Non-aqueous electrolyte for secondary battery and non-aqueous electrolyte secondary battery

Abstract

The nonaqueous electrolyte secondary battery is provided with: a positive electrode, a negative electrode, and a nonaqueous electrolyte. The nonaqueous electrolyte contains a carboxylic acid ester and lithium bisoxalate borate. The concentration of the carboxylic acid ester is 0.01% by volume or more and less than 10% by volume with respect to the volume of a nonaqueous solvent. In addition, the concentration of lithium bisoxalate borate is 0.01 M or more and less than 0.2 M.

Description

Technical Field

[0001] This invention relates to a non-aqueous electrolyte for secondary batteries and a non-aqueous electrolyte secondary battery using the non-aqueous electrolyte. Background Technology

[0002] It is known that in non-aqueous electrolyte secondary batteries such as lithium-ion batteries, the non-aqueous electrolyte has a significant impact on battery performance, including input / output characteristics, capacity, and cycle characteristics. For example, Patent Document 1 discloses a non-aqueous electrolyte secondary battery comprising a non-aqueous electrolyte containing 3 to 30% by volume of a chain carboxylic acid ester relative to the volume of the non-aqueous solvent. Patent Document 1 describes achieving excellent low-temperature output characteristics.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: International Publication No. WO2016 / 084357 Summary of the Invention

[0006] In non-aqueous electrolyte secondary batteries, gas is sometimes generated due to the decomposition of the non-aqueous solvent during charging and discharging, sometimes requiring venting. Furthermore, increased gas generation can cause problems such as battery expansion due to gas and capacity reduction due to gas jamming between electrodes. The carboxylic acid ester used in the non-aqueous electrolyte secondary battery in Patent Document 1 has a high dielectric constant and low viscosity, which helps improve input / output characteristics, but it is prone to reduction and decomposition during initial charging. Therefore, non-aqueous electrolyte secondary batteries using carboxylic acid esters suffer from the problem of excessive gas generation.

[0007] The non-aqueous electrolyte for secondary batteries of the present invention is a non-aqueous electrolyte containing a non-aqueous solvent, comprising a carboxylic acid ester and lithium dioxalate borate. The concentration of the carboxylic acid ester is 0.01% by volume or more and less than 10% by volume relative to the volume of the non-aqueous solvent, and the concentration of the lithium dioxalate borate is 0.01M or more and less than 0.2M. It should be noted that the volume ratios here are values ​​at 25°C and 1 atmosphere.

[0008] The non-aqueous electrolyte secondary battery of the present invention comprises the above-mentioned non-aqueous electrolyte, positive electrode and negative electrode.

[0009] The non-aqueous electrolyte for secondary batteries of the present invention can suppress gas generation in secondary batteries using carboxylic acid ester non-aqueous electrolytes. The non-aqueous electrolyte secondary battery of the present invention has excellent input / output characteristics and low gas generation during the initial charging stage. Attached Figure Description

[0010] Figure 1This is a perspective view showing the appearance of a non-aqueous electrolyte secondary battery according to an example of the embodiment.

[0011] Figure 2 This is a perspective view of an electrode body according to one embodiment. Detailed Implementation

[0012] In order to develop a non-aqueous electrolyte secondary battery with excellent input / output characteristics and low gas generation during initial charging, the inventors discovered through in-depth research that the target battery performance can be obtained by adding specific amounts of carboxylic acid esters and lithium dioxalate borate to the non-aqueous electrolyte. As mentioned above, although carboxylic acid esters are helpful in improving input / output characteristics, they are prone to reduction and decomposition during initial charging. However, with the non-aqueous electrolyte of this invention, gas generation is specifically suppressed.

[0013] The following is a reference to the appendix. Figure 1 An example of an embodiment of the non-aqueous electrolyte secondary battery of the present invention will be described in detail below. It should be noted that the selective combination of the various embodiments and modifications illustrated below is foreseeable from the outset.

[0014] Figure 1 This is a perspective view showing the appearance of a non-aqueous electrolyte secondary battery 10 according to an embodiment; Figure 2 This is a three-dimensional view of the electrode body 11 that constitutes the non-aqueous electrolyte secondary battery 10. Figure 1 The non-aqueous electrolyte secondary battery 10 shown has a bottom-shaped cylindrical outer can 14 as its outer casing, but the outer casing is not limited to this. The non-aqueous electrolyte secondary battery of the present invention can be, for example, a cylindrical battery having a bottom-shaped cylindrical outer can, a coin-shaped battery having a coin-shaped outer can, or a laminated battery having an outer casing composed of a laminate containing a metal layer and a resin layer.

