Non-aqueous electrolyte secondary batteries and non-aqueous electrolytes

Abstract

A non-aqueous electrolyte secondary battery is provided that simultaneously suppresses self-discharge, suppresses expansion, reduces internal resistance, and reduces capacity loss during continuous charging. The problem is solved by a non-aqueous electrolyte secondary battery comprising: a positive electrode with a positive electrode active material capable of absorbing and releasing metal ions, a negative electrode with a negative electrode active material capable of absorbing and releasing metal ions, and a non-aqueous electrolyte. The positive electrode active material is a metal composite oxide with a high Ni content, and the non-aqueous electrolyte contains a specific compound.

Description

Technical Field

[0001] This invention relates to non-aqueous electrolyte secondary batteries and non-aqueous electrolytes. Background Technology

[0002] Lithium-ion non-aqueous electrolyte secondary batteries, which use lithium-containing transition metal oxides as the cathode and non-aqueous solvents as the electrolyte, can achieve high energy density and are therefore widely used in applications ranging from small power supplies for mobile phones and laptops to large power supplies for automobiles, railways, and load balancing. However, in recent years, the demand for high-performance non-aqueous electrolyte secondary batteries has been increasing, creating a strong need for improvements in various characteristics.

[0003] For example, Patent Document 1 discloses a non-aqueous electrolyte containing specific zwitterions, which improves the high-temperature charging and storage characteristics of the energy storage device.

[0004] For example, Patent Document 2 discloses a non-aqueous electrolyte containing a compound having cations and anions within the molecule, and discloses that a non-aqueous electrolyte secondary battery containing this electrolyte can suppress the characteristic degradation caused by storage at high temperatures and the degradation accompanying charge-discharge cycles.

[0005] Patent document 3 discloses an electrolyte containing specific onium cations as additives, which can improve the discharge maintenance rate under high voltage, suppress gas generation, and improve overcharge protection performance.

[0006] Patent document 4 discloses an additive for non-aqueous electrolytes, which contains a compound comprising SO2-, SO3- or SO4- and containing N or O heteroatoms, and discloses that it can improve overcharge stability.

[0007] Patent document 5 discloses an electrolyte containing pyridinium propane sulfonate salts, which can improve the high-temperature storage characteristics of batteries and reduce internal resistance.

[0008] Patent document 6 discloses a non-aqueous electrolyte secondary battery that uses a positive electrode with a high nickel content and an electrolyte containing monofluorophosphate and / or difluorophosphate. It discloses that the battery has high capacity retention after high-temperature storage, low storage gas volume after high-temperature storage, low resistance after high-temperature storage, low metal dissolution from the positive electrode, and low heat generation at high temperatures.

[0009] Existing technical documents

[0010] Patent documents

[0011] Patent Document 1: International Publication No. 2020 / 017318

[0012] Patent Document 2: Japanese Patent Application Publication No. 2012-204100

[0013] Patent Document 3: Korean Patent Publication No. 20150024225

[0014] Patent Document 4: US Patent Publication No. 2017 / 0125847

[0015] Patent Document 5: Chinese Patent Publication No. 106099183

[0016] Patent Document 6: International Publication No. 2019 / 031508 Summary of the Invention

[0017] The problem the invention aims to solve

[0018] In recent years, the requirements for non-aqueous electrolyte secondary batteries, especially those used in automobiles, have been increasing, demanding significantly improved battery durability. However, the aforementioned technologies have not yet achieved a high level of combined performance across all aspects of non-aqueous electrolyte secondary batteries. For example, the non-aqueous electrolyte secondary batteries in Patent Documents 1-5 require further capacity improvements, and those in Patent Documents 1-4 suffer from high self-discharge. Furthermore, the non-aqueous electrolyte secondary batteries in Patent Documents 5 and 6 exhibit problems with high self-discharge, expansion, and increased internal resistance. Moreover, conventional non-aqueous electrolyte secondary batteries also suffer from significant capacity loss during continuous charging.

[0019] The first objective of this invention is to solve the above-mentioned problems in non-aqueous electrolyte secondary batteries and to provide a non-aqueous electrolyte secondary battery that can simultaneously suppress self-discharge, suppress expansion, reduce internal resistance, and reduce capacity loss during continuous charging.

[0020] Furthermore, the non-aqueous electrolyte secondary batteries described in Patent Documents 1-3 exhibit high self-discharge and insufficient capacity retention during high-temperature storage. Additionally, the non-aqueous electrolyte secondary battery described in Patent Document 4 still exhibits insufficient discharge characteristic retention at low temperatures.

[0021] The second objective of this invention is to solve the above-mentioned problems in non-aqueous electrolyte secondary batteries and to provide a non-aqueous electrolyte that can suppress self-discharge and synergistically improve capacity retention at high temperatures and discharge characteristics at low temperatures.

[0022] Solution for solving the problem

[0023] The inventors conducted in-depth research to solve the first problem mentioned above, and found that by manufacturing a non-aqueous electrolyte secondary battery that uses a specific positive electrode and a non-aqueous electrolyte containing a specific zwitterionic compound, the above problem can be solved, thus completing the present invention.

[0024] That is, the first embodiment of the present invention is shown below as [A1] to [A6].

[0025] [A1] A non-aqueous electrolyte secondary battery, characterized in that it comprises: 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.

[0026] The non-aqueous electrolyte contains compounds represented by formula (I) and / or formula (II) below.

[0027] The positive electrode active material comprises a lithium transition metal compound as shown in the following formula (IV).

[0028] Li 1+x MO2……(IV)

[0029] (In the above composition formula (IV), x is greater than or equal to -0.1 and less than or equal to 0.5, M is a plurality of elements containing at least Ni, and the Ni / M molar ratio is greater than or equal to 0.40 and less than or equal to 1.0.)

[0030]

[0031] In equations (I) and (II), R 1 ~R 5 R is an organic group consisting of 1 to 18 carbon atoms, either independently or bonded to each other. 6 (A hydrocarbon group with 1 to 4 carbon atoms, where n is an integer from 2 to 4.)

[0032] [A2] According to the non-aqueous electrolyte secondary battery of [A1], it further contains at least one compound selected from the group consisting of fluorophosphates having P=O bonds, salts having FSO2 skeletons, oxalates and organic compounds having S=O bonds, and the content of the compound is 0.001 to 5 by mass.

[0033] [A3] The non-aqueous electrolyte secondary battery according to [A1] or [A2], wherein the organic compound having S=O bonds is a sulfonate ester or a sulfate ester.

[0034] [A4] A non-aqueous electrolyte secondary battery according to any one of [A1] to [A3], wherein, in formula (I), R 1 ~R 3 These are hydrocarbon groups with 1 to 15 carbon atoms that are independent of each other or bonded to each other.

[0035] [A5] A non-aqueous electrolyte secondary battery according to any one of [A1] to [A4], wherein, in formula (I), R 1 ~R 3 It can be methyl or ethyl.

[0036] [A6] A non-aqueous electrolyte secondary battery according to any one of [A1] to [A5], wherein the positive electrode active material comprises more than 10 μmol / g of carbonate.

[0037] The inventors conducted in-depth research to solve the second problem mentioned above, and found that by containing specific additives and specific zwitterionic compounds in a specific mass ratio within a specific range in the non-aqueous electrolyte, the above problem can be solved, thus completing the present invention. That is, the second solution of the present invention is shown below as [B1] to [B6].

[0038] [B1] A non-aqueous electrolyte, characterized in that it contains a compound (X) represented by formula (I) and / or formula (II) and at least one compound (Y) selected from the group consisting of fluorophosphates having P=O bonds, salts having an FSO2 skeleton, oxalates and organic compounds having S=O bonds, wherein the content of compound (Y) is 0.001 to 5% by mass, and the content (by mass) of compound (X) in the non-aqueous electrolyte is less than or equal to the content (by mass) of compound (Y).

[0039]

[0040] In equations (I) and (II), R 1 ~R 5 R is an organic group consisting of 1 to 18 carbon atoms, either independently or bonded to each other. 6 (A hydrocarbon group with 1 to 4 carbon atoms, where n is an integer from 2 to 4.)

[0041] [B2] According to the non-aqueous electrolyte described in [B2], the fluorophosphate with P=O bonds, the salt with FSO2 framework and the oxalate are lithium fluorophosphate with P=O bonds, lithium salt with FSO2 framework and lithium salt with oxalate framework.

[0042] [B3] The non-aqueous electrolyte according to [B1] or [B2], wherein the non-aqueous electrolyte contains an electrolyte (C) other than the compound (Y), and the content ratio (C) / (X) of the electrolyte (C) is more than 2 and less than 10,000.

[0043] [B4] 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 as described in any one of [B1] to [B3].

[0044] [B5] The non-aqueous electrolyte secondary battery according to [B4], wherein the non-aqueous electrolyte secondary battery comprises a lithium transition metal compound as shown in the following formula (IV).

[0045] Li 1+x MO2……(IV)

[0046] (In the above composition formula (IV), x is greater than or equal to -0.1 and less than or equal to 0.5, M is a plurality of elements containing at least Ni, and the Ni / M molar ratio is greater than or equal to 0.40 and less than or equal to 1.0.)

[0047] [B6] According to the non-aqueous electrolyte secondary battery described in [B5], wherein in formula (IV), M includes Mn.

[0048] The effects of the invention

[0049] According to the first aspect of the present invention, a non-aqueous electrolyte secondary battery can be provided that simultaneously suppresses self-discharge, suppresses expansion, reduces internal resistance, and reduces capacity loss during continuous charging.

[0050] The inventors speculate the following reasons for the superior performance of the non-aqueous electrolyte secondary battery with the configuration of the present invention. Specifically, while using a cathode with a high Ni ratio is effective for increasing battery capacity, a cathode with a high Ni ratio presents the following problem: compared to conventional cathodes with a high Co ratio, the oxygen atoms in the cathode are unstable and prone to side reactions with the electrolyte. Although known additives such as lithium monofluorophosphate and lithium difluorophosphate have the effect of stabilizing the large number of Ni atoms in the cathode, the stabilization effect on the oxygen atoms in the cathode is insufficient.

[0051] On the other hand, a feature of the present invention is that the electrolyte of a non-aqueous electrolyte secondary battery having a high Ni ratio contains the aforementioned compounds (I) and / or (II). Not only can the SO3 anion sites in compounds (I) and / or (II) act on the Ni atoms of the positive electrode to stabilize them, but the intramolecular nitrogen cations can also act on the oxygen atoms of the positive electrode to stabilize them, further suppressing side reactions between the positive electrode and the electrolyte compared to the prior art. Therefore, the inventors hypothesize that it is possible to maintain the internal resistance of the non-aqueous electrolyte secondary battery at a high level, suppress expansion, suppress self-discharge, and improve continuous charging characteristics.

[0052] According to a second aspect of the present invention, a non-aqueous electrolyte can be provided that can suppress self-discharge and synergistically improve capacity retention during high-temperature storage and discharge characteristic maintenance performance at low temperatures. Furthermore, a non-aqueous electrolyte secondary battery incorporating this non-aqueous electrolyte can be provided.

[0053] The inventors speculate the following reasons for the superior effect of the non-aqueous electrolyte with the second embodiment of the present invention. Specifically, the technology described in Patent Documents 1-3 adds zwitterionic compounds, which suppress electrolyte side reactions at the positive electrode, thus improving battery characteristics during high-temperature storage and charge-discharge cycles. However, on the other hand, the cationic portion of the zwitterionic compounds hinders the formation of a carbonate coating on the negative electrode, thereby accelerating the degradation of the negative electrode, promoting battery self-discharge, and accelerating the deterioration of capacity and discharge characteristics.

[0054] On the other hand, by including specific lithium salt additives and specific zwitterionic compounds in a specific ratio in the electrolyte, the lithium cations contained in the lithium salt additives have a higher adsorption capacity to the negative electrode than the cation sites of the zwitterionic compounds. Therefore, they can preferentially act on the negative electrode over betaine compounds, thus protecting the negative electrode. The inventors believe that this effect is more significant when the content of zwitterionic compounds is less than that of lithium salt additives, protecting both the negative and positive electrodes. This can suppress the self-discharge of non-aqueous electrolyte secondary batteries and improve the capacity retention rate at high temperatures and the discharge characteristics at low temperatures to a higher level than before. Detailed Implementation

[0055] <A. First Embodiment>

[0056] The following is a detailed description of the methods for implementing the present invention. However, the description below is only one example (representative example) of an embodiment of the present invention, and the present invention is not limited thereto as long as it does not exceed the spirit of the claims.

[0057] The first embodiment of the present invention relates to a non-aqueous electrolyte secondary battery, which includes 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 components will now be described.

[0058] [A1. Non-aqueous electrolyte]

[0059] [A1-1. Compounds represented by formula (I) and / or formula (II)]

[0060] Similar to conventional non-aqueous electrolytes, the non-aqueous electrolytes for non-aqueous secondary batteries according to embodiments of the present invention contain an electrolyte and a non-aqueous solvent for dissolving it, particularly containing compounds represented by formula (I) and / or formula (II).

[0061]

[0062] In equations (I) and (II) above, R 1 ~R5 These are organic groups having 1 to 18 carbon atoms, either independently or bonded together. The organic group has a carbon-based backbone, which may optionally have alkyl, alkenyl, alkynyl, aryl, or alkoxy groups as substituents. Hydrogen atoms bonded to the carbon atoms of the carbon-based group may optionally be replaced by halogen atoms. Some carbon atoms of the carbon-based group may optionally be replaced by oxygen atoms to form ether or ester bonds. Some carbon atoms of the carbon-based group may optionally be replaced by nitrogen atoms. R 1 ~R 5 (especially R) 1 ~R 3 The preferred radicals are hydrocarbon groups with 1 to 15 carbon atoms, either independently or bonded to each other; more preferably, they are alkyl groups, and from the viewpoint of suppressing the increase of internal resistance, methyl or ethyl radicals are even more preferred. Additionally, R... 1 ~R 3 and R 4 ~R 5 Each ring is selectively bonded to the others to form a ring. The number of rings formed can be one or more. Furthermore, preferably, in formula (I) above, R... 1 and R 2 Compounds containing methyl groups.

[0063] R 6 It is a spacer group, which is a divalent hydrocarbon group with 1 to 4 carbon atoms, preferably a divalent hydrocarbon group with 1 to 3 carbon atoms.

[0064] n is 2 to 4, preferably 3 or 4, and more preferably 3.

[0065] As compounds represented by formulas (I) and (II) above, the following compounds can be listed as having a positive charge on the nitrogen atom and a negative charge on the oxygen atom bonded to the sulfur atom.

[0066]

[0067]

[0068]

[0069] Preferably, in equation (I) above, R 1 and R 2 Compounds containing methyl groups. Additionally, in formulas (I) and (II), R... 1 ~R 3 and R 4 ~R 5When the rings are formed by bonding with each other, the formed ring is preferably a nitrogen-containing heterocycle with substituents that is a 5- or 6-membered ring, more preferably a nitrogen-containing heterocycle with substituents that is a 6-membered ring. One or more rings may be further condensed on the formed ring, and the formed ring may further contain oxygen atoms.

[0070] Examples of nitrogen-containing heterocycles that are 5- or 6-membered rings include pyrrolidineonium, piperidinium, pyridinium, imidazolineonium, pyrazoliumonium, pyrimidineonium, triazineonium, and triazoliumonium. Among these, piperidinium and pyridiniumonium are preferred from the viewpoint of suppressing side reactions with the negative electrode.

[0071] Regarding the substituents optionally present in the aforementioned ring, examples include alkyl, alkenyl, and alkynyl groups, and it may also contain fluorine atoms and / or oxygen atoms. Among these, alkyl and alkenyl groups are preferred from the viewpoint of adsorption to the positive electrode.

[0072] Of the above formula (II), the compound shown in formula (III) is particularly preferred.

[0073]

[0074] It should be noted that in equation (III) above, R 6 The definition of R in equation (II) above is the same as that in equation (II). 6 same.

[0075] R 7 ~R 11 They can be the same as each other or different from each other, and can be hydrogen atoms, halogen atoms or hydrocarbon groups.

[0076] The definition of n is the same as that in equation (II) above.

[0077] Regarding halogen atoms, chlorine atoms and fluorine atoms can be listed. Fluorine atoms are preferred.

[0078] Regarding hydrocarbon groups, alkyl, alkenyl, and alkynyl groups can be listed, and they may also contain fluorine atoms and / or oxygen atoms. Alkenyl and alkenyl groups are preferred.

[0079] Specific examples of alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, n-pentyl, hexyl, heptyl, octyl, nonyl, and decyl. Among these, methyl, ethyl, n-propyl, n-butyl, tert-butyl, n-pentyl, and hexyl are preferred; methyl, ethyl, n-propyl, n-butyl, tert-butyl, and n-pentyl are further preferred; and methyl, ethyl, n-butyl, and tert-butyl are particularly preferred. When the alkyl group is one of the above, the compound represented by formula (III) tends to be locally present near the surface of the positive electrode active material, and is therefore preferred.

[0080] Specific examples of alkenyl groups include vinyl, allyl, methanalyl, 2-butenyl, 3-methyl-2-butenyl, 3-butenyl, and 4-pentenyl. Among these, vinyl, allyl, methanalyl, and 2-butenyl are preferred, more preferably vinyl, allyl, and methanalyl, and particularly preferably vinyl or allyl. When the alkenyl group is one of the above, the compound represented by formula (III) tends to be locally present near the surface of the positive electrode active material, and is therefore preferred.

