Positive electrode active material, positive electrode material, secondary battery including the positive electrode material, and method for producing positive electrode active material

Abstract

To provide a positive electrode active material capable of providing a secondary battery with excellent cycle characteristics, a positive electrode material including the positive electrode active material, and a manufacturing method of the positive electrode active material.SOLUTION: A positive electrode active material according to the present invention includes a sulfide of a transition metal element M1, and at least one transition metal element M2 other than the transition metal element M1. A manufacturing method of a positive electrode active material according to the present invention includes a step A of obtaining a product by heat-treating a raw material including a transition metal element M1 source, a transition metal element M2 source, a sulfur source, and a solvent, and a step B of firing the product obtained in the step A.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a positive electrode active material, a positive electrode material, a secondary battery including the positive electrode material, and a method for manufacturing the positive electrode active material.

Background Art

[0002] The requirements for secondary batteries such as next-generation lithium-ion batteries have been increasing year by year. In recent years, in addition to high safety, it has also been required to achieve high energy density and high cycle characteristics. In order to meet such high requirements for next-generation secondary batteries, various electrode materials have been actively developed to improve their performance, and various high-performance electrode (positive and negative) active material materials have been developed (see, for example, Patent Document 1).

[0003] For example, two-dimensional layered sulfide MS2 (where M represents a metal atom) has been attracting increasing attention as a promising electrode material for energy storage applications because the van der Waals force between the stacked layers is weak. From this perspective, recently, the design of nanostructures for improving the performance of MS2 as an electrode material for batteries has been emphasized.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, although the interlayer spacing of MS2 (0.615 nm) is large, its conductivity is low. For this reason, it is difficult to improve the Coulomb efficiency, and it is also difficult to increase the capacity. Therefore, there are problems with the cycle characteristics of the battery, and the application to the energy storage field has been limited. From such a perspective, it has been required to further improve the cycle characteristics of the electrode material using MS2.

[0006] The present invention has been made in view of the above, and an object thereof is to provide a positive electrode active material capable of providing excellent cycle characteristics to a secondary battery, a positive electrode material containing the positive electrode active material, and a method for manufacturing the positive electrode active material.

Means for Solving the Problems

[0007] As a result of intensive studies to achieve the above object, the present inventors have found that the above object can be achieved by using a sulfide of a specific transition metal element as a constituent component, and have completed the present invention.

[0008] That is, the present invention includes, for example, the subject matters described in the following items. Item 1 A positive electrode active material containing a sulfide of a transition metal element M1 and at least one transition metal element M2 other than the transition metal element M1. Item 2 The positive electrode active material according to Item 1, wherein the transition metal element M1 is Mo, W, or V. Item 3 The positive electrode active material according to Item 1 or 2, wherein the transition metal element M2 is at least one selected from the group consisting of Mo, W, and V. Item 4 The positive electrode active material according to any one of Items 1 to 3, wherein in the sulfide, a part of the transition metal element M1 is replaced by the transition metal element M2. Item 5 The positive electrode active material according to any one of Items 1 to 4, which has a laminated structure. Item 6 A positive electrode material containing the positive electrode active material according to any one of Items 1 to 5. Item 7 A secondary battery including the positive electrode material according to Item 6. Item 8 A method for manufacturing the positive electrode active material according to any one of Items 1 to 5, Step A of obtaining a product by heat-treating a raw material containing a transition metal element M1 source, a transition metal element M2 source, a sulfur source, and a solvent; Step B of firing the product obtained in the above step A A method for manufacturing a positive electrode active material, comprising:

Advantages of the Invention

[0009] The positive electrode active material of the present invention can provide excellent cycle characteristics to a secondary battery.

Brief Description of the Drawings

[0010]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0011] Hereinafter, embodiments of the present invention will be described in detail. In this specification, the expressions "containing" and "comprising" include the concepts of "containing", "comprising", "consisting essentially of", and "consisting only of".

[0012] 1. Positive electrode active material The positive electrode active material of the present invention contains a sulfide of a transition metal element M1 and at least one transition metal element M2 other than the transition metal element M1. The positive electrode active material of the present invention can be used as a positive electrode material for constructing various secondary batteries, and can provide excellent cycle characteristics to the secondary battery.

