Non-aqueous electrolyte secondary battery and non-aqueous electrolyte

Abstract

Provided is a nonaqueous electrolytic solution secondary battery in which a suppression of self-discharging, a suppression of swelling, a reduction in internal resistance, and a reduction in capacity loss during contact charging can all be achieved. The present invention solves these problems by means of a nonaqueous electrolytic solution secondary battery comprising a positive electrode having a positive electrode active material that can store and release metal ions, a negative electrode having a negative electrode active material that can store and release metal ions, and a nonaqueous electrolytic solution, wherein a metal composite oxide having a high Ni content is used as the positive electrode active material, and a specific compound is included in the nonaqueous electrolytic solution.

Description

[Technical Field]

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

[0002] Lithium nonaqueous electrolyte secondary batteries, which use a lithium-containing transition metal oxide as a positive electrode and a nonaqueous solvent as an electrolyte, can achieve high energy density and are therefore used in a wide range of applications, from small power sources for mobile phones, laptop computers, etc. to large power sources for automobiles, railways, and load leveling. However, in recent years, there has been an increasing demand for higher performance in nonaqueous electrolyte secondary batteries, and there is a strong demand for improvements in various characteristics.

[0003] For example, Patent Document 1 discloses a non-aqueous electrolyte containing a specific zwitterion, and discloses that the non-aqueous electrolyte can improve the high-temperature charged storage characteristics of an electricity storage device.

[0004] For example, Patent Document 2 discloses a nonaqueous electrolyte solution containing a compound having a cation and an anion in the molecule, and discloses that a nonaqueous electrolyte secondary battery including this electrolyte solution can suppress deterioration of characteristics due to storage at high temperatures and deterioration due to charge / discharge cycles.

[0005] Patent Document 3 discloses an electrolyte solution containing a specific onium cation as an additive, which improves the discharge retention rate at high voltage, suppresses gas generation, and improves overcharge prevention properties.

[0006] Patent Document 4 states that SO2 - , SO3 - or SO4 - and a heteroatom of N or O, and an additive for a non-aqueous electrolyte solution is disclosed that improves overcharge stability.

[0007] Patent Document 5 discloses an electrolyte solution containing propanesulfonic acid pyridinium salts, which can improve the high-temperature storage characteristics of a battery and reduce the internal resistance.

[0008] Patent Document 6 discloses a nonaqueous electrolyte secondary battery that uses a positive electrode with a high nickel content and an electrolyte containing monofluorophosphate and / or difluorophosphate, and that has a high capacity retention rate after high-temperature storage, a small amount of storage gas after high-temperature storage, low resistance after high-temperature storage, little metal elution from the positive electrode, and a small amount of heat generation at high temperatures. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] International Publication No. 2020 / 017318 [Patent Document 2] Japanese Patent Application Laid-Open No. 2012-204100 [Patent Document 3] Korean Patent Publication No. 20150024225 [Patent Document 4] U.S. Patent Publication No. 2017 / 0125847 [Patent Document 5] China Patent Publication No. 106099183 [Patent Document 6] International Publication No. 2019 / 031508 Summary of the Invention [Problem to be solved by the invention]

[0010] In recent years, nonaqueous electrolyte secondary batteries have increasingly required higher performance, particularly in battery-equipped automobiles, and there has been a strong demand for improved battery durability. However, the above-mentioned technologies have not yet achieved a high level of performance that combines the various performance characteristics of nonaqueous electrolyte secondary batteries. For example, the nonaqueous electrolyte secondary batteries of Patent Documents 1 to 5 require further improvements in battery capacity, while the nonaqueous electrolyte secondary batteries of Patent Documents 1 to 4 suffer from the problem of large self-discharge. Furthermore, the nonaqueous electrolyte secondary batteries of Patent Documents 5 and 6 suffer from problems such as large self-discharge, swelling, and increased internal resistance. Furthermore, conventional nonaqueous electrolyte secondary batteries suffer from the problem of large capacity loss during continuous charging.

[0011] A first object of the present invention is to provide a nonaqueous electrolyte secondary battery that solves the above-mentioned problems and can simultaneously achieve suppression of self-discharge, suppression of swelling, reduction of internal resistance, and reduction of capacity loss during continuous charging.

[0012] Furthermore, the nonaqueous electrolyte secondary batteries described in Patent Documents 1 to 3 have large self-discharge rates and insufficient capacity retention rates when stored at high temperatures, and the nonaqueous electrolyte secondary battery described in Patent Document 4 still has insufficient discharge characteristic retention performance at low temperatures.

[0013] A second object of the present invention is to provide a nonaqueous electrolyte that can solve the above-mentioned problems in nonaqueous electrolyte secondary batteries, suppress self-discharge, and synergistically improve the capacity retention rate during high-temperature storage and the discharge characteristic retention performance at low temperatures. [Means for solving the problem]

[0014] As a result of extensive research aimed at solving the first problem, the present inventors have found that the above problems can be solved by using a specific positive electrode and a nonaqueous electrolyte secondary battery that uses a nonaqueous electrolyte containing a specific zwitterionic compound, and have arrived at the present invention.

[0015] That is, the first aspect of the present invention is [A1] to [A6] shown below. [A1] A non-aqueous electrolyte secondary battery comprising: a positive electrode having a positive electrode active material capable of absorbing and releasing metal ions; a negative electrode having a negative electrode active material capable of absorbing and releasing metal ions; and a non-aqueous electrolyte, The non-aqueous electrolyte solution contains a compound represented by the following formula (I) and / or (II): The positive electrode active material of the non-aqueous electrolyte secondary battery contains a lithium transition metal compound represented by the following composition formula (IV): Li 1+x MO2···(IV) (In the above composition formula (IV), x is -0.1 or more and 0.5 or less, M is a plurality of elements including at least Ni, and the Ni / M molar ratio is 0.40 or more and 1.0 or less.) [ka] (In formulas (I) and (II), R 1 ~R 5 are independent or bonded organic groups having 1 to 18 carbon atoms, and R 6 is a hydrocarbon group having 1 to 4 carbon atoms, and n is an integer of 2 to 4. [A2] The nonaqueous electrolyte secondary battery according to [A1], further comprising at least one compound selected from the group consisting of a fluorophosphate salt having a P=O bond, a salt having an FSO2 skeleton, an oxalate salt, and an organic compound having an S=O bond, wherein the content of the compound is 0.001 to 5 mass %. [A3] The nonaqueous electrolyte secondary battery according to [A1] or [A2], wherein the organic compound having an S═O bond is a sulfonate ester or a sulfate ester. [A4] In the formula (I), R 1 ~R 3 The nonaqueous electrolyte secondary battery according to any one of [A1] to [A3], wherein are each independently or bonded to each other hydrocarbon groups having 1 to 15 carbon atoms. [A5] In the above formula (I), R 1 ~R 3 The nonaqueous electrolyte secondary battery according to any one of [A1] to [A4], wherein is a methyl group or an ethyl group. [A6] The nonaqueous electrolyte secondary battery according to any one of [A1] to [A5], wherein the positive electrode active material contains 10 μmol / g or more of carbonate.

[0016] As a result of extensive research aimed at achieving the second object, the present inventors have found that the above object can be achieved by incorporating a specific additive and a specific zwitterionic compound in a nonaqueous electrolyte solution in a specific mass ratio, thereby completing the present invention. That is, the second aspect of the present invention is as follows: [B1] to [B6]. [B1] A compound (X) represented by the formula (I) and / or (II), A non-aqueous electrolyte solution comprising at least one compound (Y) selected from the group consisting of fluorophosphates having a P=O bond, salts having an FSO2 skeleton, oxalates, and organic compounds having an S=O bond, wherein the content of compound (Y) is 0.001 to 5 mass %, and the content (mass) of compound (X) contained in the non-aqueous electrolyte solution is equal to or less than the content (mass) of compound (Y). [ka] (In formulas (I) and (II), R 1 ~R 5 are independent or bonded organic groups having 1 to 18 carbon atoms, and R 6 is a hydrocarbon group having 1 to 4 carbon atoms, and n is an integer of 2 to 4. [B2] The nonaqueous electrolyte solution according to [B2], wherein the fluorophosphate salt having a P=O bond, the salt having an FSO2 skeleton, and the oxalate salt are a lithium fluorophosphate salt having a P=O bond, a lithium salt having an FSO2 skeleton, and a lithium salt having an oxalic acid skeleton. [B3] The nonaqueous electrolyte solution according to [B1] or [B2], wherein the nonaqueous electrolyte solution contains an electrolyte (C) other than the compound (Y), and the content ratio (C) / (X) of the compound (X) to the content of the electrolyte (C) is 2 or more and 10,000 or less. [B4] A nonaqueous electrolyte secondary battery comprising: a positive electrode having a positive electrode active material capable of absorbing and releasing metal ions; a negative electrode having a negative electrode active material capable of absorbing and releasing metal ions; and the nonaqueous electrolyte solution according to any one of [B1] to [B3]. [B5] The nonaqueous electrolyte secondary battery according to [B4], wherein the nonaqueous electrolyte secondary battery contains a lithium transition metal compound represented by the following composition formula (IV): Li 1+x MO2···(IV) (In the above composition formula (IV), x is -0.1 or more and 0.5 or less, M is a plurality of elements including at least Ni, and the Ni / M molar ratio is 0.40 or more and 1.0 or less.) [B6] The nonaqueous electrolyte secondary battery according to [B4] or [B5], wherein in the formula (IV), M contains Mn. [Effects of the Invention]

[0017] According to the first aspect of the present invention, self-discharge is suppressed, swelling is suppressed, and internal resistance is reduced. continuous It is possible to provide a non-aqueous electrolyte secondary battery that can also achieve a reduction in capacity loss during charging. The inventors speculate that the reason why the nonaqueous electrolyte secondary battery having the configuration of the present invention exhibits such excellent effects is as follows. Specifically, using a positive electrode with a high Ni ratio is effective for increasing battery capacity. However, while a positive electrode with a high Ni ratio improves battery capacity, it has the problem that the positive electrode oxygen atoms are less stable than in conventional positive electrodes with a high Co ratio, making them more susceptible to side reactions with the electrolyte. Known additive compounds such as lithium monofluorophosphate and lithium difluorophosphate have the effect of stabilizing the Ni atoms contained in large amounts in the positive electrode, but are insufficient in their effect of stabilizing the positive electrode oxygen atoms.

[0018] On the other hand, the present invention is characterized in that the electrolyte used in a nonaqueous electrolyte secondary battery having a positive electrode with a high Ni content contains the above-mentioned compounds (I) and / or (II). The SO3 anion site in compounds (I) and / or (II) not only acts on and stabilizes the Ni atom in the positive electrode, but also acts on and stabilizes the oxygen atom in the positive electrode, thereby suppressing side reactions between the positive electrode and the electrolyte more than in conventional techniques. The inventors speculate that this will enable the nonaqueous electrolyte secondary battery to maintain high levels of internal resistance, suppress swelling, and suppress self-discharge, while also improving continuous charge characteristics.

[0019] According to a second aspect of the present invention, a nonaqueous electrolyte solution can be provided that can suppress self-discharge and synergistically improve the capacity retention rate during high-temperature storage and the ability to maintain discharge characteristics at low temperatures, and a nonaqueous electrolyte secondary battery including the nonaqueous electrolyte solution can be provided. The inventors speculate that the reason why the nonaqueous electrolyte solution having the configuration of the second aspect of the present invention exhibits such excellent effects is as follows: The techniques described in Patent Documents 1 to 3 add a zwitterionic compound, which suppresses electrolyte side reactions on the positive electrode and thereby improves battery performance during high-temperature storage and charge-discharge cycling. However, the cationic portion of the zwitterionic compound inhibits the formation of a carbonate film on the negative electrode, accelerating deterioration of the negative electrode and promoting self-discharge of the battery, which is thought to hasten the deterioration of capacity and discharge characteristics.

[0020] On one hand, by including a specific lithium salt additive and a specific zwitterionic compound in a specific quantitative ratio in an electrolytic solution, the lithium cations contained in the lithium salt additive have a higher adsorption ability to the negative electrode than the cation site of the zwitterionic compound. Therefore, they act on the negative electrode preferentially over the betaine compound and can protect the negative electrode. When the content of the zwitterionic compound is less than that of the lithium salt additive, this effect becomes remarkable. By protecting both the negative electrode and the positive electrode, the self-discharge of the non-aqueous electrolyte secondary battery can be suppressed, and the present inventors believe that the capacity retention rate during high-temperature storage and the performance of maintaining discharge characteristics at low temperatures can be improved to a higher level than before.

Mode for Carrying Out the Invention

[0021] <A. First Embodiment> Hereinafter, modes for carrying out the present invention will be described in detail. However, the descriptions given below are examples (representative examples) of embodiments of the present invention, and the present invention is not limited to these contents as long as it does not exceed the gist described in the claims.

[0022] One embodiment according to the first aspect of the present invention relates to a non-aqueous electrolyte secondary battery, and includes a positive electrode having a positive electrode active material capable of occluding and releasing metal ions, a negative electrode having a negative electrode active material capable of occluding and releasing metal ions, and a non-aqueous electrolyte. Hereinafter, each component will be described.

[0023] [A1. Non-aqueous Electrolyte] [A1-1. Compound Represented by Formula (I) and / or (II)] The non-aqueous electrolyte used in the non-aqueous electrolyte secondary battery according to the embodiment of the present invention contains an electrolyte and a non-aqueous solvent for dissolving the electrolyte, and particularly contains a compound represented by the following formula (I) and / or (II), similar to a general non-aqueous electrolyte.

[0024]

Chemical formula

[0025] In the above formulas (I) and (II), R1 ~R 5 are mutually independent or bonded organic groups having 1 to 18 carbon atoms. The organic groups are groups having a carbon atom as a skeleton, and the group having a carbon atom as a skeleton may have an alkyl group, an alkenyl group, an alkynyl group, an aryl group, or an alkoxy group as a substituent, hydrogen atoms bonded to carbon atoms of the group having a carbon atom as a skeleton may be substituted with halogen atoms, some of the carbon atoms of the group having a carbon atom as a skeleton may be substituted with oxygen atoms to form an ether bond or an ester bond, or some of the carbon atoms of the group having a carbon atom as a skeleton may be substituted with nitrogen atoms. 1 ~R 5 (Especially R 1 ~R 3 ) are preferably hydrocarbon groups having 1 to 15 carbon atoms, each of which is independent of the other or which are bonded to one another, more preferably alkyl groups, and even more preferably methyl or ethyl groups from the viewpoint of suppressing an increase in internal resistance. 1 ~R 3 and R 4 ~R 5 may be bonded to each other to form a ring. The number of rings formed may be 1 or 2 or more. 1 and R 2 is preferably a compound in which R is a methyl group. R 6 is a spacer group, which is a divalent hydrocarbon group having 1 to 4 carbon atoms, and preferably a divalent hydrocarbon group having 1 to 3 carbon atoms. n is 2 to 4, preferably 3 or 4, and more preferably 3.

[0026] Compounds represented by the above formulas (I) and (II) include compounds in which a positive charge exists on the nitrogen atom and a negative charge exists on the oxygen atom bonded to the sulfur atom, such as the following compounds:

[0027] [ka]

[0028] [ka]

[0029] [ka]

[0030] Among these, in the above formula (I), R 1 and R 2 In addition, in the formulas (I) and (II), R 1 ~R 3 and R 4 ~R 5 are bonded to each other to form a ring, the ring formed is preferably a 5- or 6-membered nitrogen-containing heterocyclic ring which may have a substituent, more preferably a 6-membered nitrogen-containing heterocyclic ring which may have a substituent. The ring formed may be further condensed with one or more rings, and the ring formed may further have an oxygen atom. Examples of the 5- or 6-membered nitrogen-containing heterocycle include pyrrolidinium, piperidinium, pyridinium, imidazolium, pyrazolium, pyrimidinium, triazinium, and triazolium. Of these, piperidinium and pyridinium are preferred because they can suppress side reactions with the negative electrode. The substituents that may be present on the ring include alkyl groups, alkenyl groups, and alkynyl groups, which may contain fluorine atoms and / or oxygen atoms. Among these, alkyl groups and alkenyl groups are preferred in terms of adsorptivity to the positive electrode.

[0031] Of the compounds represented by the above formula (II), compounds represented by the following formula (III) are particularly preferred. [ka] In the above formula (III), R 6 is R in the above formula (II) 6 is synonymous with. R 7 ~R11 may be the same or different and are a hydrogen atom, a halogen atom, or a hydrocarbon group. n has the same meaning as n in the above formula (II).

[0032] Examples of halogen atoms include chlorine atoms and fluorine atoms, with fluorine atoms being preferred. Examples of the hydrocarbon group include an alkyl group, an alkenyl group, and an alkynyl group, which may contain a fluorine atom and / or an oxygen atom. Preferred are alkyl groups and alkenyl groups. Specific examples of the alkyl group include methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, n-pentyl, hexyl, heptyl, octyl, nonyl, and decyl groups. Among these, methyl, ethyl, n-propyl, n-butyl, tert-butyl, n-pentyl, and hexyl groups are preferred, and methyl, ethyl, n-propyl, n-butyl, tert-butyl, and n-pentyl groups are even more preferred, with methyl, ethyl, n-butyl, and tert-butyl being particularly preferred. The alkyl groups mentioned above are preferred because the compound represented by formula (III) tends to localize near the surface of the positive electrode active material.

[0033] Specific examples of the alkenyl group include a vinyl group, an allyl group, a methallyl group, a 2-butenyl group, a 3-methyl-2-butenyl group, a 3-butenyl group, and a 4-pentenyl group. Among these, a vinyl group, an allyl group, a methallyl group, and a 2-butenyl group are preferred, a vinyl group, an allyl group, and a methallyl group are more preferred, and a vinyl group or an allyl group is particularly preferred. The above-mentioned alkenyl groups are preferred because the compound represented by formula (III) tends to be localized near the surface of the positive electrode active material.

