Sulfide

Abstract

Disclosed is a positive electrode active material for sodium ion batteries, the positive electrode active material being a sulfide. The sulfide is a sulfide (i) represented by formula NaαiFe1-xiTMi xiS4 (in the formula, αi is 0 to 6 inclusive, xi is 0 to 0.6 inclusive, and TMi is a transition metal) or a sulfide (ii) represented by formula NaαiiFe2-xiiTMii xiiS6 (in the formula, αii is 0 to 8 inclusive, xii is 0 to 0.6 inclusive, and TMii is a transition metal). Consequently, the present invention provides a novel positive electrode active material that is useful for a sodium ion battery.

Description

sulfide

[0001] The present disclosure relates to sulfides, particularly sulfides useful as positive electrode active materials.

[0002] Recent research has reported that Na2FeS2 is useful as a positive electrode active material for all-solid-state batteries (Non-Patent Document 1).

[0003] A. Nasu et al., Small, 18 (2022) 2203383.

[0004] An object of the present disclosure is to provide a novel positive electrode active material that is useful as a positive electrode active material for sodium ion batteries.

[0005] The present disclosure includes the following aspects: [Item 1] A positive electrode active material for a sodium ion battery, which is a sulfide, wherein the sulfide is represented by the formula: Na αｉ Fe １－ｘｉ TM ｉ ｘｉ S ４ [Wherein, αi is 0 or more and 6 or less, xi is 0 or more and 0.6 or less, TM ｉ is a transition metal.] or a sulfide (i) represented by the formula: Na αｉｉ Fe ２－ｘｉｉ TM ｉｉ ｘｉｉ S ６ [Wherein, αii is 0 or more and 8 or less, xii is 0 or more and 0.6 or less, TM ｉｉ is a transition metal.] A positive electrode active material which is a sulfide (ii) represented by the formula: [Item 2] TM ｉ is Ni or Mn, TM ｉｉ is Ni or Mn. [Item 3] The cathode active material according to Item 1 or 2, wherein αi is 5 or 6, and αii is 7. [Item 4] The cathode active material according to any one of Items 1 to 3, wherein xi is 0.4 or less, and xii is 0.4 or less. [Item 5] The cathode active material according to any one of Items 1 to 4, which is for an all-solid-state sodium ion battery. [Item 6] A cathode comprising the cathode active material according to any one of Items 1 to 5. [Item 7] A battery comprising the cathode according to Item 6. [Item 8] A compound having the formula: Na αｉ Fe １－ｘｉ TMｉ ｘｉ S ４ [Wherein, αi is 0 or more and 6 or less, xi is more than 0 and 0.6 or less, TM ｉ is a transition metal.] or a sulfide (i) represented by the formula: Na αｉｉ Fe ２－ｘｉｉ TM ｉｉ ｘｉｉ S ６ [Wherein, αii is 0 or more and 8 or less, xii is 0 or more and 0.6 or less, TM ｉｉ is a transition metal.] Sulfide (ii) represented by the formula: Na αｉ Fe １－ｘｉ TM ｉ ｘｉ S ４ [Wherein, αi is 0 or more and 6 or less, xi is 0 or more and 0.6 or less, TM ｉ is a transition metal.] or a sulfide (i) represented by the formula: Na αｉｉ Fe ２－ｘｉｉ TM ｉｉ ｘｉｉ S ６ [Wherein, αii is 0 or more and 8 or less, xii is 0 or more and 0.6 or less, TM ｉｉ is a transition metal.] A method for producing a sulfide (ii) represented by the following formula: ２ S ｎ (n is 1 or more and 10 or less), Fe, S, and TM which is an optional component ｉ or TM ｉｉ Item 10: The method according to Item 9, wherein the heating step is carried out at normal pressure. [Item 11] The method according to Item 9 or 10, wherein the heating step is carried out at 500°C or higher and 1000°C or lower.

[0006] The sulfide in the present disclosure exhibits excellent charge / discharge characteristics as a positive electrode active material and is useful as a positive electrode active material for sodium ion batteries. In addition, since the sulfide in the present disclosure is mainly composed of a general-purpose element, it is inexpensive and can be industrially advantageous.

[0007] <Sulfide> [Characteristics of sulfide] The sulfide in the present disclosure (referring to sulfide (i) and / or sulfide (ii) described in detail below, the same applies hereinafter) exhibits excellent charge / discharge characteristics as a positive electrode active material and is useful as a positive electrode active material for sodium ion batteries. In addition, since the sulfide in the present disclosure is mainly composed of a general-purpose element, it is inexpensive and can be industrially advantageous.

[0008] [Composition of sulfide, etc.] The sulfide in the present disclosure has the formula: Na αｉ Fe １－ｘｉ TM ｉ ｘｉ S ４ [Wherein, αi is 0 or more and 6 or less, xi is 0 or more and 0.6 or less, TM ｉ is a transition metal.] or a sulfide (i) represented by the formula: Na αｉｉ Fe ２－ｘｉｉ TM ｉｉ ｘｉｉ S ６ [Wherein, αii is 0 or more and 8 or less, xii is 0 or more and 0.6 or less, TM ｉｉ is a transition metal.] The sulfide (ii) may be represented by the following formula:

[0009] αi and αii are the number of Na atoms contained in the sulfide, and change depending on the storage and release of Na during charge and discharge. Specifically, when a sulfide is used as a positive electrode active material of a battery, αi and αii decrease with charge and increase with discharge. It is preferable that αi and αii have larger values ​​(contain more Na) before charge and discharge (when the battery is assembled) from the viewpoint of reducing the amount of Na in the negative electrode (for example, from the viewpoint of facilitating the use of a Na-free negative electrode).

[0010] xi and xii relate to the degree of solid solution formation.

[0011] αi may be 0 or more, greater than 0, 1 or more, 2 or more, 3 or more, 4 or more, 5 or more, or 6 or more, preferably 4 or more, for example 5 or more, and may be 6 or less, 5 or less, 4 or less, 3 or less, 2 or less, or 1, in one aspect preferably 4 or more and 6 or less, for example 5 or 6.

[0012] Xi may be 0 or more, more than 0, 0.01 or more, 0.03 or more, 0.05 or more, 0.1 or more, 0.2 or more, 0.3 or more, 0.4 or more, or 0.5 or more, for example, 0.01 or more, and may be 0.6 or less, 0.55 or less, 0.45 or less, 0.35 or less, 0.25 or less, 0.15 or less, or 0.05 or less, for example, 0.4 or less, and in one aspect, 0 or more and 0.6 or less, 0.01 or more and 0.6 or less, or 0.01 or more and 0.4 or less.

