Nonaqueous electrolyte and nonaqueous electrolyte secondary battery

Abstract

To improve a capacity retention rate or a resistance increase rate after charge / discharge cycles.SOLUTION: A nonaqueous electrolyte contains an alkene compound represented by the following formula (I). (R11 represents a fluoro group (-F), a fluorocarbon group, a hydrocarbon group having a fluoro group (-F) as a substituent, or the like; R12 represents a fluoro group (-F), a fluorocarbon group, a hydrocarbon group having a fluoro group (-F) as a substituent, or the like; and R13 represents a silyl group, a fluorocarbon group, a hydrocarbon group having a fluoro group (-F), or the like.)SELECTED DRAWING: None

Description

Technical Field

[0001] The present disclosure relates to a non-aqueous electrolyte and a non-aqueous electrolyte secondary battery.

Background Art

[0002] Power storage devices such as lithium-ion secondary batteries that are small, lightweight, and have high output have been further improved in performance in recent years. Along with the improvement in performance, they are being increasingly used not only in small electrical products but also in large product fields such as automobiles. Lithium-ion secondary batteries are required to meet predetermined requirements for various characteristics such as output characteristics, charge and discharge characteristics, and gas generation. In lithium-ion secondary batteries, for example, the capacity retention rate and output characteristics after charge and discharge cycle tests are also very important evaluation items.

[0003] Patent Document 1 discloses a solvent for dissolving an electrolyte salt containing 3% by volume or more of a fluorine-containing cyclic carbonate (A) and 0.1 to 40 parts by volume of a fluorine-containing unsaturated hydrocarbon compound with respect to 100 parts by volume of the fluorine-containing cyclic carbonate (A). According to Patent Document 1, it has been reported that by using the solvent for dissolving an electrolyte salt of this composition, a lithium-ion secondary battery excellent in high-temperature cycle characteristics and oxidation resistance can be obtained.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, conventionally, a non-aqueous electrolyte secondary battery satisfactory in terms of the capacity retention rate or the resistance increase rate after charge and discharge cycles has not been known. Therefore, an object of one aspect of the present disclosure is to provide a non-aqueous electrolyte and a non-aqueous electrolyte secondary battery excellent in the capacity retention rate or the resistance increase rate after charge and discharge cycles. [Means for Solving the Problems]

[0006] As a result of intensive studies to solve the above problems, the present inventors have found that by incorporating an alkene compound represented by formula (I) into a non-aqueous electrolyte, it is possible to improve the capacity retention rate and the resistance increase rate after charge-discharge cycles of a non-aqueous electrolyte secondary battery. That is, as one aspect of the present disclosure, the following are exemplified. <1>A non-aqueous electrolyte containing an alkene compound represented by the following formula (I).

[0007] [Chemical formula]

[0008] (In formula (I), R 11 represents a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), an iodo group (-I), a hydrogen atom (-H), a fluorocarbon group having 1 to 12 carbon atoms, or a hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), an iodo group (-I), and an oxa group (-O-), and R 12 represents a hydrogen atom (-H), a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), an iodo group (-I), a fluorocarbon group having 1 to 12 carbon atoms, or a hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), an iodo group (-I), and an oxa group (-O-), and R 13 each independently represents a silyl group represented by the following formula (s-1), a hydrogen atom (-H), a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), an iodo group (-I), a fluorocarbon group having 1 to 12 carbon atoms, or a hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), an iodo group (-I), and an oxa group (-O-).)

[0009] [Chemical formula]

[0010] (In formula (s-1), R 14 each independently represents a hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), an iodo group (-I), and an oxa group (-O-).) <2> The non-aqueous electrolyte according to <1>, further containing at least one additive selected from the group consisting of a difluorophosphate represented by the following formula (II-1), a monofluorophosphate represented by the following formula (II-2), a salt represented by the following formula (III), an imide salt represented by the following formula (IV), a sulfonate represented by the following formula (V), a cyclic sulfate compound represented by the following formula (VI), and a cyclic sulfonate compound represented by the following formula (VII).

[0011] [Chemical formula]

[0012] (In formulas (II-1) and (II-2), M 21 + each independently represents an alkali metal ion, an alkaline earth metal ion, an ammonium ion, an imidazolium ion, a pyridinium ion, a pyrrolidinium ion, a piperidinium ion, or a phosphonium ion. In formula (III), R 31 each independently represents a single bond (-) or a divalent hydrocarbon group having 1 to 6 carbon atoms which may contain at least one functional group selected from the group consisting of a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), and an iodo group (-I), and Q 31 each independently represents an oxa group (-O-) or a secondary amino group (-NH-), and X 31each independently represents a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), or an iodo group (-I), and Z 31 represents a boron atom or a phosphorus atom, and M 31 + represents an alkali metal ion, an alkaline earth metal ion, an ammonium ion, an imidazolium ion, a pyridinium ion, a pyrrolidinium ion, a piperidinium ion, or a phosphonium ion, and h is when the said Z 31 is a boron atom, represents 1 or 2, and when the said Z 31 is a phosphorus atom, represents an integer from 1 to 3, and i is when the said Z 31 is a boron atom, represents 0 or 2, and when the said Z 31 is a phosphorus atom, represents 0, 2, or 4. In formula (IV), R 41 each independently represents a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), an iodo group (-I), a fluorocarbon group having 1 to 12 carbon atoms, or a hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), an iodo group (-I), and an oxa group (-O-), and M 41 + represents an alkali metal ion, an alkaline earth metal ion, an ammonium ion, an imidazolium ion, a pyridinium ion, a pyrrolidinium ion, a piperidinium ion, or a phosphonium ion. In formula (V), R 51 represents a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), an iodo group (-I), a fluorocarbon group having 1 to 12 carbon atoms, or a hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), an iodo group (-I), and an oxa group (-O-), and M 51 + represents an alkali metal ion, an alkaline earth metal ion, an ammonium ion, an imidazolium ion, a pyridinium ion, a pyrrolidinium ion, a piperidinium ion, or a phosphonium ion. In formula (VI), R 61 represents a group represented by formula (vi-1), a group represented by formula (vi-2), or a divalent hydrocarbon group having 1 to 6 carbon atoms. In formula (VII), R 71 each independently represents a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), an iodo group (-I), a fluorocarbon group having 1 to 12 carbon atoms, or a hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), an iodo group (-I), and an oxa group (-O-), and j represents an integer from 0 to 3.)

[0013]

Chemical formula

[0014] (In formula (vi-1), R 62 represents an oxa group (-O-), or a divalent hydrocarbon group having 1 to 6 carbon atoms which may contain an oxa group (-O-) at the terminal or in the chain, In formula (vi-2), R 63 represents a hydrocarbon group having 1 to 8 carbon atoms, or a hydrogen atom (-H).) <3>A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, the non-aqueous electrolyte according to <1> or <2>, and a separator. <4>The non-aqueous electrolyte secondary battery according to <3>, wherein the negative electrode includes a current collector and a negative electrode composite material layer provided on the current collector and containing a negative electrode active material, and the negative electrode active material includes at least one selected from the group consisting of silicon single particles, silicon oxide particles, and silicon carbide particles. <5>The non-aqueous electrolyte secondary battery according to <4>, wherein the negative electrode active material further includes carbon single particles. <6>The non-aqueous electrolyte secondary battery according to <4>, wherein the total charged mass of at least one selected from the group consisting of the silicon single particles, the silicon oxide particles, and the silicon carbide particles is 30% by mass or less when the total charged mass of the entire negative electrode active material is 100% by mass.

Advantages of the Invention

[0015] According to one aspect of the present disclosure, it is possible to improve the capacity retention rate and the resistance increase rate after charge and discharge cycles of a non-aqueous electrolyte secondary battery.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Modes for Carrying Out the Invention

[0017] Hereinafter, specific examples will be given in describing the present disclosure. However, the present disclosure is not limited to the following content as long as the gist of the present disclosure is not deviated from, and can be implemented with appropriate modifications.

[0018] In the present disclosure, a numerical range represented by “~” means a range including the numerical values described before and after “~” as a lower limit value and an upper limit value. In a numerical range described stepwise in the present disclosure, an upper limit value or a lower limit value described in one numerical range may be replaced with an upper limit value or a lower limit value of another numerically described range. Further, in the numerical range described in the present disclosure, the upper limit value or the lower limit value of the numerical range may be replaced with the value shown in the examples. In the present disclosure, the amount of each component in the composition means the total amount of the plurality of substances present in the composition when there are a plurality of substances corresponding to each component in the composition, unless otherwise specified. In the present disclosure, a combination of preferred embodiments is a more preferred embodiment. In the present disclosure, the term “step” includes not only an independent step but also the step even when it cannot be clearly distinguished from other steps as long as the intended purpose of the step is achieved.

[0019] <Non-aqueous electrolyte> A non-aqueous electrolyte which is one aspect of the present disclosure (hereinafter, may be abbreviated as "non-aqueous electrolyte") contains an alkene compound represented by the following formula (I).

[0020]

Chemical formula

[0021] (In formula (I), R 11 represents a fluorine group (-F), a chlorine group (-Cl), a bromine group (-Br), an iodine group (-I), a hydrogen atom (-H), a fluorocarbon group having 1 to 12 carbon atoms, or a hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a fluorine group (-F), a chlorine group (-Cl), a bromine group (-Br), an iodine group (-I), and an oxa group (-O-), and R 12 represents a hydrogen atom (-H), a fluorine group (-F), a chlorine group (-Cl), a bromine group (-Br), an iodine group (-I), a fluorocarbon group having 1 to 12 carbon atoms, or a hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a fluorine group (-F), a chlorine group (-Cl), a bromine group (-Br), an iodine group (-I), and an oxa group (-O-), and R 13 each independently represents a silyl group represented by the following formula (s-1), a hydrogen atom (-H), a fluorine group (-F), a chlorine group (-Cl), a bromine group (-Br), an iodine group (-I), a fluorocarbon group having 1 to 12 carbon atoms, or a hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a fluorine group (-F), a chlorine group (-Cl), a bromine group (-Br), an iodine group (-I), and an oxa group (-O-).)

[0022]

Chemical formula

[0023] (In formula (s-1), R 14independently represents a hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), an iodo group (-I), and an oxa group (-O-) as a substituent.)

[0024] By blending the alkene compound represented by the formula (I) into a non-aqueous electrolyte, the battery characteristics after charge and discharge cycles of a non-aqueous electrolyte secondary battery can be improved. Here, the battery characteristics after charge and discharge cycles mean one or both of the discharge capacity retention rate and the resistance increase rate. The battery characteristics after charge and discharge cycles can be evaluated from the discharge capacity retention rate after charge and discharge cycles calculated from the discharge capacity before the charge and discharge cycle test and the discharge capacity after the charge and discharge cycle test, and / or the resistance increase rate after charge and discharge cycles calculated from the resistance value before the charge and discharge cycle test and the resistance value after the charge and discharge cycle test, as described in the examples below.)

