifluoroethylene (CTFE), fluoroalkyl vinyl ether, hexafluoropropylene (HFP), (perfluoroalkyl)ethylene, 2,3,3,3-tetrafluoropropene, trans-1,3,3,3-tetrafluoropropene, etc. Examples of the above non-fluorinated monomers include ethylene and propylene.

[0495] In the above-mentioned PVdF, the monomer copolymerizable with VdF is preferably at least one fluorinated monomer selected from the group consisting of CTFE, fluoroalkyl vinyl ether, HFP, and 2,3,3,3-tetrafluoropropene, and more preferably at least one fluorinated monomer selected from the group consisting of CTFE, HFP, and fluoroalkyl vinyl ether.

[0496] In the above PVdF, the content of the monomer units copolymerizable with VdF is preferably 0 to 5.0 mol%, more preferably 0 to 3.0 mol%, based on the total monomer units. In the above PVdF, the content of the fluorinated monomer units copolymerizable with VdF is preferably less than 5.0 mol%, more preferably less than 3.0 mol%, and even more preferably less than 1.0 mol%, based on the total monomer units.

[0497] In the present disclosure, the composition of PVdF is, for example, 19 It can be measured by F-NMR measurement.

[0498] The PVdF may have a polar group. The polar group is not particularly limited as long as it is a functional group having polarity, but is preferably at least one selected from the group consisting of a carbonyl group-containing group, an epoxy group, a hydroxy group, a sulfonic acid group, a sulfate group, a phosphoric acid group, an amino group, an amide group, and an alkoxy group, more preferably at least one selected from the group consisting of a carbonyl group-containing group, an epoxy group, and a hydroxy group, and even more preferably a carbonyl group-containing group. The hydroxy group does not include a hydroxy group that constitutes a part of the carbonyl group-containing group. The amino group is a monovalent functional group obtained by removing hydrogen from ammonia, a primary amine, or a secondary amine.

[0499] The carbonyl-containing group is a functional group having a carbonyl group (-C(=O)-). The carbonyl-containing group is preferably a group represented by the general formula -COOR (R represents a hydrogen atom, an alkyl group, or a hydroxyalkyl group) or a carboxylic anhydride group, and more preferably a group represented by the general formula -COOR. The number of carbon atoms in the alkyl group and the hydroxyalkyl group is preferably 1 to 16, more preferably 1 to 6, and even more preferably 1 to 3. Specific examples of the group represented by the general formula -COOR include -COOCH2CH2OH, -COOCH2CH(CH3)OH, -COOCH(CH3)CH2OH, -COOH, -COOCH3, and -COOC2H5. When the group represented by the general formula -COOR is -COOH or contains -COOH, -COOH may be a carboxylate such as a metal carboxylate or an ammonium carboxylate.

[0500] The carbonyl group-containing group may be a group represented by the general formula: -X-COOR (X is composed of 2 to 15 atoms, and the molecular weight of the atomic group represented by X is preferably 350 or less, and R represents a hydrogen atom, an alkyl group, or a hydroxyalkyl group). The number of carbon atoms in the alkyl group and the hydroxyalkyl group is preferably 1 to 16, more preferably 1 to 6, and further preferably 1 to 3.

[0501] The amide group is preferably a group represented by the general formula: -CO-NRR' (R and R' independently represent a hydrogen atom or a substituted or unsubstituted alkyl group), or a bond represented by the general formula: -CO-NR"- (R" represents a hydrogen atom, a substituted or unsubstituted alkyl group, or a substituted or unsubstituted phenyl group).

[0502] The polar group can be introduced into PVdF by polymerizing VdF with a monomer having the polar group (hereinafter referred to as a polar group-containing monomer), or by reacting PVdF with a compound having the polar group. From the viewpoint of productivity, however, it is preferable to polymerize VdF with the polar group-containing monomer.

[0503] Polymerization of VdF and the polar group-containing monomer produces PVdF containing VdF units and polar group-containing monomer units. That is, PVdF preferably contains the polar group-containing monomer units. The content of the polar group-containing monomer units is preferably 0.001 to 5.0 mol%, more preferably 0.01 to 3.0 mol%, and even more preferably 0.10 to 1.5 mol% based on the total monomer units.

[0504] In the present disclosure, the content of polar group-containing monomer units in PVdF can be measured, for example, by acid-base titration of the acid group when the polar group is an acid group such as a carboxylic acid.

[0505] Examples of the polar group-containing monomer include hydroxyalkyl (meth)acrylates such as hydroxyethyl acrylate and 2-hydroxypropyl acrylate; unsaturated monobasic acids such as (meth)acrylic acid, crotonic acid, vinyl acetic acid (3-butenoic acid), 3-pentenoic acid, 4-pentenoic acid, 3-hexenoic acid, and 4-heptenoic acid; unsaturated dibasic acids such as maleic acid, maleic anhydride, citraconic acid, and citraconic anhydride; alkylidene malonic acid esters such as dimethyl methylidene malonate; vinyl carboxyalkyl ethers such as vinyl carboxymethyl ether and vinyl carboxyethyl ether; carboxyalkyl (meth)acrylates such as 2-carboxyethyl acrylate and 2-carboxyethyl methacrylate; acrylonitrile, dimethyl methylidene malonate, and the like; Examples of the acryloyloxyalkyl dicarboxylic acid esters include (meth)acryloyloxyethyl succinate, methacryloyloxyethyl succinate, acryloyloxyethyl phthalate, acryloyloxypropyl succinate, and methacryloyloxyethyl phthalate; and monoesters of unsaturated dibasic acids such as monomethyl maleate, monoethyl maleate, monomethyl citraconic acid, and monoethyl citraconic acid.

[0506] When the polar group is introduced into PVdF by reacting PVdF with the compound having the polar group, the polar group-containing monomer, or a silane coupling agent or titanate coupling agent having a group reactive with PVdF and a hydrolyzable group can be used as the compound having the polar group. The hydrolyzable group is preferably an alkoxy group. When a coupling agent is used, it can be added to PVdF by reacting with PVdF dissolved or swollen in a solvent.

[0507] Alternatively, PVdF may be obtained by partially dehydrofluorinating PVdF with a base, and then reacting the partially dehydrofluorinated PVdF with an oxidizing agent, such as hydrogen peroxide, hypochlorite, palladium halide, chromium halide, alkali metal permanganate, peracid compound, alkyl peroxide, or alkyl persulfate.

