Lithium ion secondary battery and method for improving lithium ion secondary battery

Abstract

This lithium ion secondary battery includes: a positive electrode having a positive electrode mixture layer and a positive electrode current collector; a negative electrode having a negative electrode mixture layer and a negative electrode current collector; and a nonaqueous electrolyte. The positive electrode mixture layer contains a positive electrode active material represented by Li1 + xMn1 - y - zFeyAzPO4 ... (1). The nonaqueous electrolyte contains: an electrolyte expressed by LiN(X1SO2)(X2SO2) ... (2); a nonaqueous solvent; and at least one kind of amidosulfuric acid-based compound selected from the group consisting of amidosulfuric acid, a salt of amidosulfuric acid, an amidosulfuric acid derivative represented by R1R2NSO2(OM) ... (3), and taurine.

Description

Lithium-ion secondary battery and method for improving lithium-ion secondary battery

[0001] This disclosure relates to lithium-ion secondary batteries and methods for improving lithium-ion secondary batteries.

[0002] Various studies have been conducted to improve the performance of lithium-ion secondary batteries. Recently, lithium-ion secondary batteries equipped with a positive electrode containing manganese iron lithium phosphate as the positive electrode active material have been proposed (for example, Patent Document 1). While such lithium-ion secondary batteries are expected to have high safety and cycle life, it is known that they have the problem of reduced battery performance due to metal leaching from the positive electrode into the non-aqueous electrolyte.

[0003] Special table 2024-515150 publication

[0004] Patent Document 1 states that by using a non-aqueous electrolyte containing a sulfonylimide compound such as lithium bis(fluorosulfonyl)imide, the elution of metals (Mn and Fe) from the positive electrode is suppressed, improving high-temperature cycling and high-temperature storage performance. However, there is room for improvement in this suppression effect of the non-aqueous electrolyte.

[0005] This disclosure has been made in view of the above, and its purpose is to suppress the leaching of metals (Mn and Fe) from the positive electrode during high-temperature cycling in a lithium-ion secondary battery having a positive electrode containing manganese iron lithium phosphate, thereby improving battery performance.

[0006] In other words, this disclosure provides the following lithium-ion secondary battery [1]: [1] A lithium-ion secondary battery comprising: a positive electrode having a positive electrode mixture layer and a positive electrode current collector; a negative electrode having a negative electrode mixture layer and a negative electrode current collector; and a non-aqueous electrolyte, wherein the positive electrode mixture layer is based on the following formula (1): Li １＋ｘ Mn １－ｙ－ｚ Fe ｙ A ｚ PO ４... (1) [In formula (1), -0.1 < x < 0.1, 0 < y < 1.0, 0 ≤ z < 0.1, 0 < 1 - y - z, and A is at least one atom selected from the group consisting of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Ni, Co, Ga, Sn, Sb, Nb, and Ge.] including a positive electrode active material represented by, ... The non-aqueous electrolyte is, ... the following formula (2): LiN(X １ SO ２ )(X ２ SO ２ )... (2) [In formula (2), X １ and X ２ are the same or different and represent a fluorine atom, an alkyl group having 1 to 6 carbon atoms, or a fluoroalkyl group having 1 to 6 carbon atoms.] an electrolyte represented by, ... a non-aqueous solvent, ... amidosulfuric acid, a salt of amidosulfuric acid, the following formula (3): R １ R ２ NSO ２ (OM)... (3) [In formula (3), R １ and R ２ are the same or different and represent a hydrogen atom, a hydroxyl group, an alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, an aryl group having 6 to 16 carbon atoms, an aralkyl group having 7 to 16 carbon atoms, or an alkanoyl group having 2 to 16 carbon atoms. R １ and R ２ may be bonded to each other to form a ring structure. However, when R １ is a hydrogen atom, R ２ is not a hydrogen atom. M represents a hydrogen atom or a metal atom.] a lithium ion secondary battery characterized by containing at least one amidosulfuric acid-based compound selected from the group consisting of an amidosulfuric acid derivative and taurine represented by.

[0007] The disclosure also provides the following lithium-ion secondary batteries [2] to [6]: [2] The lithium-ion secondary battery according to [1], wherein the total content of the amidosulfate compound relative to 100% by mass of the total amount of the non-aqueous electrolyte is 0.1 ppm by mass or more and 10,000 ppm by mass or less. [3] The lithium-ion secondary battery according to [1], wherein the total content of the amidosulfate compound relative to 100% by mass of the total amount of the non-aqueous electrolyte is 0.1 ppm by mass or more and 600 ppm by mass or less. [4] The non-aqueous electrolyte is the following formula (4): LiPF ａ (C ｍ F ２ｍ＋１ ) ６－ａ ... (4) A lithium-ion secondary battery according to any one of [1] to [3], comprising an electrolyte represented by formula (4) [wherein 0 ≤ a ≤ 6 and 1 ≤ m ≤ 4]. [5] A lithium-ion secondary battery according to any one of [1] to [4], wherein the non-aqueous electrolyte comprises at least one selected from the group consisting of cyclic carbonate solvents, linear carbonate solvents, cyclic ether solvents, linear ether solvents, lactone solvents, ester solvents, and nitrile solvents. [6] A lithium-ion secondary battery according to any one of [1] to [5], wherein the non-aqueous electrolyte comprises at least 90% by volume of at least one selected from the group consisting of non-fluorinated saturated cyclic carbonate solvents and non-fluorinated saturated linear carbonate solvents in total, based on 100% by volume of the total amount of the non-aqueous solvent.

[0008] Furthermore, this disclosure also includes the following method for improving a lithium-ion secondary battery [7]: [7] A positive electrode having a positive electrode mixture layer and a positive electrode current collector, a negative electrode having a negative electrode mixture layer and a negative electrode current collector, and a non-aqueous electrolyte, wherein the positive electrode mixture layer is based on the following formula (1): Li １＋ｘ Mn １－ｙ－ｚ Fe ｙ A ｚ PO ４... (1) [In formula (1), -0.1 < x < 0.1, 0 < y < 1.0, 0 ≤ z < 0.1, 0 < 1 - y - z, and A is at least one atom selected from the group consisting of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Ni, Co, Ga, Sn, Sb, Nb, and Ge.] comprises a positive electrode active material, ... The non-aqueous electrolyte is ... Formula (2) below: LiN(X １ SO ２ ) (X ２ SO ２ )...(2) [In formula (2), X １ and X ２ In a lithium-ion secondary battery comprising an electrolyte represented by ] and a non-aqueous solvent, the non-aqueous electrolyte contains amide sulfuric acid, a salt of amide sulfuric acid, and the following formula (3): R １ R ２ NSO ２ (OM)...(3) [In formula (3), R １ and R ２ R represents, either identically or distinctly, a hydrogen atom, a hydroxyl group, a C1-C10 alkyl group, a C3-C10 cycloalkyl group, a C6-C16 aryl group, a C7-C16 aralkyl group, or a C2-C16 alkanoyl group. １ and R ２ They may be bonded to each other to form a ring structure. However, R １ If R is a hydrogen atom, ２ A method for improving a lithium-ion secondary battery, characterized by including at least one amidosulfate compound selected from the group consisting of amidosulfate derivatives represented by [ ] and taurine, thereby suppressing the elution of Mn and Fe from the positive electrode into the non-aqueous electrolyte.

[0009] According to this disclosure, in a lithium-ion secondary battery having a positive electrode containing manganese iron lithium phosphate, the leaching of metals (Mn and Fe) from the positive electrode during high-temperature cycling can be suppressed, thereby improving battery performance.

[0010] The following describes these embodiments in detail. The following description of preferred embodiments is essentially illustrative and is not intended to limit the present invention, its applications, or its uses. The upper and lower limits of the various numerical values ​​shown below can be combined as appropriate to form a specific numerical range.

[0011] [Lithium-ion secondary battery] The lithium-ion secondary battery according to this embodiment comprises a positive electrode, a negative electrode, and a non-aqueous electrolyte.

[0012] <Positive Electrode> The positive electrode has a positive electrode mixture layer and a positive electrode current collector. The positive electrode is formed by having the positive electrode mixture layer on the positive electrode current collector. The positive electrode mixture layer is usually in the form of a sheet.

[0013] (Positive electrode mixture layer) The positive electrode mixture layer contains positive electrode active material, conductive additive, binder, etc.