[0025] Improvement of the battery characteristics after charge and discharge cycles means that, compared with a non-aqueous electrolyte secondary battery using a non-aqueous electrolyte containing no alkene compound according to the present disclosure, the discharge capacity retention rate of the non-aqueous electrolyte secondary battery using a non-aqueous electrolyte containing the alkene compound according to the present disclosure is high, and / or the resistance increase rate is low.)

[0026] Although this is just an example and not intended to be limiting, when the discharge capacity retention rate after charge-discharge cycles in a non-aqueous electrolyte secondary battery using a non-aqueous electrolyte that does not contain the alkene compound according to the present disclosure is set to 100, a non-aqueous electrolyte secondary battery in which the discharge capacity retention rate after charge-discharge cycles is 101 or more, preferably 102 or more, more preferably 103 or more, and still more preferably 104 or more can be judged to have improved battery characteristics after charge-discharge cycles. Also, although this is just an example and not intended to be limiting, when the increase rate of the resistance value after charge-discharge cycles in a non-aqueous electrolyte secondary battery using a non-aqueous electrolyte that does not contain the alkene compound according to the present disclosure is set to 100, a non-aqueous electrolyte secondary battery in which the discharge capacity after charge-discharge cycles is 95 or less, preferably 90 or less, more preferably 85 or less, still more preferably 80 or less, still more preferably 75 or less, still more preferably 70 or less, and still more preferably 65 or less can be judged to have improved battery characteristics after charge-discharge cycles.

[0027] Hereinafter, the "alkene compound represented by formula (I)" and the like will be described in detail. In the above formula (I), R 11represents a "fluoro group (-F)", "chloro group (-Cl)", "bromo group (-Br)", "iodo group (-I)", "hydrogen atom (-H)", "fluorocarbon group having 1 to 12 carbon atoms", or "hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a fluoro group (-F), chloro group (-Cl), bromo group (-Br), iodo group (-I), and oxa group (-O-) as a substituent". The "fluorocarbon group" means a group in which all hydrogen atoms of the hydrocarbon group are substituted with fluorine atoms, and is not limited to a fluorocarbon group having a linear structure, and may be a fluorocarbon group having at least one structure selected from the group consisting of a branched structure, a cyclic structure, and a carbon-carbon unsaturated bond structure (carbon-carbon double bond structure and carbon-carbon triple bond structure). Further, the "hydrocarbon group" is not limited to an aliphatic hydrocarbon group having a linear structure, and may be a hydrocarbon group having at least one structure selected from the group consisting of a branched structure, a cyclic structure, and a carbon-carbon unsaturated bond structure (carbon-carbon double bond structure and carbon-carbon triple bond structure). Also, in the "hydrocarbon group", the number of linear structures, branched structures, cyclic structures, and carbon-carbon unsaturated bond structures is not limited. Therefore, (acyclic) aliphatic hydrocarbon groups, monocyclic aliphatic hydrocarbon groups, polycyclic aliphatic hydrocarbon groups, monocyclic aromatic hydrocarbon groups, and polycyclic aromatic hydrocarbon groups are all included in the "hydrocarbon group". Also, alkyl groups, alkenyl groups, alkynyl groups, aryl groups, etc. are all included in the "hydrocarbon group". Furthermore, "which may contain at least one functional group selected from the group consisting of a fluoro group (-F), chloro group (-Cl), bromo group (-Br), iodo group (-I), and oxa group (-O-) as a substituent" means that a hydrogen atom of the hydrocarbon group may be substituted with a fluoro group (-F), chloro group (-Cl), bromo group (-Br), iodo group (-I), and a carbon atom of the hydrocarbon group may be substituted with an oxa group (-O-).

[0028] R 11 When R 11When it is a hydrocarbon group, the number of carbon atoms is preferably 10 or less, more preferably 8 or less, still more preferably 6 or less, and particularly preferably 4 or less.

[0029] R 11 Examples of [R] include a fluoro group (-F), a trifluoromethyl group (-CF3), a pentafluoroethyl group (-C2F5), an n-heptafluoropropyl group (-C3F7), a methyl group (-CH3), an ethyl group (-CH2CH3), a vinyl group (-CH=CH2), an n-propyl group (-CH2CH2CH3), an i-propyl group (-CH(CH3)2), an n-butyl group (-CH2CH2CH2CH3), an s-butyl group (-CH2CH(CH3)2), a t-butyl group (-C(CH3)2), a hexyl group (-CH2CH2CH2CH2CH2CH3), a cyclohexyl group (-C6H 11 )), a phenyl group (-C6H5), a benzyl group (-CH2C6H5), a trifluoromethoxymethyl group (-CH2OCF3), etc. Among them, as [R] 11 , a fluoro group (-F), a trifluoromethyl group (-CF3), a pentafluoroethyl group (-C2F5), and an n-heptafluoropropyl group (-C3F7) are particularly preferred.

[0030] R 12 represents a "hydrogen atom (-H)", a "fluoro group (-F)", a "chloro group (-Cl)", a "bromo group (-Br)", an "iodo group (-I)", a fluorocarbon group having 1 to 12 carbon atoms, or a hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), an iodo group (-I), and an oxa group (-O-). The "fluorocarbon group" and the "hydrocarbon group" in [R] 12 are synonymous with the case of [R] 11 .

[0031] R 12 When it is a fluorocarbon group, the number of carbon atoms is preferably 10 or less, more preferably 8 or less, still more preferably 6 or less, and particularly preferably 4 or less. Also, [R] 12When it is a hydrocarbon group, the number of carbon atoms is preferably 10 or less, more preferably 8 or less, still more preferably 6 or less, and particularly preferably 4 or less.

[0032] R 12 Examples of [R] include a hydrogen atom (-H), a fluoro group (-F), a trifluoromethyl group (-CF3), a pentafluoroethyl group (-C2F5), an n-heptafluoropropyl group (-C3F7), a methyl group (-CH3), an ethyl group (-CH2CH3), a vinyl group (-CH=CH2), an n-propyl group (-CH2CH2CH3), an i-propyl group (-CH(CH3)2), an n-butyl group (-CH2CH2CH2CH3), an s-butyl group (-CH2CH(CH3)2), a t-butyl group (-C(CH3)2), a hexyl group (-CH2CH2CH2CH2CH2CH3), a cyclohexyl group (-C6H 11 ), a phenyl group (-C6H5), a benzyl group (-CH2C6H5), a trifluoromethoxymethyl group (-CH2OCF3), and the like. Among them, [R 12 is particularly preferably a hydrogen atom (-H), a fluoro group (-F), a trifluoromethyl group (-CF3), a pentafluoroethyl group (-C2F5), or an n-heptafluoropropyl group (-C3F7).

[0033] R 13 each independently represents a silyl group represented by formula (s-1), a hydrogen atom (-H), a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), an iodo group (-I), a fluorocarbon group having 1 to 12 carbon atoms, or a hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), an iodo group (-I), and an oxa group (-O-). The "fluorocarbon group" and the "hydrocarbon group" in [R 13 have the same meaning as in the case of [R 11 .

[0034] R 13When it is a fluorocarbon group, the number of carbon atoms is preferably 10 or less, more preferably 8 or less, still more preferably 6 or less, and particularly preferably 4 or less. Also, R 12 When it is a hydrocarbon group, the number of carbon atoms is preferably 10 or less, more preferably 8 or less, still more preferably 6 or less, and particularly preferably 4 or less.

[0035] In formula (s-1), R 14 each independently represents a "hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), an iodo group (-I), and an oxa group (-O-)" as a substituent. The "hydrocarbon group" in R 14 is synonymous with the case of R 11 .

[0036] R 14 The number of carbon atoms of the hydrocarbon group is preferably 10 or less, more preferably 8 or less, still more preferably 6 or less, and particularly preferably 4 or less.

[0037] R 13 Examples of R include a trimethylsilyl group (-Si(CH3)3), a triethylsilyl group (-Si(C2H5)3), a triphenylsilyl group (-Si(C6H5)3), a trimethoxysilyl group (-Si(OCH3)3), a triethoxysilyl group (-Si(OC2H5)3), a triphenoxysilyl group (-Si(OC6H5)3), a hydrogen atom (-H), a fluoro group (-F), a trifluoromethyl group (-CF3), a pentafluoroethyl group (-C2F5), an n-heptafluoropropyl group (-C3F7), a methyl group (-CH3), an ethyl group (-CH2CH3), a vinyl group (-CH=CH2), an n-propyl group (-CH2CH2CH3), an i-propyl group (-CH(CH3)2), an n-butyl group (-CH2CH2CH2CH3), an s-butyl group (-CH2CH(CH3)2), a t-butyl group (-C(CH3)2), a hexyl group (-CH2CH2CH2CH2CH2CH3), a cyclohexyl group (-C6H 11) Examples include a phenyl group (-C6H5), a benzyl group (-CH2C6H5), a trifluoromethoxymethyl group (-CH2OCF3), etc. Among them, R 13 is preferably a trimethylsilyl group (-Si(CH3)3), a triethylsilyl group (-Si(C2H5)3), a triphenylsilyl group (-Si(C6H5)3), a trimethoxysilyl group (-Si(OCH3)3), a fluoro group (-F), a hydrogen atom (-H), a trifluoromethyl group (-CF3), a pentafluoroethyl group (-C2F5), an n-heptafluoropropyl group (-C3F7).

[0038] Examples of the alkene compound represented by formula (I) include compounds represented by the following formula. The non-aqueous electrolyte may contain one kind of alkene compound represented by formula (I), or may contain two or more kinds of alkene compounds represented by formula (I). [Chemical formula]

[0039] The total content of the alkene compound represented by formula (I) in the non-aqueous electrolyte is usually 0.01% by mass to 5.0% by mass with respect to the total amount of the non-aqueous electrolyte (when the total amount of the non-aqueous electrolyte is 100% by mass). The lower limit is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, still more preferably 0.3% by mass or more. The upper limit is preferably 4.0% by mass or less, more preferably 3.0% by mass or less, still more preferably 2.0% by mass or less, and particularly preferably 1.5% by mass or less. When the total content of these compounds is within the above range, the capacity retention rate and the resistance increase rate after charge-discharge cycles can be controlled to good values, and more excellent battery characteristics can be achieved.