[0015] like Figure 1 and Figure 2 As shown, the non-aqueous electrolyte secondary battery 10 includes: an electrode body 11, a non-aqueous electrolyte, a bottomed rectangular outer container 14 containing the electrode body 11 and the non-aqueous electrolyte, and a sealing plate 15 that plugs the opening of the outer container 14. The non-aqueous electrolyte secondary battery 10 is a so-called square battery. The electrode body 11 has a wound structure in which a positive electrode 20 and a negative electrode 30 are wound together with a separator 40 in between. The positive electrode 20, the negative electrode 30, and the separator 40 are all strip-shaped bodies, and the positive electrode 20 and the negative electrode 30 are wound together with the separator 40 in between. It should be noted that the electrode body can be a stacked type in which multiple positive electrodes and multiple negative electrodes are alternately stacked one sheet at a time with separators in between.

[0016] The non-aqueous electrolyte secondary battery 10 includes a positive terminal 12 electrically connected to the positive electrode 20 via a positive current collector 25; and a negative terminal 13 electrically connected to the negative electrode 30 via a negative current collector 35. In this embodiment, the sealing plate 15 has an elongated rectangular shape, and the positive terminal 12 is disposed at one end of the long side of the sealing plate 15, and the negative terminal 13 is disposed at the other end of the long side of the sealing plate 15. The positive terminal 12 and the negative terminal 13 are external connection terminals for electrical connection with other non-aqueous electrolyte secondary batteries 10, various electronic instruments, etc., and are mounted on the sealing plate 15 via an insulating member.

[0017] For ease of explanation, the height direction of the outer can 14 will be referred to as the "vertical direction" of the non-aqueous electrolyte secondary battery 10, the side of the sealing plate 15 will be referred to as "up" and the bottom side of the outer can 14 will be referred to as "down". In addition, the direction along the long side of the sealing plate 15 will be referred to as the "horizontal direction" of the non-aqueous electrolyte secondary battery 10.

[0018] The outer can 14 is a bottomed, square-shaped metal container. An opening formed at the top of the outer can 14 is sealed by a sealing plate 15 welded to its edge. The sealing plate 15 typically includes an injection port 16 for injecting non-aqueous electrolyte; a gas venting valve 17 for releasing gas in case of battery malfunction; and a current-breaking mechanism. The outer can 14 and the sealing plate 15 are, for example, made of a metal material primarily composed of aluminum.

[0019] The electrode body 11 is a flat, wound electrode body comprising a flat portion and a pair of curved portions. The electrode body 11 is housed in the outer can 14 such that the winding axis is along the transverse direction of the outer can 14, and the width direction of the pair of curved portions of the electrode body 11 is along the height direction of the battery. In this embodiment, a current collector is formed at one end of the electrode body 11 in the axial direction, consisting of stacked core exposed portions 23 of the positive electrode 20, and at the other end in the axial direction, a current collector is formed at the other end, consisting of stacked core exposed portions 33 of the negative electrode 30. Each current collector is electrically connected to a terminal via a current collector. It should be noted that an insulating electrode body support (insulating sheet) is disposed between the electrode body 11 and the inner surface of the outer can 14.

[0020] [positive electrode]

[0021] The positive electrode 20 includes a positive electrode core 21 and a positive electrode composite material layer disposed on the surface of the positive electrode core 21. The positive electrode core 21 may contain a foil of a metal stable within the potential range of the positive electrode 20, such as aluminum or an aluminum alloy, or a thin film with the metal disposed on its surface. The positive electrode composite material layer preferably includes a positive electrode active material, a conductive material, and a binder material, and is disposed on both sides of the positive electrode core 21. The positive electrode 20 can be manufactured as follows: for example, a positive electrode composite material slurry containing a positive electrode active material, a conductive material, and a binder material is coated onto the positive electrode core 21, the coating is dried, and then compressed to form a positive electrode composite material layer on both sides of the positive electrode core 21.

[0022] Lithium transition metal composite oxides can be used as positive electrode active materials. Examples of metal elements contained in lithium transition metal composite oxides include Ni, Co, Mn, Al, B, Mg, Ti, V, Cr, Fe, Cu, Zn, Ga, Sr, Zr, Nb, In, Sn, Ta, and W. Preferably, at least one of Ni, Co, and Mn is included. Examples of preferred composite oxides include lithium transition metal composite oxides containing Ni, Co, and Mn; and lithium transition metal composite oxides containing Ni, Co, and Al.