[0014] [Positive electrode active material] The positive electrode mixture layer is composed of formula (1): [Chemical formula 1] Li １＋ｘ Mn １－ｙ－ｚ Fe ｙ A ｚ PO ４ ...contains a manganese iron lithium phosphate-based cathode active material represented by (1). In the following description, the cathode active material represented by formula (1) will be referred to as LMFP-based cathode active material (1).

[0015] In formula (1), "1 + x" represents the molar ratio of Li, where -0.1 < x < 0.1. "y" represents the molar ratio of Fe, where 0 < y < 1.0. "z" represents the molar ratio of A, described below, where 0 ≤ z < 0.1. "1 - y - z" represents the molar ratio of Mn, where 0 < 1 - y - z, and more precisely, 0 < 1 - y - z < 1.0. "A" is at least one atom selected from the group consisting of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Ni, Co, Ga, Sn, Sb, Nb, and Ge. In formula (1), "x", "y", and "z" can be adjusted as appropriate within the range of the above molar ratios. The molar ratio of Mn may preferably be 0.1 ≤ 1 - y - z < 1.00 or 0.25 ≤ 1 - y - z < 1.00.

[0016] A specific example of an LMFP-based cathode active material (1) is LiMn ０．００５ Fe ０．９９５PO ４ 、LiMn ０．１ Fe ０．９ PO ４ 、LiMn ０．３ Fe ０．７ PO ４ 、LiMn ０．７ Fe ０．３ PO ４ 、LiMn ０．８５ Fe ０．１５ PO ４ 、LiMn ０．７ Fe ０．２９５ V ０．００５ PO ４ 、LiMn ０．６ Fe ０．３９３ V ０．００４ Co ０．００３ PO ４ 、LiMn ０．６５ Fe ０．３４１ V ０．００４ Co ０．００５ PO ４ 、LiMn ０．７ Fe ０．２９３ V ０．００４ Co ０．００５ PO ４ 、LiMn ０．６ Fe ０．３９３ V ０．００４ Mg ０．００３ PO ４ 、LiMn ０．６ Fe ０．３９３ V ０．００４ Ni ０．００３ PO ４ etc. may be mentioned. The LMFP-based positive electrode active material (1) may be a commercially available product or one obtained by synthesis by a conventionally known method.

[0017] The positive electrode binder layer may optionally contain another positive electrode active material different from the LMFP-based positive electrode active material (1). The other positive electrode active material is not particularly limited as long as it can be used as a positive electrode active material for a lithium-ion secondary battery. For example, lithium cobaltate; lithium nickelate; LiNi １／３ Co １／３ Mn １／３ O ２ (NCM111), LiNi ０．５ Co ０．２ Mn ０．３ O２ (NCM523), LiNi ０．６ Co ０．２ Mn ０．２ O ２ (NCM622), LiNi ０．８ Co ０．１ Mn ０．１ O ２ (NCM811) and other ternary cathode active materials having a layered rock salt type structure; LiAPO ４ (A: Phosphate-based cathode active material having an olivine structure such as Ni, Mn, Co; LiNi ｐ Mn １－ｐ O ２ (0.5≦p≦1);Li ２ NiPO ４ Cathode active material having a fluoride olivine structure such as F; LiFePO ４ Iron phosphate-based cathode active materials having an olivine structure such as; solid solution materials incorporating multiple transition metals (electrochemically inert layered Li ２ MnO ３ And, electrochemically active layered LiMO ２ (Solid solution with transition metals such as M = Co and Ni); LiCo ｘ Mn １－ｑ O ２ (0≦q≦1);Li ２ APO ４ Compounds having a fluoride olivine structure such as F(A: Fe, Mn, Co); LiMn ２．０ O ４ LiNi ０．５ Mn １．５ O ４ Positive electrode active materials having a spinel-type structure such as sulfur can be used. Other positive electrode active materials may be used individually or in combination of two or more types.

[0018] The content of positive electrode active material in the positive electrode mixture layer is, for example, 75% to 99% by mass, but may also be 80% to 98% by mass, or 85% to 95% by mass, from the viewpoint of improving the output characteristics and electrical characteristics of the battery. If the positive electrode mixture layer contains only one type of positive electrode active material, the content of positive electrode active material refers to the content of that specific positive electrode active material. If the positive electrode mixture layer contains multiple positive electrode active materials, the content of positive electrode active material refers to the sum of the individual content of all positive electrode active materials contained in the positive electrode mixture layer. The content of conductive additives and binders, etc., described later, is defined similarly.

[0019] [Conductive Additives] Conductive additives mainly consist of conductive carbon. Examples of conductive carbon include carbon black, carbon fiber, and graphite. Conductive additives may be used individually or in combination of two or more types. Among the conductive additives, carbon black is preferred. Examples of carbon black include Ketjen black and acetylene black. The content of the conductive additive in the positive electrode mixture layer is, for example, 1% by mass or more and 20% by mass or less, and may also be 1.5% by mass or more and 10% by mass or less, from the viewpoint of improving the output characteristics and electrical characteristics of the battery.

[0020] [Binding Agents] Examples of binding agents include fluororesins such as polyvinylidene fluoride (PVdF) and polytetrafluoroethylene; synthetic rubbers such as styrene-butadiene rubber (SBR) and nitrile butadiene rubber; polyamide resins such as polyamide-imide; polyolefin resins such as polyethylene and polypropylene; poly(meth)acrylic resins; polyacrylic acid; and cellulose resins such as carboxymethylcellulose (CMC). Each binding agent may be used individually, or two or more may be used in combination. Furthermore, the binding agent may be dissolved in the solvent or dispersed in the solvent at the time of use. The binding agent content in the positive electrode mixture layer is, for example, 1% to 20% by mass, or 1.5% to 10% by mass, from the viewpoint of improving the output characteristics and electrical characteristics of the battery.

[0021] [Other Components] The positive electrode mixture layer may contain, as necessary, other components such as polymers such as non-fluorinated polymers like (meth)acrylic polymers, nitrile polymers, and diene polymers, and fluorinated polymers like polytetrafluoroethylene; emulsifiers such as anionic emulsifiers, nonionic emulsifiers, and cationic emulsifiers; dispersants such as polymeric dispersants like styrene-maleic acid copolymers and polyvinylpyrrolidone; thickeners such as carboxymethylcellulose (CMC), hydroxyethylcellulose, polyvinyl alcohol, polyacrylic acid (salt), and alkali-soluble (meth)acrylic acid-(meth)acrylic acid ester copolymers; and preservatives. The content of other components in the positive electrode mixture layer may be, for example, 0% by mass or more and 15% by mass or less, or 0% by mass or more and 10% by mass or less.

[0022] (Positive electrode current collector) Examples of metals that can be used for the positive electrode current collector include iron, copper, aluminum, nickel, stainless steel, titanium, tantalum, gold, and platinum. Among these, aluminum is preferred. The shape and dimensions of the positive electrode current collector are not particularly limited.

[0023] <Method for preparing the positive electrode> The positive electrode mixture layer can be prepared from the positive electrode mixture. The positive electrode mixture contains the positive electrode active material, conductive additive, binder, etc., as described above, and a solvent for dispersing these components. The positive electrode mixture can be prepared, for example, by mixing each component and dispersing them using a bead mill, ball mill, agitator, or the like.

[0024] Examples of solvents include N-methyl-2-pyrrolidone (NMP), dimethylformamide, dimethylacetamide, methyl ethyl ketone, tetrahydrofuran, acetonitrile, acetone, ethanol, ethyl acetate, and water. Each solvent may be used individually, or two or more may be used in combination. The amount of solvent used is not particularly limited and should be determined appropriately depending on the manufacturing method and the materials used.

[0025] The method for manufacturing the positive electrode is not particularly limited, and examples include (A) applying the positive electrode mixture to the positive electrode current collector and then drying it; (B) immersing the positive electrode current collector in the positive electrode mixture and then drying it; and (C) joining a sheet formed from the positive electrode mixture to the positive electrode current collector, pressing it, and then drying it.

[0026] <Negative Electrode> The negative electrode has a negative electrode mixture layer and a negative electrode current collector. The negative electrode is formed by the negative electrode mixture layer being formed on the negative electrode current collector. The negative electrode mixture layer is usually in the form of a sheet.

[0027] (Negative electrode mixture layer) The negative electrode mixture layer contains negative electrode active material, conductive additive, binder, etc. The preferred content of each component is the same as that of the positive electrode.

