Non-aqueous electrolyte for secondary battery and secondary battery with the same

Abstract

To provide a non-aqueous electrolyte capable of preferably suppressing an increase of an internal resistance in a secondary battery to be used under a high voltage while having a good holding characteristic of electric capacitance under a high temperature environment, and to provide a secondary battery having the same.SOLUTION: A non-aqueous electrolyte contains an electrolyte and a non-aqueous solvent, and in addition, contains at least one kind of fluorophosphoric acid represented by the following formula (1) as an additive agent. (M+ is an alkali metal ion; each of R1 to R5 is a hydrocarbon group or the like of which the number of hydrogen atoms and the number of carbons are 1 to 10, independently; or each of R1 to R5 is any one of an alkoxy group or the like in which the hydrocarbon group having 1 to 10 carbon atoms and an alkoxy group having 1 to 10 carbon atoms. An annular structure is formed by mutually coupling a combination that is optionally selected, and n is an integer value of 0 to 10.)SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a nonaqueous electrolyte for secondary batteries, which has excellent capacitance retention characteristics and suppression of an increase in internal resistance when stored in a high-temperature environment, for example, for secondary batteries used at high voltage, and also has excellent capacitance retention characteristics when repeatedly charged and discharged, and a secondary battery including the same. [Background technology]

[0002] Lithium-ion secondary batteries, which are small and have high battery capacity, have come into widespread use as power sources for portable information terminals such as laptops, digital cameras, mobile phones, smartphones, and tablets. In recent years, lithium-ion secondary batteries have been installed in electric vehicles (xEVs) as a key device toward achieving carbon neutrality. In addition, their uses are expanding to include household power sources and stationary storage batteries for power storage systems such as mega solar power generation, and therefore the development of lithium-ion secondary batteries with higher energy density is underway.

[0003] Conventional lithium-ion secondary batteries use materials that can reversibly insert Li ions into the positive and negative electrode active materials. For example, the positive electrode active material is LiNiO 2 , LiCoO 2 , LiMn 2 O 4 , or LiFePO 4 The negative electrode active material is made of lithium metal, its alloy, carbon material, graphite material, etc. The electrolyte used in the lithium ion secondary battery is a mixture of ethylene carbonate, diethyl carbonate, propylene carbonate, etc., and LiPF 6 , LiBF 4 In the present invention, a material in which an electrolyte such as the above is dissolved is used.

[0004] Here, it is generally understood that a stable film (SEI: Solid Electrolyte Interphase) that has lithium ion conductivity but no electronic conductivity is formed at the interface between the electrode active material layer and the electrolyte. The process of insertion and desorption of lithium ions into the electrode active material is highly reversible, but when the electrode is stored for a long period of time under high temperature conditions or when it is repeatedly charged and discharged under high voltage conditions, cracks, dissolution, and decomposition occur in the SEI, and the accumulation of gas and decomposition products generated by this hinders the movement of lithium ions, causing the internal resistance of the lithium ion secondary battery to increase and the battery performance to decrease. Therefore, it is important to determine how to form a stable SEI for the harsh usage environment and operating conditions of the lithium ion secondary battery. From this perspective, efforts have been made to form a stable SEI by adding additives to the electrolyte.

[0005] For example, Patent Document 1 discloses an electrolyte for a secondary battery that contains a non-aqueous solvent containing a monofluorophosphate ester salt and a lithium salt as a solute. According to Patent Document 1, by using an electrolyte for a secondary battery having such a composition, a good film can be formed on the electrode interface, and the formation of this film can suppress decomposition of the electrolyte for a secondary battery, thereby improving the capacity residual rate and the capacity recovery rate.

[0006] In addition, in lithium-ion secondary batteries, the positive electrode active material has been improved to improve the durability of the charge / discharge cycle and to increase the energy density in order to cope with harsh usage environments and operating conditions. For example, LiNiO 2 By using LiNiO, the charging voltage of the lithium-ion secondary battery can be increased and the energy density can be improved. 2 When LiNiO is used as the positive electrode active material, the theoretical battery capacity is high, but the thermal stability of the battery characteristics is low. 2Instead of Li, ternary transition metal oxides containing cobalt and manganese are also used as positive electrode active materials. Furthermore, due to concerns about the amount of cobalt in the earth as a natural resource, positive electrode active materials in which the composition ratio of cobalt is reduced and the composition ratio of nickel is increased are being developed. For example, Patent Document 2 describes Li x (Ni y M 1-y )O z (wherein M is one or more selected from the group consisting of Mn, Co, Mg, Al, Ti, Cr, Fe, Cu, and Zr, x is in the range of 0.9 to 1.2, y is in the range of 0.3 to 0.95, and z is in the range of 1.8 to 2.4), in which the composition ratio of nickel is increased to 75%, is used as a positive electrode active material. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] International Publication No. 2016 / 024496 [Patent Document 2] International Publication No. 2010 / 113583 Summary of the Invention [Problem to be solved by the invention]

[0008] However, in the lithium ion secondary battery using the secondary battery electrolyte of Patent Document 1, satisfactory battery characteristics cannot be obtained when it is operated at a high charging voltage, and further improvements are required. In particular, in a high-voltage lithium ion secondary battery using a ternary transition metal oxide with a high nickel composition ratio as the positive electrode active material as disclosed in Patent Document 2, there is a problem that the electric capacity retention performance when stored in a high-temperature environment is insufficient and the internal resistance also increases.

[0009] The present invention has been made in consideration of the above problems, and an object of the present invention is to provide a nonaqueous electrolyte for a secondary battery, which has excellent electric capacity retention characteristics when stored in a high-temperature environment in a secondary battery used at high voltage, effectively suppresses an increase in internal resistance, and exhibits good electric capacity retention characteristics even when repeatedly charged and discharged at a high charging voltage after storage in a high-temperature environment, and a secondary battery including the same. [Means for solving the problem]

[0010] In order to solve the above-mentioned problems, the nonaqueous electrolyte solution for a secondary battery of the present invention is a nonaqueous electrolyte solution for a secondary battery comprising an electrolyte and a nonaqueous solvent, and further comprising at least one kind of fluorophosphate represented by the following chemical formula (1) as an additive:

[0011] [ka] (In the formula, M + R represents an alkali metal ion. 1 ~R 5 each independently represents a hydrogen atom; a hydrocarbon group having 1 to 10 carbon atoms; an alkoxy group having 1 to 10 carbon atoms; a hydrocarbon group having 1 to 10 carbon atoms and having at least one of a halogen atom or an unsaturated bond; or an alkoxy group having 1 to 10 carbon atoms and having at least one of a halogen atom or an unsaturated bond. 1 ~R 5 are each independently any of a hydrocarbon group having 1 to 10 carbon atoms; an alkoxy group having 1 to 10 carbon atoms; a hydrocarbon group having 1 to 20 carbon atoms and having at least one of a halogen atom, a hetero atom, or an unsaturated bond; or an alkoxy group having 1 to 20 carbon atoms and having at least one of a halogen atom, a hetero atom, or an unsaturated bond, any combination of which is bonded to each other to form a cyclic structure. n represents an integer of 0 to 10.

[0012] In the above-mentioned composition, the amount of the fluorophosphate added is preferably within a range of 0.01% by mass or more and 2% by mass or less with respect to the total mass of the nonaqueous electrolyte for a secondary battery.

[0013] In the above-mentioned configuration, the fluorophosphate is preferably lithium phenyl fluorophosphate, sodium phenyl fluorophosphate, lithium benzyl fluorophosphate, sodium benzyl fluorophosphate, lithium 4-tert-amylphenyl fluorophosphate, or sodium 4-tert-amylphenyl fluorophosphate.

[0014] The secondary battery according to the present invention is characterized by comprising at least the nonaqueous electrolyte for secondary batteries described above, a positive electrode, and a negative electrode.

[0015] In the above configuration, the charging voltage is preferably 4.3 V or higher.

[0016] In the above configuration, the secondary battery is preferably stored in an environment of 40° C. or higher after being charged with a charging voltage of 4.3 V or higher.

[0017] In the above-mentioned configuration, the positive electrode active material constituting the positive electrode active material layer in the positive electrode preferably contains a binary transition metal oxide or a ternary transition metal oxide. Effect of the Invention

[0018] According to the present invention, by adding at least one fluorophosphate represented by the above chemical formula (1) as an additive to a non-aqueous electrolyte for a secondary battery, even if a secondary battery used at high voltage is stored in a high temperature environment, an increase in the internal resistance of the secondary battery can be suppressed well. In addition, the electric capacity of the secondary battery can be well maintained, and the storage performance of the secondary battery can be improved. Furthermore, even if the secondary battery after storage in a high temperature environment is charged and discharged at a high charging voltage, a high discharge capacity can be maintained, and cycle characteristics can be improved. [Brief description of the drawings]

[0019] [Figure 1] 1 is a schematic cross-sectional view showing an outline of a lithium ion secondary battery including a nonaqueous electrolyte for a secondary battery according to one embodiment of the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] (Nonaqueous electrolyte for secondary batteries) The nonaqueous electrolyte for secondary batteries according to the present embodiment (hereinafter referred to as "nonaqueous electrolyte") contains at least an electrolyte, a nonaqueous solvent, and at least one kind of fluorophosphate as an additive. The nonaqueous electrolyte of the present embodiment is suitably used as an electrolyte for secondary batteries such as lithium ion secondary batteries used at high voltages.

[0021] In a lithium ion secondary battery, it is presumed that an irreversible decomposition reaction of the non-aqueous electrolyte occurs at the interface between the electrode and the non-aqueous electrolyte during initial charging, and a film is formed on the electrode surface. It is considered that the properties of the formed film, such as the withstand voltage, thermal stability, ion conductivity, morphology, and denseness, vary greatly depending on the electrode active material, the non-aqueous solvent, electrolyte, and additives in the non-aqueous electrolyte, and the composition ratio. In this embodiment, a fluorophosphate phenyl salt is added as an additive to the non-aqueous electrolyte to form a film on the surface of the electrode (electrode active material layer). Then, due to the properties of the withstand voltage and thermal stability of this film, when the lithium ion secondary battery is used at a high charging voltage, it is considered that the capacity retention property and the suppression of the internal resistance increase when stored in a high temperature environment are excellent, and the capacity is well maintained even when the battery is repeatedly charged and discharged after storage in a high temperature environment, and excellent cycle characteristics are obtained.

