Non-aqueous electrolytic solution for non-aqueous electrolytic solution battery, and non-aqueous electrolytic solution battery

Abstract

This non-aqueous electrolytic solution for a non-aqueous electrolytic solution battery comprises a positive electrode that contains a positive electrode active material having an olivine structure, wherein: the non-aqueous electrolytic solution contains an electrolyte and an additive different from the electrolyte; the additive is a compound represented by general formula (1); and the concentration of the additive with respect to the total amount of the non-aqueous electrolytic solution exceeds 1 mass%.

Description

Nonaqueous electrolyte for nonaqueous electrolyte battery and nonaqueous electrolyte battery

[0001] One embodiment of the present disclosure relates to a nonaqueous electrolyte for a nonaqueous electrolyte battery. Also, one embodiment of the present disclosure relates to a nonaqueous electrolyte battery.

[0002] Nonaqueous electrolyte batteries are used in a wide range of applications. In particular, lithium ion secondary batteries, which are one type of nonaqueous electrolyte battery, are small and lightweight and are therefore used as power sources for portable electronic devices such as mobile phones, smartphones, and laptop computers. In recent years, from the viewpoint of safety and cost reduction of nonaqueous electrolyte batteries, lithium iron phosphate compounds (LiFePO) with an olivine structure have been developed. ４ However, LiFePO is not widely used as a positive electrode active material. ４ In non-aqueous electrolyte batteries using iron compounds, iron contained in the positive electrode active material dissolves into the non-aqueous electrolyte and is reduced and precipitated on the negative electrode. In this case, the layer structure of the positive electrode active material changes, resulting in a decrease in capacity. Furthermore, the deposition of iron on the negative electrode increases the interfacial resistance. Therefore, various methods have been attempted to suppress iron dissolution in non-aqueous electrolyte batteries using positive electrode active materials containing iron compounds (Patent Documents 1 to 4).

[0003] Japanese Patent No. 5141582, Japanese Patent No. 5678539, Japanese Patent No. 4423888, Japanese Patent Application Laid-Open No. 2009-004357

[0004] An object of one embodiment of the present disclosure is to provide a nonaqueous electrolyte battery including a positive electrode containing a positive electrode active material having an olivine structure, in which iron deposition is suppressed.An object of another embodiment of the present disclosure is to provide a nonaqueous electrolyte battery including a positive electrode containing a positive electrode active material having an olivine structure, in which iron deposition is suppressed.

[0005] A nonaqueous electrolyte solution for a nonaqueous electrolyte battery according to one embodiment of the present disclosure is a nonaqueous electrolyte solution for a nonaqueous electrolyte battery including a positive electrode containing a positive electrode active material having an olivine structure, the nonaqueous electrolyte solution containing an electrolyte and an additive different from the electrolyte, the additive being a compound represented by the following general formula (1), and the concentration of the additive relative to the total amount of the nonaqueous electrolyte solution exceeds 1 mass %:

[0006] [In general formula (1), M ａ１＋ is an alkali metal cation, an alkaline earth metal cation, or an onium cation, and a1 represents an integer equal to the valence of the corresponding cation. a1 to d1 represent integers of 1 to 2, and a1×b1=c1×d1 is satisfied. X is a sulfur atom or a phosphorus atom, and when X is a sulfur atom, m is 2, and R ４ is absent, and when X is a phosphorus atom, m is 1. １ ~R ４ are each independently an organic group selected from a fluorine atom, an oxygen atom, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an alkenyloxy group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, an alkynyloxy group having 2 to 10 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, a cycloalkoxy group having 3 to 10 carbon atoms, a cycloalkenyl group having 3 to 10 carbon atoms, a cycloalkenyloxy group having 3 to 10 carbon atoms, an aryl group having 6 to 10 carbon atoms, and an aryloxy group having 6 to 10 carbon atoms, and the organic group may also contain a fluorine atom, an oxygen atom, or an unsaturated bond.]

[0007] In the non-aqueous electrolyte, the concentration of the additive relative to the total amount of the non-aqueous electrolyte may be 5 mass % or less.

[0008] In the non-aqueous electrolyte, the positive electrode active material having an olivine structure may be lithium iron phosphate, lithium manganese iron phosphate, sodium iron phosphate, or sodium manganese iron phosphate.

[0009] In the non-aqueous electrolyte, the additive may be at least one selected from the group consisting of (difluorophosphoryl)(fluorosulfonyl)imide salts and bis(difluorophosphoryl)imide salts.

[0010] A nonaqueous electrolyte battery according to one embodiment of the present disclosure includes a positive electrode including a positive electrode active material having an olivine structure, a negative electrode, a separator between the positive electrode and the negative electrode, and a nonaqueous electrolyte including an electrolyte and an additive different from the electrolyte, wherein the additive is a compound represented by the following general formula (1), and the concentration of the additive relative to the total amount of the nonaqueous electrolyte exceeds 1 mass %:

[0011] [In general formula (1), M ａ１＋ is an alkali metal cation, an alkaline earth metal cation, or an onium cation, and a1 represents an integer equal to the valence of the corresponding cation. a1 to d1 represent integers of 1 to 2, and a1×b1=c1×d1 is satisfied. X is a sulfur atom or a phosphorus atom, and when X is a sulfur atom, m is 2, and R ４ is absent, and when X is a phosphorus atom, m is 1. １ ~R ４ are each independently an organic group selected from a fluorine atom, an oxygen atom, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an alkenyloxy group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, an alkynyloxy group having 2 to 10 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, a cycloalkoxy group having 3 to 10 carbon atoms, a cycloalkenyl group having 3 to 10 carbon atoms, a cycloalkenyloxy group having 3 to 10 carbon atoms, an aryl group having 6 to 10 carbon atoms, and an aryloxy group having 6 to 10 carbon atoms, and the organic group may also contain a fluorine atom, an oxygen atom, or an unsaturated bond.]

[0012] In the nonaqueous electrolyte battery, the concentration of the additive relative to the total amount of the nonaqueous electrolyte may be 5 mass % or less.

[0013] In the nonaqueous electrolyte battery, the positive electrode active material having an olivine structure may be lithium iron phosphate, lithium manganese iron phosphate, sodium iron phosphate, or sodium manganese iron phosphate.

[0014] In the nonaqueous electrolyte battery, the additive may be at least one selected from the group consisting of (difluorophosphoryl)(fluorosulfonyl)imide salts and bis(difluorophosphoryl)imide salts.

[0015] In a nonaqueous electrolyte battery using a nonaqueous electrolyte according to an embodiment of the present disclosure, iron deposition is suppressed, resulting in improved charge / discharge cycle characteristics in the nonaqueous electrolyte battery.

[0016] An embodiment of the present disclosure will be described below. However, the present disclosure can be embodied in various forms without departing from the spirit of the present disclosure, and should not be construed as being limited to the description of the embodiment exemplified below.