[0028] [Negative Electrode Active Material] Specific examples of negative electrode active materials include graphite materials such as artificial graphite and natural graphite; carbon materials such as mesophase calcined bodies made from coal and petroleum pitch, and non-graphitizable carbon; Si-based negative electrode materials such as Si, Si alloys, and SiOx; Sn-based negative electrode materials such as Sn alloys; lithium metal; lithium alloys such as lithium-aluminum alloys; and composite materials of graphite and Si-based negative electrode materials (hereinafter also referred to as "Si-containing graphite"). Specific examples of Si-containing graphite include those with a mass ratio (Si:C) of Si-based negative electrode material to graphite of 3:97 or more and 50:50 or less. The negative electrode active materials may be used individually or in combination of two or more types.

[0029] (Negative electrode current collector) Examples of metals that can be used for the negative electrode current collector include iron, copper, aluminum, nickel, stainless steel (SUS), titanium, tantalum, gold, and platinum. Of these, copper is preferred. The shape and dimensions of the negative electrode current collector are not particularly limited.

[0030] <Method for manufacturing the negative electrode> The method for manufacturing the negative electrode may be the same as the method for manufacturing the positive electrode.

[0031] <Non-aqueous electrolyte> A non-aqueous electrolyte contains an electrolyte, a non-aqueous solvent, and an amidosulfate compound.

[0032] (Electrolyte) The non-aqueous electrolyte is given by formula (2): [Chemical formula 2] LiN(X１ SO ２ ) (X ２ SO ２ ) ... (2) contains an electrolyte represented by (2) (hereinafter also referred to as "sulfonylimide compound (2)").

[0033] In equation (2), X １ and X ２ These represent, either identically or distinctly, a fluorine atom (F), a C1-C6 alkyl group, or a C1-C6 fluoroalkyl group.

[0034] In formula (2), examples of C1-C6 alkyl groups include linear or branched alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, pentyl, and hexyl groups. Among C1-C6 alkyl groups, linear alkyl groups are preferred.

[0035] In formula (2), the carbon-1 to carbon-6 fluoroalkyl group can be any alkyl group in which some or all of the hydrogen atoms are substituted with fluorine atoms. Examples of carbon-1 to carbon-6 fluoroalkyl groups include fluoromethyl, difluoromethyl, trifluoromethyl, fluoroethyl, difluoroethyl, trifluoroethyl, and pentafluoroethyl groups. The fluoroalkyl group may also be a perfluoroalkyl group in which all of the hydrogen atoms of the alkyl group have carbon-1 to carbon-6 are substituted with fluorine atoms.

[0036] In equation (2), X １ and X ２ Preferably, the components are a fluorine atom and a perfluoroalkyl group; more preferably, a fluorine atom, a trifluoromethyl group, and a pentafluoroethyl group; even more preferably, a fluorine atom and a trifluoromethyl group; and particularly preferably, a fluorine atom.

[0037] Examples of sulfonyliimide compounds (2) include lithium bis(fluorosulfonyl)imide (LiN(FSO) ２ ) ２ , hereafter also referred to as "LiFSI"), lithium bis(trifluoromethylsulfonyl)imide (LiN(CF ３ SO２ ) ２ Examples include lithium(fluorosulfonyl)(methylsulfonyl)imide, lithium(fluorosulfonyl)(ethylsulfonyl)imide, lithium(fluorosulfonyl)(trifluoromethylsulfonyl)imide, lithium(fluorosulfonyl)(pentafluoroethylsulfonyl)imide, lithium(fluorosulfonyl)(heptafluoropropylsulfonyl)imide, lithiumbis(pentafluoroethylsulfonyl)imide, lithiumbis(heptafluoropropylsulfonyl)imide, etc. Each sulfonylimide compound (2) may be used individually or in combination of two or more types. The sulfonylimide compound (2) may be a commercially available product or one obtained by synthesis using a conventionally known method.

[0038] Non-aqueous electrolytes are used to improve battery performance, such as LiN(FSO). ２ ) ２ and LiN(CF ３ SO ２ ) ２ Preferably, it contains at least one selected from the group consisting of LiN(FSO) ２ ) ２ It is more preferable to include it.

[0039] The non-aqueous electrolyte may, if necessary, contain other electrolytes different from sulfonylime compound (2). The other electrolytes are not particularly limited as long as they can be used as electrolytes in lithium-ion secondary batteries, but may include the electrolyte represented by formula (4) (hereinafter also referred to as "fluorophosphate compound (4)"), the electrolyte represented by formula (5) (hereinafter also referred to as "fluoroboric acid compound (5)"), and LiAsF ６ LiSbF ６ LiClO ４ , LiSCN, LiAlF ４ CF ３ SO ３ Li, LiC [(CF ３ SO ２ ) ３ ], LiN (NO ２ ), LiN[(CN) ２ Examples include: [Chemical Formula 3] LiPFａ (C ｍ F ２ｍ＋１ ) ６－ａ ... (4) In equation (4), 0 ≤ a ≤ 6 and 1 ≤ m ≤ 4. The fluorophosphate compound (4) is LiPF ６ LiPF ３ (CF ３ ) ３ LiPF ３ (C ２ F ５ ) ３ LiPF ３ (C ３ F ７ ) ３ LiPF ３ (C ４ F ９ ) ３ These are some examples. Among the fluorophosphate compounds (4), LiPF ６ This is preferable. [Chemical Formula 4] LiBF ｂ (C ｎ F ２ｎ+１ ) ４－ｂ ... (5) In equation (5), 0 ≤ b ≤ 4 and 1 ≤ n ≤ 4. The fluoroboric acid compound (5) is LiBF ４ LiBF (CF ３ ) ３ LiBF(C ２ F ５ ) ３ LiBF(C ３ F ７ ) ３ These are some examples. Among the fluoroboric acid compounds (5), LiBF ４ It is preferable.

[0040] Among other electrolytes, fluorophosphate compounds (4), fluoroboric acid compounds (5), and LiAsF are selected from the perspective of ionic conductivity and cost. ６ Preferably, fluorophosphate compound (4) is more preferred, LiPF ６ That is even more preferable.

[0041] Therefore, the non-aqueous electrolyte consists of a sulfonylimide compound (2), a fluorophosphate compound (4), a fluoroboric acid compound (5), and LiAsF ６It may also include at least one selected from the group consisting of LiN(FSO ２ ) ２ and LiN(CF ３ SO ２ ) ２ At least one selected from the group consisting of the following, and a fluorophosphate compound (4), a fluoroboric acid compound (5), and LiAsF ６ It can be said that it may include at least one selected from the group consisting of the following.

[0042] Furthermore, the non-aqueous electrolyte may also contain a sulfonylimide compound (2) and a fluorophosphate compound (4), such as LiN(FSO). ２ ) ２ and LiN(CF ３ SO ２ ) ２ It can be said that the compound may include at least one selected from the group consisting of the above, and a fluorophosphate compound (4).

[0043] Furthermore, the non-aqueous electrolyte is a sulfonylime compound (2) and LiPF ６ It may also include LiN(FSO ２ ) ２ and LiN(CF ３ SO ２ ) ２ At least one selected from the group consisting of and LiPF ６ It can be said that it may also contain. Furthermore, the non-aqueous electrolyte is LiN(FSO). ２ ) ２ and LiPF ６ It can be said that it may include and.

[0044] Furthermore, the sulfonylimide compound (2) and other electrolytes may exist in ionic form.

[0045] The content of sulfonylimide compound (2) in the non-aqueous electrolyte is, for example, 0.01 mol / L to 5.0 mol / L, from the viewpoint of improving battery performance. This content may also be 0.05 mol / L to 3.0 mol / L, 0.1 mol / L to 2.0 mol / L, 0.2 mol / L to 1.5 mol / L, or 0.5 mol / L to 1.0 mol / L. By doing so, it is possible to improve the capacity retention rate of lithium-ion secondary batteries after high-temperature cycling and suppress the rise in DCR, while suppressing the deterioration of battery performance due to the rise in electrolyte viscosity. Furthermore, it is possible to further suppress the elution of metals (Mn and Fe) from the positive electrode during high-temperature cycling. Note that if the non-aqueous electrolyte contains only one type of sulfonylimide compound (2), the content of sulfonylimide compound (2) refers to the content of that sulfonylimide compound (2). When a non-aqueous electrolyte contains multiple sulfonylimide compounds (2), the content of sulfonylimide compounds (2) refers to the sum of the individual content of all sulfonylimide compounds (2) contained in the non-aqueous electrolyte.