[0081] Specific examples of alkynyl groups include ethynyl, 2-propynyl, 2-butynyl, 3-butynyl, 4-pentynyl, and 5-hexynyl. Among these, ethynyl, 2-propynyl, 2-butynyl, and 3-butynyl are preferred, 2-propynyl and 3-butynyl are more preferred, and 2-propynyl is particularly preferred. When the alkynyl group is one of the above, the compound represented by formula (III) tends to be locally present near the surface of the positive electrode active material, and is therefore preferred.

[0082] The compounds shown in formulas (I) and (II) may contain only one type or more types.

[0083] The molecular weight of the compounds shown in formulas (I) and (II) above is not particularly limited, but is generally 100 or more, and typically 2000 or less, preferably 1000 or less, more preferably 500 or less, and particularly preferably 300 or less. By falling within the above range, the compounds are easy to process, and the viscosity of the electrolyte containing the compound can be made moderate.

[0084] The content of the compounds represented by formulas (I) and (II) above in the non-aqueous electrolyte is not particularly limited, but is generally 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and generally 8% by mass or less, more preferably 4% by mass or less, more preferably 2% by mass or less, and most preferably 1% by mass or less.

[0085] The contents of compounds (I) and / or (II) were determined using methods such as magnetic resonance spectroscopy.

[0086] [A1-2. Electrolytes]

[0087] <Lithium Salts>

[0088] Lithium salts are commonly used as electrolytes in non-aqueous electrolytes. There are no particular restrictions on the lithium salt used, as long as it is known for this application; any lithium salt can be used. Specifically, the following lithium salts can be listed.

[0089] Examples include fluorinated inorganic lithium salts, lithium fluorophosphates, lithium tungstates, lithium carboxylate salts, lithium sulfonates, lithium imides, methyl lithium salts, lithium oxalate, and fluorinated organic lithium salts.

[0090] From the perspective of improving low-temperature output characteristics, high-speed charge-discharge characteristics, impedance characteristics, high-temperature storage characteristics, and cycle characteristics, LiBF4, LiSbF6, and LiTaF6 are more preferred as fluorinated inorganic lithium salts; LiPF6, Li2PO3F, and LiPO2F2 are more preferred as lithium fluorophosphate salts; LiFSO3 and CH3SO3Li are more preferred as lithium sulfonate salts; and LiN(FSO2)2 and LiN(FSO2) are more preferred as lithium imide salts. Lithium 1,2-perfluoroethanedisulfonylimide and lithium 1,3-perfluoropropanedisulfonylimide are preferred as methyl lithium salts, along with LiC(FSO2)3, LiC(CF3SO2)3, and LiC(C2F5SO2)3. Lithium oxalate salts are also preferred, including lithium difluorooxalateborate, lithium di(oxalate)borate, lithium tetrafluorooxalate phosphate, lithium difluorodi(oxalate)phosphate, and lithium tri(oxalate)phosphate. LiPF6, LiN(FSO2)2, lithium di(oxalate)borate, and LiFSO3 are particularly preferred. Furthermore, the above electrolyte salts can be used alone or in combination of two or more.

[0091] There are no particular limitations on the combination of two or more electrolyte salts, and examples include LiPF6 with LiFSO3, LiPF6 with LiPO2F2, LiPF6 with lithium di(oxalate)borate, LiPF6 with lithium difluorodi(oxalate)phosphate, LiPF6 with lithium difluorooxalateborate, LiPF6 with LiN(FSO2)2, and LiBF4 with LiPF6 and LiN(FSO2)2. Among these, LiPF6 with LiFSO3, LiPF6 with LiPO2F2, and LiPF6 with lithium di(oxalate)borate are preferred.

[0092] There is no particular limitation on the total concentration of these electrolytes in the non-aqueous electrolyte, but relative to the total amount of the non-aqueous electrolyte, it is generally 8% by mass or more, preferably 8.5% by mass or more, more preferably 9% by mass or more, and generally 18% by mass or less, preferably 17% by mass or less, more preferably 16% by mass or less. When the total concentration of the electrolyte is within the above range, the conductivity is suitable for battery operation, and therefore there is a tendency to obtain sufficient output characteristics.

[0093] [A1-3. Non-aqueous solvents]

[0094] Similar to conventional non-aqueous electrolytes, non-aqueous electrolytes typically contain a non-aqueous solvent as their main component to dissolve the aforementioned electrolytes. There are no particular limitations on the non-aqueous solvent used here; any known organic solvent can be used. Examples of organic solvents include, but are not limited to, saturated cyclic carbonates, chain carbonates, chain carboxylic esters, cyclic carboxylic esters, ether compounds, and sulfone compounds. One of these substances can be used alone, or two or more can be used in combination.

[0095] There are no particular limitations on the combination of two or more organic solvents, and examples include saturated cyclic carbonates and chain carboxylic acid esters, cyclic carboxylic acid esters and chain carbonates, and saturated cyclic carbonates, chain carbonates and chain carboxylic acid esters. Among these, saturated cyclic carbonates and chain carbonates, and saturated cyclic carbonates, chain carbonates and chain carboxylic acid esters are preferred.

[0096] [A1-3-1. Saturated cyclic carbonate]

[0097] Saturated cyclic carbonates are typically categorized as having 2 to 4 alkylene groups. From the viewpoint of improving lithium-ion dissociation and thus battery performance, saturated cyclic carbonates with 2 to 3 carbon groups are preferred.

[0098] Examples of saturated cyclic carbonates include ethylene carbonate, propylene carbonate, and butyl carbonate. Ethyl carbonate and propylene carbonate are preferred, with ethylene carbonate, which is less prone to oxidation / reduction, being even more preferred. A single saturated cyclic carbonate can be used alone, or two or more can be used in any combination and ratio.

[0099] The content of saturated cyclic carbonate is not particularly limited and is arbitrary as long as it does not significantly impair the effects of the invention involved in this embodiment. However, when using a single type alone, the lower limit of its content relative to the total amount of solvent in the non-aqueous electrolyte is generally 3% by volume or more, preferably 5% by volume or more, and on the other hand, generally 90% by volume or less, preferably 85% by volume or less, and more preferably 80% by volume or less. By setting it within this range, the decrease in conductivity due to the decrease in the dielectric constant of the non-aqueous electrolyte can be avoided, and it is easy to achieve a good range of high-current discharge characteristics, stability against the negative electrode, and cycle characteristics of the non-aqueous electrolyte secondary battery. There is a tendency for the oxidation / reduction resistance of the non-aqueous electrolyte to be improved and the stability during high-temperature storage to be improved.

[0100] It should be noted that the volume % in this embodiment refers to the volume at 25°C and 1 atmosphere.

[0101] [A1-3-2. Chain carbonates]

[0102] As a chain carbonate, chain carbonates with 3 to 7 carbon atoms are usually used. In order to adjust the viscosity of the electrolyte to a suitable range, chain carbonates with 3 to 5 carbon atoms are preferred.

[0103] Specifically, examples of chain carbonates include dimethyl carbonate, diethyl carbonate, di-n-propyl carbonate, diisopropyl carbonate, n-propyl isopropyl carbonate, methyl ethyl carbonate, and methyl n-propyl carbonate. Dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate are particularly preferred.

[0104] Furthermore, it is also preferable to use chain carbonates having fluorine atoms (hereinafter, sometimes simply referred to as "fluorinated chain carbonates"). There is no particular limitation on the number of fluorine atoms in the fluorinated chain carbonate, as long as it is 1 or more, typically 6 or less, and preferably 4 or less. When the fluorinated chain carbonate has multiple fluorine atoms, these fluorine atoms can be bonded to the same carbon atom or to different carbon atom. Examples of fluorinated chain carbonates include dimethyl carbonate derivatives such as fluoromethyl methyl carbonate, ethyl methyl carbonate derivatives such as 2-fluoroethyl methyl carbonate, and diethyl carbonate derivatives such as ethyl (2-fluoroethyl) carbonate.

[0105] Chain carbonates can be used alone or in any combination and ratio of two or more.

[0106] The content of the chain carbonate is not particularly limited, but relative to the total solvent content of the non-aqueous electrolyte, it is typically 15% by volume or more, preferably 20% by volume or more, more preferably 25% by volume or more, and typically 90% by volume or less, preferably 85% by volume or less, more preferably 80% by volume or less. By keeping the content of the chain carbonate within the above range, it is easy to make the viscosity of the non-aqueous electrolyte within a suitable range, suppress the decrease in ionic conductivity, and thus make the output characteristics of the non-aqueous electrolyte secondary battery within a good range.

[0107] Furthermore, compared to specific chain carbonates, combining ethylene carbonate in specific amounts can significantly improve battery performance.

[0108] 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 within the range that does not significantly impair the effects of the invention involved in this embodiment. However, relative to the total amount of solvent in the non-aqueous electrolyte, it is generally 15% by volume or more, preferably 20% by volume or more, and also generally 45% by volume or less, preferably 40% by volume or less. The content of dimethyl carbonate relative to the total amount of solvent in the non-aqueous electrolyte is generally 20% by volume or more, preferably 30% by volume or more, and also generally 50% by volume or less, preferably 45% by volume or less. The content of ethyl methyl carbonate is generally 20% by volume or more, preferably 30% by volume or more, and also generally 50% by volume or less, preferably 45% by volume or less. By keeping the content within the above range, there is excellent high-temperature stability and a tendency to suppress gas generation.

[0109] [A1-3-3. Chain carboxylic acid ester]

[0110] Examples of chain-like carboxylic acid esters include methyl acetate, ethyl acetate, propyl acetate, butyl acetate, methyl propionate, ethyl propionate, methyl butyrate, ethyl butyrate, methyl valerate, methyl isobutyrate, ethyl isobutyrate, and methyl pivalate. From the viewpoint of improving battery performance, methyl acetate, ethyl acetate, propyl acetate, and butyl acetate are preferred. Chain-like carboxylic acid esters obtained by replacing some of the hydrogen atoms in the above compounds with fluorine (e.g., methyl trifluoroacetate, ethyl trifluoroacetate, etc.) are also preferred.

[0111] [A1-3-4. Cyclic carboxylic esters]

[0112] Examples of cyclic carboxylic acid esters include γ-butyrolactone and γ-valerolactone. γ-Butyrolactone is more preferred. Cyclic carboxylic acid esters obtained by replacing some of the hydrogen atoms of the above compounds with fluorine are also preferred.

[0113] [A1-3-5. Ether compounds]

[0114] As ether compounds, preferred are chain ethers with 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, as well as cyclic ethers with 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.

[0115] Among these, for chain ethers with 3 to 10 carbon atoms, dimethoxymethane, diethoxymethane, and ethoxymethoxymethane are preferred due to their high solubility with lithium ions, improved ion dissociation, low viscosity, and high ionic conductivity. For cyclic ethers with 3 to 6 carbon atoms, tetrahydrofuran, 1,3-dioxane, and 1,4-dioxane are preferred due to their high ionic conductivity.

[0116] The content of the ether compound is not particularly limited and is arbitrary as long as it does not significantly impair the effects of the invention involved in this embodiment. However, in 100% by volume of a non-aqueous solvent, it is generally 1% by volume or more, preferably 2% by volume or more, more preferably 3% by volume or more, and generally 30% by volume or less, preferably 25% by volume or less, more preferably 20% by volume or less. When the content of the ether compound is within the above-mentioned preferred range, it is easy to ensure the effect of improving the lithium-ion dissociation degree of the ether and the effect of improving the ionic conductivity due to the decrease in viscosity. In addition, when the negative electrode active material is a carbonaceous material, the phenomenon of chain ethers being co-intercalated with lithium ions can be suppressed, so that the input-output characteristics and charge-discharge rate characteristics can be within a suitable range.

[0117] [A1-3-6. Sulfone compounds]

[0118] As a sulfone compound, there are no particular limitations on whether it is a cyclic sulfone or a chain sulfone. In the case of a cyclic sulfone, it usually has 3 to 6 carbon atoms, preferably 3 to 5. In the case of a chain sulfone, it usually has 2 to 6 carbon atoms, preferably compounds with 2 to 5 carbon atoms. In addition, there are no particular limitations on the number of sulfonyl groups in one molecule of a sulfone compound, usually 1 or 2.

[0119] Examples of cyclic sulfones include trimethylene sulfones, tetramethylene sulfones, and hexamethylene sulfones as monosulfone compounds; and trimethylene disulfones, tetramethylene disulfones, and hexamethylene disulfones as disulfone compounds. From the viewpoint of dielectric constant and viscosity, tetramethylene sulfones, tetramethylene disulfones, hexamethylene sulfones, and hexamethylene disulfones are more preferred, and tetramethylene sulfones (sulfolane) are particularly preferred.

[0120] As sulfolane compounds, sulfolane and / or sulfolane derivatives are preferred (hereinafter, including sulfolane, sometimes simply referred to as "sulfolane compounds"). As sulfolane derivatives, compounds obtained by replacing one or more hydrogen atoms bonded to the carbon atoms constituting the sulfolane ring with fluorine atoms or alkyl groups are preferred.

[0121] From the perspective of high ionic conductivity and high input-output ratio, 2-methylcyclobutanesulfone, 3-methylcyclobutanesulfone, 2-fluorocyclobutanesulfone, 3-fluorocyclobutanesulfone, 2,3-difluorocyclobutanesulfone, 2-trifluoromethylcyclobutanesulfone, and 3-trifluoromethylcyclobutanesulfone are preferred.

[0122] In addition, examples of chain sulfones include dimethyl sulfone, ethyl methyl sulfone, diethyl sulfone, monofluoromethyl methyl sulfone, difluoromethyl methyl sulfone, trifluoromethyl methyl sulfone, and pentafluoroethyl methyl sulfone. Among these, dimethyl sulfone, ethyl methyl sulfone, and monofluoromethyl methyl sulfone are preferred from the viewpoint of improving the high-temperature storage stability of the electrolyte.

[0123] The content of the sulfone compound is not particularly limited and is arbitrary as long as it does not significantly impair the effects of the invention involved in this embodiment. Relative to the total amount of solvent in the non-aqueous electrolyte, it is typically 0.3% by volume or more, preferably 0.5% by volume or more, more preferably 1% by volume or more, and typically 40% by volume or less, preferably 35% by volume or less, more preferably 30% by volume or less. When the content of the sulfone compound is within the aforementioned range, there is a tendency to obtain an electrolyte with excellent high-temperature storage stability.

[0124] [A1-4. Additives]

[0125] The non-aqueous electrolyte may contain various additives, provided that the effects of the present invention are not significantly impaired. Any conventionally known additive may be used. It should be noted that one additive may be used alone, or two or more additives may be used in any combination and ratio.

[0126] Previously known additives (hereinafter also referred to as combined additives) that can be contained in non-aqueous electrolytes include: cyclic carbonates with carbon-carbon unsaturated bonds, fluorinated cyclic carbonates, compounds with isocyanate groups, compounds with isocyanuric acid skeletons, organic compounds with S=O bonds, phosphorus-containing organic compounds, organic compounds with cyano groups, silicon-containing compounds, aromatic compounds, non-fluorinated carboxylic acid esters, cyclic compounds with multiple ether bonds, compounds with isocyanuric acid skeletons, fluorophosphates with P=O bonds, borates, oxalates, salts with FSO2 skeletons, etc. For example, compounds described in International Publication No. 2015 / 111676 can be listed.

[0127] Preferably, it contains at least one compound selected from the group consisting of organic compounds with S=O bonds, fluorophosphates with P=O bonds, oxalates, and salts with an FSO2 skeleton.

[0128] From the viewpoint of suppressing continuous charging capacity loss rate, it is more preferable to contain at least one compound selected from the group consisting of organic compounds having S=O bonds, oxalates and salts having an FSO2 skeleton, further preferably containing salts having an FSO2 skeleton, particularly preferably containing fluorosulfonates, and most preferably containing lithium fluorosulfonate.

[0129] Furthermore, from the viewpoint of suppressing the increase in internal resistance and expansion, it is more preferable to contain at least one compound selected from the group consisting of organic compounds with S=O bonds, fluorophosphates with P=O bonds, and salts with an FSO2 skeleton.

[0130] More preferably, it contains at least one compound selected from the group consisting of sulfates or sulfonates, difluorophosphates and fluorosulfonates.

[0131] More preferably, it contains two or more compounds selected from the group consisting of sulfates or sulfonates, difluorophosphates, and fluorosulfonates.

[0132] More preferably, difluorophosphate and sulfate or sulfonate, or difluorophosphate and fluorosulfonate.

[0133] The preferred materials are lithium difluorophosphate and 1,2-ethylene sulfate or methane disulfonate, or lithium difluorophosphate and lithium fluorosulfonate.

[0134] The additive can be used alone or in any combination and ratio of two or more. The content of the additive (total amount when there are two or more) in 100% by mass of the non-aqueous electrolyte 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 also be 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less. When the additive content is within this range, the characteristics of the non-aqueous electrolyte secondary battery, especially its durability or storage characteristics, can be significantly improved. Although the principle is not yet clear, it is believed that by mixing in this ratio, side reactions of the additives on the electrodes can be suppressed to a minimum.

[0135] Regarding the mass ratio of the compound shown in Formula (I) and / or Formula (II) to the additive (total amount when there are two or more), the ratio of compound / additive shown in Formula (I) and / or Formula (II) is generally 1 / 100 or more, preferably 10 / 100 or more, more preferably 20 / 100 or more, further preferably 25 / 100 or more, generally 10000 / 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. When the mass ratio is within this range, the characteristics of non-aqueous electrolyte secondary batteries, especially their durability or storage characteristics, can be significantly improved. Although the principle is not yet clear, it is believed that by mixing at this ratio, the side reactions of the additives on the electrodes can be suppressed to a minimum.