[0040] The non-aqueous electrolyte of the present disclosure preferably contains at least one additive selected from the group consisting of a difluorophosphate represented by the following formula (II-1), a monofluorophosphate represented by the following formula (II-2), a salt represented by the following formula (III), an imide salt represented by the following formula (IV), a sulfonate represented by the following formula (V), a cyclic sulfate compound represented by the following formula (VI), and a cyclic sulfonate compound represented by the following formula (VII) in addition to the alkene compound represented by the above-described formula (I).

[0041] (Difluorophosphate represented by formula (II-1) and monofluorophosphate represented by formula (II-2)) The non-aqueous electrolyte preferably further contains at least one additive selected from the group consisting of a difluorophosphate represented by the following formula (II-1) and a monofluorophosphate represented by the following formula (II-2).

[0042] [Chemical formula]

[0043] In formulas (II-1) and (II-2), M 21 + each independently represents an "alkali metal ion", an "alkaline earth metal ion", an "ammonium ion", an "imidazolium ion", a "pyridinium ion", a "pyrrolidinium ion", a "piperidinium ion", or a "phosphonium ion". Among them, M 21 + is particularly preferably a lithium ion.

[0044] Examples of the difluorophosphate represented by formula (II-1) and the monofluorophosphate represented by formula (II-2) include lithium difluorophosphate (LiPO2F2) represented by the following formula (II-1-1), lithium monofluorophosphate (Li2PO3F) represented by the following formula (II-2-1), and the like. The non-aqueous electrolyte may contain one type of difluorophosphate represented by formula (II-1), or may contain one type of monofluorophosphate represented by formula (II-2). Further, the non-aqueous electrolyte may contain two or more types of difluorophosphates represented by formula (II-1), or may contain two or more types of monofluorophosphates represented by formula (II-2). Furthermore, the non-aqueous electrolyte may contain one type or two or more types of difluorophosphates represented by formula (II-1) and one type or two or more types of monofluorophosphates represented by formula (II-2).

[0045]

Chemical formula

[0046] The total content of the difluorophosphate represented by formula (II-1) and the monofluorophosphate represented by formula (II-2) in the non-aqueous electrolyte is usually 0.01% by mass to 5.0% by mass with respect to the total amount of the non-aqueous electrolyte (when the total amount of the non-aqueous electrolyte is 100% by mass). The lower limit is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, still more preferably 0.3% by mass or more. The upper limit is preferably 4.0% by mass or less, more preferably 3.0% by mass or less, still more preferably 2.0% by mass or less, and particularly preferably 1.5% by mass or less. When the total content of these compounds is within the above range, the capacity retention rate and the resistance increase rate after charge and discharge cycles can be controlled to good values, and more excellent battery characteristics can be achieved.

[0047] (Salt represented by formula (III)) The non-aqueous electrolyte preferably further contains a salt represented by the following formula (III).

[0048]

Chemical formula

[0049] In formula (III), R 31 each independently represents a "single bond (-)" or a "divalent hydrocarbon group having 1 to 6 carbon atoms which may contain at least one functional group selected from the group consisting of a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), and an iodo group (-I) as a substituent". R 31 being a "single bond (-)" means that the two carbonyl groups (>C=O) adjacent to R 31 are directly bonded. Also, the "divalent hydrocarbon group" means a hydrocarbon group having two bonding positions, and is not limited to an aliphatic hydrocarbon group having a linear structure, and may be a group having at least one structure selected from the group consisting of a branched structure, a cyclic structure, and a carbon-carbon unsaturated bond structure (a carbon-carbon double bond structure and a carbon-carbon triple bond structure), or may be an aromatic hydrocarbon group. That is, an alkylene group, an alkenylene group, an alkynylene group, an arylene group, etc. are all included in the "divalent hydrocarbon group".

[0050] R 31 of the hydrocarbon group preferably has 5 or less carbon atoms, more preferably 4 or less carbon atoms, still more preferably 3 or less carbon atoms, and particularly preferably 2 or less carbon atoms.

[0051] R 31 includes, for example, a single bond (-), a methylene group (-CH2-), an ethylene group (-CH2CH2-), an n-propylene group (-CH2CH2CH2-), etc. Among them, R 31 is particularly preferably a single bond (-) or a methylene group (-CH2-).

[0052] In formula (III), Q 31 each independently represents an "oxa group (-O-)" or a "secondary amino group (-NH-)", and when two Q 31 are an "oxa group (-O-)" and R 31 is a "single bond (-)", this is an oxalate ion (C2O4 2-) serves as a polydentate ligand, meaning that it forms an oxalato complex. Q 31 Among them, an oxo group (-O-) is particularly preferred.

[0053] In formula (III), X 31 each independently represents a "fluoro group (-F)", "chloro group (-Cl)", "bromo group (-Br)", or "iodo group (-I)". Among these, X 31 is particularly preferably a fluoro group (-F).

[0054] In formula (III), Z 31 represents a "boron atom" or a "phosphorus atom". Among these, Z 31 is particularly preferably a boron atom.

[0055] In formula (III), M 31 + represents an "alkali metal ion", "alkaline earth metal ion", "ammonium ion", "imidazolium ion", "pyridinium ion", "pyrrolidinium ion", "piperidinium ion", or "phosphonium ion". Among these, M 31 + is particularly preferably a lithium ion.

[0056] In formula (III), h represents 1 or 2 when the aforementioned Z 31 is a boron atom, and represents an integer from 1 to 3 when the aforementioned Z 31 is a phosphorus atom. i represents 0 or 2 when the aforementioned Z 31 is a boron atom, and represents 0, 2, or 4 when the aforementioned Z 31 is a phosphorus atom. Among these, when Z 31 is a boron atom, it is particularly preferred that h is 2 and i is 0.

[0057] Examples of the salt represented by formula (III) include lithium bis(oxalato)borate (LiBOB) represented by the following formula (III-1-1), lithium difluorooxalatoborate (LiDFOB) represented by the following formula (III-1-2), lithium difluorobis(oxalato)phosphate (LiDFBOP) represented by the following formula (III-2-1), lithium tetrafluorooxalatophosphate (LiTFOP) represented by the following formula (III-2-2), and the like. The non-aqueous electrolyte may contain one kind of the salt represented by formula (III) or may contain two or more kinds of the salts represented by formula (III).

[0058]

Chemical formula

[0059] The total content of the salt represented by formula (III) in the non-aqueous electrolyte is usually 0.01% by mass to 5.0% by mass with respect to the total amount of the non-aqueous electrolyte (when the total amount of the non-aqueous electrolyte is 100% by mass). The lower limit is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, still more preferably 0.3% by mass or more. The upper limit is preferably 4.0% by mass or less, more preferably 3.0% by mass or less, still more preferably 2.0% by mass or less, and particularly preferably 1.5% by mass or less. When the total content of these compounds is within the above range, the capacity retention rate and the resistance increase rate after charge and discharge cycles can be controlled to good values, and more excellent battery characteristics can be achieved.

[0060] (Imide salt represented by formula (IV)) The non-aqueous electrolyte preferably further contains an imide salt represented by the following formula (IV).

[0061]

Chemical formula

[0062] In formula (IV), R 41Each independently represents a "fluoro group (-F)", "chloro group (-Cl)", "bromo group (-Br)", "iodo group (-I)", "fluorocarbon group having 1 to 12 carbon atoms", or "hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a fluoro group (-F), chloro group (-Cl), bromo group (-Br), iodo group (-I), and oxa group (-O-)" as a substituent. R 41 The "fluorocarbon group" and "hydrocarbon group" in 11 are synonymous with those in the case of R

[0063] R 41 When R is a fluorocarbon group, the number of carbon atoms is preferably 10 or less, more preferably 8 or less, still more preferably 6 or less, and particularly preferably 4 or less. Also, when R 41 is a hydrocarbon group, the number of carbon atoms is preferably 10 or less, more preferably 8 or less, still more preferably 6 or less, and particularly preferably 4 or less.

[0064] R 41 Examples of R include a fluoro group (-F), trifluoromethyl group (-CF3), pentafluoroethyl group (-C2F5), n-heptafluoropropyl group (-C3F7), methyl group (-CH3), ethyl group (-CH2CH3), vinyl group (-CH=CH2), n-propyl group (-CH2CH2CH3), i-propyl group (-CH(CH3)2), n-butyl group (-CH2CH2CH2CH3), s-butyl group (-CH2CH(CH3)2), t-butyl group (-C(CH3)2), hexyl group (-CH2CH2CH2CH2CH2CH3), cyclohexyl group (-C6H 11 ), phenyl group (-C6H5), benzyl group (-CH2C6H5), trifluoromethoxymethyl group (-CH2OCF3), and the like. Among them, as R 41 , a fluoro group (-F), trifluoromethyl group (-CF3), pentafluoroethyl group (-C2F5), and n-heptafluoropropyl group (-C3F7) are particularly preferred.

[0065] In formula (IV), M 41+ represents "alkali metal ion", "alkaline earth metal ion", "ammonium ion", "imidazolium ion", "pyridinium ion", "pyrrolidinium ion", "piperidinium ion", or "phosphonium ion". Among them, M 41 + is particularly preferably a lithium ion.

[0066] Examples of the imide salt represented by the formula (IV) include lithium bis(fluorosulfonyl)imide (LiFSI) represented by the following formula (IV-1-1), lithium bis(trifluoromethylsulfonyl)imide (LiTFSI) represented by the following formula (IV-1-2), lithium bis(pentafluoroethylsulfonyl)imide represented by the following formula (IV-1-3), and the like. The non-aqueous electrolyte may contain one type of imide salt represented by the formula (IV), or may contain two or more types of imide salts represented by the formula (IV).

[0067]

Chemical formula

[0068] The total content of the imide salt represented by the formula (IV) in the non-aqueous electrolyte is usually 0.01% by mass to 5.0% by mass with respect to the total amount of the non-aqueous electrolyte (when the total amount of the non-aqueous electrolyte is 100% by mass). The lower limit is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, still more preferably 0.3% by mass or more. The upper limit is preferably 4.0% by mass or less, more preferably 3.0% by mass or less, still more preferably 2.0% by mass or less, and particularly preferably 1.5% by mass or less. When the total content of these compounds is within the above range, the capacity retention rate and the resistance increase rate after charge-discharge cycles can be controlled to good values, and more excellent battery characteristics can be achieved.

[0069] (Sulfonate represented by the formula (V)) The non-aqueous electrolyte preferably further contains a sulfonate represented by the following formula (V).

[0070] [Chemical formula]

[0071] In formula (V), R 51 represents "fluoro group (-F)", "chloro group (-Cl)", "bromo group (-Br)", "iodo group (-I)", "hydrofluorocarbon group having 1 to 12 carbon atoms", or "hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of fluoro group (-F), chloro group (-Cl), bromo group (-Br), iodo group (-I), and oxa group (-O-)" as a substituent. Among them, R 51 is preferably a functional group containing fluorine element. When R 51 is a functional group containing fluorine element, the sulfonate represented by formula (V) becomes fluorosulfonate. Note that the "hydrofluorocarbon group" and "hydrocarbon group" in R 51 have the same meaning as in the case of R 11 .