[0034] Specific examples of the alkynyl group include an ethynyl group, a 2-propynyl group, a 2-butynyl group, a 3-butynyl group, a 4-pentynyl group, and a 5-hexynyl group. Among these, an ethynyl group, a 2-propynyl group, a 2-butynyl group, and a 3-butynyl group are preferred, a 2-propynyl group and a 3-butynyl group are more preferred, and a 2-propynyl group is particularly preferred. The above-mentioned alkynyl groups are preferred because the compound represented by formula (III) tends to be localized near the surface of the positive electrode active material. The compound represented by formula (I) and (II) may be contained either alone or in combination of two or more.

[0035] The molecular weight of the compounds represented by the above formulas (I) and (II) is not particularly limited, but is usually 100 or more and usually 2000 or less, preferably 1000 or less, more preferably 500 or less, and particularly preferably 300 or less. When the molecular weight is within the above range, the compound is easy to handle and the viscosity of the electrolyte solution when it is contained can be made appropriate.

[0036] The content of the compounds represented by the above formulas (I) and (II) in the nonaqueous electrolyte solution is not particularly limited, but is usually 0.001% by mass or more, preferably 0.01% by mass or more, and more preferably 0.1% by mass or more, and is usually 8% by mass or less, more preferably 4% by mass or less, further preferably 2% by mass or less, and most preferably 1% by mass or less. The content of the compounds (I) and / or (II) is measured by magnetic resonance spectroscopy or the like.

[0037] [A1-2. Electrolyte] <Lithium salt> As the electrolyte in the non-aqueous electrolytic solution, a lithium salt is usually used. The lithium salt is not particularly limited as long as it is known to be used for this purpose, and any lithium salt can be used, and specific examples thereof include the following:

[0038] Examples include fluorinated inorganic lithium salts, lithium fluorophosphate salts, lithium tungstate salts, lithium carboxylate salts, lithium sulfonate salts, lithium imide salts, lithium methide salts, lithium oxalate salts, and fluorine-containing organic lithium salts.

[0039] Among them, fluorinated inorganic lithium salts include LiBF4, LiSbF6, and LiTaF6; lithium fluorophosphate salts include LiPF6, Li2PO3F, and LiPO2F2; lithium sulfonate salts include LiFSO3 and CH3SO3Li; lithium imide salts include LiN(FSO2)2, LiN(FSO2)(CF3SO2), LiN(CF3SO2)2, and LiN(C2F5SO2)2, lithium cyclic 1,2-perfluoroethanedisulfonylimide, and lithium cyclic 1,3-perfluoropropanedisulfonylimide; and lithium methide. As salts, LiC(FSO2)3, LiC(CF3SO2)3, LiC(C2F5SO2)3; as lithium oxalate salts, lithium difluorooxalatoborate, lithium bis(oxalato)borate, lithium tetrafluorooxalatophosphate, lithium difluorobis(oxalato)phosphate, lithium tris(oxalato)phosphate, etc. are more preferred because they have the effect of improving low-temperature output characteristics, high-rate charge / discharge characteristics, impedance characteristics, high-temperature storage characteristics, cycle characteristics, etc. Particularly preferred are LiPF6, LiN(FSO2)2, lithium bis(oxalato)borate, and LiFSO3. The above electrolyte salts may be used alone or in combination of two or more. The combination of two or more electrolyte salts is not particularly limited, but examples thereof include LiPF6 and LiFSO3, LiPF6 and LiPO2F2, LiPF6 and lithium bis(oxalato)borate, LiPF6 and lithium difluorobis(oxalato)phosphate, LiPF6 and lithium difluorooxalatoborate, LiPF6 and LiN(FSO2)2, and LiBF4, LiPF6 and LiN(FSO2)2. Of these, LiPF6 and LiFSO3, LiPF6 and LiPO2F2, and LiPF6 and lithium bis(oxalato)borate are preferred.

[0040] The total concentration of these electrolytes in the non-aqueous electrolyte solution is not particularly limited, but is usually 8% by mass or more, preferably 8.5% by mass or more, more preferably 9% by mass or more, and is usually 18% by mass or less, preferably 17% by mass or less, more preferably 16% by mass or less, based on the total amount of the non-aqueous electrolyte solution. When the total concentration of the electrolytes is within the above range, the electrical conductivity becomes appropriate for battery operation, and sufficient output characteristics tend to be obtained.

[0041] [A1-3. Non-aqueous solvents] Like common non-aqueous electrolytes, non-aqueous electrolytes usually contain a non-aqueous solvent as its main component, which dissolves the above-mentioned electrolyte. There are no particular limitations on the non-aqueous solvent used here, and known organic solvents can be used. Examples of organic solvents include saturated cyclic carbonates, chain carbonates, chain carboxylic acid esters, cyclic carboxylic acid esters, ether-based compounds, and sulfone-based compounds, but are not limited thereto. These can be used alone or in combination of two or more. The combination of two or more organic solvents is not particularly limited, and examples thereof include a saturated cyclic carbonate and a chain carboxylic acid ester, a cyclic carboxylic acid ester and a chain carbonate, and a saturated cyclic carbonate, a chain carbonate and a chain carboxylic acid ester. Among these, a saturated cyclic carbonate and a chain carbonate, and a saturated cyclic carbonate, a chain carbonate and a chain carboxylic acid ester are preferred.

[0042] [A1-3-1. Saturated cyclic carbonates] The saturated cyclic carbonate typically includes one having an alkylene group having 2 to 4 carbon atoms, and saturated cyclic carbonates having 2 to 3 carbon atoms are preferably used from the viewpoint of improving battery characteristics resulting from an improved degree of lithium ion dissociation.

[0043] Examples of saturated cyclic carbonates include ethylene carbonate, propylene carbonate, and butylene carbonate. Among these, ethylene carbonate and propylene carbonate are preferred, and ethylene carbonate, which is less susceptible to oxidation and reduction, is more preferred. The saturated cyclic carbonates may be used alone or in any combination and ratio of two or more.

[0044] The content of the saturated cyclic carbonate is not particularly limited and may be any content as long as it does not significantly impair the effects of the present invention, but when one type is used alone, the lower limit of the content is usually 3% by volume or more, preferably 5% by volume or more, and usually 90% by volume or less, preferably 85% by volume or less, and more preferably 80% by volume or less, based on the total amount of solvent in the nonaqueous electrolyte. By setting the content within this range, a decrease in electrical conductivity resulting from a decrease in the dielectric constant of the nonaqueous electrolyte can be avoided, and the large-current discharge characteristics, stability with respect to the negative electrode, and cycle characteristics of the nonaqueous electrolyte secondary battery tend to be in good ranges, and the oxidation / reduction resistance of the nonaqueous electrolyte and stability during high-temperature storage tend to be improved. In this embodiment, the volume % refers to the volume at 25° C. and 1 atmosphere.

[0045] [A1-3-2. Chain carbonate] As the chain carbonate, one having 3 to 7 carbon atoms is usually used, and in order to adjust the viscosity of the electrolyte solution within an appropriate range, a chain carbonate having 3 to 5 carbon atoms is preferably used.

[0046] Specific examples of the chain carbonate include dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, diisopropyl carbonate, n-propyl isopropyl carbonate, ethyl methyl carbonate, and methyl-n-propyl carbonate. Dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate are particularly preferred.

[0047] Furthermore, a chain carbonate having fluorine atoms (hereinafter sometimes abbreviated as "fluorinated chain carbonate") can also be suitably used. The number of fluorine atoms in the fluorinated chain carbonate is not particularly limited as long as it is 1 or more, but is usually 6 or less, and preferably 4 or less. When the fluorinated chain carbonate has multiple fluorine atoms, they may be bonded to the same carbon or different carbons. Examples of the fluorinated chain carbonate include fluorinated dimethyl carbonate derivatives such as fluoromethyl methyl carbonate, fluorinated ethyl methyl carbonate derivatives such as 2-fluoroethyl methyl carbonate, and fluorinated diethyl carbonate derivatives such as ethyl-(2-fluoroethyl) carbonate.

[0048] The chain carbonate may be used alone or in any combination of two or more kinds in any ratio.

[0049] The content of the chain carbonate is not particularly limited, but is usually 15% by volume or more, preferably 20% by volume or more, more preferably 25% by volume or more, and usually 90% by volume or less, preferably 85% by volume or less, more preferably 80% by volume or less, based on the total volume of the solvent in the nonaqueous electrolyte. By setting the content of the chain carbonate within the above range, the viscosity of the nonaqueous electrolyte can be set within an appropriate range, a decrease in ionic conductivity can be suppressed, and the output characteristics of the nonaqueous electrolyte secondary battery can be easily set within a good range.

[0050] Furthermore, by combining a specific chain carbonate with ethylene carbonate in a specific content, the battery performance can be significantly improved.

[0051] For example, when dimethyl carbonate and ethyl methyl carbonate are selected as specific chain carbonates, the content of ethylene carbonate is not particularly limited and is arbitrary as long as it does not significantly impair the effects of the present invention, but is usually 15% by volume or more, preferably 20% by volume or more, and usually 45% by volume or less, preferably 40% by volume or less, based on the total amount of solvent in the non-aqueous electrolyte solution. The content of dimethyl carbonate is usually 20% by volume or more, preferably 30% by volume or more, and usually 50% by volume or less, preferably 45% by volume or less, based on the total amount of solvent in the non-aqueous electrolyte solution. The content of ethyl methyl carbonate is usually 20% by volume or more, preferably 30% by volume or more, and usually 50% by volume or less, preferably 45% by volume or less. By setting the content within the above range, high temperature stability is excellent and gas generation tends to be suppressed.

[0052] [A1-3-3. Chain carboxylic acid esters] Examples of chain carboxylic acid esters include methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, methyl valerate, methyl isobutyrate, ethyl isobutyrate, and methyl pivalate. Among these, methyl acetate, ethyl acetate, propyl acetate, and butyl acetate are preferred from the viewpoint of improving battery characteristics. Chain carboxylic acid esters in which some of the hydrogen atoms of the above-mentioned compounds are substituted with fluorine atoms (e.g., methyl trifluoroacetate, ethyl trifluoroacetate, etc.) can also be suitably used.

[0053] [A1-3-4. Cyclic carboxylic acid esters] Examples of cyclic carboxylic acid esters include γ-butyrolactone and γ-valerolactone. Among these, γ-butyrolactone is more preferred. Cyclic carboxylic acid esters in which some of the hydrogen atoms in the above-mentioned compounds are substituted with fluorine atoms can also be used preferably.

[0054] [A1-3-5. Ether compounds] Preferred ether compounds are chain ethers having 3 to 10 carbon atoms, such as dimethoxymethane, diethoxymethane, ethoxymethoxymethane, ethylene glycol di-n-propyl ether, ethylene glycol di-n-butyl ether, and diethylene glycol dimethyl ether, and cyclic ethers having 3 to 6 carbon atoms, such as tetrahydrofuran, 2-methyltetrahydrofuran, 3-methyltetrahydrofuran, 1,3-dioxane, 2-methyl-1,3-dioxane, 4-methyl-1,3-dioxane, and 1,4-dioxane. Among these, as the chain ethers having 3 to 10 carbon atoms, dimethoxymethane, diethoxymethane, and ethoxymethoxymethane are preferred because they have a high solvation ability for lithium ions, improve ion dissociation, have low viscosity, and provide high ionic conductivity, and as the cyclic ethers having 3 to 6 carbon atoms, tetrahydrofuran, 1,3-dioxane, 1,4-dioxane, and the like are preferred because they provide high ionic conductivity.

[0055] The content of the ether-based compound is not particularly limited and may be any amount as long as it does not significantly impair the effects of the present invention. However, it is usually 1% by volume or more, preferably 2% by volume or more, more preferably 3% by volume or more, and usually 30% by volume or less, preferably 25% by volume or less, more preferably 20% by volume or less, based on 100% by volume of the non-aqueous solvent. When the content of the ether-based compound is within the above-mentioned preferred range, it is easy to ensure the effects of improving the degree of lithium ion dissociation of the ether and improving ionic conductivity due to reduced viscosity. Furthermore, when the negative electrode active material is a carbonaceous material, the phenomenon of co-insertion of the chain ether with the lithium ion can be suppressed, thereby allowing the input / output characteristics and charge / discharge rate characteristics to be within appropriate ranges.

[0056] [A1-3-6. Sulfone compounds] The sulfone compound is not particularly limited and may be a cyclic sulfone or a chain sulfone, but in the case of a cyclic sulfone, it usually has 3 to 6 carbon atoms, preferably 3 to 5 carbon atoms, and in the case of a chain sulfone, it is usually a compound having 2 to 6 carbon atoms, preferably 2 to 5 carbon atoms. In addition, the number of sulfonyl groups in one molecule of the sulfone compound is not particularly limited, but is usually 1 or 2.

[0057] Examples of cyclic sulfones include monosulfone compounds such as trimethylene sulfones, tetramethylene sulfones, and hexamethylene sulfones; and disulfone compounds such as trimethylene disulfones, tetramethylene disulfones, and hexamethylene disulfones. Among these, from the viewpoints of dielectric constant and viscosity, tetramethylene sulfones, tetramethylene disulfones, hexamethylene sulfones, and hexamethylene disulfones are more preferred, and tetramethylene sulfones (sulfolanes) are particularly preferred.

[0058] The sulfolanes are preferably sulfolane and / or sulfolane derivatives (hereinafter, sulfolane may also be abbreviated as "sulfolanes"). The sulfolane derivatives are preferably those in which one or more hydrogen atoms bonded to the carbon atoms constituting the sulfolane ring are substituted with a fluorine atom or an alkyl group.

[0059] Among these, 2-methylsulfolane, 3-methylsulfolane, 2-fluorosulfolane, 3-fluorosulfolane, 2,3-difluorosulfolane, 2-trifluoromethylsulfolane, 3-trifluoromethylsulfolane, and the like are preferred because they have high ionic conductivity and high input / output.

[0060] Examples of the chain sulfone include dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, monofluoromethyl methyl sulfone, difluoromethyl methyl sulfone, trifluoromethyl methyl sulfone, pentafluoroethyl methyl sulfone, etc. Among these, dimethyl sulfone, ethyl methyl sulfone, and monofluoromethyl methyl sulfone are preferred in terms of improving the high-temperature storage stability of the electrolyte solution.

[0061] The content of the sulfone compound is not particularly limited and may be any content as long as it does not significantly impair the effects of the present invention, but is usually 0.3% by volume or more, preferably 0.5% by volume or more, more preferably 1% by volume or more, and usually 40% by volume or less, preferably 35% by volume or less, more preferably 30% by volume or less, based on the total amount of solvent in the nonaqueous electrolyte solution. If the content of the sulfone compound is within the above range, an electrolyte solution with excellent high-temperature storage stability tends to be obtained.

[0062] [A1-4. Additives] The non-aqueous electrolyte may contain various additives within the range that does not significantly impair the effects of the present invention. Any conventionally known additives may be used as the additive. The additives may be used alone or in any combination and ratio of two or more.

[0063] Examples of conventional additives (hereinafter also referred to as co-additives) that can be contained in non-aqueous electrolyte solutions include cyclic carbonates having carbon-carbon unsaturated bonds, fluorine-containing cyclic carbonates, compounds having an isocyanate group, compounds having an isocyanuric acid skeleton, organic compounds having an S=O bond, phosphorus-containing organic compounds, organic compounds having a cyano group, silicon-containing compounds, aromatic compounds, non-fluorine-containing carboxylic acid esters, cyclic compounds having multiple ether bonds, compounds having an isocyanuric acid skeleton, fluorophosphates having a P=O bond, borates, oxalates, salts having an FSO2 skeleton, etc. Examples include compounds described in International Publication No. 2015 / 111676.

[0064] Among these, it is preferable to contain at least one compound selected from the group consisting of organic compounds having an S=O bond, fluorophosphates having a P=O bond, oxalates, and salts having an FSO2 skeleton. From the viewpoint of suppressing the continuous charge capacity loss rate, it is more preferable that the battery contains at least one compound selected from the group consisting of organic compounds having an S=O bond, oxalates, and salts having an FSO2 skeleton, it is even more preferable that the battery contains a salt having an FSO2 skeleton, it is particularly preferable that the battery contains a fluorosulfonate, and it is most preferable that the battery contains lithium fluorosulfonate. Furthermore, from the viewpoint of suppressing an increase in internal resistance and swelling, it is more preferable that the composition contains at least one compound selected from the group consisting of an organic compound having an S=O bond, a fluorophosphate having a P=O bond, and a salt having an FSO2 skeleton, It is more preferable that the composition contains at least one compound selected from the group consisting of sulfate esters or sulfonate esters, difluorophosphates, and fluorosulfonates, It is more preferable that the composition contains two or more compounds selected from the group consisting of sulfate esters or sulfonate esters, difluorophosphates, and fluorosulfonates, Difluorophosphate and sulfate or sulfonate, or difluorophosphate and fluorosulfonate are more preferred; Most preferred are lithium difluorophosphate and 1,2-ethylene sulfate or methylenemethane disulfonate, or lithium difluorophosphate and lithium fluorosulfonate.

[0065] The additives may be used alone or in any combination and ratio of two or more. The content of the additives (total amount when two or more types are used) can be 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and can be 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, based on 100% by mass of the nonaqueous electrolyte solution. If the content of the additives is within this range, the characteristics of the nonaqueous electrolyte secondary battery, particularly the durability and storage characteristics, can be significantly improved. Although the principle behind this is unclear, it is thought that by mixing the additives at this ratio, side reactions of the additives on the electrode can be minimized.