[0022] In this specification, the phrase "containing a fluorophosphate as an additive" in the non-aqueous electrolyte means that the fluorophosphate is contained so as to function as an additive, separately from the electrolyte and the non-aqueous solvent. Here, the fluorophosphate functions as an additive in that it forms a film having properties such as voltage resistance and thermal stability on the surface of the electrode (electrode active material layer), as described above.

[0023] <Fluorophosphate> The fluorophosphate of the present embodiment is represented by the following chemical formula (1).

[0024] [ka]

[0025] In the above chemical formula (1), the M + represents an alkali metal ion. The alkali metal ion is not particularly limited, and examples thereof include a lithium ion, a sodium ion, a potassium ion, a rubidium ion, and a cesium ion. These may be used alone or in combination of two or more.

[0026] Said M + Among the above, lithium ions are preferred from the viewpoint of battery characteristics, and lithium ions and sodium ions are preferred from the viewpoints of availability and ease of synthesis of fluorophosphates.

[0027] In the above chemical formula (1), R 1 ~R 5 each independently represents a hydrogen atom; a hydrocarbon group having 1 to 10 carbon atoms; an alkoxy group having 1 to 10 carbon atoms; a hydrocarbon group having 1 to 10 carbon atoms and having at least one of a halogen atom or an unsaturated bond (hereinafter referred to as a "hydrocarbon group having a halogen atom, etc."); or an alkoxy group having 1 to 10 carbon atoms and having at least one of a halogen atom or an unsaturated bond (hereinafter referred to as an "alkoxy group having a halogen atom, etc."). 1 ~R 5each independently represents any of a hydrocarbon group having 1 to 10 carbon atoms; an alkoxy group having 1 to 10 carbon atoms; a hydrocarbon group having 1 to 20 carbon atoms and having at least one of a halogen atom, a hetero atom, or an unsaturated bond; or an alkoxy group having 1 to 20 carbon atoms and having at least one of a halogen atom, a hetero atom, or an unsaturated bond, any combination of which is bonded to each other to form a cyclic structure.

[0028] In this specification, when a range of carbon numbers is expressed, the range means that all integer carbon numbers included in the range are included. Therefore, for example, a hydrocarbon group having "1 to 3 carbon atoms" means all hydrocarbon groups having 1, 2, and 3 carbon atoms.

[0029] R 1 ~R 5 The hydrocarbon group having 1 to 10 carbon atoms is not particularly limited, and examples thereof include linear or branched chain alkyl groups and cyclic alkyl groups. Examples of the chain alkyl groups include methyl, ethyl, propyl, butyl, pentyl, hexyl, heptyl, octyl, nonyl, and decyl groups. Examples of the cyclic alkyl groups include cyclopentyl and cyclohexyl groups. The number of carbon atoms in the hydrocarbon group is preferably 1 to 8, and more preferably 1 to 6.

[0030] R 1 ~R 5 The alkoxy group having 1 to 10 carbon atoms is not particularly limited, and examples thereof include linear alkoxy groups and cyclic alkoxy groups. The linear alkoxy group is not particularly limited, and examples thereof include methoxy group, ethoxy group, propoxy group, butoxy group, pentoxy group, and hexoxy group. The cyclic alkoxy group is not particularly limited, and examples thereof include cyclopentoxy group and cyclohexoxy group. The number of carbon atoms in the alkoxy group is preferably 1 to 8, and more preferably 1 to 6.

[0031] R1 ~R 5 In the above, the hydrocarbon group having 1 to 10 carbon atoms and containing a halogen atom means a functional group in which some or all of the hydrogen atoms in the hydrocarbon group are substituted with halogen atoms. Examples of the halogen atom include fluorine, chlorine, bromine, and iodine atoms. Among the hydrocarbon group having 1 to 10 carbon atoms and containing a halogen atom, a hydrocarbon group having 1 to 8 carbon atoms and containing a halogen atom is preferred, and a hydrocarbon group having 1 to 6 carbon atoms and containing a halogen atom is more preferred.

[0032] R 1 ~R 5 In the above, the hydrocarbon group having 1 to 10 carbon atoms and an unsaturated bond means a hydrocarbon group having a carbon-carbon double bond or triple bond. The number of unsaturated bonds is preferably in the range of 1 to 6, more preferably in the range of 1 to 4, and particularly preferably in the range of 1 to 3.

[0033] The hydrocarbon group having a halogen atom or the like is not particularly limited, and examples thereof include a 2-iodoethyl group, a 2-bromoethyl group, a 2-chloroethyl group, a 2-fluoroethyl group, a 1,2-diiodoethyl group, a 1,2-dibromoethyl group, a 1,2-dichloroethyl group, a 1,2-difluoroethyl group, a 2,2-diiodoethyl group, a 2,2-dibromoethyl group, a 2,2-dichloroethyl group, a 2,2-difluoroethyl group, a 2,2,2-tribromoethyl group, a 2,2,2-trichloroethyl group, and the like. chain-like halogen-containing alkyl groups such as 2-iodocyclohexyl group, 2-bromocyclohexyl group, 2-chlorocyclohexyl group, and 2-fluorocyclohexyl group; chain-like alkenyl groups such as 2-propenyl group, isopropenyl group, 2-butenyl group, and 3-butenyl group; chain-like alkenyl groups such as 2-cyclopentenyl group, 2-cyclohexenyl group, and 3-cyclohexenyl group; Cyclic alkenyl groups; chain alkynyl groups such as 2-propynyl group, 1-butynyl group, 2-butynyl group, 3-butynyl group, 1-pentynyl group, 2-pentynyl group, 3-pentynyl group, and 4-pentynyl group; aryl groups such as phenyl group; alkoxyphenyl groups such as 3-methoxyphenyl group, 4-methoxyphenyl group, 3,5-dimethoxyphenyl group, and 4-phenoxyphenyl group; 2-iodophenyl group, 2-bromophenyl group, 2-chlorophenyl group, 2-fluorophenyl group, halogen-containing phenyl groups such as a 3-iodophenyl group, a 3-bromophenyl group, a 3-chlorophenyl group, a 3-fluorophenyl group, a 4-iodophenyl group, a 4-bromophenyl group, a 4-chlorophenyl group, a 4-fluorophenyl group, a 3,5-diiodophenyl group, a 3,5-dibromophenyl group, a 3,5-dichlorophenyl group, and a 3,5-difluorophenyl group; and naphthyl groups such as a 1-naphthyl group, a 2-naphthyl group, and a 3-amino-2-naphthyl group.

[0034] R 1 ~R 5In the above, the alkoxy group having 1 to 10 carbon atoms and containing a halogen atom means a functional group in which some or all of the hydrogen atoms in the alkoxy group are substituted with halogen atoms. Examples of the halogen atom include fluorine, chlorine, bromine, and iodine atoms. In the alkoxy group having 1 to 10 carbon atoms and containing a halogen atom, an alkoxy group having 1 to 8 carbon atoms and containing a halogen atom is preferred, and an alkoxy group having 1 to 6 carbon atoms and containing a halogen atom is more preferred.

[0035] R 1 ~R 5 In the above, the alkoxy group having 1 to 10 carbon atoms and an unsaturated bond means, for example, an alkoxy group having a carbon-carbon double bond or triple bond. The number of unsaturated bonds is preferably in the range of 1 to 6, more preferably in the range of 1 to 4, and particularly preferably in the range of 1 to 3.

[0036] The alkoxy group having a halogen atom or the like is not particularly limited, and examples thereof include a 2-iodoethoxy group, a 2-bromoethoxy group, a 2-chloroethoxy group, a 2-fluoroethoxy group, a 1,2-diiodoethoxy group, a 1,2-dibromoethoxy group, a 1,2-dichloroethoxy group, a 1,2-difluoroethoxy group, a 2,2-diiodoethoxy group, a 2,2-dibromoethoxy group, a 2,2-dichloroethoxy group, a 2,2-difluoroethoxy group, a 2,2,2-tribromoethoxy group, a 2,2,2 - Chain halogen-containing alkoxy groups such as trichloroethoxy, 2,2,2-trifluoroethoxy, and 1,1,1,3,3,3-hexafluoro-2-propoxy; cyclic halogen-containing alkoxy groups such as 2-iodocyclohexoxy, 2-bromocyclohexoxy, 2-chlorocyclohexoxy, and 2-fluorocyclohexoxy; chain alkenylalkoxy groups such as 2-propenoxy, isopropenoxy, 2-butenoxy, and 3-butenoxy; 2-cyclopentyloxy, 2-cyclopentyloxy, and 3-cyclopentyloxy; cyclic alkenylalkoxy groups such as phenoxy, 2-cyclohexenoxy, and 3-cyclohexenoxy; chain alkynylalkoxy groups such as 2-propynoxy, 1-butynoxy, 2-butynoxy, 3-butynoxy, 1-pentynoxy, 2-pentynoxy, 3-pentynoxy, and 4-pentynoxy; aryloxy groups such as phenoxy, 3-methylphenoxy, 4-methylphenoxy, and 3,5-dimethylphenoxy; and 2-iodophenoxy. Examples of halogen-containing phenoxy groups include a 2-bromophenoxy group, a 2-chlorophenoxy group, a 2-fluorophenoxy group, a 3-iodophenoxy group, a 3-bromophenoxy group, a 3-chlorophenoxy group, a 3-fluorophenoxy group, a 4-iodophenoxy group, a 4-bromophenoxy group, a 4-chlorophenoxy group, a 4-fluorophenoxy group, a 3,5-diiodophenoxy group, a 3,5-dibrophenoxy group, a 3,5-dichlorophenoxy group, and a 3,5-difluorophenoxy group.