[0136] When LiPF6 is present in a non-aqueous electrolyte, the mass ratio of additives (total amount when there are two or more) to the LiPF6 content is typically 0.00005 or more, preferably 0.001 or more, more preferably 0.01 or more, further preferably 0.02 or more, particularly preferably 0.025 or more, typically 1.0 or less, preferably 0.5 or less, more preferably 0.4 or less, and further preferably 0.35 or less. When this mass ratio is within this range, the characteristics of non-aqueous electrolyte secondary batteries, especially their durability and continuous charging characteristics, can be significantly improved. Although the principle is not yet clear, it is believed that by mixing at this ratio, the decomposition side reactions of LiPF6 in non-aqueous electrolyte secondary batteries can be suppressed to a minimum.

[0137] [A1-4-1. Organic compounds with S=O bonds]

[0138] There are no particular limitations on the type of organic compound having an S=O bond, as long as it is an organic compound having at least one S=O bond within its molecule. Preferably, it is an organic compound having an S=O bond, and more preferably, it is a compound selected from at least one of the groups consisting of sulfonates (chain sulfonates or cyclic sulfonates), sulfates (chain sulfates or cyclic sulfates), or sulfites (chain sulfites or cyclic sulfites). Specific examples are given below. However, substances belonging to the category of salts having an FSO2 skeleton are included in "salts having an FSO2 skeleton" below, but not in "organic compounds having an S=O bond," and compounds represented by formula (I) above are not included.

[0139] alkyl disulfonates and other chain sulfonates, such as methyl fluorosulfonate, methyl methanesulfonate, ethyl methanesulfonate, busulfan, methyl methanesulfonyloxyacetate, methyl vinyl sulfonate, allyl vinyl sulfonate, propargyl allyl sulfonate, methyl methanedisulfonate methoxycarbonyl, methyl methanedisulfonate ethoxycarbonyl, methyl 1,3-butanedisulfonate methoxycarbonyl, methyl 1,3-butanedisulfonate ethoxycarbonyl, ethyl 1,3-butanedisulfonate methoxycarbonyl, and ethyl 1,3-butanedisulfonate ethoxycarbonyl.

[0140] Cyclic sulfonates such as 1,3-propanesulfonate lactone, 1-fluoro-1,3-propanesulfonate lactone, 1-methyl-1,3-propanesulfonate lactone, 1-propenyl-1,3-sulfonate lactone, 2-propenyl-1,3-sulfonate lactone, 1-fluoro-1-propenyl-1,3-sulfonate lactone, 1-methyl-1-propenyl-1,3-sulfonate lactone, 1,4-butanesulfonate lactone, 1,5-pentanesulfonate lactone, methanedisulfonate methylene ester, and methanedisulfonate ethylene ester.

[0141] Chain sulfates such as dimethyl sulfate, methyl ethyl sulfate, and diethyl sulfate;

[0142] Cyclic sulfates such as 1,2-ethylene sulfate, 1,2-propylene sulfate, 1,3-propylene sulfate, and 1,2-butylene sulfate;

[0143] Chain sulfites such as dimethyl sulfite, methyl ethyl sulfite, and diethyl sulfite;

[0144] Cyclic sulfites such as 1,2-ethylidene sulfite, 1,2-propylidene sulfite, 1,3-propylidene sulfite, and 1,2-butylidene sulfite.

[0145] In particular, from the viewpoint of not only improving the gas suppression effect during high-temperature storage, but also improving the charge / discharge rate characteristics and impedance characteristics, sulfonic acid (chain sulfonate or cyclic sulfonate) or sulfate ester (chain sulfate or cyclic sulfate) is preferred, chain sulfonate, cyclic sulfonate, and cyclic sulfate are more preferred, and 1,3-propanesulfonate lactone, methanedisulfonate methylene ester, and 1,2-ethylene sulfate are even more preferred.

[0146] Organic compounds containing S=O bonds can be used alone or in combination with two or more compounds in any ratio. The content of organic compounds containing S=O bonds (total amount when there are two or more) in 100% by mass of the non-aqueous electrolyte 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. When the content of organic compounds containing S=O bonds is within this range, the characteristics of the non-aqueous electrolyte secondary battery, especially its durability or continuous charging characteristics, can be significantly improved. Although the principle is not yet clear, it is believed that by mixing in this ratio, side reactions of additives on the electrodes can be suppressed to a minimum.

[0147] The mass ratio of the compound shown in formula (I) to the total amount of organic compounds having S=O bonds (when there are two or more), calculated as the ratio of the compound shown in formula (I) to the organic compounds having S=O bonds, is typically 1 / 100 or more, preferably 10 / 100 or more, more preferably 20 / 100 or more, even more preferably 25 / 100 or more, typically 10000 / 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. When this mass ratio is within this range, the characteristics of non-aqueous electrolyte secondary batteries, especially their durability or continuous charging characteristics, can be significantly improved. Although the principle is not yet clear, it is believed that by mixing at this ratio, side reactions of additives on the electrodes can be suppressed to a minimum.

[0148] When LiPF6 is present in a non-aqueous electrolyte, the mass ratio of organic compounds with S=O bonds (total amount when there are two or more) to the LiPF6 content (organic compounds with S=O bonds / LiPF6) is typically 0.00005 or more, preferably 0.001 or more, more preferably 0.01 or more, further preferably 0.02 or more, particularly preferably 0.025 or more, typically 1.0 or less, preferably 0.5 or less, more preferably 0.4 or less, and further preferably 0.35 or less. When this mass ratio is within this range, the characteristics of non-aqueous electrolyte secondary batteries, especially their durability and continuous charging characteristics, can be significantly improved. Although the principle is not yet clear, it is believed that by mixing at this ratio, the decomposition side reactions of LiPF6 in non-aqueous electrolyte secondary batteries can be suppressed to a minimum.

[0149] It should be noted that the content of organic compounds with S=O bonds is determined by nuclear magnetic resonance (NMR) analysis. NMR analysis is usually performed, but gas chromatography (GC) or ion chromatography (IC) analysis is also performed when solvent peaks are difficult to attribute to other compounds.

[0150] [A1-4-2. Fluorophosphates with P=O bonds]

[0151] There are no particular restrictions on the fluorophosphates used in this embodiment, as long as they are phosphates with P=O and PF bonds within the molecule.

[0152] Alkali metals such as lithium, sodium, and potassium can be listed as counter cations for phosphates with PF bonds, among which lithium is preferred.

[0153] As fluorophosphates with P=O bonds, the following can be listed:

[0154] Li2PO3F and other monofluorophosphates;

[0155] Difluorophosphates such as LiPO2F2, NaPO2F2, and KPO2F2; etc.

[0156] In particular, from the viewpoint of not only improving the gas suppression effect during high-temperature storage, but also improving the charge / discharge rate characteristics and impedance characteristics, difluorophosphate is preferred, and lithium difluorophosphate is even more preferred.

[0157] Fluorophosphates containing P=O bonds can be used alone or in combination with two or more in any ratio. In 100% by mass of the non-aqueous electrolyte, the content of fluorophosphates containing P=O bonds (total amount when there are two or more types) 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. When the content of fluorophosphates containing P=O bonds is within this range, the characteristics of the non-aqueous electrolyte secondary battery, especially its durability and continuous charging characteristics, can be significantly improved. Although the principle is not yet clear, it is believed that by mixing in this ratio, side reactions of the additives on the electrodes can be suppressed to a minimum.

[0158] The mass ratio of the compound shown in Formula (I) to the fluorophosphates having P=O bonds (total amount when there are two or more) is typically 1 / 100 or more, preferably 10 / 100 or more, more preferably 20 / 100 or more, even more preferably 25 / 100 or more, typically 10000 / 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. When this mass ratio is within this range, the characteristics of non-aqueous electrolyte secondary batteries, especially their durability or continuous charging characteristics, can be significantly improved. Although the principle is not yet clear, it is believed that by mixing at this ratio, side reactions of the additives on the electrodes can be suppressed to a minimum.

[0159] When a non-aqueous electrolyte contains LiPF6, the mass ratio (fluorophosphate / LiPF6) of fluorophosphates with P=O bonds (total amount when there are two or more types) to the LiPF6 content is typically 0.00005 or more, preferably 0.001 or more, more preferably 0.01 or more, further preferably 0.02 or more, particularly preferably 0.025 or more, typically 1.0 or less, preferably 0.5 or less, more preferably 0.4 or less, and further preferably 0.35 or less. When this mass ratio is within this range, the characteristics of non-aqueous electrolyte secondary batteries, especially their durability and continuous charging characteristics, can be significantly improved. Although the principle is not yet clear, it is believed that by mixing at this ratio, the decomposition side reactions of LiPF6 in non-aqueous electrolyte secondary batteries can be suppressed to a minimum.

[0160] It should be noted that the content of fluorophosphates with P=O bonds is determined by nuclear magnetic resonance (NMR) analysis. NMR analysis is usually performed, but ion chromatography (IC) analysis is also used when solvent peaks are difficult to attribute to other compounds.

[0161] [A1-4-3. Salts with an FSO2 framework]

[0162] There are no particular restrictions on the salt with an FSO2 skeleton used in this embodiment, as long as it has an intramolecular FSO2 skeleton.

[0163] Alkali metals such as lithium, sodium, and potassium can be listed as counter cations for salts with an FSO2 framework, with lithium being the preferred choice.

[0164] For example, fluorosulfonates such as FSO3Li, FSO3Na, FSO3K, FSO3(CH3)4N, FSO3(C2H5)4N, and FSO3(n-C4H9)4N can be listed;

[0165] Fluorosulfonyl imide salts such as LiN(FSO2)2 and LiN(FSO2)(CF3SO2);

[0166] LiC(FSO2)3 and other fluorosulfonyl methyl lithium salts; etc.

[0167] In particular, from the viewpoint of not only improving the gas suppression effect during high-temperature storage, but also improving the charge / discharge rate characteristics and impedance characteristics, fluorosulfonates are preferred, and lithium fluorosulfonate is even more preferred.

[0168] Salts with an FSO2 framework can be used alone or in combination with two or more salts in any ratio. In 100% by mass of the non-aqueous electrolyte, the content of salts with an FSO2 framework (total amount when there are two or more types) 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. When the content of salts with an FSO2 framework is within this range, the characteristics of the non-aqueous electrolyte secondary battery, especially its durability and continuous charging characteristics, can be significantly improved. Although the principle is not yet clear, it is believed that by mixing in this ratio, side reactions of additives on the electrodes can be suppressed to a minimum.

[0169] The mass ratio of the compound shown in formula (I) to the salt having the FSO2 framework (total amount when there are two or more) is typically 1 / 100 or more, preferably 10 / 100 or more, more preferably 20 / 100 or more, further preferably 25 / 100 or more, typically 10000 / 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. When this mass ratio is within this range, the characteristics of non-aqueous electrolyte secondary batteries, especially their durability or continuous charging characteristics, can be significantly improved. Although the principle is not yet clear, it is believed that by mixing at this ratio, side reactions of the additives on the electrodes can be suppressed to a minimum.

[0170] When a non-aqueous electrolyte contains LiPF6, the mass ratio of salts with an FSO2 framework (total amount when there are two or more) to the LiPF6 content (salts with an FSO2 framework / LiPF6) is typically 0.00005 or more, preferably 0.001 or more, more preferably 0.01 or more, further preferably 0.02 or more, particularly preferably 0.025 or more, typically 1.0 or less, preferably 0.5 or less, more preferably 0.4 or less, and further preferably 0.35 or less. When this mass ratio is within this range, the characteristics of non-aqueous electrolyte secondary batteries, especially their durability and continuous charging characteristics, can be significantly improved. Although the principle is not yet clear, it is believed that by mixing at this ratio, the decomposition side reactions of LiPF6 in non-aqueous electrolyte secondary batteries can be suppressed to a minimum.

[0171] It should be noted that the content of salts with the FSO2 framework is determined by nuclear magnetic resonance (NMR) analysis. NMR analysis is usually performed, but ion chromatography (IC) analysis is also used when solvent peaks are difficult to attribute to other compounds.

[0172] [A1-4-4. Oxalate]

[0173] There are no particular restrictions on whether a compound is an oxalate, as long as it has at least one oxalate skeleton in its molecule.

[0174] Alkali metals such as lithium, sodium, and potassium can be listed as countercations for oxalates, with lithium being the preferred choice.

[0175] For example, lithium di(oxalate)borate and lithium difluorooxalateborate are examples of oxalate borates.

[0176] Lithium tetrafluorooxalate phosphate, lithium difluorodi(oxalate) phosphate, lithium tri(oxalate) phosphate, and other oxalate phosphates; etc.

[0177] In particular, from the viewpoint of not only improving the gas suppression effect during high-temperature storage, but also improving the charge / discharge rate characteristics and impedance characteristics, oxalate borates are preferred, and lithium di(oxalate)borate is more preferred.

[0178] Oxalate can be used alone or in combination with two or more in any ratio. In 100% by mass of the non-aqueous electrolyte, the oxalate content (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. When the oxalate content is within this range, the characteristics of the non-aqueous electrolyte secondary battery, especially its durability and continuous charging characteristics, can be significantly improved. Although the principle is not yet clear, it is believed that by mixing in this ratio, side reactions of the additives on the electrodes can be suppressed to a minimum.

[0179] The mass ratio of the compound shown in Formula (I) to the oxalate (total amount when there are two or more) is typically 1 / 100 or more, preferably 10 / 100 or more, more preferably 20 / 100 or more, even more preferably 25 / 100 or more, typically 10000 / 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. When this mass ratio is within this range, the characteristics of non-aqueous electrolyte secondary batteries, especially their durability or continuous charging characteristics, can be significantly improved. Although the principle is not yet clear, it is believed that by mixing at this ratio, side reactions of the additives on the electrodes can be suppressed to a minimum.

[0180] When LiPF6 is present in a non-aqueous electrolyte, the mass ratio of oxalate (total amount when there are two or more types) to the LiPF6 content (oxalate / LiPF6) is typically 0.00005 or more, preferably 0.001 or more, more preferably 0.01 or more, further preferably 0.02 or more, particularly preferably 0.025 or more, typically 1.0 or less, preferably 0.5 or less, more preferably 0.4 or less, and further preferably 0.35 or less. When this mass ratio is within this range, the characteristics of non-aqueous electrolyte secondary batteries, especially their durability and continuous charging characteristics, can be significantly improved. Although the principle is not yet clear, it is believed that by mixing at this ratio, the decomposition side reactions of LiPF6 in non-aqueous electrolyte secondary batteries can be suppressed to a minimum.

[0181] It should be noted that the oxalate content is determined by nuclear magnetic resonance (NMR) analysis. NMR analysis is usually performed, but ion chromatography (IC) analysis is also used when solvent peaks are difficult to attribute to other compounds.

[0182] It should be noted that some additives include substances listed as electrolyte salts. In such cases, the concentration range can be used for identification. For example, a non-aqueous electrolyte containing 10% by mass of a certain fluorinated inorganic salt can be identified as an electrolyte, while a non-aqueous electrolyte containing 0.5% by mass of a certain salt with an oxalic acid skeleton can be identified as an additive.

[0183] [A2. Non-aqueous electrolyte secondary battery]

[0184] As one embodiment of the present invention, the non-aqueous electrolyte secondary battery is a non-aqueous electrolyte secondary battery having a positive electrode with a positive electrode active material capable of absorbing and releasing metal ions and a negative electrode active material capable of absorbing and releasing metal ions, and comprising a non-aqueous electrolyte.

[0185] [A2-1. Non-aqueous electrolyte]

[0186] The above-described non-aqueous electrolyte is used as the non-aqueous electrolyte. It should be noted that, as the non-aqueous electrolyte, only the above-described non-aqueous electrolyte may be used, but without departing from the spirit of the present invention, other non-aqueous electrolytes may be mixed into the above-described non-aqueous electrolyte for use.

[0187] [A2-2. Negative electrode]

[0188] A negative electrode is an object that has at least a portion of its surface containing negatively active material.

[0189] [A2-2-1. Negative Electrode Active Material]

[0190] There are no particular restrictions on the negative electrode active material used, as long as it can electrochemically absorb and release metal ions. Specific examples include carbonaceous materials, metal particles that can form alloys with Li, lithium-containing metal composite oxide materials, and mixtures thereof. From the viewpoint of good cycle performance, safety, and excellent continuous charging characteristics, carbonaceous materials, metal particles that can form alloys with Li, and mixtures of metal particles that can form alloys with Li and graphite particles are preferred. One of these materials can be used alone, or two or more can be combined in any combination.

[0191] [A2-2-2. Carbon-based materials]

[0192] Carbon-based materials include natural graphite, artificial graphite, amorphous carbon, carbon-coated graphite, graphite-coated graphite, and resin-coated graphite. Natural graphite is preferred. A single carbon-based material can be used alone, or two or more materials can be used in any combination and ratio.

[0193] Examples of natural graphite include flake graphite, scaly graphite, and / or graphite particles obtained by spheroidizing, densifying, or other treatments on these graphites. Among these, spherical or oval graphite particles that have undergone spheroidizing treatment are particularly preferred from the viewpoint of particle filling properties and charge / discharge rate characteristics.

[0194] The average particle size (d50) of graphite particles is typically greater than 1 μm and typically less than 100 μm.

[0195] [A2-2-3. Physical Properties of Carbon-Based Materials]

[0196] The carbon-based material used as the negative electrode active material preferably satisfies at least one of the following physical properties and shape characteristics as shown in (1) to (5), and it is particularly preferred that multiple characteristics are satisfied at the same time.

