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 including the negative electrode material, and a method of manufacturing a negative electrode active material that can give excellent capacity characteristics and cycle characteristics to the alkali ion battery.SOLUTION: A negative electrode active material for an alkali ion battery contains metal sulfide doped with carbon and nitrogen. A metal in the metal sulfide contains at least one kind selected from the group consisting of Co, Cr, Ni, and Fe.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 alkali-ion batteries, such as high-performance sodium-ion batteries (SIBs).

[0003] For example, Non-Patent Document 1 proposes the use of a composite of cobalt sulfide (Co3S4) and graphene as an anode material for sodium-ion batteries. Such an anode material is believed to be capable of significantly improving the storage performance of sodium-ion batteries. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Journal of Materials Chemistry A 2015,3(13),6787 Summary of the Invention [Problem to be solved by the invention]

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

[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 capacity characteristics and 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 specific metal sulfide doped with carbon and nitrogen as a constituent component, 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: containing a metal sulfide doped with carbon and nitrogen, The metal in the metal sulfide contains at least one metal selected from the group consisting of Co, Cr, Ni, and Fe. Section 2 Item 2. The negative electrode active material according to Item 1, wherein the metal sulfide is a porous particle. Section 3 The BET specific surface area of ​​the metal sulfide is 15m 2 Item 3. The negative electrode active material according to Item 1 or 2, wherein the negative electrode active material has a densitometric value of 1 / g or more. Section 4 Item 4. A negative electrode material comprising the negative electrode active material according to any one of items 1 to 3. Section 5 Item 5. An alkaline ion battery comprising the negative electrode material according to item 4. Section 6 Item 1 to 3, a method for producing a negative electrode active material according to any one of items 1 to 3, Step 1: obtaining a precursor by reacting a metal source containing at least one metal selected from the group consisting of Co, Cr, Ni, and Fe with an organic acid salt; Step 2: heat treating the precursor in the presence of a sulfur source; 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 capacity characteristics and cycle characteristics to an alkali ion battery. [Brief explanation of the drawings]

[0010] [Figure 1] The results of X-ray diffraction measurement (XRD) of the negative electrode active materials obtained in each of the Examples and Comparative Examples are shown. [Figure 2] (a) to (b) show SEM images of the negative electrode active material obtained in Comparative Example 1, (c) to (d) show SEM images of the negative electrode active material obtained in Example 1, and (e) to (f) show SEM images of the negative electrode active material obtained in Example 2. [Figure 3] The results of a constant current charge / discharge test of the batteries assembled in each production example are shown below. [Figure 4] (a) shows the results of a constant current charge / discharge test of the batteries assembled in each example, and (b) shows the Nyquist plot results. 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 an alkali ion battery, and contains a metal sulfide doped with carbon and nitrogen, wherein the metal in the metal sulfide contains at least one metal selected from the group consisting of Co, Cr, Ni, and Fe.

[0013] 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 capacity characteristics and cycle characteristics. Specifically, the negative electrode active material of the present invention has high initial discharge capacity and charge capacity, and can also exhibit high initial coulombic efficiency. Furthermore, it can increase the capacity retention rate even after repeated charge and discharge.

[0014] A carbon- and nitrogen-doped metal sulfide (hereinafter simply referred to as a "metal sulfide") contains carbon and nitrogen atoms. In the metal sulfide, the carbon and nitrogen atoms may be chemically bonded to the metal or sulfur atoms of the metal sulfide. For example, the carbon and nitrogen atoms may be present in the framework of the sulfide. In addition, the carbon and nitrogen atoms may be chemically bonded (-CN- bond) in the metal sulfide.

[0015] As described above, the metal in the metal sulfide contains at least one metal selected from the group consisting of Co, Cr, Ni, and Fe. The metal in the metal sulfide is preferably Co, since it can provide an alkali ion battery with excellent capacity characteristics and cycle characteristics and can be produced by a simple method.

