Anode active material, anode material, alkali ion battery including the anode material, and method for manufacturing the anode active material

Abstract

To provide a negative electrode active material, a negative electrode material, an alkali ion battery comprising the negative electrode material, and a method of manufacturing a negative electrode active material that are capable of bringing excellent cycle characteristics on an alkali ion battery.SOLUTION: A negative electrode active material for an alkali ion battery contains metal sulfide, the metal sulfide containing at least three kinds of transition metals selected from the group consisting of Co, Ni, Zn, Mo, Mn, Cu, Fe and V. A method of manufacturing a negative electrode active material includes: a step 1 of obtaining a metal organic structure by mixing a metal source containing at least three kinds of transition metals selected from the group consisting of Co, Ni, Zn, Mo, Mn, Cu, Fe and V, and a material containing an organic ligand; and a step 2 of obtaining a product by performing heat treatment of a material containing the metal organic structure obtained in the step 1 and a sulfur source.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a negative electrode active material, a negative electrode material, an alkali ion battery including the negative electrode material, and a method for producing the negative electrode active material. [Background technology]

[0002] Metal sulfides have excellent redox reaction properties, thermal stability, and mechanical performance, making them promising compounds for use as anode active materials in alkaline ion batteries, such as high-performance sodium ion batteries (SIBs).

[0003] For example, Non-Patent Document 1 proposes the use of cobalt sulfide fixed to a sponge-like carbon matrix, synthesized by freeze-drying and hydrothermal processes, as a negative electrode material for sodium-ion batteries. Such a negative electrode material is believed to be capable of significantly improving the storage performance of sodium-ion batteries. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Chemical Engineering Journal 332 (2018) 370-376 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in recent years, there has been a strong demand in the battery field for further improvement in cycle characteristics, and accordingly, there is a demand for the development of battery materials that can provide excellent cycle characteristics. From this perspective, it can be said that the development of a negative electrode active material that can provide excellent cycle characteristics when used as a negative electrode material for alkali ion batteries is extremely important in the battery field.

[0006] The present invention has been made in view of the above, and aims to provide a negative electrode active material that can provide an alkali ion battery with excellent cycle characteristics, a negative electrode material, an alkali ion battery including the negative electrode material, and a method for manufacturing the negative electrode active material. [Means for solving the problem]

[0007] As a result of extensive research into achieving the above object, the inventors have discovered that the above object can be achieved by using a metal sulfide containing a specific transition metal, and have thus completed the present invention.

[0008] That is, the present invention includes, for example, the subject matter described in the following sections. Item 1 A negative electrode active material for an alkali ion battery, comprising: Contains metal sulfides, The metal sulfide is a negative electrode active material containing at least three transition metals selected from the group consisting of Co, Ni, Zn, Mo, Mn, Cu, Fe, and V. Section 2 Item 2. The negative electrode active material according to Item 1, wherein the metal sulfide is in particulate form. Section 3 Item 1 or 2. A negative electrode material comprising the negative electrode active material. Section 4 Item 3. An alkaline ion battery comprising the negative electrode material according to item 3. Section 5 Item 1 or 2, in the method for producing a negative electrode active material, Step 1 of obtaining a metal organic framework by mixing a metal source containing at least three transition metals selected from the group consisting of Co, Ni, Zn, Mo, Mn, Cu, Fe, and V with a raw material containing an organic ligand; Step 2: heat-treating the raw material containing the metal organic framework and the sulfur source obtained in Step 1 to obtain a product; The method for producing a negative electrode active material includes the steps of: [Effects of the Invention]

[0009] The negative electrode active material of the present invention can provide excellent cycle characteristics to an alkali ion battery. [Brief explanation of the drawings]

[0010] [Figure 1] (a) shows an SEM image of the negative electrode active material obtained in Example 1, (b) shows an SEM image of the negative electrode active material obtained in Example 2, and (c) shows an SEM image of the negative electrode active material obtained in Example 3. [Figure 2] The results of X-ray diffraction measurement (XRD) of the negative electrode active materials obtained in each example are shown. [Figure 3] The results of a constant current charge / discharge test of the batteries assembled in each production example are shown below. DETAILED DESCRIPTION OF THE INVENTION

[0011]

[0023] In the present specification, the terms "contain" and "comprise" include the concepts of "contain," "comprise," "consist essentially of," and "consist only of."