[0066] The mass ratio of the compound represented by formula (I) and / or (II) to the additive (total amount when two or more types are used) is typically 1 / 100 or more, preferably 10 / 100 or more, more preferably 20 / 100 or more, and even more preferably 25 / 100 or more, and typically 10,000 / 100 or less, preferably 500 / 100 or less, more preferably 100 / 100 or less, particularly preferably 80 / 100 or less, and most preferably 40 / 100 or less. This mass ratio range significantly improves the characteristics of nonaqueous electrolyte secondary batteries, particularly their durability and storage characteristics. While the underlying mechanism is unclear, it is believed that mixing at this ratio minimizes side reactions of the additive on the electrode.

[0067] When LiPF6 is contained in a non-aqueous electrolyte, the mass ratio of the additives (total amount when two or more additives are used) to the content of LiPF6 is usually 0.00005 or more, preferably 0.001 or more, more preferably 0.01 or more, even more preferably 0.02 or more, and particularly preferably 0.025 or more, and usually 1.0 or less, preferably 0.5 or less, more preferably 0.4 or less, and even more preferably 0.35 or less. This mass ratio range significantly improves the characteristics of non-aqueous electrolyte secondary batteries, particularly their durability and continuous charging characteristics. While the underlying mechanism is unclear, it is believed that mixing these additives at this ratio minimizes the decomposition side reaction of LiPF6 in non-aqueous electrolyte secondary batteries.

[0068] [A1-4-1. Organic compounds with S=O bond] The organic compound having an S=O bond is not particularly limited as long as it is an organic compound having at least one S=O bond in the molecule. It is preferably an organic compound having an S=O bond, and more preferably at least one compound selected from the group consisting of sulfonate esters (linear sulfonate esters or cyclic sulfonate esters), sulfate esters (linear sulfate esters or cyclic sulfate esters), and sulfite esters (linear sulfite esters or cyclic sulfite esters). Specific examples are shown below. However, salts having an FSO2 skeleton are not considered "organic compounds having an S=O bond" but are included in the "salts having an FSO2 skeleton" described below, and do not include the compounds represented by formula (I) above.

[0069] Chain sulfonate esters such as alkyl disulfonates, such as methyl fluorosulfonate, methyl methanesulfonate, ethyl methanesulfonate, busulfan, methyl methanesulfonyloxyacetate, methyl vinylsulfonate, allyl vinylsulfonate, propargyl allylsulfonate, methoxycarbonylmethyl methanedisulfonate, ethoxycarbonylmethyl methanedisulfonate, methoxycarbonylmethyl 1,3-butanedisulfonate, ethoxycarbonylmethyl 1,3-butanedisulfonate, 1-methoxycarbonylethyl 1,3-butanedisulfonate, and 1-ethoxycarbonylethyl 1,3-butanedisulfonate; cyclic sulfonic acid esters such as 1,3-propane sultone, 1-fluoro-1,3-propane sultone, 1-methyl-1,3-propane sultone, 1-propene-1,3-sultone, 2-propene-1,3-sultone, 1-fluoro-1-propene-1,3-sultone, 1-methyl-1-propene-1,3-sultone, 1,4-butane sultone, 1,5-pentane sultone, methylenemethane disulfonate, and ethylenemethane disulfonate; Chain sulfate esters such as dimethyl sulfate, ethyl methyl sulfate, and diethyl sulfate; cyclic sulfates such as 1,2-ethylene sulfate, 1,2-propylene sulfate, 1,3-propylene sulfate, 1,2-butylene sulfate, etc.; Chain sulfites such as dimethyl sulfite, ethyl methyl sulfite, and diethyl sulfite; Cyclic sulfites such as 1,2-ethylene sulfite, 1,2-propylene sulfite, 1,3-propylene sulfite, 1,2-butylene sulfite, etc.:

[0070] In particular, from the viewpoint of further enhancing the effect of improving charge / discharge rate characteristics and impedance characteristics in addition to the gas suppression effect during high-temperature storage, sulfonic acid (chain sulfonate ester or cyclic sulfonate ester) or sulfate ester (chain sulfate ester or cyclic sulfate ester) is preferred, chain sulfonate ester, cyclic sulfonate ester, and cyclic sulfate ester are more preferred, and 1,3-propane sultone, methylenemethane disulfonate, and 1,2-ethylene sulfate are even more preferred.

[0071] The organic compound having an S=O bond may be used alone or in any combination and ratio of two or more. The content of the organic compound having an S=O bond (total amount when two or more types are used) can be 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, based on 100% by mass of the non-aqueous electrolyte solution. If the content of the organic compound having an S=O bond is within this range, the characteristics of the non-aqueous electrolyte secondary battery, particularly the durability characteristics or continuous charging characteristics, can be significantly improved. Although the mechanism behind this is unclear, it is thought that mixing at this ratio minimizes side reactions of the additive on the electrode.

[0072] The mass ratio of the compound represented by formula (I) to the organic compound having an S=O bond (total amount when two or more types are used) is usually 1 / 100 or more, preferably 10 / 100 or more, more preferably 20 / 100 or more, and even more preferably 25 / 100 or more, and usually 10,000 / 100 or less, preferably 500 / 100 or less, more preferably 100 / 100, particularly preferably 80 / 100 or less, and most preferably 40 / 100 or less. This mass ratio range significantly improves the characteristics of nonaqueous electrolyte secondary batteries, particularly their durability and continuous charging characteristics. While the underlying mechanism is unclear, it is believed that mixing at this ratio minimizes side reactions of the additives on the electrode.

[0073] When LiPF6 is contained in a non-aqueous electrolyte, the mass ratio of the organic compound having an S=O bond (total amount if two or more types are used) to the content of LiPF6 (organic compound having an S=O bond / LiPF6) is usually 0.00005 or more, preferably 0.001 or more, more preferably 0.01 or more, even more preferably 0.02 or more, and particularly preferably 0.025 or more, and usually 1.0 or less, preferably 0.5 or less, more preferably 0.4 or less, and even more preferably 0.35 or less. This mass ratio range significantly improves the characteristics of non-aqueous electrolyte secondary batteries, particularly their durability and continuous charging characteristics. While the underlying mechanism is unclear, it is believed that mixing at this ratio minimizes the decomposition side reaction of LiPF6 in non-aqueous electrolyte secondary batteries. The content of organic compounds with S=O bonds is measured by nuclear magnetic resonance (NMR) analysis. NMR analysis is usually performed, but when the solvent peak makes it difficult to identify other compounds, gas chromatography (GC) analysis or ion chromatography (IC) analysis is also performed.

[0074] [A1-4-2. Fluorophosphates with P=O bonds] The fluorophosphate used in this embodiment is not particularly limited as long as it is a phosphate having a P═O bond and a PF bond in the molecule. Counter cations of phosphate salts having a PF bond include alkali metals such as lithium, sodium, and potassium, with lithium being preferred. Fluorophosphates having a P=O bond include: Monofluorophosphates such as Li2PO3F; Difluorophosphates such as LiPO2F2, NaPO2F2, KPO2F2; etc. In particular, difluorophosphates are preferred, and lithium difluorophosphate is more preferred, from the viewpoint of further enhancing the effects of improving charge / discharge rate characteristics and impedance characteristics in addition to the effect of suppressing gas generation during high-temperature storage.

[0075] The fluorophosphate salts having a P=O bond may be used alone or in any combination and ratio of two or more. The content of the fluorophosphate salts having a P=O bond (total amount when two or more types are used) can be 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and can be 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, based on 100% by mass of the non-aqueous electrolyte solution. If the content of the fluorophosphate salts having a P=O bond is within this range, the characteristics of the non-aqueous electrolyte secondary battery, particularly the durability characteristics or continuous charging characteristics, can be significantly improved. Although the mechanism behind this is unclear, it is thought that mixing at this ratio minimizes side reactions of the additives on the electrode.

[0076] The mass ratio of the compound represented by formula (I) to the fluorophosphate having a P=O bond (total amount when two or more types are used) is usually 1 / 100 or more, preferably 10 / 100 or more, more preferably 20 / 100 or more, and even more preferably 25 / 100 or more, and usually 10,000 / 100 or less, preferably 500 / 100 or less, more preferably 100 / 100, particularly preferably 80 / 100 or less, and most preferably 40 / 100 or less. This mass ratio range significantly improves the characteristics of nonaqueous electrolyte secondary batteries, particularly their durability and continuous charging characteristics. While the underlying mechanism is unclear, it is believed that mixing at this ratio minimizes side reactions of the additives on the electrode.

[0077] When LiPF6 is contained in a non-aqueous electrolyte, the mass ratio of fluorophosphates having P=O bonds (total amount when two or more types are used) to the content of LiPF6 (fluorophosphate / LiPF6) is usually 0.00005 or more, preferably 0.001 or more, more preferably 0.01 or more, even more preferably 0.02 or more, and particularly preferably 0.025 or more, and usually 1.0 or less, preferably 0.5 or less, more preferably 0.4 or less, and even more preferably 0.35 or less. This mass ratio range significantly improves the characteristics of non-aqueous electrolyte secondary batteries, particularly their durability and continuous charging characteristics. While the underlying mechanism is unclear, it is believed that mixing at this ratio minimizes the decomposition side reaction of LiPF6 in non-aqueous electrolyte secondary batteries. The content of fluorophosphates with P=O bonds is measured by nuclear magnetic resonance (NMR) analysis. NMR analysis is usually performed, but when the solvent peak makes it difficult to identify other compounds, ion chromatography (IC) analysis is also performed.

[0078] [A1-4-3. Salts with FSO2 skeleton] The salt having an FSO2 skeleton used in this embodiment is not particularly limited as long as it is a salt having an FSO2 skeleton in the molecule. Counter cations of salts having an FSO2 skeleton include alkali metals such as lithium, sodium, and potassium, with lithium being preferred. For example, fluorosulfonates such as FSO3Li, FSO3Na, FSO3K, FSO3(CH3)4N, FSO3(C2H5)4N, and FSO3(n-C4H9)4N; Fluorosulfonylimide salts such as LiN(FSO2)2, LiN(FSO2)(CF3SO2), etc.; Fluorosulfonylmethide salts such as LiC(FSO2)3; etc. In particular, fluorosulfonates are preferred, and lithium fluorosulfonate is more preferred, from the viewpoint of further enhancing the effects of improving charge / discharge rate characteristics and impedance characteristics in addition to the effect of suppressing gas generation during high-temperature storage.

[0079] The salt having an FSO2 skeleton may be used singly or in any combination and ratio of two or more. The content of the salt having an FSO2 skeleton (total amount when two or more types are used) can be 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and can be 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, based on 100% by mass of the nonaqueous electrolyte. If the content of the salt having an FSO2 skeleton is within this range, the characteristics of the nonaqueous electrolyte secondary battery, particularly its durability and continuous charging characteristics, can be significantly improved. Although the mechanism behind this is unclear, it is thought that mixing at this ratio minimizes side reactions of the additive on the electrode.

[0080] The mass ratio of the compound represented by formula (I) to the salt having an FSO2 skeleton (total amount when two or more types are used) is typically 1 / 100 or more, preferably 10 / 100 or more, more preferably 20 / 100 or more, and even more preferably 25 / 100 or more, and typically 10,000 / 100 or less, preferably 500 / 100 or less, more preferably 100 / 100, particularly preferably 80 / 100 or less, and most preferably 40 / 100 or less. This mass ratio range significantly improves the characteristics of nonaqueous electrolyte secondary batteries, particularly their durability and continuous charge characteristics. While the underlying mechanism is unclear, it is believed that mixing at this ratio minimizes side reactions of the additives on the electrode.

[0081] When LiPF6 is contained in a non-aqueous electrolyte, the mass ratio of the salt having an FSO2 skeleton (total amount when two or more types are used) to the content of LiPF6 (salt having an FSO2 skeleton / LiPF6) is typically 0.00005 or more, preferably 0.001 or more, more preferably 0.01 or more, even more preferably 0.02 or more, and particularly preferably 0.025 or more, and typically 1.0 or less, preferably 0.5 or less, more preferably 0.4 or less, and even more preferably 0.35 or less. This mass ratio range significantly improves the characteristics of non-aqueous electrolyte secondary batteries, particularly their durability and continuous charge characteristics. While the underlying mechanism is unclear, it is believed that mixing at this ratio minimizes the decomposition side reaction of LiPF6 in non-aqueous electrolyte secondary batteries. The content of salts with an FSO2 skeleton is measured by nuclear magnetic resonance (NMR) analysis. NMR analysis is usually performed, but when the solvent peak makes it difficult to identify other compounds, ion chromatography (IC) analysis is also performed.

[0082] [A1-4-4. Oxalates] The oxalate is not particularly limited as long as it is a compound having at least one oxalic acid skeleton in the molecule. Counter cations of the oxalate include alkali metals such as lithium, sodium, and potassium, with lithium being preferred. For example, oxalatoborate salts such as lithium bis(oxalato)borate and lithium difluorooxalatoborate; oxalate phosphate salts such as lithium tetrafluorooxalate phosphate, lithium difluorobis(oxalate)phosphate, and lithium tris(oxalate)phosphate; etc. In particular, from the viewpoint of further enhancing the effects of suppressing gas generation during high-temperature storage as well as improving charge / discharge rate characteristics and impedance characteristics, oxalatoborate salts are preferred, and lithium bis(oxalato)borate is more preferred.

[0083] One type of oxalate may be used alone, or two or more types may be used in any combination and ratio. The content of the oxalate (total amount when two or more types are used) can be 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and can be 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, based on 100% by mass of the non-aqueous electrolyte solution. If the content of the oxalate is within this range, the characteristics of the non-aqueous electrolyte secondary battery, particularly the durability characteristics or continuous charging characteristics, can be significantly improved. Although the mechanism behind this is unclear, it is thought that by mixing at this ratio, side reactions of the additive on the electrode can be minimized.

[0084] The mass ratio of the compound represented by formula (I) to the oxalate (total amount when two or more types are used) is typically 1 / 100 or more, preferably 10 / 100 or more, more preferably 20 / 100 or more, and even more preferably 25 / 100 or more, and typically 10,000 / 100 or less, preferably 500 / 100 or less, more preferably 100 / 100, particularly preferably 80 / 100 or less, and most preferably 40 / 100 or less. This mass ratio range significantly improves the characteristics of non-aqueous electrolyte secondary batteries, particularly their durability and continuous charging characteristics. While the underlying mechanism is unclear, it is believed that mixing at this ratio minimizes side reactions of the additives on the electrode.

[0085] When LiPF6 is contained in a non-aqueous electrolyte, the mass ratio of oxalate (total amount when two or more types are used) to the LiPF6 content (oxalate / LiPF6) is typically 0.00005 or more, preferably 0.001 or more, more preferably 0.01 or more, even more preferably 0.02 or more, and particularly preferably 0.025 or more, and typically 1.0 or less, preferably 0.5 or less, more preferably 0.4 or less, and even more preferably 0.35 or less. This mass ratio range significantly improves the characteristics of non-aqueous electrolyte secondary batteries, particularly their durability and continuous charging characteristics. While the underlying mechanism is unclear, it is believed that mixing at this ratio minimizes the decomposition side reaction of LiPF6 in non-aqueous electrolyte secondary batteries.

[0086] The oxalate content is measured by nuclear magnetic resonance (NMR) analysis. NMR analysis is usually performed, but when the solvent peak makes it difficult to identify other compounds, ion chromatography (IC) analysis is also performed. Some additives are considered to be electrolyte salts, and in such cases, they are distinguished based on their concentration range. For example, if a certain fluorinated inorganic salt is contained in a non-aqueous electrolyte at 10% by mass, it can be distinguished as an electrolyte, and if a certain salt having an oxalic acid skeleton is contained at 0.5% by mass, it can be distinguished as an additive.

[0087] [A2. Non-aqueous electrolyte secondary battery] A nonaqueous electrolyte secondary battery according to one embodiment of the present invention is a nonaqueous electrolyte secondary battery including a positive electrode having a positive electrode active material capable of absorbing and releasing metal ions, and a negative electrode having a negative electrode active material capable of absorbing and releasing metal ions, and containing a nonaqueous electrolyte.

[0088] [A2-1. Non-aqueous electrolyte] The nonaqueous electrolyte solution is the nonaqueous electrolyte solution described above. Although the nonaqueous electrolyte solution may be the only one described above, it is also possible to use a mixture of the nonaqueous electrolyte solution described above and other nonaqueous electrolyte solutions within the scope of the present invention.

[0089] [A2-2. Negative electrode] The negative electrode refers to a current collector having a negative electrode active material on at least a portion of its surface. [A2-2-1. Negative electrode active material] The negative electrode active material used in the negative electrode is not particularly limited as long as it can electrochemically absorb and release metal ions. Specific examples include carbonaceous materials, metal particles that can be alloyed with Li, lithium-containing metal composite oxide materials, and mixtures thereof. Among these, carbonaceous materials, metal particles that can be alloyed with Li, and mixtures of metal particles that can be alloyed with Li and graphite particles are preferred because of their excellent cycle characteristics, safety, and continuous charge characteristics. These materials may be used alone or in any combination of two or more.

[0090] [A2-2-2. Carbon-based materials] Examples of carbonaceous materials include natural graphite, artificial graphite, amorphous carbon, carbon-coated graphite, graphite-coated graphite, and resin-coated graphite. Of these, natural graphite is preferred. One carbonaceous material may be used alone, or two or more carbonaceous materials may be used in any combination and ratio. Examples of natural graphite include scaly graphite, scaly graphite, and / or graphite particles obtained by treating such graphite as a raw material with treatments such as spheroidization and densification. Among these, spherical or ellipsoidal graphite particles that have been subjected to a spheroidization treatment are particularly preferred from the viewpoints of particle packing properties and charge / discharge rate characteristics. The average particle size (d50) of the graphite particles is usually 1 μm or more and usually 100 μm or less.