[0508] The content of VdF units in PVdF is preferably more than 95.0 mol%, more preferably more than 97.0 mol%, and even more preferably more than 99.0 mol%, based on the total monomer units. The content of VdF units in PVdF is preferably 95.0 to 99.999 mol%, more preferably 97.0 mol% or more, even more preferably 98.5 mol% or more, more preferably 99.99 mol% or less, and even more preferably 99.90 mol% or less, based on the total monomer units.

[0509] The weight average molecular weight of PVdF (polystyrene equivalent) is preferably 50,000 to 3,000,000, more preferably 80,000 or more, even more preferably 100,000 or more, particularly preferably 200,000 or more, more preferably 2,400,000 or less, even more preferably 2,200,000 or less, and particularly preferably 2,000,000 or less. The weight average molecular weight can be measured by gel permeation chromatography (GPC) using N,N-dimethylformamide as a solvent. The weight average molecular weight of PVdF may be 1,000,000 or more, or 1,500,000 or more.

[0510] The number average molecular weight of PVdF (polystyrene equivalent) is preferably 20,000 to 1,500,000, more preferably 40,000 or more, even more preferably 70,000 or more, particularly preferably 140,000 or more, more preferably 1,400,000 or less, even more preferably 1,200,000 or less, and particularly preferably 1,100,000 or less. The number average molecular weight can be measured by gel permeation chromatography (GPC) using dimethylformamide as a solvent.

[0511] The melting point of PVdF is preferably 100 to 240° C. The melting point can be determined as the temperature corresponding to the maximum value on the heat of fusion curve when the temperature is increased at a rate of 10° C. / min using a differential scanning calorimetry (DSC) device.

[0512] When the binder contains PVdF and a fluorine-containing copolymer, the mass ratio of PVdF to the fluorine-containing copolymer in the binder (PVdF / fluorine-containing copolymer) is preferably 99 / 1 to 1 / 99, more preferably 97 / 3 to 3 / 97, even more preferably 95 / 5 to 5 / 95, particularly preferably 90 / 10 to 10 / 90, particularly preferably 85 / 15 to 15 / 85, and most preferably 80 / 20 to 40 / 60.

[0513] The binder may contain other polymers in addition to PVdF and the fluorine-containing copolymer, such as polymethacrylate, polymethyl methacrylate, polyacrylonitrile, polyimide, polyamide, polyamideimide, polycarbonate, styrene rubber, butadiene rubber, etc.

[0514] The content of the fluorine-containing copolymer in the binder is preferably 1 mass% or more, more preferably 3 mass% or more, even more preferably 5 mass% or more, particularly preferably 10 mass% or more, and most preferably 15 mass% or more, and may be 100 mass% or less, based on the mass of the binder.

[0515] The content of the binder in the negative electrode mixture prepared for forming the negative electrode material layer is preferably 0.1 to 20 mass %, more preferably 0.2 to 10 mass %, and even more preferably 0.5 to 7 mass %, relative to the mass of the solid content in the negative electrode mixture.

[0516] (solvent) The negative electrode mixture preferably contains a solvent. Examples of the solvent include water or an organic solvent, and an organic solvent is preferred because it significantly reduces the possibility of moisture remaining in the negative electrode material layer when the negative electrode mixture is used to form the negative electrode material layer.

[0517] Examples of the organic solvent include nitrogen-containing organic solvents such as N-methyl-2-pyrrolidone, N,N-dimethylacetamide, dimethylformamide, etc.; ketone solvents such as acetone, methyl ethyl ketone, cyclohexanone, methyl isobutyl ketone, etc.; ester solvents such as ethyl acetate, butyl acetate, etc.; ether solvents such as tetrahydrofuran, dioxane, etc.; β-alkoxypropionamides such as β-methoxy-N,N-dimethylpropionamide, β-n-butoxy-N,N-dimethylpropionamide, β-n-hexyloxy-N,N-dimethylpropionamide, etc.; and mixed solvents thereof, as well as other general-purpose organic solvents having a low boiling point.

[0518] As the organic solvent, a solvent represented by the general formula (60) can also be used.

[0519] General formula (60): [ka] (In the formula, R 1 , R 2 and R 3 are independently H or a monovalent substituent, with the proviso that R 1 , R 2 and R 3 The total number of carbon atoms in R is 6 or more. 1 , R 2 and R 3 At least one of R is an organic group having a carbonyl group. 1 , R 2 and R 3 Any two of them may be bonded to form a ring.)

[0520] The solvent represented by general formula (60) is preferably at least one selected from the group consisting of 3-methoxy-N,N-dimethylpropanamide, N-ethyl-2-pyrrolidone (NEP), N-butyl-2-pyrrolidone (NBP), acryloylmorpholine, N-cyclohexyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, 3-butoxy-N,N-dimethylpropanamide, N,N,N',N'-tetraethylurea, N,N-dimethylacetoacetamide, N-octyl-2-pyrrolidone, and N,N-diethylacetamide.

[0521] As the solvent, from the viewpoint of excellent coating properties, water or at least one selected from the group consisting of N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, and the solvent represented by the general formula (1) is preferable, and N,N-dimethylformamide, N,N-dimethylacetamide, N-methyl-2-pyrrolidone, 3-methoxy-N,N-dimethylpropanamide, N-ethyl-2-pyrrolidone (NEP), N-butyl-2-pyrrolidone (NBP), acryloylmorpholine, N-cyclohexyl-2-pyrrolidone, N-vinyl-2-pyrrolidone, 3-butoxy- At least one selected from the group consisting of N,N-dimethylpropanamide, N,N,N',N'-tetraethylurea, N,N-dimethylacetoacetamide, N-octyl-2-pyrrolidone, and N,N-diethylacetamide is more preferred, at least one selected from the group consisting of N-methyl-2-pyrrolidone, N,N-dimethylacetamide, 3-methoxy-N,N-dimethylpropanamide, N-ethyl-2-pyrrolidone, and N-butyl-2-pyrrolidone is even more preferred, and at least one selected from the group consisting of N-methyl-2-pyrrolidone and N,N-dimethylacetamide is particularly preferred.

[0522] The amount of the solvent in the negative electrode mixture is determined in consideration of the applicability to the current collector, the formability of a thin film after drying, etc. Usually, the ratio of the binder to the solvent is 0.5:99.5 to 20:80 by mass.

[0523] (Other Ingredients) The negative electrode mixture of the present disclosure may further contain other components such as a leveling agent, a reinforcing material, and the like.