[0012] 1.Negative electrode active material The negative electrode active material of the present invention is a negative electrode active material for use in alkali ion batteries, and contains a metal sulfide. The metal sulfide contains at least three transition metals selected from the group consisting of Co, Ni, Zn, Mo, Mn, Cu, Fe, and V. The negative electrode active material of the present invention can be used as a negative electrode material for constituting an alkali ion battery (e.g., a sodium ion battery), and can provide the alkali ion battery with excellent cycle characteristics.

[0013] The metal sulfide is a sulfide containing at least three of the transition metals. The transition metals contained in the metal sulfide may be only three. Examples of metal sulfides include composite sulfides containing multiple transition metal elements. In these composite sulfides, each transition metal can exist within the sulfide framework, specifically, each transition metal can exist bonded to sulfur. In composite sulfides, two or more different transition metals can be bonded to one sulfur atom. In addition, as another embodiment of the negative electrode active material, the negative electrode active material can contain multiple metal sulfides, for example, a mixture of three or more different metal sulfides, or a mixture of a composite sulfide composed of two transition metals and a sulfide composed of one transition metal.

[0014] The metal sulfide is preferably a composite sulfide, more preferably a composite sulfide composed of three or more transition metals, in that it can provide excellent cycle characteristics to an alkali ion battery and can be produced by a simple method.

[0015] The transition metals contained in the metal sulfide preferably contain at least Co, Ni, and Zn. In this case, a negative electrode active material can be produced by a simple method, and particularly excellent cycle characteristics can be achieved in an alkali ion battery. The transition metals contained in the metal sulfide may be only three types, Co, Ni, and Zn, and among these, a composite sulfide of Co, Ni, and Zn is preferred. However, this does not exclude metal elements that are inevitably contained in the metal sulfide.

[0016] In the metal sulfide, the content ratio of each transition metal is not particularly limited, and as long as it contains at least three transition metal elements, any content ratio can be used to form the desired negative electrode active material. For example, when the metal sulfide contains Co, Ni, and Zn as described above, for example, the content of Co per 100 parts by mass of Ni is preferably 10 parts by mass or more, more preferably 50 parts by mass or more, even more preferably 80 parts by mass or more, and particularly preferably 100 parts by mass or more. Furthermore, the content of Co per 100 parts by mass of Ni is preferably 1000 parts by mass or less, more preferably 800 parts by mass or less, even more preferably 500 parts by mass or less, even more preferably 300 parts by mass or less, and particularly preferably 200 parts by mass or less.

[0017] Furthermore, when the metal sulfide contains Co, Ni, and Zn as described above, for example, the content of Zn per 100 parts by mass of Ni is preferably at least parts by mass, more preferably at least 5 parts by mass, more preferably at least 10 parts by mass, even more preferably at least 20 parts by mass, and particularly preferably at least 25 parts by mass. Furthermore, the content of Zn per 100 parts by mass of Ni is preferably at most 100 parts by mass, more preferably at most 80 parts by mass, even more preferably at most 60 parts by mass, even more preferably at most 50 parts by mass, and particularly preferably at most 40 parts by mass.

[0018] The shape of the metal sulfide is not particularly limited, and various shapes can be formed. In particular, the metal sulfide is preferably in the form of particles. In this case, the metal sulfide can take various shapes such as porous particles, hollow particles, irregular particles, spherical particles, etc.

[0019] When the metal sulfide is particulate, its average particle diameter is not particularly limited and can be, for example, 500 nm to 100 μm. In this case, the negative electrode active material is likely to provide excellent cycle characteristics to an alkali ion battery. When the metal sulfide is particulate, its average particle diameter is preferably 1 to 50 μm, more preferably 2 to 80 μm, even more preferably 3 to 60 μm, and particularly preferably 5 to 30 μm. The average particle diameter here refers to the arithmetic average of the circle-equivalent diameters measured by directly observing the metal sulfide with a scanning electron microscope and randomly selecting 50 particles.