[0091] [A2-2-3. Physical properties of carbon-based materials] The carbonaceous material as the negative electrode active material preferably satisfies at least one of the characteristics such as physical properties and shape shown in the following items (1) to (5), and it is particularly preferable that it simultaneously satisfies several items. (1) X-ray parameters The d value (interlayer distance) of the lattice plane (002 plane) of carbonaceous materials determined by X-ray diffraction using the Gakushin method is usually 0.335 nm or more and 0.360 nm or less. Also, the crystallite size (Lc) of carbonaceous materials determined by X-ray diffraction using the Gakushin method is 1.0 nm or more. (2) Volume-based average particle size The volume-based average particle size of the carbonaceous material is the volume-based average particle size (median diameter) determined by a laser diffraction / scattering method, and is usually 1 μm or more and 100 μm or less. (3) Raman R value, Raman half-width The Raman R value of the carbonaceous material is a value measured using argon ion laser Raman spectroscopy, and is usually 0.01 or more and 1.5 or less. In addition, the carbonaceous material has a peak at 1580 cm -1 The Raman half-width in the vicinity is not particularly limited, but is usually 10 cm -1 More than 100cm -1 The following is the result. (4) BET specific surface area The BET specific surface area of ​​a carbonaceous material is the value of the specific surface area measured using the BET method, and is usually 0.1 m 2 ·g -1 More than 100m 2 ·g -1 The following is the result. The negative electrode active material may contain two or more carbonaceous materials with different properties, where the properties refer to one or more characteristics selected from the group consisting of X-ray diffraction parameters, median diameter, Raman R value, and BET specific surface area. Preferred examples include a case where the volume-based particle size distribution is not symmetrical about the median diameter, a case where two or more carbonaceous materials having different Raman R values ​​are contained, and a case where X-ray parameters are different.

[0092] [A2-2-4. Metal particles that can be alloyed with Li] Any conventionally known metal particles that can be alloyed with Li can be used, but from the viewpoint of capacity and cycle life, the metal particles are preferably a metal selected from the group consisting of Sb, Si, Sn, Al, As, and Zn, or a compound thereof. Furthermore, an alloy consisting of two or more metals may be used, and the metal particles may be alloy particles formed from two or more metal elements. Examples of metal compounds include metal oxides, metal nitrides, and metal carbides. Also, alloys of two or more metals may be used. Among these, metal Si (hereinafter sometimes referred to as Si) or Si-containing compounds are preferred in terms of achieving high capacity.

[0093] In this specification, Si or Si-containing compounds are collectively referred to as Si compounds. Specific examples of Si compounds include SiO x ,SiN x ,SiC x , SiZ x O y (Z=C, N), etc. Si compounds include Si oxides (SiO x ) is preferred because it has a larger theoretical capacity than graphite, and amorphous Si or nano-sized Si crystals are preferred because they allow alkali ions such as lithium ions to easily enter and exit, making it possible to obtain a high capacity. This general formula SiO x is obtained from silicon dioxide (SiO2) and Si as raw materials, where the value of x is usually 0≦x<2. The average particle size (d50) of metal particles that can be alloyed with Li is usually 0.01 μm or more and usually 10 μm or less from the viewpoint of cycle life.

[0094] [A2-2-5. A mixture of metal particles that can be alloyed with Li and graphite particles] The mixture of metal particles that can be alloyed with Li and graphite particles used as the negative electrode active material may be a mixture in which the above-mentioned metal particles that can be alloyed with Li and the above-mentioned graphite particles are mixed in the state of independent particles, or may be a composite in which the metal particles that can be alloyed with Li are present on the surface or inside of graphite particles. The content of the metal particles that can be alloyed with Li relative to the total of the metal particles that can be alloyed with Li and the graphite particles is usually 1% by mass or more and 99% by mass or less.

[0095] [A2-2-6. Lithium-containing metal composite oxide material] The lithium-containing metal composite oxide material used as the negative electrode active material is not particularly limited as long as it is capable of absorbing and releasing lithium. However, from the viewpoint of high current density charge / discharge characteristics, a lithium-containing composite metal oxide material containing titanium is preferred, a composite oxide of lithium and titanium (hereinafter sometimes abbreviated as "lithium titanium composite oxide") is more preferred, and a lithium titanium composite oxide having a spinel structure is particularly preferred because it significantly reduces output resistance.

[0096] Furthermore, the lithium or titanium of the lithium titanium composite oxide may be substituted with another metal element, for example, at least one element selected from the group consisting of Al, Ga, Cu, and Zn. As a lithium titanium composite oxide, Li 4 / 3 Ti 5 / 3 O4, Li1Ti2O4 and Li 4 / 5 Ti 11 / 5 O4 is preferred. In addition, examples of lithium titanium composite oxides in which part of lithium and titanium is replaced with other elements include Li 4 / 3 Ti 4 / 3 Al 1 / 3 O4 is preferred.

[0097] [A2-2-7. Negative electrode structure and manufacturing method] The negative electrode can be manufactured by any known method as long as it does not significantly impair the effects of the present invention. For example, the negative electrode can be formed by adding a binder, a solvent, and, if necessary, a thickener, a conductive material, a filler, etc. to the negative electrode active material to form a slurry, applying the slurry to a current collector, drying it, and then pressing it.

[0098] [A2-2-7-1. Current collector] Any known current collector can be used to support the negative electrode active material. Examples of the negative electrode current collector include metal materials such as aluminum, copper, nickel, stainless steel, and nickel-plated steel, but copper is particularly preferred from the standpoints of ease of processing and cost.

[0099] [A2-2-7-2. Binder] The binder for binding the negative electrode active material is not particularly limited as long as it is a material that is stable to the non-aqueous electrolyte solution and the solvent used in producing the electrode. Specific examples include rubber-like polymers such as SBR (styrene-butadiene rubber), isoprene rubber, butadiene rubber, fluororubber, NBR (acrylonitrile-butadiene rubber), and ethylene-propylene rubber, as well as fluorine-containing polymers such as polyvinylidene fluoride, polytetrafluoroethylene, and polytetrafluoroethylene-ethylene copolymers. These may be used alone or in any combination and ratio of two or more. The ratio of the binder to the negative electrode active material is usually 0.1% by mass or more and 20% by mass or less. In particular, when a rubber-like polymer such as SBR is contained as a main component, the ratio of the binder to the negative electrode active material is usually 0.1% by mass to 5% by mass, and when a fluorine-containing polymer such as polyvinylidene fluoride is contained as a main component, the ratio of the binder to the negative electrode active material is usually 1% by mass to 15% by mass.

[0100] [A2-2-7-3. Thickener] Thickeners are usually used to adjust the viscosity of the slurry. Examples of thickeners include, but are not limited to, carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, polyvinyl alcohol, etc. These may be used alone or in any combination and ratio of two or more. Furthermore, when a thickener is used, the ratio of the thickener to the negative electrode active material is usually 0.1% by mass or more and 5% by mass or less.

[0101] [A2-2-8. Electrode density] There are no particular restrictions on the electrode structure when the negative electrode active material is made into an electrode, but the density of the negative electrode active material on the current collector is usually 1 g cm -3 More than 2.2g cm -3 The following is the result.

[0102] [A2-2-9. Thickness of negative electrode plate] The thickness of the negative electrode plate is designed to match the positive electrode plate to be used and is not particularly limited, but the thickness of the composite layer minus the thickness of the metal foil of the core material is usually 15 μm or more and 300 μm or less.

[0103] [A2-2-10. Surface coating of negative electrode plate] Alternatively, a substance having a different composition from the above-mentioned negative electrode plate may be attached to the surface of the negative electrode plate (surface-attached substance). Examples of the surface-attached substance include oxides such as aluminum oxide, sulfates such as lithium sulfate, and carbonates such as lithium carbonate.

[0104] [A2-3. Positive electrode] The positive electrode refers to a current collector having a positive electrode active material on at least a portion of its surface. [A2-3-1. Positive electrode active material] In an embodiment of the present invention, the positive electrode active material used in the positive electrode contains a lithium transition metal compound represented by the following composition formula (IV). Li 1+x MO2···(IV) In the composition formula (IV), x is -0.1 or more and 0.5 or less. In particular, the lower limit of x is preferably -0.05 or more, more preferably -0.03 or more, particularly preferably -0.02 or more, and most preferably -0.01 or more. The upper limit of x may be 0.1 or less, preferably 0.06 or less, more preferably 0.028 or less, even more preferably 0.020 or less, and most preferably 0.0 It is particularly preferable that x is 10 or less, and most preferably 0.005 or less. When x is within the above range, the combination with the compound represented by formula (I) and / or (II) contained in the electrolyte solution can suppress self-discharge, suppress swelling, reduce internal resistance, and continuous This is preferable because the effect of reducing capacity loss during charging is easily achieved.

[0105] In composition formula (IV), M represents a plurality of elements including at least Ni, and may also include Co and / or Mn. The Ni / M molar ratio is 0.40 or more and 1.0 or less. The lower limit of the molar ratio is preferably 0.45 or more, more preferably 0.50 or more, and particularly preferably 0.55 or more. The upper limit of the molar ratio may be 0.95 or less, preferably 0.90 or less, and even more preferably 0.85 or less. If the Ni / M molar ratio is within the above range, the proportion of Ni involved in charging and discharging becomes sufficiently large, and the battery has a high capacity, which is preferable.

[0106] When M contains Co, the Co / M molar ratio in composition formula (IV) is not particularly limited, but is preferably 0.05 or more, more preferably 0.08 or more, and even more preferably 0.10 or more. Also, it is preferably 0.35 or less, more preferably 0.30 or less, even more preferably 0.25 or less, particularly preferably 0.20 or less, and most preferably 0.15 or less. It is preferable for the Co / M molar ratio to be within the above range, since the charge / discharge capacity is increased.

[0107] When M contains Mn, the Mn / M molar ratio is not particularly limited, but is greater than 0, preferably 0.05 or greater, more preferably 0.08 or greater, and even more preferably 0.10 or greater. It may be 0.35 or less, preferably 0.30 or less, more preferably 0.25 or less, even more preferably 0.20 or less, and particularly preferably 0.15 or less. If the Mn / M molar ratio is within the above range, the ratio of Mn that is not involved in charging and discharging becomes sufficiently small, and the battery has a high capacity, which is preferable.

[0108] Among these, lithium transition metal composite oxides having a layered structure are preferred, and the following composition formula is (V) More preferably, the transition metal oxide is represented by the formula: Li a1 Ni b1 Co c1 M d1 O2 (V) In the composition formula (V), a1, b1, c1, and d1 are numerical values ​​that satisfy the following conditions: 0.90≦a1≦1.10, 0.40≦b1≦0.98, 0.01≦c1≦0.5, and 0.00≦d1≦0.50, and satisfy the conditions: 0.50≦b1+c1 and b1+c1+d1=1. M represents at least one element selected from the group consisting of Mn, Al, Mg, Zr, Fe, Ti, and Er. In the composition formula (V), it is preferable that the value d1 satisfies 0.01≦d1≦0.50.

[0109] In particular, the following composition formula (VI) It is preferable that the transition metal oxide is a transition metal oxide represented by the formula: Li a2 Ni b2 Co c2 M d2 O2···(VI) In formula (VI), a2, b2, c2, and d2 are numerical values ​​that satisfy 0.90≦a2≦1.10, 0.60≦b2≦0.98, 0.01≦c2<0.50, and 0.01≦d2<0.50, and b2+c2+d2=1. M represents at least one element selected from the group consisting of Mn, Al, Mg, Zr, Fe, Ti, and Er. A preferred example of the lithium transition metal oxide represented by the composition formula (VI) is LiNi 0.85 Co 0.10 Al 0.05 O2, LiNi 0.80 Co 0.15 Al 0.05 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, Li 1.05 Ni 0.50 Co 0.20 Mn 0.30 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 Examples include O2.

[0110] In each of the above composition formulas, M preferably contains Mn or Al, more preferably contains Mn, and further preferably is Mn or Al, because this increases the structural stability of the lithium transition metal oxide and suppresses structural deterioration during repeated charge and discharge.

[0111] [A2-3-1-1. Introduction of different elements] The lithium transition metal compound may contain other elements than those defined in the above composition formula (I).

[0112] [A2-3-1-2.Surface coating] The positive electrode active material may have a different composition (surface-attached substance) attached to its surface. This surface-attached substance is considered to be included in the positive electrode active material. Examples of the surface-attached substance include oxides such as aluminum oxide, sulfates such as lithium sulfate, and carbonates such as lithium carbonate. Carbonates are preferred because they improve the affinity between the compounds represented by formulas (I) and (II) and the positive electrode. These surface-adhering substances can be attached to the surface of the positive electrode active material by, for example, dissolving or suspending them in a solvent, adding them to the positive electrode active material by impregnation, and drying them. The amount of the surface-attached substance is preferably 1 μmol / g or more, more preferably 10 μmol / g or more, more preferably 15 μmol / g or more, and even more preferably 20 μmol / g or more, by mass relative to the positive electrode active material, and is usually 1 mmol / g or less. In this specification, the term "positive electrode active material" also refers to a positive electrode active material having a substance of a different composition attached to its surface. The amount of the substance adhering to the surface of the positive electrode active material described above is measured by ion chromatography.

[0113] [A2-3-1-3. Blend] These positive electrode active materials may be used alone or in any combination of two or more in any ratio.

[0114] [A2-3-2. Positive electrode structure and manufacturing method] The configuration of the positive electrode will be described below. In this embodiment, the positive electrode can be produced by forming a positive electrode active material layer containing a positive electrode active material and a binder on a current collector. A positive electrode using a positive electrode active material can be produced by a conventional method. That is, the positive electrode active material, the binder, and, if necessary, a conductive material and a thickener, etc., are dry-mixed to form a sheet, which is then pressed onto the positive electrode current collector. Alternatively, these materials are dissolved or dispersed in a liquid medium to form a slurry, which is then applied to the positive electrode current collector and dried to form a positive electrode active material layer on the current collector, thereby obtaining a positive electrode. Alternatively, for example, the above-mentioned positive electrode active material may be roll-formed into a sheet electrode or compression-molded into a pellet electrode. Hereinafter, the case where the slurry is applied to the positive electrode current collector and then dried will be described.

[0115] [A2-3-2-1. Active material content] The content of the positive electrode active material in the positive electrode active material layer is usually 80% by mass or more and 98% by mass or less.

[0116] [A2-3-2-2. Density of the positive electrode active material layer] The positive electrode active material layer obtained by coating and drying is preferably compacted by a hand press, a roller press, or the like to increase the packing density of the positive electrode active material. The density of the positive electrode active material layer is usually 1.5 g / cm. 3 or more, 3.0 g / cm 3 It is preferable that the concentration is 3.3 g / cm or more. 3 More preferably, 3.8 g / cm or more is usually used. 3 The following is the result.

[0117] [A2-3-2-3. Conductive material] Any known conductive material can be used as the conductive material. Specific examples include metal materials such as copper and nickel. These materials may be used alone or in any combination and ratio of two or more. The conductive material is typically used in an amount of 0.01% by mass to 50% by mass in the positive electrode active material layer.

[0118] [A2-3-2-4. Binder] The binder used in producing the positive electrode active material layer is not particularly limited, and in the case of a coating method, the type is not particularly limited as long as it is a material that can be dissolved or dispersed in the liquid medium used in producing the electrode. However, in view of weather resistance, chemical resistance, heat resistance, flame retardancy, etc., preferred binders include fluorine-based resins such as polyvinyl fluoride, polyvinylidene fluoride, and polytetrafluoroethylene; and CN group-containing polymers such as polyacrylonitrile and polyvinylidene cyanide. Also usable are mixtures, modified products, derivatives, random copolymers, alternating copolymers, graft copolymers, block copolymers, etc. The binder may be used alone or in any combination and ratio of two or more types. Furthermore, when a resin is used as a binder, the weight-average molecular weight of the resin is optional as long as it does not significantly impair the effects of the present invention, but is usually from 10,000 to 3,000,000. When the molecular weight is in this range, the strength of the electrode is improved, and the electrode can be suitably formed. The proportion of the binder in the positive electrode active material layer is usually 0.1 mass % or more and 80 mass % or less.

[0119] [A2-3-2-5. Solvent] The solvent for forming the slurry is not particularly limited in type as long as it is capable of dissolving or dispersing the positive electrode active material, conductive material, binder, and thickener used as needed, and either an aqueous solvent or an organic solvent may be used.

[0120] [A2-3-2-6. Current collector] The material of the positive electrode current collector is not particularly limited, and any known material can be used. Specific examples include metal materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum. Among these, aluminum is preferred. The current collector may be in the form of a metal foil, a metal cylinder, a metal coil, a metal plate, a metal thin film, an expanded metal, a punched metal, a foamed metal, or the like. Of these, a metal thin film is preferred. The thin film may be formed into a mesh as appropriate.

[0121] [A2-3-2-7. Thickness of the positive electrode plate] The thickness of the positive electrode plate is not particularly limited, but from the viewpoint of high capacity and high output, the thickness of the composite layer minus the thickness of the metal foil of the core material is usually 10 μm or more and 500 μm or less on one side of the current collector.

[0122] [A2-3-2-7. Surface coating of positive electrode plate] Furthermore, a substance having a different composition may be attached to the surface of the positive electrode plate, and the same substance as the above-mentioned surface-attached substance may be used.

[0123] [A2-4. Separator] A separator is usually interposed between the positive electrode and the negative electrode to prevent short circuits, and in this case, the non-aqueous electrolyte is usually impregnated into the separator before use. The separator is not particularly limited in material or shape, and any known material may be used as long as it does not significantly impair the effects of the present invention. Among these, it is preferable to use a material that is stable against a non-aqueous electrolyte solution, such as a resin, glass fiber, or inorganic material, and that is in the form of a porous sheet or nonwoven fabric having excellent liquid retention.

[0124] [A2-4-1. Material] Examples of separator materials include glass filters and polyolefins, preferably polyolefins, and particularly preferably polyethylene and polypropylene. These materials may be used alone or in any combination and ratio of two or more. The above materials may also be used in a laminated state.