[0013] The transition metal element M1 can be exemplified by various transition metal elements. In terms of being likely to provide excellent cycle characteristics by the secondary battery, the transition metal element M1 is preferably Mo, W, or V.

[0014] Therefore, the sulfide of the transition metal element M1 can be exemplified by the sulfides of various transition metal elements, and in terms of being likely to provide excellent cycle characteristics by the secondary battery, it is preferably the sulfide of Mo, the sulfide of W, or the sulfide of V.

[0015] The sulfide of the transition metal element M1 is particularly preferably the sulfide of Mo (for example, MoS2) in terms of being likely to provide particularly excellent cycle characteristics to the secondary battery.

[0016] As described above, the positive electrode active material of the present invention further contains a transition metal element M2 different from the transition metal element M1 in addition to the sulfide of the transition metal element M1. The transition metal element M2 contained in the positive electrode active material may be only one kind, or may include two or more kinds.

[0017] The transition metal element M2 can be exemplified by various transition metal elements. Among them, in terms of being likely to provide excellent cycle characteristics by the secondary battery, the transition metal element M2 is preferably at least one selected from the group consisting of Mo, W, and V, and more preferably at least V.

[0018] In the positive electrode active material of the present invention, the state of existence of the transition metal element M2 is not particularly limited. For example, the transition metal element M2 can exist by replacing the transition metal element M1 in the sulfide (that is, the transition metal element M2 can also bond with sulfur). Specifically, the sulfide can have a structure in which a part of the transition metal element M1 is replaced by the transition metal element M2 (that is, in the positive electrode active material of the present invention, the transition metal element M2 can exist, for example, in the framework of the sulfide of the transition metal element M1). In this case, the positive electrode active material is likely to provide excellent cycle characteristics to the secondary battery.

[0019] The presence of the transition metal element M2 in the framework of the sulfide of the transition metal element M1 can be determined by various known methods, for example, it can be determined from the XRD spectrum of the positive electrode active material.

[0020] In the positive electrode active material, the abundance ratios of the transition metal element M1 and the transition metal element M2 are not particularly limited. For example, the molar ratio of the transition metal M1 to the transition metal M2 in the positive electrode active material, M1:M2, is preferably 1:0.2 to 1:5, and more preferably 1:1 to 1:4. Thereby, the positive electrode active material can bring more excellent cycle characteristics to the secondary battery.

[0021] In the positive electrode active material, it is preferable that the transition metal element M1, the transition metal element M2, and the sulfur atoms are uniformly dispersed throughout the positive electrode active material. The dispersion state of the transition metal element M1, the transition metal element M2, and the sulfur atoms in the positive electrode active material can be grasped, for example, by elemental mapping based on an SEM image.

[0022] As long as the positive electrode active material contains the sulfide of the transition metal element M1 and the transition metal element M as essential components, it can contain other components to such an extent that the effects of the present invention are not inhibited. For example, the positive electrode active material can contain other metals other than the transition metal elements M1 and M2. Examples thereof include metal elements inevitably contained in the positive electrode active material. When the positive electrode active material contains other components in addition to the sulfide of the transition metal element M1 and the transition metal element M2, the content ratio thereof is 5% by mass or less, preferably 1% by mass or less, more preferably 0.1% by mass or less based on the total mass of the sulfide of the transition metal element M1 and the transition metal element M2.

[0023] The positive electrode active material is, for example, in a solid state such as powder, but its shape is not particularly limited and can form various shapes. Among them, the positive electrode active material preferably has a laminated structure. More specifically, the positive electrode active material preferably has a so-called layer-by-layer structure formed by laminating a plurality of layers in a layer shape. Thereby, the positive electrode active material can provide more excellent cycle characteristics to the secondary battery. In particular, the layer-by-layer structure can provide a buffering effect against the volume expansion of the positive electrode material during battery charge and discharge. In addition, it is easier to provide an ion diffusion channel in the electrode material, which is advantageous for the rapid diffusion of ions. In addition, the positive electrode active material can also form a nanoflower structure.

[0024] The method for manufacturing the positive electrode active material is not particularly limited. For example, the positive electrode active material of the present invention can be manufactured by a manufacturing method including the following step A and step B.

[0025] 2. Method for producing positive electrode active material The manufacturing method of the positive electrode active material of the present invention can include, for example, the following step A and step B. Step A: A step of obtaining a product by heat-treating a raw material containing a transition metal element M1 source, a transition metal element M2 source, a sulfur source, and a solvent. Step B: A step of firing the product obtained in the above step A.