[0197] (1) X-ray parameters

[0198] The d-value (interlayer distance) of the lattice plane (002 plane) of carbonaceous materials, obtained by X-ray diffraction according to the method of the Japan Society for the Promotion of Science, is typically 0.335 nm or more and 0.360 nm or less. Furthermore, the cell size (Lc) of carbonaceous materials, obtained by X-ray diffraction according to the method of the Japan Society for the Promotion of Science, is 1.0 nm or more.

[0199] (2) Volume-based average particle size

[0200] The volume-based average particle size of carbonaceous materials is the average particle size (median particle size) of the volume-based standard obtained by laser diffraction / scattering method, which is usually above 1 μm and below 100 μm.

[0201] (3) Raman R value, Raman half-width

[0202] The Raman R value of carbonaceous materials is determined using argon-ion laser Raman spectroscopy, and is typically above 0.01 and below 1.5.

[0203] In addition, the 1580cm of carbonaceous material -1 There is no particular limitation on the width of the Raman half-value in the vicinity; it is usually 10 cm. -1 Above and 100cm -1 the following.

[0204] (4) BET specific surface area

[0205] The BET specific surface area of ​​carbonaceous materials is the value of the specific surface area measured using the BET method, typically 0.1 m². 2 ·g -1 Above and 100m 2 ·g -1 the following.

[0206] The negative electrode active material may contain two or more carbonaceous materials with different properties. Here, "properties" refers to one or more characteristics selected from the group consisting of X-ray diffraction parameters, median particle size, Raman R value, and BET specific surface area.

[0207] Preferred examples include: asymmetrical particle size distribution with median particle size as the center, the presence of two or more carbonaceous materials with different Raman R values, and different X-ray parameters.

[0208] [A2-2-4. Metal particles that can form alloys with Li]

[0209] For metal particles capable of forming an alloy with Li, any conventionally known metal particles can be used. However, from the viewpoint of capacity and cycle life, the metal particles are preferably metals or compounds selected from the group consisting of Sb, Si, Sn, Al, As, and Zn. Alternatively, alloys composed of two or more metals can be used, and the metal particles can also be alloy particles formed from two or more metallic elements.

[0210] Examples of metal compounds include metal oxides, metal nitrides, and metal carbides. Additionally, alloys composed of two or more metals can also be used. From the viewpoint of maximizing capacity, metal Si (hereinafter sometimes referred to as Si) or Si-containing compounds are preferred.

[0211] In this specification, Si or Si-containing compounds are collectively referred to as Si compounds. Specifically, SiO₂ can be listed as an example of a Si compound. x SiN x SiC x SiZx O y (Z = C, N), etc. As a Si compound, Si oxide (SiO₂) is preferred from the viewpoint that its theoretical capacity is greater than that of graphite. x Alternatively, from the perspective that alkaline ions such as lithium ions can easily enter and exit, resulting in high capacity, amorphous Si or nanoscale Si crystals are preferred.

[0212] The general formula SiO x It can be obtained from silicon dioxide (SiO2) and Si, and its x value is usually 0≤x<2.

[0213] From the perspective of cycle life, the average particle size (d50) of metal particles that can form alloys with Li is typically above 0.01 μm and typically below 10 μm.

[0214] [A2-2-5. A mixture of metal particles and graphite particles that can form alloys with Li]

[0215] Regarding the mixture of metal particles and graphite particles that can form alloys with Li as the negative electrode active material, it can be a mixture in which the metal particles that can form alloys with Li and the graphite particles are mixed in a state of independent particles, or it can be a composite in which the metal particles that can form alloys with Li exist on the surface or inside the graphite particles.

[0216] The proportion of metal particles that can form alloys with Li is typically between 1% by mass and 99% by mass, relative to the total amount of metal particles and graphite particles that can form alloys with Li.

[0217] [A2-2-6. Lithium-containing metal composite oxide materials]

[0218] As a lithium-containing metal composite oxide material used as a negative electrode active material, there are no particular restrictions as long as it can absorb and release lithium. However, from the viewpoint of high current density charge and discharge characteristics, lithium-containing composite metal oxide materials containing titanium are preferred, and composite oxides of lithium and titanium (hereinafter, sometimes simply referred to as "lithium-titanium composite oxides") are more preferred. Lithium-titanium composite oxides with spinel structure can significantly reduce output resistance, so they are particularly preferred.

[0219] In addition, the lithium and titanium in lithium-titanium composite oxides can be replaced by other metallic elements, such as at least one element selected from the group consisting of Al, Ga, Cu and Zn.

[0220] Li is preferred as a lithium-titanium composite oxide. 4 / 3 Ti 5 / 3 O4, Li1Ti2O4 and Li 4 / 5 Ti 11 / 5O4. Additionally, lithium-titanium composite oxides obtained by replacing one element with another, such as Li, are preferred. 4 / 3 Ti 4 / 3 Al 1 / 3 O4.

[0221] [A2-2-7. The Structure and Manufacturing Method of the Negative Electrode]

[0222] Regarding the manufacture of the negative electrode, any known method may be used without significantly impairing the effects of the present invention. For example, it can be formed by adding a binder, solvent, thickener, conductive material, filler, etc., to the negative electrode active material to prepare a slurry, coating it onto the current collector, drying it, and then pressing it.

[0223] [A2-2-7-1. Current Collector]

[0224] As the current collector for maintaining the active material of the negative electrode, any known material can be used. Examples of metal materials that can be used as the current collector for the negative electrode include aluminum, copper, nickel, stainless steel, and nickel-plated steel, but copper is particularly preferred from the viewpoint of ease of processing and cost.

[0225] [A2-2-7-2. Adhesive]

[0226] As a binder for bonding negative electrode active materials, there are no particular restrictions as long as it is a material that is stable to non-aqueous electrolytes and solvents used in electrode manufacturing.

[0227] 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 fluorinated polymers such as polyvinylidene fluoride, polytetrafluoroethylene, and polytetrafluoroethylene / ethylene copolymers. These substances can be used individually or in any combination and ratio of two or more.

[0228] The ratio of the binder to the negative electrode active material is typically 0.1% by mass or more and 20% by mass or less.

[0229] In particular, when the main component contains a rubber-like polymer such as SBR, the proportion of the binder relative to the negative electrode active material is typically 0.1% by mass or more and 5% by mass or less. Furthermore, when the main component contains a fluorinated polymer such as polyvinylidene fluoride, the proportion relative to the negative electrode active material is typically 1% by mass or more and 15% by mass or less.

[0230] [A2-2-7-3. Thickener]

[0231] Thickeners are commonly used to adjust the viscosity of slurries. There are no particular limitations on thickeners; examples include carboxymethyl cellulose, methyl cellulose, hydroxymethyl cellulose, ethyl cellulose, and polyvinyl alcohol. These substances can be used individually or in any combination and ratio of two or more.

[0232] When thickeners are used further, the ratio of thickener to negative electrode active material is usually 0.1% by mass or more and 5% by mass or less.

[0233] [A2-2-8. Electrode Density]

[0234] There are no particular restrictions on the electrode structure when fabricating the negative electrode active material, but the density of the negative electrode active material on the current collector is usually 1 g·cm³. -3 Above and 2.2 g·cm -3 the following.

[0235] [A2-2-9. Thickness of the negative electrode plate]

[0236] The thickness of the negative electrode plate is designed according to the positive electrode plate used, and there is no particular limitation. However, the thickness of the composite material layer after subtracting the thickness of the core material metal foil is usually above 15μm and below 300μm.

[0237] [A2-2-10. Surface coating of the negative electrode plate]

[0238] Alternatively, a negative electrode plate with a different composition (surface-attached substance) attached to its surface can also be used. Examples of surface-attached substances include oxides such as aluminum oxide, sulfates such as lithium sulfate, and carbonates such as lithium carbonate.

[0239] [A2-3. Positive electrode]

[0240] A positive electrode is an object that has positively active material on at least a portion of the surface of a current collector.

[0241] [A2-3-1. Positive Electrode Active Material]

[0242] In embodiments of the present invention, the positive electrode active material used in the positive electrode comprises a lithium transition metal compound as shown in the following formula (IV).

[0243] Li 1+x MO2……(IV)

[0244] In formula (IV), x is -0.1 or more and 0.5 or less. 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 can be 0.1 or less, preferably 0.06 or less, more preferably 0.028 or less, further 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 effects of suppressing self-discharge, suppressing expansion, reducing internal resistance, and reducing capacity loss during continuous charging, resulting from the combination with the compounds of formula (I) and / or formula (II) contained in the electrolyte, are readily and sufficiently manifested, and are therefore preferred.

[0245] In the 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. Furthermore, the upper limit of the molar ratio can be 0.95 or less, preferably 0.90 or less, and even more preferably 0.85 or less.

[0246] When the Ni / M molar ratio is within the above range, the proportion of Ni participating in charging and discharging is sufficiently large, and the battery becomes high-capacity, which is therefore preferred.

[0247] When M contains Co, the Co / M molar ratio in composition (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. Furthermore, 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. When the Co / M molar ratio is within the above range, the charge / discharge capacity increases, therefore it is preferred.

[0248] When M contains Mn, the Mn / M molar ratio is not particularly limited, but it is greater than 0, preferably 0.05 or more, more preferably 0.08 or more, and even more preferably 0.10 or more. Alternatively, it can 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.

[0249] When the above-mentioned Mn / M molar ratio is within the above range, the proportion of Mn that does not participate in charging and discharging is sufficiently small, and the battery becomes high-capacity, which is therefore preferred.

[0250] Preferably, the lithium transition metal composite oxide has a layered structure, and more preferably, it is a transition metal oxide with the following compositional formula (V).

[0251] Li a1 Ni b1 Co c1M d1 O2……(V)

[0252] In the composition formula (V), a1, b1, c1, and d1 represent values ​​that satisfy 0.90≤a1≤1.10, 0.40≤b1≤0.98, 0.01≤c1≤0.5, and 0.00≤d1≤0.50, respectively, and satisfy 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.

[0253] In the composition formula (V), it is preferred to represent a value of 0.01≤d1≤0.50.

[0254] Particularly preferred are transition metal oxides with the following composition (VI).

[0255] Li a2 Ni b2 Co c2 M d2 O2……(VI)

[0256] In equation (VI), a2, b2, c2, and d2 represent values ​​that satisfy 0.90≤a2≤1.10, 0.60≤b2≤0.98, 0.01≤c2<0.50, and 0.01≤d2<0.50, respectively, 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.

[0257] As a preferred specific example of a lithium transition metal oxide represented by formula (VI), LiNi can be cited as an example. 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 O2, etc.

[0258] In the above-mentioned formulations, M preferably contains Mn or Al, more preferably Mn, and even more preferably Mn or Al. This is because the structural stability of lithium transition metal oxides is improved, and structural degradation during repeated charge-discharge cycles is suppressed.

[0259] [A2-3-1-1. Introduction of Different Elements]

[0260] Lithium transition metal compounds may also incorporate different elements other than those specified in the above formula (I).

[0261] [A2-3-1-2. Surface Coating]

[0262] Alternatively, a substance with a different composition (surface-attached substance) may be used on the surface of the aforementioned positive electrode active material. This surface-attached substance is considered to be a substance contained in the positive electrode active material. Examples of surface-attached substances include oxides such as aluminum oxide, sulfates such as lithium sulfate, and carbonates such as lithium carbonate. When it is a carbonate, the compounds shown in formulas (I) and (II) above have increased affinity with the positive electrode, and are therefore preferred.

[0263] These surface-adhering substances can be added to the positive electrode active material by means of dissolving or suspending them in a solvent and then drying them, so that they adhere to the surface of the positive electrode active material.

[0264] The amount of surface-attached material relative to the positive electrode active material, by mass, 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. It is usually used in an amount of 1 mmol / g or less.

[0265] In this specification, a substance with a different composition than the positive electrode active material that is attached to the surface of the positive electrode active material is also referred to as the "positive electrode active material".

[0266] It should be noted that the amount of surface-attached substances in the above-listed positive electrode active materials was determined by ion chromatography.

[0267] [A2-3-1-3. Blending]

[0268] It should be noted that these positive electrode active materials can be used alone, or two or more can be used in any combination and ratio.

[0269] [A2-3-2. Composition and Manufacturing Method of the Positive Electrode]

[0270] The structure of the positive electrode will now be described. In this embodiment, the positive electrode can be manufactured by forming a layer of positive electrode active material containing a positive electrode active material and a binder on a current collector. The positive electrode using the positive electrode active material can be manufactured by conventional methods. That is, the positive electrode active material, binder, conductive material and thickener used as needed can be dry-mixed and formed into a sheet, and then the resulting sheet can be pressed onto the positive electrode current collector; or, these materials can be dissolved or dispersed in a liquid medium to form a slurry, which can be coated onto the positive electrode current collector and dried, thereby forming a layer of positive electrode active material on the current collector, thus obtaining the positive electrode. Alternatively, the above-mentioned positive electrode active material can be rolled to form a sheet electrode, or compressed to form a granular electrode.

[0271] The following describes the process of coating the positive current collector with slurry and then drying it.

[0272] [A2-3-2-1. Content of Active Substances]

[0273] The content of positive electrode active material in the positive electrode active material layer is usually above 80% by mass and below 98% by mass.

[0274] [A2-3-2-2. Density of the positive electrode active material layer]

[0275] To increase the filling density of the positive electrode active material, it is preferable to use a hand press or roller press to compact the positive electrode active material layer obtained through coating and drying. The density of the positive electrode active material layer is typically 1.5 g / cm³. 3 The above, preferably 3.0 g / cm³ 3 The above is further preferred to be 3.3 g / cm³. 3 The above is also true; it is usually 3.8 g / cm³. 3 the following.

[0276] [A2-3-2-3. Conductive Materials]

[0277] As a conductive material, any known conductive material can be used. Specific examples include metals such as copper and nickel. It should be noted that these materials can be used individually or in any combination and ratio. Conductive materials are typically used in a manner where they comprise 0.01% to 50% by mass in the positive electrode active material layer.

[0278] [A2-3-2-4. Adhesive]

[0279] As a binder used to manufacture the positive electrode active material layer, there are no particular limitations. In the case of coating method, as long as the material can be dissolved or dispersed in the liquid medium used in electrode manufacturing, there are no particular restrictions on its type. From the perspective of weather resistance, chemical resistance, heat resistance, flame retardancy, etc., fluorinated resins such as polyvinylidene fluoride, polyvinylidene fluoride, and polytetrafluoroethylene are preferred; polymers containing CN groups such as polyacrylonitrile and polyvinylidene cyanide are also preferred.

[0280] Alternatively, mixtures, modifiers, derivatives, random copolymers, alternating copolymers, graft copolymers, block copolymers, etc., of the aforementioned polymers may also be used. It should be noted that a single adhesive may be used alone, or two or more may be used in any combination and ratio.

[0281] Furthermore, when using a resin as a binder, the weight-average molecular weight of the resin is arbitrary, within a range that does not significantly impair the effects of the present invention, but is typically between 10,000 and 3 million. When the molecular weight is within this range, the strength of the electrode is improved, and the electrode can be appropriately formed.

[0282] The proportion of binder in the positive electrode active material layer is usually above 0.1% by mass and below 80% by mass.

[0283] [A2-3-2-5. Solvent]

[0284] As a solvent used to form the slurry, there are no particular restrictions on its type, as long as it is capable of dissolving or dispersing the positive electrode active material, conductive material, binder, and thickener as needed. Either aqueous solvent or organic solvent can be used.

[0285] [A2-3-2-6. Current Collector]

[0286] There are no particular restrictions on the material used for the positive current collector; any known material can be used. Specific examples include aluminum, stainless steel, nickel-plated materials, titanium, and tantalum. Aluminum is preferred.

[0287] Examples of current collector shapes include metal foil, metal cylinder, metal coil, metal plate, metal film, expanded metal, punched metal, and foamed metal. Among these, metal film is preferred. It should be noted that the film can also be appropriately shaped into a mesh.

[0288] [A2-3-2-7. Thickness of the positive electrode plate]

[0289] There is no particular limitation on the thickness of the positive electrode plate. From the perspective of high capacity and high output, the thickness of the composite material layer after subtracting the thickness of the core material metal foil is usually more than 10μm and less than 500μm relative to one side of the current collector.

[0290] [A2-3-2-7. Surface coating of the positive electrode plate]

[0291] Alternatively, a positive electrode plate with a different composition can be used on the surface of the aforementioned positive electrode plate, or the same material as the material on the surface can be used.

[0292] [A2-4. Divider]

[0293] To prevent short circuits, a separator is usually inserted between the positive and negative terminals. In this case, a non-aqueous electrolyte is typically used to immerse the separator.

[0294] There are no particular restrictions on the material and shape of the separator. Any known material and shape can be used without significantly impairing the effect of the present invention. Among them, it is preferable to use a separator made of a material that is stable for non-aqueous electrolytes, such as resin, glass fiber, or inorganic materials, and which has excellent liquid retention properties, in the form of a porous sheet or non-woven fabric.

[0295] [A2-4-1. Materials]

[0296] Materials used as separators include, for example, glass filters, polyolefins, preferably polyolefins, and particularly preferably polyethylene and polypropylene. These materials can be used individually or in any combination and ratio of two or more. Alternatively, the above materials can be layered.

[0297] [A2-4-2. Thickness]

[0298] The thickness of the separator is arbitrary, but it is usually above 1 μm and below 5 μm.