[0020] The negative electrode active material may contain other components in addition to the metal sulfide, as long as the effects of the present invention are not impaired. Alternatively, the negative electrode active material may consist solely of the metal sulfide. The content of the metal sulfide in the negative electrode active material is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more. Whether the metal sulfide is present in the negative electrode active material can be determined from the XRD spectrum of the negative electrode active material.

[0021] The method for producing the negative electrode active material is not particularly limited. For example, the negative electrode active material of the present invention can be produced by a production method including steps 1 and 2 described below.

[0022] 2. Method for producing negative electrode active material The method for producing a negative electrode active material of the present invention can include, for example, the following steps 1 and 2. Step 1: A step of mixing a metal source containing at least three transition metals selected from the group consisting of Co, Ni, Zn, Mo, Mn, Cu, Fe, and V with a raw material containing an organic ligand to obtain a metal organic framework. Step 2: A step of obtaining a product by heat-treating a raw material containing the metal organic framework obtained in Step 1 and a sulfur source.

[0023] A negative electrode active material can be produced by a production method including the above-mentioned steps 1 and 2, and for example, the above-mentioned negative electrode active material of the present invention can be produced.

[0024] (Process 1) In step 1, a metal source containing at least three transition metals selected from the group consisting of Co, Ni, Zn, Mo, Mn, Cu, Fe, and V is mixed with a raw material containing an organic ligand.

[0025] The metal source may be a simple transition metal, a transition metal compound, or a mixture thereof, and preferably contains at least three transition metal compounds.

[0026] The type of transition metal compound is not particularly limited, and examples thereof include inorganic compounds of various transition metals, chlorides of various transition metals, and organic compounds of various transition metals. Examples of inorganic compounds of transition metals include oxides of transition metals, compounds containing oxoanions of transition metals (metallates), nitrates, sulfates, chlorides, chlorates, perchlorates, chloride complexes, carbonates, hydrogencarbonates, phosphates, and hydrogenphosphates of transition metals, and among these, nitrates are preferred as inorganic compounds of transition metals. Examples of organic compounds of transition metals include acetates, oxalates, formates, and succinates.

[0027] The metal source preferably contains at least three compounds selected from the group consisting of Co compounds, Ni compounds, Zn compounds, Mo compounds, Mn compounds, Cu compounds, Fe compounds, and V compounds, and more preferably contains at least three nitrates selected from the group consisting of Co nitrate, Ni nitrate, Zn nitrate, Mo nitrate, Mn nitrate, Cu nitrate, Fe nitrate, and V nitrate. In this case, the negative electrode active material can be produced by a simpler method. For example, the metal source used in step 1 preferably contains Co nitrate, Ni nitrate, and zinc nitrate. The transition metals contained in the metal source used in step 1 may be only Co, Ni, and Zn.

[0028] The metal source can be dissolved or dispersed in a solvent. Examples of such solvents include alcoholic solvents such as water, ethanol, and isopropanol; and ketone solvents such as acetone and methyl ethyl ketone. Other examples include N,N-dimethylformamide, glycerol, ethylene glycol, N,N-diethylformamide, N-methyl-2-pyrrolidone, acetonitrile, triethylamine, and tetrahydrofuran. The solvent may be a mixture of water and an organic solvent. By dissolving or dispersing the metal source in a solvent, the metal source containing a transition metal is in the form of a solution or dispersion.

[0029] The concentration of the metal source solution or dispersion is not particularly limited, and for example, the total concentration of the transition metals can be 1 to 1000 g / L, preferably 5 to 500 g / L, and more preferably 10 to 100 g / L.