[0023] Examples of conductive materials included in the positive electrode composite layer include carbon materials such as carbon black, acetylene black, Ketjen black, and graphite. Examples of binder materials included in the positive electrode composite layer include fluoropolymers such as polytetrafluoroethylene (PTFE) and polyvinylidene fluoride (PVdF); polyacrylonitrile (PAN), polyimide resins, acrylic resins, and polyolefin resins. These resins can also be used in combination with cellulose derivatives such as carboxymethyl cellulose (CMC) or its salts, and polyethylene oxide (PEO).

[0024] [negative electrode]

[0025] The negative electrode 30 includes a negative electrode core 31 and a negative electrode composite material layer disposed on the surface of the negative electrode core 31. The negative electrode core 31 may use a foil of a metal stable within the potential range of the negative electrode 30, such as copper, or a thin film with the metal disposed on its surface. The negative electrode composite material layer preferably includes a negative electrode active material and a binder material, and is disposed on both sides of the negative electrode core 31. The negative electrode 30 can be manufactured as follows: for example, a negative electrode composite material slurry comprising a negative electrode active material, a conductive material, and a binder material is coated onto the surface of the negative electrode core 31, the coating is dried, and then compressed to form a negative electrode composite material layer on both sides of the negative electrode core 31.

[0026] The negative electrode composite material layer contains, for example, a carbon-based active material capable of reversibly absorbing, storing, and releasing lithium ions. Preferred carbon-based active materials include natural graphite such as flake graphite, block graphite, and amorphous graphite; and artificial graphite such as block graphite (MAG) and mesophase carbon microsphere graphite (MCMB). Alternatively, Si-based active materials composed of at least one of Si and Si-containing compounds may be used as the negative electrode active material, or a combination of carbon-based and Si-based active materials may be used.

[0027] As the conductive material included in the negative electrode composite layer, it is the same as in the case of the positive electrode 20, and carbon materials such as carbon black, acetylene black, Ketjen black, and graphite can be used. As the binder material included in the negative electrode composite layer, it is the same as in the case of the positive electrode 20, and fluoropolymers, PAN, polyimide, acrylic resins, polyolefins, etc. can be used, but styrene-butadiene rubber (SBR) is preferred. In addition, the negative electrode composite layer preferably also includes CMC or its salts, polyacrylic acid (PAA) or its salts, polyvinyl alcohol (PVA), etc. Preferably, SBR, CMC or its salts, and PAA or its salts are used in combination.

[0028] [Separator]

[0029] The separator 40 uses a porous sheet with ion permeability and insulation properties. Specific examples of porous sheets include microporous films, woven fabrics, and nonwoven fabrics. The material of the separator 40 is preferably polyolefins such as polyethylene, polypropylene, copolymers of ethylene and α-olefins, or cellulose. The separator 40 can be either a single-layer structure or a multilayer structure. A heat-resistant layer containing inorganic particles can be formed on the surface of the separator 40; a heat-resistant layer composed of resins with high heat resistance such as aromatic polyamide resins, polyimides, and polyamide-imides can also be used.

[0030] [Non-aqueous electrolytes]

[0031] Non-aqueous electrolytes comprise non-aqueous solvents and electrolyte salts. Non-aqueous solvents may include, for example, nitrile compounds such as ethers, esters, and acetonitrile; amides such as dimethylformamide; and mixtures of two or more of these compounds. Non-aqueous solvents may also contain halogen-substituted derivatives in which at least a portion of the hydrogen atoms of these solvents are replaced by halogen atoms such as fluorine. Examples of halogen-substituted derivatives include fluorinated cyclic carbonates such as fluoroethylene carbonate (FEC), fluorinated chain carbonates, and fluorinated chain carboxylic acid esters such as methyl fluoropropionate (FMP).

[0032] Examples of the aforementioned ethers include cyclic ethers such as 1,3-dioxolane, 4-methyl-1,3-dioxolane, tetrahydrofuran, 2-methyltetrahydrofuran, propylene oxide, 1,2-epoxybutane, 1,3-dioxane, 1,4-dioxane, 1,3,5-trioxane, furan, 2-methylfuran, 1,8-eucalyptol, and crown ethers; and cyclic ethers such as 1,2-dimethoxyethane, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, dihexyl ether, and ethyl ether. Chain ethers such as vinyl ethers, butyl vinyl ethers, methyl phenyl ethers, ethyl phenyl ethers, butyl phenyl ethers, pentyl phenyl ethers, methoxytoluene, benzyl ethyl ethers, diphenyl ethers, dibenzyl ethers, o-dimethoxybenzene, 1,2-diethoxyethane, 1,2-dibutoxyethane, diethylene glycol dimethyl ether, diethylene glycol diethyl ether, diethylene glycol dibutyl ether, 1,1-dimethoxymethane, 1,1-diethoxyethane, triethylene glycol dimethyl ether, and tetraethylene glycol dimethyl ether.