[0524] The above-mentioned negative electrode mixture can be prepared, for example, by mixing a binder and a solvent, then adding a negative electrode active material to the obtained mixture and further mixing. The obtained negative electrode mixture is then uniformly applied to a current collector such as a metal foil or a metal mesh, dried, and pressed as necessary to form a thin negative electrode material layer on the current collector to form a thin film electrode. Alternatively, the negative electrode mixture may be prepared by first mixing the negative electrode active material and the binder, and then adding a solvent.

[0525] The negative electrode of the present disclosure includes a negative electrode material layer and a current collector. The negative electrode material layer is formed using the above-mentioned negative electrode mixture and may be provided on one side or both sides of the current collector.

[0526] Examples of the current collector provided in the negative electrode of the present disclosure include metal foils or metal meshes of iron, stainless steel, copper, aluminum, nickel, titanium, etc., carbon materials such as carbon cloth and carbon paper, etc., and among these, copper foil is preferred.

[0527] The negative electrode of the present disclosure can be suitably manufactured by a manufacturing method in which the negative electrode mixture of the present disclosure is applied to a current collector. After the negative electrode mixture is applied, the coating may be dried and optionally heat-treated, and the resulting dried coating may be pressed.

[0528] The shape of the current collector may be metal foil, metal cylinder, metal coil, metal plate, expanded metal, punched metal, foam metal, etc. in the case of metal materials, and carbon plate, carbon thin film, carbon cylinder, etc. in the case of carbon materials. Of these, metal foil is preferred. The thin film may be appropriately formed into a mesh shape. The thickness of the thin film is optional, but is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and usually 1 mm or less, preferably 100 μm or less, more preferably 50 μm or less. If the thin film is thinner than this range, the strength required as a current collector may be insufficient. Conversely, if the thin film is thicker than this range, the handling may be impaired.

[0529] The thickness of the negative electrode plate is designed to match the positive electrode plate to be used and is not particularly limited, but the thickness of the composite layer minus the thickness of the metal foil of the core material is usually 15 μm or more, preferably 20 μm or more, more preferably 30 μm or more, and is usually 300 μm or less, preferably 280 μm or less, more preferably 250 μm or less.

[0530] <Positive electrode> The positive electrode is suitably composed of a positive electrode active material layer containing a positive electrode active material, and a current collector.

[0531] The positive electrode active material is not particularly limited as long as it can electrochemically absorb and release alkali metal ions, but for example, a material containing an alkali metal and at least one transition metal is preferable. Specific examples include an alkali metal-containing transition metal complex oxide and an alkali metal-containing transition metal phosphate compound. Among them, the positive electrode active material is preferably an alkali metal-containing transition metal complex oxide that produces high voltage. Examples of the alkali metal ion include lithium ion, sodium ion, potassium ion, etc. In a preferred embodiment, the alkali metal ion may be a lithium ion. That is, in this embodiment, the alkali metal ion secondary battery is a lithium ion secondary battery.

[0532] Examples of the alkali metal-containing transition metal composite oxide include: Formula (3-1): MaMn 2-b M 1 b O4 (Wherein, M is at least one metal selected from the group consisting of Li, Na, and K; 0.9≦a; 0≦b≦1.5; M 1 and wherein at least one metal selected from the group consisting of Fe, Co, Ni, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si and Ge), Formula (3-2): MNi 1-c M 2 c O2 (Wherein, M is at least one metal selected from the group consisting of Li, Na, and K; 0≦c≦0.5; M 2 is at least one metal selected from the group consisting of Fe, Co, Mn, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si and Ge), or Formula (3-3):MCo 1-d M 3 d O2 (Wherein, M is at least one metal selected from the group consisting of Li, Na, and K; 0≦d≦0.5; M 3 is at least one metal selected from the group consisting of Fe, Ni, Mn, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si and Ge) In the above, M is preferably one metal selected from the group consisting of Li, Na and K, more preferably Li or Na, and further preferably Li.

[0533] Among these, MCoO2, MMnO2, MNiO2, MMn2O4, and MNi are the most popular because they can provide high energy density and high output secondary batteries. 0.8 Co 0.15 Al 0.05 O2, or MNi 1 / 3 Co 1 / 3 Mn1 / 3 O2 and the like are preferred, and a compound represented by the following formula (3-4) is preferred. MNi h Co i Mn j M 5 k O2(3-4) (Wherein, M is M 5 represents at least one selected from the group consisting of Fe, Cu, Zn, Al, Sn, Cr, V, Ti, Mg, Ca, Sr, B, Ga, In, Si, and Ge, and (h+i+j+k)=1.0, 0≦h≦1.0, 0≦i≦1.0, 0≦j≦1.5, and 0≦k≦0.2.

[0534] The alkali metal-containing transition metal phosphate compound is, for example, a compound represented by the following formula (70): M e M 4 f (PO4) g (In the formula, M is at least one metal selected from the group consisting of Li, Na, and K, and M 4 represents at least one selected from the group consisting of V, Ti, Cr, Mn, Fe, Co, Ni and Cu, and 0.5≦e≦3, 1≦f≦2, 1≦g≦3) are included. In the above, M is preferably one metal selected from the group consisting of Li, Na and K, more preferably Li or Na, and even more preferably Li.

[0535] The transition metal of the lithium-containing transition metal phosphate compound is preferably V, Ti, Cr, Mn, Fe, Co, Ni, Cu, etc., and specific examples include iron phosphates such as LiFePO4, Li3Fe2(PO4)3, LiFeP2O7, cobalt phosphates such as LiCoPO4, and lithium transition metal phosphate compounds in which a part of the transition metal atoms that constitute the main part of these compounds has been substituted with other elements such as Al, Ti, V, Cr, Mn, Fe, Co, Li, Ni, Cu, Zn, Mg, Ga, Zr, Nb, Si, etc. The lithium-containing transition metal phosphate compound preferably has an olivine structure.

[0536] As other positive electrode active materials, MFePO4, MNi 0.8 Co 0.2 O2, M 1.2 Fe 0.4 Mn 0.4 O2, MNi 0.5 Mn 1.5 O4, MV3O6, M2MnO3 and the like can be mentioned. In particular, positive electrode active materials such as MNi 0.5 Mn 1.5 O4 are preferable in that the crystal structure does not collapse even when the secondary battery is operated at a voltage exceeding 4.4 V or a voltage of 4.6 V or higher. Therefore, an electrochemical device such as a secondary battery using a positive electrode material containing the positive electrode active material exemplified above is preferable because the remaining capacity hardly decreases even when stored at a high temperature, the resistance increase rate hardly changes, and the battery performance does not deteriorate even when operated at a high voltage.