[0125] [A2-4-2. Thickness] The thickness of the separator is not limited, but is usually 1 μm or more and 5 μm or less.

[0126] [A2-4-3. Porosity] When a porous material such as a porous sheet or nonwoven fabric is used as the separator, the porosity of the separator is not limited, but is usually 20% or more and 90% or less.

[0127] [A2-4-4.Form] As for the form, a thin film such as a nonwoven fabric, a woven fabric, or a microporous film is used. In the thin film form, a film with a pore size of 0.01 to 1 μm and a thickness of 5 to 50 μm is preferably used. In addition to the above independent thin film form, a separator may be used in which a composite porous layer containing the above inorganic particles is formed on the surface layer of the positive electrode and / or negative electrode using a resin binder.

[0128] [A2-4-5.Air permeability] The characteristics of a separator in a nonaqueous electrolyte secondary battery can be understood by its Gurley value. The Gurley value indicates the difficulty of air passing through the film in the thickness direction, and is expressed as the number of seconds required for 100 ml of air to pass through the film. The Gurley value of a separator is arbitrary, but is usually 10 to 1000 seconds / 100 ml.

[0129] [A2-5.Battery design] [A2-5-1. Electrode group] The electrode group may have either a laminated structure of the positive electrode plate and the negative electrode plate sandwiched between the separator, or a structure of the positive electrode plate and the negative electrode plate spirally wound with the separator sandwiched between them. The ratio of the volume of the electrode group to the internal volume of the battery (hereinafter referred to as the electrode group occupancy rate) is usually 40% to 90%.

[0130] [A2-5-2. Current collection structure] When the electrode group has the aforementioned laminated structure, a structure in which the metal core portions of the electrode layers are bundled and welded to a terminal is preferably used. It is also preferable to provide multiple terminals within the electrode to reduce resistance. When the electrode group has the aforementioned wound structure, the internal resistance can be reduced by providing multiple lead structures on each of the positive and negative electrodes and bundling them to a terminal.

[0131] [A2-5-3.Protection elements] The protective element may be a PTC (Positive Temperature Coefficient), whose resistance increases when abnormal heat is generated or excessive current flows, a thermal fuse, a thermistor, or a valve (current cutoff valve) that cuts off the current flowing in the circuit due to a sudden rise in the internal pressure or temperature of the battery when abnormal heat is generated. It is preferable to select the above protective element so that it will not operate under normal use at high current, and it is even more preferable to design it so that abnormal heat generation or thermal runaway does not occur even without the protective element.

[0132] [A2-5-4. Exterior body] A non-aqueous electrolyte secondary battery is usually constructed by housing the above-mentioned non-aqueous electrolyte, negative electrode, positive electrode, separator, etc. in an exterior body (exterior case). There are no limitations on this exterior body, and any known exterior body can be used as long as it does not significantly impair the effects of the present invention. The material of the exterior case is not particularly limited as long as it is a stable substance with respect to the non-aqueous electrolyte used. However, from the perspective of weight reduction, metals such as aluminum or aluminum alloy, and laminate films are preferably used. In the exterior case using the above metals, examples include those in which the metals are welded to each other by laser welding, resistance welding, or ultrasonic welding to form a sealed structure, or those in which the above metals are caulked through a resin gasket.

[0133] [A2-5-5. Shape] Also, the shape of the exterior case is arbitrary, and it may be any of, for example, a cylindrical shape, a rectangular shape, a laminate shape, a coin shape, a large size, etc.

[0134] [B. Second Embodiment]

[0135] Hereinafter, the embodiments for carrying out the present invention will be described in detail. However, the description given below is an example (representative example) of the embodiments of the present invention, and the present invention is not limited to these contents as long as it does not exceed the gist described in the claims.

[0136] The second embodiment of the present invention relates to a non-aqueous electrolyte and a non-aqueous electrolyte secondary battery including the non-aqueous electrolyte, and includes a positive electrode having a positive electrode active material capable of occluding and releasing metal ions, a negative electrode having a negative electrode active material capable of occluding and releasing metal ions, and a non-aqueous electrolyte. Hereinafter, each component will be described.

[0137] [B1. Non-aqueous electrolyte] [B1-1-1. Compound represented by formula (I) and / or (II)] The non-aqueous electrolyte used in the non-aqueous electrolyte secondary battery according to the embodiment of the present invention contains an electrolyte and a non-aqueous solvent in which the electrolyte is dissolved, similar to a general non-aqueous electrolyte, and particularly contains a compound represented by the following formula (I) and / or (II).

[0138] [Chemical formula]

[0139] In the above formulas (I) and (II), R 1 ~R 5 are mutually independent or bonded organic groups having 1 to 18 carbon atoms. The organic groups are groups having a carbon atom as a skeleton, and the group having a carbon atom as a skeleton may have an alkyl group, an alkenyl group, an alkynyl group, an aryl group, or an alkoxy group as a substituent, hydrogen atoms bonded to carbon atoms of the group having a carbon atom as a skeleton may be substituted with halogen atoms, some of the carbon atoms of the group having a carbon atom as a skeleton may be substituted with oxygen atoms to form an ether bond or an ester bond, or some of the carbon atoms of the group having a carbon atom as a skeleton may be substituted with nitrogen atoms. 1 ~R 5 (Especially R 1 ~R 3 ) are preferably hydrocarbon groups having 1 to 15 carbon atoms, each of which is independent of the other or which are bonded to one another, more preferably alkyl groups, and even more preferably methyl or ethyl groups from the viewpoint of suppressing an increase in internal resistance. 1 ~R 3 and R 4 ~R 5 may be bonded to each other to form a ring. The number of rings formed may be 1 or 2 or more. 1 and R 2 is preferably a compound in which R is a methyl group. R 6 is a spacer group, which is a divalent hydrocarbon group having 1 to 4 carbon atoms, and preferably a divalent hydrocarbon group having 1 to 3 carbon atoms. n is 2 to 4, preferably 3 or 4, and more preferably 3.

[0140] Compounds represented by the above formulas (I) and (II) include compounds in which a positive charge exists on the nitrogen atom and a negative charge exists on the oxygen atom bonded to the sulfur atom, such as the following compounds:

[0141] [ka]

[0142] [ka]

[0143] [ka]

[0144] Among these, in the above formula (I), R 1 and R 2 In addition, in the formulas (I) and (II), R 1 ~R 3 and R 4 ~R 5 are bonded to each other to form a ring, the ring formed is preferably a 5- or 6-membered nitrogen-containing heterocyclic ring which may have a substituent, more preferably a 6-membered nitrogen-containing heterocyclic ring which may have a substituent. The ring formed may be further condensed with one or more rings, and the ring formed may further have an oxygen atom. Examples of the 5- or 6-membered nitrogen-containing heterocycle include pyrrolidinium, piperidinium, pyridinium, imidazolium, pyrazolium, pyrimidinium, triazinium, and triazolium. Of these, piperidinium and pyridinium are preferred because they can suppress side reactions with the negative electrode. The substituents that may be present on the ring include alkyl groups, alkenyl groups, and alkynyl groups, which may contain fluorine atoms and / or oxygen atoms. Among these, alkyl groups and alkenyl groups are preferred in terms of adsorptivity to the positive electrode.

[0145] Of the compounds represented by the above formula (II), compounds represented by the following formula (III) are particularly preferred. [ka] In the above formula (III), R 6 is R in the above formula (II) 6is synonymous with. R 7 ~R 11 may be the same or different and are a hydrogen atom, a halogen atom, or a hydrocarbon group. n has the same meaning as n in the above formula (II).

[0146] Examples of halogen atoms include chlorine atoms and fluorine atoms, with fluorine atoms being preferred. Examples of the hydrocarbon group include an alkyl group, an alkenyl group, and an alkynyl group, which may contain a fluorine atom and / or an oxygen atom. Preferred are alkyl groups and alkenyl groups. Specific examples of the alkyl group include methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, n-pentyl, hexyl, heptyl, octyl, nonyl, and decyl groups. Among these, methyl, ethyl, n-propyl, n-butyl, tert-butyl, n-pentyl, and hexyl groups are preferred, and methyl, ethyl, n-propyl, n-butyl, tert-butyl, and n-pentyl groups are even more preferred, with methyl, ethyl, n-butyl, and tert-butyl being particularly preferred. The alkyl groups mentioned above are preferred because the compound represented by formula (III) tends to localize near the surface of the positive electrode active material.

[0147] Specific examples of the alkenyl group include a vinyl group, an allyl group, a methallyl group, a 2-butenyl group, a 3-methyl-2-butenyl group, a 3-butenyl group, and a 4-pentenyl group. Among these, a vinyl group, an allyl group, a methallyl group, and a 2-butenyl group are preferred, a vinyl group, an allyl group, and a methallyl group are more preferred, and a vinyl group or an allyl group is particularly preferred. The above-mentioned alkenyl groups are preferred because the compound represented by formula (III) tends to be localized near the surface of the positive electrode active material.

[0148] Specific examples of the alkynyl group include an ethynyl group, a 2-propynyl group, a 2-butynyl group, a 3-butynyl group, a 4-pentynyl group, and a 5-hexynyl group. Among these, an ethynyl group, a 2-propynyl group, a 2-butynyl group, and a 3-butynyl group are preferred, a 2-propynyl group and a 3-butynyl group are more preferred, and a 2-propynyl group is particularly preferred. The above-mentioned alkynyl groups are preferred because the compound represented by formula (III) tends to be localized near the surface of the positive electrode active material. The compound represented by formula (I) and (II) may be contained either alone or in combination of two or more.

[0149] The molecular weight of the compounds represented by the above formulas (I) and (II) is not particularly limited, but is usually 100 or more and usually 2000 or less, preferably 1000 or less, more preferably 500 or less, and particularly preferably 300 or less. When the molecular weight is within the above range, the compound is easy to handle and the viscosity of the electrolyte solution when it is contained can be made appropriate.

[0150] The content of the compounds represented by the above formulas (I) and (II) in the nonaqueous electrolyte solution is not particularly limited, but is usually 0.001% by mass or more, preferably 0.01% by mass or more, and more preferably 0.1% by mass or more, and is usually 8% by mass or less, more preferably 4% by mass or less, further preferably 2% by mass or less, and most preferably 1% by mass or less. The content of the compounds (I) and / or (II) is measured by magnetic resonance spectroscopy or the like.

[0151] [B1-1-2. Specific additives] The nonaqueous electrolyte used in the nonaqueous electrolyte secondary battery according to an embodiment of the present invention further contains at least one compound (Y) (hereinafter also referred to as a co-additive) selected from the group consisting of fluorophosphates having a P=O bond, salts having an FSO2 skeleton, oxalates, and organic compounds having an S=O bond, and the content of the compound is 0.001 to 5 mass %. Among these, from the viewpoint of low-temperature discharge characteristics, it is preferable to contain at least one compound selected from the group consisting of fluorophosphates having a P=O bond, salts having an FSO2 skeleton, and oxalates. The compound (Y) is contained in the non-aqueous electrolyte solution in an amount of usually 0.001% by mass or more, preferably 0.01% by mass or more, and usually 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, even more preferably 2% by mass or less, and particularly preferably 1% by mass or less. In this embodiment, the content (mass) of the compound (X) represented by the formula (I) and / or (II) contained in the non-aqueous electrolyte solution is equal to or less than the content (mass) of the compound (X). The content (mass) of the compound (X) contained in the non-aqueous electrolyte solution may be equal to or less than 80% of the content (mass) of the compound (Y), preferably equal to or less than 60%, and more preferably equal to or less than 40%. The effect obtained by the configuration of this embodiment becomes more pronounced when the content of the compound (X) is within a specific range compared to the content of the compound (Y). [B1-1-2-1. Organic compounds with S=O bond] The organic compound having an S=O bond is not particularly limited as long as it is an organic compound having at least one S=O bond in the molecule. An ester compound having an S=O bond is preferred, and a compound selected from the group consisting of sulfonate esters (linear sulfonate esters or cyclic sulfonate esters), sulfate esters (linear sulfate esters or cyclic sulfate esters), or sulfite esters (linear sulfite esters or cyclic sulfite esters) is more preferred. Specific examples are shown below. However, salts having an FSO2 skeleton are not considered "organic compounds having an S=O bond" but are included in the "salts having an FSO2 skeleton" described below, and do not include the compound represented by formula (I) above.

[0152] Chain sulfonate esters such as alkyl disulfonates, such as methyl fluorosulfonate, methyl methanesulfonate, ethyl methanesulfonate, busulfan, methyl methanesulfonyloxyacetate, methyl vinylsulfonate, allyl vinylsulfonate, propargyl allylsulfonate, methoxycarbonylmethyl methanedisulfonate, ethoxycarbonylmethyl methanedisulfonate, methoxycarbonylmethyl 1,3-butanedisulfonate, ethoxycarbonylmethyl 1,3-butanedisulfonate, 1-methoxycarbonylethyl 1,3-butanedisulfonate, and 1-ethoxycarbonylethyl 1,3-butanedisulfonate; cyclic sulfonic acid esters such as 1,3-propane sultone, 1-fluoro-1,3-propane sultone, 1-methyl-1,3-propane sultone, 1-propene-1,3-sultone, 2-propene-1,3-sultone, 1-fluoro-1-propene-1,3-sultone, 1-methyl-1-propene-1,3-sultone, 1,4-butane sultone, 1,5-pentane sultone, methylenemethane disulfonate, and ethylenemethane disulfonate; Chain sulfate esters such as dimethyl sulfate, ethyl methyl sulfate, and diethyl sulfate; cyclic sulfates such as 1,2-ethylene sulfate, 1,2-propylene sulfate, 1,3-propylene sulfate, 1,2-butylene sulfate, etc.; Chain sulfites such as dimethyl sulfite, ethyl methyl sulfite, and diethyl sulfite; Cyclic sulfites such as 1,2-ethylene sulfite, 1,2-propylene sulfite, 1,3-propylene sulfite, 1,2-butylene sulfite, etc.:

[0153] In particular, from the viewpoint of further enhancing the effect of improving charge / discharge rate characteristics and impedance characteristics in addition to the gas suppression effect during high-temperature storage, sulfonic acid (chain sulfonate ester or cyclic sulfonate ester) or sulfate ester (chain sulfate ester or cyclic sulfate ester) is preferred, chain sulfonate ester, cyclic sulfonate ester, and cyclic sulfate ester are more preferred, and 1,3-propane sultone, methylenemethane disulfonate, and 1,2-ethylene sulfate are even more preferred.

[0154] The organic compound having an S=O bond may be used alone or in any combination and ratio of two or more. The content of the organic compound having an S=O bond (total amount when two or more types are used) is 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and 5% by mass or less, preferably 3% by mass or less, based on 100% by mass of the non-aqueous electrolyte. If the content of the organic compound having an S=O bond is within this range, the characteristics of the non-aqueous electrolyte secondary battery, particularly the durability characteristics or continuous charging characteristics, can be significantly improved. Although the mechanism behind this is unclear, it is thought that by mixing at this ratio, side reactions of the additive on the electrode can be minimized.

[0155] The mass ratio of the compound represented by formula (I) to the organic compound having an S=O bond (total amount when two or more types are used) is usually 1 / 100 or more, preferably 10 / 100 or more, more preferably 20 / 100 or more, and even more preferably 25 / 100 or more, and usually 10,000 / 100 or less, preferably 500 / 100 or less, more preferably 100 / 100, particularly preferably 80 / 100 or less, and most preferably 40 / 100 or less. This mass ratio range significantly improves the characteristics of nonaqueous electrolyte secondary batteries, particularly their durability and continuous charging characteristics. While the underlying mechanism is unclear, it is believed that mixing at this ratio minimizes side reactions of the additives on the electrode.

[0156] When LiPF6 is contained in a non-aqueous electrolyte, the mass ratio of the organic compound having an S=O bond (total amount if two or more types are used) to the content of LiPF6 (organic compound having an S=O bond / LiPF6) is usually 0.00005 or more, preferably 0.001 or more, more preferably 0.01 or more, even more preferably 0.02 or more, and particularly preferably 0.025 or more, and usually 1.0 or less, preferably 0.5 or less, more preferably 0.4 or less, and even more preferably 0.35 or less. This mass ratio range significantly improves the characteristics of non-aqueous electrolyte secondary batteries, particularly their durability and continuous charging characteristics. While the underlying mechanism is unclear, it is believed that mixing at this ratio minimizes the decomposition side reaction of LiPF6 in non-aqueous electrolyte secondary batteries.

[0157] [B1-1-2-2. Fluorophosphates with P=O bonds] The fluorophosphate having a P═O bond used in this embodiment is not particularly limited as long as it is a phosphate having a P═O bond and a PF bond in the molecule. Counter cations of phosphates having a P=O bond and a PF bond include alkali metals such as lithium, sodium, and potassium, with lithium being preferred. Fluorophosphates having a P=O bond include: Monofluorophosphates such as Li2PO3F; Difluorophosphates such as LiPO2F2, NaPO2F2, KPO2F2; etc. In particular, difluorophosphates are preferred, and lithium difluorophosphate is more preferred, from the viewpoint of further enhancing the effects of improving charge / discharge rate characteristics and impedance characteristics in addition to the effect of suppressing gas generation during high-temperature storage.

[0158] The fluorophosphate salts having a P=O bond may be used alone or in any combination and ratio of two or more. The content of the fluorophosphate salts having a P=O bond (total amount when two or more types are used) is 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and 5% by mass or less, preferably 3% by mass or less, based on 100% by mass of the non-aqueous electrolyte solution. If the content of the fluorophosphate salts having a P=O bond is within this range, the characteristics of the non-aqueous electrolyte secondary battery, particularly the durability characteristics or continuous charging characteristics, can be significantly improved. Although the mechanism behind this is unclear, it is thought that by mixing at this ratio, side reactions of the additives on the electrode can be minimized.