[0026] By the manufacturing method including the above step A and step B, a positive electrode active material can be manufactured. For example, the positive electrode active material of the present invention described above can be manufactured.

[0027] (Step A) Step A is a step of heat-treating a raw material containing a transition metal element M1 source, a transition metal element M2 source, a sulfur source, and a solvent.

[0028] Various transition metal elements can be exemplified for the transition metal element M1. Among them, in terms of being likely to provide more excellent cycle characteristics by the secondary battery, the transition metal element M1 is preferably Mo, W, or V.

[0029] The transition metal element M2 can be exemplified by various transition metal elements. Among them, in terms of being likely to bring excellent cycle characteristics by a secondary battery, the transition metal element M2 is preferably at least one selected from the group consisting of Mo, W, and V, and more preferably at least V.

[0030] The transition metal element M1 source (hereinafter simply referred to as "M1 source") may be the transition metal element M1 alone or a compound containing the transition metal element M1, but is preferably a compound containing the transition metal element M1.

[0031] The type of the compound containing the transition metal element M1 is not particularly limited, and for example, various inorganic compounds containing the transition metal element M1 can be mentioned. Examples of the inorganic compound containing the transition metal element M1 include, for example, oxides of the transition metal element M1, compounds containing oxoanions of the transition metal element M1 (metal salts), as well as nitrates, sulfates, chlorides, chlorates, perchlorates, carbonates, hydrogen carbonates, phosphates, and hydrogen phosphates of the transition metal element M1, etc. Among them, the inorganic compound containing the transition metal element M1 is preferably a compound containing an oxoanion of the transition metal element M1.

[0032] Specific examples of the compound containing an oxoanion of the transition metal element M1 include vanadate, molybdate, tungstate, etc. The type of the salt is not particularly limited, and for example, ammonium salts, alkali metal salts, etc. can be mentioned. Examples of vanadate include sodium metavanadate (NaVO3). Examples of molybdate include sodium molybdate (Na2MoO4). Examples of tungstate include sodium metavanadate (NaVO3).

[0033] The M1 source can also include various organic compounds of the transition metal element M1, and for example, acetates, oxalates, formates, and succinates of the transition metal element M1 can be mentioned.

[0034] The transition metal element M2 source (hereinafter simply referred to as "M2 source") may be a simple substance of the transition metal element M2 or a compound containing the transition metal element M2, but it is preferably a compound containing the transition metal element M2.

[0035] The types of compounds containing the transition metal element M2 are not particularly limited, and for example, various inorganic compounds containing the transition metal element M2 can be mentioned. Examples of the inorganic compound containing the transition metal element M2 include, for example, oxides of the transition metal element M2, compounds containing oxoanions of the transition metal element M2 (metal salts), as well as nitrates, sulfates, chlorides, chlorates, perchlorates, carbonates, hydrogen carbonates, phosphates and hydrogen phosphates of the transition metal element M2, etc. Among them, the inorganic compound containing the transition metal element M2 is preferably a compound containing an oxoanion of the transition metal element M2.

[0036] Specific examples of the compounds containing oxoanions of the transition metal element M2 include vanadates, molybdates, tungstates, etc. The types of salts are not particularly limited, and for example, ammonium salts, alkali metal salts, etc. can be mentioned. Examples of vanadates include sodium metavanadate (NaVO3). Examples of molybdates include sodium molybdate (Na2MoO4). Examples of tungstates include sodium metavanadate (NaVO3).

[0037] The M2 source can also include various organic compounds of the transition metal element M2, and for example, acetates, oxalates, formates, succinates, etc. of the transition metal element M1 can be mentioned.

[0038] The sulfur source used in step A may be a simple substance of sulfur or a compound containing sulfur, but it is preferably a compound containing sulfur.

[0039] Examples of the sulfur-containing compound include, but are not limited to, well-known sulfur compounds such as thioacetamide (CH3CSNH2), thiourea (SC(NH2)2), cysteine (C3H7NO2S), sodium thiosulfate (Na2S2O3), ammonium sulfide ((NH4)2S), sodium sulfide (Na2S), etc. Note that in the sulfur-containing compound, a part of the sulfur element may be replaced by Se and / or Te elements.