[0016] The metal sulfide is particularly preferably Co3S4 doped with carbon and nitrogen, since it can provide particularly excellent capacity characteristics and cycle characteristics to an alkali ion battery.

[0017] The content of each element in the metal sulfide is not particularly limited. For example, the content of sulfur atoms relative to the total mass of the metal sulfide can be 10 to 40 mass%, preferably 15 to 35 mass%, and more preferably 20 to 30 mass%.

[0018] The carbon atom content relative to the total mass of the metal sulfide can be 0.01 to 5 mass %, preferably 0.1 to 3 mass %, and more preferably 0.3 to 1 mass %.

[0019] The content of nitrogen atoms relative to the total mass of the metal sulfide can be 0.01 to 5 mass %, preferably 0.03 to 3 mass %, and more preferably 0.05 to 1 mass %.

[0020] In the metal sulfide, the remainder other than sulfur, carbon, and nitrogen is the metal, but other elements that may be inevitably contained, such as oxygen, may also be contained. Examples of elements that may be inevitably contained include elements derived from the raw materials used in producing the metal sulfide.

[0021] The form of the metal sulfide is not particularly limited and may take various forms such as powder, lump, granule, fiber, etc. When the metal sulfide is in powder form, the metal sulfide may take various forms such as porous particles, hollow particles, irregular particles, spherical particles, etc., and the metal sulfide is preferably a porous particle in that it can provide excellent capacity characteristics and cycle characteristics to an alkaline ion battery. One embodiment of the porous particle is a tremella-like porous particle having nanosheets interconnected in a staggered pattern.

[0022] 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.

[0023] The BET specific surface area of ​​the metal sulfide is not particularly limited, and is, for example, 15 m 2 / g or more. In this case, the alkaline ion battery is likely to have better capacity characteristics and cycle characteristics. The BET specific surface area of ​​the metal sulfide is 20 m 2 / g or more is more preferable, and 25m 2 / g or more is more preferable. 2 It is particularly preferable that the saturation coefficient is 1 / g or more.

[0024] 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.

[0025] 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.

[0026] 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 obtaining a precursor by reacting a metal source containing at least one metal selected from the group consisting of Co, Cr, Ni, and Fe with an organic acid salt. Step 2: Heat treating the precursor in the presence of a sulfur source.

[0027] 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.

[0028] (Process 1) In step 1, a metal source containing at least one metal selected from the group consisting of Co, Cr, Ni, and Fe is reacted with an organic acid salt to obtain a precursor.

[0029] The metal source is preferably a metal source containing Co, in that it is easy to produce a negative electrode active material that can provide excellent capacity characteristics and cycle characteristics to an alkali ion battery, and can be produced by a simple method.

[0030] The metal source may be a simple metal, a metal compound, or a mixture thereof, and is preferably a metal compound. In that step 1 does not require the use of a carbon source or a nitrogen source other than the metal source, the metal source is particularly preferably a compound containing a metal, carbon, and nitrogen.

[0031] The type of metal compound is not particularly limited, and examples thereof include inorganic compounds of various metals, chlorides of various metals, and organic compounds of various metals. Examples of inorganic metal compounds include metal cyanides, metal cyanide salts, metal oxides, compounds containing metal oxoanions (metallates), nitrates, sulfates, chlorides, chlorates, perchlorates, chloride complexes, carbonates, hydrogencarbonates, phosphates, and hydrogenphosphates of metals. Examples of organic metal compounds include acetates, oxalates, formates, and succinates.

[0032] The metal source is preferably a metal cyanide or a cyanide salt. That is, the metal source is preferably a compound having a C-N moiety or a salt thereof. In this case, the metal source contains a carbon source and a nitrogen source, which makes it easy to produce the desired metal sulfide.

[0033] However, even when a metal cyanide compound or a cyanide salt is used as the metal source, if an organic acid salt described below is not used, the metal sulfide finally obtained will not be doped with nitrogen.