[0046] The content of sulfonylimide compound (2) relative to 100% by mass of the total amount of non-aqueous electrolyte is, for example, 0.1% by mass or more and 80% by mass or less, from the viewpoint of improving battery performance. This content may also be 0.5% by mass or more and 50% by mass or less, 1% by mass or more and 30% by mass or less, 3% by mass or more and 20% by mass or less, or 5% by mass or more and 10% by mass or less. By doing so, it is possible to improve the capacity retention rate of lithium-ion secondary batteries after high-temperature cycling and suppress the rise in DCR, while suppressing the deterioration of battery performance due to the rise in electrolyte viscosity. Furthermore, it is possible to further suppress the elution of metals (Mn and Fe) from the positive electrode during high-temperature cycling.

[0047] The content of sulfonylimide compound (2) relative to 100 mol% of the total amount of electrolyte contained in the non-aqueous electrolyte is, for example, 1 mol% to 100 mol% from the viewpoint of improving battery performance. This content may be 5 mol% to 95 mol%, 15 mol% to 90 mol%, 20 mol% to 85 mol%, 25 mol% to 75 mol%, 30 mol% to 70 mol%, or 35 mol% to 65 mol%. By doing so, it is possible to improve the capacity retention rate of lithium-ion secondary batteries after high-temperature cycling and suppress the increase in DCR, while suppressing the deterioration of battery performance due to the increase in electrolyte viscosity. Furthermore, it is possible to further suppress the elution of metals (Mn and Fe) from the positive electrode during high-temperature cycling. Furthermore, the fact that the sulfonyliimide compound (2) content in the non-aqueous electrolyte is 100 mol% relative to the total amount of sulfonyliimide compound (2) and other electrolytes means that the non-aqueous electrolyte does not contain any electrolytes other than sulfonyliimide compound (2).

[0048] (Non-aqueous solvent) The non-aqueous electrolyte contains a non-aqueous solvent. Preferably, the non-aqueous electrolyte contains at least one non-aqueous solvent (6) selected from the group consisting of cyclic carbonate solvents, linear carbonate solvents, cyclic ether solvents, linear ether solvents, lactone solvents, ester solvents, and nitrile solvents. The non-aqueous solvent (6) may be used individually or in combination of two or more types.

[0049] Examples of cyclic carbonate solvents include non-fluorinated saturated cyclic carbonate solvents, non-fluorinated unsaturated cyclic carbonate solvents, and fluorinated cyclic carbonate solvents. Specific examples of non-fluorinated saturated cyclic carbonate solvents include ethylene carbonate, propylene carbonate, 2,3-dimethylethylene carbonate, and 1,2-butylene carbonate. ２－６Examples include alkylene carbonates and erythritol carbonate. Specific examples of non-fluorinated unsaturated cyclic carbonate solvents include vinylene carbonate, methylvinylene carbonate, ethylvinylene carbonate, 2-vinylethylene carbonate, and phenylethylene carbonate, which are cyclic carbonates having unsaturated bonds. Specific examples of fluorinated cyclic carbonate solvents include fluoroethylene carbonate, 4,5-difluoroethylene carbonate, and trifluoropropylene carbonate. Among cyclic carbonate solvents, non-fluorinated saturated cyclic carbonate solvents are preferred, and ethylene carbonate is more preferred.

[0050] Examples of linear carbonate solvents include diC １－４ Alkyl carbonate solvent, C １－４ Examples include alkylphenyl carbonate solvents and diaryl carbonate solvents. １－４ Specific examples of alkyl carbonate solvents include non-fluorinated saturated chain carbonate solvents such as dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate. １－４ Specific examples of alkylphenyl carbonate solvents include methylphenyl carbonate. Specific examples of diaryl carbonate solvents include diphenyl carbonate. Among chain-like carbonate solvents, diC １－４ Alkyl carbonate solvents are preferred, non-fluorinated saturated chain carbonate solvents are more preferred, dimethyl carbonate and ethyl methyl carbonate are even more preferred, and ethyl methyl carbonate is particularly preferred.

[0051] Examples of cyclic ether solvents include tetrahydrofuran solvents, tetrahydropyran solvents, dioxane solvents, dioxolane solvents, and crown ethers. Specific examples of tetrahydrofuran solvents include tetrahydrofuran, 2-methyltetrahydrofuran, and 2,6-dimethyltetrahydrofuran. Specific examples of tetrahydropyran solvents include tetrahydropyran. Specific examples of dioxane solvents include 1,4-dioxane. Specific examples of dioxolane solvents include 1,3-dioxolane.

[0052] Examples of linear ether solvents include alkanediol dialkyl ether solvents and polyalkanediol dialkyl ether solvents. Specific examples of alkanediol dialkyl ether solvents include ethylene glycol dimethyl ether and ethylene glycol diethyl ether. Specific examples of polyalkanediol dialkyl ether solvents include triethylene glycol dimethyl ether and tetraethylene glycol dimethyl ether.

[0053] Specific examples of lactone-based solvents include cyclic ester solvents such as γ-butyrolactone, γ-valerolactone, and δ-valerolactone.

[0054] Examples of ester solvents include linear ester solvents and aromatic carboxylic acid ester solvents. Specific examples of linear ester solvents include ethyl acetate, butyl acetate, methyl propionate, ethyl propionate, and propyl propionate. Specific examples of aromatic carboxylic acid ester solvents include methyl benzoate and ethyl benzoate.

[0055] Examples of nitrile solvents include aliphatic nitrile solvents and aromatic nitrile solvents. Specific examples of aliphatic nitrile solvents include acetonitrile, propionitrile, methoxypropionitrile, glutaronitrile, adiponitrile, 2-methylglutaronitrile, valeronitrile, butyronitrile, and isobutyronitrile. Specific examples of aromatic nitrile solvents include benzonitrile and tolunitrile.

[0056] Among the non-aqueous solvents (6), cyclic carbonate solvents, linear carbonate solvents, and ester solvents are preferred, cyclic carbonate solvents and linear carbonate solvents are more preferred, non-fluorinated saturated cyclic carbonate solvents and non-fluorinated saturated linear carbonate solvents are even more preferred, and ethylene carbonate and ethyl methyl carbonate are particularly preferred. Therefore, the non-aqueous electrolyte preferably contains at least one non-aqueous solvent (6-1) selected from the group consisting of cyclic carbonate solvents, linear carbonate solvents, and ester solvents; more preferably contains at least one non-aqueous solvent (6-2) selected from the group consisting of cyclic carbonate solvents and linear carbonate solvents; even more preferably contains at least one non-aqueous solvent (6-3) selected from the group consisting of non-fluorinated saturated cyclic carbonate solvents and non-fluorinated saturated linear carbonate solvents; and particularly preferably contains at least one non-aqueous solvent (6-4) selected from the group consisting of ethylene carbonate and ethyl methyl carbonate.

[0057] The non-aqueous electrolyte preferably contains, in 100% by volume of the total amount of non-aqueous solvent, a total of 90% by volume of at least one non-aqueous solvent (6-3) selected from the group consisting of non-fluorinated saturated cyclic carbonate solvents and non-fluorinated saturated chain carbonate solvents. This content may be 95% by volume or more, or 100% by volume. Note that a content of 100% by volume of non-aqueous solvent (6-3) relative to 100% by volume of the total amount of non-aqueous solvent means that the non-aqueous solvent does not contain any non-aqueous solvent other than non-aqueous solvent (6-3).

[0058] The non-aqueous electrolyte may, if necessary, contain other non-aqueous solvents different from the non-aqueous solvent (6). Other non-aqueous solvents are not particularly limited as long as they can be used as non-aqueous solvents for lithium-ion secondary batteries, but examples include phosphate ester solvents, sulfur compound solvents, nitromethane, 1,3-dimethyl-2-imidazolidinone, 1,3-dimethyl-3,4,5,6-tetrahydro-2(1H)-pyrimidinone, 3-methyl-2-oxazolidinone, etc. Specific examples of phosphate ester solvents include alkyl phosphates such as trimethyl phosphate, ethyldimethyl phosphate, diethylmethyl phosphate, and triethyl phosphate. Specific examples of sulfur compound solvents include sulfone solvents such as dimethyl sulfone, ethylmethyl sulfone, and diethyl sulfone; and sulfolane solvents such as sulfolane, 3-methylsulfolane, and 2,4-dimethylsulfolane.