[0013] TM ｉ is a transition metal and may be selected from Co, Ni, Mn, Ti, V, Cr, Cu, Zn, Zr, Nb, Mo, Ru, Pd, and Cd, such as Co, Ni, Mn, Fe, Ni, or Mn, in particular Ni or Mn.

[0014] αii may be 0 or more, greater than 0, 1 or more, 2 or more, 3 or more, 4 or more, 5 or more, 6 or more, 7 or more, or 8, preferably 5 or more, for example 6 or more, and may be 8 or less, 7 or less, 6 or less, 5 or less, 4 or less, 3 or less, 2 or less, or 1, in one aspect preferably 5 or more and 7 or less, for example 7.

[0015] xii may be 0 or more, more than 0, 0.01 or more, 0.03 or more, 0.05 or more, 0.1 or more, 0.2 or more, 0.3 or more, 0.4 or more, or 0.5 or more, for example, 0.01 or more, and may be 0.6 or less, 0.55 or less, 0.45 or less, 0.35 or less, 0.25 or less, 0.15 or less, or 0.05 or less, for example, 0.4 or less, and in one aspect, 0 or more and 0.6 or less, 0.01 or more and 0.6 or less, or 0.01 or more and 0.4 or less.

[0016] TM ｉ is a transition metal and may be selected from Co, Ni, Mn, Ti, V, Cr, Cu, Zn, Zr, Nb, Mo, Ru, Pd, and Cd, such as Co, Ni, Mn, Fe, Ni, or Mn, in particular Ni or Mn.

[0017] The sulfide in the present disclosure may be crystalline, glass, or glass ceramic (crystallized glass). Glass ceramic refers to a mixture of crystalline and amorphous materials, particularly a material having a glass phase and a crystalline phase dispersed (precipitated) in the glass phase. The crystalline content of the sulfide may be 10% by weight or more, 30% by weight or more, 50% by weight or more, or 70% by weight or more, and may be 90% by weight or less, 70% by weight or less, 50% by weight or less, or 30% by weight or less, and in one embodiment, 10% by weight or more and 90% by weight or less. The proportion of the crystalline portion can be measured by transmission electron microscope observation or crystal structure analysis by the Rietveld method, and can be adjusted by changing the heating temperature or cooling condition in the manufacturing process.

[0018] The crystalline phase of the sulfides in this disclosure may be orthorhombic, hexagonal, or triclinic. For example, Na αｉ Fe １－ｘｉ TM ｉ ｘｉ S ４ may be orthorhombic or hexagonal, and in particular, Na5FeS4 may be orthorhombic (space group Pbca), and Na6FeS4 may be hexagonal (space group P63mc). αｉｉ Fe ２－ｘｉｉ TM ｉｉ ｘｉｉ S ６ may be triclinic, and in particular Na7Fe2S6 may be triclinic (space group P1).

[0019] [Method for Producing Sulfide] The method for producing a sulfide according to the present disclosure is not particularly limited, and may include: a raw material mixing step of mixing raw materials to obtain a mixture; a heating step of heating the mixture to obtain a heat-treated product; and a cooling step of cooling the heat-treated product. In each step, an inert gas atmosphere such as a nitrogen gas atmosphere or an argon gas atmosphere is preferably used to suppress side reactions of the materials. The raw material mixing step and the heating step may be performed simultaneously.

[0020] [Raw material mixing step] In the raw material mixing step, raw materials are mixed. The mixing ratio of each raw material can be mixed so as to obtain the composition of the sulfide of the present disclosure described above.

[0021] Examples of raw materials include Na ２ S ｎ (n is 1 or more and 10 or less, and may be 8 or less, 6 or less, 4 or less, or 2 or less, for example, 1), and combinations of Fe, S, and optional transition metals in predetermined ratios.

[0022] As a mixing method, various methods that can uniformly mix the raw materials can be used, such as mortar mixing, mechanical milling, coprecipitation, a method in which the raw materials are dispersed in a solvent and then mixed, a method in which the raw materials are dispersed in a solvent at once and then mixed, etc.

[0023] [Heating step] The heating temperature in the heating step may be 250 ° C. or higher, 300 ° C. or higher, 400 ° C. or higher, 450 ° C. or higher, 500 ° C. or higher, 550 ° C. or higher, 600 ° C. or higher, 650 ° C. or higher, 700 ° C. or higher, 750 ° C. or higher, 800 ° C. or higher, 850 ° C. or higher, or 900 ° C. or higher, for example, 500 ° C. or higher, particularly 600 ° C. or higher, and may be 2000 ° C. or lower, 1500 ° C. or lower, 1200 ° C. or lower, 1000 ° C. or lower, 800 ° C. or lower, 600 ° C. or lower, or 500 ° C. or lower, for example, 1000 ° C. or lower. A temperature of not lower than the above lower limit is preferable from the viewpoint of sufficiently proceeding the reaction, and a temperature of not higher than the above upper limit is preferable from the viewpoint of suppressing loss of Na or S and side reactions between the container and the raw materials, etc.

[0024] The heating step may be carried out at atmospheric pressure without using a sealed tube process. Because it can be carried out at atmospheric pressure, the production method of the present disclosure is relatively easy to use for large-scale synthesis.

[0025] The heating rate may be 10°C / hour or more, 60°C / hour or more, 120°C / hour or more, 180°C / hour or more, 240°C / hour or more, or 300°C / hour or more, and may be 3000°C / hour or less, 2000°C / hour or less, 1500°C / hour or less, 1000°C / hour or less, or 500°C / hour or less, and in one aspect, 50°C / hour or more and 3000°C / hour or less, or 100°C / hour or more and 1000°C / hour or less. When simple substance S is contained, from the viewpoint of favorably forming low-volatile sodium polysulfide, the heating rate may be 1200°C / hour or less, particularly 600°C / hour or less.

[0026] The heating method is not particularly limited as long as the above-mentioned temperature rise rate can be realized. For example, an electric furnace, a hot plate, a muffle furnace, a high-frequency induction heating device, a rotary kiln, a sand bath, a salt bath, etc. can be used for heating. It is preferable that the heating device has a function of adjusting the temperature and time. The raw material may be in a molten state in the heating step, and it is preferable to select a heating device with a configuration that can heat-treat the melt.

[0027] The heating time in the heating step may be 0.1 hours or more, 0.5 hours or more, 1 hour or more, 2 hours or more, 2 hours or more, 4 hours or more, 6 hours or more, or 8 hours or more, for example, 0.5 hours or more, particularly 5 hours or more, and may also be 30 hours or less, 25 hours or less, 20 hours or less, 15 hours or less, 12 hours or less, 10 hours or less, 5 hours or less, or 3 hours or less, for example, 15 hours or less, and in one embodiment, 0.1 hours or more and 20 hours or less, particularly 1 hour or more and 15 hours or less. In the present disclosure, heating time means the maintenance time at the highest temperature reached. A heating time of at least the above lower limit is preferable from the viewpoint of sufficiently progressing the reaction, and a heating time of not more than the above upper limit is preferable from the viewpoint of suppressing loss of Na and S and side reactions between the container and raw materials, etc.