[0537] As other positive electrode active materials, solid solution materials such as M2MnO3 and MM 6 O2 (wherein M is at least one metal selected from the group consisting of Li, Na, and K, and M 6 is a transition metal such as Co, Ni, Mn, Fe, etc.) can also be mentioned.

[0538] As the solid solution material, for example, an alkali metal manganese oxide represented by the general formula Mx[Mn(1-y)M 7 y]Oz. Here, M in the formula is at least one metal selected from the group consisting of Li, Na, and K, and M 7 consists of at least one metal element other than M and Mn, and includes, for example, one or more elements selected from the group consisting of Co, Ni, Fe, Ti, Mo, W, Cr, Zr, and Sn. Also, the values of x, y, and z in the formula are in the range of 1 < x < 2, 0 ≤ y < 1, and 1.5 < z < 3. Among them, Li 1.2 Mn 0.5 Co 0.14 Ni 0.14A manganese-containing solid solution material, such as O2, based on Li2MnO3 and containing LiNiO2 or LiCoO2 as a solid solution, is preferable because it can provide an alkali metal ion secondary battery having a high energy density.

[0539] In addition, it is preferable to include lithium phosphate in the positive electrode active material, since the continuous charging characteristics are improved. Although there is no limitation on the use of lithium phosphate, it is preferable to use the positive electrode active material and lithium phosphate mixed together. The amount of lithium phosphate used is preferably 0.1% by mass or more, more preferably 0.3% by mass or more, and even more preferably 0.5% by mass or more, with respect to the total of the positive electrode active material and lithium phosphate, and is preferably 10% by mass or less, more preferably 8% by mass or less, and even more preferably 5% by mass or less.

[0540] In addition, a material having a different composition from the positive electrode active material may be attached to the surface of the positive electrode active material. Examples of the surface-attaching material include oxides such as aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, and bismuth oxide, sulfates such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate, carbonates such as lithium carbonate, calcium carbonate, and magnesium carbonate, and carbon.

[0541] These surface-attaching substances can be attached to the surface of the positive electrode active material by, for example, a method of dissolving or suspending in a solvent, impregnating and adding to the positive electrode active material, and drying, a method of dissolving or suspending a surface-attaching substance precursor in a solvent, impregnating and adding to the positive electrode active material, and then reacting by heating, etc., a method of adding to a positive electrode active material precursor and simultaneously baking, etc. When carbon is attached, a method of mechanically attaching carbonaceous material in the form of, for example, activated carbon, etc., afterwards can also be used.

[0542] The amount of the surface-attached substance is preferably 0.1 ppm or more, more preferably 1 ppm or more, and even more preferably 10 ppm or more, and preferably 20% or less, more preferably 10% or less, and even more preferably 5% or less, as a lower limit, by mass relative to the positive electrode active material. The surface-attached substance can suppress the oxidation reaction of the electrolyte on the surface of the positive electrode active material, and can improve the battery life, but if the amount of attachment is too small, the effect is not fully manifested, and if it is too large, the ingress and egress of lithium ions is inhibited, and resistance may increase.

[0543] The shape of the particles of the positive electrode active material may be any of the conventional shapes such as block, polyhedron, sphere, oval sphere, plate, needle, column, etc. Primary particles may be aggregated to form secondary particles.

[0544] The tap density of the positive electrode active material is preferably 0.5 g / cm 3 More preferably, 0.8 g / cm 3 More preferably, 1.0 g / cm 3 That is all. If the tap density of the positive electrode active material is below the lower limit, the amount of dispersion medium required during the formation of the positive electrode active material layer increases, and the amount of conductive material and binder required also increases, restricting the filling rate of the positive electrode active material in the positive electrode active material layer and possibly restricting the battery capacity. By using a composite oxide powder with a high tap density, a high density positive electrode active material layer can be formed. Generally, the higher the tap density, the more preferable it is, and there is no particular upper limit, but if it is too high, the diffusion of lithium ions in the positive electrode active material layer using the electrolyte as a medium becomes rate-limiting, and the load characteristics may be easily deteriorated, so that the upper limit is preferably 4.0 g / cm. 3 Less than or equal to 3.7 g / cm 3 More preferably, 3.5 g / cm 3 The following is the result. In the present disclosure, the tap density is the powder packing density (tap density) g / cm when 5 to 10 g of the positive electrode active material powder is placed in a 10 ml glass measuring cylinder and tapped 200 times with a stroke of about 20 mm. 3 is required.

[0545] The median diameter d50 of the particles of the positive electrode active material (secondary particle diameter when primary particles are aggregated to form secondary particles) is preferably 0.3 μm or more, more preferably 0.5 μm or more, even more preferably 0.8 μm or more, and most preferably 1.0 μm or more, and is also preferably 30 μm or less, more preferably 27 μm or less, even more preferably 25 μm or less, and most preferably 22 μm or less. If it is below the lower limit, a high tap density product may not be obtained, and if it exceeds the upper limit, it may take time for lithium to diffuse within the particles, resulting in a decrease in battery performance, or problems such as streaking may occur when preparing the positive electrode of a battery, that is, when the active material, conductive material, binder, etc. are slurried with a solvent and applied in a thin film. Here, by mixing two or more types of the above positive electrode active materials having different median diameters d50, the filling property during preparation of the positive electrode can be further improved.

[0546] In the present disclosure, the median diameter d50 is measured by a known laser diffraction / scattering type particle size distribution analyzer. When using HORIBA's LA-920 as the particle size distribution analyzer, a 0.1% by mass sodium hexametaphosphate aqueous solution is used as the dispersion medium for the measurement, and the measurement is performed after ultrasonic dispersion for 5 minutes with a measurement refractive index set to 1.24.

[0547] In the case where the primary particles are aggregated to form secondary particles, the average primary particle diameter of the positive electrode active material is preferably 0.05 μm or more, more preferably 0.1 μm or more, and even more preferably 0.2 μm or more, and the upper limit is preferably 5 μm or less, more preferably 4 μm or less, even more preferably 3 μm or less, and most preferably 2 μm or less. If the upper limit is exceeded, it is difficult to form spherical secondary particles, which may adversely affect powder packing properties, or the specific surface area may be significantly reduced, which may increase the possibility of reducing battery performance such as output characteristics. Conversely, if the lower limit is exceeded, problems such as poor reversibility of charge and discharge may occur due to underdeveloped crystals.