[0017] 1. Structure of a Non-Aqueous Electrolyte Battery In an embodiment of the present disclosure, a non-aqueous electrolyte battery includes a positive electrode, a negative electrode, a separator, a non-aqueous electrolyte, and an exterior. When the non-aqueous electrolyte battery is a lithium-ion battery, the non-aqueous electrolyte battery can be charged and discharged by the movement of lithium ions from the positive electrode to the negative electrode or from the negative electrode to the positive electrode. When the non-aqueous electrolyte battery is a sodium-ion battery, the non-aqueous electrolyte battery can be charged and discharged by the movement of sodium ions from the positive electrode to the negative electrode or from the negative electrode to the positive electrode. A non-aqueous electrolyte battery has a structure in which, for example, an electrode element in which a positive electrode and a negative electrode are arranged opposite each other with a separator interposed therebetween, and a non-aqueous electrolyte are enclosed in an exterior. The shape of the non-aqueous electrolyte battery may be, but is not limited to, a coin, a cylinder, a square, a sheet, or the like. Below, the components of a non-aqueous electrolyte battery, namely, the positive electrode, the negative electrode, the separator, the non-aqueous electrolyte, and the exterior, are described in detail.

[0018] <1-1. Positive Electrode> The positive electrode includes a positive electrode active material, a conductive additive, a binder, and a positive electrode current collector. The positive electrode is fabricated by mixing the positive electrode active material, the conductive additive, and the binder, adding an organic solvent such as N-methylpyrrolidone (hereinafter sometimes referred to as "NMP") to prepare a slurry or paste, and then applying the prepared slurry or paste to one or both surfaces of a positive electrode current collector and drying it. That is, the positive electrode has a structure including the positive electrode active material, the conductive additive, and the binder formed on at least one surface of the positive electrode current collector. The mixture ratio of the positive electrode active material, the conductive additive, and the binder is, for example, 80% by mass to 99% by mass of the positive electrode active material, 1% by mass to 10% by mass of the conductive additive, and 1% by mass to 10% by mass of the binder.

[0019] In the case of lithium ion batteries, lithium iron phosphate (hereinafter referred to as "LiFePO") is used as a positive electrode active material having an olivine structure. ４ " or "LFP"). ｘ Mn １－ｙ Fe ｙ P.O. ４ , 0<x≦1, 0<y≦1", or "LMFP". In the case of a sodium ion battery, sodium iron phosphate or sodium manganese iron phosphate can be used as a positive electrode active material having an olivine structure.

[0020] The positive electrode active material having an olivine structure may further contain metal elements other than iron and manganese in addition to the lithium iron phosphate, lithium manganese iron phosphate, sodium iron phosphate, or sodium manganese iron phosphate, such as cobalt, nickel, aluminum, vanadium, and titanium.

[0021] Although details will be described later, by using the nonaqueous electrolyte according to an embodiment of the present disclosure, the elution of iron contained in the positive electrode is suppressed, and therefore the amount of iron deposited on the negative electrode and separator is also suppressed.

[0022] The conductive additive can improve the electronic conductivity between the positive electrode active materials. Examples of the conductive additive include carbon materials such as graphite, carbon nanotubes, ketjen black, and acetylene black.

[0023] The binder can bind the positive electrode active material. Examples of the binder that can be used include polyvinylidene fluoride (hereinafter, sometimes referred to as "PVDF"), polytetrafluoroethylene (hereinafter, sometimes referred to as "PTFE"), styrene butadiene rubber (hereinafter, sometimes referred to as "SBR"), carboxymethyl cellulose (hereinafter, sometimes referred to as "CMC"), and polyvinylpyrrolidone (hereinafter, sometimes referred to as "PVP").

[0024] The positive electrode current collector can be made of, for example, aluminum, titanium, an alloy thereof, or stainless steel, etc. The shape of the positive electrode current collector is, but is not limited to, a plate or foil.

[0025] <1-2. Negative Electrode> The negative electrode includes a negative electrode active material, a binder, and a negative electrode current collector. The negative electrode is produced by mixing the negative electrode active material and the binder, adding an organic solvent such as NMP to prepare a slurry or paste, and then applying the prepared slurry or paste to one or both surfaces of the negative electrode current collector and drying it. That is, the negative electrode has a structure including the negative electrode active material and the binder formed on at least one surface of the negative electrode current collector. The mixing ratio of the negative electrode active material and the binder is, for example, 80% by mass to 99% by mass of the negative electrode active material and 1% by mass to 20% by mass of the binder.

[0026] Examples of the negative electrode active material include lithium, alloys or oxides of lithium and other elements, silicon (element), silicon oxide, carbon materials, and compounds or mixtures of these. The other elements in the alloy or oxide include silicon, tin, zinc, lead, and antimony. Examples of the carbon material include graphite (natural graphite or artificial graphite), carbon nanotubes, non-graphitizable carbon, and easily graphitizable carbon. The negative electrode active material is not limited to these materials and may be any material capable of absorbing or releasing lithium ions. The shape of the negative electrode active material may be, for example, fibrous, spherical, granular, or scaly.

[0027] As the binder for the negative electrode, the same material as that for the binder for the positive electrode can be used.

[0028] The negative electrode current collector may be made of, for example, copper, nickel, titanium, an alloy thereof, or stainless steel, etc. The shape of the negative electrode current collector is, but is not limited to, a plate or foil.

[0029] The negative electrode may contain a conductive additive, which may be the same material as the conductive additive for the positive electrode.

[0030] <1-3. Separator> The separator is a film that electrically insulates the positive electrode and negative electrode and is permeable to lithium ions. The separator can be a nonwoven fabric or porous film made of polyolefins such as polyethylene (hereinafter sometimes referred to as "PE") or polypropylene (hereinafter sometimes referred to as "PP"), cellulose, paper, or glass fiber. The separator is preferably microporous so that the nonaqueous electrolyte can penetrate and ions can easily pass through.

[0031] The polyolefin separator is, for example, a microporous polymer film such as a porous polyolefin film. The porous polyolefin film may be, for example, a single-layer film using only a porous polyethylene film, or a multi-layer film in which a porous polyethylene film and a porous polypropylene film are laminated together.

[0032] <1-4. Nonaqueous Electrolyte> The nonaqueous electrolyte contains a nonaqueous solvent, an electrolyte, and an additive. The nonaqueous electrolyte is prepared by dissolving the electrolyte and the additive in the nonaqueous solvent.

[0033] Examples of non-aqueous solvents that can be used include cyclic carbonates such as propylene carbonate, ethylene carbonate, and butylene carbonate, chain carbonates such as diethyl carbonate, dimethyl carbonate, and ethyl methyl carbonate, cyclic esters such as γ-butyrolactone and γ-valerolactone, chain esters such as methyl acetate and methyl propionate, cyclic ethers such as tetrahydrofuran, 2-methyltetrahydrofuran, and dioxane, chain ethers such as dimethoxyethane and diethyl ether, and sulfone compounds or sulfoxide compounds such as dimethyl sulfoxide and sulfolane. In embodiments of the present disclosure, one type of non-aqueous solvent may be used as the non-aqueous electrolyte, or two or more types of non-aqueous solvents may be mixed and used. From the viewpoint of electrochemical stability in oxidation-reduction and chemical stability, it is preferable to use propylene carbonate (hereinafter sometimes referred to as "PC"), ethylene carbonate (hereinafter sometimes referred to as "EC"), diethyl carbonate (hereinafter sometimes referred to as "DEC"), dimethyl carbonate (hereinafter sometimes referred to as "DMC"), or ethyl methyl carbonate (hereinafter sometimes referred to as "EMC") as the non-aqueous solvent.