[0034] Specific examples of metal cyanide salts include K3[Co(CN)6], K3Cr(CN)6, K2Ni(CN)4, and K3[Fe(CN)6], with K3[Co(CN)6] being preferred in that it facilitates the production of a negative electrode active material that can provide alkaline ion batteries with excellent capacity and cycle characteristics.

[0035] When the metal source does not contain a carbon source and a nitrogen source, a carbon source and a nitrogen source are separately used in step 1. In this case, for example, a wide range of known carbon sources and nitrogen sources can be used as the carbon source and the nitrogen source.

[0036] 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 the metal is in the form of a solution or dispersion.

[0037] The concentration of the metal source solution or dispersion is not particularly limited, and for example, the concentration of the metal source is preferably 0.1 to 50 mM, more preferably 0.5 to 10 mM, even more preferably 1 to 5 mM, and particularly preferably 1.5 to 3 mM.

[0038] The organic acid salt used in step 1 is not particularly limited, and for example, a wide variety of known organic acid salts can be used. Examples of the organic acid salt include citrate, acetate, oxalate, formate, and succinate. Examples of the organic acid salt include alkali metal salts, alkaline earth metal salts, and amine salts of various organic acids, with alkali metal salts being preferred.

[0039] The organic acid salt is preferably a citrate, and more preferably a sodium salt of citric acid, for example, trisodium citrate dihydrate (NaCHO 2HO), because it has excellent reactivity with the metal source and can easily produce a negative electrode active material that can provide excellent capacity and cycle characteristics in alkali-ion batteries.

[0040] The organic acid salt used in step 1 can also be dissolved or dispersed in a solvent. Examples of such a solvent include the same type of solvent as the solvent for dissolving or dispersing the metal source, and water is preferred. The solvent for dissolving or dispersing the metal source and the solvent for dissolving or dispersing the organic acid salt may be the same or different.

[0041] The concentration of the solution or dispersion of the organic acid salt is not particularly limited, and for example, the concentration of the organic acid salt is preferably 0.1 to 50 mM, more preferably 0.5 to 10 mM, even more preferably 1 to 5 mM, and particularly preferably 1.5 to 3 mM.

[0042] In step 1, the reaction between the metal source and the organic acid salt is not particularly limited, and the reaction can be carried out, for example, by mixing the metal source and the organic acid salt by an appropriate method. Specifically, there can be mentioned a method of mixing a solution of the metal source with an aqueous solution of the organic acid salt and subjecting the mixture to hydrothermal treatment (hydrothermal synthesis method).

[0043] The temperature during the hydrothermal treatment can be, for example, the same as that used in known hydrothermal synthesis methods, for example, 80 to 400°C, preferably 100 to 300°C, and more preferably 120 to 200°C, and the reaction time can be appropriately selected depending on the temperature, for example, 1 to 10 hours. In the reaction of step 1, for example, a known reactor can be used.

[0044] The product obtained in the reaction of step 1 is, for example, a solid content, and can be separated by an appropriate method to obtain the product. Such a product can also be further subjected to purification treatment, drying treatment, etc. by an appropriate method.

[0045] By using an organic acid salt in step 1, the metal sulfide finally obtained is doped with carbon and nitrogen. If an organic acid salt is not used, a metal sulfide doped with carbon and nitrogen cannot be obtained, and in particular, a metal sulfide doped with nitrogen cannot be obtained.

[0046] The product obtained in the reaction of step 1 is a precursor of a metal sulfide. This precursor is subjected to the next step, step 2.

[0047] (Process 2) In step 2, the precursor obtained in step 1 is heat-treated in the presence of a sulfur source. The product obtained by this heat treatment is the metal sulfide.

[0048] 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.

[0049] 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.

[0050] In step 2, the method for heat-treating the precursor obtained in step 1 and the raw materials containing the sulfur source is not particularly limited. For example, a method in which the solid precursor and the sulfur source are placed in a reactor and heat-treated at a predetermined temperature can be mentioned. 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.

[0051] 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.