[0548] In the present disclosure, the primary particle diameter is measured by observation using a scanning electron microscope (SEM). Specifically, in a photograph at a magnification of 10,000 times, the longest intercept value of a horizontal line at the left and right boundaries of a primary particle is calculated for any 50 primary particles, and the average value is calculated.

[0549] The BET specific surface area of ​​the positive electrode active material is preferably 0.1 m 2 / g or more, more preferably 0.2m 2 / g or more, more preferably 0.3m 2 / g or more, and the upper limit is preferably 50m 2 / g or less, more preferably 40m 2 / g or less, more preferably 30m 2 If the BET specific surface area is smaller than this range, the battery performance is likely to decrease, whereas if it is larger, it is difficult to increase the tap density, and problems may easily occur in the application property when forming the positive electrode active material layer.

[0550] In the present disclosure, the BET specific surface area is defined as a value measured by a surface area meter (e.g., a fully automatic surface area measuring device manufactured by Okura Riken Co., Ltd.) using a nitrogen adsorption BET single-point method based on a gas flow method, after pre-drying a sample at 150°C for 30 minutes under a nitrogen flow and using a nitrogen-helium mixed gas precisely adjusted so that the relative pressure of nitrogen to atmospheric pressure is 0.3.

[0551] When the secondary battery of the present disclosure is used as a large-scale lithium-ion secondary battery for hybrid automobiles or distributed power sources, high output is required, so that the particles of the positive electrode active material are preferably mainly secondary particles. The positive electrode active material particles preferably contain 0.5 to 7.0 volume % of fine particles having an average secondary particle size of 40 μm or less and an average primary particle size of 1 μm or less. By containing fine particles having an average primary particle size of 1 μm or less, the contact area with the electrolyte increases, and the diffusion of lithium ions between the electrode and the electrolyte can be made faster, resulting in improved output performance of the battery.

[0552] The manufacturing method of the positive electrode active material is a general method for manufacturing inorganic compounds.In particular, various methods can be considered for making spherical or elliptical active materials, for example, the raw material of transition metal is dissolved or crushed and dispersed in a solvent such as water, and the pH is adjusted while stirring to make and recover spherical precursors, which are dried as necessary, and then LiOH, Li2CO3, LiNO3, or other Li sources are added and calcined at high temperature to obtain active materials.

[0553] For the production of the positive electrode, the positive electrode active material may be used alone, or two or more of different compositions may be used in any combination or ratio. In this case, a preferred combination is LiCoO2 and LiNi 0.33 Co 0.33 Mn 0.33 Examples of such a combination include a combination of LiMn2O4 such as LiO2 or a combination in which a part of the Mn has been replaced with another transition metal or the like, and a combination of LiCoO2 or a combination in which a part of the Co has been replaced with another transition metal or the like.

[0554] The content of the positive electrode active material is preferably 50 to 99.5% by mass, and more preferably 80 to 99% by mass, of the positive electrode mixture in terms of high battery capacity. The content of the positive electrode active material in the positive electrode active material layer is preferably 80% by mass or more, more preferably 82% by mass or more, and particularly preferably 84% by mass or more. The upper limit is preferably 99% by mass or less, more preferably 98% by mass or less. If the content of the positive electrode active material in the positive electrode active material layer is low, the electric capacity may be insufficient. Conversely, if the content is too high, the strength of the positive electrode may be insufficient.

[0555] The positive electrode mixture preferably further contains a binder, a thickener, a conductive material, a solvent, and the like. Any material may be used as the binder as long as it is safe against the solvent and electrolyte used in the production of the electrodes. Examples of such binders include resin-based polymers such as polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, aromatic polyamide, chitosan, alginic acid, polyacrylic acid, polyimide, cellulose, and nitrocellulose; rubber-like polymers such as SBR (styrene-butadiene rubber), isoprene rubber, butadiene rubber, fluororubber, NBR (acrylonitrile-butadiene rubber), and ethylene-propylene rubber; styrene-butadiene-styrene block copolymers or hydrogenated products thereof; and EPDM (ethylene-propylene glycol). Examples of suitable materials include thermoplastic elastomer-like polymers such as styrene-ethylene-propylene-diene terpolymers, styrene-ethylene-butadiene-styrene copolymers, styrene-isoprene-styrene block copolymers, and hydrogenated products thereof; soft resin-like polymers such as syndiotactic-1,2-polybutadiene, polyvinyl acetate, ethylene-vinyl acetate copolymers, and propylene-α-olefin copolymers; fluorine-based polymers such as polyvinylidene fluoride, polytetrafluoroethylene, vinylidene fluoride copolymers, and tetrafluoroethylene-ethylene copolymers; and polymer compositions having ionic conductivity for alkali metal ions (especially lithium ions). These may be used alone or in any combination and ratio of two or more.

[0556] The content of the binder is usually 0.1% by mass or more, preferably 1% by mass or more, more preferably 1.5% by mass or more, and usually 80% by mass or less, preferably 60% by mass or less, more preferably 40% by mass or less, and most preferably 10% by mass or less, as the ratio of the binder in the positive electrode active material layer. If the ratio of the binder is too low, the positive electrode active material cannot be sufficiently held, resulting in insufficient mechanical strength of the positive electrode, which may deteriorate the battery performance such as cycle characteristics. On the other hand, if the ratio is too high, it may lead to a decrease in battery capacity and conductivity.

[0557] Examples of the thickener include carboxymethylcellulose, methylcellulose, hydroxymethylcellulose, ethylcellulose, polyvinyl alcohol, oxidized starch, phosphorylated starch, casein, polyvinylpyrrolidone, and salts thereof, etc. One type may be used alone, or two or more types may be used in any combination and ratio.

[0558] The ratio of the thickener to the active material is usually 0.1% by mass or more, preferably 0.2% by mass or more, more preferably 0.3% by mass or more, and usually 5% by mass or less, preferably 3% by mass or less, more preferably 2% by mass or less. If it is below this range, the coating property may be significantly reduced. If it is above this range, the ratio of the active material in the positive electrode active material layer may decrease, causing problems such as a decrease in the capacity of the battery and an increase in the resistance between the positive electrode active materials.

[0559] Any known conductive material can be used as the conductive material. Specific examples include metal materials such as copper and nickel, graphite such as natural graphite and artificial graphite, carbon black such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black, and carbon materials such as needle coke, carbon nanotubes, fullerene, and amorphous carbon such as VGCF. These materials may be used alone or in any combination and ratio of two or more. The conductive material is used in such a manner that it is contained in the positive electrode active material layer in an amount of usually 0.01% by mass or more, preferably 0.1% by mass or more, more preferably 1% by mass or more, and usually 50% by mass or less, preferably 30% by mass or less, more preferably 15% by mass or less. If the content is lower than this range, the conductivity may be insufficient. Conversely, if the content is higher than this range, the battery capacity may decrease.