[0037] R 1 ~R 5As described above, each of the groups may be independently any of a hydrocarbon group having 1 to 10 carbon atoms; an alkoxy group having 1 to 10 carbon atoms; a hydrocarbon group having 1 to 20 carbon atoms and having at least one of a halogen atom, a hetero atom, or an unsaturated bond; or an alkoxy group having 1 to 20 carbon atoms and having at least one of a halogen atom, a hetero atom, or an unsaturated bond, any combination of which may be bonded to each other to form a cyclic structure.

[0038] R 1 ~R 5 In the case where the ring structure is formed, the hydrocarbon group having 1 to 10 carbon atoms and the alkoxy group having 1 to 10 carbon atoms are the same as those described above, and therefore detailed description thereof will be omitted.

[0039] Also, the above R 1 ~R 5 In the case where the ring structure is formed, the hydrocarbon group having 1 to 20 carbon atoms and containing a halogen atom means a functional group in which some or all of the hydrogen atoms in the hydrocarbon group are substituted with halogen atoms. Examples of the halogen atom include fluorine, chlorine, bromine, and iodine atoms. The hydrocarbon group having 1 to 20 carbon atoms and containing a halogen atom is preferably a hydrocarbon group having 3 to 10 carbon atoms and more preferably a hydrocarbon group having 3 to 5 carbon atoms and containing a halogen atom.

[0040] Also, the above R 1 ~R 5 In the case where the ring structure is formed, the hydrocarbon group having a carbon number of 1 to 20 and a heteroatom means a functional group in which some or all of the hydrogen atoms and carbon atoms in the hydrocarbon group are substituted with heteroatoms. The heteroatom represents an atom such as oxygen, nitrogen, or sulfur. In the hydrocarbon group having a carbon number of 1 to 20 and a heteroatom, a hydrocarbon group having a carbon number of 2 to 10 and a heteroatom is more preferred, and a hydrocarbon group having a carbon number of 2 to 5 and a heteroatom is more preferred.

[0041] Also, the above R1 ~R 5 In the case where the ring structure is formed, the hydrocarbon group having 1 to 20 carbon atoms and an unsaturated bond means, for example, a hydrocarbon group having a carbon-carbon double bond or a triple bond. The number of unsaturated bonds is preferably in the range of 1 to 6, more preferably in the range of 1 to 4, and particularly preferably in the range of 1 to 3.

[0042] Also, the above R 1 ~R 5 In the case where the alkoxy group having 1 to 20 carbon atoms and containing a halogen atom forms the above-mentioned cyclic structure, the alkoxy group refers to a functional group in which some or all of the hydrogen atoms in the alkoxy group are substituted with halogen atoms. Examples of the halogen atom include fluorine, chlorine, bromine, and iodine atoms. In the alkoxy group having 1 to 20 carbon atoms and containing a halogen atom, an alkoxy group having 3 to 10 carbon atoms and containing a halogen atom is preferred, and an alkoxy group having 3 to 5 carbon atoms and containing a halogen atom is more preferred.

[0043] Also, the above R 1 ~R 5 In the case where the alkoxy group having a heteroatom has a carbon number of 1 to 20 and forms the above-mentioned cyclic structure, the alkoxy group having a heteroatom means a functional group in which some or all of the hydrogen atoms and carbon atoms in the alkoxy group are substituted with heteroatoms. The heteroatom represents an atom such as oxygen, nitrogen, or sulfur. In the alkoxy group having a heteroatom having a carbon number of 1 to 20, an alkoxy group having a heteroatom having a carbon number of 2 to 10 is preferred, and an alkoxy group having a heteroatom having a carbon number of 2 to 5 is more preferred.

[0044] Also, the above R 1 ~R 5 In the case where the cyclic structure is formed, the alkoxy group having 1 to 20 carbon atoms and an unsaturated bond means, for example, an alkoxy group having a carbon-carbon double bond or a triple bond. The number of unsaturated bonds is preferably in the range of 1 to 6, more preferably in the range of 1 to 4, and particularly preferably in the range of 1 to 3.

[0045] R 1 ~R 5Specific examples of the cyclic structure formed by any combination include linear alkylene groups such as methylene, ethylene, propylene, butylene, pentylene, hexylene, heptylene, octylene, and nonylene; iodomethylene, diiodomethylene, bromomethylene, dibromomethylene, fluoromethylene, difluoromethylene, iodoethylene, 1,1-diiodoethylene, 1,2-diiodoethylene, triiodoethylene, tetra ... halogen-containing linear alkylene groups such as a chloroethylene group, a chloroethylene group, a 1,1-dichloroethylene group, a 1,2-dichloroethylene group, a trichloroethylene group, a tetrachloroethylene group, a fluoroethylene group, a 1,1-difluoroethylene group, a 1,2-difluoroethylene group, a trifluoroethylene group, and a tetrafluoroethylene group; and cyclic hydrocarbon groups such as a cyclohexylene group, a phenylene group, a benzylene group, a naphthylene group, an anthracylene group, a naphthasylene group, and a pentasylene group.Further, linear alkylenedioxy groups such as a methylenedioxy group, an ethylenedioxy group, a propylenedioxy group, a butylenedioxy group, a pentylenedioxy group, a hexylenedioxy group, a heptylenedioxy group, an octylenedioxy group, and a nonylenedioxy group; cyclic alkylenedioxy groups such as a cyclohexylenedioxy group; an iodomethylenedioxy group, a diiodomethylenedioxy group, a bromomethylenedioxy group, a dibromomethylenedioxy group, a fluoromethylenedioxy group, a difluoromethylenedioxy group, an iodoethylenedioxy group, a 1,1-diiodoethylenedioxy group, a 1,2-diiodoethylenedioxy group, a triiodoethylenedioxy group, a tetraiodoethylenedioxy group, a chloroethylenedioxy group, a tetraiodo ... Examples of the halogen-containing linear alkylenedioxy groups include ethylenedioxy group, 1,1-dichloroethylenedioxy group, 1,2-dichloroethylenedioxy group, trichloroethylenedioxy group, tetrachloroethylenedioxy group, fluoroethylenedioxy group, 1,1-difluoroethylenedioxy group, 1,2-difluoroethylenedioxy group, trifluoroethylenedioxy group, and tetrafluoroethylenedioxy group; arylenedioxy groups such as phenylenedioxy group, benzylenedioxy group, naphthylenedioxy group, anthraciledioxy group, naphthaciledioxy group, and pentasiledioxy group; and those in which a part or all of these functional groups are replaced with halogen atoms, etc. Examples of the halogen atoms include fluorine, chlorine, bromine, and iodine atoms.

[0046] In the above chemical formula (1), n ​​represents an integer of 0 to 10. When n is 0, the fluorophosphate represented by chemical formula (1) has a structure in which the phosphate skeleton and the benzene skeleton are directly bonded to each other, as shown below.

[0047] [ka] (In the formula, M + , and R 1 ~R 5 is the same as in the previous case.)

[0048] When n is an integer of 1 to 10, -(CH 2 ) n - is a methylene group (n=1), an ethylene group (n=2), a propylene group (n=3), a butylene group (n=4), a pentylene group (n=5), a hexylene group (n=6), a heptylene group (n=7), an octylene group (n=8), a nonylene group (n=9), or a decanylene group (n=10). Among these, from the viewpoint of availability, a methylene group, an ethylene group, a propylene group, a butylene group, a pentylene group, and a hexylene group, in which n is in the range of 1 to 6, are preferred. In addition, -(CH 2 ) n - may be either linear or branched.

[0049] Of the fluorophosphates represented by chemical formula (1), lithium phenyl fluorophosphate, sodium phenyl fluorophosphate, lithium benzyl fluorophosphate, sodium benzyl fluorophosphate, lithium 4-tert-amylphenyl fluorophosphate, and sodium 4-tert-amylphenyl fluorophosphate are preferred from the viewpoints of resource amount and availability of raw materials.

[0050] The amount of the fluorophosphate added is preferably within the range of 0.01% by mass to 2% by mass, more preferably within the range of 0.05% by mass to 1% by mass, and even more preferably within the range of 0.1% by mass to 0.5% by mass, based on the total mass of the non-aqueous electrolyte. By making the amount added 0.01% by mass or more, it is possible to maintain a high discharge capacity even after storage in a high-temperature environment, and to further improve cycle characteristics even at a high charging voltage. On the other hand, by making the amount added 2% by mass or less, it is possible to maintain good solubility of the fluorophosphate in the non-aqueous solvent. Here, "solubility" means that 0.005 g or more of the fluorophosphate dissolves in 100 g of the non-aqueous solvent at 25°C.

[0051] <Electrolytes> The electrolyte may be any known electrolyte used in various secondary batteries. From the viewpoint of solubility in a non-aqueous solvent and the characteristics of the secondary battery, the electrolyte preferably has an alkali metal ion as a cation. Examples of the alkali metal ion include lithium ion, sodium ion, and potassium ion. For example, when the secondary battery is a lithium ion secondary battery, a lithium salt may be used as the electrolyte.

[0052] The electrolyte preferably has a fluorine-containing anion. The fluorine-containing anion is not particularly limited, and for example, BF 4 - , P.F. 6 - , B.F. 3 CF 3 - , B.F. 3 C 2 F 5 - , C.F. 3 SO 3 - , C 2 F 5 SO 3 - , C 3 F 7 SO 3 - , C 4 F 9 SO 3 - , N(SO 2 F) 2 - , N(CF 3 SO 2 ) 2 - , N(C 2 F 5 SO 2 ) 2 - , N(CF 3 SO 2 )(CF 3 CO) - , N(CF 3 SO 2 )(C 2 F 5 SO 2 ) -, and C(CF 3 SO 2 ) 3 - The electrolytes having these fluorine-containing anions can be used alone or in combination of two or more. Among the fluorine-containing anions, from the viewpoints of safety and stability of the nonaqueous electrolyte, as well as improvement of electrical conductivity and cycle characteristics, BF 4 - , P.F. 6 - and N(CF 3 SO 2 ) 2 - is preferred, and BF 4 - and P.F. 6 - is particularly preferred.