[0028] [Cooling Step] In the cooling step, the heat-treated product obtained in the heating step is cooled to a stable state (usually room temperature), and the cooling treatment at this time may be rapid cooling or slow cooling.

[0029] The temperature decreasing rate may be 10°C / hour or more, 60°C / hour or more, 150°C / hour or more, 300°C / hour or more, 600°C / hour or more, 1000°C / hour or more, 1000°C / hour or more, 5000°C / hour or more, 10000°C / hour or more, 15000°C / hour or more, 100,000°C / hour or more, 500,000°C / hour or more, or 1,000,000°C / hour or more, and may be 30,000°C / hour or more. The heating rate may be 100°C / hour or less, 1,000,000°C / hour or less, 500,000°C / hour or less, 100,000°C / hour or less, 50,000°C / hour or less, 10,000°C / hour or less, 1,000°C / hour or less, 500°C / hour or less, 250°C / hour or less, 100°C / hour or less, or 60°C / hour or less, and in one aspect it is 10°C / hour or more and 3,000,000°C / hour or less.

[0030] In the case of quenching, the quenching can be carried out by iron pressing (pressing with a cooling plate), pouring the melt into a cooling medium such as twin roller quenching or single roller method, spraying the melt, or the like, and from the viewpoint of vitrification, the temperature-lowering rate may be 100,000°C / hour or more, 500,000°C / hour or more, or 1,000,000°C / hour or more.

[0031] When cooling by slow cooling, examples of the cooling method include temperature control of the heat-treated product by an electric furnace program or cooling by natural heat dissipation including air cooling, and the temperature drop rate may be, for example, 50,000°C / hour or less, 10,000°C / hour or less, 5,000°C / hour or less, 3,000°C / hour or less, 1,000°C / hour or less, 500°C / hour or less, 300°C / hour or less, 300°C / hour or less, or 100°C / hour or less.

[0032] The cooling rate near the melting point and at the glass transition temperature is particularly important for crystallinity, so if you want to increase the glassiness, you can cool it quickly near the melting point and the glass transition temperature, and if you want to increase the crystallinity, you can cool it slowly near the melting point and the glass transition temperature.

[0033] <Battery Components / Batteries> [Types of Batteries, etc.] The sulfides in the present disclosure can be suitably used as a positive electrode active material for batteries, particularly sodium ion batteries. The battery (sodium ion battery) may be a battery using a liquid electrolyte or an all-solid-state battery, and is preferably an all-solid-state battery.

[0034] The shape of the battery is not particularly limited, and may be cylindrical, rectangular, or the like.

[0035] [Positive Electrode] The positive electrode includes a positive electrode active material that is the sulfide of the present disclosure. The positive electrode may include other components such as a positive electrode active material other than the sulfide of the present disclosure, an electrolyte, a conductive additive, a binder, etc. as needed.

[0036] Examples of positive electrode active materials other than sulfides in the present disclosure include materials that can absorb or release sodium ions during charge and discharge, such as sodium cobaltate (NaCoO ２ ), sodium nickelate (NaNiO ２ ), sodium manganate (NaMn ２ O ４ ), sodium iron phosphate (NaFePO ４ ), vanadium oxide-based materials, sulfur-based materials, etc., and a specific example is NaCoO ２ , NaCoN, NaMnO ２ , NaMn ２ O ４ , Na ０．４４ MnO ２ , NaNi ０．５ Mn ０．５ O ２ , NaCo １／３ Ni １／３ Mn １／３ O ２ , NaNiO ２ , NaVO ２ , NaFeO ２ , NaCrO ２ , NaVPO ４ F, Na ２ FePO ４ F, Na ３ V ２ (P.O. ４ ) ３ , Na ２ FeS ２ -Na ３ P.S. ４ , V ２ O ５ , MoO ３ , TiS ２ , FeS, InSb, CuSb, MnSb, NaSn, NaSi, NaAl, NaGe, NaSb, Na(Ni ｘ Mn １－ｘ) O ２ (0<x<1), Na(Fe ｘ Mn １－ｘ ) O ２ (0<x<1), Na １＋ｘ Mn ２－ｘ－ｙ M ｙ O ４ (M is one or more metal elements selected from Al, Mg, Co, Fe, Ni and Zn, 0<x+y<2), etc.

[0037] The amount of sulfide of the present disclosure in the positive electrode may be 10 wt% or more, 20 wt% or more, 30 wt% or more, 40 wt% or more, 60 wt% or more, 80 wt% or more, 90 wt% or more, or 95 wt% or more, for example 50 wt% or more, preferably 75 wt% or more, more preferably 85 wt% or more, particularly 90 wt% or more, and may be 100 wt% or less, 95 wt% or less, 90 wt% or less, 80 wt% or less, 70 wt% or less, 60 wt% or less, 50 wt% or less, 40 wt% or less, 30 wt% or less, or 20 wt% or less.

[0038] The amount of the positive electrode active material in the positive electrode may be 10% by weight or more, 20% by weight or more, 30% by weight or more, 40% by weight or more, 60% by weight or more, 80% by weight or more, 90% by weight or more, or 95% by weight or more, for example, 50% by weight or more, preferably 75% by weight or more, more preferably 85% by weight or more, and particularly 90% by weight or more, and may be 100% by weight or less, 95% by weight or less, 90% by weight or less, 80% by weight or less, 70% by weight or less, 60% by weight or less, 50% by weight or less, 40% by weight or less, 30% by weight or less, or 20% by weight or less.

[0039] Examples of the electrolyte include the electrolyte in the electrolyte layer described below.

[0040] The amount of electrolyte in the positive electrode may be 0.1 wt % or more, 0.3 wt % or more, 0.4 wt % or more, 0.5 wt % or more, 1 wt % or more, 3 wt % or more, 5 wt % or more, 10 wt % or more, or 20 wt % or more, and may be 30 wt % or less, 20 wt % or less, 10 wt % or less, 5 wt % or less, 3 wt % or less, 2 wt % or less, 1 wt % or less, or 0.5 wt % or less, and in one aspect, preferably 0.2 wt % or more and 10 wt % or less, and particularly 0.4 wt % or more and 2 wt % or less.

[0041] Examples of the conductive additive include carbon materials such as graphite, coke, carbon black, acicular carbon, carbon fiber, and carbon nanotubes.