[0560] The solvent for forming the slurry is not particularly limited in type, and may be either an aqueous solvent or an organic solvent, as long as it can dissolve or disperse the positive electrode active material, the conductive material, the binder, and the thickener used as needed. Examples of the aqueous solvent include water, a mixture of alcohol and water, and the like. Examples of the organic solvent include aliphatic hydrocarbons such as hexane; aromatic hydrocarbons such as benzene, toluene, xylene, and methylnaphthalene; heterocyclic compounds such as quinoline and pyridine; ketones such as acetone, methyl ethyl ketone, and cyclohexanone; esters such as methyl acetate and methyl acrylate; amines such as diethylenetriamine and N,N-dimethylaminopropylamine; ethers such as diethyl ether, propylene oxide, and tetrahydrofuran (THF); amides such as N-methylpyrrolidone (NMP), dimethylformamide, and dimethylacetamide; aprotic polar solvents such as hexamethylphosphatamide and dimethylsulfoxide.

[0561] Examples of the material for the positive electrode current collector include metals such as aluminum, titanium, tantalum, stainless steel, and nickel, or metal materials such as alloys thereof, and carbon materials such as carbon cloth and carbon paper. Among these, metal materials, particularly aluminum or its alloys, are preferred.

[0562] The shape of the current collector may be metal foil, metal cylinder, metal coil, metal plate, expanded metal, punched metal, foam metal, etc. in the case of metal materials, and carbon plate, carbon thin film, carbon cylinder, etc. in the case of carbon materials. Of these, metal foil is preferred. The thin film may be appropriately formed into a mesh shape. The thickness of the thin film is optional, but is usually 1 μm or more, preferably 3 μm or more, more preferably 5 μm or more, and usually 1 mm or less, preferably 100 μm or less, more preferably 50 μm or less. If the thin film is thinner than this range, the strength required as a current collector may be insufficient. Conversely, if the thin film is thicker than this range, the handling may be impaired.

[0563] In addition, it is also preferable that the surface of the current collector is coated with a conductive assistant from the viewpoint of reducing the electrical contact resistance between the current collector and the positive electrode active material layer. Examples of the conductive assistant include carbon and precious metals such as gold, platinum, and silver.

[0564] The thickness ratio of the current collector to the positive electrode active material layer is not particularly limited, but the value of (thickness of the positive electrode active material layer on one side immediately before the electrolyte is poured) / (thickness of the current collector) is preferably 20 or less, more preferably 15 or less, most preferably 10 or less, and is preferably 0.5 or more, more preferably 0.8 or more, most preferably 1 or more. If it exceeds this range, the current collector may generate heat due to Joule heat during high current density charge and discharge. If it is below this range, the volume ratio of the current collector to the positive electrode active material may increase, and the capacity of the battery may decrease.

[0565] The positive electrode may be manufactured by a conventional method, for example, by adding the above-mentioned binder, thickener, conductive material, solvent, etc. to the above-mentioned positive electrode active material to prepare a slurry-like positive electrode mixture, which is then applied to a current collector, dried, and pressed to increase density.

[0566] The densification can be performed by hand pressing, roller pressing, etc. The density of the positive electrode active material layer is preferably 1.5 g / cm 3 More preferably, 2 g / cm 3 More preferably, 2.2 g / cm 3 More preferably, it is 5 g / cm 3 Less than or equal to 4.5 g / cm 3 More preferably, 4 g / cm 3 The range is as follows. If the range is exceeded, the permeability of the electrolyte to the vicinity of the current collector / active material interface will decrease, and the charge / discharge characteristics, especially at high current density, will decrease, and high output may not be obtained. If the range is exceeded, the conductivity between the active materials will decrease, and the battery resistance will increase, and high output may not be obtained.

[0567] When the electrolyte solution of the present disclosure is used, from the viewpoint of increasing the stability at high output and high temperature, it is preferable that the area of ​​the positive electrode active material layer is larger than the outer surface area of ​​the battery exterior case. Specifically, it is preferable that the sum of the electrode areas of the positive electrodes is 15 times or more, and more preferably 40 times or more, in terms of area ratio, relative to the surface area of ​​the exterior of the secondary battery. In the case of a bottomed rectangular shape, the outer surface area of ​​the battery exterior case refers to the total area calculated from the vertical, horizontal and thickness dimensions of the case part filled with the power generating element excluding the protruding part of the terminal. In the case of a bottomed cylindrical shape, it is the geometric surface area of ​​the case part filled with the power generating element excluding the protruding part of the terminal as a cylinder. The sum of the electrode areas of the positive electrodes is the geometric surface area of ​​the positive electrode mixture layer facing the mixture layer containing the negative electrode active material, and in a structure in which a positive electrode mixture layer is formed on both sides via a collector foil, it refers to the sum of the areas calculated separately for each side.

[0568] The thickness of the positive electrode plate is not particularly limited, but from the viewpoint of high capacity and high output, the thickness of the mixture layer minus the thickness of the metal foil of the core material is, as a lower limit, preferably 10 μm or more, more preferably 20 μm or more, and also preferably 500 μm or less, more preferably 450 μm or less on one side of the current collector.

[0569] The positive electrode plate may have a surface to which a substance having a different composition is attached, such as oxides, such as aluminum oxide, silicon oxide, titanium oxide, zirconium oxide, magnesium oxide, calcium oxide, boron oxide, antimony oxide, and bismuth oxide, sulfates, such as lithium sulfate, sodium sulfate, potassium sulfate, magnesium sulfate, calcium sulfate, and aluminum sulfate, carbonates, such as lithium carbonate, calcium carbonate, and magnesium carbonate, and carbon.

[0570] <separator> The secondary battery of the present disclosure preferably further includes a separator. The material and shape of the separator are not particularly limited as long as they are stable to the electrolyte and have excellent liquid retention, and any known material can be used. Among them, it is preferable to use a material formed of a material stable to the electrolyte of the present disclosure, such as a resin, glass fiber, or inorganic material, and to use a porous sheet or nonwoven fabric having excellent liquid retention.