[0033] Examples of the aforementioned esters include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate (PC), and butyl carbonate; and chain carbonates such as dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), methyl propyl carbonate, ethyl propyl carbonate, and methyl isopropyl carbonate. Preferably, at least one solvent selected from EC, EMC, and DMC is used, and particularly preferably, a mixture of EC, EMC, and DMC is used. In one example, the EC content is 20% by volume or more and 30% by volume or less relative to the volume of the non-aqueous medium. In another example, the EMC and DMC contents are 30% by volume or more and 40% by volume or less relative to the volume of the non-aqueous medium.

[0034] In addition, the non-aqueous solvent contains a carboxylic acid ester as an essential component. The carboxylic acid ester can be a cyclic carboxylic acid ester such as γ-butyrolactone (GBL) or γ-valerolactone (GVL), and is preferably a linear carboxylic acid ester. The carboxylic acid ester is included in an amount of 0.01 vol% or more and less than 10 vol% relative to the volume of the non-aqueous solvent. By adding 0.01 vol% or more of a carboxylic acid ester, especially a linear carboxylic acid ester, to the non-aqueous electrolyte, the input-output characteristics of the battery are improved.

[0035] The content of carboxylic acid ester relative to the volume of the non-aqueous solvent is preferably 0.1% by volume or more, more preferably 0.5% by volume or more, and particularly preferably 1% by volume or more. The upper limit of the content of carboxylic acid ester relative to the volume of the non-aqueous solvent is preferably 8% by volume, more preferably 6% by volume, and particularly preferably 5% by volume. It should be noted that when the amount of carboxylic acid ester added is 10% by volume or more, it becomes difficult to suppress the amount of gas generated.

[0036] The chain-like carboxylic acid esters are preferably compounds with 3 or more but fewer than 10 carbon atoms. Specific examples include methyl acetate, ethyl acetate, n-propyl acetate, isopropyl acetate, n-butyl acetate, isobutyl acetate, tert-butyl acetate, methyl propionate, ethyl propionate, n-propyl propionate, isopropyl propionate, n-butyl propionate, isobutyl propionate, tert-butyl propionate, methyl butyrate, ethyl butyrate, n-propyl butyrate, isopropyl butyrate, methyl isobutyrate, ethyl isobutyrate, n-propyl isobutyrate, and isopropyl isobutyrate. Preferably, the esters are selected from at least one of methyl acetate, ethyl acetate, methyl propionate, and ethyl propionate, with methyl acetate and methyl propionate being particularly preferred.

[0037] In addition, lithium oxalate borate (LiBOB) is an essential component of the non-aqueous electrolyte. The concentration of LiBOB in the non-aqueous electrolyte is 0.01 M (mol / L) or higher and less than 0.2 M. By adding more than 0.01 M of LiBOB to the non-aqueous electrolyte, the decomposition of carboxylic acid esters is specifically suppressed, and the amount of gas generated during the initial charging phase is significantly reduced. The combined use of carboxylic acid esters and LiBOB can achieve both improved battery input and output characteristics and reduced gas generation.

[0038] The concentration of LiBOB in the non-aqueous electrolyte is preferably 0.015 M or higher, more preferably 0.018 M or higher, and particularly preferably 0.020 M or higher. The upper limit of the LiBOB concentration is preferably 0.15 M, more preferably 0.10 M, and particularly preferably 0.08 M. It should be noted that even when LiBOB is added at a concentration of 0.2 M or higher, the reduction effect on gas production is small, and the input-output characteristics of excess LiBOB are reduced.

