Non-aqueous secondary battery and method for manufacturing the same

Abstract

To provide an acetonitrile-containing nonaqueous secondary battery which has a high capacity maintenance rate after a cycle test at 50°C.SOLUTION: A nonaqueous secondary battery comprises a positive electrode, a negative electrode and a nonaqueous electrolyte. The nonaqueous electrolyte contains an acetonitrile-containing nonaqueous solvent, a lithium salt, and a sulfone compound represented by the general formula (1). The content of the sulfone compound is 0.1 mass% or more and 3 mass% or less relative to a total mass of the nonaqueous electrolyte. The nonaqueous electrolyte has an ion conductivity of 12 mS / cm or more at 25°C. With regard to 10-sec discharge DCIR represented by (voltage change during 10 sec after start of discharge) / (discharge current value during 10 sec after start of discharge), a rate of change before and after storage at 85°C and for 12 hrs, given by (10-sec discharge DCIR after storage at 85°C) / (10-sec discharge DCIR before storage at 85°C) is more than 0 and 1.3 or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a non-aqueous secondary battery and a method for manufacturing the same. [Background technology]

[0002] Lithium-ion secondary batteries have been widely used in mobile devices, but in recent years, amid the global trend towards automobile electrification, their primary use has shifted to powering electric vehicles. For use as automotive batteries, a wide range of characteristics are required, including not only improved energy density and long-term cycle performance, but also high-temperature durability and low-temperature charge / discharge characteristics. In this context, several technologies have been reported that address these broad performance requirements by using electrolytes with high ionic conductivity and adding additives to the electrolyte that form a stable electrode protective film.

[0003] For example, Patent Document 1 discloses a non-aqueous secondary battery that operates with thick-film electrodes using a highly ionic conductive acetonitrile electrolyte. It also reports a method for enhancing the SEI (Solid Electrolyte Interface) by combining multiple electrode protection additives. Similarly, Patent Document 2 reports that the SEI is enhanced by a specific organolithium salt, and the decomposition of the highly ionic conductive electrolyte is suppressed. Patent Document 3 describes how to obtain a non-aqueous secondary battery with excellent storage characteristics and cycle performance by adding a sulfone-based additive to a non-aqueous electrolyte containing vinylene carbonate.

[0004] Furthermore, Patent Document 4 shows that by adding a sulfone compound having a phenyl group to a carbonate-based electrolyte, a non-aqueous secondary battery with excellent cycle characteristics and low-temperature performance can be obtained. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2013 / 062056 [Patent Document 2] International Publication No. 2012 / 057311 [Patent Document 3] International Publication No. 2021 / 049648 [Patent Document 4] Japanese Patent Publication No. 2000-133305 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] While acetonitrile-containing electrolytes such as those described in Patent Documents 1-3 exhibit good ionic conductivity, they may have issues with their cycle characteristics after high-temperature storage, such as at 50°C, depending on the conditions.

[0007] Carbonate-based electrolytes, such as those described in Patent Document 4, have the problem of insufficient ionic conductivity because they do not contain highly ionically conductive solvents such as acetonitrile.

[0008] The object of the present invention is to provide an acetonitrile-containing non-aqueous secondary battery with a high capacity retention rate after a 50°C cycle test, and a method for producing the same. [Means for solving the problem]

[0009] This invention was made in view of the above circumstances, and as a result of the investigation, it was found that the above problems can be solved by providing the following components, and thus the invention was completed.

[0010] In other words, one aspect of the present invention is as follows. [1] A non-aqueous secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, The aforementioned non-aqueous electrolyte comprises a non-aqueous solvent containing acetonitrile, a lithium salt, The following general formula (1): [ka] A sulfone compound represented by {wherein R1 and R2 each independently represent a halogen group or an alkyl group which may be substituted with a halogen atom.}, The content of the sulfone compound is 0.1% by mass or more and 3% by mass or less, relative to the total amount of the non-aqueous electrolyte. The ionic conductivity of the non-aqueous electrolyte at 25°C is 12 mS / cm or more and 30 mS / cm or less. The following equation (1-1): 10-second discharge DCIR = (voltage change during the first 10 seconds after discharge) / (discharge current value during the first 10 seconds after discharge) ... Equation (1-1) For the 10-second discharge DCIR represented by the following formula (1-2), the following equations apply before and after storage at 85°C for 12 hours: 10-second discharge DCIR change rate = (10-second discharge DCIR after 85°C storage) / (10-second discharge DCIR before 85°C storage) ... Equation (1-2) The 10-second discharge DCIR change rate, as represented by [formula], is greater than 0 and less than or equal to 1.3. Non-aqueous secondary battery. [2] The non-aqueous secondary battery according to [1], wherein vinylene carbonate is less than 2% by volume relative to the total amount of the non-aqueous solvent. [3] The non-aqueous secondary battery according to [1] or [2], wherein the acetonitrile content in the non-aqueous electrolyte is 20 to 60% by volume relative to the total amount of the non-aqueous solvent. [4] The non-aqueous secondary battery according to any one of [1] to [3], wherein the lithium salt is at least one selected from the group consisting of lithium-containing imide salts and lithium hexafluoride phosphate (LiPF6). [5] A non-aqueous secondary battery according to any one of [1] to [4], comprising diphenylsulfone as the sulfone compound represented by the general formula (1). [6] The positive electrode contains one or more materials selected from the group consisting of materials capable of intercepting and releasing lithium ions as a positive electrode active material, and the negative electrode contains one or more materials selected from the group consisting of materials capable of intercepting and releasing lithium ions and metallic lithium as a negative electrode active material, according to any one of [1] to [5]. [7] The non-aqueous secondary battery according to [6], wherein the positive electrode active material is a composite oxide of lithium and a transition metal, and the negative electrode active material is graphite. [8] A method for manufacturing a non-aqueous secondary battery according to any one of items [1] to [7], A method for manufacturing a non-aqueous secondary battery, comprising a step of performing the initial charge at a charging speed of 0.1C or higher, where 1C is defined as the current that can discharge the set capacity in one hour. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide an acetonitrile-containing non-aqueous secondary battery with a high capacity retention rate after a 50°C cycle test, and a method for producing the same. Furthermore, according to a preferred embodiment of the present invention, the addition of a diphenyl sulfone-substituted compound provides sufficient negative electrode protection even at high temperatures, and the capacity retention rate in the initial stages of a 50°C cycle test after high-temperature storage is stable, and a non-aqueous secondary battery and a method for manufacturing the same can be provided. [Brief explanation of the drawing]

[0012] [Figure 1] This is a schematic plan view showing an example of a non-aqueous secondary battery according to this embodiment. [Figure 2] This is a cross-sectional view along line AA in Figure 1. [Modes for carrying out the invention]

[0013] The embodiments for carrying out the present invention (hereinafter simply referred to as "this embodiment") will be described in detail below. In this specification, numerical ranges indicated using "~" include the numerical values ​​indicated before and after them. In this specification, an upper or lower limit stated in a numerical range described in steps may be replaced with an upper or lower limit in a numerical range described in another step. In this specification, an upper or lower limit stated in a numerical range may also be replaced with a value described in an example. The scale, shape, and length of parts of the drawings may be exaggerated for further clarity.

[0014] One aspect of this embodiment is, A non-aqueous secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, The non-aqueous electrolyte consists of a non-aqueous solvent containing acetonitrile, a lithium salt, The following general formula (1): [ka] A sulfone compound represented by {wherein R1 and R2 each independently represent a halogen group or an alkyl group which may be substituted with a halogen atom.}, The sulfone compound content is 0.1% by mass or more and 3% by mass or less relative to the total amount of the non-aqueous electrolyte. The ionic conductivity of the non-aqueous electrolyte at 25°C is between 12 mS / cm and 30 mS / cm. The following equation (1-1): 10-second discharge DCIR = (voltage change during the first 10 seconds after discharge) / (discharge current value during the first 10 seconds after discharge) ... Equation (1-1) For the 10-second discharge DCIR represented by the following formula (1-2), the following equations apply before and after storage at 85°C for 12 hours: 10-second discharge DCIR change rate = (10-second discharge DCIR after 85°C storage) / (10-second discharge DCIR before 85°C storage) ... Equation (1-2) This is a non-aqueous secondary battery in which the 10-second discharge DCIR change rate, represented by [formula], is greater than 0 and less than or equal to 1.3. According to this, it is possible to provide an acetonitrile-containing non-aqueous secondary battery with a high capacity retention rate after a 50°C cycle test. <Non-aqueous secondary battery> The non-aqueous secondary battery of this embodiment is a secondary battery comprising a positive electrode and a negative electrode along with the non-aqueous electrolyte, and may be, for example, a lithium-ion battery, and more specifically, a lithium-ion battery whose schematic plan view is shown in Figure 1 and whose schematic cross-sectional view is shown in Figure 2. The lithium-ion battery 100 shown in Figures 1 and 2 comprises a separator 170, a positive electrode 150 and a negative electrode 160 that sandwich the separator 170 from both sides, a positive electrode lead 130 (connected to the positive electrode 150) and a negative electrode lead 140 (connected to the negative electrode 160) that sandwich the laminate of these (separator 170, positive electrode 150 and negative electrode 160), and a battery casing 110 that houses them. The laminate formed by stacking the positive electrode 150, the separator 170 and the negative electrode 160 is impregnated with the non-aqueous electrolyte according to this embodiment.

[0015] <1.Non-aqueous electrolyte> In this embodiment, "non-aqueous electrolyte" refers to a non-aqueous electrolyte containing a non-aqueous solvent including acetonitrile, a lithium salt, and a predetermined sulfone compound. While it is preferable that the non-aqueous electrolyte in this embodiment contains as little water as possible, it may contain a very small amount of water as long as it does not hinder the resolution of the problem of the present invention. Such water content is 1% by mass or less, and 300 ppm by mass or less, preferably 200 ppm by mass or less, based on the total amount of the non-aqueous electrolyte. Regarding the non-aqueous electrolyte, as long as it has the configuration necessary to achieve the resolution of the problem of the present invention, other components can be appropriately selected and applied from known non-aqueous electrolyte materials used in lithium-ion batteries.