[0059] Non-aqueous electrolytes may be used as a medium such as a polymer or polymer gel in addition to the non-aqueous solvent mentioned above. When using a polymer or polymer gel instead of a non-aqueous solvent, the following methods may be employed: a method in which a solution of an electrolyte dissolved in a non-aqueous solvent is dropped onto a polymer that has been formed into a film by a conventionally known method, thereby impregnating and supporting the electrolyte and non-aqueous solvent; a method in which the polymer and electrolyte are melted and mixed at a temperature above the melting point of the polymer, a film is formed, and the non-aqueous solvent is impregnated therein (a gel electrolyte); a method in which a non-aqueous electrolyte, in which the electrolyte is dissolved in a non-aqueous solvent beforehand, is mixed with a polymer, a film is formed by a casting method or a coating method, and the non-aqueous solvent is volatilized; a method in which the polymer and electrolyte are melted and mixed at a temperature above the melting point of the polymer and then molded (an intrinsic polymer electrolyte).

[0060] Polymers that can be used in addition to non-aqueous solvents include polyether polymers such as polyethylene oxide (PEO) and polypropylene oxide, which are homopolymers or copolymers of epoxy compounds (ethylene oxide, propylene oxide, butylene oxide, allyl glycidyl ether, etc.), methacrylic polymers such as polymethyl methacrylate (PMMA), nitrile polymers such as polyacrylonitrile (PAN), fluorine polymers such as polyvinylidene fluoride (PVdF) and polyvinylidene fluoride-hexafluoropropylene, and copolymers thereof. These polymers may be used individually or in combination of two or more types.

[0061] (Amidosulfate compounds) Non-aqueous electrolytes include amidosulfate (also called sulfamic acid, H ３ NSO ３ ), salts of amide sulfuric acid, amide sulfuric acid derivatives and taurine [2-aminoethanesulfonic acid (also called aminoethylsulfonic acid), H ２ N-CH ２ -CH ２ -SO ３ It contains at least one amidosulfate compound (7) selected from the group consisting of H. The amidosulfate compounds (7) may be used individually or in combination of two or more types.

[0062] The amidosulfate compound (7) is not particularly limited, for example, a neutral type (H ２ NSO ２ (OH), HN=SO(OH) ２ (etc.) is also acceptable, and zwitterionic form (H ３ N ＋ SO ３ － , H ２ N ＋ = SO(OH)O － (etc.) is also acceptable, and any of these may be included.

[0063] Salts of amidosulfate can be, for example, salts in which amidosulfate is either a base or an acid, and usually salts in which amidosulfate is an acid (salts of amidosulfate and a base). Examples of amidosulfate salts include metal salts and nonmetal salts of amidosulfate. Specific examples of metal salts include alkali metal salts (lithium salt, sodium salt, potassium salt, etc.), alkaline earth metal salts (magnesium salt, calcium salt, barium salt, etc.), aluminum salt, manganese salt, copper salt, zinc salt, iron salt, cobalt salt, nickel salt, etc. Specific examples of non-precious metal salts include ammonium salt and guanidine salt. Among the amidosulfate salts, alkali metal salts of amidosulfate are preferred, and lithium salts of amidosulfate (lithium amidosulfate, etc.) and sodium salts of amidosulfate (sodium amidosulfate, etc.) are more preferred. The salt may also be a salt corresponding to the cation of the electrolyte it is combined with. For example, when using a lithium salt as the electrolyte, lithium salt of amidosulfate (lithium amidosulfate, etc.) may be used.

[0064] Amidosulfuric acid derivatives are given by formula (3): [Chemical formula 5] R １ R ２ NSO ２ It is represented by (OM)...(3). Note that although formula (3) is shown in the neutral form, it may also represent the zwitterionic form, and may contain both.

[0065] In formula (3), R １ and R ２ R represents, either identically or differently, a hydrogen atom (H), a hydroxyl group (-OH), an alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, an aryl group having 6 to 16 carbon atoms, an aralkyl group having 7 to 16 carbon atoms, or an alkanoyl group having 2 to 16 carbon atoms. １ and R ２ They may be bonded to each other to form a ring structure. However, R １ If R is a hydrogen atom, ２ It is not a hydrogen atom.

[0066] In formula (3), examples of alkyl groups having 1 to 10 carbon atoms include the methyl group. Examples of cycloalkyl groups having 3 to 10 carbon atoms include the cyclopropyl group. Examples of aryl groups having 6 to 16 carbon atoms include the phenyl group and the naphthyl group. Examples of aralkyl groups having 7 to 16 carbon atoms include the benzyl group and the phenethyl group. Examples of alkanoyl groups having 2 to 16 carbon atoms include the benzoyl group.

[0067] In formula (3), M represents a hydrogen atom or a metal atom. Examples of metal atoms represented by M include alkali metal atoms such as lithium, sodium, and potassium; alkaline earth metal atoms such as magnesium, calcium, and barium; and aluminum.

[0068] Specific examples of amidosulfate derivatives [N-substituted amidosulfates and their salts (or compounds represented by formula (3))] include N-hydroxyamidosulfate; N-mono or dialkylamidosulfate [N-methylamidosulfate, N-ethylamidosulfate, N-(1-methylpropyl)amidosulfate, N-(2-methylbutyl)amidosulfate, N-(2,2-dimethylpropyl)amidosulfate, N,N-diethylamidosulfate, N-(3-hydroxypropyl)amidosulfate, N-methyl-N-(2,3-dihydroxy [Propyl)amidosulfate, N,N-bis(2-hydroxyethyl)amidosulfate, N-(2,3-dihydroxypropyl)amidosulfate, N-(3-methoxy-4-methylphenyl)amidosulfate, N-methyl-N-(2-hydroxy-3-chloropropyl)amidosulfate, N-(2-hydroxy-3-chloropropyl)amidosulfate, N-ethyl-N-(2-hydroxy-3-chloropropyl)amidosulfate, etc.]; N-mono or dicycloalkylamidosulfate (N-cyclohexylamidosulfate, N,N- Dicyclohexylamide sulfate, etc.); N-mono or diarylamide sulfate [N-phenylamide sulfate, N-naphthylamide sulfate, N-hydroxy-N-(2-hydroxy-1-naphthyl)amide sulfate, N-(4-bromophenyl)amide sulfate, etc.]; N-mono or dialkylamide sulfate [N-benzylamide sulfate, N-(β-methylphenethyl)amide sulfate, etc.]; N-alkyl-N-arylamide sulfate (N-ethyl-N-phenylamide sulfate, etc.); N-mono or diacylamide sulfate [ Examples include N-benzoylamide sulfate, N-(3-chloroalanyl)amide sulfate, N-(3-chloro-3-methylalanyl)amide sulfate, etc.; N-thiocycloalkylamide sulfate [N-(thiepan-4-yl)amide sulfate, N-thiocan-4-ylamide sulfate, thiocan-5-ylamide sulfate, N-thietan-3-ylamide sulfate, N-1,3-dithian-5-ylamide sulfate, N-(thian-3-yl)amide sulfate, N-(thiolan-3-yl)amide sulfate, etc.]; and salts thereof.

[0069] Among the amidosulfate compounds (7), amidosulfate, lithium amidosulfate, sodium amidosulfate, and taurine are preferred; amidosulfate, lithium amidosulfate, and sodium amidosulfate are more preferred; and amidosulfate and lithium amidosulfate are even more preferred. Therefore, the non-aqueous electrolyte preferably contains at least one amidosulfate compound (7-1) selected from the group consisting of amidosulfate, lithium amidosulfate, sodium amidosulfate, and taurine; more preferably contains at least one amidosulfate compound (7-2) selected from the group consisting of amidosulfate, lithium amidosulfate, and sodium amidosulfate; and even more preferably contains at least one amidosulfate compound (7-3) selected from the group consisting of amidosulfate and lithium amidosulfate.

[0070] The total content of the amidosulfuric acid compound (7) relative to 100% by mass of the total amount of the non-aqueous electrolyte is preferably 0.1 ppm by mass or more and 10,000 ppm by mass or less, from the viewpoint of improving battery performance. The content may also be 0.5 ppm by mass or more and 5,000 ppm by mass or less, 1 ppm by mass or more and 1,000 ppm by mass or less, 3 ppm by mass or more and 600 ppm by mass or less, 5 ppm by mass or more and 550 ppm by mass or less, 10 ppm by mass or more and 500 ppm by mass or less, 50 ppm by mass or more and 450 ppm by mass or less, 100 ppm by mass or more and 400 ppm by mass or less, or 200 ppm by mass or more and 350 ppm by mass or less. In this way, the non-aqueous electrolyte can be easily manufactured.