[0053] The concentration of the electrolyte relative to the non-aqueous solvent is not particularly limited, but is usually within the range of 0.1 M to 2 M, preferably within the range of 0.15 M to 1.8 M, more preferably within the range of 0.2 M to 1.5 M, and particularly preferably within the range of 0.3 M to 1.2 M. By making the concentration of the electrolyte 0.1 M or more, it is possible to prevent the electrical conductivity of the non-aqueous electrolyte from becoming insufficient. On the other hand, by making the concentration of the electrolyte 2 M or less, it is possible to suppress the decrease in electrical conductivity due to an increase in the viscosity of the non-aqueous electrolyte, and to prevent the secondary battery performance from decreasing.

[0054] <Non-aqueous solvent> The non-aqueous solvent (organic solvent) used in the non-aqueous electrolyte is not particularly limited, and examples thereof include cyclic carbonate esters, chain carbonate esters, phosphate esters, cyclic ethers, chain ethers, lactone compounds, chain esters, nitrile compounds, amide compounds, and sulfone compounds. These non-aqueous solvents can be used alone or in combination of two or more. Among these non-aqueous solvents, cyclic carbonate esters and chain carbonate esters are preferred in this embodiment.

[0055] The cyclic carbonate ester is not particularly limited, and examples thereof include cyclic carbonate esters in which at least a portion of hydrogen atoms is substituted with fluorine atoms, such as ethylene carbonate, propylene carbonate, butylene carbonate, fluoroethylene carbonate, trans-difluoroethylene carbonate, and cis-difluoroethylene carbonate. These cyclic carbonate esters may be used alone or in combination of two or more.

[0056] The chain carbonate ester is not particularly limited, and examples thereof include dimethyl carbonate; ethyl methyl carbonate; diethyl carbonate; fluoromethyl methyl carbonate, difluoromethyl methyl carbonate, trifluoromethyl methyl carbonate, bis(fluoromethyl)carbonate, bis(difluoro)methyl carbonate, bis(trifluoromethyl)carbonate, 2-fluoroethyl methyl carbonate, ethyl fluoromethyl carbonate, 2,2-difluoroethyl methyl carbonate, 2-fluoroethyl fluoromethyl carbonate, ethyl difluoromethyl carbonate, 2,2,2-trifluoroethyl methyl carbonate, 2,2-difluoroethyl fluoromethyl carbonate, 2-fluoroethyl fluoromethyl carbonate, Examples of the chain carbonate ester include those in which at least a part of the hydrogen atoms is replaced by a fluorine atom, such as oroethyl difluoromethyl carbonate, ethyl trifluoromethyl carbonate, ethyl (2-fluoroethyl) carbonate, ethyl (2,2-difluoroethyl) carbonate, bis (2-fluoroethyl) carbonate, ethyl (2,2,2-trifluoroethyl) carbonate, 2,2-difluoroethyl-2'-fluoroethyl carbonate, bis (2,2-difluoroethyl) carbonate, 2,2,2-trifluoroethyl-2'-fluoroethyl carbonate, 2,2,2-trifluoroethyl-2',2'-difluoroethyl carbonate, and bis (2,2,2-trifluoroethyl) carbonate. These chain carbonate esters can be used alone or in combination of two or more.

[0057] The phosphate ester is not particularly limited, and examples thereof include phosphate esters in which at least a part of hydrogen atoms is replaced by fluorine atoms, such as trimethyl phosphate, triethyl phosphate, ethyl dimethyl phosphate, diethyl methyl phosphate, trifluoroethyl dimethyl phosphate, bis(trifluoroethyl)methyl phosphate, and tris(trifluoroethyl)phosphate. These phosphate esters can be used alone or in combination of two or more.

[0058] The cyclic ether is not particularly limited, and examples thereof include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, 1,3-dioxolane, etc. These cyclic ethers can be used alone or in combination of two or more.

[0059] The chain ether is not particularly limited, and examples thereof include dimethoxyethane, ethylene glycol diethyl ether, triethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, etc. These chain ethers can be used alone or in combination of two or more.

[0060] The lactone compound is not particularly limited, and examples thereof include γ-butyrolactone, γ-valerolactone, δ-valerolactone, etc. These lactone compounds may be used alone or in combination of two or more.

[0061] The chain ester is not particularly limited, and examples thereof include chain esters in which at least a portion of hydrogen atoms is substituted with fluorine atoms, such as methyl propionate, methyl acetate, ethyl acetate, methyl formate, methyl difluoroacetate, and ethyl trifluoroacetate. These chain esters may be used alone or in combination of two or more.

[0062] The nitrile compound is not particularly limited, and examples thereof include acetonitrile, adiponitrile, valeronitrile, etc. These nitrile compounds may be used alone or in combination of two or more.

[0063] The amide compound is not particularly limited, and examples thereof include dimethylformamide.

[0064] The sulfone compound is not particularly limited, and examples thereof include sulfolane, sulfolene, and 3-methylsulfolane, etc. These sulfone compounds may be used alone or in combination of two or more.

[0065] <Other additives> In the nonaqueous electrolyte of the present embodiment, other additives may be contained in addition to the nonaqueous solvent, electrolyte, and fluorophosphate for the purpose of improving the performance of the secondary battery.

[0066] The other additives are not particularly limited, and examples thereof include at least one compound selected from the group consisting of phosphorus compounds, boron compounds, acid anhydrides, cyclic carbonates having an unsaturated bond, sulfur compounds, and amines having an acetoacetyl group.

[0067] The phosphorus compound is not particularly limited in type and may be selected from a variety of compounds as long as they do not impair the characteristics of the nonaqueous electrolyte solution of the present embodiment and the secondary battery using the same. Examples of the phosphorus compound include phosphines, phosphonic acids, phosphates, phosphoric acid ester salts, and phosphorus complex salts.

[0068] Furthermore, the phosphines are not particularly limited, and examples thereof include trimerylphosphine, triethylphosphine, triisopropylphosphine, and triphenylphosphine. The phosphonic acids are not particularly limited, and examples thereof include dimethyl phosphite, diethyl phosphite, dibutyl phosphite, diphenyl phosphite, and bis(2,2,2,-trifluoroethyl)phosphite. The phosphates are not particularly limited, and examples thereof include lithium fluorophosphate, sodium fluorophosphate, potassium fluorophosphate, lithium difluorophosphate, sodium difluorophosphate, and potassium difluorophosphate. The phosphate ester salt is not particularly limited, and examples thereof include lithium dimethyl phosphate, sodium dimethyl phosphate, potassium dimethyl phosphate, lithium diethyl phosphate, sodium diethyl phosphate, potassium diethyl phosphate, lithium dipropyl phosphate, sodium dipropyl phosphate, potassium dipropyl phosphate, lithium diphenyl phosphate, sodium diphenyl phosphate, potassium diphenyl phosphate, lithium bis(2,2,2-trifluoroethyl)phosphate, sodium bis(2,2,2-trifluoroethyl)phosphate, potassium bis(2,2,2-trifluoroethyl)phosphate, lithium bis(1,1,1,3,3,3-hexafluoroisopropyl)phosphate, sodium bis(1,1,1,3,3,3-hexafluoroisopropyl)phosphate, potassium bis(1,1,1,3,3,3-hexafluoroisopropyl)phosphate, etc. The phosphorus complex salt is not particularly limited, and examples thereof include lithium difluorobisoxalate phosphate, sodium difluorobisoxalate phosphate, lithium tetrafluorooxalate phosphate, and sodium tetrafluorooxalate phosphate. From the viewpoints of availability and battery characteristics, the phosphorus compound is preferably lithium difluorophosphate, lithium difluorobisoxalate phosphate, or lithium tetrafluorooxalate phosphate.

[0069] The boron compound is not particularly limited in type and may be selected from a variety of compounds as long as it does not impair the characteristics of the nonaqueous electrolyte solution of the present embodiment and the secondary battery using the same. Examples of the boron compound include borate salts, borate esters, and boron complex salts.

[0070] The borate is not particularly limited, and examples thereof include lithium tetraborate, sodium tetraborate, potassium tetraborate, lithium tetrafluoroborate, sodium tetrafluoroborate, and potassium tetrafluoroborate. The borate ester is not particularly limited, and examples thereof include trimethyl borate, triethyl borate, triisopropyl borate, tributyl borate, tripentyl borate, trihexyl borate, triheptyl borate, triphenyl borate, tris(2,2,2-triiodoethyl) borate, tris(2,2,2-tribromoethyl) borate, tris(2,2,2-trichloroethyl) borate, tris(2,2,2-trifluoroethyl) borate, tris(4-iodophenyl) borate, tris(4-bromophenyl) borate, tris(4-chlorophenyl) borate, tris(4-fluorophenyl) borate, diethylmethyl borate, and ethyldimethyl borate. The boron complex salt is not particularly limited, and examples thereof include lithium difluorooxalatoborate, sodium difluorooxalatoborate, potassium difluorooxalatoborate, lithium bisoxalatoborate, sodium bisoxalatoborate, potassium bisoxalatoborate, lithium bissalicylate borate, sodium bissalicylate borate, potassium bissalicylate borate, lithium bis[1,2'-bendiolato(2)-O,O']borate, sodium bis[1,2'-bendiolato(2)-O,O']borate, and potassium bis[1,2'-bendiolato(2)-O,O']borate. In addition, as the boron compound, lithium difluorooxalatoborate, lithium bisoxalatoborate, and lithium bissalicylate borate are preferred from the viewpoints of availability and battery characteristics.