[0030] The content ratio of each transition metal in the metal source is not particularly limited, and as long as it contains at least three transition metal elements, the desired negative electrode active material can be produced at any content ratio. For example, when the transition metals contained in the metal source include Co, Ni, and Zn, for example, the content of Co per 100 parts by mass of Ni is preferably 10 parts by mass or more, more preferably 50 parts by mass or more, even more preferably 80 parts by mass or more, and particularly preferably 100 parts by mass or more. Furthermore, the content of Co per 100 parts by mass of Ni is preferably 1000 parts by mass or less, more preferably 800 parts by mass or less, even more preferably 500 parts by mass or less, even more preferably 300 parts by mass or less, and particularly preferably 200 parts by mass or less. Furthermore, the content ratio of Zn per 100 parts by mass of Ni is preferably 1 part by mass or more, preferably 5 parts by mass or more, more preferably 10 parts by mass or more, even more preferably 20 parts by mass or more, and particularly preferably 25 parts by mass or more. Furthermore, the Zn content per 100 parts by mass of Ni is preferably 100 parts by mass or less, more preferably 80 parts by mass or less, even more preferably 60 parts by mass or less, even more preferably 50 parts by mass or less, and particularly preferably 40 parts by mass or less.

[0031] The type of organic ligand used in the raw material containing the organic ligand in step 1 is not particularly limited, and a wide variety of organic ligands capable of coordinating with a transition metal can be used. Examples include aromatic carboxylic acid compounds, imidazole compounds, and amino compounds, which are known to function as ligands.

[0032] Specific organic ligands include p-benzenedicarboxylic acid (H2BDC), o-benzenedicarboxylic acid, m-benzenedicarboxylic acid, 2,5-dihydroxyterephthalic acid (H4DOBDC), 1,3,5-benzenetricarboxylic acid (H3BTC), 1,4-benzenedicarboxylate, 2,4,6-tris(4-carboxyphenyl)-1,3,5-triazine (H3TATB), 2-aminoterephthalic acid (NH2BDC), 2-methylimidazole (2-MIM), 1- Examples of suitable organic ligands include methylimidazole (1-MIM), 1,4-bis(imidazol-1-yl)benzene (1,4-BIB), 4-(imidazol-1-yl)phthalic acid (H2IPC), 4,4'-dimethyl-2,2'-bipyridyl, 4,4'-oxybisbenzoic acid, fumaric acid, oxalic acid, succinic acid, biphenyl-3,4',5-tricarboxylic acid (BPTC), 4,4'-biphenyldicarboxylate (BPDC), and 2,5-dioxide terephthalate (DOT). One type of organic ligand may be used alone, or two or more types may be used in combination.

[0033] The organic ligand is particularly preferably p-benzenedicarboxylic acid (H2BDC) in that the resulting negative electrode active material is likely to provide excellent cycle characteristics to an alkali ion battery.

[0034] The raw material containing an organic ligand may contain a solvent. Examples of such solvents include alcoholic solvents such as water, ethanol, and isopropanol; ketone solvents such as acetone and methyl ethyl ketone; and other solvents such as N,N-dimethylformamide, glycerol, ethylene glycol, N,N-diethylformamide, N-methyl-2-pyrrolidone, acetonitrile, triethylamine, and tetrahydrofuran. The solvent may be a mixture of water and an organic solvent. When the raw material containing an organic ligand contains a solvent, the raw material containing an organic ligand is in the form of a solution or dispersion.

[0035] When the raw material containing an organic ligand contains a solvent, the total concentration of the organic ligand can be, for example, 0.1 to 100 g / L, preferably 1 to 50 g / L, and more preferably 3 to 30 g / L.

[0036] In step 1, when a metal source dissolved or dispersed in a solvent is used and the raw material containing an organic ligand contains a solvent, the solvents may be the same or different.

[0037] In step 1, raw materials including a metal source and an organic ligand are mixed together to cause a reaction between the metal source and the organic ligand, thereby producing a metal-organic framework. Examples of the metal-organic framework include various metal-organic frameworks (MOFs).

[0038] The mixing method is not particularly limited, and for example, the mixing can be performed using a known mixing means. The temperature during the mixing can be 80 to 400°C, preferably 100 to 300°C, and more preferably 120 to 200°C, and the mixing time can be appropriately selected depending on the temperature, and is, for example, 1 to 10 hours.

[0039] In the mixing treatment of step 1, the ratio of the transition metal element to the organic ligand is not particularly limited. For example, the amount of the organic ligand used is preferably 1 to 150 mass%, more preferably 5 to 100 mass%, even more preferably 10 to 80 mass%, and particularly preferably 20 to 50 mass%, relative to the total mass of the transition metal element.