[0072] R 51 When it is a hydrofluorocarbon group, the number of carbon atoms is preferably 10 or less, more preferably 8 or less, still more preferably 6 or less, and particularly preferably 4 or less. Also, when R 51 is a hydrocarbon group, the number of carbon atoms is preferably 10 or less, more preferably 8 or less, still more preferably 6 or less, and particularly preferably 4 or less.

[0073] R 51 includes fluoro group (-F), trifluoromethyl group (-CF3), pentafluoroethyl group (-C2F5), n-heptafluoropropyl group (-C3F7), methyl group (-CH3), ethyl group (-CH2CH3), vinyl group (-CH=CH2), n-propyl group (-CH2CH2CH3), i-propyl group (-CH(CH3)2), n-butyl group (-CH2CH2CH2CH3), s-butyl group (-CH2CH(CH3)2), t-butyl group (-C(CH3)2), hexyl group (-CH2CH2CH2CH2CH2CH3), cyclohexyl group (-C6H 11) include a phenyl group (-C6H5), a benzyl group (-CH2C6H5), a trifluoromethoxymethyl group (-CH2OCF3), etc. Among them, R 51 is particularly preferably a fluoro group (-F), a trifluoromethyl group (-CF3), a pentafluoroethyl group (-C2F5), or an n-heptafluoropropyl group (-C3F7).

[0074] In formula (V), M 51 + represents an "alkali metal ion", an "alkaline earth metal ion", an "ammonium ion", an "imidazolium ion", a "pyridinium ion", a "pyrrolidinium ion", a "piperidinium ion", or a "phosphonium ion". Among them, M 51 + is particularly preferably a lithium ion.

[0075] Examples of the sulfonate represented by formula (V) include lithium fluorosulfonate (LiSO3F) represented by the following formula (V-1-1), lithium trifluoromethanesulfonate represented by the following formula (V-1-2), etc. The non-aqueous electrolyte may contain one type of sulfonate represented by formula (V), or may contain two or more types of sulfonates represented by formula (V).

[0076]

Chemical formula

[0077] The total content of the sulfonate represented by the formula (V) in the non-aqueous electrolyte is usually 0.01% by mass or more and 5.0% by mass or less, preferably 0.05% by mass or more, more preferably 0.1% by mass or more, still more preferably 0.3% by mass or more as the lower limit value, and preferably 4.0% by mass or less, more preferably 3.0% by mass or less, still more preferably 2.0% by mass or less, particularly preferably 1.5% by mass or less with respect to the total amount of the non-aqueous electrolyte (when the total amount of the non-aqueous electrolyte is 100% by mass). When the total content of these compounds is within the above range, the capacity retention rate and the resistance increase rate after charge and discharge cycles can be controlled to good values, and more excellent battery characteristics can be achieved.

[0078] (Cyclic sulfate compound represented by formula (VI)) The non-aqueous electrolyte preferably further contains a cyclic sulfate compound represented by the following formula (VI).

[0079]

Chemical formula

[0080] In formula (VI), R 61 represents "a group represented by formula (vi-1)", "a group represented by formula (vi-2)", or "a divalent hydrocarbon group having 1 to 6 carbon atoms". In R 61 , the "divalent hydrocarbon group" has the same meaning as in the case of R 31 .

[0081]

Chemical formula

[0082] R 61 When it is a hydrocarbon group, the number of carbon atoms is preferably 5 or less, more preferably 4 or less, still more preferably 3 or less.

[0083] The wavy lines in Formula (vi-1) and Formula (vi-2) mean that their ends are respectively bonded to the oxygen atoms (-O-) that constitute the two oxa groups in Formula (VI), forming a cyclic sulfate structure. Also, R 62 represents an oxa group (-O-), or a divalent hydrocarbon group having 1 to 6 carbon atoms which may contain an oxa group (-O-) at the terminal or in the chain. Specifically, R 62 can be an "oxymethylene group (-OCH2 -)", an "oxyethylene group (-OCH2CH2 -)", an "oxa group (-O -)", or a "divalent hydrocarbon group having 1 to 6 carbon atoms". In R 62 , the "divalent hydrocarbon group" has the same meaning as in the case of R 31 . Also, when R 62 is an oxymethylene group (-OCH2 -), an oxyethylene group (-OCH2CH2 -), or an oxa group (-O -), it means that the oxa group is bonded to the sulfur atom (-S(=O)2O -) in Formula (vi-1), forming a cyclic sulfate structure.

[0084] R 62 is particularly preferably an oxymethylene group (-OCH2 -) or an oxyethylene group (-OCH2CH2 -).

[0085] R 63 represents a "hydrocarbon group having 1 to 8 carbon atoms" or a "hydrogen atom (-H)". Examples of R 63 include a methyl group (-CH3), an ethyl group (-CH2CH3), a vinyl group (-CH=CH2), an n-propyl group (-CH2CH2CH3), an i-propyl group (-CH(CH3)2), an n-butyl group (-CH2CH2CH2CH3), an s-butyl group (-CH2CH(CH3)2), a t-butyl group (-C(CH3)2), a hexyl group (-CH2CH2CH2CH2CH2CH3), a cyclohexyl group (-C6H 11 ), and a phenyl group (-C6H5). Among them, R 63 is particularly preferably an n-butyl group (-CH2CH2CH2CH3) or a hydrogen atom (-H).

[0086] Examples of the cyclic sulfate compound represented by formula (VI) include a cyclic sulfate compound represented by the following formula (VI-1-1), a cyclic sulfate compound represented by the following formula (VI-2-1), a cyclic sulfate compound represented by the following formula (VI-2-2), and the like. The non-aqueous electrolyte may contain one type of cyclic sulfate compound represented by formula (VI), or may contain two or more types of cyclic sulfate compounds represented by formula (VI).

[0087]

Chemical formula

[0088] The total content of the cyclic sulfate compound represented by formula (VI) in the non-aqueous electrolyte is usually 0.01% by mass to 5.0% by mass with respect to the total amount of the non-aqueous electrolyte (when the total amount of the non-aqueous electrolyte is 100% by mass). The lower limit is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, still more preferably 0.3% by mass or more. The upper limit is preferably 4.0% by mass or less, more preferably 3.0% by mass or less, still more preferably 2.0% by mass or less, and particularly preferably 1.5% by mass or less. When the total content of these compounds is within the above range, the capacity retention rate and the resistance increase rate after charge and discharge cycles can be controlled to good values, and more excellent battery characteristics can be achieved.

[0089] (Cyclic sulfonic acid ester compound represented by formula (VII)) The non-aqueous electrolyte preferably further contains a cyclic sulfonic acid ester compound represented by the following formula (VII).

[0090]

Chemical formula

[0091] The double solid and dotted line in formula (VII) means a single bond (-) or a double bond (=).

[0092] In formula (VII), R 71Each independently represents a "fluoro group (-F)", "chloro group (-Cl)", "bromo group (-Br)", "iodo group (-I)", "hydrofluorocarbon group having 1 to 12 carbon atoms", or "hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a fluoro group (-F), chloro group (-Cl), bromo group (-Br), iodo group (-I), and oxa group (-O-)" as a substituent. R 71 In, the "hydrofluorocarbon group" and the "hydrocarbon group" are synonymous with the case of R 11 The case is the same.

[0093] R 71 When R is a hydrofluorocarbon group, the number of carbon atoms is preferably 10 or less, more preferably 8 or less, still more preferably 6 or less, and particularly preferably 4 or less. Also, when R 71 is a hydrocarbon group, the number of carbon atoms is preferably 10 or less, more preferably 8 or less, still more preferably 6 or less, and particularly preferably 4 or less.

[0094] R 71 Examples of R include a fluoro group (-F), a trifluoromethyl group (-CF3), a pentafluoroethyl group (-C2F5), an n-heptafluoropropyl group (-C3F7), a methyl group (-CH3), an ethyl group (-CH2CH3), a vinyl group (-CH=CH2), an n-propyl group (-CH2CH2CH3), an i-propyl group (-CH(CH3)2), an n-butyl group (-CH2CH2CH2CH3), an s-butyl group (-CH2CH(CH3)2), a t-butyl group (-C(CH3)2), a hexyl group (-CH2CH2CH2CH2CH2CH3), a cyclohexyl group (-C6H 11 ), a phenyl group (-C6H5), a benzyl group (-CH2C6H5), a trifluoromethoxymethyl group (-CH2OCF3), and the like. Among them, as R 71 , a hydrogen atom (-H), a fluoro group (-F), a trifluoromethyl group (-CF3), a pentafluoroethyl group (-C2F5), and an n-heptafluoropropyl group (-C3F7) are particularly preferred.

[0095] j represents an integer from 0 to 3, preferably 0.

[0096] Examples of the cyclic sulfonic acid ester compound represented by formula (VII) include 1,3 - propene sultone (PRS) represented by the following formula (VII - 1 - 1), 1,3 - propane sultone (PS) represented by the following formula (VII - 1 - 2), etc. The non - aqueous electrolyte may contain one type of cyclic sulfonic acid ester compound represented by formula (VII) or may contain two or more types of cyclic sulfonic acid ester compounds represented by formula (VII).

[0097] [Chemical formula]

[0098] The total content of the cyclic sulfonic acid ester compound represented by formula (VII) in the non - aqueous electrolyte is usually 0.01% by mass to 5.0% by mass with respect to the total amount of the non - aqueous electrolyte (when the total amount of the non - aqueous electrolyte is 100% by mass). The lower limit is preferably 0.05% by mass or more, more preferably 0.1% by mass or more, still more preferably 0.3% by mass or more. The upper limit is preferably 4.0% by mass or less, more preferably 3.0% by mass or less, still more preferably 2.0% by mass or less, and particularly preferably 1.5% by mass or less. When the total content of these compounds is within the above range, the capacity retention rate and the resistance increase rate after charge - discharge cycles can be controlled to good values, and more excellent battery characteristics can be achieved.

[0099] (Non - aqueous solvent) The non - aqueous electrolyte contains a non - aqueous solvent. Various known non - aqueous solvents can be appropriately selected. The non - aqueous solvent may be only one type or two or more types.

[0100] Examples of the non-aqueous solvent include cyclic carbonates, fluorine-containing cyclic carbonates, chain carbonates, fluorine-containing chain carbonates, aliphatic carboxylic acid esters, fluorine-containing aliphatic carboxylic acid esters, γ-lactones, fluorine-containing γ-lactones, cyclic ethers, fluorine-containing cyclic ethers, chain ethers, fluorine-containing chain ethers, nitriles, amides, lactams, nitromethane, nitroethane, sulfolane, trimethyl phosphate, dimethyl sulfoxide, dimethyl sulfoxide phosphate, and the like.