[0034] In the case of a lithium ion battery, the electrolyte is LiBF ４ , LiPF ６ , or LiN(SO ２ F) ２From the viewpoint of heat resistance, it is preferable to use the above-mentioned electrolytes, but other electrolytes such as LiClO ４ , LiAsF ６ , LiSbF ６ , LiCF ３ SO ３ , LiCF ３ CO ２ , Li ２ C ２ F ４ (SO ３ ) ２ , LiN(CF ３ SO ２ ) ２ , LiC(CF ３ SO ２ ) ３ , LiC ｎ F ２ｎ＋１ SO ３ (2≦n≦7), or LiN(R ｆ OSO ２ ) ２ (where R ｆ is a fluoroalkyl group.) can also be used. In the case of a sodium ion battery, NaBF ４ , NaPF ６ , or NaN(SO ２ F) ２ From the viewpoint of heat resistance, it is preferable to use the above-mentioned electrolytes, but other electrolytes such as NaClO ４ , NaAsF ６ , NaSbF ６ , NaCF ３ SO ３ , NaCF ３ CO ２ , Na ２ C ２ F ４ (SO ３ ) ２ , NaN(CF ３ SO ２ ) ２ , NaC(CF ３ SO ２ ) ３ , NaC ｎ F ２ｎ＋１ SO ３(2≦n≦7), or NaN(R ｆ OSO ２ ) ２ (where R ｆ is a fluoroalkyl group.

[0035] The total concentration of the electrolytes in the nonaqueous electrolyte solution may be 0.6 mol / L or more and 1.8 mol / L or less, preferably 0.6 mol / L or more and 1.6 mol / L or less, and more preferably 0.9 mol / L or more and 1.6 mol / L or less.

[0036] The additive is a compound represented by the following general formula (1).

[0037]

[0038] M in general formula (1) ａ１＋ Examples of the alkali metal cation represented by M include a lithium ion, a sodium ion, a potassium ion, a rubidium ion, and a cesium ion. ａ１＋ Examples of the alkaline earth metal cation represented by include magnesium ion, calcium ion, and barium ion.

[0039] M ａ１＋ Examples of the onium cation represented by the formula (I) include tetraalkylammonium, tetraalkylphosphonium, and imidazolium derivatives, etc. a1 represents the valence of the corresponding cation and may be 1 or 2.

[0040] M ａ１＋ In particular, from the viewpoint of helping ion conduction in a non-aqueous electrolyte battery, M is preferably a lithium ion, a sodium ion, a potassium ion, a tetramethylammonium ion, a tetraethylammonium ion, or a tetrabutylphosphonium ion. ａ１＋ is more preferably a lithium ion in the case of a lithium ion battery, and is more preferably a sodium ion in the case of a sodium ion battery.

[0041] Specific examples of the anion structure of the compound represented by formula (1) are shown below, but formula (1) is not limited to these.

[0042]

[0043]

[0044] In general formula (1), R １ ~R ４ are preferably all fluorine atoms. That is, the additive is preferably at least one selected from the group consisting of (difluorophosphoryl)(fluorosulfonyl)imide salts and bis(difluorophosphoryl)imide salts.

[0045] In the case of lithium ion batteries, at least one selected from the group consisting of lithium (difluorophosphoryl)(fluorosulfonyl)imide and lithium bis(difluorophosphoryl)imide is preferred, and lithium (difluorophosphoryl)(fluorosulfonyl)imide is particularly preferred. In the case of sodium ion batteries, at least one selected from the group consisting of sodium (difluorophosphoryl)(fluorosulfonyl)imide and sodium bis(difluorophosphoryl)imide is particularly preferred, and sodium (difluorophosphoryl)(fluorosulfonyl)imide is particularly preferred.

[0046] The concentration of the additive is greater than 1.0 mass% relative to the total amount of the nonaqueous electrolyte. The concentration of the additive may be 5.0 mass% or less relative to the total amount of the nonaqueous electrolyte. The concentration of the additive is preferably greater than 1.0 mass% and less than 3.0 mass%, and more preferably greater than 1.0 mass% and less than 2.0 mass%. In an embodiment of the present disclosure, adding a compound represented by general formula (1) as an additive to the nonaqueous electrolyte can suppress iron precipitation in a nonaqueous electrolyte battery, thereby improving the charge-discharge characteristics of the nonaqueous electrolyte battery. However, it is important that the concentration of the additive exceeds 1.0 mass% relative to the total amount of the nonaqueous electrolyte. By satisfying this requirement, iron precipitation can be further suppressed. Furthermore, if the concentration of the additive is 5.0 mass% or less relative to the total amount of the nonaqueous electrolyte, the charge-discharge characteristics of the nonaqueous electrolyte battery can be easily maintained. Therefore, the concentration of the additive in the nonaqueous electrolyte is preferably within the above range.

[0047] <1-5. Exterior Body> As the exterior body, a coin-shaped, cylindrical, or rectangular metal can member, or a laminate film can be used. As the metal can member, for example, steel, stainless steel, aluminum, nickel, titanium, or alloys thereof can be used. The surface of the metal can member may be nickel-plated. As the laminate film, for example, an aluminum laminate film, a stainless steel laminate film, or a silica-coated polyethylene or polypropylene laminate film can be used.

[0048] As described above, in an embodiment of the present disclosure, by adding a compound represented by general formula (1) at a predetermined concentration as an additive to a nonaqueous electrolyte, iron deposition can be suppressed in a nonaqueous electrolyte battery containing iron in the positive electrode, thereby improving the charge / discharge characteristics of the nonaqueous electrolyte battery. Although the detailed mechanism of the embodiment of the present disclosure is unknown, it is believed that the formation of a coating due to the additive on the positive electrode suppresses iron elution from the positive electrode. Furthermore, to facilitate the formation of a coating on the positive electrode, the concentration of the additive is set to be greater than 1.0 mass % relative to the total amount of the nonaqueous electrolyte.

[0049] The present disclosure will be described in more detail below based on examples. Note that the examples described below do not limit the embodiments of the present disclosure.

[0050] <1. Examples 1 and 2 and Comparative Examples 1 to 3> <1-1. Fabrication of Nonaqueous Electrolyte Battery> (1) Example 1 (Preparation of Nonaqueous Electrolyte) LiPF 6 was added to a mixed solvent of EC:EMC=3:7 by volume ratio to give a concentration of 1 mol / L. ６ In the nonaqueous electrolyte solution of Example 1, the concentration of lithium (difluorophosphoryl) (fluorosulfonyl) imide relative to the total amount of the nonaqueous electrolyte solution was 1.5 mass %.