[0071] If the amidosulfate compound (7) is a salt, the above content and proportion shall be expressed in terms of the proportion in non-salt form [amidosulfate, amidosulfate derivatives in which M is a hydrogen atom in formula (3)].

[0072] The amidosulfate compound (7) may exist (be contained) in ionic form in the non-aqueous electrolyte. The amidosulfate compound (7) may be added to the electrolyte in whole or in part, or it may be used as a product generated during the manufacturing process of the electrolyte salt.

[0073] (Additives) The non-aqueous electrolyte may further contain additives as needed. Examples of additives include succinic anhydride, glutaric anhydride, maleic anhydride, citraconic anhydride, glutaconic anhydride, itaconic anhydride, diglycolic anhydride, cyclohexanedicarboxylic anhydride, cyclopentanetetracarboxylic dianhydride, phenylsuccinic anhydride, and other carboxylic acid anhydrides; ethylene sulfite, 1,3-propanesultone, 1,4-butanesultone, 2,4-butanesultone, methyl methanesulfonate, busulfan, sulfolane, sulfolene, dimethyl sulfone, tetramethylthiuram monosulfide, trimethyleneglycolate Sulfur-containing compounds such as cholsulfate; nitrogen-containing compounds such as 1-methyl-2-pyrrolidinone, 1-methyl-2-piperidone, 3-methyl-2-oxazolidinone, 1,3-dimethyl-2-imidazolidinone, and N-methylsuccinimide; saturated hydrocarbon compounds such as heptane, octane, and cycloheptane; carbonate compounds such as vinylene carbonate, fluoroethylene carbonate (FEC), trifluoropropylene carbonate, phenylethylene carbonate, and erythritol carbonate; lithium fluorosulfonate (LiFSO4). ３ ), sodium fluorosulfonate (NaFSO ３ ), potassium fluorosulfonate (KFSO ３ ), magnesium fluorosulfonate [Mg(FSO ３ ) ２ Fluorosulfonic acid compounds such as ]; Lithium monofluorophosphate (Li ２ PO ３ F) Lithium difluorophosphate (LiPO ２ F ２Examples include fluorophosphate compounds such as lithium bis(oxalato)borate (LiBOB), lithium difluorooxalatoborate (LiDFOB), lithium difluorooxalatophosphate (LIDFOP), lithium tetrafluorooxalatophosphate (LITFOP), lithium difluorobis(oxalato)phosphate (LiDFBOP), lithium tris(oxalato)phosphate, and other lithium salts having an oxalic acid skeleton. Each additive may be used individually, or two or more may be used in combination.

[0074] The additive content may be, for example, 0.1% to 10% by mass, 0.2% to 8% by mass, or 0.3% to 5% by mass, based on 100% by mass of the total amount of the non-aqueous electrolyte.

[0075] <Method for preparing a non-aqueous electrolyte> A non-aqueous electrolyte can be prepared by mixing three components: a sulfonylimide compound (2), a non-aqueous solvent, and an amidosulfuric acid compound (7). Other electrolytes and additives may be added as needed.

[0076] <Other components of lithium-ion secondary batteries> Lithium-ion secondary batteries may also include separators, battery casing materials, etc.

[0077] (Separator) The separator is positioned to separate the positive electrode and the negative electrode. There are no particular restrictions on the separator, and conventionally known separators can be used in this disclosure. Specific examples of separators include porous sheets made of polymers capable of absorbing and retaining non-aqueous electrolytes (e.g., polyolefin-based microporous separators and cellulose-based separators), nonwoven fabric separators, porous metal bodies, and the like.

[0078] (Battery casing material) A battery element, comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte (and a separator), is usually housed in a battery casing material to protect it from external shocks, environmental degradation, etc., during battery use. The material of the battery casing material is not particularly limited, and any conventionally known casing material can be used. The battery casing material may include expanded metal, fuses, overcurrent protection elements such as PTC elements, lead plates, etc., as needed, to prevent pressure rise inside the battery and overcharging / discharging.

[0079] [Method for Manufacturing Lithium-Ion Secondary Batteries] Lithium-ion secondary batteries can be easily manufactured by the following procedure. For example, the positive electrode and the negative electrode are stacked (with a separator in place if necessary) to form a laminate. Next, the laminate is placed in a battery casing. Finally, a non-aqueous electrolyte is poured into the battery casing and sealed.

[0080] [Shape of Lithium-ion Secondary Batteries] The shape of lithium-ion secondary batteries is not particularly limited; any conventionally known battery shape, such as cylindrical, prismatic, laminated, coin-type, or large, can be used. Furthermore, when used as a high-voltage power source (several tens to several hundred volts) for electric vehicles, hybrid electric vehicles, etc., a battery module can be constructed by connecting individual batteries in series.

[0081] [Rated Charging Voltage of Lithium-ion Secondary Batteries] The rated charging voltage of lithium-ion secondary batteries is not particularly limited, but may be 3.6V or higher, preferably 4.0V or higher, more preferably 4.1V or higher, and even more preferably 4.2V or higher. A higher rated charging voltage can increase energy density, but from the viewpoint of battery safety, the rated charging voltage may be 4.6V or lower (for example, 4.5V or lower).

[0082] [Summary] The lithium-ion secondary battery according to this embodiment, configured as described above, comprises: a positive electrode having a positive electrode mixture layer containing an LMFP-based positive electrode active material (1) and a positive electrode current collector; a negative electrode having a negative electrode mixture layer and a negative electrode current collector; and a non-aqueous electrolyte containing a sulfonylime compound (2), a non-aqueous solvent, and an amidosulfuric acid-based compound (7). By configuring the lithium-ion secondary battery in this way, the elution of metals (Mn and Fe) from the positive electrode during high-temperature cycling can be suppressed. This suppresses the reduction deposition of Mn and Fe elutes at the negative electrode. Furthermore, as a result of this suppression, in a lithium-ion secondary battery using an LMFP-based positive electrode active material (1), it is possible to improve the capacity retention rate and suppress the increase in DCR during the high-temperature cycling process.

[0083] Therefore, from a different perspective, this embodiment can also be described as a method for improving a lithium-ion secondary battery, comprising: a positive electrode having a positive electrode mixture layer containing an LMFP-type positive electrode active material (1) and a positive electrode current collector; a negative electrode having a negative electrode mixture layer and a negative electrode current collector; and a non-aqueous electrolyte containing a sulfonylime compound (2) and a non-aqueous solvent, wherein the battery performance is improved by suppressing the elution of Mn and Fe from the positive electrode into the non-aqueous electrolyte by including an amidosulfuric acid compound (7) in the non-aqueous electrolyte.

[0084] The present disclosure will be described below based on examples. However, the present disclosure is not limited to the following examples, and the following examples can be modified or changed in accordance with the spirit of the present disclosure, and such modifications do not exclude them from the scope of the present disclosure.

[0085] [Non-aqueous electrolyte] (Example) LiFSI [manufactured by Nippon Shokubai Co., Ltd., sulfonyliimide compound (2)] was dissolved in ethyl methyl carbonate (EMC) to obtain an EMC solution containing 40% by mass of LiFSI. The LiFSI content is as follows: １９Measurements were taken by F-NMR. Subsequently, the amidosulfate compounds shown in Table 1 (amidosulfate, lithium amidosulfate, taurine, sodium amidosulfate) were added to the above EMC solution. Lithium amidosulfate was prepared by slurrying amidosulfate with pure water, adding lithium hydroxide monohydrate while stirring and monitoring the exothermic reaction, filtering out insoluble matter, and then drying the filtrate under reduced pressure at 80°C. When the obtained lithium amidosulfate was analyzed by XRD (X-ray diffraction), no impurities were found.

[0086] After adding the amidosulfate compound, the EMC solution was stirred for one day and filtered through a membrane filter. LiPF was added to the filtered EMC solution. ６ Ethylene carbonate (EC) and EMC were added. Therefore, LiFSI and LiPF were used as electrolytes. ６ Non-aqueous electrolytes [non-aqueous solvent: EC / EMC (volume ratio) = 3 / 7] containing the specified molar concentration and an amidosulfate compound were obtained for each example. In these non-aqueous electrolytes, the electrolyte was dissolved, and no undissolved residue was observed visually.