[0101] Examples of the cyclic carbonates include ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and the like. Examples of the fluorine-containing cyclic carbonates include fluoroethylene carbonate (FEC), and the like. Examples of the chain carbonates include dimethyl carbonate (DMC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), dipropyl carbonate (DPC), and the like.

[0102] Examples of the aliphatic carboxylic acid esters include methyl formate, methyl acetate, methyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylbutyrate, ethyl formate, ethyl acetate, ethyl propionate, ethyl butyrate, ethyl isobutyrate, ethyl trimethylbutyrate, and the like. Examples of the γ-lactones include γ-butyrolactone, γ-valerolactone, and the like.

[0103] Examples of cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, tetrahydropyran, 1,3-dioxolane, 4-methyl-1,3-dioxolane, 1,3-dioxane, 1,4-dioxane, and the like. Examples of chain ethers include 1,2-ethoxyethane (DEE), ethoxymethoxyethane (EME), diethyl ether, 1,2-dimethoxyethane, 1,2-dibutoxyethane, and the like. Examples of nitriles include acetonitrile, glutaronitrile, adiponitrile, methoxyacetonitrile, 3-methoxypropionitrile, and the like. Examples of amides include N,N-dimethylformamide, and the like. Examples of lactams include N-methylpyrrolidinone, N-methyloxazolidinone, N,N'-dimethylimidazolidinone, and the like.

[0104] The non-aqueous solvent preferably contains at least one selected from the group consisting of cyclic carbonates, fluorine-containing cyclic carbonates, chain carbonates, and fluorine-containing chain carbonates. In this case, the total proportion of cyclic carbonates, fluorine-containing cyclic carbonates, chain carbonates, and fluorine-containing chain carbonates is preferably 50% by mass to 100% by mass, more preferably 60% by mass to 100% by mass, and still more preferably 80% by mass to 100% by mass with respect to the total amount of the non-aqueous solvent.

[0105] The non-aqueous solvent preferably contains at least one selected from the group consisting of cyclic carbonates and chain carbonates. In this case, the total proportion of cyclic carbonates and chain carbonates in the non-aqueous solvent is preferably 50% by mass to 100% by mass, more preferably 60% by mass to 100% by mass, and still more preferably 80% by mass to 100% by mass with respect to the total amount of the non-aqueous solvent.

[0106] The upper limit of the content of the non-aqueous solvent is preferably 99% by mass, preferably 97% by mass, and more preferably 90% by mass with respect to the total amount of the non-aqueous electrolyte. The lower limit of the content of the non-aqueous solvent is preferably 60% by mass or more, more preferably 70% by mass or more with respect to the total amount of the non-aqueous electrolyte.

[0107] From the viewpoint of further improving the dissociation property of the electrolyte and the mobility of ions, the intrinsic viscosity of the non-aqueous solvent is preferably 10.0 mPa·s or less at 25°C.

[0108] (Electrolyte) The non-aqueous electrolyte contains an electrolyte.

[0109] The electrolyte preferably contains at least one of a lithium salt containing fluorine (hereinafter sometimes referred to as "fluorine-containing lithium salt") and a lithium salt not containing fluorine.

[0110] Examples of the fluorine-containing lithium salt include inorganic acid anion salts and organic acid anion salts. Examples of the inorganic acid anion salt include lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium hexafluorotantalate (LiTaF6), etc. Examples of the organic acid anion salt include lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethanesulfonyl)imide (Li(CF3SO2)2N), lithium bis(pentafluoroethanesulfonyl)imide (Li(C2F5SO2)2N), etc. Among them, lithium hexafluorophosphate (LiPF6) is more preferable as the fluorine-containing lithium salt.

[0111] Examples of the lithium salt not containing fluorine include lithium perchlorate (LiClO4), lithium aluminum tetrachloride (LiAlCl4), lithium decachlorodecaborate (Li2B 10 Cl 10 ) etc.

[0112] When the electrolyte contains a fluorine-containing lithium salt, the content ratio of the fluorine-containing lithium salt is preferably 50% by mass to 100% by mass, more preferably 60% by mass to 100% by mass, and still more preferably 80% by mass to 100% by mass based on the total amount of the electrolyte. When the fluorine-containing lithium salt contains lithium hexafluorophosphate (LiPF6), the content ratio of lithium hexafluorophosphate (LiPF6) is preferably 50% by mass to 100% by mass, more preferably 60% by mass to 100% by mass, and still more preferably 80% by mass to 100% by mass based on the total amount of the electrolyte.

[0113] When the non-aqueous electrolyte contains an electrolyte, the concentration of the electrolyte in the non-aqueous electrolyte is preferably 0.1 mol / L to 3 mol / L, more preferably 0.5 mol / L to 2 mol / L.

[0114] When the non-aqueous electrolyte contains lithium hexafluorophosphate (LiPF6), the concentration of lithium hexafluorophosphate (LiPF6) in the non-aqueous electrolyte is preferably 0.1 mol / L to 3 mol / L, more preferably 0.5 mol / L to 2 mol / L.

[0115] <Non-aqueous electrolyte secondary battery> A non-aqueous electrolyte secondary battery, which is another aspect of the present disclosure, is a non-aqueous electrolyte secondary battery including a "positive electrode", a "negative electrode", the "non-aqueous electrolyte" of the present disclosure described above, and a "separator". Hereinafter, the "positive electrode", "negative electrode", "separator", etc. will be described in detail.

[0116] (Positive electrode) Generally, the positive electrode is prepared by dispersing a positive electrode active material, a binder, a conductive assistant and a thickener in a solvent to form a slurry, applying this slurry to a current collector, drying and compressing it to form a positive electrode composite layer (also called a "positive electrode active material layer") on the current collector.

[0117] Examples of the positive electrode active material include transition metal oxides or transition metal sulfides such as MoS2, TiS2, MnO2, and V2O5; LiCoO2, LiMnO2, LiMn2O4, LiNiO2, LiNiX Co (1-X) O2 (0 < X < 1), LiNi x Co y Mn z O2 (x, y, and z are each independently greater than 0 and less than 1.00, and the sum of x, y, and z is between 0.99 and 1.00.) (so-called "NCM"; for example, LiNi 0.33 Co 0.33 Mn 0.33 O2, LiNi 0.5 Co 0.3 Mn 0.2 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2) and other composite oxides composed of lithium and transition metals; Li t Ni 1-x-y Co x Al y O2 (t is between 0.95 and 1.15, x is between 0 and 0.3, y is between 0.1 and 0.2, and the sum of x and y is less than 0.5.) (so-called "NCA"; for example, LiNi 0.8 Co 0.15 Al 0.05 O2) and other composite oxides composed of lithium, transition metals, and typical metals; conductive polymer materials such as polyaniline, polythiophene, polypyrrole, polyacetylene, polyacene, dimercaptothiadiazole, and polyaniline composites; lithium iron phosphate (LiFePO4), lithium manganese phosphate (LiMnPO4), lithium manganese iron phosphate (LiMn x Fe 1-x PO4; 0 < x < 1), lithium cobalt phosphate (LiCoPO4), lithium nickel phosphate (LiNiPO4), and other lithium metal phosphates; etc.

[0118] Examples of the binder for the positive electrode include polyvinylidene fluoride, etc. Examples of the conductive assistant for the positive electrode include carbon black (e.g., acetylene black), amorphous whiskers, graphite, etc. Examples of the thickening agent for the positive electrode include carboxymethyl cellulose, etc. Further, examples of the solvent for the slurry for forming the positive electrode include organic solvents such as N-methylpyrrolidone.

[0119] The total content of the positive electrode active material in the positive electrode composite material layer is usually 70% by mass to 97% by mass, preferably 75% by mass or more and preferably 95% by mass or less when the total content of the positive electrode composite material layer is taken as 100% by mass.

[0120] Examples of the material of the current collector for the positive electrode include aluminum, aluminum alloy, stainless steel, nickel, titanium, tantalum, carbon cloth, carbon paper, etc.

[0121] (Negative electrode) Generally, the negative electrode is produced by dispersing a negative electrode active material, a binder, a conductive assistant and a thickening agent, if necessary, in a solvent to form a slurry, applying this slurry to a current collector, drying and compressing it to form a negative electrode composite material layer (also referred to as a "negative electrode active material layer") on the current collector.

[0122] The simple substance or compound serving as the negative electrode active material can be classified into (1) simple carbon substances and carbon compounds capable of doping / dedoping lithium ions, (2) metals and alloys capable of alloying with lithium, (3) oxides, nitrides, carbides, etc. capable of doping / dedoping lithium ions. When the negative electrode active material is simple silicon, etc., usually a simple substance or compound in the form of particles (powder) is used. Further, the negative electrode active material to be used is not limited to one type, and two or more types may be mixed and used.

[0123] As the negative electrode active material, it is preferable to contain at least one selected from the group consisting of silicon single crystal particles, silicon oxide particles, and silicon carbide particles. Further, as the negative electrode active material, in addition to at least one selected from the group consisting of silicon single crystal particles, silicon oxide particles, and silicon carbide particles, it is preferable to further contain carbon single crystal particles. Examples of the carbon single crystal particles include graphite (natural graphite, artificial graphite) particles, carbon black particles, activated carbon particles, amorphous carbon particles, etc. Examples of the artificial graphite include graphitized MCMB, graphitized MCF, etc. Examples of the amorphous carbon material include hard carbon, coke, mesocarbon microbeads (MCMB) fired at 1500 °C or lower, mesophase pitch carbon fiber (MCF), etc.

[0124] When the single substance or compound serving as the negative electrode active material is in the form of through particles (powder), specific shapes include fibrous, spherical, potato-shaped, and flake-shaped.

[0125] When the negative electrode active material contains carbon single crystal particles, the median diameter D50 of the carbon single crystal is usually 1 μm to 30 μm, preferably 10 μm or more, more preferably 15 μm or more, preferably 25 μm or less, and more preferably 20 μm or less.

[0126] When the negative electrode active material contains carbon single crystal particles, the BET specific surface area of the carbon single crystal is usually 1.0 m 2 / g to 5.0 m 2 / g, preferably 2.0 m 2 / g or more, more preferably 3.0 m 2 / g or more, preferably 4.5 m 2 / g or less, more preferably 4.0 m 2 / g or less.