[0016] <1-1. Non-aqueous solvents> In this embodiment, "non-aqueous solvent" refers to the elements remaining in a non-aqueous electrolyte, excluding the lithium salt, a predetermined sulfone compound, and various additives. If the non-aqueous electrolyte contains an electrode protection additive, "non-aqueous solvent" refers to the elements remaining in the non-aqueous electrolyte, excluding the lithium salt, the predetermined sulfone compound, and additives other than the electrode protection additive. Examples of non-aqueous solvents include alcohols such as methanol and ethanol; and aprotic solvents. Among these, aprotic solvents are preferred as non-aqueous solvents. The non-aqueous solvent may contain solvents other than aprotic solvents, as long as it does not hinder the resolution of the problem of the present invention.

[0017] The non-aqueous solvent in the non-aqueous electrolyte of this embodiment contains acetonitrile as an aprotic solvent. The inclusion of acetonitrile in the non-aqueous solvent improves the ionic conductivity of the non-aqueous electrolyte, thereby increasing the diffusibility of lithium ions within the battery. Therefore, when the non-aqueous electrolyte contains acetonitrile, lithium ions can diffuse well even to areas near the current collector, which are difficult for lithium ions to reach during high-load discharge, particularly in positive electrodes where the positive electrode active material layer is thickened and the amount of positive electrode active material is increased. This makes it possible to extract sufficient capacity even during high-load discharge, resulting in a non-aqueous secondary battery with excellent load characteristics. In the case of carbonate-based solvents that do not contain acetonitrile, the ionic conductivity is insufficient because they do not contain a highly ionic conductive solvent like acetonitrile, and the charge-discharge rate is limited to the range that lithium ion movement can keep up with.

[0018] Furthermore, the inclusion of acetonitrile in the non-aqueous solvent can improve the rapid charging characteristics of non-aqueous secondary batteries. In constant current (CC)-constant voltage (CV) charging of non-aqueous secondary batteries, the capacity per unit time during the CC charging period is greater than the capacity per unit time during the CV charging period. When acetonitrile is used as the non-aqueous solvent in the non-aqueous electrolyte, the area in which CC charging can be performed can be enlarged (the CC charging time can be extended), and the charging current can also be increased, thus significantly shortening the time it takes to bring a non-aqueous secondary battery from the start of charging to a fully charged state.

[0019] Furthermore, acetonitrile is readily reductively decomposed electrochemically. Therefore, when using acetonitrile, it is preferable to use another solvent (for example, an aprotic solvent other than acetonitrile) in combination with acetonitrile as a non-aqueous solvent, and / or to add an electrode protective additive for forming a protective film on the electrode.

[0020] The acetonitrile content in the non-aqueous solvent is preferably 10 to 60% by volume relative to the total volume of the non-aqueous solvent. The upper limit of the acetonitrile content is more preferably 50% by volume or less, and even more preferably 40% by volume or less, relative to the total volume of the non-aqueous solvent. The lower limit of the acetonitrile content is more preferably 20% by volume or more, relative to the total volume of the non-aqueous solvent. When the lower limit of the acetonitrile content is within the above range, the ionic conductivity of the non-aqueous electrolyte tends to increase, enabling the non-aqueous secondary battery to exhibit high power output characteristics, and further promoting the dissolution of lithium salts. In addition, when the acetonitrile content in the non-aqueous solvent is within the above range, the high-temperature cycle characteristics and other battery characteristics of the non-aqueous secondary battery tend to be further improved while maintaining the excellent performance of acetonitrile.

[0021] Examples of aprotic solvents other than acetonitrile include cyclic carbonates, lactones, organic compounds having sulfur atoms, linear fluorinated carbonates, cyclic ethers, mononitriles other than acetonitrile, alkoxy-substituted nitriles, dinitriles, cyclic nitriles, short-chain fatty acid esters, linear ethers, fluorinated ethers, ketones, and compounds in which some or all of the H atoms of the aprotic solvent are substituted with halogen atoms.

[0022] Since acetonitrile, a component of non-aqueous solvents, is readily subjected to electrochemical reductive decomposition, the non-aqueous electrolyte according to this embodiment contains a specific sulfone compound in addition to acetonitrile in the non-aqueous solvent.

[0023] The non-aqueous solvent according to this embodiment comprises acetonitrile and a sulfone compound, and preferably further comprises ethylene carbonate as a cyclic carbonate. Even if the amount of vinylene carbonate is less than 2% by volume relative to the total amount of the non-aqueous solvent (for example, even if the non-aqueous electrolyte does not contain vinylene carbonate), when the non-aqueous electrolyte is used in a non-aqueous secondary battery, it forms a thermally durable SEI and suppresses deterioration of the negative electrode. In acetonitrile-containing electrolytes such as those described in Patent Documents 1-3, SEI formation has conventionally been performed using fluoroethylene carbonate (FEC) or vinylene carbonate (VC). On the other hand, in these electrolytes, the SEI decomposes thermally at high temperatures, resulting in a loss of negative electrode protection effect. Under certain conditions, this can lead to unstable cycle characteristics after high-temperature conditions. Furthermore, if VC itself decomposes within the battery at high temperatures, it can lead to a decrease in battery performance. Therefore, it is preferable that the amount of vinylene carbonate is less than 2% by volume relative to the total amount of the non-aqueous solvent. For example, it is preferable that the non-aqueous electrolyte does not contain vinylene carbonate.

[0024] Examples of cyclic carbonates include ethylene carbonate, propylene carbonate, 1,2-butylene carbonate, trans-2,3-butylene carbonate, cis-2,3-butylene carbonate, 1,2-pentylene carbonate, trans-2,3-pentylene carbonate, and cis-2,3-pentylene carbonate.

[0025] Examples of lactones include γ-butyrolactone, α-methyl-γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, δ-caprolactone, and ε-caprolactone;

[0026] Examples of linear carbonates include ethyl methyl carbonate, dimethyl carbonate, diethyl carbonate, methyl propyl carbonate, methyl isopropyl carbonate, dipropyl carbonate, methyl butyl carbonate, dibutyl carbonate, ethyl propyl carbonate, and diisobutyl carbonate;

[0027] Examples of cyclic ethers include tetrahydrofuran, 2-methyltetrahydrofuran, 1,4-dioxane, and 1,3-dioxane;

[0028] Other mononitriles besides acetonitrile include, for example, propionitrile, butyronitrile, valeronitrile, benzonitrile, and acrylonitrile;

[0029] Examples of alkoxy-substituted nitriles include methoxyacetonitrile and 3-methoxypropionitrile;

[0030] Examples of dinitriles include malononitrile, succinonitrile, glutaronitrile, adiponitrile, 1,4-dicyanoheptane, 1,5-dicyanopentane, 1,6-dicyanohexane, 1,7-dicyanoheptane, 2,6-dicyanoheptane, 1,8-dicyanooctane, 2,7-dicyanooctane, 1,9-dicyanononane, 2,8-dicyanononane, 1,10-dicyanodecane, 1,6-dicyanodecane, and 2,4-dimethylglutaronitrile;

[0031] Examples of cyclic nitriles include benzonitrile;

[0032] Examples of short-chain fatty acid esters include methyl acetate, methyl propionate, methyl isobutyrate, methyl butyrate, methyl isovalerate, methyl valerate, methyl pivalate, methyl hydroangelicaate, methyl caproate, ethyl acetate, ethyl propionate, ethyl isobutyrate, ethyl butyrate, ethyl isovalerate, ethyl valerate, ethyl pivalate, ethyl hydroangelicaate, ethyl caproate, propyl acetate, propyl propionate, propyl isobutyrate, propyl butyrate, propyl isovalerate, propyl valerate, propyl pivalate, propyl hydroangelicaate, propyl caproate, isopropyl acetate, isopropyl propionate, isopropyl isobutyrate, isopropyl butyrate, isopropyl isovalerate, isopropyl valerate, isopropyl pivalate Propyl, isopropyl hydroangelicaate, isopropyl caproate, butyl acetate, butyl propionate, butyl isobutyrate, butyl butyrate, butyl isovalerate, butyl valerate, butyl pivalate, butyl hydroangelicaate, butyl caproate, isobutyl acetate, isobutyl propionate, isobutyrate, isobutyrate, isobutyl isovalerate, isobutyl valerate, isobutyl pivalate, isobutyl hydroangelicaate, isobutyl caproate, tert-butyl acetate, tert-butyl propionate, tert-butyl isobutyrate, tert-butyl butyrate, tert-butyl isovalerate, tert-butyl valerate, tert-butyl pivalate, tert-butyl hydroangelicaate, and tert-butyl caproate;

[0033] Examples of the acyclic ether include dimethoxyethane, diethyl ether, 1,3-dioxolane, diglyme, triglyme, and tetraglyme;

[0034] Examples of the fluorinated ether include Rf , 8 , 7 -OR 21 (wherein, Rf 20 represents an alkyl group containing a fluorine atom, and R 7 represents a monovalent organic group which may contain a fluorine atom.);

[0035] Examples of the ketone include acetone, methyl ethyl ketone, and methyl isobutyl ketone;

[0036] Examples of the compound in which some or all of the H atoms of the aprotic solvent are substituted with halogen atoms include a compound in which the halogen atom is fluorine; can be mentioned.