[0299] [A2-4-3. Porosity]

[0300] When using porous materials such as porous sheets or non-woven fabrics as separators, the porosity of the separators is arbitrary, but it is usually above 20% and below 90%.

[0301] [A2-4-4. Morphology]

[0302] As a form, objects in the shape of thin films such as nonwoven fabrics, woven fabrics, and microporous membranes can be used. Among the thin film shapes, those with a pore size of 0.01 to 1 μm and a thickness of 5 to 50 μm are preferred. In addition to the above-mentioned independent thin film shapes, separators formed by using a resin-based adhesive to form a composite porous layer containing the aforementioned inorganic particles on the surface of the positive and / or negative electrodes can also be used.

[0303] [A2-4-5. Breathability]

[0304] The characteristics of separators in non-aqueous electrolyte secondary batteries can be understood through the Gurley value. The Gurley value indicates the difficulty of air passage in the thickness direction of the film, expressed as the number of seconds required for 100 ml of air to pass through the film. The Gurley value of a separator can be arbitrary, but is typically between 10 and 1000 seconds per 100 ml.

[0305] [A2-5. Battery Design]

[0306] [A2-5-1. Electrode Assembly]

[0307] The electrode assembly can be either a stacked structure formed by separating the positive and negative electrode plates with the separator, or a structure in which the positive and negative electrode plates are wound into a spiral shape with the separator. The proportion of the volume of the electrode assembly in the internal volume of the battery (hereinafter referred to as the electrode assembly proportion) is typically 40% or more and 90% or less.

[0308] [A2-5-2. Collector Structure]

[0309] When the electrode assembly has the above-described stacked structure, it is preferable to use a structure formed by bundling the metal core portions of each electrode layer together and welding them to terminals. It is also preferable to provide multiple terminals within the electrodes to reduce resistance. When the electrode assembly has the above-described wound structure, internal resistance can be reduced by providing multiple lead structures on the positive and negative electrodes respectively and bundling them to terminals.

[0310] [A2-5-3. Protective Components]

[0311] As protective components, the following can be used: PTC (Positive Temperature Coefficient) devices whose impedance increases when abnormally heated or when excessive current flows through them; thermal fuses; thermistors; and valves (current shut-off valves) that cut off the current flowing in the circuit when the internal pressure and / or internal temperature of the battery rises sharply due to abnormal heating. Preferably, the above protective components are selected based on conditions that prevent activation during normal use at high currents, and more preferably, they are designed so that abnormal heating and thermal runaway will not occur even without protective components.

[0312] [A2-5-4. Outer Shell]

[0313] Non-aqueous electrolyte secondary batteries are typically constructed by housing the aforementioned non-aqueous electrolyte, negative electrode, positive electrode, separator, etc., within a casing. This casing is not limited and can be made of any known material and shape without significantly impairing the effects of the invention.

[0314] Regarding the material of the casing, there are no particular restrictions as long as it is a stable substance for the non-aqueous electrolyte used. However, from the perspective of lightweighting, it is preferable to use aluminum or aluminum alloy metals or laminated films.

[0315] Among the metal casings used above, examples include casings formed by welding metals together to form a sealed structure using laser welding, resistance welding, or ultrasonic welding, or casings formed by using the metals to form a riveted structure using resin gaskets.

[0316] [A2-5-5. Shape]

[0317] In addition, the shape of the outer shell is also arbitrary, such as any shape including cylindrical, square, laminated, coin-shaped, large, etc.

[0318] <B. Second Implementation>

[0319] The following is a detailed description of the methods for implementing the present invention. However, the description below is only one example (representative example) of an embodiment of the present invention, and the present invention is not limited thereto as long as it does not exceed the spirit of the claims.

[0320] The second embodiment of the present invention relates to a non-aqueous electrolyte and a non-aqueous electrolyte secondary battery comprising the non-aqueous electrolyte, wherein the battery comprises 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 components will now be described.

[0321] [B1. Non-aqueous electrolyte]

[0322] [B1-1-1. Compounds represented by formula (I) and / or formula (II)]

[0323] Similar to conventional non-aqueous electrolytes, the non-aqueous electrolytes for non-aqueous secondary batteries according to embodiments of the present invention contain an electrolyte and a non-aqueous solvent for dissolving it, particularly containing compounds represented by formula (I) and / or formula (II).

[0324]

[0325] In equations (I) and (II) above, R 1 ~R 5 These are organic groups having 1 to 18 carbon atoms, either independently or bonded together. The organic group has a carbon-based backbone, which may optionally have alkyl, alkenyl, alkynyl, aryl, or alkoxy groups as substituents. Hydrogen atoms bonded to the carbon atoms of the carbon-based group may optionally be replaced by halogen atoms. Some carbon atoms of the carbon-based group may optionally be replaced by oxygen atoms to form ether or ester bonds. Some carbon atoms of the carbon-based group may optionally be replaced by nitrogen atoms. R 1 ~R 5 (especially R)1 ~R 3 The preferred radicals are hydrocarbon groups with 1 to 15 carbon atoms, either independently or bonded to each other; more preferably, they are alkyl groups, and from the viewpoint of suppressing the increase of internal resistance, methyl or ethyl radicals are even more preferred. Additionally, R... 1 ~R 3 and R 4 ~R 5 Each ring is selectively bonded to the others to form a ring. The number of rings formed can be one or more. Furthermore, preferably, in formula (I) above, R... 1 and R 2 Compounds containing methyl groups.

[0326] R 6 It is a spacer group, which is a divalent hydrocarbon group with 1 to 4 carbon atoms, preferably a divalent hydrocarbon group with 1 to 3 carbon atoms.

[0327] n is 2 to 4, preferably 3 or 4, and more preferably 3.

[0328] As compounds represented by formulas (I) and (II) above, the following compounds can be listed as having a positive charge on the nitrogen atom and a negative charge on the oxygen atom bonded to the sulfur atom.

[0329]

[0330]

[0331]

[0332] Preferably, in equation (I) above, R 1 and R 2 Compounds containing methyl groups. Additionally, in formulas (I) and (II), R... 1 ~R 3 and R 4 ~R 5 When the rings are formed by bonding with each other, the formed ring is preferably a nitrogen-containing heterocycle with substituents that is a 5- or 6-membered ring, more preferably a nitrogen-containing heterocycle with substituents that is a 6-membered ring. One or more rings may be further condensed on the formed ring, and the formed ring may further contain oxygen atoms.

[0333] Examples of nitrogen-containing heterocycles that are 5- or 6-membered rings include pyrrolidineonium, piperidinium, pyridinium, imidazolineonium, pyrazoliumonium, pyrimidineonium, triazineonium, and triazoliumonium. Among these, piperidinium and pyridiniumonium are preferred from the viewpoint of suppressing side reactions with the negative electrode.

[0334] Regarding the substituents optionally present in the aforementioned ring, examples include alkyl, alkenyl, and alkynyl groups, and it may also contain fluorine atoms and / or oxygen atoms. Among these, alkyl and alkenyl groups are preferred from the viewpoint of adsorption to the positive electrode.

[0335] Of the above formula (II), the compound shown in formula (III) is particularly preferred.

[0336]

[0337] It should be noted that in equation (III) above, R 6 The definition of R in equation (II) above is the same as that in equation (II). 6 same.

[0338] R 7 ~R 11 They can be the same as each other or different from each other, and can be hydrogen atoms, halogen atoms or hydrocarbon groups.

[0339] The definition of n is the same as that in equation (II) above.

[0340] Regarding halogen atoms, chlorine atoms and fluorine atoms can be listed. Fluorine atoms are preferred.

[0341] Regarding hydrocarbon groups, alkyl, alkenyl, and alkynyl groups can be listed, and they may also contain fluorine atoms and / or oxygen atoms. Alkenyl and alkenyl groups are preferred.

[0342] Specific examples of alkyl groups include methyl, ethyl, n-propyl, isopropyl, n-butyl, tert-butyl, n-pentyl, hexyl, heptyl, octyl, nonyl, and decyl. Among these, methyl, ethyl, n-propyl, n-butyl, tert-butyl, n-pentyl, and hexyl are preferred; methyl, ethyl, n-propyl, n-butyl, tert-butyl, and n-pentyl are further preferred; and methyl, ethyl, n-butyl, and tert-butyl are particularly preferred. When the alkyl group is one of the above, the compound represented by formula (III) tends to be locally present near the surface of the positive electrode active material, and is therefore preferred.

[0343] Specific examples of alkenyl groups include vinyl, allyl, methanalyl, 2-butenyl, 3-methyl-2-butenyl, 3-butenyl, and 4-pentenyl. Among these, vinyl, allyl, methanalyl, and 2-butenyl are preferred, more preferably vinyl, allyl, and methanalyl, and particularly preferably vinyl or allyl. When the alkenyl group is one of the above, the compound represented by formula (III) tends to be locally present near the surface of the positive electrode active material, and is therefore preferred.

[0344] Specific examples of alkynyl groups include ethynyl, 2-propynyl, 2-butynyl, 3-butynyl, 4-pentynyl, and 5-hexynyl. Among these, ethynyl, 2-propynyl, 2-butynyl, and 3-butynyl are preferred, 2-propynyl and 3-butynyl are more preferred, and 2-propynyl is particularly preferred. When the alkynyl group is one of the above, the compound represented by formula (III) tends to be locally present near the surface of the positive electrode active material, and is therefore preferred.

[0345] The compounds shown in formulas (I) and (II) may contain only one type or more types.

[0346] The molecular weight of the compounds shown in formulas (I) and (II) above is not particularly limited, but is generally 100 or more, and typically 2000 or less, preferably 1000 or less, more preferably 500 or less, and particularly preferably 300 or less. By falling within the above range, the compounds are easy to process, and the viscosity of the electrolyte containing the compound can be made moderate.

[0347] The content of the compounds represented by formulas (I) and (II) above in the non-aqueous electrolyte is not particularly limited, but is generally 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and generally 8% by mass or less, more preferably 4% by mass or less, more preferably 2% by mass or less, and most preferably 1% by mass or less.

[0348] The contents of compounds (I) and / or (II) were determined using methods such as magnetic resonance spectroscopy.

[0349] [B1-1-2. Specific Additives]

[0350] The non-aqueous electrolyte for non-aqueous electrolyte secondary batteries according to embodiments of the present invention further contains at least one compound (hereinafter also referred to as a synergistic additive) selected from the group consisting of fluorophosphates having P=O bonds, salts having an FSO2 skeleton, oxalates, and organic compounds having S=O bonds, and the content of the compound is 0.001 to 5% by mass. 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 P=O bonds, salts having an FSO2 skeleton, and oxalates.

[0351] In the non-aqueous electrolyte, the content of the above-mentioned compound (Y) is 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, further preferably 2% by mass or less, and particularly preferably 1% by mass or less.

[0352] In this embodiment, the content (by mass) of compound (X) represented by formula (I) and / or formula (II) in the non-aqueous electrolyte is less than or equal to the content (by mass) of compound (X). Furthermore, the content (by mass) of compound (X) in the non-aqueous electrolyte can be less than 80% of the content (by mass) of compound (Y), preferably less than 60%, and more preferably less than 40%. Because the content of compound (X) is within a specific range compared to the content of compound (Y), the effect obtained by the configuration of this embodiment is more significant.

[0353] [B1-1-2-1. Organic compounds with S=O bonds]

[0354] As an organic compound having an S=O bond, there is no particular limitation as long as it is an organic compound having at least one S=O bond within its molecule. Preferably, it is an ester compound having an S=O bond, more preferably a compound selected from the group consisting of sulfonates (chain sulfonates or cyclic sulfonates), sulfates (chain sulfates or cyclic sulfates), or sulfites (chain sulfites or cyclic sulfites). Specific examples are given below. However, substances belonging to salts having an FSO2 skeleton are included in "salts having an FSO2 skeleton" below, but not in "organic compounds having an S=O bond," and compounds represented by formula (I) above are not included.

[0355] alkyl disulfonates and other chain sulfonates, such as methyl fluorosulfonate, methyl methanesulfonate, ethyl methanesulfonate, busulfan, methyl methanesulfonyloxyacetate, methyl vinyl sulfonate, allyl vinyl sulfonate, propargyl allyl sulfonate, methyl methanedisulfonate methoxycarbonyl, methyl methanedisulfonate ethoxycarbonyl, methyl 1,3-butanedisulfonate methoxycarbonyl, methyl 1,3-butanedisulfonate ethoxycarbonyl, ethyl 1,3-butanedisulfonate methoxycarbonyl, and ethyl 1,3-butanedisulfonate ethoxycarbonyl.

[0356] Cyclic sulfonates such as 1,3-propanesulfonate lactone, 1-fluoro-1,3-propanesulfonate lactone, 1-methyl-1,3-propanesulfonate lactone, 1-propenyl-1,3-sulfonate lactone, 2-propenyl-1,3-sulfonate lactone, 1-fluoro-1-propenyl-1,3-sulfonate lactone, 1-methyl-1-propenyl-1,3-sulfonate lactone, 1,4-butanesulfonate lactone, 1,5-pentanesulfonate lactone, methanedisulfonate methylene ester, and methanedisulfonate ethylene ester.

[0357] Chain sulfates such as dimethyl sulfate, methyl ethyl sulfate, and diethyl sulfate;

[0358] Cyclic sulfates such as 1,2-ethylene sulfate, 1,2-propylene sulfate, 1,3-propylene sulfate, and 1,2-butylene sulfate;

[0359] Chain sulfites such as dimethyl sulfite, methyl ethyl sulfite, and diethyl sulfite;

[0360] Cyclic sulfites such as 1,2-ethylidene sulfite, 1,2-propylidene sulfite, 1,3-propylidene sulfite, and 1,2-butylidene sulfite.

[0361] In particular, from the viewpoint of not only improving the gas suppression effect during high-temperature storage, but also improving the charge / discharge rate characteristics and impedance characteristics, sulfonic acid (chain sulfonate or cyclic sulfonate) or sulfate ester (chain sulfate or cyclic sulfate) is preferred, chain sulfonate, cyclic sulfonate, and cyclic sulfate are more preferred, and 1,3-propanesulfonate lactone, methanedisulfonate methylene ester, and 1,2-ethylene sulfate are even more preferred.

[0362] Organic compounds containing S=O bonds can be used alone or in combination of two or more in any ratio. In 100% by mass of the non-aqueous electrolyte, the content of organic compounds containing S=O bonds (total amount when there are two or more) is 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and further preferably 5% by mass or less, preferably 3% by mass or less. When the content of organic compounds containing S=O bonds is within this range, the characteristics of the non-aqueous electrolyte secondary battery, especially its durability or continuous charging characteristics, can be significantly improved. Although the principle is not yet clear, it is believed that by mixing in this ratio, side reactions of additives on the electrodes can be suppressed to a minimum.

[0363] The mass ratio of the compound shown in formula (I) to the total amount of organic compounds having S=O bonds (when there are two or more), calculated as the ratio of the compound shown in formula (I) to the organic compounds having S=O bonds, is typically 1 / 100 or more, preferably 10 / 100 or more, more preferably 20 / 100 or more, even more preferably 25 / 100 or more, typically 10000 / 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. When this mass ratio is within this range, the characteristics of non-aqueous electrolyte secondary batteries, especially their durability or continuous charging characteristics, can be significantly improved. Although the principle is not yet clear, it is believed that by mixing at this ratio, side reactions of additives on the electrodes can be suppressed to a minimum.

[0364] When LiPF6 is present in a non-aqueous electrolyte, the mass ratio of organic compounds with S=O bonds (total amount when there are two or more) to the LiPF6 content (organic compounds with S=O bonds / LiPF6) is typically 0.00005 or more, preferably 0.001 or more, more preferably 0.01 or more, further preferably 0.02 or more, particularly preferably 0.025 or more, typically 1.0 or less, preferably 0.5 or less, more preferably 0.4 or less, and further preferably 0.35 or less. When this mass ratio is within this range, the characteristics of non-aqueous electrolyte secondary batteries, especially their durability and continuous charging characteristics, can be significantly improved. Although the principle is not yet clear, it is believed that by mixing at this ratio, the decomposition side reactions of LiPF6 in non-aqueous electrolyte secondary batteries can be suppressed to a minimum.

[0365] [B1-1-2-2. Fluorophosphates with P=O bonds]

[0366] There are no particular restrictions on the fluorophosphates with P=O bonds used in this embodiment, as long as they are phosphates with both P=O and PF bonds within the molecule.

[0367] Alkali metals such as lithium, sodium, and potassium can be listed as counter cations for phosphates with P=O and PF bonds, with lithium being the preferred choice.

[0368] As fluorophosphates with P=O bonds, the following can be listed:

[0369] Li2PO3F and other monofluorophosphates;

[0370] Difluorophosphates such as LiPO2F2, NaPO2F2, and KPO2F2; etc.

[0371] In particular, from the viewpoint of not only improving the gas suppression effect during high-temperature storage, but also improving the charge / discharge rate characteristics and impedance characteristics, difluorophosphate is preferred, and lithium difluorophosphate is even more preferred.

[0372] Fluorophosphates containing P=O bonds can be used alone or in combination with two or more in any ratio. In 100% by mass of the non-aqueous electrolyte, the content of fluorophosphates containing P=O bonds (total amount when there are two or more types) is 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and further preferably 5% by mass or less, preferably 3% by mass or less. When the content of fluorophosphates containing P=O bonds is within this range, the characteristics of the non-aqueous electrolyte secondary battery, especially its durability and continuous charging characteristics, can be significantly improved. Although the principle is not yet clear, it is believed that by mixing in this ratio, side reactions of the additives on the electrodes can be suppressed to a minimum.