[0571] Examples of materials that can be used for the resin and glass fiber separator include polyolefins such as polyethylene and polypropylene, aromatic polyamides, polytetrafluoroethylene, polyethersulfone, and glass filters. These materials may be used alone or in any combination and ratio, such as polypropylene / polyethylene two-layer film and polypropylene / polyethylene / polypropylene three-layer film. Among these, the separator is preferably a porous sheet or nonwoven fabric made of polyolefins such as polyethylene and polypropylene, because of its excellent electrolyte permeability and shutdown effect.

[0572] The thickness of the separator is arbitrary, but is usually 1 μm or more, preferably 5 μm or more, more preferably 8 μm or more, and is usually 50 μm or less, preferably 40 μm or less, more preferably 30 μm or less. If the separator is thinner than the above range, the insulating properties and mechanical strength may be reduced. If the separator is thicker than the above range, not only may the battery performance such as rate characteristics be reduced, but also the energy density of the entire electrolyte battery may be reduced.

[0573] Furthermore, when a porous material such as a porous sheet or nonwoven fabric is used as the separator, the porosity of the separator is optional, but is usually 20% or more, preferably 35% or more, more preferably 45% or more, and is usually 90% or less, preferably 85% or less, more preferably 75% or less. If the porosity is too small, the membrane resistance tends to increase and the rate characteristics tend to deteriorate. If the porosity is too large, the mechanical strength of the separator tends to decrease and the insulating properties tend to decrease.

[0574] The average pore size of the separator is also optional, but is usually 0.5 μm or less, preferably 0.2 μm or less, and usually 0.05 μm or more. If the average pore size exceeds the above range, short circuits are likely to occur. If the average pore size is below the above range, the membrane resistance increases and the rate characteristics may deteriorate.

[0575] On the other hand, examples of inorganic materials that can be used include oxides such as alumina and silicon dioxide, nitrides such as aluminum nitride and silicon nitride, and sulfates such as barium sulfate and calcium sulfate, and these are in the form of particles or fibers.

[0576] As for the form, a thin film such as a nonwoven fabric, a woven fabric, or a microporous film is used. In the thin film form, a film with a pore size of 0.01 to 1 μm and a thickness of 5 to 50 μm is preferably used. In addition to the above independent thin film form, a separator can be used in which a composite porous layer containing the above inorganic particles is formed on the surface layer of a positive electrode and / or a negative electrode using a resin binder. For example, a porous layer can be formed on both sides of a positive electrode using alumina particles with a 90% particle size of less than 1 μm and a fluororesin as a binder.

[0577] <Battery design> The electrode group may be either a laminated structure of the positive and negative plates with the separator interposed therebetween, or a structure of the positive and negative plates spirally wound with the separator interposed therebetween. The ratio of the volume of the electrode group to the internal volume of the battery (hereinafter referred to as the electrode group occupancy rate) is usually 40% or more, preferably 50% or more, and usually 90% or less, preferably 80% or less.

[0578] If the electrode group occupancy rate is below the above range, the battery capacity will be small, while if it exceeds the above range, the void space will be small, and the battery will become hot, causing the members to expand and the vapor pressure of the electrolyte liquid component to increase, resulting in an increase in internal pressure, which will degrade various characteristics of the battery, such as repeated charge / discharge performance and high-temperature storage, and may even cause the gas release valve that releases the internal pressure to operate.

[0579] The current collecting structure is not particularly limited, but in order to more effectively improve the charge / discharge characteristics at high current density using the electrolyte of the present disclosure, it is preferable to use a structure that reduces the resistance of wiring parts and joint parts. When the internal resistance is reduced in this way, the effect of using the electrolyte of the present disclosure is particularly excellent.

[0580] In the case where the electrode group has the above-mentioned laminated structure, a structure formed by bundling the metal core parts of each electrode layer and welding them to a terminal is preferably used. When the surface area of ​​one electrode is large, the internal resistance increases, so it is also preferably used to reduce the resistance by providing multiple terminals in the electrode. In the case where the electrode group has the above-mentioned wound structure, the internal resistance can be reduced by providing multiple lead structures on each of the positive electrode and the negative electrode and bundling them to a terminal.

[0581] The material of the exterior case is not particularly limited as long as it is a material stable against the electrolyte used. Specifically, metals such as nickel-plated steel plate, stainless steel, aluminum or aluminum alloy, magnesium alloy, or a laminate film of resin and aluminum foil (laminate film) are used. From the viewpoint of weight reduction, metals such as aluminum or aluminum alloy, and laminate film are preferably used.

[0582] In the case of an exterior case using metals, there are cases in which the metals are welded together by laser welding, resistance welding, or ultrasonic welding to form a sealed structure, or cases in which the metals are used via a resin gasket to form a crimped structure. In the case of an exterior case using the laminate film, there are cases in which the resin layers are heat-sealed together to form a sealed structure. In order to improve the sealing property, a resin different from the resin used in the laminate film may be interposed between the resin layers. In particular, when the resin layer is heat-sealed via a current collecting terminal to form a sealed structure, the joining between the metal and the resin is performed, so that a resin having a polar group or a modified resin into which a polar group has been introduced is preferably used as the interposed resin.

[0583] The shape of the secondary battery of the present disclosure is arbitrary, and examples of the shape include a cylindrical shape, a square shape, a laminated shape, a coin shape, a large shape, etc. The shapes and configurations of the positive electrode, the negative electrode, and the separator can be changed according to the shape of each battery. EXAMPLES

[0584] The present disclosure will now be described with reference to examples, but the present disclosure is not limited to these examples. In the following examples, unless otherwise specified, "parts" and "%" represent "parts by mass" and "% by mass", respectively.

[0585] The fluorinated ethers (A-1) to (A-3) used are shown below. (A-1) HCF2CF2OCH2CF2CF2H (A-2) HCF2CF2OCH2CF2CF3 (A-3) HCF2CF2OCH2CF3

[0586] The additives used are shown below. VC: Vinylene carbonate Succinic Anhydride Maleic Anhydride Adiponitrile FEC: Fluoroethylene carbonate VEC: Vinyl ethylene carbonate DFEC: Difluoroethylene carbonate CH3CH2OSO3Li FSO3Li Et2NSO3Li (CF3CH2)2NSO3L (CF3CH2)(CH3)NSO3Li (CNCH2)2NSO3Li Tris(trimethylsilyl)phosphate Tris(triethylsilyl)phosphate Tris(t-butyldimethylsilyl)phosphate Tris(trimethylsilyl) phosphite Tristriethylsilyl phosphite Tris(t-butyldimethylsilyl) phosphite

[0587] Example 1 [Preparation of electrolyte] Ethylene carbonate (EC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC) were mixed in a volume ratio of 30 / 40 / 30, and LiPF6 was added to this mixture to give a concentration of 1.0 mol / L to prepare a basic electrolyte. A nonaqueous electrolyte solution was prepared by adding 0.001% by mass of the fluorinated ether (A-1) to the basic electrolyte solution and mixing.