[0051] (Preparation of Positive Electrode) 94% by mass of lithium iron phosphate powder was mixed with 2% by mass of acetylene black and 1% by mass of carbon nanotubes as conductive additives, and 3% by mass of PVDF as a binder, and NMP was further added to obtain a slurry. This slurry was applied to one side of aluminum foil and then dried at 150°C for 12 hours to form a layer containing a positive electrode active material on the current collector (hereinafter, sometimes simply referred to as the "positive electrode active material layer"), thereby obtaining a positive electrode for a nonaqueous electrolyte battery.

[0052] (Fabrication of Negative Electrode) 90% by mass of graphite powder was mixed with 10% by mass of PVDF as a binder, and NMP was further added to obtain a slurry. This slurry was applied to one side of a copper foil and then dried at 150°C for 12 hours to form a layer containing a negative electrode active material on the current collector (hereinafter, sometimes simply referred to as the "negative electrode active material layer"), thereby obtaining a negative electrode for a nonaqueous electrolyte battery.

[0053] (Fabrication of Nonaqueous Electrolyte Battery) Terminals were welded to the fabricated positive and negative electrodes. An electrode element was fabricated by sandwiching a single cellulose separator between the positive and negative electrodes so that the positive and negative active material layers faced each other. The electrode element was placed in an aluminum laminate bag with an opening on one side, and the nonaqueous electrolyte of Example 1 was vacuum-injected into it. The opening was then heat-sealed to fabricate the nonaqueous electrolyte battery of Example 1. The total area of ​​the negative electrode (i.e., the area of ​​the current collector where the negative active material layer was formed) was 20.25 cm. ２ (= 4.5 cm × 4.5 cm). The total area of ​​the positive electrode (i.e., the area of ​​the current collector where the positive electrode active material layer is formed) is 16.0 cm ２ (= 4.0 cm x 4.0 cm).

[0054] (2) Example 2 In the nonaqueous electrolyte solution of Example 2, a nonaqueous electrolyte solution was prepared so that the concentration of lithium (difluorophosphoryl) (fluorosulfonyl) imide relative to the total amount of the nonaqueous electrolyte solution was 2.0 mass %. A nonaqueous electrolyte battery of Example 2 was fabricated by the same fabrication method as in Example 1, except that the nonaqueous electrolyte solution of Example 2 was used.

[0055] (3) Comparative Example 1 The nonaqueous electrolyte of Comparative Example 1 did not dissolve lithium (difluorophosphoryl) (fluorosulfonyl) imide. That is, the concentration of lithium (difluorophosphoryl) (fluorosulfonyl) imide relative to the total amount of the nonaqueous electrolyte was 0 mass %. A nonaqueous electrolyte battery of Comparative Example 1 was fabricated using the same fabrication method as in Example 1, except that the nonaqueous electrolyte of Comparative Example 1 was used.

[0056] (4) Comparative Example 2 In the nonaqueous electrolyte solution of Comparative Example 2, a nonaqueous electrolyte solution was prepared so that the concentration of lithium (difluorophosphoryl)(fluorosulfonyl)imide relative to the total amount of the nonaqueous electrolyte solution was 0.5 mass %. A nonaqueous electrolyte battery of Comparative Example 2 was fabricated by the same fabrication method as in Example 1, except that the nonaqueous electrolyte solution of Comparative Example 2 was used.

[0057] (5) Comparative Example 3 In the nonaqueous electrolyte solution of Comparative Example 3, a nonaqueous electrolyte solution was prepared so that the concentration of lithium (difluorophosphoryl)(fluorosulfonyl)imide relative to the total amount of the nonaqueous electrolyte solution was 1.0 mass %. A nonaqueous electrolyte battery of Comparative Example 3 was fabricated by the same fabrication method as in Example 1, except that the nonaqueous electrolyte solution of Comparative Example 3 was used.

[0058] As described above, each of the nonaqueous electrolyte batteries of Examples 1 and 2 and Comparative Examples 1 to 3 contains lithium iron phosphate in the positive electrode. Furthermore, the nonaqueous electrolyte batteries of Examples 1 and 2 and Comparative Examples 1 to 3 differ in the concentration of lithium (difluorophosphoryl)(fluorosulfonyl)imide added to the nonaqueous electrolyte.

[0059] <1-2. Evaluation of non-aqueous electrolyte battery> (1) High-temperature cycle test First, at an ambient temperature of 25°C, the battery was subjected to constant current-constant voltage charging at 0.2 C up to 3.5 V, followed by constant current discharging at 0.2 C up to 2.0 V, and then left to stand for 3 hours. Thereafter, the non-aqueous electrolyte battery was subjected to 10 charge-discharge cycles at an ambient temperature of 25°C, and the non-aqueous electrolyte battery was aged. Note that in the aging, one cycle consisted of constant current-constant voltage charging at 1 C up to 3.5 V, followed by constant current discharging at 1 C down to 2.0 V.

[0060] Next, the nonaqueous electrolyte battery was subjected to a high-temperature cycle test of 200 cycles at an ambient temperature of 60°C. In the high-temperature cycle test, one cycle consisted of constant current-constant voltage charging at 3C up to 3.5V, followed by constant current discharging at 3C down to 2.0V. The discharge capacity retention rate of the nonaqueous electrolyte battery after the high-temperature cycle test was calculated, and the degree of deterioration of the nonaqueous electrolyte battery was evaluated. The discharge capacity retention rate was calculated using the following formula: Discharge capacity retention rate (%) = (discharge capacity after 200 cycles / discharge capacity after 1 cycle) x 100

[0061] (2) Evaluation of Iron Deposition After the high-temperature cycle test, the nonaqueous electrolyte battery was disassembled, and the negative electrode and separator were immersed in EMC for 1 hour to clean the negative electrode and separator and remove the nonaqueous electrolyte. The cleaned negative electrode and separator were then immersed separately in an acidic solution for 1 hour to dissolve the iron deposited on the negative electrode and separator. The immersion solution was then diluted to a specified volume, and the amount of iron in the immersion solution was measured using inductively coupled plasma (ICP) atomic emission spectrometry. The amount of iron measured by ICP atomic emission spectrometry corresponds to the amount of iron deposited on the negative electrode or the separator, allowing for evaluation of iron deposition after the high-temperature cycle test.

[0062] Table 1 shows the capacity retention rates in high-temperature cycle tests and the amount of iron deposited on the negative electrode alone in the iron deposition evaluation for the nonaqueous electrolyte batteries of Examples 1 and 2 and Comparative Examples 1 to 3. Note that the "concentration" in Tables 1 to 3 refers to the concentration of lithium (difluorophosphoryl)(fluorosulfonyl)imide, which is an additive to the nonaqueous electrolyte. Furthermore, the "amount of iron deposited per unit area of ​​negative electrode" in Table 1 was calculated as the amount of iron deposited relative to the total area of ​​the current collector in the portion where the negative electrode active material layer was formed.