[0373] The mass ratio of the compound shown in Formula (I) to the fluorophosphates having P=O bonds (total amount when there are two or more) is typically 1 / 100 or more, preferably 10 / 100 or more, more preferably 20 / 100 or more, even more preferably 25 / 100 or more, typically 10000 / 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. When this mass ratio is within this range, the characteristics of non-aqueous electrolyte secondary batteries, especially their durability or continuous charging characteristics, can be significantly improved. Although the principle is not yet clear, it is believed that by mixing at this ratio, side reactions of the additives on the electrodes can be suppressed to a minimum.

[0374] When LiPF6 is present in a non-aqueous electrolyte, the mass ratio of fluorophosphates with P=O bonds (total amount when there are two or more types) to the LiPF6 content (fluorophosphates with P=O bonds / LiPF6) is typically 0.00005 or more, preferably 0.001 or more, more preferably 0.01 or more, further preferably 0.02 or more, particularly preferably 0.025 or more, typically 1.0 or less, preferably 0.5 or less, more preferably 0.4 or less, and further preferably 0.35 or less. When this mass ratio is within this range, the characteristics of non-aqueous electrolyte secondary batteries, especially their durability and continuous charging characteristics, can be significantly improved. Although the principle is not yet clear, it is believed that by mixing at this ratio, the decomposition side reactions of LiPF6 in non-aqueous electrolyte secondary batteries can be suppressed to a minimum.

[0375] [B1-1-2-3. Salts with an FSO2 framework]

[0376] There are no particular restrictions on the salt with an FSO2 skeleton used in this embodiment, as long as it has an intramolecular FSO2 skeleton.

[0377] Alkali metals such as lithium, sodium, and potassium can be listed as counter cations for salts with an FSO2 framework, with lithium being the preferred choice.

[0378] For example, fluorosulfonates such as FSO3Li, FSO3Na, FSO3K, FSO3(CH3)4N, FSO3(C2H5)4N, and FSO3(n-C4H9)4N can be listed;

[0379] Fluorosulfonyl imide salts such as LiN(FSO2)2 and LiN(FSO2)(CF3SO2);

[0380] LiC(FSO2)3 and other fluorosulfonyl methyl lithium salts; etc.

[0381] In particular, from the viewpoint of not only improving the gas suppression effect during high-temperature storage, but also improving the charge / discharge rate characteristics and impedance characteristics, fluorosulfonates are preferred, and lithium fluorosulfonate is even more preferred.

[0382] Salts with an FSO2 framework can be used alone or in combination with two or more salts in any ratio. In 100% by mass of the non-aqueous electrolyte, the content of salts with an FSO2 framework (total amount when there are two or more types) can be 0.001% by mass or more, preferably 0.01% by mass or more, more preferably 0.1% by mass or more, and further preferably 5% by mass or less, preferably 3% by mass or less. When the content of salts with an FSO2 framework is within this range, the characteristics of the non-aqueous electrolyte secondary battery, especially its durability and continuous charging characteristics, can be significantly improved. Although the principle is not yet clear, it is believed that by mixing in this ratio, side reactions of additives on the electrodes can be suppressed to a minimum.

[0383] The mass ratio of the compound shown in formula (I) to the salt having the FSO2 framework (total amount when there are two or more) is typically 1 / 100 or more, preferably 10 / 100 or more, more preferably 20 / 100 or more, further preferably 25 / 100 or more, typically 10000 / 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. When this mass ratio is within this range, the characteristics of non-aqueous electrolyte secondary batteries, especially their durability or continuous charging characteristics, can be significantly improved. Although the principle is not yet clear, it is believed that by mixing at this ratio, side reactions of the additives on the electrodes can be suppressed to a minimum.

[0384] When a non-aqueous electrolyte contains LiPF6, the mass ratio of salts with an FSO2 framework (total amount when there are two or more) to the LiPF6 content (salts with an FSO2 framework / LiPF6) is typically 0.00005 or more, preferably 0.001 or more, more preferably 0.01 or more, further preferably 0.02 or more, particularly preferably 0.025 or more, typically 1.0 or less, preferably 0.5 or less, more preferably 0.4 or less, and further preferably 0.35 or less. When this mass ratio is within this range, the characteristics of non-aqueous electrolyte secondary batteries, especially their durability and continuous charging characteristics, can be significantly improved. Although the principle is not yet clear, it is believed that by mixing at this ratio, the decomposition side reactions of LiPF6 in non-aqueous electrolyte secondary batteries can be suppressed to a minimum.

[0385] [B1-1-2-4. Oxalate]

[0386] There are no particular restrictions on whether a compound is an oxalate, as long as it has at least one oxalate skeleton in its molecule.

[0387] Alkali metals such as lithium, sodium, and potassium can be listed as countercations for oxalates, with lithium being the preferred choice.

[0388] For example, lithium di(oxalate)borate and lithium difluorooxalateborate are examples of oxalate borates.

[0389] Lithium tetrafluorooxalate phosphate, lithium difluorodi(oxalate) phosphate, lithium tri(oxalate) phosphate, and other oxalate phosphates; etc.

[0390] In particular, from the viewpoint of not only improving the gas suppression effect during high-temperature storage, but also improving the charge / discharge rate characteristics and impedance characteristics, oxalate borates are preferred, and lithium di(oxalate)borate is more preferred.

[0391] Oxalate can be used alone or in combination with two or more in any ratio. In 100% by mass of the non-aqueous electrolyte, the oxalate content (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 further preferably 5% by mass or less, preferably 3% by mass or less. When the oxalate content is within this range, the characteristics of the non-aqueous electrolyte secondary battery, especially its durability and continuous charging characteristics, can be significantly improved. Although the principle is not yet clear, it is believed that by mixing in this ratio, side reactions of the additives on the electrodes can be suppressed to a minimum.

[0392] The mass ratio of the compound shown in Formula (I) to the oxalate (total amount when there are two or more) is typically 1 / 100 or more, preferably 10 / 100 or more, more preferably 20 / 100 or more, even more preferably 25 / 100 or more, typically 10000 / 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. When this mass ratio is within this range, the characteristics of non-aqueous electrolyte secondary batteries, especially their durability or continuous charging characteristics, can be significantly improved. Although the principle is not yet clear, it is believed that by mixing at this ratio, side reactions of the additives on the electrodes can be suppressed to a minimum.

[0393] When LiPF6 is present in a non-aqueous electrolyte, the mass ratio of oxalate (total amount when there are two or more types) to the LiPF6 content (oxalate / LiPF6) is typically 0.00005 or more, preferably 0.001 or more, more preferably 0.01 or more, further preferably 0.02 or more, particularly preferably 0.025 or more, typically 1.0 or less, preferably 0.5 or less, more preferably 0.4 or less, and further preferably 0.35 or less. When this mass ratio is within this range, the characteristics of non-aqueous electrolyte secondary batteries, especially their durability and continuous charging characteristics, can be significantly improved. Although the principle is not yet clear, it is believed that by mixing at this ratio, the decomposition side reactions of LiPF6 in non-aqueous electrolyte secondary batteries can be suppressed to a minimum.

[0394] It should be noted that the content of the additives listed above was determined by magnetic resonance spectroscopy.

[0395] It should be noted that some additives include substances listed as electrolyte salts. In such cases, the concentration range can be used for identification. For example, a non-aqueous electrolyte containing 10% by mass of a certain fluorinated inorganic salt can be identified as an electrolyte, while a non-aqueous electrolyte containing 0.5% by mass of a certain salt with an oxalic acid skeleton can be identified as an additive.

[0396] [B1-2. Electrolytes]

[0397] The electrolyte can be the same as in the first embodiment, wherein it may contain an electrolyte (C) other than the aforementioned compound Y. When this electrolyte (C) is included, the mass ratio of electrolyte (C) to compound (X) (C) / (X) is preferably 2 or more, more preferably 3 or more, further preferably 4 or more, and particularly preferably 5 or more. Furthermore, it is preferably 10,000 or less, preferably 2,000 or less, further preferably 1,000 or less, and particularly preferably 200 or less. With the (C) / (X) ratio within the above range, compound (X) can function appropriately on the electrode, sufficiently suppressing self-discharge and synergistically improving capacity retention during high-temperature storage and discharge characteristic maintenance at low temperatures.

[0398] [B1-3. Non-aqueous solvents]

[0399] The non-aqueous solvent can be the same as in the first embodiment.

[0400] [B1-4. Additives]

[0401] Within the scope that does not significantly impair the effects of the present invention, the non-aqueous electrolyte may contain various additives (hereinafter also referred to as combined additives). As additives, any conventionally known additives may be used. It should be noted that one additive may be used alone, or two or more additives may be used in any combination and ratio.

[0402] Previously known additives that can be included in non-aqueous electrolytes include cyclic carbonates with carbon-carbon unsaturated bonds, fluorinated cyclic carbonates, compounds with isocyanate groups, compounds with isocyanuric acid skeletons, phosphorus-containing organic compounds, cyano-containing organic compounds, silicon-containing compounds, aromatic compounds, non-fluorinated carboxylic acid esters, cyclic compounds with multiple ether bonds, compounds with isocyanuric acid skeletons, and borates. For example, compounds described in International Publication No. 2015 / 111676 can be listed.

[0403] The additive can be used alone or in any combination and ratio of two or more. The content of the additive (total amount when there are two or more) in 100% by mass of the non-aqueous electrolyte 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 also be 10% by mass or less, preferably 5% by mass or less, more preferably 3% by mass or less. When the additive content is within this range, the characteristics of the non-aqueous electrolyte secondary battery, especially its durability or continuous charging characteristics, can be significantly improved. Although the principle is not yet clear, it is believed that by mixing in this ratio, side reactions of the additives on the electrodes can be suppressed to a minimum.

[0404] Regarding the mass ratio of the compound shown in Formula (I) and / or Formula (II) to the additive (total amount when there are two or more), the ratio of compound / additive shown in Formula (I) and / or Formula (II) is generally 1 / 100 or more, preferably 10 / 100 or more, more preferably 20 / 100 or more, further preferably 25 / 100 or more, generally 10000 / 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. When the mass ratio is within this range, the characteristics of non-aqueous electrolyte secondary batteries, especially their durability or storage characteristics, can be significantly improved. Although the principle is not yet clear, it is believed that by mixing at this ratio, the side reactions of the additives on the electrodes can be suppressed to a minimum.

[0405] When LiPF6 is present in a non-aqueous electrolyte, the mass ratio of additives (total amount when there are two or more) to the LiPF6 content is typically 0.00005 or more, preferably 0.001 or more, more preferably 0.01 or more, further preferably 0.02 or more, particularly preferably 0.025 or more, typically 1.0 or less, preferably 0.5 or less, more preferably 0.4 or less, and further preferably 0.35 or less. When this mass ratio is within this range, the characteristics of non-aqueous electrolyte secondary batteries, especially their durability and continuous charging characteristics, can be significantly improved. Although the principle is not yet clear, it is believed that by mixing at this ratio, the decomposition side reactions of LiPF6 in non-aqueous electrolyte secondary batteries can be suppressed to a minimum.

[0406] [B2. Non-aqueous electrolyte secondary battery]

[0407] As one embodiment of the present invention, the non-aqueous electrolyte secondary battery is a non-aqueous electrolyte secondary battery having a positive electrode with a positive electrode active material capable of absorbing and releasing metal ions and a negative electrode active material capable of absorbing and releasing metal ions, and comprising a non-aqueous electrolyte.

[0408] [B2-1. Non-aqueous electrolyte]

[0409] The non-aqueous electrolyte can be the same as in the first embodiment.

[0410] [B2-2. Negative electrode]

[0411] The negative electrode can be the same as in the first embodiment.

[0412] [B2-3. Positive electrode]

[0413] A positive electrode is an object that has positively active material on at least a portion of the surface of a current collector.

[0414] [B2-3-1. Positive Electrode Active Material]

[0415] In embodiments of the present invention, there are no particular limitations on the positive electrode active material used in the positive electrode, but it is preferred to include lithium transition metal compounds.

[0416] Lithium transition metal compounds are compounds with structures that allow lithium ions to be decoupled or inserted. Examples include sulfides, phosphate compounds, silicate compounds, borate compounds, and lithium transition metal complex oxides. Among these, lithium transition metal complex oxides are preferred.

[0417] As lithium transition metal composite oxides, examples include substances with three-dimensionally diffusing spinel structures and layered structures that enable two-dimensional lithium-ion diffusion. Substances with spinel structures are generally represented as LixM'₂O₄ (where M' is at least one transition metal), specifically including LiMn₂O₄, LiCoMnO₄, and LiNi. 0.5 Mn 1.5 O4, LiCoVO4, etc. Substances with a layered structure are generally represented as LixMO2 (where M is at least one transition metal). Specifically, examples include LiCoO2, LiNiO2, and 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 Mn 0.29 Co 0.21 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, etc.

[0418] The positive electrode active material preferably comprises a lithium transition metal compound as shown in the following formula (IV).

[0419] Li 1+x MO2……(IV)

[0420] In formula (IV), x is -0.1 or more and 0.5 or less. 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 can be 0.1 or less, preferably 0.06 or less, more preferably 0.028 or less, further 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 effects of suppressing self-discharge, suppressing expansion, reducing internal resistance, and reducing capacity loss during continuous charging, resulting from the combination with the compounds of formula (I) and / or formula (II) contained in the electrolyte, are readily and sufficiently manifested, and are therefore preferred.

[0421] In the 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. Furthermore, the upper limit of the molar ratio can be 0.95 or less, preferably 0.85 or less, and more preferably 0.80 or less.

[0422] When the Ni / M molar ratio is within the above range, the proportion of Ni participating in charging and discharging is sufficiently large, and the battery becomes high-capacity, which is therefore preferred.

[0423] When M contains Co, the Co / M molar ratio in composition (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. Furthermore, 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. When the Co / M molar ratio is within the above range, the charge / discharge capacity increases, therefore it is preferred.

[0424] When M contains Mn, the Mn / M molar ratio is not particularly limited, but it is greater than 0, preferably 0.05 or more, more preferably 0.08 or more, and even more preferably 0.10 or more. Alternatively, it can 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.

[0425] When the above-mentioned Mn / M molar ratio is within the above range, the proportion of Mn that does not participate in charging and discharging is sufficiently small, and the battery becomes high-capacity, which is therefore preferred.

[0426] Preferably, the lithium transition metal composite oxide has a layered structure, and more preferably, it is a transition metal oxide with the following compositional formula (V).

[0427] Li a1 Ni b1 Co c1 M d1 O2……(V)

[0428] In the composition formula (V), a1, b1, c1, and d1 represent values ​​that satisfy 0.90≤a1≤1.10, 0.40≤b1≤0.98, 0.01≤c1≤0.5, and 0.00≤d1≤0.50, respectively, and satisfy 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.

[0429] In the composition formula (V), it is preferred to represent a value of 0.01≤d1≤0.50.

[0430] The preferred option is a transition metal oxide as shown in the following formula (2).

[0431] Li a2 Ni b2 Co c2 M d2 O2……(VI)

[0432] In equation (VI), a2, b2, c2, and d2 represent values ​​that satisfy 0.90≤a2≤1.10, 0.60≤b2≤0.98, 0.01≤c2<0.50, and 0.01≤d2<0.50, respectively, 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.

[0433] As a preferred specific example of a lithium transition metal oxide represented by formula (VI), LiNi can be cited as an example. 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 O2, etc.

[0434] In the above-mentioned formulations, M preferably contains Mn or Al, more preferably Mn, and even more preferably Mn or Al. This is because the structural stability of lithium transition metal oxides is improved, and structural degradation during repeated charge-discharge cycles is suppressed.

[0435] [B2-3-1-1. Introduction of Different Elements]

[0436] Lithium transition metal compounds may also incorporate different elements other than those specified in the above formula (IV).

[0437] [B2-3-1-2. Surface Coating]

[0438] Alternatively, a substance with a different composition (surface-attached substance) may be used on the surface of the above-mentioned positive electrode active material. Examples of surface-attached substances include oxides such as aluminum oxide, sulfates such as lithium sulfate, and carbonates such as lithium carbonate. When carbonates are used, the compounds shown in formulas (II) and (III) above have increased affinity with the positive electrode, and are therefore preferred.

[0439] These surface-adhering substances can be added to the positive electrode active material by means of dissolving or suspending them in a solvent and then drying them, so that they adhere to the surface of the positive electrode active material.

[0440] The amount of surface-attached material relative to the positive electrode active material, by mass, 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. It is usually used in an amount of 1 mmol / g or less.

[0441] In this specification, a substance with a different composition than the positive electrode active material that is attached to the surface of the positive electrode active material is also referred to as the "positive electrode active material".

[0442] [B2-3-1-3. Blending]

[0443] It should be noted that these positive electrode active materials can be used alone, or two or more can be used in any combination and ratio.

[0444] [B2-3-2. Composition and Manufacturing Method of the Positive Electrode]

[0445] The structure of the positive electrode will now be described. In this embodiment, the positive electrode can be manufactured by forming a layer of positive electrode active material containing a positive electrode active material and a binder on a current collector. The positive electrode using the positive electrode active material can be manufactured by conventional methods. That is, the positive electrode active material, binder, conductive material and thickener used as needed can be dry-mixed and formed into a sheet, and then the resulting sheet can be pressed onto the positive electrode current collector; or, these materials can be dissolved or dispersed in a liquid medium to form a slurry, which can be coated onto the positive electrode current collector and dried, thereby forming a layer of positive electrode active material on the current collector, thus obtaining the positive electrode. Alternatively, the above-mentioned positive electrode active material can be rolled to form a sheet electrode, or compressed to form a granular electrode.