[0037] Here, examples of the fluoride of the acyclic carbonate include methyl trifluoroethyl carbonate, trifluorodimethyl carbonate, trifluorodiethyl carbonate, trifluoroethyl methyl carbonate, methyl 2,2-difluoroethyl carbonate, methyl 2,2,2-trifluoroethyl carbonate, and methyl 2,2,3,3-tetrafluoropropyl carbonate. The above fluorinated acyclic carbonates have the following general formula: R 7 -O-C(O)O-R 8 (wherein, R 7 and R 8 are at least one selected from the group consisting of CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, and CH2Rf 9 , Rf 9 is an alkyl group having 1 to 3 carbon atoms in which at least one hydrogen atom is substituted with at least one fluorine atom, and R 7 and / or R 8 contain at least one fluorine atom.) can be represented by.

[0038] Furthermore, examples of fluorinated short-chain fatty acid esters include fluorinated short-chain fatty acid esters such as 2,2-difluoroethyl acetate, 2,2,2-trifluoroethyl acetate, and 2,2,3,3-tetrafluoropropyl acetate. Fluorinated short-chain fatty acid esters are represented by the following general formula: R 10 -C(O)OR 11 {where, R 10 is CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, CF3CF2H, CFH2, CF2Rf 12 CFHRf 12 , and CH2Rf 13 At least one selected from the group consisting of R 11 These are CH3, CH2CH3, CH2CH2CH3, CH(CH3)2, and CH2Rf 13 At least one selected from the group consisting of Rf 12 Rf is a C1-C3 alkyl group in which at least one fluorine atom may substitute for a hydrogen atom. 13 is an alkyl group having 1 to 3 carbon atoms in which at least one fluorine atom replaces a hydrogen atom, and R 10 and / or R 11 It contains at least one fluorine atom, R 10 If R is CF2H, 11 It is not CH3. It can be expressed as follows.

[0039] In this embodiment, the aprotic solvent other than acetonitrile may be used alone or in combination of two or more.

[0040] In this embodiment, the non-aqueous solvent preferably contains one or more cyclic carbonates and linear carbonates together with acetonitrile, from the viewpoint of improving the stability of the non-aqueous electrolyte. From this viewpoint, it is more preferable to use a cyclic carbonate together with acetonitrile in this embodiment, and even more preferable to use both cyclic carbonates and linear carbonates together with acetonitrile.

[0041] When using a cyclic carbonate with acetonitrile, it is particularly preferable that such cyclic carbonate contains ethylene carbonate.

[0042] <1-2. Lithium Salts> The non-aqueous electrolyte of this embodiment preferably contains LiPF6, but is not particularly limited to other lithium salts. For example, it is preferable that the lithium salt contains at least one selected from the group consisting of LiPF6 and lithium-containing imide salts. This makes it easier to achieve the effects of the present invention.

[0043] Lithium-containing imide salts are LiN(SO2C) m F 2m+1 The lithium salt is represented by )² [wherein m is an integer from 0 to 8], and more preferably contains at least one of LiN(SO₂F)₂ and LiN(SO₂CF₃)₂. It may contain only one or both of these imide salts. It may also contain imide salts other than these imide salts.

[0044] In this embodiment, where acetonitrile is included in the non-aqueous solvent, the saturation concentration of the lithium-containing imide salt relative to acetonitrile is higher than the saturation concentration of LiPF6. Therefore, it is preferable to include the lithium-containing imide salt at a molar concentration such that LiPF6 ≤ lithium-containing imide salt, as this suppresses the association and precipitation of the lithium salt and acetonitrile at low temperatures. Furthermore, from the viewpoint of ion supply, it is preferable that the lithium-containing imide salt content is 0.5 mol or more and 3 mol or less per liter of non-aqueous solvent. An acetonitrile-containing non-aqueous electrolyte containing at least one of LiN(SO2F)2 and LiN(SO2CF3)2 can effectively suppress the reduction in ionic conductivity at low temperatures such as -10°C or -30°C, thereby obtaining excellent low-temperature characteristics. In this way, by limiting the content, it is also possible to more effectively suppress the increase in resistance during high-temperature heating.

[0045] Furthermore, the lithium salt may also contain other fluorine-containing inorganic lithium salts besides LiPF6, such as LiBF4, LiAsF6, Li2SiF6, LiSbF6, and Li2B 12 F b H 12-bThe formula may include fluorine-containing inorganic lithium salts such as [wherein b is an integer from 0 to 3]. "Inorganic lithium salt" refers to a lithium salt that does not contain carbon atoms as anions and is soluble in acetonitrile. "Fluorine-containing inorganic lithium salt" refers to a lithium salt that does not contain carbon atoms as anions, contains fluorine atoms as anions, and is soluble in acetonitrile. Fluorine-containing inorganic lithium salts are excellent in that they form a passive film on the surface of the metal foil that is the positive electrode current collector, thereby suppressing corrosion of the positive electrode current collector. These fluorine-containing inorganic lithium salts can be used individually or in combination of two or more. As the fluorine-containing inorganic lithium salt, a compound that is a double salt of LiF and a Lewis acid is desirable, and among these, a fluorine-containing inorganic lithium salt having a phosphorus atom is more preferable because it makes it easier to release free fluorine atoms. A typical fluorine-containing inorganic lithium salt is LiPF6, which dissolves and releases the PF6 anion. When a fluorine-containing inorganic lithium salt containing boron atoms is used as the fluorine-containing inorganic lithium salt, it is preferable because it makes it easier to capture excess free acid components that may lead to battery degradation, and from this viewpoint, LiBF4 is particularly preferred.

[0046] In this embodiment, there are no particular restrictions on the content of fluorine-containing inorganic lithium salt in the non-aqueous electrolyte, but it is preferably 0.01 mol or more, more preferably 0.02 mol or more, and even more preferably 0.03 mol or more per liter of non-aqueous solvent. When the content of fluorine-containing inorganic lithium salt is within the above range of 0.01 mol or more, the ionic conductivity tends to increase, and high power characteristics can be exhibited. Furthermore, the content of fluorine-containing inorganic lithium salt is preferably less than 1.5 mol, more preferably less than 0.5 mol, and even more preferably less than 0.1 mol per liter of non-aqueous solvent. When the content of fluorine-containing inorganic lithium salt is within the above range of less than 1.5 mol, the ionic conductivity increases, high power characteristics can be exhibited, and the decrease in ionic conductivity due to viscosity increase at low temperatures tends to be suppressed. This tends to improve the high-temperature cycle characteristics and other battery characteristics of the non-aqueous secondary battery while maintaining the excellent performance of the non-aqueous electrolyte.

[0047] The non-aqueous electrolyte of this embodiment may further contain an organolithium salt. An "organolithium salt" refers to a lithium salt that contains a carbon atom as an anion and is soluble in acetonitrile.

[0048] Examples of organolithium salts include organolithium salts having an oxalic acid group. Specific examples of organolithium salts having an oxalic acid group include, for example, organolithium salts represented as LiB(C2O4)2, LiBF2(C2O4), LiPF4(C2O4), and LiPF2(C2O4)2, respectively. Among these, at least one lithium salt selected from the lithium salts represented as LiB(C2O4)2 and LiBF2(C2O4) is preferred. Furthermore, it is more preferable to use one or more of these together with a fluorine-containing inorganic lithium salt. These organolithium salts having an oxalic acid group may be added to a non-aqueous electrolyte or incorporated into the negative electrode (negative electrode active material layer).

[0049] From the viewpoint of ensuring better effects from its use, the amount of organolithium salt having an oxalic acid group added to a non-aqueous electrolyte is preferably 0.005 moles or more, more preferably 0.02 moles or more, and even more preferably 0.05 moles or more, per liter of non-aqueous solvent in the non-aqueous electrolyte. However, if the amount of organolithium salt having an oxalic acid group in the non-aqueous electrolyte is too large, precipitation may occur. Therefore, the amount of organolithium salt having an oxalic acid group added to a non-aqueous electrolyte is preferably less than 1.0 mole, more preferably less than 0.5 moles, and even more preferably less than 0.2 moles, per liter of non-aqueous solvent in the non-aqueous electrolyte.

[0050] Organolithium salts containing oxalic acid groups are known to be poorly soluble in low-polarity organic solvents, particularly in linear carbonates. Organolithium salts containing oxalic acid groups may contain trace amounts of lithium oxalate, and furthermore, when mixed as a non-aqueous electrolyte, they may react with trace amounts of water contained in other raw materials, generating a new white precipitate of lithium oxalate. Therefore, while the lithium oxalate content in the non-aqueous electrolyte of this embodiment is not particularly limited, it is preferably 0 to 500 ppm.

[0051] In this embodiment, in addition to the lithium salts listed above, lithium salts commonly used for non-aqueous secondary batteries may be added as auxiliary salts. Specific examples of other lithium salts include, for example, LiClO4, LiAlO4, LiAlCl4, and LiB 10 Cl 10 Inorganic lithium salts that do not contain a fluorine atom as an anion, such as chloroborane Li; LiCF3SO3, LiCF3CO2, Li2C2F4(SO3)2, LiC(CF3SO2)3, LiC n F (2n+1) SO3 {wherein n≧2}, organolithium salts such as lower aliphatic carboxylic acid Li, tetraphenylborate Li, LiB(C3O4H2)2; LiPF5(CF3), etc. n (C p F 2p+1 ) 6-n Organolithium salts represented by the formula [wherein n is an integer from 1 to 5 and p is an integer from 1 to 8]; LiBF such as LiBF3(CF3) q (C s F 2s+1 ) 4-q Organolithium salts represented by the formula [wherein q is an integer between 1 and 3, and s is an integer between 1 and 8]; lithium salts bonded to polyvalent anions; The following formula (a): LiC(SO2R A )(SO2R B )(SO2R C ) (a) {where, R A , R B , and R CThese may be identical or different from each other, and represent a perfluoroalkyl group having 1 to 8 carbon atoms. The following formula (b): LiN(SO2OR D )(SO2OR E (b) {where, R D , and R E These may be identical or different from each other, and represent a perfluoroalkyl group having 1 to 8 carbon atoms. The following formula (c) LiN(SO2R F )(SO2OR G ) (c) {where, R F , and R G These may be identical or different from each other, and represent a perfluoroalkyl group having 1 to 8 carbon atoms. Examples include organolithium salts represented by each of the above, and one or more of these can be used together with a fluorine-containing inorganic lithium salt.