[0063]

[0064] As can be seen from Table 1, the amount of iron deposited per unit area of ​​the negative electrode of the nonaqueous electrolyte batteries of Examples 1 and 2 was 0.4 μg / cm ２ On the other hand, the amount of iron deposited per unit area of ​​the negative electrode of the nonaqueous electrolyte batteries of Comparative Examples 1 to 3 was 0.4 μg / cm ２ This shows that iron precipitation is suppressed in the nonaqueous electrolyte batteries of Examples 1 and 2. The capacity retention rates of the nonaqueous electrolyte batteries of Examples 1 and 2 are also higher than the capacity retention rates of the nonaqueous electrolyte batteries of Comparative Examples 1 to 3. This suggests that the charge-discharge characteristics of the nonaqueous electrolyte batteries of Examples 1 and 2 are improved due to the suppression of iron precipitation.

[0065] Table 2 shows the results of measuring the capacity retention rate and the amount of iron deposited only on the separator of the nonaqueous electrolyte batteries in the high-temperature cycle test of Examples 1 and 2 and Comparative Examples 1 to 3. In Table 2, the "amount of iron deposited per unit area of ​​separator" is the average value for a total separator area of ​​25 cm. ２ The amount of precipitated iron was calculated per 5 cm x 5 cm.

[0066]

[0067] As can be seen from Table 2, less iron was deposited on the separators of the nonaqueous electrolytes of Examples 1 and 2 than on the separators of the nonaqueous electrolytes of Comparative Examples 1 to 3. In particular, no iron was deposited on the separator of the nonaqueous electrolyte battery of Example 2. That is, in the nonaqueous electrolyte batteries of Examples 1 and 2, iron was less likely to be deposited on the separator, which is thought to have improved the charge-discharge characteristics of the nonaqueous electrolyte batteries.

[0068] Table 3 shows the capacity retention rates in the high-temperature cycle test and the total amount of iron deposited on the negative electrode and separator in the iron deposition evaluation for the nonaqueous electrolyte batteries of Examples 1 and 2 and Comparative Examples 1 to 3. The total amount of deposition refers to the amount of iron eluted from the positive electrode. The "amount of iron eluted per unit area of ​​positive electrode" in Table 3 was calculated as the amount of iron eluted relative to the total area of ​​the current collector where the positive electrode active material layer was formed.

[0069]

[0070] As can be seen from Table 3, the amount of iron eluted per unit area of ​​the positive electrode of the nonaqueous electrolyte batteries of Examples 1 and 2 was 0.5 μg / cm ２ On the other hand, the amount of iron eluted per unit area of ​​the positive electrode of the nonaqueous electrolyte batteries of Comparative Examples 1 to 3 was 0.5 μg / cm ２exceeding 100%. Specifically, the amount of iron elution from the nonaqueous electrolyte batteries of Examples 1 and 2 is 1 / 10 or less of the amount of iron elution from the nonaqueous electrolyte battery of Comparative Example 1, which does not contain lithium (difluorophosphoryl)(fluorosulfonyl)imide. This indicates that the nonaqueous electrolyte batteries of Examples 1 and 2 suppress the elution of iron itself. Furthermore, the capacity retention rates of the nonaqueous electrolyte batteries of Examples 1 and 2 are higher than those of the nonaqueous electrolyte batteries of Comparative Examples 1 to 3. This suggests that the nonaqueous electrolyte batteries of Examples 1 and 2 suppress the elution of iron itself, thereby suppressing iron deposition on the negative electrode and separator, thereby improving charge-discharge characteristics.

[0071] 2. Examples 3 and 4 and Comparative Examples 4 to 6 2-1. Fabrication of a Non-Aqueous Electrolyte Battery (1) Example 3 LiPF was added to a mixed solvent of EC:EMC=3:7 by volume to give a concentration of 1 mol / L. ６ A nonaqueous electrolyte solution was prepared by dissolving lithium bis(difluorophosphoryl)imide in the nonaqueous electrolyte solution of Example 3, and then dissolving lithium bis(difluorophosphoryl)imide in the nonaqueous electrolyte solution of Example 3. The concentration of lithium bis(difluorophosphoryl)imide in the nonaqueous electrolyte solution of Example 3 was 1.25% by mass. A nonaqueous electrolyte battery of Example 3 was prepared by the same method as in Example 1, except that the nonaqueous electrolyte solution of Example 3 was used.

[0072] (2) Example 4 In the nonaqueous electrolyte of Example 4, the concentration of lithium bis(difluorophosphoryl)imide relative to the total amount of the nonaqueous electrolyte was prepared to be 1.5 mass %. A nonaqueous electrolyte battery of Example 4 was fabricated by the same fabrication method as in Example 1, except that the nonaqueous electrolyte of Example 4 was used.

[0073] (3) Comparative Example 4 In the nonaqueous electrolyte solution of Comparative Example 4, lithium bis(difluorophosphoryl)imide was not dissolved. That is, the concentration of lithium bis(difluorophosphoryl)imide relative to the total amount of the nonaqueous electrolyte solution was 0 mass %. A nonaqueous electrolyte battery of Comparative Example 4 was fabricated in the same manner as in Example 1, except that the nonaqueous electrolyte solution of Comparative Example 4 was used.

[0074] (4) Comparative Example 5 In the nonaqueous electrolyte solution of Comparative Example 5, a nonaqueous electrolyte solution was prepared so that the concentration of lithium bis(difluorophosphoryl)imide relative to the total amount of the nonaqueous electrolyte solution was 0.5 mass %. A nonaqueous electrolyte battery of Comparative Example 5 was fabricated by the same fabrication method as in Example 1, except that the nonaqueous electrolyte solution of Comparative Example 5 was used.

[0075] (5) Comparative Example 6 In the nonaqueous electrolyte solution of Comparative Example 6, a nonaqueous electrolyte solution was prepared so that the concentration of lithium bis(difluorophosphoryl)imide relative to the total amount of the nonaqueous electrolyte solution was 1.0 mass %. A nonaqueous electrolyte battery of Comparative Example 6 was fabricated by the same fabrication method as in Example 1, except that the nonaqueous electrolyte solution of Comparative Example 6 was used.

[0076] As described above, each of the nonaqueous electrolyte batteries of Examples 3 and 4 and Comparative Examples 4 to 6 contains lithium iron phosphate in the positive electrode. Furthermore, the nonaqueous electrolyte batteries of Examples 3 and 4 and Comparative Examples 4 to 6 differ in the concentration of lithium bis(difluorophosphoryl)imide added to the nonaqueous electrolyte.

[0077] 2-2. Evaluation of Nonaqueous Electrolyte Batteries Table 4 shows the capacity retention rates in the high-temperature cycle test and the amount of iron deposited only on the negative electrode in the iron deposition evaluation for the nonaqueous electrolyte batteries of Examples 3 and 4 and Comparative Examples 4 to 6. The conditions for the high-temperature cycle test and the iron deposition evaluation were the same as those described above. Note that the "concentration" in Tables 4 to 6 refers to the concentration of lithium bis(difluorophosphoryl)imide, an additive to the nonaqueous electrolyte.