[0040] The sulfur source can be used alone or in combination of two or more.

[0041] The raw materials used in Step A include a solvent in addition to the M1 source, M2 source, and sulfur source. As the solvent, water can be used, and various organic solvents can also be used. Examples of the organic solvent include N-methyl-2-pyrrolidone (NMP), dimethylformamide (DMF), oleic acid, ethylene glycol, octadecene, ethylenediamine, etc. The solvent used in Step A can also be a mixture of water and an organic solvent.

[0042] The solvent can contain various additives. Examples of the additives include ammonia water, as well as dispersion stabilizers and surfactants such as polyvinylpyrrolidone (PVP), cetyltrimethylammonium bromide (CTAB), sodium laurylsulfonate (SDS), ethylenediaminetetraacetic acid (EDTA), etc. When the solvent contains additives, it is easier to obtain the cathode active material having the aforementioned layer-by-layer structure. When the solvent contains additives, the content ratio of the additives to the total mass of the solvent can be 5% by mass or less, preferably 3% by mass or less, and more preferably 1% by mass or less.

[0043] In the raw materials used in Process A, the content ratios of the M1 source, M2 source, sulfur source, and solvent are not particularly limited. For example, in the raw materials used in Process A, it is preferable that the M1 source and M2 source are included such that the molar ratio of transition metal element M1 to transition metal element M2, M1:M2, is 1:0.2 to 1:5, preferably 1:1 to 1:4. Thereby, the obtained positive electrode active material can bring more excellent cycle characteristics to the secondary battery.

[0044] Also, in the raw materials used in Process A, the content ratio of the sulfur source is preferably 1 to 30 mol%, more preferably 2 to 15 mol%, and even more preferably 3 to 10 mol% with respect to the total number of moles of the M1 source and M2 source in terms of facilitating the formation of the sulfide of transition metal element M1 and facilitating the obtaining of the desired positive electrode active material.

[0045] The amount of the solvent contained in the raw materials used in Process A is not particularly limited. For example, the amount of the solvent used in the raw materials can be adjusted such that the concentration of transition metal element M1 in the raw materials is 1 to 1000 mM, a more preferable concentration is 10 to 500 mM, and an even more preferable concentration is 20 to 100 mM.

[0046] In Process A, the above raw materials are heat-treated. Thereby, a product containing a sulfide is produced. Examples of the heat treatment method include a method of accommodating the raw materials in a container, sealing the container, and heating the inside of the container. When the solvent in the raw materials is water, it becomes a so-called hydrothermal synthesis method.

[0047] The temperature inside the container during the heat treatment in Process A is not particularly limited and can be, for example, 100 to 400 °C, preferably 150 to 250 °C. The heating time is also not particularly limited and can be appropriately determined according to the heating temperature and can be, for example, 6 to 40 hours. The pressure inside the container during the heat treatment can also be set as appropriate.

[0048] In Project A, after the heat treatment is completed, the product can be taken out by an appropriate method. For example, when the product is obtained as a solid content, the solid content can be separated by a method such as centrifugation, washed, and dried to obtain the product as a solid.

[0049] (Project B) In Project B, the product obtained in the above Project A is fired. By such firing, the target positive electrode active material can be obtained.

[0050] In Project B, the firing method is not particularly limited, and a well-known firing method can be widely adopted. For example, the temperature of the firing treatment can be 200 to 1000 °C, preferably 220 to 800 °C, more preferably 250 to 600 °C, and even more preferably 280 to 500 °C.

[0051] The firing time can be appropriately selected according to the firing temperature. For example, it can be 0.5 to 5 hours. In Step 2, the heating rate during firing is not particularly limited either and can be appropriately set. For example, it is 1 to 10 °C / min.

[0052] The firing treatment may be carried out either in air or in an inert gas atmosphere. For the firing treatment, for example, a well-known heating device such as a commercially available heating furnace can be used.

[0053] By the firing treatment in Project B, for example, unreacted raw materials such as remaining by-products and sulfur sources are removed, the target positive electrode active material can be obtained with high purity, and the crystallinity of the obtained positive electrode active material can be increased.

[0054] According to the manufacturing method including the above Project A and Project B, the positive electrode active material of the present invention can be easily obtained by a simple process.