[0040] A metal-organic framework (MOF) having at least three transition metal elements is obtained, for example, as a solid content by the mixing treatment in step 1. Such a solid content can be separated and washed by an appropriate method.

[0041] The metal organic framework obtained in step 1 has a structure formed using the transition metal element contained in the metal source as a constituent element.

[0042] (Process 2) In step 2, a raw material containing the metal organic framework (MOF) obtained in step 1 and a sulfur source is heat-treated. The product obtained by this heat treatment is the metal sulfide.

[0043] The sulfur source used in step 2 may be elemental sulfur (sulfur powder or sublimated sulfur) or a compound containing sulfur, but is preferably a compound containing sulfur.

[0044] Examples of sulfur-containing compounds include a wide variety of known sulfur compounds, such as thioacetamide (CHCSNH), thiourea (SC(NH)), cysteine ​​(CHNOS), sodium thiosulfate (NaS0), ammonium sulfide ((NH)S), and sodium sulfide (NaS). In addition, sulfur-containing compounds may contain a portion of the sulfur element substituted with Se and / or Te. The sulfur source may be used alone or in combination of two or more.

[0045] In step 2, the method for heat-treating the raw materials containing the metal-organic framework (MOF) obtained in step 1 and the sulfur source is not particularly limited. For example, a method can be used in which the solid metal-organic framework (MOF) and the sulfur source are placed in a reactor and heat-treated at a predetermined temperature. This heat treatment can be carried out in an air atmosphere, an inert gas atmosphere, or the like. For example, a known heating device such as a commercially available heating furnace can be used for the heat treatment.

[0046] In step 2, the temperature for the heat treatment is not particularly limited and can be, for example, 200 to 2000° C., preferably 250 to 1000° C., and more preferably 300 to 800° C. The time for the heat treatment is appropriately selected depending on the temperature and is, for example, 1 to 10 hours.

[0047] There are no particular limitations on the proportions of the metal organic framework (MOF) and the sulfur source in the raw materials used in step 2. For example, the amount of sulfur source used per 100 parts by mass of the metal organic framework (MOF) is preferably 50 to 1000 parts by mass, more preferably 80 to 800 parts by mass, and even more preferably 100 to 600 parts by mass, in that a sulfide of a transition metal is easily formed and a desired negative electrode active material is easily obtained.

[0048] The product obtained in step 2 is, for example, a metal sulfide containing at least three of the transition metal elements. A purified metal sulfide can also be obtained by treating the product obtained in step 2 by an appropriate method.

[0049] The metal sulfide obtained in step 2 can be used as the negative electrode active material of the present invention, or can be mixed with other components as needed to obtain the negative electrode active material of the present invention.

[0050] According to the production method including the above-mentioned steps 1 and 2, the negative electrode active material of the present invention can be easily obtained through simple steps, and it is a low-energy production method. Furthermore, the raw materials used in the production are inexpensive and can be obtained from abundant resources.

[0051] 3. Anode materials The negative electrode material of the present invention may contain other components as long as it contains the above-mentioned negative electrode active material, and examples thereof include known components used in negative electrode materials for alkali ion batteries (e.g., sodium ion batteries). For example, the negative electrode material of the present invention may contain a conductive additive and a binder in addition to the above-mentioned negative electrode active material.

[0052] Examples of the conductive additive include a wide range of known conductive additives used to form electrode materials for various batteries. Examples of the conductive additive include various carbon materials, such as hard carbon, soft carbon, graphene, reduced graphene oxide, natural graphite, artificial graphite, conductive carbon black, and carbon fiber. Examples of carbon fiber include carbon nanofibers and carbon nanotubes. Other conductive additives that can be used include metal powders such as copper and nickel, metal fibers, and conductive ceramic materials.

[0053] Binders include a wide range of known binders used to form electrode materials for various batteries. Examples of binders include various resin materials, such as polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), polyethylene terephthalate, polyacrylonitrile (PAN), polyvinyl alcohol (PVA), polyethylene oxide (PEO), polyethylene, and polypropylene.

[0054] The content of the negative electrode active material in the negative electrode material is not particularly limited. For example, the content of the negative electrode active material is preferably 50 to 95 mass %, more preferably 60 to 90 mass %, of the total mass of the negative electrode active material, conductive additive, and binder contained in the negative electrode material.