[0071] The acid anhydride is not particularly limited in type, and various types can be selected as long as it does not impair the characteristics of the nonaqueous electrolyte solution of the present embodiment and the secondary battery using the same. Specific examples of the acid anhydride include acetic anhydride, propionic anhydride, butyric anhydride, valeric anhydride, hexanoic anhydride, heptanoic anhydride, octanoic anhydride, nonanoic anhydride, decanoic anhydride, eicosanoic anhydride, docosanoic anhydride, benzoic anhydride, 4-methoxybenzoic anhydride, diphenylacetic anhydride, crotonic anhydride, cyclohexanecarboxylic anhydride, elaidic anhydride, isobutyric anhydride, isovaleric anhydride, lauric anhydride, linoleic anhydride, myristic anhydride, angelica anhydride, cyclohexane ... linear carboxylic acid anhydrides such as phthalic anhydride, chlorodifluoroacetic anhydride, trichloroacetic anhydride, difluoroacetic anhydride, trifluoroacetic anhydride, and 4-trifluoromethylbenzoic anhydride; phthalic anhydride, 3-acetamidophthalic anhydride, 4,4'-carbonyldiphthalic anhydride, 4,4'-biphthalic anhydride, 3-iodophthalic anhydride, 3-bromophthalic anhydride, 3-chlorophthalic anhydride, 3-fluorophthalic anhydride, 4-iodophthalic anhydride, 4-bromophthalic anhydride, 4-chlorophthalic anhydride, Phthalic anhydride, 4-fluorophthalic anhydride, 4,5-diiodophthalic anhydride, 4,5-dibromophthalic anhydride, 4,5-dichlorophthalic anhydride, 4,5-difluorophthalic anhydride, 4,4'-sulfonyldiphthalic anhydride, 3-nitrophthalic anhydride, 4-nitrophthalic anhydride, exo-3,6-epoxyhexahydrophthalic anhydride, exo-3,6-epoxy-1,2,3,6-tetrahydrophthalic anhydride, tetraiodophthalic anhydride, tetrachlorophthalic anhydride, tetrafluorophthalic anhydride phthalic anhydride, 4-tert-butylphthalic anhydride, 4-ethynylphthalic anhydride, 4,4'-(hexafluoroisopropylidene)diphthalic anhydride, succinic anhydride, (R)-(+)-2-acetoxysuccinic anhydride, (S)-(-)-2-acetoxysuccinic anhydride, 2-buten-1-ylsuccinic anhydride, butylsuccinic anhydride, decylsuccinic anhydride, 2,3-dimethylsuccinic anhydride, 2-dodecen-1-ylsuccinic anhydride, dodecylsuccinic anhydride, octadecenic anhydride, (2,7-Octadien-1-yl)succinic anhydride, n-octylsuccinic anhydride, hexadecylsuccinic anhydride, maleic anhydride, 2,3-bis(2,4,5-trimethyl-3-thienyl)maleic anhydride, 2-(2-carboxyethyl)-3-methyl-maleic anhydride, 2,3-dimethylmaleic anhydride, 2,3-diphenylmaleic anhydride, phenylmaleic anhydride, 4-pentene-1,2-dicarboxylic anhydride, 2,3-anthracene dicarboxylic anhydride, bicyclo[2,2,2]octo- 5-ene-2,3-dicarboxylic anhydride, 4-bromo-1,8-naphthalenedicarboxylic anhydride, (±)-trans-1,2-cyclohexanedicarboxylic anhydride, cis-4-cyclohexene-1,2-dicarboxylic anhydride, 2,5-dibromo-3,4-thiophenedicarboxylic anhydride, 5,6-dihydro-1,4-dithiine-2,3-dicarboxylic anhydride, 2,2'-biphenyldicarboxylic anhydride, 4-methylcyclohexane-1,2-dicarboxylic anhydride, 3-methyl-4-cyclohexene-1, 2-Dicarboxylic anhydride, 4-methyl-4-cyclohexene-1,2-dicarboxylic anhydride, 2,3-naphthalenedicarboxylic anhydride, 3,4-thiophenedicarboxylic anhydride, 1,8-naphthalenedicarboxylic anhydride, 5-norbornene-2,3-dicarboxylic anhydride, 1,2-cyclopropanedicarboxylic anhydride, glutaric anhydride, 3,3-pentamethyleneglutaric anhydride, 2,2-dimethylglutaric anhydride, 3,3-dimethylglutaric anhydride, 3-methylglutaric anhydride, 2-phthalimidoglutaric anhydride Isatoic anhydride, 3,3-tetramethyleneglutaric anhydride, N-methylisatoic anhydride, 4-iodoisatoic anhydride, 4-bromoisatoic anhydride, 4-chloroisatoic anhydride, 4-fluoroisatoic anhydride, 5-iodoisatoic anhydride, 5-bromoisatoic anhydride, 5-chloroisatoic anhydride, 5-fluoroisatoic anhydride, itaconic anhydride, caronic anhydride, citraconic anhydride, diglycolic anhydride, 1,2-naphthalic anhydride, pyromellitic anhydride, hett anhydride, and 2,2,3,3,4,Cyclic carboxylic anhydrides such as 4-hexafluoropentanedioic anhydride; linear sulfonic anhydrides such as trifluoromethanesulfonic anhydride and p-toluenesulfonic anhydride; cyclic sulfonic anhydrides such as 2-sulfobenzoic anhydride, tetraiodo-O-sulfobenzoic anhydride, tetrabromo-O-sulfobenzoic anhydride, tetrachloro-O-sulfobenzoic anhydride, and tetrafluoro-O-sulfobenzoic anhydride; linear phosphinic anhydrides such as diphenylphosphinic acid; cyclic phosphonic anhydrides such as 1-propanephosphonic anhydride; and 3,4-diiodophenyl Examples of the acid anhydride include boronic acid anhydride, 3,4-dibromophenylboronic acid anhydride, 3,4-dichlorophenylboronic acid anhydride, 3,4-difluorophenylboronic acid anhydride, 4-iodophenylboronic acid anhydride, 4-bromophenylboronic acid anhydride, 4-chlorophenylboronic acid anhydride, 4-fluorophenylboronic acid anhydride, m-terphenylboronic acid anhydride, 3,4,5-triiodophenylboronic acid anhydride, 3,4,5-tribromophenylboronic acid anhydride, 3,4,5-trichlorophenylboronic acid anhydride, and 3,4,5-trifluorophenylboronic acid anhydride. In addition, as the acid anhydride, maleic acid anhydride is preferable from the viewpoint of availability and battery characteristics.

[0072] The cyclic carbonate having an unsaturated bond is not particularly limited in type, and various types can be selected as long as it does not impair the characteristics of the nonaqueous electrolyte of the present embodiment and the secondary battery using the same. Examples of the cyclic carbonate having an unsaturated bond include vinylene carbonate, iodovinylene carbonate, bromovinylene carbonate, chlorovinylene carbonate, fluorovinylene carbonate, 1,2-diiodovinylene carbonate, 1,2-dibromovinylene carbonate, 1,2-dichlorovinylene carbonate, 1,2-difluorovinylene carbonate, methylvinylene carbonate, iodomethylvinylene carbonate, bromomethylvinylene carbonate, chloromethylvinylene carbonate, fluoromethylvinylene carbonate, dichlorovinylene carbonate, methyl ... Examples of the cyclic carbonate having an unsaturated bond include methyl vinylene carbonate, dibromomethyl vinylene carbonate, dichloromethyl vinylene carbonate, difluoromethyl vinylene carbonate, triiodomethyl vinylene carbonate, tribromomethyl vinylene carbonate, trichloromethyl vinylene carbonate, trifluoromethyl vinylene carbonate, ethyl vinylene carbonate, propyl vinylene carbonate, butyl vinylene carbonate, dimethyl vinylene carbonate, diethyl vinylene carbonate, dipropyl vinylene carbonate, and vinyl ethylene carbonate. In addition, as the cyclic carbonate having an unsaturated bond, vinylene carbonate and vinyl ethylene carbonate are preferable from the viewpoints of availability and battery characteristics.

[0073] The sulfur compound is not particularly limited in type and may be selected from a variety of compounds as long as it does not impair the characteristics of the nonaqueous electrolyte solution of the present embodiment and the secondary battery using the same. Examples of the sulfur compound include sulfates, sulfonates, sulfonic acid esters, and sulfones.

[0074] The sulfate salt is not particularly limited, and examples thereof include lithium sulfate, sodium sulfate, potassium sulfate, lithium fluorosulfate, sodium fluorosulfate, potassium fluorosulfate, lithium methylsulfate, sodium methylsulfate, potassium methylsulfate, lithium ethylsulfate, sodium ethylsulfate, and potassium ethylsulfate. The sulfonate salt is not particularly limited, and examples thereof include lithium trifluoromethanesulfonate, sodium trifluoromethanesulfonate, and potassium trifluoromethanesulfonate. The sulfonic acid ester is not particularly limited, and examples thereof include 1,3-propane sultone, 2,4-butane sultone, 1,4-butane sultone, ethylene sulfite, methyl methanesulfonate, and ethyl methanesulfonate. The sulfones are not particularly limited, and examples thereof include dimethyl sulfone, diethyl sulfone, diphenyl sulfone, methyl phenyl sulfone, sulfolane, and sulfolene. In addition, the sulfur compound is preferably lithium fluorosulfate, lithium trifluoromethanesulfonate, 1,3-propane sultone, or ethylene sulfite, in terms of availability and battery characteristics.

[0075] The amines having an acetoacetyl group are not particularly limited in type and can be selected from various types as long as they do not impair the characteristics of the nonaqueous electrolyte of the present embodiment and the secondary battery using the same. Examples of amines having an acetoacetyl group include N,N-dimethylacetoacetamide, N,N-diethylacetoacetamide, N,N-dipropylacetoacetamide, N,N-dibutylacetoacetamide, N,N-ethylmethylacetoacetamide, N,N-methylpropylacetoacetamide, and N,N-butylmethylacetoacetamide.