[0042] The amount of the conductive additive in the positive electrode may be 0.1% by weight or more, 0.3% by weight or more, 0.4% by weight or more, 0.5% by weight or more, 1% by weight or more, 3% by weight or more, 5% by weight or more, 10% by weight or more, or 20% by weight or more, and may be 30% by weight or less, 20% by weight or less, 10% by weight or less, 5% by weight or less, 3% by weight or less, 2% by weight or less, 1% by weight or less, or 0.5% by weight or less, and in one aspect, is preferably 0.2% by weight or more and 10% by weight or less, particularly 0.4% by weight or more and 2% by weight or less.

[0043] Examples of binders include polyvinylidene fluoride (PVDF), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), polytetrafluoroethylene (PTFE), polyimide (PI), polyamide, polyamideimide, polyacrylic, styrene butadiene rubber (SBR), styrene-ethylene-butylene-styrene copolymer (SEBS), carboxymethyl cellulose (CMC), and the like. The mixing of the positive electrode raw materials may be carried out by a wet or dry method, but the sulfide of the present disclosure has poor dispersibility in organic solvents, making it difficult to form a positive electrode slurry and making it difficult to prepare a coated electrode. Therefore, a dry method is preferred, and a dry method using PTFE as a binder is particularly preferred. The use of PTFE is particularly useful in batteries that use liquid electrolytes.

[0044] The amount of binder in the positive electrode may be 0.1 wt % or more, 0.3 wt % or more, 0.4 wt % or more, 0.5 wt % or more, 1 wt % or more, 3 wt % or more, 5 wt % or more, 10 wt % or more, or 20 wt % or more, and may be 30 wt % or less, 20 wt % or less, 10 wt % or less, 5 wt % or less, 3 wt % or less, 2 wt % or less, 1 wt % or less, or 0.5 wt % or less, and in one embodiment, preferably 0.2 wt % or more and 10 wt % or less, and particularly 0.4 wt % or more and 2 wt % or less.

[0045] The positive electrode containing the above-mentioned components is connected to a positive electrode current collector made of Al, Ni, stainless steel, carbon cloth, etc. The positive electrode may be formed by coating a slurry obtained by mixing the above-mentioned components with an inert solvent on the surface of the current collector and drying the slurry.

[0046] [Negative Electrode] The negative electrode contains a negative electrode active material and may contain other components such as an electrolyte, a conductive additive, and a binder, as necessary.

[0047] Examples of negative electrode active materials are materials that can absorb or release sodium ions during charge and discharge, and include metallic sodium, carbon-based materials (activated carbon, graphite, etc.), silicon, silicon oxide, Si—SiO-based materials, and sodium titanium oxide. Specific examples include Na, Na alloys, carbon-based negative electrode active materials (hard carbon, natural graphite, artificial graphite, etc.), Sn-based negative electrode active materials (NaSn ２ , Na ２ Sn, Na ２ Sn ５ , Na １５ Sn ４、 SnO ２、 NaSnO, CaSnO ３ , BaSnO ３、 Sn ４ P ３ , SnP), sodium titanate (Na ２ Ti ３ O ７ , Na ４ Ti ５ O １２ etc.), lithium titanate (e.g., Li ２ Ti ３ O ７ , Li ４ Ti ５ O１２ etc.), Si, Si alloys, Si-based negative electrode active materials, cobalt oxide, iron sulfide, Sb, Na—Sb alloys, P, P alloys, etc.

[0048] The amount of the negative electrode active material in the negative electrode may be 10% by weight or more, 20% by weight or more, 30% by weight or more, 40% by weight or more, 60% by weight or more, 80% by weight or more, 90% by weight or more, or 95% by weight or more, for example, 50% by weight or more, preferably 75% by weight or more, more preferably 85% by weight or more, and particularly 90% by weight or more, and may be 100% by weight or less, 95% by weight or less, 90% by weight or less, 80% by weight or less, 70% by weight or less, 60% by weight or less, 50% by weight or less, 40% by weight or less, 30% by weight or less, or 20% by weight or less.

[0049] Examples of the electrolyte include the electrolyte in the electrolyte layer described below.

[0050] The amount of electrolyte in the negative electrode may be 0.5 wt % or more, 1 wt % or more, 3 wt % or more, 5 wt % or more, 10 wt % or more, 20 wt % or more, 30 wt % or more, or 40 wt % or more, and may be 80 wt % or less, 70 wt % or less, 60 wt % or less, 50 wt % or less, 40 wt % or less, 30 wt % or less, 20 wt % or less, 10 wt % or less, 5 wt % or less, or 3 wt % or less.

[0051] Examples of the conductive additive include carbon materials such as graphite, coke, carbon black, acicular carbon, carbon fiber, and carbon nanotubes.

[0052] The amount of the conductive additive in the negative electrode may be 0.1% by weight or more, 0.3% by weight or more, 0.4% by weight or more, 0.5% by weight or more, 1% by weight or more, 3% by weight or more, 5% by weight or more, 10% by weight or more, or 20% by weight or more, and may be 30% by weight or less, 20% by weight or less, 10% by weight or less, 5% by weight or less, 3% by weight or less, 2% by weight or less, 1% by weight or less, or 0.5% by weight or less, and in one aspect, is preferably 0.2% by weight or more and 10% by weight or less, particularly 0.4% by weight or more and 2% by weight or less.

[0053] Examples of binders include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), polyimide (PI), polyamide, polyamideimide, polyacrylic, styrene butadiene rubber (SBR), styrene-ethylene-butylene-styrene copolymer (SEBS), and carboxymethyl cellulose (CMC).

[0054] The amount of binder in the negative electrode may be 0.1 wt % or more, 0.3 wt % or more, 0.4 wt % or more, 0.5 wt % or more, 1 wt % or more, 3 wt % or more, 5 wt % or more, 10 wt % or more, or 20 wt % or more, and may be 30 wt % or less, 20 wt % or less, 10 wt % or less, 5 wt % or less, 3 wt % or less, 2 wt % or less, 1 wt % or less, or 0.5 wt % or less, and in one embodiment, preferably 0.2 wt % or more and 10 wt % or less, and particularly 0.4 wt % or more and 2 wt % or less.

[0055] The negative electrode containing the above-mentioned components is connected to a negative electrode current collector made of Al, Ni, Cu, stainless steel, carbon cloth, etc. The negative electrode may be formed by coating a slurry containing the above-mentioned components mixed with an inert solvent on the surface of the current collector and drying the slurry.

[0056] [Electrolyte Layer] The electrolyte layer contains an electrolyte. The electrolyte layer may contain other components such as a binder, as necessary. In the battery, the electrolyte layer is disposed so as to connect the positive electrode and the negative electrode.