[0446] The following describes the process of coating the positive current collector with slurry and then drying it.

[0447] [B2-3-2-1. Content of Active Substances]

[0448] The content of positive electrode active material in the positive electrode active material layer is usually above 80% by mass and below 98% by mass.

[0449] [B2-3-2-2. Density of the positive electrode active material layer]

[0450] To increase the filling density of the positive electrode active material, it is preferable to use a hand press or roller press to compact the positive electrode active material layer obtained through coating and drying. The density of the positive electrode active material layer is typically 1.5 g / cm³. 3 The above, preferably 3.0 g / cm³ 3 The above is further preferred to be 3.3 g / cm³. 3 The above is also true; it is usually 3.8 g / cm³. 3 the following.

[0451] [B2-3-2-3. Conductive Materials]

[0452] As a conductive material, any known conductive material can be used. Specific examples include metals such as copper and nickel. It should be noted that these materials can be used individually or in any combination and ratio. Conductive materials are typically used in a manner where they comprise 0.01% to 50% by mass in the positive electrode active material layer.

[0453] [B2-3-2-4. Adhesive]

[0454] As a binder used to manufacture the positive electrode active material layer, there are no particular limitations. In the case of coating method, as long as the material can be dissolved or dispersed in the liquid medium used in electrode manufacturing, there are no particular restrictions on its type. From the perspective of weather resistance, chemical resistance, heat resistance, flame retardancy, etc., fluorinated resins such as polyvinylidene fluoride, polyvinylidene fluoride, and polytetrafluoroethylene are preferred; polymers containing CN groups such as polyacrylonitrile and polyvinylidene cyanide are also preferred.

[0455] Alternatively, mixtures, modifiers, derivatives, random copolymers, alternating copolymers, graft copolymers, block copolymers, etc., of the aforementioned polymers may also be used. It should be noted that a single adhesive may be used alone, or two or more may be used in any combination and ratio.

[0456] Furthermore, when using a resin as a binder, the weight-average molecular weight of the resin is arbitrary, within a range that does not significantly impair the effects of the present invention, but is typically between 10,000 and 3 million. When the molecular weight is within this range, the strength of the electrode is improved, and the electrode can be appropriately formed.

[0457] The proportion of binder in the positive electrode active material layer is usually above 0.1% by mass and below 80% by mass.

[0458] [B2-3-2-5. Solvent]

[0459] As a solvent used to form the slurry, there are no particular restrictions on its type, as long as it is capable of dissolving or dispersing the positive electrode active material, conductive material, binder, and thickener as needed. Either aqueous solvent or organic solvent can be used.

[0460] [B2-3-2-6. Current Collector]

[0461] There are no particular restrictions on the material used for the positive current collector; any known material can be used. Specific examples include aluminum, stainless steel, nickel-plated materials, titanium, and tantalum. Aluminum is preferred.

[0462] Examples of current collector shapes include metal foil, metal cylinder, metal coil, metal plate, metal film, stretched metal mesh, perforated metal mesh, and foamed metal. Among these, metal film is preferred. It should be noted that the film can also be appropriately shaped into a mesh.

[0463] [B2-3-2-7. Thickness of the positive electrode plate]

[0464] There is no particular limitation on the thickness of the positive electrode plate. From the perspective of high capacity and high output, the thickness of the composite material layer after subtracting the thickness of the core material metal foil is usually more than 10μm and less than 500μm relative to one side of the current collector.

[0465] [B2-3-2-8. Surface coating of the positive electrode plate]

[0466] Alternatively, a positive electrode plate with a different composition can be used on the surface of the aforementioned positive electrode plate, or the same material as the material on the surface can be used.

[0467] [B2-4. Separator]

[0468] The separator can be the same as in the first embodiment.

[0469] [B2-5. Battery Design]

[0470] The battery design can be the same as in the first embodiment.

[0471] Example

[0472] [Experiment A1]

[0473] The specific solutions of the present invention will be described in more detail below through examples, but the present invention is not limited to these examples.

[0474] The compounds A1 to A11 and the additives used in this embodiment are as follows.

[0475] Compound A1:

[0476] Compound A2:

[0477] Compound A3:

[0478] Compound A4:

[0479] Compound A5:

[0480] Compound A6:

[0481] Compound A7:

[0482] Compound A8:

[0483] Compound A9:

[0484] Compound A10:

[0485] Compound A11:

[0486] (Hereinafter referred to as combined additives)

[0487] Lithium difluorophosphate (F₂PO₂Li)

[0488] Lithium bis(fluorosulfonyl)imide (LiFSI)

[0489] Lithium fluorosulfonate, (FSO3Li)

[0490] Lithium dioxalatoborate (LiBOB)

[0491] 1,2-Ethylene sulfate (ESA)

[0492] Ethyl methanesulfonate (EMS)

[0493] 1,3-Propanesulfonate lactone (PS)

[0494] Methylene methane disulfonate (MMDS)

[0495] [Examples A2-A11, Comparative Examples A2-A11]

[0496] [Fabrication of Non-Aqueous Electrolyte Secondary Batteries]

[0497] <Preparation of Non-Aqueous Electrolytes>

[0498] Using a non-aqueous electrolyte obtained by dissolving 1.2 mol / L (based on the concentration in the non-aqueous electrolyte) of thoroughly dried LiPF6 in a mixture of ethylene carbonate, methyl ethyl carbonate, and dimethyl carbonate (capacity ratio 3:4:3) under a dry argon atmosphere, and dissolving 1% by mass of ethylene carbonate as a base, a non-aqueous electrolyte was further prepared by dissolving additives in the combination described in Table A1.

[0499] Using this non-aqueous electrolyte, a non-aqueous electrolyte secondary battery was fabricated using the following method, and the above evaluation was performed.

[0500] <The Making of Positive Electrode 1>

[0501] Li will be used 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 are mixed in N-methyl-2-pyrrolidone and slurried. This mixture is then uniformly coated onto an aluminum foil with a thickness of 15 μm. After drying, it is rolled to form a positive electrode (hereinafter, this positive electrode is sometimes referred to as positive electrode 1). It should be noted that the plate density of the positive electrode is 3.3 g / cm³. 3 .

[0502] <The Making of Positive Electrode 2>

[0503] Li is used as the positive electrode active material. 1.05 Ni 0.52 Mn 0.29 Co 0.20 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 are used to form positive electrode 2 in the same manner as positive electrode 1. It should be noted that the plate density of positive electrode 2 is 3.3 g / cm³. 3 .

[0504] <The Making of Positive Electrode 3>

[0505] Li is used as the positive electrode active material. 1.05 Ni 0.34 Mn 0.33 Co 0.33 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 were used to form positive electrode 3 in the same manner as positive electrode 1. It should be noted that the plate density of positive electrode 3 is 2.6 g / cm³. 3 .

[0506] <The Making of Positive Electrode 4>

[0507] Positive electrode 4 was formed 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, in the same manner as positive electrode 1. It should be noted that the plate density of positive electrode 4 is 3.6 g / cm³. 3 .

[0508] <Making the Negative Electrode>

[0509] To 49 parts by weight of graphite powder, 50 parts by weight of an aqueous dispersion of sodium carboxymethyl cellulose (1% by weight) as a thickener and 1 part by weight of an aqueous dispersion of styrene-butadiene rubber (50% by weight) as a binder were added, and the mixture was stirred using a disperser to form a slurry. The resulting slurry was uniformly coated onto a copper foil with a thickness of 10 μm and dried, then rolled to form a negative electrode.

[0510] <Manufacturing of Non-Aqueous Electrolyte Secondary Batteries>

[0511] The positive electrode, negative electrode, and polyolefin separator are stacked in the order of negative electrode, separator, and positive electrode. The resulting battery element is wrapped with an aluminum laminate, injected with the aforementioned non-aqueous electrolyte, and then vacuum-sealed to produce a sheet-like non-aqueous electrolyte secondary battery. Non-aqueous electrolyte secondary batteries are fabricated using the electrolytes described in Table A1 to form the non-aqueous electrolyte secondary batteries of Examples A2 to A11 and Comparative Examples A2 to A11.

[0512] Table 1

[0513] Table A1

[0514]

[0515] [Evaluation of Non-Aqueous Electrolyte Secondary Batteries]

[0516] The non-aqueous electrolyte secondary batteries prepared in the examples are evaluated as follows.

[0517] Initial charge and discharge

[0518] In a constant temperature bath at 25°C, the sheet-shaped non-aqueous electrolyte secondary battery was charged to 3.7V at a constant current of 0.05C (the rated capacity of the 1-hour discharge rate is defined as the current value for discharging for 1 hour. The same applies below). Then, it was charged to 4.2V at a constant current-constant voltage of 0.2C. After that, it was discharged to 2.5V at a constant current of 0.2C.

[0519] Furthermore, after charging to 4.1V at a constant current-constant voltage of 0.2C, the non-aqueous electrolyte secondary battery was stabilized by storing it at 60°C for 24 hours. Then, it was discharged at a constant current of 25°C to 2.5V, followed by constant current-constant voltage charging at 0.2C until the voltage reached 4.2V. Afterward, it was discharged at a constant current of 0.2C to 2.5V, and the discharge capacity at this point was taken as the initial capacity (A).

[0520] Then, it was charged at 0.2C at 25℃ using a constant current-constant voltage method until the voltage reached 3.7V. It was then discharged at -20℃ at 0.05C, 0.1C, 0.25C, 0.5C, 0.75C, and 1C respectively, and the voltage was measured after 10 seconds. The internal resistance was determined using this current-voltage linear relationship and used as the initial resistance (R1).

[0521] Next, constant current-constant voltage charging is performed at 0.2C until the voltage reaches 4.2V, thus ending the initial charge and discharge process.

[0522] Evaluation of expansion, self-discharge, and increased internal resistance

[0523] The non-aqueous electrolyte secondary batteries after the initial charge and discharge were placed at 60°C for 14 days. During this time, the non-aqueous electrolyte secondary batteries were immersed in an ethanol bath at room temperature before and after placement, and the volume was measured. The volume change during the placement process was taken as the "expansion" of the battery, and the proportion of the reduction in expansion caused by the additive was taken as the "expansion inhibition rate" (for example, the expansion inhibition rate (%) of Example 1 = {(expansion of Comparative Example 1 - expansion of Example 1) / expansion of Comparative Example 1} × 100).

[0524] The non-aqueous electrolyte secondary battery was subjected to constant current discharge at 0.2C in a constant temperature bath at 25℃ until it reached 2.5V. The discharge capacity at that point was taken as the capacity after placement (B). The ratio of the difference between the initial capacity (A) and the capacity after placement (B) ((AB) / A×100) was taken as the "self-discharge rate".

[0525] Then, constant current-constant voltage charging was performed at 0.2C at 25°C until the voltage reached 3.7V. It was then discharged at -20°C at 0.05C, 0.1C, 0.25C, 0.5C, 0.75C, and 1C, and the voltage was measured after 10 seconds. The internal resistance was calculated using this current-voltage line and used as the resistance (R2) after placement. The rate of change between R1 and R2 [(R2-R1) / R1×100-100] was used as the "internal resistance increase rate". Furthermore, the proportion of the reduction in the internal resistance increase rate due to the additive was used as the "internal resistance increase suppression rate" (for example, the 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}×100).

[0526] It should be noted that it is generally better to have smaller expansion, self-discharge rate, and internal resistance increase rate, while better to have larger values ​​for expansion inhibition rate and internal resistance increase inhibition rate.

[0527] Evaluation of continuous charging capacity loss rate

[0528] The initial charge-discharge conditions were changed from 4.2V to 4.3V for initial charge-discharge. The non-aqueous electrolyte secondary battery after the initial charge-discharge was then charged at a constant voltage of 60°C for 7 days until it reached 4.3V. The amount of electricity flowing during the constant voltage charging period was taken as the continuous charge capacity loss (C), and the ratio between C and the initial capacity (A) (C / A) was taken as the "continuous charge capacity loss rate". Furthermore, the proportion of the reduction in the continuous charge capacity loss rate due to the additive was taken as the "continuous charge capacity loss suppression rate" (for example, the 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).

[0529] It should be noted that, generally speaking, the lower the continuous charging capacity loss rate, the better, and the higher the continuous charging capacity loss suppression rate, the better.

[0530] Table A2 shows the internal resistance increase rate and expansion of Examples A2-1 to A2-15 and Comparative Examples A2-1 to A2-3, which use electrolytes with various compositions but have the same positive electrode 1.

[0531] Table A3 shows the internal resistance suppression rates of Examples A3-1 to A3-2 and Comparative Examples A3-1 to A3-2, which have the same electrolyte composition and use positive electrodes 1 to 4.

[0532] Table A4 shows the expansion suppression rates of Example A4-1 and Comparative Examples A4-1 to A4-2, which have the same electrolyte composition and use positive electrodes 1, 3, and 4.

[0533] Table A5 shows the expansion of Examples A5-1 to A5-3 and Comparative Example A5-1, which use the same positive electrode 1 and electrolytes with various compositions.

[0534] As shown in Table A2, compared to the case without compounds A1 to A7 (Comparative Example A2-1), the non-aqueous electrolyte of the secondary battery containing a positive electrode active material with a specific composition, when containing compounds A1 to A7 (Examples A2-1 to A2-8), exhibits suppressed increases in internal resistance and expansion. However, the electrolyte containing compound A11 used in the prior art (Patent Document 2) (Comparative Example A2-2) tends to show increased internal resistance and significant expansion.

[0535] When lithium difluorophosphate (F₂PO₂Li), 1,2-ethylhexene sulfate (ESA), or methylene disulfonate (MMDS) is contained, the increase in internal resistance and expansion can be suppressed to a high level by including compound A1 or A3 (Examples A2-9 to A2-12). Furthermore, when fluorophosphates with P=O bonds are used in combination with lithium fluorosulfonate, ethyl methanesulfonate (EMS), or 1,2-ethylhexene sulfate (ESA), the increase in internal resistance can be suppressed to an even higher level by including compound A1 (Examples A2-13 to A2-15).

[0536] Furthermore, as shown in Table A3, the non-aqueous electrolyte secondary batteries using positive electrodes 1 and 2 containing a specific composition (Examples A3-1 and A3-2) exhibited a suppressive effect on the increase in internal resistance caused by compound A4. On the other hand, the suppressive effect on the increase in internal resistance caused by compound A4 was small and poor in the non-aqueous electrolyte secondary batteries using positive electrodes 3 and 4 containing a positive electrode active material without a specific composition (Comparative Examples A3-3 and A3-4).

[0537] Furthermore, as shown in Table A4, the expansion suppression effect of compound A4 was observed in the non-aqueous electrolyte secondary battery using positive electrode 1 containing a positive electrode active material with a specific composition (Example A4-1). However, no expansion suppression effect from compound A4 was observed in the non-aqueous electrolyte secondary batteries using positive electrodes 3 and 4 containing positive electrode active materials without a specific composition (Comparative Examples A4-2 and A4-3).

[0538] Furthermore, as shown in Table A5, regardless of the SO content in the non-aqueous electrolyte... n The structure of the betaine compound showed an expansion suppression effect in non-aqueous electrolyte secondary batteries (Examples A5-1 to A5-3) using a positive electrode 1 containing a positive electrode active material with a specific composition.

[0539] Table 2

[0540] Table A2

[0541]

[0542] Table 3

[0543] Table A3

[0544]

[0545] Table 4

[0546] Table A4

[0547] positive electrode Electrolyte composition Inflation inhibition rate Example A4-1 Positive electrode 1 A4-1 25 Comparative Example A4-1 Positive electrode 3 A4-1 -17 Comparative Example A4-2 Positive electrode 4 A4-1 -360

[0548] Table 5

[0549] Table A5

[0550]

[0551] Table A6 shows the self-discharge rates of Examples A6-1 to A6-4 and Comparative Examples A6-1 to A6-8 (relative values ​​with Comparative Example A6-1 set to 100). As can be seen from Table A6, compared to batteries without compounds A1 to A4 and batteries using non-aqueous electrolytes containing positive electrode active materials without specific compositions, the self-discharge rate is improved when the non-aqueous electrolyte of a battery containing positive electrode active materials with specific compositions contains compounds A1 to A4 (Examples A6-1 to A6-4). On the other hand, the self-discharge rate is higher and worse when the electrolyte contains compounds A10 or A11 used in the prior art (Patent Document 2) (Comparative Examples A6-2 and A6-3) compared to when these substances are not contained (Comparative Example A6-1). Furthermore, for secondary batteries containing non-aqueous electrolytes with positive electrode active materials that do not have a specific composition, no improvement in self-discharge rate was observed even when the non-aqueous electrolyte contained compound A4 (Comparative Examples A6-5 to A6-8).

[0552] Table 6

[0553] Table A6

[0554]

[0555] Table A7 shows the continuous charging capacity loss rates for Examples A7-1 to A7-5 and Comparative Examples A7-1 to A7-8.

[0556] Table A8 shows the continuous charging capacity loss rates of Examples A8-1 to A8-2 and Comparative Examples A8-1 to A8-3, which used positive electrodes 1, 3, and 4.

[0557] Table A9 shows the continuous charging capacity loss suppression rates for Example A9-1 and Comparative Examples A9-1 to A9-2, which used positive electrodes 1, 3, and 4.