[0159] The mass ratio of the compound represented by formula (I) to the fluorophosphate having a P=O bond (total amount when two or more types are used) is usually 1 / 100 or more, preferably 10 / 100 or more, more preferably 20 / 100 or more, and even more preferably 25 / 100 or more, and usually 10,000 / 100 or less, preferably 500 / 100 or less, more preferably 100 / 100, particularly preferably 80 / 100 or less, and most preferably 40 / 100 or less. This mass ratio range significantly improves the characteristics of nonaqueous electrolyte secondary batteries, particularly their durability and continuous charging characteristics. While the underlying mechanism is unclear, it is believed that mixing at this ratio minimizes side reactions of the additives on the electrode.

[0160] When LiPF6 is contained in a non-aqueous electrolyte, the mass ratio of the fluorophosphate having a P=O bond (total amount if two or more types are used) to the content of LiPF6 (fluorophosphate having a P=O bond / LiPF6) is usually 0.00005 or more, preferably 0.001 or more, more preferably 0.01 or more, even more preferably 0.02 or more, and particularly preferably 0.025 or more, and usually 1.0 or less, preferably 0.5 or less, more preferably 0.4 or less, and even more preferably 0.35 or less. This mass ratio range significantly improves the characteristics of non-aqueous electrolyte secondary batteries, particularly their durability and continuous charging characteristics. While the underlying mechanism is unclear, it is believed that mixing at this ratio minimizes the decomposition side reaction of LiPF6 in non-aqueous electrolyte secondary batteries.

[0161] [B1-1-2-3. Salts with FSO2 skeleton] The salt having an FSO2 skeleton used in this embodiment is not particularly limited as long as it is a salt having an FSO2 skeleton in the molecule. Counter cations of salts having an FSO2 skeleton include alkali metals such as lithium, sodium, and potassium, with lithium being preferred. For example, fluorosulfonates such as FSO3Li, FSO3Na, FSO3K, FSO3(CH3)4N, FSO3(C2H5)4N, and FSO3(n-C4H9)4N; Fluorosulfonylimide salts such as LiN(FSO2)2, LiN(FSO2)(CF3SO2), etc.; Fluorosulfonylmethide salts such as LiC(FSO2)3; etc. In particular, fluorosulfonates are preferred, and lithium fluorosulfonate is more preferred, from the viewpoint of further enhancing the effects of improving charge / discharge rate characteristics and impedance characteristics in addition to the effect of suppressing gas generation during high-temperature storage.

[0162] The salt having an FSO2 skeleton may be used singly or in any combination and ratio of two or more. The content of the salt having an FSO2 skeleton (total amount when two or more types are used) can be 0.001 mass% or more, preferably 0.01 mass% or more, more preferably 0.1 mass% or more, and 5 mass% or less, preferably 3 mass% or less, based on 100 mass% of the nonaqueous electrolyte. If the content of the salt having an FSO2 skeleton is within this range, the characteristics of the nonaqueous electrolyte secondary battery, particularly the durability characteristics and continuous charge characteristics, can be significantly improved. Although the mechanism behind this is unclear, it is thought that mixing at this ratio minimizes side reactions of the additive on the electrode.

[0163] The mass ratio of the compound represented by formula (I) to the salt having an FSO2 skeleton (total amount when two or more types are used) is typically 1 / 100 or more, preferably 10 / 100 or more, more preferably 20 / 100 or more, and even more preferably 25 / 100 or more, and typically 10,000 / 100 or less, preferably 500 / 100 or less, more preferably 100 / 100, particularly preferably 80 / 100 or less, and most preferably 40 / 100 or less. This mass ratio range significantly improves the characteristics of nonaqueous electrolyte secondary batteries, particularly their durability and continuous charge characteristics. While the underlying mechanism is unclear, it is believed that mixing at this ratio minimizes side reactions of the additives on the electrode.

[0164] When LiPF6 is contained in a non-aqueous electrolyte, the mass ratio of the salt having an FSO2 skeleton (total amount when two or more types are used) to the content of LiPF6 (salt having an FSO2 skeleton / LiPF6) is typically 0.00005 or more, preferably 0.001 or more, more preferably 0.01 or more, even more preferably 0.02 or more, and particularly preferably 0.025 or more, and typically 1.0 or less, preferably 0.5 or less, more preferably 0.4 or less, and even more preferably 0.35 or less. This mass ratio range significantly improves the characteristics of non-aqueous electrolyte secondary batteries, particularly their durability and continuous charge characteristics. While the underlying mechanism is unclear, it is believed that mixing at this ratio minimizes the decomposition side reaction of LiPF6 in non-aqueous electrolyte secondary batteries.

[0165] [B1-1-2-4. Oxalates] The oxalate is not particularly limited as long as it is a compound having at least one oxalic acid skeleton in the molecule. Counter cations of the oxalate include alkali metals such as lithium, sodium, and potassium, with lithium being preferred. For example, oxalatoborate salts such as lithium bis(oxalato)borate and lithium difluorooxalatoborate; oxalate phosphate salts such as lithium tetrafluorooxalate phosphate, lithium difluorobis(oxalate)phosphate, and lithium tris(oxalate)phosphate; etc. In particular, from the viewpoint of further enhancing the effects of suppressing gas generation during high-temperature storage as well as improving charge / discharge rate characteristics and impedance characteristics, oxalatoborate salts are preferred, and lithium bis(oxalato)borate is more preferred.

[0166] One type of oxalate may be used alone, or two or more types may be used in any combination and ratio. The content of the oxalate (total amount when two or more types are used) can be 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and 5% by mass or less, preferably 3% by mass or less, based on 100% by mass of the non-aqueous electrolyte solution. If the content of the oxalate is within this range, the characteristics of the non-aqueous electrolyte secondary battery, particularly the durability characteristics or continuous charging characteristics, can be significantly improved. Although the mechanism behind this is unclear, it is thought that by mixing at this ratio, side reactions of the additive on the electrode can be minimized.

[0167] The mass ratio of the compound represented by formula (I) to the oxalate (total amount when two or more types are used) is typically 1 / 100 or more, preferably 10 / 100 or more, more preferably 20 / 100 or more, and even more preferably 25 / 100 or more, and typically 10,000 / 100 or less, preferably 500 / 100 or less, more preferably 100 / 100, particularly preferably 80 / 100 or less, and most preferably 40 / 100 or less. This mass ratio range significantly improves the characteristics of non-aqueous electrolyte secondary batteries, particularly their durability and continuous charging characteristics. While the underlying mechanism is unclear, it is believed that mixing at this ratio minimizes side reactions of the additives on the electrode.

[0168] When LiPF6 is contained in a non-aqueous electrolyte, the mass ratio of oxalate (total amount when two or more types are used) to the LiPF6 content (oxalate / LiPF6) is typically 0.00005 or more, preferably 0.001 or more, more preferably 0.01 or more, even more preferably 0.02 or more, and particularly preferably 0.025 or more, and typically 1.0 or less, preferably 0.5 or less, more preferably 0.4 or less, and even more preferably 0.35 or less. This mass ratio range significantly improves the characteristics of non-aqueous electrolyte secondary batteries, particularly their durability and continuous charging characteristics. While the underlying mechanism is unclear, it is believed that mixing at this ratio minimizes the decomposition side reaction of LiPF6 in non-aqueous electrolyte secondary batteries.

[0169] The contents of the additives listed above were determined by magnetic resonance spectroscopy. Measure . Some additives are considered to be electrolyte salts, and in such cases, they are distinguished based on their concentration range. For example, if a certain fluorinated inorganic salt is contained in a non-aqueous electrolyte at 10% by mass, it can be distinguished as an electrolyte, and if a certain salt having an oxalic acid skeleton is contained at 0.5% by mass, it can be distinguished as an additive.

[0170] [B1-2. Electrolyte] The electrolyte may be the same as that in the first embodiment, and may contain an electrolyte (C) other than the compound Y. When such an electrolyte (C) is contained, the mass ratio (C) / (X) of the electrolyte (C) to the compound (X) is preferably 2 or more, more preferably 3 or more, even more preferably 4 or more, and particularly preferably 5 or more. It is also preferably 10,000 or less, preferably 2,000 or less, more preferably 1,000 or less, and particularly preferably 200 or less. When (C) / (X) is within the above range, the compound (X) acts appropriately on the electrode, sufficiently suppressing self-discharge and synergistically improving the capacity retention rate during high-temperature storage and the discharge characteristic retention at low temperatures.

[0171] [B1-3. Non-aqueous solvents] The non-aqueous solvent may be the same as in the first embodiment.

[0172] [B1-4. Additives] The non-aqueous electrolyte may contain various additives (hereinafter also referred to as co-additives) within the range that does not significantly impair the effects of the present invention. Any conventionally known additives may be used as the additives. The additives may be used alone or in any combination and ratio of two or more.

[0173] Examples of conventional additives that can be contained in non-aqueous electrolyte solutions include cyclic carbonates having a carbon-carbon unsaturated bond, fluorine-containing cyclic carbonates, compounds having an isocyanate group, compounds having an isocyanuric acid skeleton, phosphorus-containing organic compounds, organic compounds having a cyano group, silicon-containing compounds, aromatic compounds, fluorine-free carboxylic acid esters, cyclic compounds having multiple ether bonds, compounds having an isocyanuric acid skeleton, borates, etc. Examples include compounds described in International Publication No. 2015 / 111676.

[0174] The additives may be used alone or in any combination and ratio of two or more. The content of the additives (total amount when two or more types are used) can be 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less, based on 100% by mass of the nonaqueous electrolyte solution. If the content of the additives is within this range, the characteristics of the nonaqueous electrolyte secondary battery, particularly the durability characteristics or continuous charging characteristics, can be significantly improved. Although the principle behind this is unclear, it is thought that by mixing the additives at this ratio, side reactions of the additives on the electrode can be minimized.

[0175] The mass ratio of the compound represented by formula (I) and / or (II) to the additive (total amount when two or more types are used) is typically 1 / 100 or more, preferably 10 / 100 or more, more preferably 20 / 100 or more, and even more preferably 25 / 100 or more, and typically 10,000 / 100 or less, preferably 500 / 100 or less, more preferably 100 / 100 or less, particularly preferably 80 / 100 or less, and most preferably 40 / 100 or less. This mass ratio range significantly improves the characteristics of nonaqueous electrolyte secondary batteries, particularly their durability and storage characteristics. While the underlying mechanism is unclear, it is believed that mixing at this ratio minimizes side reactions of the additive on the electrode.

[0176] When LiPF6 is contained in a non-aqueous electrolyte, the mass ratio of the additives (total amount when two or more additives are used) to the content of LiPF6 is usually 0.00005 or more, preferably 0.001 or more, more preferably 0.01 or more, even more preferably 0.02 or more, and particularly preferably 0.025 or more, and usually 1.0 or less, preferably 0.5 or less, more preferably 0.4 or less, and even more preferably 0.35 or less. This mass ratio range significantly improves the characteristics of non-aqueous electrolyte secondary batteries, particularly their durability and continuous charging characteristics. While the underlying mechanism is unclear, it is believed that mixing these additives at this ratio minimizes the decomposition side reaction of LiPF6 in non-aqueous electrolyte secondary batteries.

[0177] [B2. Non-aqueous electrolyte secondary battery] A nonaqueous electrolyte secondary battery according to one embodiment of the present invention is a nonaqueous electrolyte secondary battery including a positive electrode having a positive electrode active material capable of absorbing and releasing metal ions, and a negative electrode having a negative electrode active material capable of absorbing and releasing metal ions, and containing a nonaqueous electrolyte.

[0178] [B2-1. Non-aqueous electrolyte] The non-aqueous electrolyte may be the same as that in the first embodiment.

[0179] [B2-2. Negative electrode] The negative electrode can be the same as in the first embodiment.

[0180] [B2-3. Positive electrode] The positive electrode refers to a current collector having a positive electrode active material on at least a portion of its surface. [B2-3-1. Positive electrode active material] In the embodiment of the present invention, the positive electrode active material used in the positive electrode is not particularly limited, but preferably contains a lithium transition metal compound. The lithium transition metal compound is a compound having a structure capable of desorbing and inserting lithium ions, and examples thereof include sulfides, phosphate compounds, silicate compounds, borate compounds, lithium transition metal composite oxides, etc. Among these, lithium transition metal composite oxides are preferred.

[0181] Lithium transition metal composite oxides include those with a spinel structure that allows three-dimensional diffusion and those with a layered structure that allows two-dimensional diffusion of lithium ions. x M'2O4 (M' is at least one transition metal), specifically LiMn2O4, LiCoMnO4, LiNi 0.5 Mn 1.5 O4, LiCoVO4, etc. Those with layered structures are generally Li x It is expressed as MO2 (M is at least one transition metal). Specifically, LiCoO2, LiNiO2, LiNi 0.85 Co 0.10 Al 0.05 O2, LiNi 0.80 Co 0.15 Al 0.05 O2, LiNi 0.33 Co 0.33 Mn 0.33 O2, Li 1.05 Ni 0.33 Mn 0.33 Co 0.33 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, Li 1.05 Ni 0.50 Mn0.29 Co 0.21 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 Examples include O2.

[0182] In particular, the positive electrode active material preferably contains a lithium transition metal compound represented by the following composition formula (IV). Li 1+x MO2···(IV) In the composition formula (IV), x is -0.1 or more and 0.5 or less. In particular, the lower limit of x is preferably -0.05 or more, more preferably -0.03 or more, particularly preferably -0.02 or more, and most preferably -0.01 or more. The upper limit of x may be 0.1 or less, preferably 0.06 or less, more preferably 0.028 or less, even more preferably 0.020 or less, particularly preferably 0.010 or less, and most preferably 0.005 or less. When x is within the above range, the combination with the compound represented by formula (I) and / or (II) contained in the electrolyte solution can suppress self-discharge, suppress swelling, reduce internal resistance, and further continuous This is preferable because the effect of reducing capacity loss during charging is easily achieved.

[0183] In composition formula (IV), M represents a plurality of elements including at least Ni, and may also include Co and Mn, preferably Mn. The Ni / M molar ratio is 0.40 or more and 1.0 or less. The Ni / M molar ratio is 0.2 or more and 1.0 or less. The lower limit of the molar ratio is preferably 0.30 or more, more preferably 0.40 or more, more preferably 0.45 or more, more preferably 0.55 or more, more preferably 0.65 or more, and more preferably 0.75 or more. The upper limit of the molar ratio may be 0.95 or less, preferably 0.85 or less, and more preferably 0.80 or less. If the Ni / M molar ratio is within the above range, the proportion of Ni involved in charging and discharging becomes sufficiently large, and the battery has a high capacity, which is preferable.

[0184] When M contains Co, the Co / M molar ratio in composition formula (IV) is not particularly limited, but is preferably 0.05 or more, more preferably 0.08 or more, and even more preferably 0.10 or more. Also, it is preferably 0.35 or less, more preferably 0.30 or less, even more preferably 0.25 or less, particularly preferably 0.20 or less, and most preferably 0.15 or less. It is preferable for the Co / M molar ratio to be within the above range, since the charge / discharge capacity is increased.

[0185] When M contains Mn, the Mn / M molar ratio is not particularly limited, but is greater than 0, preferably 0.05 or greater, more preferably 0.08 or greater, and even more preferably 0.10 or greater. It may be 0.35 or less, preferably 0.30 or less, more preferably 0.25 or less, even more preferably 0.20 or less, and particularly preferably 0.15 or less. If the Mn / M molar ratio is within the above range, the ratio of Mn that is not involved in charging and discharging becomes sufficiently small, and the battery has a high capacity, which is preferable.

[0186] Among these, lithium transition metal composite oxides having a layered structure are preferred, and transition metal oxides represented by the following composition formula (V) are more preferred. Li a1 Ni b1 Co c1 M d1 O2 (V) In the composition formula (V), a1, b1, c1, and d1 are numerical values ​​that satisfy the following conditions: 0.90≦a1≦1.10, 0.40≦b1≦0.98, 0.01≦c1≦0.5, and 0.00≦d1≦0.50, and satisfy the conditions: 0.50≦b1+c1 and b1+c1+d1=1. M represents at least one element selected from the group consisting of Mn, Al, Mg, Zr, Fe, Ti, and Er. In the composition formula (V), it is preferable that the value d1 satisfies 0.01≦d1≦0.50.

[0187] In particular, a transition metal oxide represented by the following composition formula (2) is preferred. Li a2 Ni b2 Co c2 M d2 O2···(VI) In formula (VI), a2, b2, c2, and d2 are numerical values ​​that satisfy 0.90≦a2≦1.10, 0.60≦b2≦0.98, 0.01≦c2<0.50, and 0.01≦d2<0.50, and b2+c2+d2=1. M represents at least one element selected from the group consisting of Mn, Al, Mg, Zr, Fe, Ti, and Er. A preferred example of the lithium transition metal oxide represented by the composition formula (VI) is LiNi 0.85 Co 0.10 Al 0.05 O2, LiNi 0.80 Co 0.15 Al 0.05 O2, LiNi 0.5 Co 0.2 Mn 0.3 O2, Li 1.05 Ni 0.50 Co 0.20 Mn 0.30 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 Examples include O2.

[0188] In each of the above composition formulas, M preferably contains Mn or Al, more preferably contains Mn, and further preferably is Mn or Al, because this increases the structural stability of the lithium transition metal oxide and suppresses structural deterioration during repeated charge and discharge.

[0189] [B2-3-1-1. Introduction of different elements] The lithium transition metal compound may contain other elements than those defined in the above composition formula (IV).