[0052] <1-3. Sulfonates> The non-aqueous electrolyte according to this embodiment includes, in addition to the non-aqueous solvent and lithium salt described above, The following general formula (1): [ka] {where, R 1 and R 2 Each of these independently represents a halogen group or an alkyl group which may be substituted with a halogen atom. The compound includes a sulfone compound represented by ( ).

[0053] The sulfone compound represented by formula (1) forms a protective film on the negative electrode surface by forming a polymer through a radical polymerization reaction at the phenyl group. Substitution of a functional group with a phenyl group alters the reactivity of the sulfone. Examples of such compounds include diphenyl sulfone, dichlorodiphenyl sulfone, difluorodiphenyl sulfone, ditolyl sulfone, diethyldiphenyl sulfone, di-n-butyl sulfone, and di-iso-butyl sulfone. Among these, diphenyl sulfone is preferred from the viewpoint of having low steric hindrance and not interfering with SEI construction.

[0054] In this embodiment, the content of the sulfone compound represented by formula (1) is within the range of 0.1% by mass or more and 3% by mass or less relative to the total amount of the non-aqueous electrolyte. The lower limit of the content of the sulfone compound represented by formula (1) is preferably 0.3% by mass, and more preferably 0.5% by mass or more, relative to the total amount of the non-aqueous electrolyte. Furthermore, the upper limit of the content of the sulfone compound is more preferably 2% by mass or less, relative to the total amount of the non-aqueous electrolyte, from the viewpoint of suppressing internal resistance. By adjusting the content of the sulfone compound represented by formula (1) within the above range, it is possible to add even better battery characteristics without impairing the basic functions of the non-aqueous secondary battery, and the effects of the present invention are more easily achieved.

[0055] <Ionic conductivity> The non-aqueous electrolyte of this embodiment has an ionic conductivity of 12 mS / cm or higher at 25°C. An ionic conductivity of 12 mS / cm or higher allows for the full expression of high-power characteristics. The ionic conductivity can be controlled by adjusting the various raw materials and their contents as described in the Examples Table, and its upper limit may be, for example, 30 mS / cm. The ionic conductivity can be controlled, for example, by the following method: The conductivity can be measured by connecting a TOADKK Corporation platinum conductivity cell CT-58101B (product name) to a TOADKK Corporation CM-41M (product name) conductivity meter, immersing the conductivity cell in 5 mL of electrolyte under 25°C conditions, and checking the conductivity at that time.

[0056] <10-second discharge DCIR and 10-second discharge DCIR change rate> The non-aqueous electrolyte of this embodiment is given by the following formula (1-1): 10-second discharge DCIR = (voltage change during the first 10 seconds after discharge) / (discharge current value during the first 10 seconds after discharge) ... Equation (1-1) For the 10-second discharge DCIR represented by the following formula (1-2), the following equations apply before and after storage at 85°C for 12 hours: 10-second discharge DCIR change rate = (10-second discharge DCIR after 85°C storage) / (10-second discharge DCIR before 85°C storage) ... Equation (1-2) The 10-second discharge DCIR change rate, represented by [formula], is greater than 0 and less than or equal to 1.3.

[0057] Here, a 10-second discharge DCIR change rate greater than 0 and less than or equal to 1.3 means that degradation of the negative electrode can be suppressed and side reactions can be suppressed even with a thermal history of 85°C and 12 hours. The specific measurement methods for the 10-second discharge DCIR and the 10-second discharge DCIR change rate are as described in the examples.

[0058] <Other electrode protection additives> Other electrode protection additives are not particularly limited as long as they do not hinder the resolution of the problem according to the present invention, and may substantially overlap with substances that play a role as a solvent for dissolving lithium salts (i.e., the non-aqueous solvents mentioned above) (except for acetonitrile and sulfone compounds). Electrode protection additives are preferably substances that contribute to improving the performance of the non-aqueous electrolyte and non-aqueous secondary battery in this embodiment, but also include substances that do not directly participate in electrochemical reactions.

[0059] Other specific examples of electrode protection additives include lactones such as γ-butyrolactone, γ-valerolactone, γ-caprolactone, δ-valerolactone, δ-caprolactone, and ε-caprolactone; cyclic ethers such as 1,4-dioxane; linear acid anhydrides such as acetic anhydride, propionic anhydride, and benzoic anhydride; cyclic acid anhydrides such as malonic acid anhydride, succinic anhydride, glutaric acid anhydride, maleic anhydride, phthalic anhydride, 1,2-cyclohexanedicarboxylic acid anhydride, 2,3-naphthalenedicarboxylic acid anhydride, or naphthalene-1,4,5,8-tetracarboxylic dianhydride; and mixed acid anhydrides with structures formed by the dehydration condensation of different types of acids, such as two different carboxylic acids. These can be used individually or in combination of two or more.

[0060] In this embodiment, there are no particular restrictions on the content of the electrode protection additive in the non-aqueous electrolyte, but it is preferably 0.1 to 30% by volume, more preferably 0.3 to 15% by volume, and even more preferably 0.5 to 4% by volume relative to the total amount of the non-aqueous solvent.

[0061] In this embodiment, the higher the content of the electrode protection additive, the more the degradation of the non-aqueous electrolyte is suppressed. However, the lower the content of the electrode protection additive, the better the high-power characteristics of the non-aqueous secondary battery in low-temperature environments. Therefore, by adjusting the content of the electrode protection additive within the above range, it is possible to maximize the excellent performance based on the high ionic conductivity of the non-aqueous electrolyte without impairing the basic functions of the non-aqueous secondary battery. By preparing a non-aqueous electrolyte with such a composition, it is possible to further improve the cycle performance, high-power performance in low-temperature environments, and other battery characteristics of the non-aqueous secondary battery.

[0062] <Other optional additives> In this embodiment, for the purpose of improving the charge-discharge cycle characteristics of the non-aqueous secondary battery, improving high-temperature storage capacity and safety (e.g., overcharge prevention), the non-aqueous electrolyte may appropriately contain optional additives selected from, for example, sulfonic acid esters, diphenyl disulfide, cyclohexylbenzene, biphenyl, fluorobenzene, tert-butylbenzene, phosphate esters [ethyl diethyl phosphonoacetate (EDPA): (C2H5O)2(P=O)-CH2(C=O)OC2H5, tris(trifluoroethyl) phosphate (TFEP): (CF3CH2O)3P=O, triphenyl phosphate (TPP): (C6H5O)3P=O: (CH2=CHCH2O)3P=O, triallyl phosphate, etc.], nitrogen-containing cyclic compounds without steric hindrance around lone pairs [pyridine, 1-methyl-1H-benzotriazole, 1-methylpyrazole, etc.], and derivatives of these compounds. Phosphate esters, in particular, are effective in suppressing side reactions during storage.

[0063] In this embodiment, the content of other optional additives is calculated as a mass percentage of the total mass of all components constituting the non-aqueous electrolyte. There are no particular restrictions on the content of other optional additives, but it is preferably in the range of 0.01% to 10% by mass, more preferably 0.02% to 5% by mass, and even more preferably 0.05% to 3% by mass, relative to the total amount of the non-aqueous electrolyte. By adjusting the content of other optional additives to the above range, it is possible to add even better battery characteristics without impairing the basic functions of the non-aqueous secondary battery.

[0064] <2. Positive electrode and positive electrode current collector> The positive electrode 150 shown in Figures 1 and 2 consists of a positive electrode active material layer made from a positive electrode mixture and a positive electrode current collector. The positive electrode 150 is not particularly limited as long as it acts as the positive electrode of a non-aqueous secondary battery, and may be a known material. The positive electrode active material in the present invention is preferably a composite oxide of lithium and a transition metal, and preferably contains nickel (Ni) in a relatively high proportion.

[0065] The positive electrode active material layer preferably contains a positive electrode active material and, if necessary, further contains a conductive assistant and a binder.

[0066] The positive electrode active material layer preferably contains, as the positive electrode active material, a material capable of occluding and releasing lithium ions. When such a material is used, it is preferable because a high voltage and a high energy density tend to be obtained.

[0067] Examples of the positive electrode active material include a positive electrode active material containing at least one transition metal element selected from the group consisting of Ni, Mn, and Co, and the following general formula (a): Li p Ni q Co r Mn s M t O u ···(a) {In the formula, M is at least one metal selected from the group consisting of aluminum (Al), tin (Sn), indium (In), iron (Fe), vanadium (V), copper (Cu), magnesium (Mg), titanium (Ti), zinc (Zn), molybdenum (Mo), zirconium (Zr), strontium (Sr), and barium (Ba), and 0 < p < 1.3, 0 < q < 1.2, 0 < r < 1.2, < 0 ≦ s < 0.5, 0 ≦ t < 0.3, 0.7 ≦ q + r + s + t ≦ 1.2, 1.8 < u < 2.2, and p is a value determined by the charge and discharge state of the battery.} At least one Li-containing metal oxide selected from lithium (Li)-containing metal oxides represented by the formula is suitable.