[0087] The obtained non-aqueous electrolyte was analyzed by the following ion chromatography. For example, as shown in Table 1, the non-aqueous electrolyte of Example 1 contained LiFSI at 0.6 M (9.3 mass%) and LiPFA based on its total volume. ６ It was found that the solution contains 0.6 M (7.5 mass%) of [substance name] and 6 mass ppm of amidosulfate (ions) as an amidosulfate compound (36 mass ppm relative to the total amount of electrolyte and amidosulfate compound). The content of lithium amidosulfate and sodium amidosulfate was calculated using amidosulfate.

[0088] (Comparative Example) LiFSI and LiPF were prepared in the same manner as in each example, except that no amidosulfate compound was added to the above EMC solution containing 40% by mass of LiFSI. ６ Non-aqueous electrolytes [EC / EMC (volume ratio) = 3 / 7] were obtained for each comparative example, containing the specified molar concentration while not containing the amidosulfate compound. In these non-aqueous electrolytes, the electrolyte was dissolved, and no undissolved residue was observed visually.

[0089] [１９ F-NMR] １９ F-NMR was measured using a Varian Unity Plus-400 (internal standard: benzenesulfonyl fluoride, number of cumulative measurements: 16).

[0090] [Ion Chromatography] The non-aqueous electrolyte was diluted approximately 1000 times with ultrapure water (greater than 18.2 Ω·cm). The resulting diluted solution was measured using an ion chromatography system ICS-3000 (manufactured by Nippon Dionex Co., Ltd.). Separation mode: Ion exchange. Eluent: 7-20 mM KOH aqueous solution. Detector: Electrical conductivity detector. Column: Anion analysis column Ion PAC AS-17C (manufactured by Nippon Dionex Co., Ltd.).

[0091] [Positive electrode] LiMn ０．７ Fe ０．３ PO ４ A positive electrode slurry was prepared by weighing [LMFP-based positive electrode active material (1), commercially available], acetylene black [Denka Black (registered trademark) manufactured by Denka Co., Ltd.], and polyvinylidene fluoride resin (PVDF, manufactured by Kureha Corporation, product number: KF Polymer L#7208, solids content: 8% by weight) in a solids content ratio (mass ratio) of 100:9:6 and dispersing them in N-methylpyrrolidone (NMP) as a solvent. Subsequently, the positive electrode slurry was applied to one side of an aluminum foil (positive electrode current collector) (coating weight 20.2 mg / cm²). ２ The mixture was dried on a 130°C hot plate and then dried for 12 hours in a vacuum drying oven set to 130°C. The dried positive electrode was pressed with a roll press. As a result, a positive electrode mixture layer consisting of positive electrode slurry was formed on the positive electrode current collector, with a mixture density of 1.9 g / cm³. ３ We fabricated an LMFP-based cathode.

[0092] [Negative electrode] A water-based slurry (negative electrode slurry) was prepared using the following materials in a mass ratio of 85:15:2:1:1: graphite (OMAC-R, manufactured by Osaka Gas Chemical Co., Ltd.): graphite (SFG-15, manufactured by Imerys): carbon fiber (VGCF®, manufactured by Resonac Co., Ltd.): styrene-butadiene rubber (SBR, commercially available): carboxymethylcellulose (CMC, commercially available). Subsequently, the negative electrode slurry was applied to one side of copper foil (negative electrode current collector) (coating weight 8.8 mg / cm²). ２ The resulting material was dried in the same manner as the positive electrode and roll-pressed. As a result, a negative electrode mixture layer consisting of the negative electrode slurry was formed on the negative electrode current collector, with a mixture density of 1.5 g / cm³. ３ The negative electrode was fabricated.

[0093] [Battery Fabrication] LMFP-type positive electrode with an effective area of ​​12 cm² ２ The material was cut, and the polarity lead was welded using an ultrasonic welding machine. The negative electrode had an effective area of ​​13.44 cm². ２The polarity leads were cut and welded using an ultrasonic welding machine. These positive and negative electrodes were placed opposite each other via a 25 μm thick polyethylene separator, covered with a laminate casing, and three sides of the laminate casing were sealed. Subsequently, 500 μL of electrolyte was injected from the unsealed end, and then vacuum-sealed to produce a 4.2 V, 25 mAh laminate-type lithium-ion battery. The obtained battery was charged at room temperature (25°C, same below) at a constant current of 2.5 mA (0.1 C) for 3 hours using a charge / discharge test apparatus (Asuka Electronics Co., Ltd., part number: ACD-01, same below), and then degassed by splitting one side and vacuum-sealing it again. The degassed battery was stored at 25°C for 48 hours. The stored battery was then charged under the following conditioning conditions to complete the laminate-type lithium-ion secondary battery. (Conditioning conditions) 1st cycle charge: Constant current constant voltage charge at 2.5mA, 4.2V, terminate at 0.25mA, ⇒Discharge: Discharge at 5mA, terminate at 2.5V. 2nd cycle charge: Constant current constant voltage charge at 12.5mA, 4.2V, terminate at 0.5mA, ⇒Discharge: Discharge at 5mA, terminate at 2.5V. 3rd cycle charge: Constant current constant voltage charge at 12.5mA, 4.2V, terminate at 0.5mA, ⇒Discharge: Discharge at 25mA, terminate at 2.5V. 4th cycle charge: Constant current constant voltage charge at 12.5mA, 4.2V, terminate at 0.5mA, ⇒Discharge: Discharge at 50mA, terminate at 2.5V.

[0094] [Battery Evaluation] For each evaluation battery, a high-temperature cycle test was performed at 60°C to evaluate the capacity retention rate and DCR fluctuation (DCR increase rate). The amount of metal (Mn and Fe) leached from the LMFP positive electrode was determined by analyzing the amount of metal (Mn and Fe) deposited at the negative electrode using ICP.

[0095] (Initial DCR) Laminated lithium-ion secondary batteries were fully charged (SOC 100%) by constant current constant voltage (CCCV) charging at 25 mA (1 C) and 0.5 mA until the voltage reached 4.2 V. The 25°C DCR (initial DCR) was measured using the fully charged batteries. For the DCR measurement, the batteries were left standing for 30 minutes after full charge, then discharged at 5 mA (0.2 C) for 10 seconds. Subsequently, the batteries were left standing for another 30 minutes, then discharged at 25 mA (1 C) for 10 seconds. Finally, the batteries were left standing for another 30 minutes, then discharged at 75 mA (3 C) for 10 seconds. An I-V line was created from the relationship between each discharge current (horizontal axis) and the difference (ΔV, vertical axis) between the voltage immediately before the start of discharge and the voltage 10 seconds later at each discharge current. The slope of the I-V line was calculated as the battery's DCR.

[0096] <500 Cycles at 60°C (Cycle Characteristics)> (Cycle Test) Using a battery after initial DCR measurement, a 500-cycle test was performed in a 60°C environment under the following charge / discharge conditions. (Charge / Discharge Conditions) Charging (60°C): 4.2V, 2.5mA constant current constant voltage charge, 0.5mA termination. Discharging (60°C): 2.5mA constant current discharge, discharge termination at 2.5V.

[0097] <Capacity Retention Rate> The discharge capacity before and after the cycle was measured under the following capacity measurement conditions. The capacity retention rate was calculated as the capacity ratio of the discharge capacity after 500 cycles to the initial discharge capacity of the first cycle [(discharge capacity at 500 cycles / discharge capacity at 1 cycle) × 100]. Note that a higher capacity retention rate indicates better cycle performance and improved battery performance. (Capacity Measurement Conditions) Charging (25℃): 4.2V, 2.5mA constant current constant voltage charging, 0.5mA termination. Discharging (25℃): 2.5mA constant current discharge, discharge termination at 2.5V.

[0098] <DCR Increase Rate> Using a battery after 500 cycles (after discharge capacity measurement), the DCR (DCR after 500 cycles) was measured under the same conditions as the initial DCR. The ratio of the post-cycle DCR to the initial DCR was calculated as the DCR increase rate [(DCR after 500 cycles / initial DCR) × 100]. Note that a smaller DCR increase rate indicates that the DCR increase is suppressed and the battery performance is improved.