[0190] [B2-3-1-2. Surface coating] The positive electrode active material may have a different composition (surface-attached substance) attached to its surface. Examples of the surface-attached substance include oxides such as aluminum oxide, sulfates such as lithium sulfate, and carbonates such as lithium carbonate. Carbonates are preferred because they improve the affinity between the compounds represented by the formulas (II) and (III) and the positive electrode. These surface-adhering substances can be attached to the surface of the positive electrode active material by, for example, dissolving or suspending them in a solvent, adding them to the positive electrode active material by impregnation, and drying them. The amount of the surface-attached substance is preferably 1 μmol / g or more, more preferably 10 μmol / g or more, more preferably 15 μmol / g or more, and even more preferably 20 μmol / g or more, by mass relative to the positive electrode active material, and is usually 1 mmol / g or less. In this specification, the term "positive electrode active material" also refers to a positive electrode active material having a substance of a different composition attached to its surface.

[0191] [B2-3-1-3. Blend] These positive electrode active materials may be used alone or in any combination of two or more in any ratio.

[0192] [B2-3-2. Positive electrode structure and manufacturing method] The configuration of the positive electrode will be described below. In this embodiment, the positive electrode can be produced by forming a positive electrode active material layer containing a positive electrode active material and a binder on a current collector. A positive electrode using a positive electrode active material can be produced by a conventional method. That is, the positive electrode active material, the binder, and, if necessary, a conductive material and a thickener, etc., are dry-mixed to form a sheet, which is then pressed onto the positive electrode current collector. Alternatively, these materials are dissolved or dispersed in a liquid medium to form a slurry, which is then applied to the positive electrode current collector and dried to form a positive electrode active material layer on the current collector, thereby obtaining a positive electrode. Alternatively, for example, the above-mentioned positive electrode active material may be roll-formed into a sheet electrode or compression-molded into a pellet electrode. Hereinafter, the case where the slurry is applied to the positive electrode current collector and then dried will be described.

[0193] [B2-3-2-1. Active material content] The content of the positive electrode active material in the positive electrode active material layer is usually 80% by mass or more and 98% by mass or less.

[0194] [B2-3-2-2. Density of the positive electrode active material layer] The positive electrode active material layer obtained by coating and drying is preferably compacted by a hand press, a roller press, or the like to increase the packing density of the positive electrode active material. The density of the positive electrode active material layer is usually 1.5 g / cm. 3 or more, 3.0 g / cm 3 It is preferable that the concentration is 3.3 g / cm or more. 3 More preferably, 3.8 g / cm or more is usually used. 3 The following is the result.

[0195] [B2-3-2-3.Conductive materials] Any known conductive material can be used as the conductive material. Specific examples include metal materials such as copper and nickel. These materials may be used alone or in any combination and ratio of two or more. The conductive material is typically used in an amount of 0.01% by mass to 50% by mass in the positive electrode active material layer.

[0196] [B2-3-2-4. Binder] The binder used in producing the positive electrode active material layer is not particularly limited, and in the case of a coating method, the type is not particularly limited as long as it is a material that can be dissolved or dispersed in the liquid medium used in producing the electrode. However, in view of weather resistance, chemical resistance, heat resistance, flame retardancy, etc., preferred binders include fluorine-based resins such as polyvinyl fluoride, polyvinylidene fluoride, and polytetrafluoroethylene; and CN group-containing polymers such as polyacrylonitrile and polyvinylidene cyanide. Also usable are mixtures, modified products, derivatives, random copolymers, alternating copolymers, graft copolymers, block copolymers, etc. The binder may be used alone or in any combination and ratio of two or more types. Furthermore, when a resin is used as a binder, the weight-average molecular weight of the resin is optional as long as it does not significantly impair the effects of the present invention, but is usually from 10,000 to 3,000,000. When the molecular weight is in this range, the strength of the electrode is improved, and the electrode can be suitably formed. The proportion of the binder in the positive electrode active material layer is usually 0.1 mass % or more and 80 mass % or less.

[0197] [B2-3-2-5. Solvent] The solvent for forming the slurry is not particularly limited in type as long as it is capable of dissolving or dispersing the positive electrode active material, conductive material, binder, and thickener used as needed, and either an aqueous solvent or an organic solvent may be used.

[0198] [B2-3-2-6. Current collector] The material of the positive electrode current collector is not particularly limited, and any known material can be used. Specific examples include metal materials such as aluminum, stainless steel, nickel plating, titanium, and tantalum. Among these, aluminum is preferred. The current collector may be in the form of a metal foil, a metal cylinder, a metal coil, a metal plate, a metal thin film, an expanded metal, a punched metal, a foamed metal, or the like. Of these, a metal thin film is preferred. The thin film may be formed into a mesh as appropriate.

[0199] [B2-3-2-7. Thickness of the positive electrode plate] The thickness of the positive electrode plate is not particularly limited, but from the viewpoint of high capacity and high output, the thickness of the composite layer minus the thickness of the metal foil of the core material is usually 10 μm or more and 500 μm or less on one side of the current collector.

[0200] [B2-3-2 -8 .Surface coating of positive electrode plate] Furthermore, a substance having a different composition may be attached to the surface of the positive electrode plate, and the same substance as the above-mentioned surface-attached substance may be used. [B2-4. Separator] The separator may be the same as in the first embodiment. [B2-5.Battery design] The battery design can be the same as in the first embodiment. [Example]

[0201] [Experiment A1] Next, specific embodiments of the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. The compounds A1 to A11 and the additives used in this example are shown below.

[0202] [ka]

[0203] [ka]

[0204] [ka]

[0205] [ka]

[0206] [ka]

[0207] [ka]

[0208] [ka]

[0209] [ka]

[0210] [ka]

[0211] [ka]

[0212] [ka]

[0213] (Hereinafter, concomitant additives) Lithium difluorophosphate (F2PO2Li) Lithium bis(fluorosulfonyl)imide (LiFSI) Lithium Fluorosulfonate, (FSO3Li) Lithium bis(oxalato)borate (LiBOB) 1,2-Ethylene sulfate, (ESA) Ethyl methanesulfonate (EMS) 1,3-Propane sultone (PS) Methylenemethane disulfonate (MMDS)

[0214] [Examples A2 to A11, Comparative Examples A2 to A11] [Fabrication of non-aqueous electrolyte secondary battery] <Preparation of non-aqueous electrolyte> Under a dry argon atmosphere, thoroughly dried LiPF was dissolved at 1.2 mol / L (as the concentration in the non-aqueous electrolyte) in a mixture of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate (volume ratio 3:4:3). Using a non-aqueous electrolyte solution prepared by dissolving 1% by mass of vinylene carbonate as a reference, additives were further dissolved in the combinations shown in Table A1 to prepare non-aqueous electrolyte solutions. Using this nonaqueous electrolyte, a nonaqueous electrolyte secondary battery was fabricated in the following manner, and the above evaluations were carried out.

[0215] <Preparation of positive electrode 1> Li as the positive electrode active material 1.00 Ni 0.61 Mn 0.19 Co 0.20 94 parts by mass of O2 (Ni / M molar ratio = 0.61, carbonate concentration 91 μmol / g), 3 parts by mass of acetylene black as a conductive material, and 3 parts by mass of polyvinylidene fluoride (PVdF) as a binder were mixed and slurried in N-methyl-2-pyrrolidone, and this was uniformly applied to a 15 μm thick aluminum foil, dried, and then roll-pressed to form a positive electrode (hereinafter, this positive electrode may be referred to as positive electrode 1). The plate density of the positive electrode was 3.3 g / cm 3 It was.

[0216] <Preparation of positive electrode 2> Li as the positive electrode active material 1.05 Ni 0.52 Mn 0.29 Co 0.20 Positive electrode 2 was prepared in the same manner as positive electrode 1, using 90 parts by mass of O2 (Ni / M molar ratio = 0.52, carbonate concentration 16 μmol / g), 7 parts by mass of acetylene black as a conductive material, and 3 parts by mass of polyvinylidene fluoride (PVdF) as a binder. The plate density of positive electrode 2 was 3.3 g / cm. 3 It was.

[0217] <Preparation of positive electrode 3> Li as the positive electrode active material 1.05 Ni 0.34 Mn 0.33 Co 0.33 Positive electrode 3 was prepared in the same manner as positive electrode 1, using 85 parts by mass of O2 (Ni / M molar ratio = 0.34, carbonate concentration 12 μmol / g), 10 parts by mass of acetylene black as a conductive material, and 5 parts by mass of polyvinylidene fluoride (PVdF) as a binder. The plate density of positive electrode 3 was 2.6 g / cm. 3 It was.

[0218] <Preparation of Positive Electrode 4> Positive electrode 4 was prepared in the same manner as positive electrode 1, using 97 parts by mass of LiCoO2 (Ni / M molar ratio = 0, carbonate concentration 6 μmol / g) as the positive electrode active material, 1.5 parts by mass of acetylene black as the conductive material, and 1.5 parts by mass of polyvinylidene fluoride (PVdF) as the binder. The plate density of positive electrode 4 was 3.6 g / cm 3 It was.

[0219] <Preparation of negative electrode> 49 parts by weight of graphite powder was mixed with 50 parts by weight of an aqueous dispersion of sodium carboxymethylcellulose (concentration of sodium carboxymethylcellulose: 1% by weight) as a thickener and 1 part by weight of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber: 50% by weight) as a binder, and the mixture was mixed in a disperser to form a slurry. The resulting slurry was uniformly applied to a 10 μm-thick copper foil, dried, and roll-pressed to form a negative electrode.

[0220] <Production of non-aqueous electrolyte secondary battery> The positive electrode, negative electrode, and polyolefin separator were stacked in this order: negative electrode, separator, positive electrode. The battery element thus obtained was wrapped in an aluminum laminate film, and the nonaqueous electrolyte solution was injected and then vacuum-sealed to prepare a sheet-shaped nonaqueous electrolyte secondary battery. Nonaqueous electrolyte secondary batteries were prepared using the electrolyte solutions listed in Table A1, and the nonaqueous electrolyte secondary batteries of Examples A2 to A11 and Comparative Examples A2 to A11 were prepared.

[0221] [Table 1]

[0222] [Evaluation of non-aqueous electrolyte secondary batteries] The non-aqueous electrolyte secondary batteries prepared in the examples were evaluated as follows. ·Initial charge / discharge In a thermostatic bath at 25°C, a sheet-shaped non-aqueous electrolyte secondary battery was charged at a constant current of 0.05C (the current value at which the rated capacity based on the discharge capacity at a 1-hour rate is discharged in 1 hour is defined as 1C; the same applies below) up to 3.7V, then charged at a constant current / constant voltage of 0.2C up to a voltage of 4.2V, and then discharged at a constant current of 0.2C down to 2.5V. The nonaqueous electrolyte secondary battery was then stabilized by charging at a constant current and constant voltage of 0.2 C to 4.1 V and then storing at 60° C. for 24 hours. It was then discharged at a constant current to 2.5 V at 25° C., and then charged at a constant current and constant voltage of 0.2 C to a voltage of 4.2 V. It was then discharged at a constant current of 0.2 C to 2.5 V, and the discharge capacity at this time was defined as the initial capacity (A). Thereafter, constant current-constant voltage charging was performed at 0.2 C at 25 °C to a voltage of 3.7 V. This was then discharged at 0.05 C, 0.1 C, 0.25 C, 0.5 C, 0.75 C, and 1 C at -20 °C, and the voltage was measured after 10 seconds. The internal resistance was calculated from this current-voltage line and used as the initial resistance (R1). Next, constant current-constant voltage charging was carried out at 0.2 C up to a voltage of 4.2 V, and the initial charge-discharge was completed.

[0223] -Evaluation of swelling, self-discharge and increase in internal resistance The nonaqueous electrolyte secondary battery after the initial charge and discharge was left for 14 days at 60° C. Before and after leaving the battery, the nonaqueous electrolyte secondary battery was immersed in an ethanol bath at room temperature to measure its volume, and the change in volume during leaving the battery was defined as the "swelling" of the battery, and the percentage of the swell reduction due to the additive was defined as the "swelling suppression rate" (for example, swell suppression rate (%) of Example 1 = {(swelling of Comparative Example 1 - swelling of Example 1) / swelling of Comparative Example 1} × 100). This nonaqueous electrolyte secondary battery was placed in a thermostatic chamber at 25°C and subjected to constant current discharge at 0.2 C down to 2.5 V. The discharge capacity was defined as the capacity after storage (B), and the ratio of the difference between the initial capacity (A) and the capacity after storage (B) ((AB) / A × 100) was defined as the "self-discharge rate." Subsequently, at 25°C, constant current-constant voltage charging was performed at 0.2 C to a voltage of 3.7 V. The cells were then discharged at -20°C at 0.05 C, 0.1 C, 0.25 C, 0.5 C, 0.75 C, and 1 C, respectively, and the voltage was measured 10 seconds after discharge. The internal resistance was calculated from this current-voltage line and used as the resistance after storage (R2). The rate of change between R1 and R2 [(R2 - R1) / R1 x 100-100] was defined as the "internal resistance increase rate." The percentage reduction in the internal resistance increase rate due to the additive was defined as the "internal resistance increase suppression rate" (for example, internal resistance increase suppression rate (%) of Example 1 = {(internal resistance increase rate of Comparative Example 1 - internal resistance increase rate of Example 1) / internal resistance increase rate of Comparative Example 1} x 100). It can be said that the smaller the swelling, self-discharge rate, and internal resistance increase rate, the better, and the larger the swelling suppression rate and internal resistance increase suppression rate, the better.

[0224] -Evaluation of continuous charge capacity loss rate The initial charge / discharge conditions were changed from 4.2 V to 4.3 V, and the nonaqueous electrolyte secondary battery that had been initially charged / discharged was subjected to constant voltage charging up to 4.3 V at 60°C for 7 days. The amount of electricity that flowed during the constant voltage charging was defined as the continuous charge capacity loss (C), and the ratio (C / A) of this to the initial capacity (A) was defined as the "continuous charge capacity loss rate." The percentage of reduction in the continuous charge capacity loss rate due to the additive was defined as the "continuous charge capacity loss suppression rate" (for example, continuous charge capacity loss suppression rate (%) of Example 1 = {(continuous charge capacity loss rate of Comparative Example 1 - continuous charge capacity loss rate of Example 1) / continuous charge capacity loss rate of Comparative Example 1} × 100). It can be said that the smaller the continuous charge capacity loss rate, the more preferable, and the larger the continuous charge capacity loss suppression rate, the more preferable.

[0225] Table A2 shows the internal resistance increase rate and swelling in Examples A2-1 to A2-15 and Comparative Examples A2-1 to A2-3 in which the same positive electrode 1 was used but electrolyte solutions of various compositions were used. Table A3 shows the internal resistance suppression rates of Examples A3-1 to A3-2 and Comparative Examples A3-1 to A3-2 in which positive electrodes 1 to 4 were used with the same electrolyte composition. Table A4 shows the blister suppression rates for Example A4-1 and Comparative Examples A4-1 and A4-2 in which positive electrodes 1, 3 and 4 were used with the same electrolyte composition. Table A5 shows the swelling in Examples A5-1 to A5-3 and Comparative Example A5-1 in which the same positive electrode 1 was used but electrolyte solutions of various compositions were used.

[0226] As is clear from Table A2, when compounds A1 to A7 are added to the nonaqueous electrolyte solution of a nonaqueous electrolyte secondary battery containing a positive electrode active material of a specific composition (Examples A2-1 to A2-8), the internal resistance increase rate and swelling are suppressed compared to when compounds A1 to A7 are not included (Comparative Example A2-1). On the other hand, the electrolyte solution containing compound A11 used in the prior art (Patent Document 2) (Comparative Example A2-2) tends to show a large increase in internal resistance and swelling. When lithium difluorophosphate (F2PO2Li), 1,2-ethylene sulfate (ESA), or methylenemethane disulfonate (MMDS) was added, the inclusion of Compound A1 or A3 significantly suppressed the increase in internal resistance and swelling (Examples A2-9 to A2-12). Furthermore, when a fluorophosphate having a P=O bond was used in combination with lithium fluorosulfonate, ethyl methanesulfonate (EMS), or 1,2-ethylene sulfate (ESA), the inclusion of Compound A1 significantly suppressed the increase in internal resistance (Examples A2-13 to A2-15).

[0227] As is clear from Table A3, the effect of compound A4 in suppressing an increase in internal resistance was exhibited in the nonaqueous electrolyte secondary batteries (Examples A3-1 and A3-2) using positive electrodes 1 and 2 containing positive electrode active materials of specific compositions. On the other hand, the effect of compound A4 in suppressing an increase in internal resistance was small and inferior in the nonaqueous electrolyte secondary batteries (Comparative Examples A3-3 and A3-4) using positive electrodes 3 and 4 containing positive electrode active materials not having the specific compositions.

[0228] Furthermore, as is clear from Table A4, the swell suppression effect of Compound A4 was exhibited in the nonaqueous electrolyte secondary battery (Example A4-1) using Positive Electrode 1 containing a positive electrode active material having a specific composition. On the other hand, the swell suppression effect of Compound A4 was not observed in the nonaqueous electrolyte secondary batteries (Comparative Examples A4-2 and A4-3) using Positive Electrodes 3 and 4 containing positive electrode active materials not having the specific composition.

[0229] As is clear from Table A5, the SO 2 contained in the non-aqueous electrolyte n Regardless of the structure of the betaine compound, the swollenness suppression effect is exhibited in the nonaqueous electrolyte secondary batteries (Examples A5-1 to A5-3) using a positive electrode 1 containing a positive electrode active material with a specific composition.

[0230] [Table 2]

[0231] [Table 3]

[0232] [Table 4]

[0233] [Table 5]

[0234] Table A6 shows the self-discharge rates (relative values ​​with Comparative Example A6-1 set to 100) of Examples A6-1 to A6-4 and Comparative Examples A6-1 to A6-8. As is clear from Table A6, when compounds A1 to A4 were added to the nonaqueous electrolyte solution of a nonaqueous electrolyte secondary battery containing a positive electrode active material of a specific composition (Examples A6-1 to A6-4), the self-discharge rate was improved compared to when compounds A1 to A4 were not added or when a nonaqueous electrolyte secondary battery containing a positive electrode active material without a specific composition was used. On the other hand, the electrolytes containing compounds A10 or A11 used in prior art (Patent Document 2) (Comparative Examples A6-2 and A6-3) showed a larger and worse self-discharge rate than when they were not added (Comparative Example A6-1). Furthermore, in nonaqueous electrolyte secondary batteries containing a positive electrode active material without a specific composition, the addition of compound A4 to the nonaqueous electrolyte solution did not improve the self-discharge rate (Comparative Examples A6-5 to A6-8).