[0078]

[0079] As can be seen from Table 4, even when the additive to the nonaqueous electrolyte is lithium bis(difluorophosphoryl)imide, the amount of iron deposited per unit area of ​​the negative electrode decreases as the concentration of lithium bis(difluorophosphoryl)imide increases. The amount of iron deposited per unit area of ​​the negative electrode in the nonaqueous electrolyte batteries of Examples 3 and 4 was 1.5 μg / cm ２ On the other hand, the amount of deposition per unit area of ​​the negative electrode of the nonaqueous electrolyte batteries of Comparative Examples 4 to 6 was 1.5 μg / cm ２The capacity retention rates of the nonaqueous electrolyte batteries of Examples 3 and 4 are higher than the capacity retention rates of the nonaqueous electrolyte batteries of Comparative Examples 4 to 6. This suggests that the charge-discharge characteristics of the nonaqueous electrolyte batteries of Examples 3 and 4 were improved due to the suppression of iron precipitation.

[0080] Table 5 shows the results of measuring the capacity retention rate and the amount of iron deposited only on the separator of the nonaqueous electrolyte batteries of Examples 3 and 4 and Comparative Examples 4 to 6 in the high-temperature cycle test.

[0081]

[0082] As can be seen from Table 5, less iron was deposited on the separators of the nonaqueous electrolyte batteries of Examples 3 and 4 than on the separators of the nonaqueous electrolyte batteries of Comparative Examples 4 to 6.

[0083] Table 6 shows the capacity retention rates in the high-temperature cycle test for Examples 3 and 4 and Comparative Examples 4 to 6, and the total amount of iron deposited on the negative electrode and separator in the iron deposition evaluation.

[0084]

[0085] As can be seen from Table 6, even when the additive to the nonaqueous electrolyte is lithium bis(difluorophosphoryl)imide, the amount of iron eluted per unit area of ​​the positive electrode decreases as the concentration of lithium bis(difluorophosphoryl)imide increases. The amount of iron eluted per unit area of ​​the positive electrode of the nonaqueous electrolyte batteries of Examples 3 and 4 was 2.5 μg / cm. ２ On the other hand, the amount of iron eluted per unit area of ​​the positive electrode of the nonaqueous electrolyte batteries of Comparative Examples 4 to 6 was 2.5 μg / cm ２ Specifically, the amount of iron elution from the nonaqueous electrolyte batteries of Examples 3 and 4 is one-third or less of the amount of iron elution from the nonaqueous electrolyte battery of Comparative Example 4, which does not contain lithium bis(difluorophosphoryl)imide. In the nonaqueous electrolyte batteries of Examples 3 and 4, the elution of iron itself is suppressed, which in turn suppresses iron deposition on the negative electrode and separator, presumably resulting in improved charge-discharge characteristics.

[0086] 3. Examples 5-7 and Comparative Examples 7-9 3-1. Fabrication of Non-Aqueous Electrolyte Batteries (1) Example 5 In Example 5, a non-aqueous electrolyte solution was prepared such that the concentration of (difluorophosphoryl)(fluorosulfonyl)imide lithium relative to the total amount of the non-aqueous electrolyte was 1.25% by mass. Furthermore, 93% by mass of manganese iron lithium phosphate powder was mixed with 3.9% by mass of carbon black and 0.1% by mass of carbon nanotubes as conductive additives, and 3% by mass of PVDF as a binder, and NMP was further added to obtain a slurry. This slurry was applied to one side of aluminum foil and then dried at 150°C for 12 hours to form a positive electrode active material layer on the current collector, thereby obtaining a positive electrode for a non-aqueous electrolyte battery. Furthermore, a non-aqueous electrolyte battery of Example 5 was fabricated using the same fabrication method as Example 1, except that the non-aqueous electrolyte and positive electrode of Example 5 were used.

[0087] (2) Example 6 In the nonaqueous electrolyte solution of Example 6, a nonaqueous electrolyte solution was prepared so that the concentration of lithium (difluorophosphoryl) (fluorosulfonyl) imide relative to the total amount of the nonaqueous electrolyte solution was 1.5 mass %. A nonaqueous electrolyte battery of Example 6 was fabricated by the same fabrication method as in Example 5, except that the nonaqueous electrolyte solution of Example 6 was used.

[0088] (3) Example 7 In the nonaqueous electrolyte of Example 7, a nonaqueous electrolyte was prepared so that the concentration of lithium (difluorophosphoryl) (fluorosulfonyl) imide relative to the total amount of the nonaqueous electrolyte was 2.0 mass %. A nonaqueous electrolyte battery of Example 7 was fabricated by the same fabrication method as in Example 5, except that the nonaqueous electrolyte of Example 7 was used.

[0089] (4) Comparative Example 7 The nonaqueous electrolyte of Comparative Example 7 did not dissolve lithium (difluorophosphoryl) (fluorosulfonyl) imide. That is, the concentration of lithium (difluorophosphoryl) (fluorosulfonyl) imide relative to the total amount of the nonaqueous electrolyte was 0 mass%. A nonaqueous electrolyte battery of Comparative Example 7 was fabricated using the same fabrication method as in Example 5, except that the nonaqueous electrolyte of Comparative Example 7 was used.

[0090] (5) Comparative Example 8 In the nonaqueous electrolyte solution of Comparative Example 8, a nonaqueous electrolyte solution was prepared so that the concentration of lithium (difluorophosphoryl)(fluorosulfonyl)imide relative to the total amount of the nonaqueous electrolyte solution was 0.5 mass %. A nonaqueous electrolyte battery of Comparative Example 8 was fabricated by the same fabrication method as in Example 5, except that the nonaqueous electrolyte solution of Comparative Example 8 was used.

[0091] (6) Comparative Example 9 In the nonaqueous electrolyte solution of Comparative Example 9, a nonaqueous electrolyte solution was prepared so that the concentration of lithium (difluorophosphoryl)(fluorosulfonyl)imide relative to the total amount of the nonaqueous electrolyte solution was 1.0 mass %. A nonaqueous electrolyte battery of Comparative Example 9 was fabricated by the same fabrication method as in Example 5, except that the nonaqueous electrolyte solution of Comparative Example 9 was used.

[0092] As described above, each of the nonaqueous electrolyte batteries of Examples 5 to 7 and Comparative Examples 7 to 9 contains lithium manganese iron phosphate in the positive electrode. Furthermore, the nonaqueous electrolyte batteries of Examples 5 to 7 and Comparative Examples 7 to 9 differ in the concentration of lithium (difluorophosphoryl)(fluorosulfonyl)imide added to the nonaqueous electrolyte.

[0093] <3-2. Evaluation of non-aqueous electrolyte batteries>

[0094] Table 7 shows the capacity retention rate in the high-temperature cycle test and the amount of iron deposited on the negative electrode only in the iron deposition evaluation for the nonaqueous electrolyte batteries of Examples 5 to 7 and Comparative Examples 7 to 9. The conditions for the high-temperature cycle test and the iron deposition evaluation were the same as those described above. Note that the "concentration" in Tables 7 to 9 refers to the concentration of lithium (difluorophosphoryl)(fluorosulfonyl)imide, which is an additive to the nonaqueous electrolyte.