[0055] The content of the conductive additive in the negative electrode material is not particularly limited. For example, the conductive additive is preferably contained in an amount of 3 to 30 mass %, more preferably 5 to 20 mass %, based on the total mass of the negative electrode active material, conductive additive, and binder contained in the negative electrode material.

[0056] The content of the binder in the negative electrode material is not particularly limited. For example, the binder is preferably contained in an amount of 3 to 30 mass %, more preferably 5 to 20 mass %, based on the total mass of the negative electrode active material, conductive additive, and binder contained in the negative electrode material.

[0057] The negative electrode material may be composed of only a negative electrode active material, a conductive additive, and a binder, or may contain other components.

[0058] The method for preparing the negative electrode material is not particularly limited, and for example, a wide variety of known methods for preparing negative electrode materials can be used. For example, the negative electrode material can be prepared by mixing a negative electrode active material, a conductive additive, and a binder in a predetermined ratio using an appropriate method. When preparing the negative electrode material, a solvent can be used to disperse the negative electrode active material, the conductive additive, and the binder. Examples of the solvent include water and various organic solvents, such as lower alcohol compounds having 1 to 3 carbon atoms and NMP (N-methyl-2-pyrrolidone). When the negative electrode material contains a solvent, it is in the form of, for example, a slurry or a paste.

[0059] 4. Alkaline-ion batteries The alkali ion battery of the present invention is not particularly limited in other configuration as long as it includes the negative electrode material, and can have, for example, the same configuration as known alkali ion batteries. The type of alkali ion battery is not particularly limited, and examples include sodium secondary batteries, lithium ion batteries, and potassium secondary batteries. The alkali ion battery of the present invention is preferably a sodium battery, and more preferably a sodium ion secondary battery.

[0060] An alkali ion battery may include, for example, a positive electrode, a negative electrode, an electrolyte, and a separator. The size and shape of the battery may be determined appropriately depending on the intended use.

[0061] The positive electrode can have a structure composed of, for example, a metal foil and a positive electrode material. Examples of metals for forming the metal foil include aluminum, titanium, platinum, molybdenum, stainless steel, and copper. A wide range of known positive electrode materials can be used as the positive electrode material. For example, materials constituting the positive electrode material include sodium metal, lithium metal, NaFePO4, Na3V2(PO4)3, Na x MO4(M=Co, Mn, V, Fe), LiTiS2, LiCoO2, LiNiO2, LiMnO2, LiNi 0.33 Mn 0.33 Co 0.33 O2, LiNi 0.8 Mn 0.15 Al0.05 Examples of the cathode include O2, LiMn2O4, LiFePO4, etc. The cathode can be prepared by a known method, for example, by coating a cathode material on a metal foil.

[0062] The negative electrode may have a structure in which the negative electrode active material of the present invention is supported on a metal foil. Examples of the metal foil include aluminum, titanium, platinum, molybdenum, stainless steel, and copper. The negative electrode may be produced by a known method.

[0063] In the alkali ion battery, the type of electrolyte is not particularly limited, and for example, a known electrolyte can be used. The electrolyte may be either a solid electrolyte or a liquid electrolyte.

[0064] The liquid electrolyte may be a solution in which the electrolyte is dissolved in a solvent. The electrolyte may be various alkaline salts depending on the type of battery, such as NaPF6, NaClO4, NaCF3SO3, NaFSI, NaTFSI, LiPF6, LiClO4, LiBF4, LiBOB, LiAsF6, LiCF3SO3, LiTFSI, LiFSI, KPF6, KFSI, KTFSI, and KBF4. Other examples include known magnesium salts, aluminum salts, and zinc salts. Examples of the solvent include water, diglyme, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, propyl acetate, fluoroethylene carbonate, propylene carbonate, ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, and diethyl carbonate.

[0065] Examples of solid electrolytes include inorganic materials such as sulfides and oxides, and polymeric materials such as PEO (polyethylene oxide).