[0235] [Table 6]

[0236] Table A7 shows the continuous charge capacity loss rates for Examples A7-1 to A7-5 and Comparative Examples A7-1 to A7-8. Table A8 shows the continuous charge capacity loss rates of Examples A8-1 to A8-2 and Comparative Examples A8-1 to A8-3 using positive electrodes 1, 3, and 4. Table A9 shows the continuous charge capacity loss suppression rates for Example A9-1 and Comparative Examples A9-1 and A9-2 using positive electrodes 1, 3, and 4. As is clear from Tables A7 and A8, when compounds A1 and A4 are added to the nonaqueous electrolyte solution of a nonaqueous electrolyte secondary battery containing a positive electrode active material of a specific composition (Examples A7-1 and A7-2), the continuous charge capacity loss rate is improved compared to when compounds A1 and A4 are not included (Comparative Example A7-1). On the other hand, when the electrolyte solution containing compounds A10 or A11 used in the prior art (Patent Document 2) (Comparative Examples A8-2 and A8-3) is added, the continuous charge capacity loss rate is large and inferior compared to when compounds A1 and A4 are added (Examples A8-1 and A8-2). The continuous charge capacity loss rate is improved when the additive is used in combination in the amount of the auxiliary salt compared to when the additive used in the prior art (Patent Document 1) is used in combination in the amount of the main salt. When LiFSI is contained alone, the continuous charge capacity loss rate tends to be large regardless of the type of positive electrode (Comparative Examples A7-2 and A7-7). When positive electrode 3 is used, even when compound A1 is further contained in LiFSI, the continuous charge capacity loss rate is larger than when either compound is contained alone (Comparative Example A7-8). However, when using positive electrode 1, the continuous charge capacity loss rate was found to be smaller when compound A1 was further added to LiFSI than when LiFSI was added alone (Example A7-4). This confirms the synergistic effect of using positive electrode 1 in combination with LiFSI and compound A1 in amounts of auxiliary salts. Furthermore, when positive electrode 1 is used and compound A1 is further added to LiBOB or FSO3Li, the effect of suppressing the continuous charge capacity loss rate is even greater than when compound A1 alone is added (Examples A7-2 and A7-3), confirming the synergistic effect of using positive electrode 1 in combination with an auxiliary salt amount of LiBOB or FSO3Li and compound A1.

[0237] As is clear from Table A9, the effect of compound A4 in suppressing continuous charge capacity loss was exhibited in the nonaqueous electrolyte secondary battery (Example A9-1) using positive electrode 1 containing a positive electrode active material having a specific composition. On the other hand, the effect of compound A4 in suppressing continuous charge capacity loss was not observed in the nonaqueous electrolyte secondary batteries (Comparative Examples A9-1 and A9-2) using positive electrodes 3 and 4 containing positive electrode active materials not having the specific composition.

[0238] [Table 7]

[0239] [Table 8]

[0240] [Table 9] [Experiment A2] [Evaluation of non-aqueous electrolyte secondary batteries] Evaluation of initial charge / discharge, self-discharge and internal resistance increase The "self-discharge rate" and "internal resistance increase rate" were defined in the same way as in Experiment A, except that the nonaqueous electrolyte secondary battery was initially charged and discharged in the same way as in Experiment A and left at 85°C for 24 hours. It is preferable that the self-discharge rate and the rate of increase in internal resistance are smaller.

[0241] Table A10 shows the self-discharge rates (relative values ​​with Comparative Example A10-1 set to 100) of Examples A10-1 to A10-4 and Comparative Examples A10-1 to A10-2. As is clear from Table A10, when a predetermined amount of compound A4 was added to the nonaqueous electrolyte solution of a nonaqueous electrolyte secondary battery containing a positive electrode active material of a specific composition (Examples 10-1 to A10-3), the self-discharge rate was reduced and improved compared to when compound A4 was not included (Comparative Example A10-1). A nonaqueous secondary battery (Example A10-4) containing a nonaqueous electrolyte solution in which lithium bis(oxalato)borate was further added to the electrolyte solution of Example A10-1 exhibited even greater suppression of self-discharge than when compound A4 was not included (Comparative Example A10-2).

[0242] [Table 10]

[0243] Table A11 shows the internal resistance increase rates of Examples A11-1 to A11-4 and Comparative Examples A11-1 to A11-3. As is clear from Table A11, when a predetermined amount of compound A4 according to the present invention is added to the nonaqueous electrolyte solution of a nonaqueous electrolyte secondary battery containing a positive electrode active material of a specific composition according to the present invention (Examples A11-1 to A11-2), the internal resistance increase rate is reduced and improved compared to when compound A4 is not included (Comparative Example A11-1). Nonaqueous secondary batteries (Examples A11-3 and A11-4) containing nonaqueous electrolyte solutions in which lithium difluorophosphate or lithium fluorosulfonate is further added to the electrolyte solution of Example A11-1 exhibit even greater suppression of internal resistance increase.

[0244] [Table 11]

[0245] [Experiment B] Next, specific embodiments of the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples. The compounds B1 to B3 and the additives used in this example are shown below.

[0246] [ka]

[0247] [ka]

[0248] [ka]

[0249] (Hereinafter, concomitant additives) Lithium difluorophosphate (F2PO2Li) Lithium Fluorosulfonate (FSO3Li) Lithium bis(oxalato)borate (LiBOB) Lithium difluorobis(oxalato)phosphate (LiF2OP) Lithium bis(fluorosulfonyl)imide (LiFSI) Vinylene carbonate (VC) Fluoroethylene carbonate (FEC) Lithium tetrafluoroborate (LiBF4) 1,3-Dioxane (13DO) Triethyl phosphonoacetate (EDPA)

[0250] [Examples B1 to B3, Comparative Examples B1 to B3] [Fabrication of non-aqueous electrolyte secondary battery] <Preparation of non-aqueous electrolyte> Under a dry argon atmosphere, thoroughly dried LiPF was dissolved in a mixture of ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate (volume ratio 3:4:3) to prepare a nonaqueous electrolyte solution at 1.2 mol / L (as the concentration in the nonaqueous electrolyte solution). Additives were further dissolved in the combinations shown in Table B1 to prepare nonaqueous electrolyte solutions. Using this nonaqueous electrolyte, a nonaqueous electrolyte secondary battery was fabricated and evaluated in the following manner.

[0251] <Preparation of positive electrode> Li as the positive electrode active material 1.00 Ni 0.61 Mn 0.19 Co 0.20 94 parts by mass of O2 (Ni / M molar ratio = 0.61), 3 parts by mass of acetylene black as a conductive material, and 3 parts by mass of polyvinylidene fluoride (PVdF) as a binder were mixed and slurried in N-methyl-2-pyrrolidone, and this was uniformly applied to a 15 μm thick aluminum foil, dried, and then roll-pressed to form a positive electrode (hereinafter, this positive electrode may be referred to as positive electrode 1). The plate density of the positive electrode was 3.3 g / cm 3 It was.

[0252] <Preparation of negative electrode> 49 parts by weight of graphite powder was mixed with 50 parts by weight of an aqueous dispersion of sodium carboxymethylcellulose (concentration of sodium carboxymethylcellulose: 1% by weight) as a thickener and 1 part by weight of an aqueous dispersion of styrene-butadiene rubber (concentration of styrene-butadiene rubber: 50% by weight) as a binder, and the mixture was mixed in a disperser to form a slurry. The resulting slurry was uniformly applied to a 10 μm-thick copper foil, dried, and roll-pressed to form a negative electrode.

[0253] <Production of non-aqueous electrolyte secondary battery> The positive electrode, negative electrode, and polyolefin separator were stacked in this order. The resulting battery element was wrapped in an aluminum laminate film, and the nonaqueous electrolyte solution was poured into the battery, followed by vacuum sealing to prepare a sheet-shaped nonaqueous electrolyte secondary battery. The electrolyte solution used had the composition shown in each table.

[0254] [Evaluation of non-aqueous electrolyte secondary batteries] The non-aqueous electrolyte secondary batteries prepared in the examples were evaluated as follows. ·Initial charge / discharge In a thermostatic bath at 25°C, a sheet-shaped non-aqueous electrolyte secondary battery was charged at a constant current of 0.05C (the current value at which the rated capacity based on the discharge capacity at a 1-hour rate is discharged in 1 hour is defined as 1C; the same applies below) up to 3.7V, then charged at a constant current / constant voltage of 0.2C up to a voltage of 4.2V, and then discharged at a constant current of 0.2C down to 2.5V. The nonaqueous electrolyte secondary battery was then stabilized by charging at a constant current and constant voltage of 0.2 C to 4.1 V and then storing at 60° C. for 24 hours. It was then discharged at a constant current to 2.5 V at 25° C., and then charged at a constant current and constant voltage of 0.2 C to a voltage of 4.2 V. It was then discharged at a constant current of 0.2 C to 2.5 V, and the discharge capacity at this time was defined as the initial capacity (A). Thereafter, constant current-constant voltage charging was performed at 0.2 C at 25°C up to a voltage of 3.7 V. Then, the battery was discharged at 0.05 C, 0.1 C, 0.25 C, 0.5 C, 0.75 C, and 1 C at -20°C, and the voltage was measured after 10 seconds. From this current-voltage line, the internal resistance (R 1AThe internal resistance (R 1B ) as a relative value (R 1A / R 1B × 100) was taken as the initial low-temperature discharge characteristic (R1'). Next, constant current-constant voltage charging was carried out at 0.2 C up to a voltage of 4.2 V, and the initial charge-discharge was completed.

[0255] -Evaluation of self-discharge, capacity retention rate and low-temperature discharge characteristic retention rate The nonaqueous electrolyte secondary battery after the initial charge and discharge was left at 85°C for 24 hours. This nonaqueous electrolyte secondary battery was placed in a thermostatic chamber at 25°C and subjected to constant current discharge at 0.2C to 2.5V. The discharge capacity was defined as the capacity after storage (B). The ratio ((AB) / A×100) of the difference between the initial capacity (A) and the capacity after storage (B) was defined as the "self-discharge rate." Next, constant current-constant voltage charging was performed at 0.2C to a voltage of 4.2V, and then constant current discharge was performed at 0.2C to 2.5V. The discharge capacity was defined as the recovered capacity after storage (C). The ratio (C / A×100) of the initial capacity (A) to the recovered capacity after storage (C) was defined as the "capacity retention rate." Thereafter, constant current-constant voltage charging was performed at 0.2 C at 25°C up to a voltage of 3.7 V. Then, the battery was discharged at 0.05 C, 0.1 C, 0.25 C, 0.5 C, 0.75 C, and 1 C at -20°C, and the voltage was measured after 10 seconds. From this current-voltage line, the internal resistance (R 2A The internal resistance (R 2B ) as a relative value (R 2A / R 2B The internal resistance value was taken as the low-temperature discharge characteristic after storage (R2), and the rate of change between R1 and R2 [R2 / R1 × 100] was taken as the "low-temperature discharge characteristic retention rate." It can be said that the smaller the self-discharge rate and low-temperature discharge characteristic retention rate, the better, and the larger the capacity retention rate, the better.

[0256] Table B1 shows the low-temperature discharge characteristic retention rates (relative values ​​with Comparative Example B1-1 set to 100). As is clear from Table B1, when the mass of the specific zwitterionic compound (compound B1 or B2) according to the present invention is equal to or less than the total mass of the specific salt additive, the zwitterionic compound (compound B1 or B2) reduces the low-temperature discharge characteristic retention rate and improves battery performance. On the other hand, when the mass of the specific zwitterionic compound (compound B1 or B2) according to the present invention exceeds the total mass of the salt additive, the zwitterionic compound (compound B1 or B2) does not have the effect of reducing the low-temperature discharge characteristic retention rate. Furthermore, even when vinylene carbonate, fluoroethylene carbonate, lithium tetrafluoroborate, ethynylethylene carbonate, 1,3-dioxane, triethyl phosphonoacetate, or succinic anhydride, which are used in conventional technologies (Patent Documents 1, 2, or 5), were added, no effect of reducing the low-temperature discharge characteristic retention rate was observed.

[0257] [Table 12]

[0258] Table B2 shows the self-discharge rates (relative values ​​with Comparative Example B2-1 set to 100). As is clear from Table B2, when the mass of the specific zwitterionic compound (compound B1 or B2) according to the present invention is equal to or less than the total mass of the lithium salt additives, the zwitterionic compound (compound B1 or B2) reduces the self-discharge rate and improves battery performance. On the other hand, when the mass of the specific zwitterionic compound (compound B1 or B2) according to the present invention exceeds the total mass of the salt additives, the zwitterionic compound (compound B1 or B2) does not exhibit the effect of reducing the self-discharge rate. Furthermore, even when vinylene carbonate, fluoroethylene carbonate, or lithium tetrafluoroborate used in the prior art (Patent Document 2 or 5) was added, no effect of reducing the self-discharge rate was observed.

[0259] [Table 13]

[0260] Table B3 shows the capacity retention rates (relative values ​​with Comparative Example B3-1 set to 100). As is clear from Table B3, when the mass of the specific zwitterionic compound (compound B1) according to this embodiment is equal to or less than the total mass of the salt additives, the zwitterionic compound (compound B1) improves the capacity retention rate and extends the battery life. On the other hand, when the mass of the specific zwitterionic compound (compound B1) according to this embodiment exceeds the total mass of the salt additives, the zwitterionic compound (compound B1) does not improve the capacity retention rate. Furthermore, even when fluoroethylene carbonate or lithium tetrafluoroborate used in the prior art (Patent Document 2 or 5) was added, no effect of improving the capacity retention rate was observed.

[0261] [Table 15]

Claims

1. A non-aqueous electrolyte secondary battery comprising: a positive electrode having a positive electrode active material capable of absorbing and releasing metal ions; a negative electrode having a negative electrode active material capable of absorbing and releasing metal ions; and a non-aqueous electrolyte, The non-aqueous electrolyte solution contains a compound (X) represented by the following formula (I) and / or (II), and at least one compound (Y) selected from the group consisting of a fluorophosphate salt having a P═O bond, a salt having an FSO 2 skeleton, an oxalate salt, and an organic compound having an S═O bond: death, the content of the compound (Y) is 0.001 to 5% by mass, the content (mass) of the compound (X) contained in the nonaqueous electrolyte solution is equal to or less than the content (mass) of the compound (Y), The positive electrode active material of the non-aqueous electrolyte secondary battery comprises a lithium transition metal compound represented by the following composition formula (IV): Li １＋ｘ MO ２ ・・・('V) (In the above composition formula (IV), x is −0.1 or more and 0.5 or less, M is a plurality of elements including at least Ni, and the Ni / M molar ratio is 0.40 or more and 1.0 or less.) 【Chemical 1】 (In formulas (I) and (II), R １ ~R ５ are organic groups each having 1 to 18 carbon atoms, which are independent or bonded to each other, and R ６ is a hydrocarbon group having 1 to 4 carbon atoms, and n is an integer of 2 to 4.

2. The non-aqueous electrolyte secondary battery according to claim 1, wherein in formula (IV), M includes Mn.

3. 3. The nonaqueous electrolyte secondary battery according to claim 1, wherein the organic compound having an S=O bond is a sulfonate ester or a sulfate ester.

4. In the formula (I), R １ ~R ３ 4. The nonaqueous electrolyte secondary battery according to claim 1, wherein each of the groups is independently or bonded to another hydrocarbon group having 1 to 15 carbon atoms.

5. In the formula (I), R １ ~R ３ The nonaqueous electrolyte secondary battery according to any one of claims 1 to 4, wherein is a methyl group or an ethyl group.

6. 6. The nonaqueous electrolyte secondary battery according to claim 1, wherein the positive electrode active material contains 10 μmol / g or more of carbonate.

7. A non-aqueous electrolyte solution, A compound (X) represented by the following formula (I) and / or (II), Fluorophosphate salts with P=O bonds, FSO ２ at least one compound (Y) selected from the group consisting of a salt having a hydroxyl group skeleton, an oxalate salt, and an organic compound having an S═O bond; Contains the content of compound (Y) is 0.001 to 5 mass %, and the content (mass) of compound (X) contained in the non-aqueous electrolyte solution is not more than the content (mass) of compound (Y). 【Chemistry 2】 (In formulas (I) and (II), R １ ~R ５ are organic groups each having 1 to 18 carbon atoms, which are independent or bonded to each other, and R ６ is a hydrocarbon group having 1 to 4 carbon atoms, and n is an integer of 2 to 4.

8. The fluorophosphate having a P═O bond, the FSO ２ The salt having a P═O bond is a lithium fluorophosphate salt, FSO ２ The nonaqueous electrolyte solution according to claim 7 , wherein the nonaqueous electrolyte solution is a lithium salt having an oxalic acid skeleton and a lithium salt having an oxalic acid skeleton.

9. 9. The nonaqueous electrolyte solution according to claim 7 or 8, wherein the nonaqueous electrolyte solution contains an electrolyte (C) other than the compound (Y), and the content ratio (C) / (X) of the compound (X) to the content of the electrolyte (C) is 2 or more and 10,000 or less.

10. The nonaqueous electrolyte solution according to claim 7 , wherein the compound (X) has a molecular weight of 300 or less.

11. A non-aqueous electrolyte secondary battery comprising: a positive electrode having a positive electrode active material capable of absorbing and releasing metal ions; a negative electrode having a negative electrode active material capable of absorbing and releasing metal ions; and the non-aqueous electrolyte solution according to any one of claims 7 to 10.

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