[0055] 3. Positive electrode material As long as the positive electrode material of the present invention contains the above positive electrode active material, it can also contain other components. For example, known components used in positive electrode materials of secondary batteries (especially lithium secondary batteries) can be mentioned. For example, the positive electrode material of the present invention can contain a conductive assistant and a binder in addition to the above positive electrode active material.

[0056] The conductive assistant can broadly include known conductive assistants used for forming electrode materials of secondary batteries. Examples of the conductive assistant include various carbon materials, such as natural graphite, artificial graphite, conductive carbon black, graphene, carbon fiber, etc. Examples of carbon fiber include carbon nanofiber, carbon nanotube, etc. As the conductive assistant, metal powders such as copper and nickel, metal fibers, conductive ceramic materials, etc. can also be used.

[0057] The binder can broadly include known binders used for forming electrode materials of secondary batteries. Examples of the binder include various resin materials, specifically, polyvinylidene fluoride (PVDF), styrene-butadiene rubber (SBR), polyethylene terephthalate, polyacrylonitrile (PAN), polyvinyl alcohol (PVA), polyethylene oxide (PEO), polyethylene, polypropylene, etc.

[0058] In the positive electrode material, the content ratio of the positive electrode active material is not particularly limited. For example, with respect to the total mass of the positive electrode active material, conductive assistant, and binder contained in the positive electrode material, it is preferably 50 to 95% by mass, and more preferably 60 to 90% by mass, of the positive electrode active material is contained.

[0059] In the positive electrode material, the content ratio of the conductive assistant is not particularly limited. For example, with respect to the total mass of the positive electrode active material, conductive assistant, and binder contained in the positive electrode material, it is preferably 3 to 30% by mass, and more preferably 5 to 20% by mass, of the conductive assistant is contained.

[0060] In the positive electrode material, the content ratio of the binder is not particularly limited. For example, it is preferably contained in an amount of 3 to 30% by mass, more preferably 5 to 20% by mass, based on the total mass of the positive electrode active material, conductive assistant, and binder contained in the positive electrode material.

[0061] The positive electrode material may be composed only of a positive electrode active material, a conductive assistant, and a binder, or may contain other components.

[0062] The method for preparing the positive electrode material is not particularly limited. For example, known methods for preparing positive electrode materials can be widely adopted. For example, the positive electrode material can be prepared by mixing a positive electrode active material, a conductive assistant, and a binder at a predetermined ratio by an appropriate method. When preparing the positive electrode material, a solvent can also be used to disperse the positive electrode active material, conductive assistant, and binder. Examples of the solvent include water and various organic solvents, such as lower alcohol compounds having 1 to 3 carbon atoms, NMP (N-methyl-2-pyrrolidone), etc. When the positive electrode material contains a solvent, it becomes, for example, a slurry or paste form.

[0063] 4. Secondary battery As long as the secondary battery of the present invention includes the positive electrode material, the other configurations are not particularly limited, and for example, it can have the same configuration as a known secondary battery. The type of secondary battery is not particularly limited, and examples include lithium ion secondary batteries.

[0064] The secondary battery can include, for example, a positive electrode, a negative electrode, an electrolyte, and a separator. The size and shape of the battery can be appropriately determined according to its use.

[0065] The positive electrode can have, for example, a structure in which the positive electrode active material is supported on a metal foil. Examples of the metal for forming the metal foil include aluminum, titanium, platinum, molybdenum, stainless steel, copper, and the like. The positive electrode can be manufactured by a known method. For example, a positive electrode in which the positive electrode active material is supported on a metal foil can be formed by applying the positive electrode material of the present invention described above onto the metal foil.

[0066] The negative electrode can have, for example, a structure in which the negative electrode active material is supported on a metal foil. Examples of the metal foil include aluminum, titanium, platinum, molybdenum, stainless steel, copper, and the like. Examples of the negative electrode active material include metals such as Li, Na, K, Mg, Al, Zn; graphite and other carbon materials; Si(C)-based, Si(O)-based or Sn-based alloys or metal oxides; metal sulfides; Li4Ti5O 12 ; and the like. The negative electrode can be manufactured by a known method.

[0067] In the secondary battery, the type of the electrolyte is not particularly limited, and for example, a known electrolyte used in a secondary battery can be used. The electrolyte can be either a solid electrolyte or a liquid electrolyte.