[0057] The electrolyte layer can be roughly divided into a liquid electrolyte layer that mainly uses a liquid electrolyte and a solid electrolyte layer that uses a solid electrolyte.

[0058] (Liquid Electrolyte Layer) The liquid electrolyte layer is preferably composed of a mixture of an electrolyte and a non-aqueous solvent that dissolves and disperses the electrolyte.

[0059] Examples of electrolytes in the liquid electrolyte layer include NaClO ４ , NaPF ６ , NaBF ４ , NaTiF ４ , NaVF ５ , NaAsF, NaAsF６ , NaSbF ６ , NaCF ３ SO ３ , NaB(C ２ O ４ ) ２ , NaB(C ６ H ５ ) ４ , NaB １０ Cl １０ , NaB １２ Cl １２ , Na[[ID=​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​​Examples of non-aqueous solvents include carbonates, ethers, ketones, sulfolane compounds, lactones, nitriles, chlorinated hydrocarbons, amines, esters, amides, and phosphate ester compounds. Representative examples of these include 1,2-dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, ethylene carbonate, vinylene carbonate, methyl formate, dimethyl sulfoxide, propylene carbonate, acetonitrile, γ-butyrolactone, dimethylformamide, dimethyl carbonate, diethyl carbonate, sulfolane, ethyl methyl carbonate, 1,4-dioxane, 4-methyl-2-pentanone, 1,3-dioxolane, 4-methyl-1,3-dioxolane, diethyl ether, sulfolane, methyl sulfolane, propionitrile, benzonitrile, butyronitrile, valeronitrile, 1,2-dichloroethane, trimethyl phosphate, and triethyl phosphate.

[0061] The amount of electrolyte in the liquid electrolyte layer may be 0.5 wt % or more, 1 wt % or more, 3 wt % or more, 5 wt % or more, 10 wt % or more, 20 wt % or more, 30 wt % or more, or 40 wt % or more, and may be 80 wt % or less, 70 wt % or less, 60 wt % or less, 50 wt % or less, 40 wt % or less, 30 wt % or less, 20 wt % or less, 10 wt % or less, 5 wt % or less, or 3 wt % or less.

[0062] The amount of the non-aqueous solvent in the liquid electrolyte layer may be 0.5 wt % or more, 1 wt % or more, 3 wt % or more, 5 wt % or more, 10 wt % or more, 20 wt % or more, 30 wt % or more, or 40 wt % or more, and may be 80 wt % or less, 70 wt % or less, 60 wt % or less, 50 wt % or less, 40 wt % or less, 30 wt % or less, 20 wt % or less, 10 wt % or less, 5 wt % or less, or 3 wt % or less.

[0063] The liquid electrolyte layer may include a separator to prevent short-circuiting between the positive electrode and the negative electrode. Examples of the separator include polyolefin resins such as polyethylene and polypropylene, fluororesins such as polyvinylidene fluoride, nylon, cellulose acetate, nitrocellulose, polysulfone, polyacrylonitrile, aromatic aramid, and inorganic glass, and may be in the form of a porous membrane, nonwoven fabric, woven fabric, or the like.

[0064] (Solid Electrolyte Layer) Examples of solid electrolytes constituting the solid electrolyte layer are preferably known sodium ion conductive materials, such as sulfide-based solid electrolytes and oxide-based solid electrolytes. ２ S-P ２ S ５ , Na ２ S-P ２ S ５ -NaI, Na ２ S-P ２ S ５ -NaI-NaBr, Na ２ S-P ２ S ５ -Na ２ O, Na ２ S-P ２ S ５ -Na ２ O-NaI, Na ２ S-SiS ２ , Na ２ S-SiS ２ -SiO ２ , Na ２ S-SiS ２ -NaI, Na ２ S-SiS ２ -NaBr, Na ２ S-SiS ２ -NaCl, Na ２ S-SiS ２ -B ２ S ３ -NaI, Na ２ S-SiS ２ -P ２ S ５ -NaI, Na ２ S-B ２ S ３ , Na ２ S-B ２ S３ ) ２ 、a ２ [-]3 ２ . ２ 3 ３ 、a ２ 3.P ２ 3 ５ _______________________ ２ 、a ２ [-]3 ２ 、!!!! ２ 3.P ２ . ５ 、!!!! ３ . ４  ２ 3 ５ 、a ２ 3.P ２ 3 ５ 、a １０ e. ２ 3 １２ 、a ９．５４ 3) １．７４ . １．４４ 3 １１．７ . ０．３ 、a ７ . ３ 3 １１ 、a ３ 3. ４ 、a ３．２５ . ０．７５ 3 ４ 、a ６ 3. ５ 、!a ２．８８ 3) ０．８８ _ ０．１２ 3 ４、 ! ６－ｙ 3. ５－ｘ : １＋ｙ |###||||||#|)See Facebook page. ２ .. ２ . ３  ２ . ３ 、a ２ ___) ２ 、a ２ . ２ . ５ 、a ５ fi ３ () ２ . １２ 、a ７ fi ３Zr ２ O １２ , Na ３ Zr ２ Si ２ P.O. １２ , Na ６ BaLa ２ Ta ２ O １２ , Na ３．６ Si ０．６ P ０．４ O ４ or Na ３ BO ３ -Na ２ SO ４ -Na ２ CO ３ Examples of oxide-based solid electrolytes include those mentioned above.

[0065] The amount of electrolyte in the solid electrolyte layer may be 40 wt% or more, 50 wt% or more, 60 wt% or more, 70 wt% or more, 80 wt% or more, 90 wt% or more, 95 wt% or more, or 97.5 wt% or more, preferably 80 wt% or more, more preferably 95 wt% or more, and may be 100 wt% or less, 95 wt% or less, 90 wt% or less, 85 wt% or less, 80 wt% or less, 70 wt% or less, 60 wt% or less, 50 wt% or less, 40 wt% or less, 30 wt% or less, 20 wt% or less, 10 wt% or less, 5 wt% or less, or 3 wt% or less, and in one embodiment, 80 wt% or more and 100 wt% or less, particularly 95 wt% or more and 100 wt% or less.

[0066] In addition to the electrolyte material, the electrolyte layer may contain other components such as a binder, etc. Examples of binders include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP), polyimide (PI), polyamide, polyamideimide, polyacrylic, styrene-butadiene rubber (SBR), styrene-ethylene-butylene-styrene copolymer (SEBS), and carboxymethyl cellulose (CMC).