[0039] The non-aqueous electrolyte is preferably based on LiBOB and contains other lithium salts as the electrolyte salt. Specific examples of other lithium salts include LiBF4, LiClO4, LiPF6, LiAsF6, LiSbF6, LiAlCl4, LiSCN, LiFSO3, LiCF3SO3, LiCF3CO2, Li(P(C2O4)F4), Li(P(C2O4)2F2), Li(P(C2O4)3), and LiPF6. 6-x (C n F 2n+1 ) x (1 < x < 6, n is 1 or 2), LiB 10 Cl 10 Borates such as LiCl, LiBr, LiI, lithium chloroborate, lower aliphatic carboxylic acids, Li₂B₄O₇, and Li(B(C₂O₄)F₂) are preferred. LiPF₆ is the most preferred. Furthermore, the concentration of LiPF₆ is preferably higher than that of LiBOB.

[0040] An example of a preferred non-aqueous electrolyte contains the following components.

[0041] <Non-aqueous solvent>

[0042] At least one of methyl acetate and methyl propionate, comprising more than 1% by volume and less than 5% by volume.

[0043] EC 20% to 30% by volume

[0044] EMC above 30% and below 40% by volume

[0045] DMC ≥ 30% by volume and ≤ 40% by volume

[0046] <Lithium Salts>

[0047] LiBOB with a speed of 0.02M or higher and 0.08M or lower

[0048] LiPF6 with a strength of 0.5M or higher and a strength of 1.5M or lower

[0049] <Example>

[0050] The present invention will be further described below through embodiments, but the present invention is not limited to these embodiments.

[0051] <Example 1>

[0052] [The production of the positive electrode]

[0053] As the positive electrode active material, the general formula LiNi is used 1 / 3 Co 1 / 3 Mn 1 / 3 The lithium transition metal composite oxide represented by O2. A positive electrode active material, acetylene black, and polyvinylidene fluoride were mixed in a solid component mass ratio of 90:7:3, and N-methyl-2-pyrrolidone (NMP) was used as the dispersion medium to prepare a positive electrode composite slurry. Next, the positive electrode composite slurry was coated on both sides of a positive electrode core formed from aluminum foil. After drying and compressing the coating, it was cut to a specified electrode size (50 × 234 mm). The coating containing the aluminum leads was then peeled off, resulting in a positive electrode with a positive electrode composite layer formed on both sides of the positive electrode core.

[0054] [Making the negative electrode]

[0055] Graphite was used as the negative electrode active material. The negative electrode active material, carboxymethyl cellulose (CMC), and styrene-butadiene rubber (SBR) were mixed in a solid component mass ratio of 98:1:1, and water was used as the dispersion medium to prepare a negative electrode composite slurry. Next, the negative electrode composite slurry was coated on both sides of a negative electrode core formed from copper foil. The coating was dried, compressed with a specified force, and then cut to a specified electrode size (52 × 330 mm). The coating containing the nickel leads was further peeled off, resulting in a negative electrode with a negative electrode composite layer formed on both sides of the negative electrode core.

[0056] [Preparation of non-aqueous electrolytes]

[0057] Ethyl carbonate (EC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), and methyl propionate (MP) were mixed in a volume ratio of 25:37:35:3 (25°C, 1 atm). LiPF6 was added to this mixed solvent at a concentration of 1.15 M, and lithium bis(oxalato)borate (LiBOB) was added at a concentration of 0.025 M, respectively, to obtain a non-aqueous electrolyte.

[0058] [Fabrication of the Experimental Battery Cell]

[0059] Aluminum leads are installed on the exposed core of the positive electrode, and nickel leads are installed on the exposed core of the negative electrode. The positive and negative electrodes are wound into a spiral shape with a separator in between, and then radially pressed to form a flat, wound electrode body. This electrode body is housed in a shell made of aluminum laminate. After injecting the non-aqueous electrolyte, the opening of the shell is sealed to obtain a test battery cell (non-aqueous electrolyte secondary battery).

[0060] [Evaluation of gas production]

[0061] The test battery cells, whose volumes were determined by the Archimedes method, were initially charged at 25°C (CCCV charging until the battery voltage reached 3.7V). Under this charging condition, they were then aged at 75°C for 11 hours. The volume of the aged battery cells was measured using the Archimedes method, and the gas production was calculated from the volume difference before initial charging. The gas production is shown in Table 1 as a relative value to 100 for the test battery cells of Reference Example 2 described later (the same applies to the examples below).

[0062] <Example 2>

[0063] In the preparation of the non-aqueous electrolyte, the concentration of LiPF6 was changed to 0.9M. Otherwise, the test cell was prepared in the same manner as in Example 1, and the amount of gas generated was evaluated.

[0064] <Example 3>

[0065] In the preparation of the non-aqueous electrolyte, vinylene carbonate (VC) was added at a concentration of 0.3% by mass relative to the mass of the non-aqueous electrolyte. Otherwise, the test cell was prepared in the same manner as in Example 2, and the amount of gas generated was evaluated.