[0066] The separator may be a known separator used in secondary batteries, such as a polyolefin resin such as polyethylene or polypropylene; polyimide; polyvinyl alcohol; fluororesin such as aminated polyethylene oxide polytetrafluoroethylene; acrylic resin; nylon; aromatic aramid; inorganic glass; or ceramics. The separator may be in the form of a porous membrane, nonwoven fabric, woven fabric, or the like. Other examples of the separator include various polymer membranes and inorganic electrolytes. Examples of inorganic electrolytes include LiLaTiO3 and Li7La3Zr2O. 12 (LLZO), Na3Zr2Si2PO 12 , Na 11 Sn2PS 12 , Na3PSe4, etc. [Example]

[0067] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0068] Example 1 A mixture of 100 mg of Ni(NO3)2·6H2O, 200 mg of Co(NO3)2·6H2O, and 40 mg of Zn(NO3)2·6H2O was dispersed in 15 mL of ethylene glycol to obtain Solution 1. Separately, 90 mg of p-benzenedicarboxylic acid (H2BDC) was dispersed in 24 mL of N,N-dimethylformamide (DMF) using sonication to obtain Solution 2. Next, Solutions 1 and 2 were mixed and stirred at room temperature for 1 hour to obtain a mixed solution. This mixture was then transferred to a 50 mL Teflon-lined sealed autoclave and heated at 150 °C for 6 hours. The pale pink product formed during this heat treatment was collected by centrifugation. The solid was washed several times with DMF and ethanol and then dried in a vacuum oven at 60 °C for 12 hours to obtain a Ni-Co-Zn metal-organic framework (MOF) (Step 1).

[0069] This MOF and thioacetamide (TAA) as a sulfur source in a mass ratio of 1:5 (MOF:sulfur source) were mixed together and heated at 350°C for 2 hours in an argon atmosphere (Step 2). This resulted in a black product. The resulting black product (sulfide) was named "Co-Ni-Zn-S-1" and used as the negative electrode active material.

[0070] Example 2 A black product was obtained in the same manner as in Example 1, except that the metal source was changed to a mixture of 150 mg of Ni(NO3)2·6H2O, 150 mg of Co(NO3)2·6H2O, and 40 mg of Zn(NO3)2·6H2O. The resulting black product (sulfide) was named "Co-Ni-Zn-S-2" and used as the negative electrode active material.

[0071] Example 3 A black product was obtained in the same manner as in Example 1, except that the metal source was changed to a mixture of 200 mg of Ni(NO3)2·6H2O, 100 mg of Co(NO3)2·6H2O, and 40 mg of Zn(NO3)2·6H2O. The obtained black product (sulfide) was named "Co-Ni-Zn-S-3" and used as the negative electrode active material.

[0072] (Production Example 1) A negative electrode material was prepared using the "Co-Ni-Zn-S-1" obtained in Example 1 as the negative electrode active material, superP (conductive carbon black) as the conductive additive, and polyvinylidene fluoride (PVDF) as the binder. The mass ratio of this negative electrode material was Co-Ni-Zn-S1:superP:PVDF = 7.5:1.5:1. N-methyl-2-pyrrolidone (NMP) was added to this negative electrode material as a solvent and stirred for 12 hours to achieve uniform mixing. The resulting slurry was coated onto copper foil and dried in a vacuum at 120°C for 12 hours to produce a negative electrode. A battery was assembled using this negative electrode, a positive electrode (sodium metal with aluminum foil), a liquid electrolyte, and a separator ("Whatman GF / C glass fiber filter paper" provided by Cytiva) impregnated with the liquid electrolyte, according to a known method. The electrolyte was a 1M sodium trifluoromethanesulfonate solution, and the solvent for this solution was diglyme.

[0073] (Production Example 2) A battery was assembled in the same manner as in Preparation Example 1, except that the negative electrode active material was changed from "Co-Ni-Zn-S-1" obtained in Example 1 to "Co-Ni-Zn-S2" obtained in Example 2.

[0074] (Production Example 3) A battery was assembled in the same manner as in Preparation Example 1, except that the negative electrode active material was changed from "Co-Ni-Zn-S-1" obtained in Example 1 to "Co-Ni-Zn-S-3" obtained in Example 3.