[0067] The amount of binder in the solid electrolyte layer may be 0.1 wt % or more, 0.3 wt % or more, 0.4 wt % or more, 0.5 wt % or more, 1 wt % or more, 3 wt % or more, 5 wt % or more, 10 wt % or more, or 20 wt % or more, and may be 30 wt % or less, 20 wt % or less, 10 wt % or less, 5 wt % or less, 3 wt % or less, 2 wt % or less, 1 wt % or less, or 0.5 wt % or less, and in one aspect, is preferably 0.2 wt % or more and 10 wt % or less, particularly 0.4 wt % or more and 2 wt % or less.

[0068] The solid electrolyte layer can be obtained by pressing the solid electrolyte to a predetermined thickness. The pressing pressure may be 50 to 2000 MPa.

[0069] [Method for Manufacturing a Battery] (Liquid Electrolyte Battery) When manufacturing a battery using a liquid electrolyte, for example, a sodium ion battery or secondary battery can be obtained by inserting a laminate of a positive electrode, a separator, and a negative electrode into a battery can and pouring a mixture of the electrolyte and a non-aqueous solvent into the battery can. The positive electrode, separator, and negative electrode may be laminated or wound.

[0070] (All-solid-state battery) When manufacturing an all-solid-state battery, a positive electrode, a solid electrolyte layer, a negative electrode, and a current collector are laminated and pressed to obtain a cell. The thickness of each layer may be, independently, for example, 0.1 μm or more, 1 μm or more, 10 μm or more, 100 μm or more, or 1000 μm or more, and may be 50,000 μm or less, 30,000 μm or less, 10,000 μm or less, 5,000 μm or less, 1000 μm or less, 500 μm or less, 300 μm or less, or 100 μm or less, and in one embodiment, 1 μm or more and 1000 μm or less, particularly 1 μm or more and 100 μm or less. The obtained cell is fixed to a housing as necessary.

[0071] Although the embodiments have been described above, it will be understood that various changes in form and details can be made without departing from the spirit and scope of the claims.

[0072] The present disclosure will be described in detail below with reference to examples, but the present disclosure is not limited to these examples. <Experimental Method> Since materials that are unstable to the atmosphere are mainly used, experiments were carried out in a glove box under a dry argon atmosphere unless otherwise specified below.

[0073] [Method for manufacturing all-solid-state batteries] Na5FeS4, Na5Fe 0.9 Ni 0.1 S4, Na5Fe 0.8 Ni 0.2 S4, Na5Fe 0.7 Ni 0.3 S4, Na5Fe 0.9 Mn 0.1 S4, Na6FeS4, Na6Fe 0.7 Mn 0.3 S4 or Na7Fe2S6 was used as the positive electrode active material. Na3PS4 glass ceramics was used as the solid electrolyte, and acetylene black was used as the conductive additive. The positive electrode active material, solid electrolyte, and conductive additive were mixed in a weight ratio of 40:60:6 and used as a positive electrode composite. 15 Sn4 and the conductive additive Ketjen black were composited in a 90:10 weight ratio and used as the negative electrode. 80 mg of solid electrolyte was weighed and placed on a 10 mm diameter stainless steel current collector surrounded by a polycarbonate cylinder on the sides, and the solid electrolyte was molded using a press at 36 MPa. 6 mg of the positive electrode composite was weighed on top of the molded solid electrolyte and pressed at 180 MPa for 1 minute to densify. 80 mg of the negative electrode was then weighed on top of the solid electrolyte opposite the positive electrode layer, and a stainless steel current collector was placed on top of it, and the mixture was pressed at 360 MPa for 5 minutes to densify. Finally, the two were restrained from above and below to form an all-solid-state battery.

[0074] [Method of manufacturing coin cells] Na5FeS4 was used as the positive electrode active material, acetylene black as a conductive additive, and polytetrafluoroethylene (PTFE) as a binder. The positive electrode active material, conductive additive, and binder were mixed in a weight ratio of 86:13:1. The mixture was formed into a sheet with a thickness of 150 μm and punched into a circle with a diameter of 10 mm for use as the positive electrode. NaPF6 dissolved at 1 M in a solvent containing a 1:1 volumetric mixture of ethylene carbonate and diethyl carbonate was used as the electrolyte. Metallic sodium was stretched to a thickness of 200 μm and punched into a diameter of 10 mm for use as the negative electrode. A polymer separator (CELGARD 2320) and a glass separator (Whatman TM A 2032-type coin cell was fabricated using a combination of polymer separator / glass separator / polymer separator (1820-915).

[0075] [Electronic Conductivity] A measurement cell was prepared by weighing 50 mg of the positive electrode active material and placing the stainless steel current collector on a 10 mm diameter stainless steel current collector surrounded on the sides by a polycarbonate cylinder. The current collector was then pressed at 360 MPa for 5 minutes to form a cell. DC polarization measurements were performed using this cell. The applied voltage was 0.1 V for 3600 seconds. The value at 1 second was used to calculate the electronic conductivity.

[0076] [Ionic Conductivity] 50 mg of positive electrode active material was weighed and placed on a 10 mm diameter stainless steel current collector, the sides of which were surrounded by a polycarbonate cylinder, and molded using a press at 36 MPa. 40 mg of Na3PS4 glass ceramic solid electrolyte was weighed and placed on the molded positive electrode active material, and molded using a press at 36 MPa. The other side was similarly molded with solid electrolyte added. Furthermore, Na 15 20 mg of Sn4 was added, and the mixture was pressed at 180 MPa for 1 minute. Finally, Na was applied to the opposite side in the same way. 15 20 mg of Sn4 was added and press-molded at 360 MPa for 5 minutes. 15 Sn4 / Na3PS4 glass ceramics / positive electrode active material / Na3PS4 glass ceramics / Na 15A symmetrical cell with five layers of Sn4 was fabricated and subjected to DC polarization measurements. The applied voltage was 0.1 V and the applied time was 3600 s. The ionic conductivity was calculated using the value at 3600 s.

[0077] [Charge / discharge test and cycle test] Charge / discharge test and cycle test were performed using the above-mentioned all-solid-state battery. －2 Constant current measurements were performed in the potential range of 0.6–3.2 V relative to the negative electrode at a current density of 0.1 mA cm at 25 °C. Charge / discharge tests and cycle tests were performed using the coin cell described above. －2 Constant current measurements were carried out in the potential range of 0.68-3.28 V against metallic Na at the negative electrode at a current density of 0.68-3.28 V.