[0127] The silicon oxide constituting the silicon oxide particles is SiO xIt can be represented by [the formula], where x is a variable. That is, the oxygen atom content in silicon oxide is not particularly limited, but x is usually 0 ≦ x < 2, preferably 0.2 or more, more preferably 0.4 or more, still more preferably 0.6 or more, and preferably 1.8 or less, more preferably 1.6 or less, still more preferably 1.4 or less.

[0128] The median diameter D50 of the silicon single crystal particles, silicon oxide particles, or silicon carbide particles is usually 0.5 μm to 20 μm, preferably 1.0 μm or more, more preferably 3.0 μm or more, and preferably 15 μm or less, more preferably 10 μm or less.

[0129] The BET specific surface area of the silicon single crystal particles, silicon oxide particles, or silicon carbide particles is usually 1.0 m 2 / g to 5.0 m 2 / g, preferably 1.5 m 2 / g or more, more preferably 2.0 m 2 / g or more, and preferably 4.5 m 2 / g or less, more preferably 4.0 m 2 / g or less.

[0130] When the negative electrode active material contains at least one selected from the group consisting of silicon single crystal particles, silicon oxide particles, and silicon carbide particles, the total charged mass of the silicon single crystal particles, silicon oxide particles, and silicon carbide particles in the negative electrode active material is preferably 30% by mass or less, can be 1% by mass to 20% by mass, preferably 3% by mass or more, more preferably 5% by mass or more, and preferably 18% by mass or less, more preferably 15% by mass or less, based on 100% by mass of the total charged mass of the entire negative electrode active material.

[0131] When the negative electrode active material contains carbon single - body particles and at least one selected from the group consisting of silicon single - body particles, silicon oxide particles, and silicon carbide particles, the total charged mass of the carbon single - body particles in the negative electrode active material is usually 70% to 99% by mass, preferably 80% by mass or more, preferably 95% by mass or less, more preferably 90% by mass or less, when the total charged mass of the entire negative electrode active material is 100% by mass. When the total charged mass of carbon single - body particles etc. is within the above range, it becomes easier to ensure the balance between the energy density and the capacity retention rate of the lithium - ion secondary battery.

[0132] The total content of the negative electrode active material in the negative electrode composite material layer is usually 70% to 99.5% by mass, preferably 75% by mass or more, preferably 99% by mass or less, when the entire negative electrode composite material layer is 100% by mass.

[0133] Examples of the binder for the negative electrode include styrene - butadiene rubber (SBR). The total content of the copolymer of the binder in the negative electrode composite material layer is usually 0.1% to 5% by mass, preferably 0.5% by mass or more, more preferably 1.0% by mass or more, preferably 3% by mass or less, more preferably 2% by mass or less, when the entire negative electrode composite material layer is 100% by mass.

[0134] The negative electrode composite material layer preferably further contains a conductive assistant. Examples of the conductive assistant for the negative electrode include carbon black (such as acetylene black), carbon nanotubes, amorphous whiskers, graphite, etc.

[0135] The total content of the conductive assistant in the negative electrode composite material layer is usually 0.01% to 3% by mass, preferably 0.05% by mass or more, more preferably 0.1% by mass or more, preferably 2% by mass or less, more preferably 1% by mass or less, when the entire negative electrode composite material layer is 100% by mass.

[0136] The negative electrode composite layer preferably further contains a thickening agent. By including a thickening agent, it becomes easier to adjust the viscosity of the slurry, improving productivity. Examples of the thickening agent for the negative electrode include cellulose derivatives such as carboxymethyl cellulose (CMC), carboxyethyl cellulose, and hydroxyethyl cellulose; polyoxyethylene and its modified products; polyvinyl alcohol and its modified products; polysaccharides; and the like.

[0137] When the total content of the thickening agent in the negative electrode composite layer is based on 100% by mass of the entire negative electrode composite layer, it is usually 0.1% to 5% by mass, preferably 0.5% by mass or more, more preferably 1.0% by mass or more, preferably 3% by mass or less, and more preferably 2% by mass or less.

[0138] The slurry may contain a solvent. Examples of the solvent include water, acetonitrile, N-methylpyrrolidone, acetylpyridine, cyclopentanone, dimethylformamide, dimethyl sulfoxide, methylformamide, methyl ethyl ketone, furfural, ethylenediamine, and the like. Note that the solvent may be a mixed solvent in which the aforementioned solvents are mixed.

[0139] Examples of the material of the current collector of the negative electrode include copper, nickel, stainless steel, nickel-plated steel, and the like.

[0140] <Separator> Examples of the separator in the non-aqueous electrolyte secondary battery which is one aspect of the present disclosure include a porous resin flat plate. Examples of the material of the porous resin flat plate include resin, non-woven fabric containing resin, and the like. Examples of the resin include polyethylene (PE), polypropylene (PP), polymethylpentene (PMP), polyester, cellulose, polyamide, and the like. Among them, the separator is preferably a porous resin sheet having a single-layer or multi-layer structure. The material of the porous resin sheet is mainly composed of one or more polyolefin resins. The thickness of the separator is preferably 5 μm to 30 μm. The separator is preferably disposed between the positive electrode and the negative electrode.

[0141] <Case> The shape of the case and the like are not particularly limited, and are appropriately selected according to the use of the lithium ion secondary battery precursor of the present disclosure and the like. Examples of the case include a case including a laminate film, a case including a battery can and a battery can lid, and the like.

[0142] <Specific Examples of Lithium Ion Secondary Battery Precursors> FIG. 1 is a schematic cross-sectional view showing a laminated lithium ion secondary battery precursor which is an example of the lithium ion secondary battery precursor of the present disclosure.

[0143] As shown in FIG. 1, the lithium ion secondary battery precursor 1 is a laminated battery precursor. Specifically, in the lithium ion secondary battery precursor 1, the battery element 10 is enclosed inside the exterior body 30. The exterior body 30 is formed of a laminate film. Each of the positive electrode lead 21 and the negative electrode lead 22 is attached to the battery element 10. Each of the positive electrode lead 21 and the negative electrode lead 22 is led out in opposite directions from the inside of the exterior body 30 toward the outside.

[0144] As shown in FIG. 1, the battery element 10 is formed by laminating a positive electrode 11, a separator 13, and a negative electrode 12. The positive electrode 11 is formed by forming a positive electrode composite layer 11B on both main surfaces of the positive electrode current collector 11A. The negative electrode 12 is formed by forming a negative electrode composite layer 12B on both main surfaces of the negative electrode current collector 12A. The positive electrode composite layer 11B formed on one main surface of the positive electrode current collector 11A of the positive electrode 11 and the negative electrode composite layer 12B formed on one main surface of the negative electrode current collector 12A of the negative electrode 12 adjacent to the positive electrode 11 face each other with the separator 13 interposed therebetween.

[0145] The non-aqueous electrolyte of the present disclosure is injected into the interior of the exterior body 30 of the lithium-ion secondary battery precursor 1. The non-aqueous electrolyte of the present disclosure penetrates the positive electrode composite material layer 11B, the separator 13, and the negative electrode composite material layer 12B. In the lithium-ion secondary battery precursor 1, one single battery layer 14 is formed by the adjacent positive electrode composite material layer 11B, separator 13, and negative electrode composite material layer 12B. Note that the positive electrode and the negative electrode may be those in which each active material layer is formed on one surface of each current collector.

[0146] Note that the lithium-ion secondary battery precursor 1 is a laminated lithium-ion secondary battery precursor, but the lithium-ion secondary battery precursor according to the present disclosure is not limited thereto, and for example, it may be a wound lithium-ion secondary battery precursor. In a wound lithium-ion secondary battery precursor, a positive electrode, a separator, a negative electrode, and a separator are stacked in this order and layered, and this is wound to form an electrical element. The wound lithium-ion secondary battery precursor includes a cylindrical lithium-ion secondary battery precursor and a rectangular lithium-ion secondary battery precursor.

[0147] As shown in FIG. 1, in the lithium-ion secondary battery precursor 1, the directions in which the positive electrode lead 21 and the negative electrode lead 22 each protrude from the interior of the exterior body 30 toward the exterior are opposite to the exterior body 30, but the present disclosure is not limited thereto. For example, the directions in which the positive electrode lead 21 and the negative electrode lead 22 each protrude from the interior of the exterior body 30 toward the exterior may be the same as the exterior body 30.

[0148] FIG. 2 is a schematic cross-sectional view showing a coin-type lithium-ion secondary battery precursor, which is another example of the lithium-ion secondary battery precursor of the present disclosure.

[0149] The coin-type lithium-ion secondary battery precursor shown in FIG. 2 includes a disk-shaped positive electrode 41, a disk-shaped negative electrode 42, and a separator 45 filled with a non-aqueous electrolyte disposed between the disk-shaped positive electrode 41 and the disk-shaped negative electrode 42. The lithium-ion secondary battery precursor may have spacer plates 47 and 48 formed of stainless steel, aluminum, or the like, which are disposed so as to sandwich a laminate including the disk-shaped positive electrode 41, the disk-shaped negative electrode 42, and the separator 45. In the lithium secondary electron precursor, a laminate formed by laminating the spacer plate 47, the disk-shaped positive electrode 41, the separator 45, the disk-shaped negative electrode 42, and the spacer plate 48 in this order is stored between a positive electrode can 43 (hereinafter also referred to as a "battery can") and a sealing plate 44 (hereinafter also referred to as a "battery can lid"). The positive electrode can 43 and the sealing plate 44 are caulked via a gasket 46 to seal the inside. In this example, the non-aqueous electrolyte of the present disclosure is used as the non-aqueous electrolyte injected into the separator 45.

[0150] 〔Lithium-ion secondary battery and method for manufacturing the same〕 The lithium-ion secondary battery of the present disclosure can be manufactured by charging and discharging the above-described lithium-ion secondary battery precursor. That is, the method for manufacturing a lithium-ion secondary battery of the present disclosure includes a step of preparing the above-described lithium-ion secondary battery precursor of the present disclosure (hereinafter also referred to as a "preparation step") and a step of charging and discharging the lithium-ion secondary battery precursor.

[0151] In the lithium-ion secondary battery and the method for manufacturing the same of the present disclosure, it is possible to maintain a high discharge capacity retention rate after charge and discharge cycles, particularly, and to suppress a low increase rate of resistance after charge and discharge cycles.

[0152] The preparation step may be a step of simply preparing a previously manufactured lithium-ion secondary battery precursor of the present disclosure for use in a step of charging and discharging, or may be a step of manufacturing a lithium-ion secondary battery precursor according to the present disclosure.

[0153] In the process of charging and discharging, the charging and discharging of the lithium-ion secondary battery precursor can be carried out according to a known method. In this process, the charging and discharging cycles may be repeated a plurality of times for the lithium-ion secondary battery precursor. By this charging and discharging, a SEI (Solid Electrolyte Interface) film is preferably formed on the surface of the positive electrode (especially the positive electrode active material) and / or the negative electrode (especially the negative electrode active material) in the lithium-ion secondary battery precursor.