[0068] Specific examples of the positive electrode active material include, for example, lithium cobalt oxide represented by LiCoO2; lithium manganese oxide represented by LiMnO2, LiMn2O4, and Li2Mn2O4; lithium nickel oxide represented by LiNiO2; LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2, LiNi 0.5 Co 0.2 Mn0.3 O2, LiNi 0.8 Co 0.2 Li represented by O2 z Lithium-containing composite metal oxides represented by MO2 (where M contains at least one transition metal element selected from the group consisting of Ni, Mn, and Co, and represents two or more metal elements selected from the group consisting of Ni, Mn, Co, Al, and Mg, and z represents a number greater than 0.9 and less than 1.2) and the like can be mentioned.

[0069] In particular, when the Ni content ratio q of the Li-containing metal oxide represented by the general formula (a) is 0.5 < q < 1.2, it is preferable because both reduction of the usage amount of Co, which is a rare metal, and increase in the energy density are achieved. As such a positive electrode active material, for example, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.75 Co 0.15 Mn 0.15 O2, LiNi 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.85 Co 0.075 Mn 0.075 O2, LiNi 0.8 Co 0.15 Al 0.05 O2, LiNi 0.81 Co 0.1 Al 0.09 O2, LiNi 0.85 Co 0.1 Al 0.05 Lithium-containing composite metal oxides represented by O2 and the like can be mentioned. ​​On the other hand, the higher the Ni content in the positive electrode active material layer, the more likely degradation is to occur at low voltages. The positive electrode active material of Li-containing metal oxide represented by general formula (a) inherently contains active sites that oxidize and degrade non-aqueous electrolytes, but these active sites can unintentionally consume compounds added to protect the negative electrode on the positive electrode side. Acid anhydrides, in particular, tend to be susceptible to this effect. Especially when acetonitrile is included as the non-aqueous solvent, the effect of adding acid anhydrides is so great that the consumption of acid anhydrides on the positive electrode side is a critical problem.

[0071] Furthermore, these additive decomposition products incorporated and deposited on the positive electrode side not only increase the internal resistance of non-aqueous secondary batteries but also accelerate the degradation of lithium salts. Moreover, the protection of the negative electrode surface, which was the original purpose, becomes insufficient. In order to deactivate the active sites that essentially cause oxidative degradation of non-aqueous electrolytes, the coexistence of components that control Jahn-Teller strain or act as neutralizers is important. For this reason, it is preferable that the positive electrode active material contains at least one metal selected from the group consisting of Al, Sn, In, Fe, V, Cu, Mg, Ti, Zn, Mo, Zr, Sr, and Ba.

[0072] For similar reasons, it is preferable that the surface of the positive electrode active material is coated with a compound containing at least one metal element selected from the group consisting of Zr, Ti, Al, and Nb. It is even more preferable that the surface of the positive electrode active material is coated with an oxide containing at least one metal element selected from the group consisting of Zr, Ti, Al, and Nb. Furthermore, it is particularly preferable that the surface of the positive electrode active material is coated with at least one oxide selected from the group consisting of ZrO2, TiO2, Al2O3, NbO3, and LiNbO2, as this does not hinder the permeation of lithium ions.

[0073] The positive electrode active material may be a lithium-containing compound other than the Li-containing metal oxide represented by the formula (a), and is not particularly limited as long as it contains lithium. Examples of such lithium-containing compounds include composite oxides containing lithium and transition metal elements, metal chalcogenides having lithium, metal phosphate compounds containing lithium and transition metal elements, and metal silicate compounds containing lithium and transition metal elements. From the viewpoint of obtaining a higher voltage, as the lithium-containing compound, particularly, a metal phosphate compound containing lithium and at least one transition metal element selected from the group consisting of Co, Ni, Mn, Fe, Cu, Zn, Cr, V, and Ti is preferable. As the lithium-containing compound, more specifically, the following formula (Xa): Li v M I D2(Xa) {In the formula, D represents a chalcogen element, and M I represents one or more transition metal elements including at least one transition metal element, and the value of v is determined by the charge-discharge state of the battery and represents a number from 0.05 to 1.10.}, the following formula (Xb): Li w M II PO4(Xb) {In the formula, M II represents one or more transition metal elements including at least one transition metal element, and the value of w is determined by the charge-discharge state of the battery and represents a number from 0.05 to 1.10.}, and the following formula (Xc): Li t [[ID=зо]]M III u SiO4(Xc) {In the formula, M III represents one or more transition metal elements including at least one transition metal element, the value of t is determined by the charge-discharge state of the battery and represents a number from 0.05 to 1.10, and u represents a number from 0 to 2.} <00004л5>Compounds represented by each of them are included.

[0074] The lithium-containing compound represented by formula (Xa) above has a layered structure, and the compounds represented by formulas (Xb) and (Xc) above have an olivine structure. These lithium-containing compounds may be modified in such ways as to stabilize the structure, by substituting some of the transition metal elements with Al, Mg, or other transition metal elements, incorporating these metal elements into the grain boundaries, substituting some of the oxygen atoms with fluorine atoms, or coating at least a portion of the surface of the positive electrode active material with another positive electrode active material.

[0075] In this embodiment, the positive electrode active material may be a lithium-containing compound as described above, or it may be a lithium-containing compound in combination with other positive electrode active materials.

[0076] Other positive electrode active materials include, for example, metal oxides or metal chalcogenides having tunnel and layered structures; sulfur; conductive polymers, etc. Examples of metal oxides or metal chalcogenides having tunnel and layered structures include MnO2, FeO2, FeS2, V2O5, V6O 13 Examples of conductive polymers include oxides, sulfides, and selenides of metals other than lithium, such as TiO2, TiS2, MoS2, and NbSe2. Examples of conductive polymers include polyaniline, polythiophene, polyacetylene, and polypyrrole.

[0077] The other positive electrode active materials mentioned above can be used individually or in combination of two or more, and there are no particular restrictions. However, it is preferable that the positive electrode active material layer contains at least one transition metal element selected from Ni, Mn, and Co, in order to enable reversible and stable intercalation and release of lithium ions and to achieve a high energy density.

[0078] When a lithium-containing compound and another positive electrode active material are used in combination as the positive electrode active material, the ratio of the lithium-containing compound to the total positive electrode active material is preferably 80% by mass or more, and more preferably 85% by mass or more.

[0079] Examples of conductive additives include graphite, acetylene black, carbon black such as Ketjenblack, and carbon fibers. The content ratio of the conductive additive is preferably 10 parts by mass or less, and more preferably 1 to 5 parts by mass, per 100 parts by mass of positive electrode active material.

[0080] Examples of binders include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyacrylic acid, styrene-butadiene rubber, and fluororubber. The binder content is preferably 6 parts by mass or less, and more preferably 0.5 to 4 parts by mass, per 100 parts by mass of positive electrode active material.

[0081] The positive electrode active material layer is formed by dispersing a slurry containing a positive electrode mixture, which is obtained by mixing the positive electrode active material with a conductive additive and a binder as needed, in a solvent, onto a positive electrode current collector, drying (solvent removal), and pressing as needed. There are no particular restrictions on the solvent used, and conventionally known solvents can be used. Examples include N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, and water.

[0082] The positive electrode current collector is made of a metal foil such as aluminum foil, nickel foil, or stainless steel foil. The positive electrode current collector may have a carbon coating on its surface or may be processed into a mesh shape. The thickness of the positive electrode current collector is preferably 5 to 40 μm, more preferably 7 to 35 μm, and even more preferably 9 to 30 μm.

[0083] <3. Negative electrode and negative electrode current collector> The negative electrode 160 shown in Figures 1 and 2 consists of a negative electrode active material layer made from a negative electrode mixture and a negative electrode current collector. The negative electrode 160 can function as the negative electrode of a non-aqueous secondary battery.

[0084] The negative electrode active material layer preferably contains a negative electrode active material and, if necessary, a conductive additive and a binder.

[0085] Examples of negative electrode active materials include amorphous carbon (hard carbon), graphite (e.g., artificial graphite, natural graphite), pyrolytic carbon, coke, glassy carbon, calcined organic polymer compounds, mesocarbon microbeads, carbon fibers, activated carbon, carbon colloids, and carbon black, as well as metallic lithium, metal oxides, metal nitrides, lithium alloys, tin alloys, silicon alloys, intermetallic compounds, organic compounds, inorganic compounds, metal complexes, and organic polymer compounds. The negative electrode active material can be used alone or in combination of two or more. When the negative electrode active material is graphite, it is preferable that the positive electrode active material be a composite oxide of lithium and a transition metal, from the viewpoint of easily achieving the effects of the present invention.

[0086] From the perspective of increasing the battery voltage, lithium ions are used as the negative electrode active material in the negative electrode active material, resulting in a 0.4V vs. Li / Li + It is preferable to include a material that can absorb at a lower potential.

[0087] Examples of conductive additives include graphite, acetylene black, carbon black such as Ketjenblack, and carbon fibers. The content ratio of the conductive additive is preferably 20 parts by mass or less, and more preferably 0.1 to 10 parts by mass, per 100 parts by mass of the negative electrode active material.

[0088] Examples of binders include carboxymethylcellulose, PVDF, PTFE, polyacrylic acid, and fluororubber. Diene rubbers, such as styrene-butadiene rubber, are also acceptable. The binder content is preferably 10 parts by mass or less, and more preferably 0.5 to 6 parts by mass, per 100 parts by mass of the negative electrode active material.

[0089] The negative electrode active material layer is formed by dispersing a negative electrode mixture, which is a mixture of the negative electrode active material and, if necessary, a conductive additive and a binder, in a solvent, onto a negative electrode current collector, drying (solvent removal), and pressing as necessary. There are no particular restrictions on the solvent used, and conventionally known solvents can be used. Examples include N-methyl-2-pyrrolidone, dimethylformamide, dimethylacetamide, and water.

[0090] The negative electrode current collector is made of a metal foil such as copper foil, nickel foil, or stainless steel foil. The negative electrode current collector may also have a carbon coating on its surface or be processed into a mesh shape. The thickness of the negative electrode current collector is preferably 5 to 40 μm, more preferably 6 to 35 μm, and even more preferably 7 to 30 μm.