[0078] [Structural analysis] [X-ray diffraction measurement] X-ray diffraction measurements were performed to identify the crystalline phase of the prepared samples. For the measurements, a fully automatic multipurpose horizontal X-ray diffractometer (Smart Lab) manufactured by Rigaku Denki Co., Ltd. was used. The powdered samples were measured using an airtight sample stage. The irradiation beam was CuKα radiation (λ = 1.54056 × 10 －10 The tube voltage was 40 kV, the tube current was 200 mA, and the scanning angle was 2θ = 5 to 80 deg. for normal measurements and 2θ = 5 to 120 deg. for measurements for Rietveld analysis. The sampling interval was 0.02 deg., and the scanning speed was 10 deg. min for normal measurements. －1 , 2 deg. min for measurements for Rietveld analysis －1 or 3 deg. min －1 It was decided.

[0079] [Rietveld Analysis] Rietveld analysis was performed to obtain detailed local structure information. Rietveld analysis is an analytical technique that uses measured diffraction intensity data and a crystal structure model as inputs, adjusting structural parameters to refine the calculated and measured diffraction intensities to match as closely as possible (Izumi Nakai and Fujio Izumi, eds., Practical Powder X-ray Analysis, 3rd Edition, Asakura Shoten, (2021) pp. 130-132). The crystal structure parameters refined are the lattice constant, atomic fractional coordinates, atomic site occupancy, and atomic displacement parameters. Other parameters derived from the measurement method, sample condition, and instrument (e.g., background, zero-point shift, sample displacement parameters, sample transmission parameters, surface roughness parameters, and profile symmetry parameters) are also refined. The actual Rietveld analysis was performed on experimental XRD patterns. The pattern fitting program used for Rietveld analysis was RIETAN-FP (F. Izumi and K. Momma, Solid State Phenom., 130 (2007) 15-20.).

[0080] Comparative Example: Preparation and Evaluation of Na2FeS2 [Synthesis] The preparation procedure for Na2FeS2 is as follows. The starting materials Na2S (NAGAO, 99.1%), Fe (Kojundo Chemical, 99.9%), and S (Kojundo Chemical, 99.99%) were mixed in a mortar under dry argon, then placed in a carbon crucible and heat-treated under a dry Ar atmosphere. After cooling, Na2FeS2 was obtained. The heating and cooling conditions and raw material composition were as follows. [Heating and cooling conditions] Rapid cooling 1. RT → 750°C (4 h) 2. 750°C (18 h) 3. 750°C → RT (iron press) [Raw material composition] Na2S:Fe:S = 1:1:1 (molar ratio)

[0081] [Rule 91 Correction 17.03.2025] [Evaluation of Structure and Properties] Figure 5-1 shows the XRD pattern of the prepared Na2FeS2. Figure 5-2 shows the electronic conductivity and ionic conductivity of the prepared Na2FeS2. Figure 5-3 shows the charge / discharge measurement results of the prepared Na2FeS2. Figure 5-4 shows the cycle test results of the prepared Na2FeS2.

[0082] Example 1: Preparation and Evaluation of Na5FeS4 [Synthesis] The preparation procedure for Na5FeS4 is as follows. The starting materials Na2S (NAGAO, 99.1%), Fe (Kojundo Chemical, 99.9%), and S (Kojundo Chemical, 99.99%) were mixed in a mortar under dry argon, then placed in a carbon crucible and heat-treated under a dry Ar atmosphere. After cooling, Na5FeS4 was obtained. The heating and cooling conditions and raw material composition were as follows. [Heating and cooling conditions] 1. R.T. → 750°C (4 h) 2. 750°C (16 h) 3. 750°C → R.T. (iron press quenching) [Raw material composition] Na2S:Fe:S = 2.5:1:1.5 (molar ratio)

[0083] [Evaluation of structure and properties] Figure 1-1 shows the XRD pattern of the prepared Na5FeS4. Figure 1-2 shows the electronic conductivity and ionic conductivity of the prepared Na5FeS4. Figure 1-3 shows the charge / discharge measurement results of the prepared Na5FeS4. Figure 1-4 shows the cycle test results of the prepared Na5FeS4. Figure 1-5 shows the crystal structure obtained from Rietveld analysis of the prepared Na5FeS4.

[0084] Unless otherwise specified, the charge / discharge measurement results are those of all-solid-state batteries. When measuring the charge / discharge characteristics of a coin cell using Na5FeS4, the capacity was approximately 450 mAh g at room temperature. -1 High capacity was confirmed.

[0085] Example 2: NaFe 1-x TM x Preparation and evaluation of S4 (TM = Ni, Mn) > [Synthesis] Na5Fe 1-x TM xThe procedure for preparing S4 (TM = Ni, Mn) is as follows. The starting materials Na2S (NAGAO, 99.1%), Fe (Kojundo Chemical, 99.9%), S (Kojundo Chemical, 99.99%), and Ni (Kojundo Chemical, 99.9%) or Mn (Wako, 98%) are mixed in a mortar under dry argon, then placed in a carbon crucible and heat-treated under a dry Ar atmosphere. After cooling, Na5Fe 1-x TM x S4 was obtained. The heating and cooling conditions and raw material composition were as follows. [Heating and cooling conditions] 1. RT → 750°C (4 h) 2. 750°C (11-12 h) 3. 750°C → RT (iron press quenching) [Raw material composition] (molar ratio)

[0086] [Evaluation of structure and properties] Figure 2-1 shows the Na5Fe 1-x TM x The XRD pattern of the prepared Na5Fe S4 is shown in Figure 2-2. 1-x TM x The electronic and ionic conductivity of the prepared Na5Fe S4 is shown in Figure 2-3. 1-x Ni x The charge / discharge measurement results of S4 are shown in Figure 2-4. 0.9 Mn 0.1 The charge / discharge measurement results and cycle test results for S4 are shown below.

[0087] Example 3: Na ７ Fe ２ S ６ Preparation and evaluation of Na ７ Fe ２ S ６ The preparation procedure is as follows: The starting materials Na2S (NAGAO, 99.1%), Fe (Kojundo Chemical, 99.9%), and S (Kojundo Chemical, 99.99%) are mixed in a mortar under dry argon, then placed in a carbon crucible, heat-treated under a dry Ar atmosphere, and cooled to obtain Na2S. ７ Fe ２ S ６The heating and cooling conditions and raw material composition were as follows: [Heating and cooling conditions] 1. RT → 750°C (4 h) 2. 750°C (18 h) 3. 750°C → RT (air cooling) [Raw material composition] Na2S:Fe:S = 3.5:2:2.5 (molar ratio)

[0088] [Evaluation of structure and properties] Figure 3-1 shows the Na ７ Fe ２ S ６ The XRD pattern of the prepared Na is shown in Figure 3-2. ７ Fe ２ S ６ The electronic conductivity and ionic conductivity of the prepared Na ７ Fe ２ S ６ The charge / discharge measurement results are shown in Figure 3-4. ７ Fe ２ S ６ The cycle test results are shown in Figure 3-5. ７ Fe ２ S ６ The crystal structure obtained from Rietveld analysis is shown below.