[0154] In the process of charging and discharging, it is preferable to perform the combination of charging and discharging one or more times on the lithium-ion secondary battery precursor in an environment of 25°C to 70°C.

Example

[0155] Hereinafter, examples of the present disclosure will be shown, but the present disclosure is not limited to the following examples. Hereinafter, “%” means “mass %” unless otherwise specified.

[0156] 〔Example 1〕 <Preparation of non-aqueous electrolyte> Ethylene carbonate (hereinafter, “EC”), dimethyl carbonate (hereinafter, “DMC”), and ethyl methyl carbonate (hereinafter, “EMC”) were mixed at EC:DMC:EMC = 30:35:35 (volume ratio). Thereby, a mixed solvent was obtained as a non-aqueous solvent. To the obtained mixed solvent, LiPF6 as an electrolyte was dissolved so that the concentration in the finally obtained non-aqueous electrolyte became 1.0 mol / L to obtain an electrolyte (hereinafter, also referred to as “basic electrolyte”). An alkene compound represented by the following formula (I-1-1) was blended into the obtained basic electrolyte so that the content with respect to the total amount of the finally obtained non-aqueous electrolyte became 1.0 mass % to obtain a non-aqueous electrolyte.

[0157]

Chemical formula

[0158] <Fabrication of positive electrode> LiNi as the positive electrode active material 0.8 Co 0.1 Mn 0.1 O2 (94% by mass), carbon black (3% by mass) as a conductive assistant, and polyvinylidene fluoride (PVdF) (3% by mass) as a binder were mixed to obtain a mixture. The obtained mixture was dispersed in an N-methylpyrrolidone solvent to obtain a positive electrode composite slurry. An aluminum foil with a thickness of 20 μm was prepared as the positive electrode current collector. The obtained positive electrode composite slurry was coated on the aluminum foil, dried, and then rolled with a press to obtain a sheet-shaped positive electrode. The positive electrode consists of a positive electrode current collector and a positive electrode active material layer.

[0159] <Fabrication of the negative electrode> As the negative electrode active material, 92.15% by mass of graphite and 4.85% by mass of silicon monoxide (SiO x (x = 1), silicon monoxide), 1.5% by mass of sodium carboxymethyl cellulose dispersed in pure water as a thickener, and 1.5% by mass of styrene-butadiene rubber (SBR) dispersed in pure water as a binder were mixed to obtain a negative electrode composite slurry. A copper foil with a thickness of 10 μm was prepared as the negative electrode current collector. The obtained negative electrode composite slurry was coated on the copper foil, dried, and then rolled with a press to obtain a sheet-shaped negative electrode. The negative electrode consists of a negative electrode current collector and a negative electrode active material layer.

[0160] <Preparation of the separator> A porous polyethylene film was prepared as the separator.

[0161] <Fabrication of the lithium-ion secondary battery precursor> The negative electrode was punched out in a disk shape with a diameter of 14 mm, the positive electrode was punched out in a disk shape with a diameter of 13 mm, and the separator was punched out in a disk shape with a diameter of 17 mm. As a result, a coin-shaped negative electrode, a coin-shaped positive electrode, and a coin-shaped separator were obtained respectively. The obtained coin-shaped negative electrode, coin-shaped separator, and coin-shaped positive electrode were stacked in this order inside a stainless-steel battery can (size: 2032 size). Next, 20 μL of a non-aqueous electrolyte was injected into this battery can, and the separator, positive electrode, and negative electrode were impregnated with the non-aqueous electrolyte. Next, an aluminum plate (thickness 1.2 mm, diameter 16 mm) and a spring were placed on the positive electrode, and the battery can lid was caulked through a polypropylene gasket, thereby sealing the battery. Thus, a coin-type lithium-ion secondary battery precursor (i.e., a lithium-ion secondary battery before charging and discharging) having the configuration shown in Fig. 2 was obtained. The size of the lithium-ion secondary battery precursor was 20 mm in diameter and 3.2 mm in height.

[0162] <Fabrication of Lithium-Ion Secondary Battery> The above lithium-ion secondary battery precursor was repeatedly charged up to 4.2 V and discharged up to 2.5 V three times in the temperature range of 25 °C to 70 °C to obtain a lithium-ion secondary battery.

[0163] <Measurement of Initial Discharge Capacity> The above lithium-ion secondary battery was charged up to 4.2 V in a constant-temperature bath at 25 °C, and then discharged up to 2.5 V, and the discharge capacity [mAh] (hereinafter also referred to as "initial discharge capacity") was measured.

[0164] <Measurement of Initial Resistance Value> After the measurement of the initial discharge capacity, the lithium-ion secondary battery was charged up to 3.7 V, and then in a constant-temperature bath at -20 °C, the voltage drop amount (= voltage before discharge start - voltage at the 10th second after discharge start) for each CC10s discharge at each discharge rate of 0.1C to 1.0C was measured. Here, CC10s discharge means discharge performed for 10 seconds at a constant current (Constant Current). Based on the obtained voltage drop amounts and the respective current values (i.e., the respective current values corresponding to the discharge rates of 0.1C to 1.0C), the DC resistance [Ω] as the initial resistance value was measured.

[0165] <Charge and discharge cycle test> Next, the lithium ion secondary battery after the initial resistance measurement was subjected to constant current charging up to 4.2 V at a charging rate of 0.5C in a thermostat at 25°C. Then, it was discharged at a discharge rate of 0.5C until 2.5 V. The above charge and discharge cycle was repeated 50 times.

[0166] <Measurement of discharge capacity retention rate after charge and discharge cycle and calculation of relative value> Next, the discharge capacity of the lithium ion secondary battery after the charge and discharge cycle test was measured in the same manner as the initial discharge capacity. Also for Comparative Example 1 described later, the discharge capacity of the lithium ion secondary battery after the charge and discharge cycle test was measured by the same method. When the discharge capacity retention rate after the charge and discharge cycle of Comparative Example 1 was set to 100, the discharge capacity retention rate after the charge and discharge cycle of Example 1 was calculated as a relative value (see the following formula). Discharge capacity retention rate (relative value) after charge and discharge cycle of Example 1 = (Discharge capacity retention rate after charge and discharge cycle of Example 1) / (Discharge capacity retention rate after charge and discharge cycle of Comparative Example 1) × 100

[0167] <Measurement of resistance increase rate after charge and discharge cycle and calculation of relative value> Next, the resistance value of the lithium ion secondary battery after the charge and discharge cycle test was measured in the same manner as the initial resistance value. Also for Comparative Example 1 described later, the resistance value of the lithium ion secondary battery after the charge and discharge cycle test was measured by the same method. When the resistance increase rate after the charge and discharge cycle of Comparative Example 1 was set to 100, the resistance increase rate after the charge and discharge cycle of Example 1 was calculated as a relative value (see the following formula). Resistance increase rate (relative value) after charge and discharge cycle of Example 1 = (Resistance increase rate after charge and discharge cycle of Example 1) / (Resistance increase rate after charge and discharge cycle of Comparative Example 1) × 100

[0168] 〔Comparative Example 1〕 A non-aqueous electrolyte was prepared and a lithium-ion secondary battery was fabricated in the same manner as in Example 1, except that the alkene compound represented by formula (I-1-1) was not added to the non-aqueous electrolyte. Further, in the same manner as in Example 1, the discharge capacity retention rate after charge-discharge cycles and the resistance increase rate after charge-discharge cycles were measured, and the reference values of "discharge capacity retention rate (relative value) after charge-discharge cycles" and "resistance increase rate (relative value) after charge-discharge cycles" in Example 1 were used. The results are shown in Table 1.

[0169] [Example 2] A non-aqueous electrolyte was prepared and a lithium-ion secondary battery was fabricated in the same manner as in Example 1, except that the alkene compound represented by formula (I-1-1) was added so that its content relative to the total mass of the non-aqueous electrolyte was 2.0% by mass. Further, in the same manner as in Example 1, the discharge capacity retention rate after charge-discharge cycles and the resistance increase rate after charge-discharge cycles were measured, and relative values were calculated with the "discharge capacity retention rate after charge-discharge cycles" and "resistance increase rate after charge-discharge cycles" of the lithium-ion secondary battery in Comparative Example 1 set to 100, and used as the "discharge capacity retention rate (relative value) after charge-discharge cycles" and "resistance increase rate (relative value) after charge-discharge cycles". The results are shown in Table 1.

[0170] [Example 3] A non-aqueous electrolyte was prepared and a lithium-ion secondary battery was fabricated in the same manner as in Example 1, except that in addition to the alkene compound represented by formula (I-1-1), lithium difluorophosphate (LiPO2F2) represented by the following formula (II-1-1) was added so that its content relative to the total mass of the non-aqueous electrolyte was 1.0% by mass. Further, in the same manner as in Example 1, the discharge capacity retention rate after charge-discharge cycles and the resistance increase rate after charge-discharge cycles were measured, and relative values were calculated with the "discharge capacity retention rate after charge-discharge cycles" and "resistance increase rate after charge-discharge cycles" of the lithium-ion secondary battery in Comparative Example 1 set to 100, and used as the "discharge capacity retention rate (relative value) after charge-discharge cycles" and "resistance increase rate (relative value) after charge-discharge cycles". The results are shown in Table 1.

[0171] [Chemistry]

[0172] [Example 4] In addition to the alkene compound represented by the formula (I-1-1), a non-aqueous electrolyte was prepared by the same operation as described in Example 1 except that lithium bis(oxalato)borate (LiBOB) represented by the following formula (III-1-1) was added so that the content thereof with respect to the total mass of the non-aqueous electrolyte was 1.0% by mass, and a lithium ion secondary battery was prepared. Further, by the same operation as described in Example 1, the discharge capacity retention rate after charge-discharge cycles and the resistance increase rate after charge-discharge cycles were measured, and the relative values with the "discharge capacity retention rate after charge-discharge cycles" and the "resistance increase rate after charge-discharge cycles" of the lithium ion secondary battery of Comparative Example 1 being set to 100 were calculated, and the "discharge capacity retention rate (relative value) after charge-discharge cycles" and the "resistance increase rate (relative value) after charge-discharge cycles" were obtained. The results are shown in Table 1.