[0095]

[0096] As can be seen from Table 7, even when the positive electrode active material is lithium manganese iron phosphate, the amount of iron deposited per unit area of ​​the negative electrode decreases as the concentration of lithium (difluorophosphoryl) (fluorosulfonyl) imide increases. The amount of iron deposited per unit area of ​​the negative electrode of the nonaqueous electrolyte batteries of Examples 5 to 7 was 1.0 μg / cm ２ On the other hand, the amount of deposition per unit area of ​​the negative electrode of the nonaqueous electrolyte batteries of Comparative Examples 7 to 9 was 1.0 μg / cm２ The capacity retention rates of the nonaqueous electrolyte batteries of Examples 5 to 7 are higher than the capacity retention rates of the nonaqueous electrolyte batteries of Comparative Examples 7 to 9. This suggests that the charge-discharge characteristics of the nonaqueous electrolyte batteries of Examples 5 to 7 were improved due to the suppression of iron precipitation.

[0097] Table 8 shows the results of measuring the capacity retention rate and the amount of iron deposited only on the separator of the nonaqueous electrolyte batteries of Examples 5 to 7 and Comparative Examples 7 to 9 in the high-temperature cycle test.

[0098]

[0099] As can be seen from Table 8, less iron was deposited on the separators of the nonaqueous electrolyte batteries of Examples 5 to 7 than on the separators of the nonaqueous electrolyte batteries of Comparative Examples 7 to 9.

[0100] Table 9 shows the capacity retention rates in the high-temperature cycle test for Examples 3 and 4 and Comparative Examples 4 to 6, and the total amount of iron deposited on the negative electrode and separator in the iron deposition evaluation.

[0101]

[0102] As can be seen from Table 9, even when the positive electrode active material is lithium manganese iron phosphate, the amount of iron deposited per unit area of ​​the negative electrode decreases as the concentration of lithium (difluorophosphoryl) (fluorosulfonyl) imide increases. The amount of iron leaching per unit area of ​​the positive electrode of the nonaqueous electrolyte batteries of Examples 5 to 7 was 2.0 μg / cm. ２ On the other hand, the amount of iron eluted per unit area of ​​the positive electrode of the nonaqueous electrolyte batteries of Comparative Examples 7 to 9 was 2.0 μg / cm ２ Specifically, the amount of iron elution from the nonaqueous electrolyte batteries of Examples 5 to 7 is half or less of the amount of iron elution from the nonaqueous electrolyte battery of Comparative Example 7, which does not contain lithium bis(difluorophosphoryl)(fluorosulfonyl)imide. In the nonaqueous electrolyte batteries of Examples 5 to 7, the elution of iron itself is suppressed, which in turn suppresses iron deposition on the negative electrode and separator, presumably resulting in improved charge-discharge characteristics.

[0103] 4. Examples 8 and 9 and Comparative Examples 10 to 12 4-1. Fabrication of Non-Aqueous Electrolyte Battery (1) Example 8 In the non-aqueous electrolyte solution of Example 8, a non-aqueous electrolyte solution was prepared so that the concentration of lithium bis(difluorophosphoryl)imide relative to the total amount of the non-aqueous electrolyte solution was 1.25 mass %. The non-aqueous electrolyte battery of Example 8 was fabricated in the same manner as in Example 5, except that the non-aqueous electrolyte solution of Example 8 was used.

[0104] (2) Example 9 In the nonaqueous electrolyte solution of Example 9, a nonaqueous electrolyte solution was prepared so that the concentration of lithium bis(difluorophosphoryl)imide relative to the total amount of the nonaqueous electrolyte solution was 1.5 mass %. A nonaqueous electrolyte battery of Example 9 was fabricated by the same fabrication method as in Example 5, except that the nonaqueous electrolyte solution of Example 9 was used.

[0105] (3) Comparative Example 10 In the nonaqueous electrolyte solution of Comparative Example 10, lithium bis(difluorophosphoryl)imide was not dissolved. That is, the concentration of lithium bis(difluorophosphoryl)imide relative to the total amount of the nonaqueous electrolyte solution was 0 mass %. In addition, a nonaqueous electrolyte battery of Comparative Example 10 was produced by the same production method as in Example 5, except that the nonaqueous electrolyte solution of Comparative Example 10 was used.

[0106] (4) Comparative Example 11 In the nonaqueous electrolyte solution of Comparative Example 11, a nonaqueous electrolyte solution was prepared so that the concentration of lithium bis(difluorophosphoryl)imide relative to the total amount of the nonaqueous electrolyte solution was 0.5 mass %. A nonaqueous electrolyte battery of Comparative Example 11 was fabricated by the same fabrication method as in Example 5, except that the nonaqueous electrolyte solution of Comparative Example 11 was used.

[0107] (5) Comparative Example 12 In the nonaqueous electrolyte solution of Comparative Example 12, a nonaqueous electrolyte solution was prepared so that the concentration of lithium bis(difluorophosphoryl)imide relative to the total amount of the nonaqueous electrolyte solution was 1.0 mass %. A nonaqueous electrolyte battery of Comparative Example 12 was fabricated by the same fabrication method as in Example 5, except that the nonaqueous electrolyte solution of Comparative Example 12 was used.

[0108] As described above, each of the nonaqueous electrolyte batteries of Examples 8 and 9 and Comparative Examples 10 to 12 contains lithium manganese iron phosphate in the positive electrode. Furthermore, the nonaqueous electrolyte batteries of Examples 8 and 9 and Comparative Examples 10 to 12 differ in the concentration of lithium bis(difluorophosphoryl)imide added to the nonaqueous electrolyte.

[0109] 4-2. Evaluation of Nonaqueous Electrolyte Batteries Table 10 shows the capacity retention rates in the high-temperature cycle test and the amount of iron deposited on the negative electrode only in the iron deposition evaluation for the nonaqueous electrolyte batteries of Examples 8 and 9 and Comparative Examples 10 to 12. The conditions for the high-temperature cycle test and the iron deposition evaluation were the same as those described above. Note that the "concentration" in Tables 10 to 12 refers to the concentration of lithium bis(difluorophosphoryl)imide, an additive to the nonaqueous electrolyte.

[0110]

[0111] As can be seen from Table 10, even when the positive electrode active material of the nonaqueous electrolyte is lithium manganese iron phosphate and the additive is lithium bis(difluorophosphoryl)imide, the amount of iron deposited per unit area of ​​the negative electrode decreases as the concentration of lithium bis(difluorophosphoryl)imide increases. The amount of iron deposited per unit area of ​​the negative electrode of the nonaqueous electrolyte batteries of Examples 8 and 9 was 1.5 μg / cm ２ On the other hand, the amount of deposition per unit area of ​​the negative electrode of the nonaqueous electrolyte batteries of Comparative Examples 10 to 12 was 1.5 μg / cm ２ The capacity retention rates of the nonaqueous electrolyte batteries of Examples 8 and 9 are higher than the capacity retention rates of the nonaqueous electrolyte batteries of Comparative Examples 10 to 12. This suggests that the charge-discharge characteristics of the nonaqueous electrolyte batteries of Examples 8 and 9 were improved due to the suppression of iron precipitation.

[0112] Table 11 shows the results of measuring the capacity retention rate and the amount of iron deposited only on the separator of the nonaqueous electrolyte batteries of Examples 8 and 9 and Comparative Examples 10 to 12 in the high-temperature cycle test.