[0066] <Example 4>

[0067] In the preparation of the non-aqueous electrolyte, the concentration of LiBOB was changed to 0.04M. Otherwise, the test cell was prepared in the same manner as in Example 2, and the amount of gas generated was evaluated.

[0068] <Comparative Example 1>

[0069] In the preparation of the non-aqueous electrolyte, no LiBOB was added. Otherwise, the test cell was fabricated in the same manner as in Example 2, and the amount of gas generated was evaluated.

[0070] <Comparative Example 2>

[0071] In the preparation of the non-aqueous electrolyte, VC was added at a concentration of 0.3% by mass relative to the mass of the non-aqueous electrolyte, MP was not added, and the volume ratio of EC, EMC and DMC was set to 26:38:36. Otherwise, the test cell was prepared in the same manner as in Comparative Example 1, and the amount of gas generated was evaluated.

[0072] <Comparative Example 3>

[0073] In the preparation of the non-aqueous electrolyte, LiBOB and MP were not added, and the volume ratio of EC, EMC and DMC was set to 30:30:40. Otherwise, the test battery cells were prepared in the same manner as in Example 1, and the amount of gas generated was evaluated.

[0074] <Reference Example 1>

[0075] In the preparation of the non-aqueous electrolyte, the concentration of LiBOB was changed to 0.07M, MP was not added, and the volume ratio of EC, EMC and DMC was set to 30:30:40. Otherwise, the test battery cells were prepared in the same manner as in Example 1, and the amount of gas generated was evaluated.

[0076] <Reference Example 2>

[0077] In the preparation of the non-aqueous electrolyte, the concentration of LiBOB was changed to 0.05M, and VC was added at a concentration of 0.3% by mass relative to the mass of the non-aqueous electrolyte. Otherwise, the test cell was prepared in the same manner as in Reference Example 1, and the amount of gas generated was evaluated.

[0078] [Table 1]

[0079]

[0080] As shown in Table 1, compared with the test battery cells of the comparative examples, the amount of gas generated during the initial charging phase was significantly suppressed in the test battery cells of the embodiments. MP, as a carboxylic acid ester, contributes to improved input / output characteristics but is easily reduced and decomposed during the initial charging phase. However, the gas generation was suppressed in the test battery cells of the embodiments, which were equivalent to or better than the test battery cells of the reference examples that did not contain MP. It should be noted that the test battery cells of the reference examples did not contain MP, and therefore had poorer input / output characteristics compared to the test battery cells of the embodiments.

[0081] Explanation of reference numerals in the attached figures

[0082] 10 Non-aqueous electrolyte secondary batteries

[0083] 11 Electrode Body

[0084] 12 Positive Extremes

[0085] 13 Negative extremes

[0086] 14 Outer packaging tanks

[0087] 15 Sealing board

[0088] 16 Liquid injection part

[0089] 17 Gas discharge valve

[0090] 20 Positive Electrode

[0091] 21 Positive electrode core

[0092] 23, 33 Core Exposed Parts

[0093] 25 Positive current collector

[0094] 30 Negative electrode

[0095] 31 Negative electrode core

[0096] 35 Negative current collector

[0097] 40 Separators

Claims

1. A non-aqueous electrolyte for secondary batteries, comprising a non-aqueous solvent, including a carboxylic acid ester, lithium dioxalate borate, ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate. The concentration of the carboxylic acid ester relative to the volume of the non-aqueous solvent is 0.01% by volume or more and less than 5% by volume. The concentration of lithium dioxaborate is above 0.01M and less than 0.2M. The carboxylic acid ester is a chain-like carboxylic acid ester, and the chain-like carboxylic acid ester is at least one selected from methyl acetate, ethyl acetate, methyl propionate, and ethyl propionate. The content of ethylene carbonate is 20% to 30% by volume relative to the volume of the non-aqueous solvent, the content of ethyl methyl carbonate is 30% to 40% by volume relative to the volume of the non-aqueous solvent, and the content of dimethyl carbonate is 30% to 40% by volume relative to the volume of the non-aqueous solvent.

2. The non-aqueous electrolyte for secondary batteries according to claim 1, wherein, The carboxylic acid ester is methyl propionate.

3. A non-aqueous electrolyte secondary battery, comprising: The non-aqueous electrolyte for secondary batteries as described in claim 1 or 2 Positive electrode, and negative electrode.

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