[0052] There are no particular limitations on the proportions of the precursor 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 precursor is preferably 10 to 1000 parts by mass, more preferably 30 to 800 parts by mass, and even more preferably 50 to 600 parts by mass, in that this facilitates the formation of a metal sulfide and the production of a desired negative electrode active material.

[0053] The product obtained in step 2 is a metal sulfide doped with carbon and nitrogen. A purified metal sulfide can also be obtained by treating the product obtained in step 2 by an appropriate method.

[0054] The metal sulfide obtained in step 2 (metal sulfide doped with carbon and nitrogen) can be used as the negative electrode active material of the present invention, or by blending other components as necessary, the negative electrode active material of the present invention can also be obtained.

[0055] The production method including the above-described steps 1 and 2 allows the anode active material of the present invention to be easily obtained through simple steps, resulting in a low-energy production method. Furthermore, the raw materials used in the production are inexpensive and can be obtained from abundant resources.

[0056] 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.

[0057] 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.

[0058] 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.

[0059] 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.

[0060] 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.

[0061] 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.

[0062] 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.

[0063] 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.

[0064] 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.

[0065] 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.

[0066] 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 xMO4(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 Al 0.05 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.

[0067] 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.

[0068] 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.

[0069] 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.

[0070] Examples of solid electrolytes include inorganic materials such as sulfides and oxides, and polymeric materials such as PEO (polyethylene oxide).

[0071] 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]

[0072] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples.

[0073] Example 1 Solution A was prepared by dissolving 1.8 mmol of trisodium citrate dihydrate (TSC, Na3C6H5O7·2H2O) as an organic acid salt in 30 mL of deionized water and stirring for 30 minutes. Meanwhile, solution B was prepared by dissolving 2 mmol of K3[Co(CN)6] as a metal source in 30 mL of deionized water and stirring for 30 minutes. Solution B was then poured into solution A and stirred for 1 hour to obtain a clear solution. After ultrasonic treatment for 10 minutes, the clear solution was added to a 100 mL Teflon-lined stainless steel autoclave, sealed, and hydrothermally reacted for 16 hours at 200 °C. After the reaction, the product was collected by centrifugation, washed several times with ethanol and distilled water, and finally freeze-dried for 24 hours to obtain the precursor (Step 1).

[0074] The precursor obtained in step 1 and thioacetamide (TAA) as a sulfur source in a mass ratio of 1:5 (MOF:sulfur source) were mixed together and heated at 500°C for 3 hours in an argon atmosphere (step 2). This resulted in a carbon- and nitrogen-doped metal sulfide. The resulting metal sulfide was named "Co3S4@N-C1.8" and used as the negative electrode active material.

[0075] Example 2 A metal sulfide was obtained in the same manner as in Example 1, except that the amount of trisodium citrate dihydrate used was changed to 3.6 mmol. The obtained metal sulfide was named "Co3S4@N-C3.6" and used as the negative electrode active material.

[0076] (Comparative Example 1) A metal sulfide was obtained in the same manner as in Example 1, except that trisodium citrate dihydrate was not used. The obtained metal sulfide was named "Co3S4@N-C0" and used as the negative electrode active material.

[0077] (Production Example 1) A negative electrode material slurry was prepared using the "Co3S4@N-C1.8" obtained in Example 1 as the negative electrode active material, superP (conductive carbon black) as the conductive additive, and polyvinylidene fluoride (PVDF) dissolved in methylpyrrolidinone as the binder. The mass ratio of this slurry was Co3S4@N-C1.8:superP:PVDF = 7.5:1.5:1. A negative electrode was fabricated by coating the slurry onto copper foil and drying it in a vacuum at 120°C for 12 hours. 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, using a known method. The electrolyte was a 1M sodium trifluoromethanesulfonate solution, and the solvent for this solution was diglyme.

[0078] (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 "Co3S4@N-C1.8" obtained in Example 1 to "Co3S4@N-C3.6" obtained in Example 2.