[0113]

[0114] As can be seen from Table 11, less iron was deposited on the separators of the nonaqueous electrolyte batteries of Examples 8 and 9 than on the separators of the nonaqueous electrolyte batteries of Comparative Examples 10 to 12.

[0115] Table 12 shows the capacity retention rates in the high-temperature cycle test for Examples 8 and 9 and Comparative Examples 10 to 12, and the total amount of iron deposited on the negative electrode and separator in the iron deposition evaluation.

[0116]

[0117] As can be seen from Table 12, even when the positive electrode active material of the nonaqueous electrolyte is lithium manganese iron phosphate and the additive is lithium bis(difluorophosphoryl)imide, the amount of iron eluted per unit area of ​​the positive electrode decreases as the concentration of lithium bis(difluorophosphoryl)imide increases. The amount of iron eluted per unit area of ​​the positive electrode of the nonaqueous electrolyte batteries of Examples 8 and 9 was 2.5 μg / cm ２ On the other hand, the amount of iron eluted per unit area of ​​the positive electrode of the nonaqueous electrolyte batteries of Comparative Examples 4 to 6 was 2.5 μg / cm ２ Specifically, the amount of iron elution from the nonaqueous electrolyte batteries of Examples 8 and 9 was half or less of the amount of iron elution from the nonaqueous electrolyte battery of Comparative Example 10, which did not contain lithium bis(difluorophosphoryl)imide. In the nonaqueous electrolyte batteries of Examples 8 and 9, the elution of iron itself was suppressed, which in turn suppressed the deposition of iron on the negative electrode and separator, which is thought to have resulted in improved charge-discharge characteristics.

[0118] As described above based on the examples, when a nonaqueous electrolyte battery contains more than 1.0 mass % of an additive relative to the total amount of the nonaqueous electrolyte, the amount of iron elution from the nonaqueous electrolyte battery can be reduced to ½ or less, ⅓ or less, or 1 / 10 or less of the amount of iron elution from a nonaqueous electrolyte battery that does not contain an additive. That is, in the nonaqueous electrolyte battery according to the present disclosure, iron elution is suppressed, thereby suppressing iron precipitation. As a result, the charge / discharge cycle characteristics of the nonaqueous electrolyte battery according to the present disclosure are improved.

[0119] Within the scope of the concept of the present disclosure, a person skilled in the art may conceive of various modifications and alterations, and it is understood that these modifications and alterations also fall within the scope of the present disclosure. For example, even if a person skilled in the art appropriately adds, deletes, or modifies the design of components of the embodiments of the present disclosure, or adds, omits, or modifies the conditions of steps, these modifications are also included within the scope of the present disclosure as long as they include the gist of the present disclosure.

Claims

1. A nonaqueous electrolyte for a nonaqueous electrolyte battery having a positive electrode including a positive electrode active material having an olivine structure, the nonaqueous electrolyte containing an electrolyte and an additive different from the electrolyte, the additive being a compound represented by the following general formula (1), and a concentration of the additive relative to a total amount of the nonaqueous electrolyte exceeding 1 mass %. [In general formula (1), M ａ１＋ is an alkali metal cation, an alkaline earth metal cation, or an onium cation, and a1 is an integer equal to the valence of the corresponding cation. a1 to d1 are integers from 1 to 2, and a1×b1=c1×d1 is satisfied. X is a sulfur atom or a phosphorus atom, and when X is a sulfur atom, m is 2, and R ４ is absent, and when X is a phosphorus atom, m is 1. １ ~R ４ are each independently an organic group selected from a fluorine atom, an oxygen atom, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an alkenyloxy group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, an alkynyloxy group having 2 to 10 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, a cycloalkoxy group having 3 to 10 carbon atoms, a cycloalkenyl group having 3 to 10 carbon atoms, a cycloalkenyloxy group having 3 to 10 carbon atoms, an aryl group having 6 to 10 carbon atoms, and an aryloxy group having 6 to 10 carbon atoms, and the organic group may also contain a fluorine atom, an oxygen atom, or an unsaturated bond.] 2. The nonaqueous electrolyte for a nonaqueous electrolyte battery according to claim 1, wherein a concentration of the additive relative to the total amount of the nonaqueous electrolyte is 5 mass % or less.

3. The non-aqueous electrolyte for a non-aqueous electrolyte battery according to claim 1, wherein the positive electrode active material having an olivine structure is lithium iron phosphate, lithium manganese iron phosphate, sodium iron phosphate, or sodium manganese iron phosphate.

4. The nonaqueous electrolyte for a nonaqueous electrolyte battery according to claim 1, wherein the additive is at least one selected from the group consisting of (difluorophosphoryl)(fluorosulfonyl)imide salts and bis(difluorophosphoryl)imide salts.

5. A non-aqueous electrolyte battery comprising: a positive electrode including a positive electrode active material having an olivine structure; a negative electrode; a separator between the positive electrode and the negative electrode; and a non-aqueous electrolyte solution including an electrolyte and an additive different from the electrolyte, wherein the additive is a compound represented by the following general formula (1), and a concentration of the additive relative to a total amount of the non-aqueous electrolyte solution exceeds 1 mass %. [In general formula (1), M ａ１＋ is an alkali metal cation, an alkaline earth metal cation, or an onium cation, and a1 is an integer equal to the valence of the corresponding cation. a1 to d1 are integers from 1 to 2, and a1×b1=c1×d1 is satisfied. X is a sulfur atom or a phosphorus atom, and when X is a sulfur atom, m is 2, and R ４ is absent, and when X is a phosphorus atom, m is 1. １ ~R ４ are each independently an organic group selected from a fluorine atom, an oxygen atom, an alkyl group having 1 to 10 carbon atoms, an alkoxy group having 1 to 10 carbon atoms, an alkenyl group having 2 to 10 carbon atoms, an alkenyloxy group having 2 to 10 carbon atoms, an alkynyl group having 2 to 10 carbon atoms, an alkynyloxy group having 2 to 10 carbon atoms, a cycloalkyl group having 3 to 10 carbon atoms, a cycloalkoxy group having 3 to 10 carbon atoms, a cycloalkenyl group having 3 to 10 carbon atoms, a cycloalkenyloxy group having 3 to 10 carbon atoms, an aryl group having 6 to 10 carbon atoms, and an aryloxy group having 6 to 10 carbon atoms, and the organic group may also contain a fluorine atom, an oxygen atom, or an unsaturated bond.] 6. The nonaqueous electrolyte battery according to claim 5, wherein a concentration of the additive relative to the total amount of the nonaqueous electrolyte is 5 mass % or less.

7. The nonaqueous electrolyte battery according to claim 5, wherein the positive electrode active material having an olivine structure is lithium iron phosphate, lithium manganese iron phosphate, sodium iron phosphate, or sodium manganese iron phosphate.

8. The nonaqueous electrolyte battery according to claim 5, wherein the additive is at least one selected from the group consisting of (difluorophosphoryl)(fluorosulfonyl)imide salts and bis(difluorophosphoryl)imide salts.

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