[0089] Example 4: NaFeMn x Preparation and evaluation of S4 > [Synthesis] Na6Fe 1-x Mn x The procedure for preparing S4 is as follows: The starting materials Na2S (NAGAO, 99.1%), Fe (Kojundo Chemical, 99.9%), S (Kojundo Chemical, 99.99%), and Mn (Wako, 98%) were mixed in a mortar under dry argon, then placed in a carbon crucible and heat-treated under a dry Ar atmosphere. After cooling, Na6Fe 1-x Mn x S4 was obtained. The heating and cooling conditions and raw material composition were as follows. [Heating and cooling conditions] 1. R.T. → 800°C (4.3 h) 2. 800°C (9 h) 3. 800°C → R.T. (air cooling) [Raw material composition] (molar ratio)

[0090] [Evaluation of structure and properties] Figure 4-1-1 shows the Na6Fe 1-x Mn x The XRD pattern of the prepared Na6Fe S4 is shown in Figure 4-1-2. 1-x Mn x The XRD pattern of S4 (enlarged view) is shown in Figure 4-1-3. 1-x Mn x The lattice constant and lattice volume change of S4 are shown in Figure 4-2. 1-x Mn x Figure 4-3-1 shows the charge / discharge measurement results of the prepared Na6FeS4. Figure 4-3-2 shows the charge / discharge measurement results of the prepared Na6Fe 0.7 Mn 0.3 Figure 4-4-1 shows the results of the charge / discharge measurement of Na6FeS4. Figure 4-4-2 shows the results of the cycle test of the Na6Fe 0.7 Mn 0.3 Figure 4-5 shows the crystal structure obtained from Rietveld analysis of the Na6FeS4 produced.

[0091] <Summary> In all examples, the synthesis of the target sulfide was confirmed from the results of XRD. Furthermore, the positive electrode active materials of all examples exhibited very high capacity and excellent reversibility. As is clear from a comparison with Na2FeS2, a comparative example containing the same element as the main component, the positive electrode active material of the present disclosure has remarkably excellent charge / discharge characteristics.

[0092] [Rule 91 Correction 17.03.2025] XRD pattern of Na5FeS4. Electronic and ionic conductivity of Na5FeS4. Charge / discharge measurement results of Na5FeS4. Cycle test results of Na5FeS4. Crystal structure obtained from Rietveld analysis of Na5FeS4. Na5Fe 1-x TM x XRD pattern of S4. Na5Fe 1-x TM x Electronic and ionic conductivity of S4. Na5Fe 1-x Ni x Charge and discharge measurement results for S4. Na5Fe 0.9 Mn 0.1Charge / discharge measurement results and cycle test results for S4. XRD pattern of Na7Fe2S6. Electronic and ionic conductivity of Na7Fe2S6. Charge / discharge measurement results for Na7Fe2S6. Cycle test results for Na7Fe2S6. Crystal structure obtained from Rietveld analysis of Na7Fe2S6. Na6Fe 1-x Mn x XRD pattern of S4. Na6Fe 1-x Mn x XRD pattern of S4 (enlarged view). Na6Fe 1-x Mn x Lattice constant and lattice volume change of S4. Na6Fe 1-x Mn x Electronic and ionic conductivity of Na6FeS4. Charge and discharge measurement results of Na6Fe 0.7 Mn 0.3 Charge and discharge measurement results for S4. Cycle test results for Na6FeS4. Na6Fe 0.7 Mn 0.3 Cycle test results for S4. Crystal structure obtained from Rietveld analysis of Na6FeS4. XRD pattern of Na2FeS2. Electronic and ionic conductivity of Na2FeS2. Charge / discharge measurement results for Na2FeS2. Cycle test results for Na2FeS2.

Claims

1. A positive electrode active material for a sodium ion battery, which is a sulfide, wherein the sulfide has the formula: Na αｉ Fe １－ｘｉ TM ｉ ｘｉ S ４ [Wherein, αi is 0 or more and 6 or less, xi is 0 or more and 0.6 or less, TM ｉ is a transition metal.] or a sulfide (i) represented by the formula: Na αｉｉ Fe ２－ｘｉｉ TM ｉｉ ｘｉｉ S ６ [Wherein, αii is 0 or more and 8 or less, xii is 0 or more and 0.6 or less, TM ｉｉ is a transition metal.] The positive electrode active material is a sulfide (ii) represented by the following formula:

2. TM ｉ is Ni or Mn, TM ｉｉ The positive electrode active material according to claim 1 , wherein is Ni or Mn.

3. The positive electrode active material according to claim 1 or 2, wherein αi is 5 or 6, and αii is 7.

4. The positive electrode active material according to any one of claims 1 to 3, wherein xi is 0.4 or less, and xii is 0.4 or less.

5. The positive electrode active material according to any one of claims 1 to 4, which is for use in an all-solid-state sodium ion battery.

6. A positive electrode comprising the positive electrode active material according to any one of claims 1 to 5.

7. A battery comprising the positive electrode according to claim 6.

8. Formula: Na αｉ Fe １－ｘｉ TM ｉ ｘｉ S ４ [Wherein, αi is 0 or more and 6 or less, xi is more than 0 and 0.6 or less, TM ｉ is a transition metal.] or a sulfide (i) represented by the formula: Na αｉｉ Fe ２－ｘｉｉ TM ｉｉ ｘｉｉ S ６ [Wherein, αii is 0 or more and 8 or less, xii is 0 or more and 0.6 or less, TM ｉｉ is a transition metal.] A sulfide (ii) represented by the following formula:

9. Formula: Na αｉ Fe １－ｘｉ TM ｉ ｘｉ S ４ [Wherein, αi is 0 or more and 6 or less, xi is 0 or more and 0.6 or less, TM ｉ is a transition metal.] or a sulfide (i) represented by the formula: Na αｉｉ Fe ２－ｘｉｉ TM ｉｉ ｘｉｉ S ６ [Wherein, αii is 0 or more and 8 or less, xii is 0 or more and 0.6 or less, TM ｉｉ is a transition metal.] A method for producing a sulfide (ii) represented by the following formula: ２ S ｎ (n is 1 or more and 10 or less), Fe, S, and TM which is an optional component ｉ or TM ｉｉ a raw material mixing step of mixing the above components to obtain a mixture; a heating step of heating the mixture to obtain a heat-treated product; and a cooling step of cooling the heat-treated product.

10. The method of claim 9, wherein the heating step is carried out at atmospheric pressure.

11. The manufacturing method according to claim 9 or 10, wherein the heating step is carried out at 500°C or higher and 1000°C or lower.

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