[0079] (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 "Co3S4@N-C1.8" obtained in Example 1 to "Co3S4@N-C0" obtained in Comparative Example 1.

[0080] (Evaluation results) Figure 1 shows the results of X-ray diffraction (XRD) measurements of the negative electrode active materials (metal sulfides doped with carbon and nitrogen) obtained in each example and comparative 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°.

[0081] From Figure 1, it was found that the negative electrode active material also had a Co3S4 phase. Furthermore, from Examples 1 and 2, it was found that increasing the amount of trisodium citrate dihydrate (TSC) weakened the XRD peak intensity. This may be due to the increase in the amorphous carbon content in the metal sulfide.

[0082] Table 1 shows the content ratio of each element in the negative electrode active material and the results of measuring the BET specific surface area by nitrogen gas adsorption.

[0083] [Table 1]

[0084] 2(a) to (b) show SEM images of the negative electrode active material obtained in Comparative Example 1, (c) to (d) show SEM images of the negative electrode active material obtained in Example 1, and (e) to (f) show SEM images of the negative electrode active material obtained in Example 2.

[0085] Figure 2 shows that the negative electrode active material of Comparative Example 1 has a sea urchin-like structure composed of nanoribbons (Figures 2(a) and (b)). In contrast, the negative electrode active material of Example 1 is a tremella-like porous particle with staggered interconnected nanosheets with a unidirectional size of approximately 1 to 2 μm (Figures 2(c) and (d)). This structure can increase the contact area between the electrode and electrolyte interface, which is beneficial for promoting rapid interfacial charge transfer and reaction. When the amount of TSC was further increased to 3.6 mM as in Example 2, the nanosheets became irregular and thick, and aggregation between particles was observed (Figures 2(e) and (f)).

[0086] 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 (1Ag -1 ) in Figure 3. The first Y-axis represents the capacity (mAhg -1 ) and the second Y-axis is the Coulomb efficiency (%).

[0087] Table 2 summarizes the results of the constant current charge / discharge test shown in Figure 3.

[0088] [Table 2]

[0089] From FIG. 3, it can be seen that the batteries equipped with the negative electrode materials containing the negative electrode active materials obtained in Examples 1 and 2 can provide better capacity characteristics and cycle characteristics than the battery equipped with the negative electrode active material of Comparative Example 1.

[0090] Figure 4(a) shows the results of a constant current charge / discharge test (same test conditions as in Figure 3) of the batteries assembled in each example, and (b) shows the Nyquist plot.

[0091] The negative electrode active material obtained in Example 2 was 0.1, 0.2, 0.5, 1, 2, and 3Ag -1 at current densities of 651.4, 635.6, 611.8, 599.2, and 574.4 mAhg, respectively. -1 It was found that the reversible capacity of the ZnO-based battery can be increased to 0.13Ag. -1 Returning to the original, the reversible capacity is also 606.4mAhg -1 This result also shows that the negative electrode active material obtained in the example can provide excellent capacity characteristics and cycle characteristics to an alkali ion battery.

Claims

1. A negative electrode active material for an alkali ion battery, comprising: containing a metal sulfide doped with carbon and nitrogen, The metal in the metal sulfide contains at least one metal selected from the group consisting of Co, Cr, Ni, and Fe.

2. The negative electrode active material according to claim 1 , wherein the metal sulfide is a porous particle.

3. The BET specific surface area of ​​the metal sulfide is 15 m ２ The negative electrode active material according to claim 1 or 2, wherein the Cr content is 1 / g or more.

4. A negative electrode material comprising the negative electrode active material according to any one of claims 1 to 3.

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

6. The method for producing the negative electrode active material according to any one of claims 1 to 3, Step 1: obtaining a precursor by reacting a metal source containing at least one metal selected from the group consisting of Co, Cr, Ni, and Fe with an organic acid salt; and Step 2: heat treating the precursor in the presence of a sulfur source; Equipped with The metal source includes a carbon source and a nitrogen source.

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