[0076] The content of the other additives can be appropriately set as necessary within a range that does not impair the characteristics of the secondary battery. The content of the other additives is usually preferably within a range of 0.05% by mass to 20% by mass, more preferably within a range of 0.1% by mass to 10% by mass, and particularly preferably within a range of 0.5% by mass to 5% by mass, based on the total mass of the non-aqueous electrolyte. By setting the content of the other additives to 0.05% by mass or more, the effect of the other additives, that is, a more stable film can be formed on the electrode surface. On the other hand, by setting the content of the other additives to 20% by mass or less, the solubility of the other additives in the non-aqueous solvent can be suppressed from being excessively reduced. In addition, the "solubility" here means that the other additives dissolve in an amount of 0.005 g or more in 100 g of non-aqueous solvent at 25°C.

[0077] In addition, the cyclic carbonate ester described as being used as a non-aqueous solvent, in which at least a part of the hydrogen atoms is replaced by a fluorine atom, and the chain carbonate ester, in which at least a part of the hydrogen atoms is replaced by a fluorine atom, can be used as an additive separately from the non-aqueous solvent. In this case, the content of the cyclic carbonate ester and the chain carbonate ester is preferably within a range of 0.05% by mass to 20% by mass, more preferably within a range of 0.1% by mass to 10% by mass, and particularly preferably within a range of 0.5% by mass to 5% by mass, based on the total mass of the non-aqueous electrolyte. By making the content of the cyclic carbonate ester and the chain carbonate ester 0.05% by mass or more, it is possible to exert the function as an additive, that is, to form a more stable film on the electrode surface. On the other hand, by making the content of the cyclic carbonate ester and the chain carbonate ester 20% by mass or less, it is possible to suppress an excessive decrease in the solubility of the cyclic carbonate ester and the chain carbonate ester in the non-aqueous solvent.

[0078] <Manufacture of non-aqueous electrolyte for secondary batteries> Next, a method for producing the nonaqueous electrolyte according to the present embodiment will be described below. In the non-aqueous electrolyte according to the present embodiment, for example, the electrolyte salt is added to the non-aqueous solvent (organic solvent), and then at least one of the fluorophosphates is added. Furthermore, other additives known in the art may be added. In this case, it is preferable to use the non-aqueous solvent, the electrolyte salt, the fluorophosphate, and other additives that are previously purified or the like within a range that does not reduce production efficiency, and that contain as few impurities as possible. When multiple types of the fluorophosphate or other additives are used, the order of addition thereof can be appropriately set as necessary.

[0079] (Secondary battery) Next, the secondary battery of the present invention will be described below by taking a lithium ion secondary battery as an example. Fig. 1 is a schematic cross-sectional view showing an outline of a lithium ion secondary battery provided with a non-aqueous electrolyte according to the present embodiment. The secondary battery of the present invention can be applied to a sodium ion secondary battery, a potassium ion secondary battery, a magnesium ion secondary battery, a calcium ion secondary battery, etc., in addition to a lithium ion secondary battery.

[0080] As shown in FIG. 1, the lithium ion secondary battery according to the present embodiment has a structure in which a stack of a positive electrode 1, a separator 3, a negative electrode 2, and a spacer 7 is stored in an internal space formed by a positive electrode can 4 and a negative electrode can 5 in this order from the positive electrode can 4 side. A spring 8 is interposed between the negative electrode can 5 and the spacer 7, so that the positive electrode 1 and the negative electrode 2 are appropriately pressed and fixed. The nonaqueous electrolyte containing the additive of the present embodiment is impregnated between the positive electrode 1, the separator 3, and the negative electrode 2. The positive electrode can 4 and the negative electrode can 5 are joined by sandwiching them with a gasket 6 interposed between them, and the stack is sealed.

[0081] The positive electrode active material in the positive electrode active material layer of the positive electrode 1 is not particularly limited, and examples thereof include transition metal compounds having a structure in which lithium ions can diffuse, and oxides of the transition metal compounds and lithium. More specifically, the positive electrode active material is, for example, LiCoO 2 ;LiNiO 2 ;LiMnO 2; LiMn 2 O 4 ; Li 2 MnO 3 and solid solutions with LiMeO 2 (Me = Mn, Co, Ni); LiFePO 4 ; LiMn x Fe y PO 4 (0 < x < 1, 0 < y < 1, x + y = 1); LiCoPO 4 ; LiMnPO 4 ; LiNiPO 4 ; Li 2 CoP 2 O 7 ; Li 2 FePO 4 F; Binary transition metal oxides; Ternary transition metal oxides; LiFeF 3 ; TiO 2 , V 2 O 5 and oxides such as MoO 3 ; and sulfides such as TiS 2 and FeS. Also, as the positive electrode active material, conductive polymers such as polyacetylene, polyphenylene, polyaniline, and polypyrrole; activated carbon; polymers that generate radicals; and carbon materials may be used. Among the exemplified positive electrode active materials, in this embodiment, binary transition metal oxides and ternary transition metal oxides are preferred.

[0082] The binary transition metal oxides are not particularly limited. For example, LiNi x1 Co y1 O z1 (0 < x1 < 2, 0 < y1 < 2, 2 ≤ z1 ≤ 4, 1 ≤ x1 + y1 ≤ 2), LiNi x2 Mn y2 O z2 (0 < x2 < 2, 0 < y2 < 2, 2 ≤ z2 ≤ 4, 1 ≤ x2 + y2 ≤ 2), LiCo x3 Mn y3 O z3 (0 < x3 < 2, 0 < y3 < 2, 2 ≤ z3 ≤ 4, 1 ≤ x3 + y3 ≤ 2), etc. These binary transition metal oxides may be those in which a part of the oxygen atoms is replaced by other non-metal atoms such as phosphorus atoms, boron atoms, and fluorine atoms.

[0083] The LiNi x1 Co y1 O z1 , and LiNi x2 Mn y2 O z2 In the binary transition metal oxide consisting of the above, x1 and x2 represent the composition ratio of nickel in the binary transition metal oxide. x1 and x2 are each in the range of more than 0 and less than 2, preferably in the range of 0.1 to 1.9, more preferably in the range of 0.5 to 1.5. x1 and x2 can be controlled by adjusting the supply amount of nickel when producing the positive electrode active material. Also, y1 represents the composition ratio of cobalt in the binary transition metal oxide. y1 is in the range of more than 0 and less than 2, preferably in the range of 0.1 to 1.9, more preferably in the range of 0.5 to 1.5. y1 can be controlled by adjusting the supply amount of cobalt when producing the positive electrode active material. y2 represents the composition ratio of manganese in the binary transition metal oxide. y2 is in the range of more than 0 and less than 2, preferably in the range of 0.1 to 1.9, more preferably in the range of 0.5 to 1.5. y2 can be controlled by adjusting the amount of manganese supplied when producing the positive electrode active material. x2 Mn y2 O z2 From the viewpoints of availability and battery properties, the binary transition metal oxide consisting of LiNi 0.5 Mn 1.5 O 4 is preferred.

[0084] The LiCo x3 Mn y3 O z3In the binary transition metal oxide consisting of [the specific composition], x3 represents the composition ratio of cobalt in the binary transition metal oxide. x3 exceeds 0 and is within the range of less than 2, preferably within the range of 0.1 or more and 1.9 or less, and more preferably within the range of 0.5 or more and 1.5 or less. x3 can be controlled by adjusting the supply amount of cobalt when manufacturing the positive electrode active material. y3 represents the composition ratio of manganese in the binary transition metal oxide. y3 exceeds 0 and is within the range of less than 2, preferably within the range of 0.1 or more and 1.9 or less, and more preferably within the range of 0.5 or more and 1.5 or less. y3 can be controlled by adjusting the supply amount of manganese when manufacturing the positive electrode active material.

[0085] As the ternary transition metal oxide, LiNi x4 Co y4 Mn z4 O 2 (0 < x4 < 1, 0 < y4 < 1, 0 < z4 < 1, x4 + y4 + z4 = 1), and LiNi x5 Co y5 Al z5 O 2 (0 < x5 < 1, 0 < y5 < 1, 0 < z5 < 1, x5 + y5 + z5 = 1) can be mentioned. These ternary transition metal oxides may be those in which a part of the oxygen atoms is replaced by other non-metal atoms such as phosphorus atoms, boron atoms, and fluorine atoms.

[0086] The above-mentioned LiNi x4 Co y4 Mn z4 O 2In the ternary transition metal oxide consisting of, x4 represents the composition ratio of nickel in the ternary transition metal oxide. x4 is in the range of more than 0 and less than 1, preferably in the range of 0.6 or more and less than 1, more preferably in the range of 0.6 or more and 0.9 or less. x4 can be controlled by adjusting the supply amount of nickel when producing a positive electrode active material. Also, y4 represents the composition ratio of cobalt in the ternary transition metal oxide. y4 is in the range of more than 0 and less than 1, preferably in the range of 0.05 or more and 0.2 or less, more preferably in the range of 0.05 or more and 0.1 or less. y4 can be controlled by adjusting the supply amount of cobalt when producing a positive electrode active material. Also, z4 represents the composition ratio of manganese in the ternary transition metal oxide. z4 is in the range of more than 0 and less than 1, preferably in the range of 0.05 or more and 0.2 or less, more preferably in the range of 0.05 or more and 0.1 or less. z4 can be controlled by adjusting the supply amount of manganese when producing a positive electrode active material.