[0091] <4. Separator> As shown in Figure 2, in this embodiment, the non-aqueous secondary battery 100 preferably includes a separator 170 between the positive electrode 150 and the negative electrode 160 from the viewpoint of providing safety such as preventing short circuits and shutdown of the positive electrode 150 and the negative electrode 160. The separator 170 is not limited, but may be the same as that used in known non-aqueous secondary batteries, and a thin insulating film with high ion permeability and excellent mechanical strength is preferred. Examples of separators 170 include woven fabrics, nonwoven fabrics, and microporous films made of synthetic resin, and among these, microporous films made of synthetic resin are preferred.

[0092] Suitable examples of synthetic resin microporous membranes include polyolefin-based microporous membranes, such as those containing polyethylene or polypropylene as the main component, or those containing both of these polyolefins. Examples of nonwoven fabrics include heat-resistant resin porous membranes made of glass, ceramic, polyolefin, polyester, polyamide, liquid crystal polyester, aramid, etc.

[0093] The separator 170 may have a configuration in which one type of microporous membrane is laminated in a single layer or in multiple layers, or it may have two or more types of microporous membranes laminated together. The separator 170 may also have a configuration in which a mixed resin material obtained by melt-kneading two or more types of resin materials is laminated in a single layer or in multiple layers.

[0094] For the purpose of imparting functionality, inorganic particles may be present on the surface or inside the separator, and other organic layers may be further coated or laminated. Furthermore, a cross-linked structure may be included. These methods may be combined as needed to enhance the safety performance of non-aqueous secondary batteries.

[0095] By using such a separator 170, it is possible to achieve the good input / output characteristics and low self-discharge characteristics that are particularly required for lithium-ion batteries used in the high-power applications mentioned above.

[0096] While there are no particular limitations on the film thickness of the microporous membrane that can be used as a separator, it is preferably 1 μm or more from the viewpoint of film strength and preferably 500 μm or less from the viewpoint of permeability. From the viewpoint of use in high-power applications where the heat generation is relatively high and self-discharge characteristics higher than conventional are required, such as in safety tests, and from the viewpoint of windability in large battery winding machines, the film thickness of the microporous membrane is preferably 5 μm to 30 μm, and more preferably 10 μm to 25 μm. Furthermore, when prioritizing both short-circuit resistance and output performance, the film thickness of the microporous membrane is more preferably 15 μm to 25 μm, but when prioritizing both high energy density and output performance, it is more preferably 10 μm to less than 15 μm.

[0097] The porosity of a microporous membrane usable as a separator is preferably 30% to 90%, more preferably 35% to 80%, and even more preferably 40% to 70%, from the viewpoint of following the rapid movement of lithium ions at high power output. Furthermore, if the priority is on improving power output performance while ensuring safety, a porosity of 50% to 70% is particularly preferred for the microporous membrane, and if the importance is on balancing short-circuit resistance and power output performance, a porosity of 40% to less than 50% is particularly preferred.

[0098] For microporous membranes usable as separators, the air permeability should be 1 second / 100 cm, considering the balance between film thickness and porosity. 3 More than 400 seconds / 100cm 3 The following is preferable: 100 seconds / 100 cm 3 More than 350 / 100cm 3 The following is preferable. Furthermore, if prioritizing both short-circuit resistance and output performance, the air permeability of the microporous membrane should be 150 seconds / 100 cm. 3 More than 350 seconds / 100cm 3 The following is particularly preferable, and if prioritizing improved output performance while ensuring safety, 100 / 100cm 3 seconds or more 150 seconds / 100cm 3 A value less than 30 mS / cm is particularly preferred. On the other hand, when a non-aqueous electrolyte with low ionic conductivity is combined with a separator within the above range, the rate-limiting factor for lithium ion migration is the ionic conductivity of the non-aqueous electrolyte, not the structure of the separator, and the expected input / output characteristics tend not to be obtained. For this reason, the ionic conductivity of the non-aqueous electrolyte is 12 mS / cm or higher, preferably 15 mS / cm or higher, and more preferably 20 mS / cm or higher. The ionic conductivity of the non-aqueous electrolyte may be 30 mS / cm or lower. However, the preferred values ​​for the film thickness, air permeability, and porosity of the separator, as well as the ionic conductivity of the non-aqueous electrolyte, are not limited to the above examples.

[0099] <5. Battery casing> The configuration of the battery casing 110 of the non-aqueous secondary battery 100 shown in Figures 1 and 2 is not particularly limited, but for example, either a battery can or a laminate film casing can be used. As the battery can, for example, a metal can made of steel, stainless steel, aluminum, or clad material, such as a rectangular, rectangular tube, cylindrical, elliptical, flat, coin-shaped, or button-shaped can be used. As the laminate film casing, for example, a laminate film consisting of a three-layer structure of heat-melt resin / metal film / resin can be used.

[0100] The laminate film casing can be used by stacking two sheets with the heat-melt resin side facing inward, or by folding the film so that the heat-melt resin side faces inward, and sealing the ends with heat seal. When using the laminate film casing, the positive electrode lead body 130 (or positive electrode terminal and lead tab connected to the positive electrode terminal) may be connected to the positive electrode current collector, and the negative electrode lead body 140 (or negative electrode terminal and lead tab connected to the negative electrode terminal) may be connected to the negative electrode current collector. In this case, the laminate film casing may be sealed with the ends of the positive electrode lead body 130 and the negative electrode lead body 140 (or lead tabs connected to the positive electrode terminal and the negative electrode terminal, respectively) extended to the outside of the casing.

[0101] <6. How to make a battery> The non-aqueous secondary battery 100 in this embodiment is manufactured by a known method using the above-mentioned non-aqueous electrolyte, a positive electrode 150 having a positive electrode active material layer on one or both sides of the current collector, a negative electrode 160 having a negative electrode active material layer on one or both sides of the current collector, a battery casing 110, and a separator 170 if necessary.

[0102] First, a laminate is formed consisting of a positive electrode 150, a negative electrode 160, and, if necessary, a separator 170. For example: An embodiment in which a wound laminate is formed by winding a long positive electrode 150 and a negative electrode 160 in a laminated state with the long separator interposed between the positive electrode 150 and the negative electrode 160; An embodiment in which a laminated structure is formed by alternately stacking positive electrode sheets and negative electrode sheets, obtained by cutting a positive electrode 150 and a negative electrode 160 into multiple sheets having a certain area and shape, with a separator sheet in between; An embodiment in which a long separator is folded in a zigzag pattern, and a laminated structure is formed by alternately inserting positive electrode sheets and negative electrode sheets between the zigzag-folded separators; These are possible.

[0103] Next, the laminate described above is housed in the battery casing 110 (battery case), the non-aqueous electrolyte according to this embodiment is poured into the battery case, and the laminate is immersed in the non-aqueous electrolyte and sealed to produce the non-aqueous secondary battery according to this embodiment.

[0104] Alternatively, a non-aqueous secondary battery 100 can be manufactured by first creating a gel-like electrolyte membrane by impregnating a substrate made of polymer material with a non-aqueous electrolyte, forming a laminated structure using a sheet-like positive electrode 150, a negative electrode 160, and the electrolyte membrane, and optionally a separator 170, and then housing it in a battery casing 110.

[0105] Furthermore, if the electrode arrangement is designed such that there is an overlap between the outer edge of the negative electrode active material layer and the outer edge of the positive electrode active material layer, or if there is a section of the non-opposing part of the negative electrode active material layer that is too narrow, then misalignment of the electrodes may occur during battery assembly, potentially degrading the charge-discharge cycle characteristics of the non-aqueous secondary battery. Therefore, it is preferable to fix the position of the electrodes in the electrode body used in the non-aqueous secondary battery in advance using tapes such as polyimide tape, polyphenylene sulfide tape, or polypropylene (PP) tape, or adhesives.

[0106] In a non-aqueous electrolyte using acetonitrile, as in this embodiment, due to its high ionic conductivity, lithium ions released from the positive electrode during the initial charge of a non-aqueous secondary battery may diffuse throughout the negative electrode. In non-aqueous secondary batteries, it is common to have a larger negative electrode active material layer than the positive electrode active material layer. However, if lithium ions diffuse and are intercalated in areas of the negative electrode active material layer that do not face the positive electrode active material layer, these lithium ions will remain in the negative electrode without being released during the initial discharge. As a result, the contribution of these unreleased lithium ions becomes irreversible capacity. For these reasons, non-aqueous secondary batteries using a non-aqueous electrolyte containing acetonitrile may have low initial charge-discharge efficiency.

[0107] On the other hand, if the area of ​​the positive electrode active material layer is larger than that of the negative electrode active material layer, or if the areas are the same, current concentration is more likely to occur at the edges of the negative electrode active material layer during charging, making it easier for lithium dendrites to form.

[0108] For the reasons stated above, there are no particular restrictions on the ratio of the total area of ​​the negative electrode active material layer to the area of ​​the portion where the positive electrode active material layer and the negative electrode active material layer face each other, but it is preferably greater than 1.0 and less than 1.1, more preferably greater than 1.002 and less than 1.09, even more preferably greater than 1.005 and less than 1.08, and particularly preferably greater than 1.01 and less than 1.08. In a non-aqueous secondary battery using a non-aqueous electrolyte containing acetonitrile, the initial charge-discharge efficiency can be improved by reducing the ratio of the total area of ​​the negative electrode active material layer to the area of ​​the portion where the positive electrode active material layer and the negative electrode active material layer face each other.