[0558] As shown in Tables A7 and A8, compared to the case without compounds A1 and A4 (Comparative Example A7-1), the continuous charging capacity loss rate of the non-aqueous electrolyte secondary battery containing a positive electrode active material with a specific composition is improved when compounds A1 and A4 are present in the non-aqueous electrolyte (Examples A7-1 and A7-2). On the other hand, compared to the case containing compounds A1 and A4 (Examples A8-1 and A8-2), the continuous charging capacity loss rate of the electrolyte containing compounds A10 or A11 used in the prior art (Patent Document 2) is larger and worse.

[0559] Compared with the additives used in the prior art (Patent Document 1) when the main salt amount is used in combination with the additives, the continuous charging capacity loss rate is improved when the secondary salt amount is used in combination with the additives.

[0560] Regarding LiFSI, regardless of the type of cathode, there is a tendency for increased continuous charging capacity loss when it is contained alone (Comparative Examples A7-2 and A7-7). When using cathode 3, even if compound A1 is further contained in LiFSI, the continuous charging capacity loss rate is still increased compared to when it is contained alone (Comparative Example A7-8).

[0561] However, when using cathode 1, the addition of compound A1 to the LiFSI resulted in a decrease in continuous charging capacity loss compared to using LiFSI alone (Examples A7-4). This confirms the synergistic effect of combining cathode 1 with a certain amount of LiFSI and compound A1.

[0562] Furthermore, when using cathode 1 and further containing compound A1 on the basis of LiBOB or FSO3Li, the effect of suppressing continuous charging capacity loss rate is further increased compared with the case containing only compound A1 (Examples A7-2 and A7-3), thus confirming the synergistic effect of using cathode 1 in combination with secondary salts of LiBOB or FSO3Li and compound A1.

[0563] As shown in Table A9, the non-aqueous electrolyte secondary battery using positive electrode 1 containing a positive electrode active material with a specific composition (Example A9-1) exhibited a continuous charging capacity loss suppression effect of compound A4. On the other hand, no continuous charging capacity loss suppression effect of compound A4 was observed in the non-aqueous electrolyte secondary batteries using positive electrodes 3 and 4 containing positive electrode active materials without a specific composition (Comparative Examples A9-1 and A9-2).

[0564] Table 7

[0565] Table A7

[0566]

[0567] Table 8

[0568] Table A8

[0569]

[0570] Table 9

[0571] Table A9

[0572]

[0573] [Experiment A2]

[0574] [Evaluation of Non-Aqueous Electrolyte Secondary Batteries]

[0575] • Evaluation of initial charge and discharge, as well as self-discharge and increase in internal resistance

[0576] The non-aqueous electrolyte secondary battery, which underwent the same initial charge and discharge as Experiment A, was placed at 85°C for 24 hours. Except for this, the "self-discharge rate" and "internal resistance increase rate" were defined and set in the same way as Experiment A.

[0577] It should be noted that it is generally better to have a lower self-discharge rate and a lower internal resistance increase rate.

[0578] Table A10 shows the self-discharge rates of Examples A10-1 to A10-4 and Comparative Examples A10-1 to A10-2 (with Comparative Example A10-1 set as a relative value of 100).

[0579] As shown in Table A10, compared to the case without compound A4 (Comparative Example A10-1), the non-aqueous electrolyte secondary battery containing a specific composition of positive electrode active material exhibits a lower self-discharge rate and improved performance when the non-aqueous electrolyte contains a specified amount of compound A4 (Examples 10-1 to A10-3). Compared to the case without compound A4 (Comparative Example A10-2), the non-aqueous secondary battery (Example A10-4) containing a non-aqueous electrolyte further containing lithium di(oxalate)borate in the electrolyte of Example A10-1 exhibits even higher levels of self-discharge suppression.

[0580] Table 10

[0581] Table A10

[0582]

[0583] Table A11 shows the internal resistance increase rate of Examples A11-1 to A11-4 and Comparative Examples A11-1 to A11-3.

[0584] As shown in Table A11, compared to the case without compound A4 (Comparative Example A11-1), the non-aqueous electrolyte of the secondary battery containing a positive electrode active material of the present invention, when containing a specified amount of compound A4 of the present invention in the non-aqueous electrolyte (Examples A11-1 to A11-2), shows a smaller increase in internal resistance, indicating improvement. In the non-aqueous secondary batteries (Examples A11-3 and A11-4) obtained by further containing lithium difluorophosphate and lithium fluorosulfonate in the electrolyte of Example A11-1, the increase in internal resistance is suppressed to an even higher level.

[0585] Table 11

[0586] Table A11

[0587]

[0588] [Experiment B]

[0589] The specific solutions of the present invention will be described in more detail below through examples, but the present invention is not limited to these examples.

[0590] The compounds B1 to B3 and their additives used in this embodiment are as follows.

[0591] Compound B1:

[0592] Compound B2:

[0593] Compound B3:

[0594] (Hereinafter referred to as combined additives)

[0595] Lithium difluorophosphate (F₂PO₂Li)

[0596] Lithium fluorosulfonate (FSO3Li)

[0597] Lithium dioxalatoborate (LiBOB)

[0598] Lithium difluorodi(oxalate)phosphate (LiF2OP)

[0599] Lithium bis(fluorosulfonyl)imide (LiFSI)

[0600] Vinyl carbonate (VC)

[0601] Ethyl fluorocarbonate (FEC)

[0602] Lithium tetrafluoroborate (LiBF4)

[0603] 1,3-Dioxane (13DO)

[0604] Triethyl phosphonoacetate (EDPA)

[0605] [Examples B1-B3, Comparative Examples B1-B3]

[0606] [Fabrication of Non-Aqueous Electrolyte Secondary Batteries]

[0607] <Preparation of Non-Aqueous Electrolytes>

[0608] Using a non-aqueous electrolyte obtained by dissolving 1.2 mol / L (based on the concentration in the non-aqueous electrolyte) of thoroughly dried LiPF6 in a mixture of ethylene carbonate, methyl ethyl carbonate, and dimethyl carbonate (capacity ratio 3:4:3) under a dry argon atmosphere as a reference, a non-aqueous electrolyte was further prepared by dissolving additives in the combination described in Table B1.

[0609] Using this non-aqueous electrolyte, a non-aqueous electrolyte secondary battery was fabricated and evaluated using the following method.

[0610] <The Making of Positive Electrode>

[0611] Li will be used 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 are mixed in N-methyl-2-pyrrolidone and slurried. This mixture is then uniformly coated onto an aluminum foil with a thickness of 15 μm. After drying, it is rolled to form a positive electrode (hereinafter referred to as positive electrode 1). It should be noted that the electrode plate density is 3.3 g / cm³. 3 .

[0612] <Making the Negative Electrode>

[0613] To 49 parts by weight of graphite powder, 50 parts by weight of an aqueous dispersion of sodium carboxymethyl cellulose (1% by weight) as a thickener and 1 part by weight of an aqueous dispersion of styrene-butadiene rubber (50% by weight) as a binder were added, and the mixture was stirred using a disperser to form a slurry. The resulting slurry was uniformly coated onto a copper foil with a thickness of 10 μm and dried, then rolled to form a negative electrode.

[0614] <Manufacturing of Non-Aqueous Electrolyte Secondary Batteries>

[0615] The positive electrode, negative electrode, and polyolefin separator are stacked in the order of negative electrode, separator, and positive electrode. The resulting battery element is wrapped with an aluminum laminate, injected with the aforementioned non-aqueous electrolyte, and then vacuum-sealed to produce a sheet-like non-aqueous electrolyte secondary battery. The electrolyte uses the composition described in the respective tables.

[0616] [Evaluation of Non-Aqueous Electrolyte Secondary Batteries]

[0617] The non-aqueous electrolyte secondary batteries prepared in the examples are evaluated as follows.

[0618] Initial charge and discharge

[0619] In a constant temperature bath at 25°C, the sheet-shaped non-aqueous electrolyte secondary battery was charged to 3.7V at a constant current of 0.05C (the rated capacity of the 1-hour discharge rate is defined as the current value for discharging for 1 hour. The same applies below). Then, it was charged to 4.2V at a constant current-constant voltage of 0.2C. After that, it was discharged to 2.5V at a constant current of 0.2C.

[0620] Furthermore, after charging to 4.1V at a constant current-constant voltage of 0.2C, the non-aqueous electrolyte secondary battery was stabilized by storing it at 60°C for 24 hours. Then, it was discharged at a constant current of 25°C to 2.5V, followed by constant current-constant voltage charging at 0.2C until the voltage reached 4.2V. Afterward, it was discharged at a constant current of 0.2C to 2.5V, and the discharge capacity at this point was taken as the initial capacity (A).

[0621] Then, it was charged at 0.2C at 25℃ using a constant current-constant voltage method until the voltage reached 3.7V. It was then discharged at -20℃ at 0.05C, 0.1C, 0.25C, 0.5C, 0.75C, and 1C respectively, and the voltage was measured after 10 seconds. The internal resistance (R) was calculated using this current-voltage linear relationship. 1A The internal resistance (R) of a secondary battery using a non-aqueous electrolyte without additives (Comparative Example 1) was measured. 1B The relative value (R) based on the baseline 1A / R 1B ×100) is used as the initial low-temperature discharge characteristic (R1').

[0622] Next, constant current-constant voltage charging is performed at 0.2C until the voltage reaches 4.2V, thus ending the initial charge and discharge process.

[0623] Evaluation of self-discharge, capacity retention, and low-temperature discharge characteristic retention.

[0624] The non-aqueous electrolyte secondary battery, after its initial charge and discharge, was placed at 85°C for 24 hours. The discharge capacity at 0.2C under constant current discharge in a 25°C constant current bath until 2.5V was recorded as the post-placement capacity (B). The ratio of the initial capacity (A) to the post-placement capacity (B) ((AB) / A×100) was recorded as the "self-discharge rate". The discharge capacity at 0.2C under constant current-constant voltage charging until 4.2V, followed by constant current discharge at 0.2C until 2.5V, was recorded as the post-placement recovery capacity (C). The ratio of the initial capacity (A) to the post-placement recovery capacity (C) (C / A×100) was recorded as the "capacity retention rate".

[0625] Then, it was charged at 0.2C at 25℃ using a constant current-constant voltage method until the voltage reached 3.7V. It was then discharged at -20℃ at 0.05C, 0.1C, 0.25C, 0.5C, 0.75C, and 1C respectively, and the voltage was measured after 10 seconds. The internal resistance (R) was calculated using this current-voltage linear relationship. 2A The internal resistance (R) of a secondary battery using a non-aqueous electrolyte without additives (Comparative Example 1) was measured. 2B The relative value (R) based on the baseline 2A / R 2BThe initial low-temperature discharge characteristic (R2') is defined as R1' × 100. The rate of change between R1' and R2' [R2' / R1' × 100] is defined as the "low-temperature discharge characteristic maintenance rate".

[0626] It should be noted that it is generally better to have a lower self-discharge rate and a lower low-temperature discharge characteristic retention rate, while a higher capacity retention rate is better.

[0627] Table B1 shows the low-temperature discharge characteristic retention rate (relative values ​​with Comparative Example B1-1 set to 100). As can be seen from Table B1, when the mass of the specific zwitterionic compound (compound B1 or B2) involved in this invention is less than or equal to 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 the battery performance. On the other hand, when the mass of the specific zwitterionic compound (compound B1 or B2) involved in this invention exceeds the total mass of the salt additive, no reduction in the low-temperature discharge characteristic retention rate caused by the zwitterionic compound (compound B1 or B2) is observed.

[0628] Furthermore, even when adding ethylene carbonate, fluoroethylene carbonate, lithium tetrafluoroborate, ethynyl ethylene carbonate, 1,3-dioxane, or triethyl phosphonoacetate, which are used in the prior art (Patent Documents 1, 2, or 5), no reduction in the low-temperature discharge characteristic maintenance rate was observed.

[0629] Table 12

[0630] Table B1

[0631]

[0632] Table B2 shows the self-discharge rate (relative value with Comparative Example B2-1 set to 100). As can be seen from Table B2, when the mass of the specific zwitterionic compound (compound B1 or B2) involved in this invention is less than or equal to the total mass of the lithium salt additive, the zwitterionic compound (compound B1 or B2) reduces the self-discharge rate and improves the battery performance. On the other hand, when the mass of the specific zwitterionic compound (compound B1 or B2) involved in this invention exceeds the total mass of the salt additive, no reduction in self-discharge rate effect caused by the zwitterionic compound (compound B1 or B2) is observed.

[0633] Furthermore, even with the addition of vinylene carbonate, fluoroethylene carbonate, and lithium tetrafluoroborate used in the prior art (Patent Documents 2 or 5), no reduction in self-discharge rate was observed.

[0634] Table 13

[0635] Table B2

[0636]

[0637] Table B3 shows the capacity retention rate (relative values ​​with Comparative Example B3-1 set to 100). As can be seen from Table B3, when the mass of the specific zwitterionic compound (compound B1) involved in this embodiment is less than or equal to the total mass of the salt additive, the zwitterionic compound (compound B1) improves the capacity retention rate and increases the battery life. On the other hand, when the mass of the specific zwitterionic compound (compound B1) involved in this invention exceeds the total mass of the salt additive, no improvement in capacity retention rate due to the zwitterionic compound (compound B1) was observed.

[0638] Furthermore, even with the addition of ethylene fluorocarbonate and lithium tetrafluoroborate used in the prior art (Patent Documents 2 or 5), no improvement in capacity retention was observed.

[0639] Table 14

[0640] Table B3

[0641] Additive 1 Additive 2 Capacity maintenance rate Example B3-1 Lithium di(oxalate)borate (0.5) Compound B1 (0.3%) 100.8 Example B3-2 Lithium difluorodi(oxalate)phosphate (0.5) Compound B1 (0.3%) 100.4 Comparative Example B3-1 — — 100.0 Comparative Example B3-2 — Compound B1 (0.3%) 100.3 Comparative Example B3-3 — Compound B1(1) 100.1 Comparative Examples B3-4 Lithium di(oxalate)borate (0.5) — 100.3 Comparative Example B3-5 Lithium di(oxalate)borate (0.5) Compound B1(1) 99.9 Comparative Example B3-6 — — 100.1 Comparative Example B3-7 Lithium difluorodi(oxalate)phosphate (0.5) Compound B1(1) 99.9 Comparative Example B3-8 Ethyl fluorocarbonate (0.5g) — 100.3 Comparative Example B3-9 Ethyl fluorocarbonate (0.5g) Compound B1 (0.3%) 99.7 Comparative Example B3-10 Ethyl fluorocarbonate (0.5g) Compound B1(1) 100.1 Comparative Example B3-11 Lithium tetrafluoroborate (0.5g) — 99.2 Comparative Example B3-12 Lithium tetrafluoroborate (0.5g) Compound B1 (0.3%) 98.6 Comparative Example B3-13 Lithium tetrafluoroborate (0.5g) Compound B1(1) 98.8

Claims

1. A non-aqueous electrolyte secondary battery, characterized in that, It comprises: a positive electrode with a positive active material capable of absorbing and releasing metal ions, a negative electrode with a negative active material capable of absorbing and releasing metal ions, and a non-aqueous electrolyte. The non-aqueous electrolyte contains a compound (X) represented by formula (I) and / or formula (II) and contains at least one compound (Y) selected from the group consisting of fluorophosphates having P=O bonds, salts having an FSO2 skeleton, and oxalates. The content of this compound (Y) is 0.001–5% by mass. The non-aqueous electrolyte contains less than 80% by mass of compound (X) as well as the content of compound (Y) by mass. The positive electrode active material comprises a lithium transition metal compound as shown in formula (IV) below. Li 1+x MO2... (IV) In the above composition formula (IV), x is greater than or equal to -0.1 and less than or equal to 0.5, M is a plurality of elements containing at least Ni, and the Ni / M molar ratio is greater than or equal to 0.40 and less than or equal to 1.

0. In formula (I) and formula (II), R 1 ~R 5 is an organic group having carbon number 1 to 18, which is independent of each other or bonded to each other, R 6 is a hydrocarbon group having carbon number 1 to 4, and n is an integer of 2 to 4.

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

3. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein, In the formula (I), R 1 ~R 3 is a hydrocarbon group having 1 to 15 carbons which are independent of each other or bonded to each other.

4. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein, In the formula (I), R 1 ~R 3 is a methyl group or an ethyl group.

5. The non-aqueous electrolyte secondary battery according to claim 1 or 2, wherein, The positive electrode active material contains more than 10 μmol / g of carbonate.

6. A non-aqueous electrolyte, characterized in that, It contains a compound (X) represented by formula (I) and / or formula (II) and contains at least one compound (Y) selected from the group consisting of fluorophosphates having P=O bonds, salts having an FSO2 skeleton, and oxalates, wherein the content of compound (Y) is 0.001 to 5% by mass, and the content of compound (X) in the non-aqueous electrolyte is less than 80% by mass of the content of compound (Y). In formula (I) and formula (II), R 1 ~R 5 is a carbon number 1-18 organic group which is independent of each other or bonded to each other, R 6 is a carbon number 1-4 hydrocarbon group, and n is an integer of 2-4.

7. The non-aqueous electrolyte according to claim 6, wherein, The fluorophosphate with P=O bonds, the salt with FSO2 framework, and the oxalate are lithium fluorophosphate with P=O bonds, lithium salt with FSO2 framework, and lithium salt with oxalate framework.

8. The non-aqueous electrolyte according to claim 6 or 7, wherein, The non-aqueous electrolyte contains an electrolyte (C) other than the compound (Y), and the ratio of the content of electrolyte (C) to compound (X) (C) / (X) is more than 2 and less than 10,000.

9. 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 according to any one of claims 6 to 8.

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