[0087] The LiNi x5 Co y5 Al z5 O 2In the ternary transition metal oxide consisting of, x5 represents the composition ratio of nickel in the ternary transition metal oxide. x5 is in the range exceeding 0 and less than 1, preferably in the range of 0.6 or more and less than 1, more preferably in the range of 0.6 or more and 0.9 or less. x5 can be controlled by adjusting the supply amount of nickel when manufacturing the positive electrode active material. Further, y5 represents the composition ratio of cobalt in the ternary transition metal oxide. y5 is in the range exceeding 0 and less than 1, preferably in the range of 0.05 or more and 0.2 or less, more preferably in the range of 0.05 or more and 0.1 or less. y5 can be controlled by adjusting the supply amount of cobalt when manufacturing the positive electrode active material. Further, z5 represents the composition ratio of aluminum in the ternary transition metal oxide. z5 is in the range exceeding 0 and less than 1, preferably in the range of 0.05 or more and 0.2 or less, more preferably in the range of 0.05 or more and 0.1 or less. z5 can be controlled by adjusting the supply amount of aluminum when manufacturing the positive electrode active material.

[0088] Among the positive electrode active materials exemplified above, from the viewpoints of energy density and thermal stability, LiCoO 2 ;LiNiO 2 ;Li 2 MnO 3 and the solid solution with LiMeO 2 (Me = Mn, Co, Ni); LiNi x4 Co y4 Mn z4 O 2 (0 < x4 < 1, 0 < y4 < 1, 0 < z4 < 1, x4 + y4 + z4 = 1), or LiNi x5 Co y5 Al z5 O 2 (0 < x5 < 1, 0 < y5 < 1, 0 < z5 < 1, x5 + y5 + z5 = 1) consisting of a ternary transition metal oxide is preferred, and more preferably, LiNi x4 Co y4 Mn z4 O 2 (0.6 ≦ x4 < 1, 0 < y4 ≦ 0.4, 0 < z4 ≦ 0.4, x4 + y4 + z4 = 1), or LiNi x5 Co y5Al z5 O 2 A ternary transition metal oxide consisting of (0.6 ≦ x5 < 1, 0 < y5 ≦ 0.4, 0 < z5 ≦ 0.4, x5 + y5 + z5 = 1) is used.

[0089] The positive electrode 1 can be obtained by pressure - molding the positive electrode active material listed above together with a known conductive aid and a binder, or by mixing the positive electrode active material together with a known conductive aid and a binder in an organic solvent such as pyrrolidone to form a paste, applying the paste to a current collector such as an aluminum foil, and then drying.

[0090] The material of the negative electrode active material layer in the negative electrode 2 is not particularly limited as long as it can occlude and release lithium. Examples include metal composite oxides, lithium metal, lithium alloys, silicon, silicon - based alloys, tin - based alloys, metal oxides, carbon materials, etc.

[0091] The metal composite oxide is not particularly limited. For example, Li 4 Ti 5 O 12 、Li x Fe 2 O 3 (0 ≦ x ≦ 1), Li x WO 2 (0 ≦ x ≦ 1), Sn x Me 1 1-x Me 2 y O z (Me 1 = Mn, Fe, Pb, Ge, and Me 2 = Al, B, P, Si, elements of Groups 1 - 3 of the periodic table, halogen, 0 ≦ x ≦ 1, 1 ≦ y ≦ 3, 1 ≦ z ≦ 8), etc.

[0092] The metal oxide is not particularly limited. For example, SnO, SnO 2 、SiO x (0 < x < 2), PbO, PbO 2 、Pb 2 O 3 、Pb 3 O 4 、Sb 2O 3 , Sb 2 O 4 , Sb 2 O 5 , GeO, GeO 2 , Bi 2 O 3 , Bi 2 O 4 , Bi 2 O 5 etc.

[0093] The carbon material is not particularly limited, and examples thereof include natural graphite, artificial graphite, boronized graphite, fluorinated graphite, mesocarbon microbeads, pitch-based graphitized carbon fibers, carbon nanotubes, hard carbon, and fullerene.

[0094] The electrode material in a foil or powder form can be used for the negative electrode 2. In the case of a powder form, it can be obtained by pressure molding together with a known conductive assistant and binder, or by mixing together with a known conductive assistant and binder in an organic solvent such as pyrrolidone to form a paste, which is then applied to a current collector such as copper foil and then dried.

[0095] In the lithium ion secondary battery according to the present embodiment, a separator 3 is usually interposed between the positive electrode 1 and the negative electrode 2 to prevent short circuit between them. The material and shape of the separator 3 are not particularly limited, but it is preferable that the separator 3 is made of a material that is easy to pass the non-aqueous electrolyte, is an insulator, and is chemically stable. For example, microporous films, sheets, and nonwoven fabrics made of various polymer materials, those with glass coating on their surfaces, and nonwoven fabrics made of glass fibers can be mentioned. Specific examples of polymer materials include polyolefin polymers such as nylon (registered trademark), nitrocellulose, polyacrylonitrile, polyvinylidene fluoride, polyethylene, and polypropylene. From the viewpoint of electrochemical stability and chemical stability, polyolefin polymers are preferable.

[0096] The lithium ion secondary battery of the present embodiment can be charged at a high charging voltage, which is preferably 4.3 V or higher, more preferably in the range of 4.3 V to 5 V, even more preferably in the range of 4.35 V to 4.8 V, and particularly preferably in the range of 4.4 V to 4.7 V.

[0097] In addition, the lithium ion secondary battery of the present embodiment is excellent in storage performance, since it can suppress the increase in internal resistance even when stored in a high-temperature environment after charging. In addition, even when repeatedly charged and discharged at a high charging voltage after storage in a high-temperature environment, it can maintain the discharge capacity well and exhibit excellent cycle characteristics. Here, storage in a high-temperature environment means storage at 40°C or higher, preferably within the range of 40°C or higher and 80°C or lower, more preferably within the range of 40°C or higher and 70°C or lower, and even more preferably within the range of 40°C or higher and 60°C or lower. In addition, repeated charging and discharging at a high charging voltage means that the charging voltage is preferably 4.3V or higher, more preferably within the range of 4.3V or higher and 5V or lower, even more preferably within the range of 4.35V or higher and 4.8V or lower, and particularly preferably within the range of 4.4V or higher and 4.7V or lower.

[0098] The shape of the lithium ion secondary battery of this embodiment is not particularly limited, and in addition to the coin-type cell shown in FIG. 1, examples include cylindrical, square, and laminate types.

[0099] The lithium ion secondary battery comprising the nonaqueous electrolyte of this embodiment is suitable as an on-board power source for electric vehicles (xEVs) and hybrid electric vehicles, for example, which require high operating voltage and high-temperature storage performance.

[0100] The secondary battery according to this embodiment can exhibit excellent cycle characteristics even in a high-temperature environment, and the nonaqueous electrolyte according to this embodiment can be suitably used for, for example, a lithium-ion secondary battery. However, the lithium-ion secondary battery shown in FIG. 1 is an illustrative example of one embodiment of the secondary battery of the present invention, and the secondary battery of the present invention is not limited thereto. EXAMPLES

[0101] Preferred manufacturing examples and examples of the present invention are described in detail below. However, the manufacturing examples, materials, blending amounts, etc. described herein are not intended to limit the scope of the present invention unless otherwise specified.

[0102] <Production of phenyllithium fluorophosphate> Phenyllithium fluorophosphate as the fluorophosphate salt was prepared by the following method.

[0103] That is, in a 250 mL eggplant flask containing a stirrer, 8.7 g of phenyl phosphate and 4 g of hydrofluoric acid with a concentration of 50% by mass were dissolved in 40 mL of pyridine solvent (non-aqueous solvent), and 28.6 g of trichloroacetonitrile was added little by little while stirring at 60 ° C. Next, the mixture was stirred for 15 hours and then concentrated under reduced pressure. Next, 50 mL of a 1.0 mol / L lithium hydroxide aqueous solution was added to the mixture, neutralized with an ion exchange resin, filtered, and then excess water and solvent were distilled off by drying under reduced pressure. The product thus obtained was further purified to obtain 2.2 g of a white solid.

[0104] The obtained white solid was subjected to anion analysis by ion chromatography (trade name: IC-850, manufactured by Metrohm Japan Co., Ltd.), and a peak corresponding to phenyl fluorophosphate ion was observed at a retention time of 8.8 min., and its relative area was 93%. In addition, when the obtained white solid was subjected to cation analysis by ion chromatography (trade name: Dionex ICS-1500, manufactured by Thermo Fisher Scientific Co., Ltd.), a peak corresponding to lithium ion was detected. This confirmed that the obtained white solid was phenyl lithium fluorophosphate.

[0105] Example 1 <Preparation of non-aqueous electrolyte> In an argon atmosphere dry box with a dew point of -70°C or less, LiPF was dissolved in a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) (volume ratio EC:DMC = 1:1, manufactured by Kishida Chemical Co., Ltd., lithium battery grade). 6 LiPF 6 The mixture of LiPF 6 The concentration was adjusted to 1.0 mol / L.

[0106] Next, LiPF 6 Phenyllithium fluorophosphate was added to a mixed solvent containing the above. The amount of phenyllithium fluorophosphate added was 0.3 mass% relative to the total mass of the nonaqueous electrolyte solution. In this way, a nonaqueous electrolyte solution according to this embodiment was prepared.

[0107] Example 2 In this embodiment, benzyllithium fluorophosphate was used instead of phenyllithium fluorophosphate. The amount of benzyllithium fluorophosphate added was 0.3 mass% based on the total mass of the non-aqueous electrolyte. Other than that, the non-aqueous electrolyte according to this embodiment was prepared in the same manner as in Example 1.

[0108] Example 3 In this embodiment, 4-tert-amylphenyllithium fluorophosphate was used instead of phenyllithium fluorophosphate. The amount of 4-tert-amylphenyllithium fluorophosphate added was 0.3 mass% relative to the total mass of the non-aqueous electrolyte. Other than that, the non-aqueous electrolyte according to this embodiment was prepared in the same manner as in Example 1.

[0109] Example 4 In this embodiment, 4-tert-amylphenyllithium fluorophosphate was used instead of phenyllithium fluorophosphate. The amount of 4-tert-amylphenyllithium fluorophosphate added was 0.01% by mass relative to the total mass of the non-aqueous electrolyte. Other than that, the non-aqueous electrolyte according to this embodiment was prepared in the same manner as in Example 1.