[0099] <Amount of metal (Mn and Fe) deposited after cycling> After 500 cycles (after DCR measurement), the battery was disassembled and the negative electrode mixture layer was peeled off from the negative electrode (and its negative electrode current collector). The deposited metal on the peeled negative electrode mixture layer was dissolved in nitric acid and diluted, for example, to about 100 times. The content of Mn and Fe in the obtained diluted solution was quantified using a multi-type ICP emission spectrometer ICPE-9000 (manufactured by Shimadzu Corporation). The quantified content of Mn and Fe corresponds to the amount of Mn and Fe eluted from the LMFP positive electrode.

[0100] <Improvement from the Same Salt Composition> <Capacity Retention Rate> In batteries equipped with a non-aqueous electrolyte with the same salt composition, the difference in capacity retention rate between each example and the comparative example (reference) (capacity retention rate of each example - capacity retention rate of the comparative example) was calculated as the degree of increase (improvement) in capacity retention rate from the same salt composition.

[0101] 《DCR Increase Rate》 In batteries equipped with a non-aqueous electrolyte having the same salt composition, the difference in the DCR increase rate between each example and the comparative example (reference) (DCR increase rate of the comparative example - DCR increase rate of each example) was calculated as the degree of reduction (improvement) in the DCR increase rate from the same salt composition.

[0102] 《Amount of metal (Mn and Fe) deposited after cycling》 In batteries equipped with a non-aqueous electrolyte of the same salt composition, the difference in the amount of metal deposited between each example and the comparative example (reference) (amount of metal deposited in the comparative example - amount of metal deposited in each example) was calculated as the degree of reduction (improvement) of the amount of metal deposited from the same salt composition.

[0103]

[0104] <Discussion> - Comparing each example with each comparative example, each having a non-aqueous electrolyte with the same salt composition except for the presence or absence of the amidosulfate compound, it was found that in each example containing a predetermined amount of the amidosulfate compound, metal (Mn and Fe) deposition during high-temperature cycling at 60°C was suppressed. Therefore, it was found that metal (Mn and Fe) elution during high-temperature cycling was further suppressed in the lithium-ion batteries of each example. - It was found that in the lithium-ion batteries of each example, the cycle capacity maintenance rate improved and the increase in DCR was suppressed during the high-temperature cycling process. - Comparing each comparative example with different LiFSI content, it was found that when the LiFSI content exceeds 0.8M, the amount of metal (Mn and Fe) deposition increases significantly. On the other hand, a comparison of Examples 1, 7, and 10, which contain similar amounts of the same amidosulfate compound but have different LiFSI content, or a comparison of Examples 2, 6, 8, and 11, revealed that even with a higher LiFSI content, the amount of metal (Mn and Fe) eluted remained almost unchanged. From these results, it was found that the higher the LiFSI content, the more effectively the amidosulfate compound acts, reducing the amount of metal (Mn and Fe) eluted. In other words, the degree of reduction (improvement) in the amount of metal (Mn and Fe) eluted increases. Therefore, it was confirmed that by further including the amidosulfate compound in the LiFSI-containing non-aqueous electrolyte, the elution of metal (Mn and Fe) from the positive electrode is further suppressed, even after high-temperature cycling at 60°C, for example. As a result, the cycle capacity maintenance rate is improved, and the increase in DCR is suppressed.

Claims

1. A lithium-ion secondary battery comprising a positive electrode having a positive electrode active material layer and a positive electrode current collector, a negative electrode having a negative electrode active material layer and a negative electrode current collector, and a non-aqueous electrolyte, wherein the positive electrode active material layer contains a positive electrode active material represented by the following formula (1), and the non-aqueous electrolyte contains an electrolyte represented by the following formula (2), a non-aqueous solvent, and at least one amidosulfuric acid compound selected from the group consisting of amidosulfuric acid, a salt of amidosulfuric acid, an amidosulfuric acid derivative represented by the following formula (3), and taurine. Li １＋ｘ Mn １－ｙ－ｚ Fe ｙ A ｚ PO ４ ... (1) [In formula (1), -0.1 < x < 0.1, 0 < y < 1.0, 0 ≤ z < 0.1, 0 < 1 - y - z, and A is at least one atom selected from the group consisting of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Ni, Co, Ga, Sn, Sb, Nb, and Ge.] LiN(X １ SO ２ )(X ２ SO ２ )... (2) [In formula (2), X １ and X ２ are the same or different and represent a fluorine atom, an alkyl group having 1 to 6 carbon atoms, or a fluoroalkyl group having 1 to 6 carbon atoms.] R １ R ２ NSO<000tmp>(OM)... (3) [In formula (3), R １ and R ２ are the same or different and represent a hydrogen atom, a hydroxyl group, an alkyl group having 1 to 10 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, an aryl group having 6 to 16 carbon atoms, an aralkyl group having 7 to 16 carbon atoms, or an alkanoyl group having 2 to 16 carbon atoms. R １ and R ２ may be bonded to each other to form a ring structure. However, when R １ is a hydrogen atom, R ２ is not a hydrogen atom. M represents a hydrogen atom or a metal atom.] It should be noted that there seems to be a typo in the original text where "<000tmp>" should probably be " ２ ". The translation has been made based on the corrected assumption.

2. The lithium-ion secondary battery according to claim 1, wherein the total content of the amidosulfate compound relative to 100% by mass of the total amount of the non-aqueous electrolyte is 0.1 ppm by mass or more and 10,000 ppm by mass or less.

3. The lithium-ion secondary battery according to claim 1, wherein the total content of the amidosulfate compound relative to 100% by mass of the total amount of the non-aqueous electrolyte is 0.1 ppm by mass or more and 600 ppm by mass or less.

4. The lithium-ion secondary battery according to claim 1, wherein the non-aqueous electrolyte contains an electrolyte represented by the following formula (4). LiPF ａ (C ｍ F ２ｍ＋１ ) ６－ａ ... (4) [In equation (4), 0 ≤ a ≤ 6 and 1 ≤ m ≤ 4.] 5. The lithium-ion secondary battery according to claim 1, wherein the non-aqueous electrolyte comprises at least one selected from the group consisting of cyclic carbonate solvents, linear carbonate solvents, cyclic ether solvents, linear ether solvents, lactone solvents, ester solvents, and nitrile solvents.

6. The lithium-ion secondary battery according to claim 1, wherein the non-aqueous electrolyte contains, in a total volume of 100% of the non-aqueous solvent, at least 90% by volume of at least one selected from the group consisting of non-fluorinated saturated cyclic carbonate solvents and non-fluorinated saturated linear carbonate solvents.

7. A lithium-ion secondary battery comprising: a positive electrode having a positive electrode mixture layer and a positive electrode current collector; a negative electrode having a negative electrode mixture layer and a negative electrode current collector; and a non-aqueous electrolyte, wherein the positive electrode mixture layer contains a positive electrode active material represented by the following formula (1), and the non-aqueous electrolyte contains an electrolyte represented by the following formula (2) and a non-aqueous solvent, characterized in that the elution of Mn and Fe from the positive electrode to the non-aqueous electrolyte is suppressed by including at least one amidosulfate compound selected from the group consisting of amidosulfate, a salt of amidosulfate, an amidosulfate derivative represented by the following formula (3), and taurine in the non-aqueous electrolyte. １＋ｘ Mn １－ｙ－ｚ Fe ｙ A ｚ PO ４ ... (1) [In equation (1), -0.1 < x < 0.1, 0 < y < 1.0, 0 ≤ z < 0.1, 0 < 1 - y - z, and A is at least one atom selected from the group consisting of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Ni, Co, Ga, Sn, Sb, Nb, and Ge.] LiN(X １ SO ２ ) (X ２ SO ２ )...(2) [In formula (2), X １ and X ２ This represents, either identically or differently, a fluorine atom, a C1-C6 alkyl group, or a C1-C6 fluoroalkyl group. １ R ２ NSO ２ (OM)...(3) [In formula (3), R １ and R ２ R represents, either identically or distinctly, a hydrogen atom, a hydroxyl group, a C1-C10 alkyl group, a C3-C10 cycloalkyl group, a C6-C16 aryl group, a C7-C16 aralkyl group, or a C2-C16 alkanoyl group. １ and R ２ They may be bonded to each other to form a ring structure. However, R １ If R is a hydrogen atom, ２ [This is not a hydrogen atom. M represents a hydrogen atom or a metal atom.]

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