[0075] (Evaluation results) Figure 1(a) shows an SEM image of the negative electrode active material (metal sulfide) obtained in Example 1, (b) shows an SEM image of the negative electrode active material obtained in Example 2, and (c) shows an SEM image of the negative electrode active material obtained in Example 3. These SEM images reveal that the negative electrode active material (Ni-Co-Zn sulfide) obtained in each Example is a particle with a hollow microsphere structure assembled from nanorods.

[0076] Figure 2 shows the results of X-ray diffraction measurements (XRD) of the negative electrode active materials (metal sulfides) obtained in each example. X-ray diffraction measurements were performed using a Rigaku "SmartLab" with a Cu-Kα (λ = 1.540 Å) radiation source in the 2θ range of 10 to 100°.

[0077] From the obtained XRD patterns, it was found that the diffraction peaks of Ni-Co-Zn-S1, Ni-Co-Zn-S2, and Ni-Co-Zn-S-3 all coincided with Ni3S4 (JCPDS card No. 43-1469), Co3S4 (JCPDS card No. 42-1448), and ZnS (JCPDS card No. 05-0566), and no other diffraction peaks were observed. From these results, it was found that the products (metal sulfides) obtained in each example were composite metal sulfides containing Ni, Co, and Zn.

[0078] Figure 3 shows the results of a constant current charge / discharge test of the batteries assembled in each example. This measurement was performed using a LAND battery test system "CT2001A" (Wuhan LAND electronics Co., Ltd. China). The measurement temperature was 30°C, and the applied voltage was 1.5 to 3.5 V (5 A g -1 ) was decided.

[0079] As can be seen from FIG. 3, after 300 cycles of testing, the batteries equipped with the negative electrode materials containing the negative electrode active materials of Example 1 (Ni—Co—Zn—S-1) and Example 2 (Ni—Co—Zn—S-2) showed a 2Ag -1 At a high current density of 450mAhg -1 It was also observed that the battery equipped with the negative electrode material containing the negative electrode active material of Example 3 (Ni-Co-Zn-S-3) provided a specific capacity of 2Ag -1 At a high current density of 388.5mAhg -1 It was observed that the batteries provided a specific capacity of 2Ag. Furthermore, all of the batteries equipped with the negative electrode materials containing the negative electrode active materials of Examples 1 to 3 had a coulombic efficiency of more than 90% after 300 cycles. On the other hand, the conventionally known metal sulfide consisting of only zinc and the metal sulfide consisting of only zinc and cobalt each provided a specific capacity of 2Ag after 300 cycles.-1 The specific capacities at high current densities are 173.6 and 37.6 mAhg -1 It was.

[0080] From the above, it was revealed that the negative electrode active materials containing the metal sulfides obtained in Examples 1 to 3 provide excellent cycle characteristics to alkali ion batteries. Furthermore, it is presumed that the negative electrode active material can provide excellent cycle characteristics to alkali ion batteries as long as it contains a metal sulfide containing at least three transition metals selected from the group consisting of Co, Ni, Zn, Mo, Mn, Cu, Fe, and V.

Claims

1. A negative electrode active material for an alkali ion battery, comprising: consisting only of metal sulfides, The transition metals contained in the metal sulfide are composed only of three types, Co, Ni, and Zn, and the content of Zn per 100 parts by mass of Ni is 10 parts by mass or more and 40 parts by mass or less, The metal sulfide has diffraction peaks corresponding to Ni 3 S 4 , Co 3 S 4 and ZnS obtained by X-ray diffraction (XRD) measurement, and no other diffraction peaks are observed.

2. The negative electrode active material according to claim 1 , wherein the metal sulfide is in particulate form.

3. A negative electrode material comprising the negative electrode active material according to claim 1 or 2.

4. An alkali ion battery comprising the negative electrode material of claim 3 .

5. 3. The method for producing a negative electrode active material according to claim 1 or 2, Step 1 of obtaining a metal organic framework by mixing a metal source consisting of only Co, Ni, and Zn with a raw material containing an organic ligand; Step 2: heat-treating a raw material containing the metal organic framework and a sulfur source obtained in Step 1 to obtain a product; The method for producing a negative electrode active material includes the steps of:

Images