[0588] [Preparation of negative electrode] Silicon oxide powder (SiO) (average particle size 20 μm, BET specific surface area 2.7 m) as the negative electrode active material 2 / g) and graphite powder (average particle size 5 μm, BET specific surface area 20 m 2 94% by mass of 1000g / g (mass ratio: 30 / 70) and 6% by mass of polyvinylidene fluoride (PVdF) as a binder were mixed, and N-methyl-2-pyrrolidone (NMP) was further added and mixed to form a slurry. The obtained slurry was applied to a negative electrode current collector made of copper foil with a thickness of 15 μm and dried. This was cut into a predetermined electrode size and rolled using a roll press to produce a negative electrode in which a negative electrode material layer was formed on the negative electrode current collector.

[0589] [Preparation of positive electrode] LiNi as the positive electrode active material 0.8 Mn 0.1 Co 0.1 97 parts by mass of O2 (NMC811), 1.5 parts by mass of acetylene black as a conductive assistant, and 1.5 parts by mass of polyvinylidene fluoride (8% by mass solution in NMP) as a binder were added and mixed in a disperser to form a slurry. The obtained slurry was applied to an aluminum foil with a thickness of 20 μm, dried, and rolled in a press machine, and then cut into a shape with a coated part (positive electrode material layer) of 50 mm in width and 30 mm in length and an uncoated part of 5 mm in width and 9 mm in length to form a positive electrode.

[0590] [Battery construction] The produced negative electrode having a negative electrode material layer on one side was cut into a shape having a coated portion (negative electrode material layer) of 52 mm width and 32 mm length and an uncoated portion of 5 mm width and 9 mm length to form a negative electrode.

[0591] The positive electrode and the negative electrode were placed opposite each other with a 20 μm-thick microporous polyethylene film (separator) interposed therebetween, and the nonaqueous electrolyte obtained above was poured into the cell. After the nonaqueous electrolyte had sufficiently permeated the separator and the like, the cell was sealed, precharged, and aged to produce an aluminum laminate cell (lithium ion secondary battery).

[0592] (Measurement of battery characteristics) [Cycle characteristics] The obtained aluminum laminate cell was charged at 25°C with a constant current-constant voltage (hereinafter referred to as CC / CV charging) (0.1C cut) to 4.2V at a current equivalent to 0.2C, and then discharged to 3V at a constant current of 0.2C, which constituted one cycle, and three cycles were performed. Thereafter, at 45°C, CC / CV charging (0.1C cut) was performed to 4.2V at a current equivalent to 1.0C, and then discharged to 3V at a constant current of 1.0C, which constituted one cycle, and the initial discharge capacity was calculated from the discharge capacity. The cycle was performed again, and the discharge capacity after 300 cycles was measured. The ratio of the discharge capacity after 300 cycles to the initial discharge capacity was calculated, and this was taken as the capacity retention rate (%). Capacity retention rate (%) = (discharge capacity after 300 cycles) ÷ (initial discharge capacity at 1.0 C) × 100 The results are shown as relative values ​​when the result of Comparative Example 1 is set to 1.

[0593] [IV resistance] The battery was charged to SOC 50%, discharged at 1, 3, and 5C rates, and the voltage drop (V) was measured. The resistance value was calculated from the slope of the obtained voltage and current values ​​using the formula V=IR. The value of Comparative Example 1 was set to 1, and the relative values ​​are listed in the Appendix of the Examples. The above SOC indicates the state of charge, and SOC100% is the capacity when charged to 4.2 V. For example, SOC50% indicates half the capacity of SOC100%.

[0594] [LiF amount] After the test, the battery was disassembled, the negative electrode was removed, and a specified amount of water was added. After stirring, the solution was filtered, and the amount of F in the filtered solution was calculated by ion chromatography, and the obtained value was converted into LiF.

[0595] (Examples 2 to 37) A non-aqueous electrolyte solution was prepared in the same manner as in Example 1, except that the type and amount of additives to the electrolyte solution were changed as shown in Table 1, and then a battery was fabricated and each evaluation was performed. The results are shown in Table 1.

[0596] Comparative Example 1 A non-aqueous electrolyte solution was prepared in the same manner as in Example 1 except that no additive was used, and further, a battery was fabricated and each evaluation was performed. The results are shown in Table 1.

[0597] Comparative Example 2 A non-aqueous electrolyte solution was prepared in the same manner as in Example 1 except that the additives were changed as shown in Table 1, and then a battery was fabricated and each evaluation was performed. The results are shown in Table 1.

[0598] [Table 1]

[0599] The examples in Table 1 show that the use of the electrolyte solutions obtained in the examples improved the cycle characteristics of the secondary battery and suppressed an increase in IV resistance. [Industrial Applicability]

[0600] A secondary battery using the electrolyte of the present disclosure can be used as a variety of power sources, such as a portable power source and a power source for an automobile.

Claims

1. A lithium ion secondary battery comprising a negative electrode having a negative electrode material layer containing silicon and carbon elements, and an electrolyte solution, the negative electrode material layer contains Si and / or SiOa (0<a<2) and a carbon compound, the content of the silicon-containing particles is 25 to 35 mass% relative to the mass of the solid content in the negative electrode mixture, and the content of the carbon compound is 65 to 75 mass% relative to the mass of the solid content in the negative electrode mixture; The electrolyte solution contains less than 10% by mass of a fluorinated ether represented by the following general formula (1): A lithium ion secondary battery, characterized in that the lower limit of LiF formed on the negative electrode is 3.0 μg / cm 2 and the upper limit is 4.1 μg / cm 2 . HCF ２ CF ２ -O-R (1) (In the formula, R is a fluorinated alkyl group.)

2. The lithium ion secondary battery according to claim 1, wherein the fluorinated ether represented by the general formula (1) is at least one fluorinated ether selected from the group consisting of fluorinated ethers represented by the following general formulas (2) to (4): HCF ２ CF ２ -O-CH ２ CF ２ CF ２ H (2) HCF ２ CF ２ -O-CH ２ CF ２ CF ３ (3) HCF ２ CF ２ -O-CH ２ CF ３ (4)

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