[0173] [Chemistry]

[0174] [Example 5] In addition to the alkene compound represented by the formula (I-1-1), a non-aqueous electrolyte was prepared by the same operation as described in Example 1 except that lithium bis(fluorosulfonyl)imide (LiFSI) represented by the following formula (IV-1-1) was added so that the content thereof with respect to the total mass of the non-aqueous electrolyte was 1.0% by mass, and a lithium ion secondary battery was prepared. Further, by the same operation as described in Example 1, the discharge capacity retention rate after charge-discharge cycles and the resistance increase rate after charge-discharge cycles were measured, and the relative values with the "discharge capacity retention rate after charge-discharge cycles" and the "resistance increase rate after charge-discharge cycles" of the lithium ion secondary battery of Comparative Example 1 being set to 100 were calculated, and the "discharge capacity retention rate (relative value) after charge-discharge cycles" and the "resistance increase rate (relative value) after charge-discharge cycles" were obtained. The results are shown in Table 1.

[0175] [Chemistry]

[0176] [Example 6] In addition to the alkene compound represented by the formula (I-1-1), a non-aqueous electrolyte was prepared by the same operation as described in Example 1 except that lithium fluorosulfonate (LiSO3F) represented by the following formula (V-1-1) was added so that the content thereof with respect to the total mass of the non-aqueous electrolyte was 1.0% by mass, and a lithium-ion secondary battery was prepared. Further, by the same operation as described in Example 1, the discharge capacity retention rate after charge-discharge cycles and the resistance increase rate after charge-discharge cycles were measured, and the relative values with the "discharge capacity retention rate after charge-discharge cycles" and the "resistance increase rate after charge-discharge cycles" of the lithium-ion secondary battery of Comparative Example 1 being set to 100 were calculated, and the "discharge capacity retention rate (relative value) after charge-discharge cycles" and the "resistance increase rate (relative value) after charge-discharge cycles" were obtained. The results are shown in Table 1.

[0177] [Chemical formula]

[0178] [Example 7] In addition to the alkene compound represented by the formula (I-1-1), a non-aqueous electrolyte was prepared by the same operation as described in Example 1 except that a cyclic sulfate compound represented by the following formula (VI-1-1) was added so that the content thereof with respect to the total mass of the non-aqueous electrolyte was 1.0% by mass, and a lithium-ion secondary battery was prepared. Further, by the same operation as described in Example 1, the discharge capacity retention rate after charge-discharge cycles and the resistance increase rate after charge-discharge cycles were measured, and the relative values with the "discharge capacity retention rate after charge-discharge cycles" and the "resistance increase rate after charge-discharge cycles" of the lithium-ion secondary battery of Comparative Example 1 being set to 100 were calculated, and the "discharge capacity retention rate (relative value) after charge-discharge cycles" and the "resistance increase rate (relative value) after charge-discharge cycles" were obtained. The results are shown in Table 1.

[0179] [Chemical formula]

[0180] [Example 8] In addition to the alkene compound represented by the formula (I-1-1), 1,3-propenesultone (PRS) represented by the following formula (VII-1-1) was added so that the content thereof with respect to the total mass of the non-aqueous electrolyte was 1.0% by mass. A non-aqueous electrolyte was prepared by the same operation as described in Example 1, and a lithium-ion secondary battery was prepared. Further, by the same operation as described in Example 1, the discharge capacity retention rate after charge and discharge cycles and the resistance increase rate after charge and discharge cycles were measured, and the "discharge capacity retention rate after charge and discharge cycles" and "resistance increase rate after charge and discharge cycles" of the lithium-ion secondary battery of Comparative Example 1 were set to 100. Relative values were calculated and used as the "discharge capacity retention rate (relative value) after charge and discharge cycles" and the "resistance increase rate (relative value) after charge and discharge cycles". The results are shown in Table 1.

[0181] [Chemical formula]

[0182] [Results] [Table 1]

[0183] As is clear from Table 1, the lithium-ion secondary batteries of Examples 1 to 8 using the non-aqueous electrolyte containing the alkene compound represented by the formula (I) have an increased capacity retention rate after charge and discharge cycles and a decreased resistance increase rate. Therefore, it can be said that the battery characteristics after charge and discharge cycles are superior to those of Comparative Example 1. Further, when at least one additive selected from the group consisting of the difluorophosphate represented by the formula (II-1), the salt represented by the formula (III), the imide salt represented by the formula (IV), the sulfonate represented by the formula (V), the cyclic sulfate ester compound represented by the formula (VI), and the cyclic sulfonate ester compound represented by the formula (VII) is further blended (the lithium-ion secondary batteries of Examples 3 to 8), the capacity retention rate after charge and discharge cycles further increases and the resistance increase rate further decreases. Therefore, it can be said that the battery characteristics after charge and discharge cycles are further superior.

Description of Symbols

[0184] 1…Lithium-ion secondary battery precursor 1, 10…Battery element, 11…Positive electrode, 12…Negative electrode, 13…Separator, 14…Single cell layer, 21…Positive electrode lead, 22…Negative electrode lead, 30…Outer package, 41…Disk-shaped positive electrode, 42…Disk-shaped negative electrode, 43…Positive electrode can, 44…Sealing plate, 45…Separator 46…Gasket, 47…Spacer plate, 48…Spacer plate

Claims

1. A non-aqueous electrolyte containing an alkene compound represented by the following formula (I). 【Chemical 1】 (In formula (I), R １１ represents a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), an iodo group (-I), a hydrogen atom (-H), a fluorocarbon group having 1 to 12 carbon atoms, or a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), an iodo group (-I), and an oxa group (-O-) as substituents. A hydrocarbon group having 1 to 12 carbon atoms that may contain at least one functional group selected from the group consisting of, R １２ represents a hydrogen atom (-H), a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), an iodo group (-I), a fluorocarbon group having 1 to 12 carbon atoms, or a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), an iodo group (-I), and an oxa group (-O-) as substituents. A hydrocarbon group having 1 to 12 carbon atoms that may contain at least one functional group selected from the group consisting of, R １３ each independently represents a silyl group represented by the following formula (s-1), a hydrogen atom (-H), a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), an iodo group (-I), a fluorocarbon group having 1 to 12 carbon atoms, or a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), an iodo group (-I), and an oxa group (-O-) as substituents. A hydrocarbon group having 1 to 12 carbon atoms that may contain at least one functional group selected from the group consisting of.)) 【Chemical 2】 (In formula (s-1), R １４ each independently represents a hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), an iodo group (-I), and an oxa group (-O-).)

2. Furthermore, at least one additive selected from the group consisting of a difluorophosphate represented by the following formula (II-1), a monofluorophosphate represented by the following formula (II-2), a salt represented by the following formula (III), an imide salt represented by the following formula (IV), a sulfonate represented by the following formula (V), a cyclic sulfate compound represented by the following formula (VI), and a cyclic sulfonate compound represented by the following formula (VII). The non-aqueous electrolyte according to Claim 1. [Chemical Formula 3] (In formulas (II-1) and (II-2), M ２１ ＋ each independently represents an alkali metal ion, an alkaline earth metal ion, an ammonium ion, an imidazolium ion, a pyridinium ion, a pyrrolidinium ion, a piperidinium ion, or a phosphonium ion.) In formula (III), R ３１ each independently represents a single bond (-), or a divalent hydrocarbon group having 1 to 6 carbon atoms which may contain at least one functional group selected from the group consisting of a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), and an iodo group (-I) as a substituent, and Q ３１ each independently represents an oxa group (-O-) or a secondary amino group (-NH-), and X ３１ each independently represents a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), or an iodo group (-I), Z ３１ represents a boron atom or a phosphorus atom, and M ３１ ＋ represents an alkali metal ion, an alkaline earth metal ion, an ammonium ion, an imidazolium ion, a pyridinium ion, a pyrrolidinium ion, a piperidinium ion, or a phosphonium ion. h represents 1 or 2 when the said Z ３１ is a boron atom, and represents an integer of 1 to 3 when the said Z ３１ is a phosphorus atom. i represents 0 or 2 when the said Z ３１ is a boron atom, and represents 0, 2, or 4 when the said Z ３１ is a phosphorus atom. In formula (IV), R ４１ each independently represents a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), an iodo group (-I), a fluorocarbon group having 1 to 12 carbon atoms, or a hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a fluoro group (-F), a chloro group (-Cl), a bromo group (-Br), an iodo group (-I), and an oxa group (-O-), and M ４１ ＋ represents an alkali metal ion, an alkaline earth metal ion, an ammonium ion, an imidazolium ion, a pyridinium ion, a pyrrolidinium ion, a piperidinium ion, or a phosphonium ion. In formula (V), R ５１ represents a fluoro group (–F), a chloro group (–Cl), a bromo group (–Br), an iodo group (–I), a fluorocarbon group having 1 to 12 carbon atoms, or a hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a fluoro group (–F), a chloro group (–Cl), a bromo group (–Br), an iodo group (–I), and an oxa group (–O–) as a substituent, and M ５１ ＋ represents an alkali metal ion, an alkaline earth metal ion, an ammonium ion, an imidazolium ion, a pyridinium ion, a pyrrolidinium ion, a piperidinium ion, or a phosphonium ion. In formula (VI), R ６１ represents a group represented by formula (vi-1), a group represented by formula (vi-2), or a divalent hydrocarbon group having 1 to 6 carbon atoms. In formula (VII), R ７１ each independently represents a fluoro group (–F), a chloro group (–Cl), a bromo group (–Br), an iodo group (–I), a fluorocarbon group having 1 to 12 carbon atoms, or a hydrocarbon group having 1 to 12 carbon atoms which may contain at least one functional group selected from the group consisting of a fluoro group (–F), a chloro group (–Cl), a bromo group (–Br), an iodo group (–I), and an oxa group (–O–) as a substituent, and j represents an integer of 0 to 3.) [Chemical Formula 4] (In formula (vi-1), R ６２ represents an oxa group (—O—) or a divalent hydrocarbon group having 1 to 6 carbon atoms which may contain an oxa group (—O—) at the terminal or in the chain, In formula (vi-2), R ６３ represents a hydrocarbon group having 1 to 8 carbon atoms or a hydrogen atom (-H).)

3. A non-aqueous electrolyte secondary battery comprising a positive electrode, a negative electrode, the non-aqueous electrolyte according to Claim 1 or Claim 2, and a separator.

4. The negative electrode includes a current collector and a negative electrode composite material layer provided on the current collector and containing a negative electrode active material. The non-aqueous electrolyte secondary battery according to Claim 3, wherein the negative electrode active material includes at least one selected from the group consisting of silicon single crystal particles, silicon oxide particles, and silicon carbide particles.

5. The non-aqueous electrolyte secondary battery according to Claim 4, wherein the negative electrode active material further includes carbon single crystal particles.

6. When the total charged mass of at least one selected from the group consisting of the silicon single crystal particles, the silicon oxide particles, and the silicon carbide particles is 100% by mass of the total charged mass of the entire negative electrode active material, it is 30% by mass or less. The non-aqueous electrolyte secondary battery according to Claim 4.

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