[0109] Reducing the ratio of the total area of ​​the negative electrode active material layer to the area of ​​the portion where the positive electrode active material layer and the negative electrode active material layer face each other means limiting the proportion of the negative electrode active material layer that does not face the positive electrode active material layer. This makes it possible to minimize the amount of lithium ions absorbed by the portion of the negative electrode active material layer that does not face the positive electrode active material layer (i.e., the amount of lithium ions that are not released from the negative electrode during the first discharge and become irreversible capacity) from the lithium ions released from the positive electrode during the first charge. Therefore, by designing the ratio of the total area of ​​the negative electrode active material layer to the area of ​​the portion where the positive electrode active material layer and the negative electrode active material layer face each other within the above range, it is possible to improve the load characteristics of the battery by using acetonitrile, increase the initial charge-discharge efficiency of the battery, and further suppress the formation of lithium dendrites.

[0110] In this embodiment, the manufacturing method (method for manufacturing a non-aqueous secondary battery) preferably includes a step of performing the initial charge at a charging speed of 0.1C or higher, where 1C is defined as the current that can discharge the set capacity in one hour. The non-aqueous secondary battery 100 in this embodiment can function as a battery after the initial charge, but it is stabilized by the decomposition of a portion of the non-aqueous electrolyte during the initial charge. There are no particular restrictions on the method of the initial charge, but it is preferably performed at 0.1 to 0.3C. It is also preferable that the initial charge is performed via constant voltage charging in between. 1C is the constant current that discharges the design capacity in one hour. By setting a long voltage range in which the lithium salt is involved in the electrochemical reaction, a stable and robust SEI is formed on the electrode (negative electrode 160) surface, which has the effect of suppressing the increase in internal resistance. In addition, the reaction products are not firmly fixed only on the negative electrode 160, but also have a good effect on other components such as the positive electrode 150 and separator 170 in some way. Therefore, considering the electrochemical reaction of lithium salts dissolved in a non-aqueous electrolyte during the initial charging process is highly effective.

[0111] In this embodiment, the non-aqueous secondary battery 100 can also be used as a battery pack in which multiple non-aqueous secondary batteries 100 are connected in series or in parallel. From the viewpoint of managing the charge and discharge state of the battery pack, the operating voltage range per battery is preferably 2 to 5V, more preferably 2.5 to 5V, and particularly preferably 2.75V to 5V.

[0112] Although embodiments for carrying out the present invention have been described above, the present invention is not limited to the above embodiments. The present invention can be modified in various ways without departing from its essence. [Examples]

[0113] The present invention will be described in more detail below with reference to examples. The present invention is not limited to these examples. Unless otherwise specified, the examples were carried out at room temperature.

[0114] (1) Preparation of non-aqueous electrolyte Under an inert atmosphere, acetonitrile (AcN), ethyl methyl carbonate (EMC), ethylene carbonate (EC), vinylene carbonate (VC), and ethylene sulfite (ES) were added in the volumetric amounts shown in Table 1, and the non-aqueous solvent was mixed so that each compound reached the predetermined concentration. Furthermore, non-aqueous electrolytes (S01~S09) were prepared by mixing 0.3 mol of lithium hexafluorophosphate (LiPF6) and 1 mol of lithium bis(fluorosulfonyl)imide per 1 L of the non-aqueous solvent. Further, sulfone compounds were added to the predetermined concentrations shown in Table 1 to prepare electrolytes (S01)~(S09). The abbreviations for the additives in Table 1 have the following meanings. In addition, the mass % of the sulfone compounds in Table 1 indicates the proportion to the total volume of the non-aqueous electrolyte. (Sulfone compounds) Diphenylsulfone: DPS Phenylenyl sulfone: PVS

[0115] [Table 1]

[0116] (2) Fabrication of non-aqueous secondary batteries (2-1) Preparation of the positive electrode (A) A composite oxide of lithium, nickel, manganese, and cobalt as the positive electrode active material (LiNi 0.8 Mn 0.1 Co 0.1 A positive electrode mixture was obtained by mixing (O2), (B) acetylene black powder as a conductive additive, and (C) polyvinylidene fluoride (PVDF) as a binder in a mass ratio of 94:3:3.

[0117] N-methyl-2-pyrrolidone was added as a solvent to the obtained positive electrode mixture to a solid content of 68% by mass, and the mixture was further mixed to prepare a positive electrode mixture-containing slurry. The slurry was applied to one side of a 15 μm thick, 280 mm wide aluminum foil, which would serve as the positive electrode current collector, using a three-roll transfer coater to create a coating pattern with a coating width of 240-250 mm, a coated length of 125 mm, and an uncoated length of 20 mm, while adjusting the basis weight of the slurry. The solvent was then dried and removed in a hot air drying oven. The resulting electrode rolls were trimmed on both sides and subjected to reduced-pressure drying at 130°C for 8 hours. After that, the density of the positive electrode active material layer was reduced to 2.7 g / cm³ using a roll press. 3 By rolling the material in this manner, a positive electrode (P2) consisting of a positive electrode active material layer and a positive electrode current collector was obtained. The basis weight excluding the positive electrode current collector was 8.4 mg / cm³. 2 That was the case.

[0118] (2-2) Fabrication of the negative electrode (a) Graphite powder as the negative electrode active material, (b) carbon black powder (Super-P) as a conductive additive, and (c) polyvinylidene fluoride (PVDF) as a binder were mixed in a solid content mass ratio of 90:3:7 to obtain a negative electrode mixture.

[0119] Water was added as a solvent to the obtained negative electrode mixture to a solid content of 45% by mass, and the mixture was further mixed to prepare a negative electrode mixture-containing slurry. The slurry was applied to one side of a copper foil 8 μm thick and 280 mm wide, which would serve as the negative electrode current collector, using a three-roll transfer coater, adjusting the basis weight of the slurry to create a coating pattern with a coating width of 240-250 mm, a coated length of 125 mm, and an uncoated length of 20 mm. The solvent was then dried and removed in a hot air drying oven. The resulting electrode rolls were trimmed on both sides and subjected to reduced-pressure drying at 80°C for 12 hours. After that, the density of the negative electrode active material layer was reduced to 1.3 g / cm³ using a roll press. 3 The material was rolled to obtain a negative electrode (N1) consisting of a negative electrode active material layer and a negative electrode current collector. The basis weight excluding the negative electrode current collector was 5.4 mg / cm³. 2 That was the case.

[0120] (2-3) Assembly of non-aqueous secondary batteries A polypropylene gasket was set in a CR2032 type battery case (SUS304 / Al clad), and the positive electrode obtained as described above, punched out in the shape of a 15.958 mm diameter disc, was set in the center with the positive electrode active material layer facing upwards. A glass fiber filter paper (Advantec, GA-100) punched out in the shape of a 16.156 mm diameter disc was set on top of that, and 150 μL of non-aqueous electrolyte was injected. Then, the negative electrode obtained as described above, punched out in the shape of a 16.156 mm diameter disc, was set with the negative electrode active material layer facing downwards. After setting the spacer and spring, the battery cap was fitted and crimped with a crimping machine. The overflowed electrolyte was wiped clean with a cloth. It was held at 25°C for 12 hours to allow the non-aqueous electrolyte to sufficiently permeate the laminate, thus obtaining a coin-type non-aqueous secondary battery.

[0121] (3) Evaluation of non-aqueous secondary batteries The coin-type non-aqueous secondary batteries obtained as described above were first subjected to initial charge-discharge treatment according to the procedure in (3-1) below. Next, each coin-type non-aqueous secondary battery was evaluated according to the procedure in (3-2). Charge and discharge were performed using the ACD-M01A charge-discharge device (product name) manufactured by Asuka Electronics Co., Ltd. and the IN804 programmable constant temperature bath (product name) manufactured by Yamato Scientific Co., Ltd. Here, 1C refers to the current value at which a fully charged battery is expected to complete discharge in one hour when discharged at a constant current.

[0122] (3-1) Charging and discharging of non-aqueous secondary batteries The ambient temperature of the non-aqueous secondary battery was set to 25°C. Initial charging was performed with a constant current of 0.3mA, equivalent to 0.1C, until the voltage reached 4.2V. After that, it was discharged to 3.0V with a constant current of 0.09mA, equivalent to 0.03C. Subsequently, charging was performed with a constant current equivalent to 0.1C, and charging was continued at a constant voltage of 4.2V until the current decreased to 0.025C.

[0123] (3-2) Store at 85°C for 12 hours. Next, the non-aqueous secondary battery was removed from the charge / discharge device and placed in a constant temperature bath set to 85°C for 12 hours.

[0124] (3-3) Measurement of the 10-second DCIR change rate before and after storage at 85°C For small non-aqueous secondary batteries that underwent the initial charge-discharge treatment using the method described in (3-1) above, they were charged to 4.2V with a constant current of 0.3mA, equivalent to 0.1C, under 25°C conditions, and the 10-second discharge DCIR at 0.3C discharge was measured under 25°C conditions. After storage using the method described in (3-2), the 10-second discharge DCIR at 0.3C discharge was measured under 50°C conditions. The rate of change before and after storage was investigated using the following formula (1-2). The voltage change during the first 10 seconds after the start of discharge was determined from the charge-discharge voltage values ​​obtained using the ACD-M01A charge-discharge device manufactured by Asuka Electronics Co., Ltd. Equation (1-1): 10-second discharge DCIR = (voltage change during the first 10 seconds after discharge) / (discharge current value during the first 10 seconds after discharge) Equation (1-2): 10-second discharge DCIR change rate = (10-second discharge DCIR after storage at 85°C) / (10-second discharge DCIR before storage at 85°C)

[0125] (3-4) Non-aqueous secondary battery [Examples 1-2 and Comparative Examples 1-5] Using the electrolytes shown in Table 1, ionic conductivity and the initial charge-discharge process and 10-second DCIR change rate were measured for non-aqueous secondary batteries assembled as described above. The interpretation of each test result is discussed below.