[0110] Example 5 In this embodiment, the volume ratio of EC:DMC was changed from 1:1 to 1:4, and 4-tert-amylphenyllithium fluorophosphate was used instead of phenyllithium fluorophosphate. The amount of 4-tert-amylphenyllithium fluorophosphate added was 2 mass% relative to the total mass of the non-aqueous electrolyte. Other than these, the non-aqueous electrolyte according to this embodiment was prepared in the same manner as in Example 1.

[0111] Comparative Example 1 In this comparative example, ethyllithium fluorophosphate was used instead of phenyllithium fluorophosphate. The amount of ethyllithium fluorophosphate added was 0.5% by mass relative to the total mass of the non-aqueous electrolyte solution. Other than that, the non-aqueous electrolyte solution according to this comparative example was prepared in the same manner as in Example 1.

[0112] Comparative Example 2 In this comparative example, methyllithium fluorophosphate was used instead of phenyllithium fluorophosphate. The amount of methyllithium fluorophosphate added was 0.5% by mass relative to the total mass of the nonaqueous electrolyte. Other than that, the nonaqueous electrolyte according to this comparative example was prepared in the same manner as in Example 1.

[0113] Comparative Example 3 In this comparative example, a nonaqueous electrolyte solution according to this comparative example was prepared in the same manner as in Example 1, except that phenyllithium fluorophosphate was not added.

[0114] Comparative Example 4 In this comparative example, a nonaqueous electrolyte solution according to this comparative example was prepared in the same manner as in Example 1, except that the volume ratio of EC:DMC was changed from 1:1 to 1:4 and phenyllithium fluorophosphate was not added.

[0115] (Evaluation of high temperature storage performance and cycle characteristics) <Coin cell production> Using the nonaqueous electrolyte solutions prepared in each of Examples 1 to 5 and Comparative Examples 1 to 4, coin-type lithium ion secondary batteries (coin cells) as shown in FIG. 1 were fabricated and their electrochemical properties were evaluated.

[0116] That is, the positive electrode is a LiNi 0.6 Co 0.2 Mn 0.2 O 2 A positive electrode (manufactured by Piotrek Co., Ltd.) was used as the separator, and glass filter paper (product name: GC-50, manufactured by Advantec Toyo Co., Ltd.) was used as the separator. Natural graphite (manufactured by Piotrek Co., Ltd.) cut to a diameter of 13 mm was used as the negative electrode. Furthermore, the positive electrode, separator, and negative electrode were laminated in this order to form a laminate, which was then impregnated with the nonaqueous electrolyte prepared in Examples 1 to 5 and Comparative Examples 1 to 4, respectively, and the laminate was then sealed to produce each of the coin cells. The coin cells were all assembled in an argon glove box with a dew point of -70°C or less.

[0117] <Coin cell break-in> Each coin cell was charged in a thermostatic chamber at 25°C with a charging current of 0.3mA / cm 2 The battery was charged to a final voltage of 4.3 V at a charging current of 0.075 mA / cm 2 The potential was held constant at 4.3 V until the discharge current was below 0.3 mA / cm. 2 The battery was discharged at 1000 V to a final voltage of 3.0 V. Under these charge / discharge conditions, three cycles of charge / discharge were performed by a constant current / constant voltage method, and the discharge capacity at the third cycle was defined as the initial discharge capacity.

[0118] <High temperature storage test> Next, after the break-in, each coin cell was placed in a thermostatic chamber at 25°C and charged at 0.3mA / cm 2 The battery was charged to a final voltage of 4.3 V at a charging current of 0.075 mA / cm 2 The charging was terminated by maintaining a constant potential of 4.3 V until the voltage dropped below 4.3 V. The temperature in the thermostatic chamber was then changed to 60°C, and each charged coin cell was stored at high temperature for two weeks.

[0119] After two weeks, the temperature in the thermostatic chamber was returned to 25°C, and the discharge current for each coin cell after high-temperature storage was 0.3mA / cm 2 The capacity at that time was recorded as the discharge capacity after high-temperature storage. Table 1 shows the ratio of the discharge capacity after storage to the initial discharge capacity of 100.

[0120] <Measuring the internal resistance of a coin cell> The internal resistance of each coin cell was determined by the AC impedance method. After high-temperature storage, each coin cell was placed in a thermostatic chamber at 25°C and charged at a current of 0.3 mA / cm. 2 The coin cells were charged to 4.3 V at 100 V, and a sine wave with an amplitude of ±10 mV and a frequency of 1 MHz to 50 mHz was superimposed to obtain a Nyquist plot, from which the internal resistance of each coin cell was calculated. Table 1 shows the ratio of the internal resistance of each coin cell to the internal resistance of the coin cell using the non-electrolyte solution of Comparative Example 3, which is taken as 100.

[0121] [Table 1]

[0122] <Cycle characteristic test 1> After high-temperature storage, each coin cell was charged in a thermostatic chamber at 25°C with a charging current of 1.5mA / cm 2 The battery was charged to a final voltage of 4.2 V at a charging current of 0.075 mA / cm 2 The potential was held constant at 4.2 V until the discharge current was below 1.5 mA / cm. 2 The battery was discharged at 100 V to a final voltage of 3.0 V. Under these charge / discharge conditions, 100 cycles of charge / discharge were performed using a constant current / voltage method. Table 2 shows the ratio of the discharge capacity at the 100th cycle to the discharge capacity at the 1st cycle, which is set to 100.

[0123] [Table 2]

[0124] <Cycle characteristic test 2> After high-temperature storage, each coin cell was charged in a thermostatic chamber at 25°C with a charging current of 1.5mA / cm2 The battery was charged to a final voltage of 4.4 V at a charging current of 0.075 mA / cm 2 The potential was held constant at 4.4 V until the discharge current was below 1.5 mA / cm. 2 The battery was discharged at 100 V to a final voltage of 3.0 V. Under these charge / discharge conditions, 100 cycles of charge / discharge were performed using a constant current / voltage method. Table 3 shows the ratio of the discharge capacity at the 100th cycle to the discharge capacity at the 1st cycle, which is set to 100.

[0125] [Table 3]

[0126] (result) As can be seen from Table 1, the coin cells using the nonaqueous electrolytes of Examples 1 to 5 had higher discharge capacities and lower internal resistance within the coin cells after being charged at a charging voltage of 4.3 V and then stored at 60°C for two weeks, compared to the coin cells using the nonaqueous electrolytes of Comparative Examples 1 to 4.

[0127] Furthermore, as shown in Table 2, in cycle characteristic test 1 conducted at a charging voltage of 4.2 V, no significant difference in discharge capacity was confirmed between the coin cells using the nonaqueous electrolytes of Examples 1 to 5 and the coin cells using the nonaqueous electrolytes of Comparative Examples 1 to 4. However, in cycle characteristic test 2 conducted at a charging voltage of 4.4 V, the coin cells using the nonaqueous electrolytes of Examples 1 to 5 had a higher discharge capacity after 100 charge / discharge cycles than the coin cells using the nonaqueous electrolytes of Comparative Examples 1 to 4.

[0128] These results confirm that the lithium ion secondary batteries using the nonaqueous electrolyte solutions of Examples 1 to 5 have excellent storage performance in high temperature environments, suppress an increase in the internal resistance of the battery, and have excellent cycle characteristics even at high charging voltages. [Explanation of symbols]

[0129] 1 positive electrode 2 negative electrode 3. Separator 4 Positive electrode can 5 Anode can 6 Gasket 7 Spacer 8. Spring

Claims

1. A non-aqueous electrolyte solution for a secondary battery comprising an electrolyte and a non-aqueous solvent, The nonaqueous electrolyte for a secondary battery further comprises at least one fluorophosphate salt represented by the following chemical formula (1) as an additive: 【Chemistry 1】 (In the formula, M ＋ represents an alkali metal ion. １ ~R ５ each independently represents a hydrogen atom; a hydrocarbon group having 1 to 10 carbon atoms; an alkoxy group having 1 to 10 carbon atoms; a hydrocarbon group having 1 to 10 carbon atoms and having at least one of a halogen atom or an unsaturated bond; or an alkoxy group having 1 to 10 carbon atoms and having at least one of a halogen atom or an unsaturated bond. １ ~R ５ are each independently any of a hydrocarbon group having 1 to 10 carbon atoms; an alkoxy group having 1 to 10 carbon atoms; a hydrocarbon group having 1 to 20 carbon atoms and having at least one of a halogen atom, a hetero atom, or an unsaturated bond; or an alkoxy group having 1 to 20 carbon atoms and having at least one of a halogen atom, a hetero atom, or an unsaturated bond, any combination of which is bonded to each other to form a cyclic structure. n represents an integer of 0 to 10.

2. 2. The non-aqueous electrolyte solution for a secondary battery according to claim 1, wherein the amount of the fluorophosphate added is in the range of 0.01% by mass or more and 2% by mass or less with respect to the total mass of the non-aqueous electrolyte solution for a secondary battery.

3. 2. The nonaqueous electrolyte for a secondary battery according to claim 1, wherein the fluorophosphate is lithium phenyl fluorophosphate, sodium phenyl fluorophosphate, lithium benzyl fluorophosphate, sodium benzyl fluorophosphate, 4-tert-amylphenyl lithium fluorophosphate, or 4-tert-amylphenyl sodium fluorophosphate.

4. A secondary battery comprising at least the nonaqueous electrolyte for secondary batteries according to any one of claims 1 to 3, a positive electrode, and a negative electrode.

5. 5. The secondary battery according to claim 4, wherein the charging voltage is 4.3 V or higher.

6. The secondary battery according to claim 5 , which is stored in an environment of 40° C. or higher after being charged with a charging voltage of 4.3 V or higher.

7. 5. The secondary battery according to claim 4, wherein the positive electrode active material constituting the positive electrode active material layer in the positive electrode contains a binary transition metal oxide or a ternary transition metal oxide.

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