[0126] The resistance of the negative electrode after thermal treatment increases due to the decomposition of the SEI (seal protective film) and the resulting degradation of the electrode. It is preferable that the 10-second DCIR value after thermal treatment be less than 23Ω, and more preferably less than 21Ω. The rate of change of the 10-second DCIR is preferably 1.3 or less (e.g., 1.30 or less) and 1.2 or less (e.g., 1.20 or less). Here, the resistance of batteries using electrolytes S01, S03, S04, S06, S07, and S08 is compared to electrolyte S05, which does not contain sulfone compounds, to investigate the effects of side reactions. The measurement results are shown in Table 2.

[0127] [Table 2]

[0128] As shown in Table 2, in Examples 1-2 and Comparative Examples 1-5, the acetonitrile-containing electrolyte showed high ionic conductivity of 14.0 mS / cm or higher. In the example where DPS was added up to 2% by mass, the 10-second DCIR change rate was 1.15, and it was found that the change rate increased to 1.67 when the amount added was increased to 4% by mass. In Comparative Example 2, the 10-second DCIR change rate of the electrolyte without additives was 2.52, which confirmed that the addition of DPS up to 2% by mass suppressed the deterioration of the negative electrode without showing the effects of side reactions. In Comparative Examples 3 and 5, it was confirmed that the 10-second DCIR change rate increased when vinylene carbonate was added. Furthermore, it was confirmed from Comparative Example 4 that the combination with diphenyl sulfone had superior thermal durability compared to the combination of vinylene carbonate and ethylene sulfite.

[0129] Based on the above, it is considered that, in the examples, the addition of an appropriate amount of sulfone compound suppresses the increase in negative electrode resistance due to thermal history, and the battery operates stably.

[0130] (3-5) 50°C Cycle Test For non-aqueous secondary batteries that underwent the initial charge-discharge treatment using the method described in (3-1) above, the ambient temperature was set to 50°C, and the battery was charged to 4.2V with a constant current of 6mA (equivalent to 2C). Then, it was charged at a constant voltage of 4.2V until the current decreased to 0.025C, and then discharged once to 3V with a current of 0.9mA (equivalent to 0.3C). Subsequently, the same charging procedure as above was performed, and the battery was discharged to 3V with a current of 6mA (equivalent to 2C) for 100 cycles of the charge-discharge test.

[0131] The discharge capacity of each cycle in the cycle test was calculated as the capacity retention rate, with the discharge capacity of the first cycle in the cycle test set to 100%.

[0132] (3-6) Non-aqueous secondary battery [Examples 3-5 and Comparative Examples 6-11] Using the electrolytes shown in Table 1, non-aqueous secondary batteries were assembled as described above, and initial charge-discharge treatments and cycle tests were performed. The interpretation of the test results is described below.

[0133] The capacity retention rate is an index that shows the ratio of the discharge capacity of each cycle to the discharge capacity of the first cycle. The above cycle test involves repeated charging and discharging at a higher current density compared to general cycle tests, and the higher the value, the less capacity degradation occurs when repeated charging and discharging is used. Furthermore, if the capacity retention rate increases during the cycle, it suggests that the condition of the electrode surface is not stable, which is undesirable. A capacity retention rate of 85% or higher (e.g., 85.0% or higher) is preferable, 86% or higher (e.g., 86.0% or higher) is more preferable, and 87% or higher (e.g., 87.0% or higher) is even more preferable.

[0134] [Table 3]

[0135] In Examples 3-5, it was confirmed that adding 0.5-2.0% by mass of DPS resulted in a capacity retention rate exceeding 87.0% at 100 cycles. On the other hand, in Comparative Example 6, it was confirmed that the capacity retention rate decreased when the amount of DPS added was 4% by mass. In Comparative Example 7, it was confirmed that the addition of DPS improved cycle performance. In Comparative Example 8, an increase in the capacity retention rate was observed at 10 cycles, indicating instability. This is because SEI decomposed due to high-temperature storage, and then power was consumed for SEI reformation in cycles 1-9. From this, it was confirmed that the addition of DPS improved thermal resistance. In Comparative Example 9, it was confirmed that the thermal stability was superior to the composition deemed preferable in Patent Document 3. In Comparative Example 10, similar to Comparative Example 8, the capacity retention rate exceeded 100% at 10 cycles, confirming instability in the initial cycles. In Comparative Example 11, in the phenylvinyl sulfone-added electrolyte, decomposition of the electrolyte occurred during the first charge, making charging and discharging impossible, and it became clear that diphenyl sulfone-substituted compounds are effective for the formation of thermally stable SEI. This is presumably due to the relatively stable anionic radical of the diphenylsulfone-substituted compound.

[0136] From the results described above, it was confirmed that by adding a sulfone compound having a specific structure, such as DPS, to a non-aqueous solvent, it is possible to provide a non-aqueous secondary battery that is thermally stable and has excellent cycle performance.

[0137] (3-7) Low-rate initial charge / discharge For coin-type non-aqueous batteries containing electrolytes S1 to S3, the initial charging rate was investigated at a lower rate than in (3-1) (Comparative Examples 12 to 14). The ambient temperature of the non-aqueous secondary battery was set to 25°C, and the initial charge was performed with a constant current of 0.075mA, corresponding to 0.025C, until it reached 4.2V. After that, it was discharged with a constant current of 0.09mA, corresponding to 0.03C, until it reached 3.0V. Then, it was charged with a constant current of 0.1C until it reached a constant voltage of 4.2V and the current decayed to 0.025C. Subsequently, high-temperature storage and cycle tests were performed using the methods described in (3-2) and (3-4), and the capacity retention rate of each was evaluated.

[0138] [Table 4]

[0139] While Examples 3-5 showed a high capacity retention rate of over 87.0% at 100 cycles, Comparative Examples 12-14, which underwent initial charging at 0.025C, were found to have a capacity retention rate of 50.0% or less at 100 cycles, regardless of the diphenylsulfone concentration. Furthermore, Comparative Examples 12-14 showed a decrease in capacity retention even in the initial stage at 10 cycles, suggesting that a dense SEI (System Integrity) was not established during the initial charge-discharge process. This is thought to be because all the diphenylsulfone was consumed during the initial low-rate charging at 0.1C or less, and a defect in the SEI occurred due to the expansion of the active material during the subsequent charge-discharge process.

[0140] Based on the above, it is considered that in the examples, the addition of an appropriate amount of diphenylsulfone and appropriate initial charging suppressed the increase in negative electrode resistance due to thermal storage, and the battery operated stably. [Industrial applicability]

[0141] The non-aqueous secondary battery of the present invention is expected to be used not only as a battery for automobiles such as hybrid vehicles, plug-in hybrid vehicles, and electric vehicles, but also as a battery for industrial use such as power tools, drones, and electric motorcycles, and even as a residential energy storage system. [Explanation of symbols]

[0142] 100 Nonaqueous secondary battery 110 Battery casing 120 Battery enclosure space 130 Positive electrode lead body 140 Negative electrode lead body 150 positive electrode 160 negative electrode 170 Separator

Claims

1. A non-aqueous secondary battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, The aforementioned non-aqueous electrolyte comprises a non-aqueous solvent containing acetonitrile, a lithium salt, The following general formula (1): 【Chemistry 1】 {In the formula, R １ and R ２ Each independently represents a hydrogen atom, a halogen group, or an alkyl group which may be substituted with a halogen atom. ) comprises a sulfone compound represented by , The content of the sulfone compound is 0.5% by mass or more and 2% by mass or less relative to the total amount of the non-aqueous electrolyte. The ionic conductivity of the non-aqueous electrolyte at 25°C is 12 mS / cm or more and 30 mS / cm or less. The following formula (1-1): DCIR for 10-second discharge = (voltage change during the first 10 seconds after discharge) / (discharge current value during the first 10 seconds after discharge) ... Equation (1-1) For the 10-second discharge DCIR represented by the following formula (1-2), the following results are obtained before and after storage at 85°C for 12 hours: Change rate of DCIR after 10 seconds of discharge = (DCIR after 10 seconds of discharge after storage at 85°C) / (DCIR after 10 seconds of discharge before storage at 85°C) ... Equation (1-2) The 10-second discharge DCIR change rate, as represented by [formula], is greater than 0 and less than or equal to 1.

3. Non-aqueous secondary battery.

2. The non-aqueous secondary battery according to claim 1, wherein the amount of vinylene carbonate is less than 2% by volume relative to the total amount of the non-aqueous solvent.

3. The non-aqueous secondary battery according to claim 1 or 2, wherein the acetonitrile content in the non-aqueous electrolyte is 10 to 60% by volume relative to the total amount of the non-aqueous solvent.

4. The lithium salt is a lithium-containing imide salt and lithium hexafluoride phosphate (LiPF) ６ A non-aqueous secondary battery according to any one of claims 1 to 3, wherein at least one is selected from the group consisting of ).

5. A non-aqueous secondary battery according to any one of claims 1 to 4, comprising diphenylsulfone as the sulfone compound represented by the general formula (1).

6. The non-aqueous secondary battery according to any one of claims 1 to 5, wherein the positive electrode contains one or more materials selected from the group consisting of materials capable of intercalating and releasing lithium ions as a positive electrode active material, and the negative electrode contains one or more materials selected from the group consisting of a material capable of intercalating and releasing lithium ions and metallic lithium as a negative electrode active material.

7. The non-aqueous secondary battery according to claim 6, wherein the positive electrode active material is a composite oxide of lithium and a transition metal, and the negative electrode active material is graphite.

8. A method for manufacturing a non-aqueous secondary battery according to any one of claims 1 to 7, A method for manufacturing a non-aqueous secondary battery, comprising a step of performing the initial charge at a charging speed of 0.1C or higher, where 1C is defined as the current that can discharge the set capacity in one hour.

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