[0068] Examples of the liquid electrolyte include a solution in which an electrolyte is dissolved in a solvent. Examples of the electrolyte include various alkali salts, such as NaPF6, NaClO4, NaCF3SO3, NaFSI, NaTFSI, LiPF6, LiClO4, LiBF4, LiBOB, LiAsF6, LiCF3SO3, LiTFSI, LiFSI, KPF6, KFSI, KTFSI, KBF4, and the like. In addition, known magnesium salts, aluminum salts, zinc salts, and the like are also included. Examples of the solvent include water, diethylene glycol dimethyl ether, triethylene glycol dimethyl ether, propyl acetate, fluoroethylene carbonate, propylene carbonate, ethylene carbonate, dimethyl carbonate, ethyl methyl carbonate, diethyl carbonate, and the like.

[0069] Examples of solid electrolytes include inorganic materials such as sulfide-based and oxide-based materials, and polymer materials such as PEO (polyethylene oxide)-based materials.

[0070] As the separator, known separators applied to secondary batteries can be used. For example, polyolefin resins such as polyethylene and polypropylene; polyimide; polyvinyl alcohol; fluorine resins such as end-aminoated polyethylene oxide polytetrafluoroethylene; acrylic resins; nylon; aromatic aramids; inorganic glass; materials formed of ceramics, etc. can be mentioned. The separator can be in the form of a porous membrane, non-woven fabric, woven fabric, etc. In addition, various polymer membranes and inorganic electrolytes can be mentioned as the separator. Examples of inorganic electrolytes include LiLaTiO3, Li7La3Zr2O 12 (LLZO), Na3Zr2Si2PO 12 , Na 11 Sn2PS 12 , Na3PSe4, etc.

Examples

[0071] Hereinafter, the present invention will be described more specifically by way of examples, but the present invention is not limited to the aspects of these examples.

[0072] (Example 1) 0.234 g of NH4VO3, 0.3629 g of Na2MoO4·2H2O, 30 mL of distilled water, and 0.25 ml of 28 mass% ammonia water were mixed, and 2.402 g of C2H5NS was added thereto, and the raw materials were prepared by stirring for 1 hour.

[0073] The obtained raw materials were transferred to a 50 mL autoclave lined with Teflon (registered trademark), the autoclave was sealed, and heated at 220 °C for 24 hours (Step 1). Subsequently, the product in the autoclave was recovered by centrifugation, washed several times using distilled water and ethanol, and then dried in a vacuum oven at 60 °C for 12 hours. Finally, it was calcined at 300 °C for 1 hour under an argon atmosphere to obtain the target positive electrode active material (Step 2). The obtained positive electrode active material was designated as "LS-VMS".

[0074] (Production Example 1) A positive electrode material composed of LS-VMS obtained in Example 1 as the positive electrode active material, super P (conductive carbon black) as the conductive additive, and polyvinylidene fluoride (PVDF) as the binder was prepared. In this positive electrode material, LS-VMS:super P:PVDF = 8:1:1 (mass ratio). N-methyl-2-pyrrolidone (NMP) was added as a solvent to the positive electrode material and stirred for 12 hours to mix uniformly. The obtained slurry was coated on an Al current collector (aluminum foil) and dried in vacuo at 120 °C for 12 hours to fabricate a positive electrode. Using this positive electrode, a negative electrode (lithium metal with a copper foil), a liquid electrolyte, and a separator (Whatman GF / C glass fiber filter paper provided by Cytiva) impregnated with this liquid electrolyte, a battery was assembled by a known method. The electrolyte was a 1 M lithium hexafluorophosphate (LiPF6) solution, and the solvent of such a solution was a mixed solvent of ethylene carbonate and ethyl methyl carbonate (volume ratio 1:1).

[0075] (Production Example 2) A battery was assembled in the same manner as in Production Example 1, except that commercially available LiFePO4 (HEOLOTECHNALOGYGROUP Co., Ltd, China) was used instead of LS-VMS as the positive electrode active material.

[0076] Figure 1 shows the SEM image of the LS-VMS obtained in Example 1. From this SEM image, it was found that the LS-VMS obtained in Example 1 formed a layered structure for each layer, that is, a layer-by-layer structure.

[0077] Figure 2 shows the elemental mapping images of sulfur element (S), molybdenum element (Mo), and vanadium element (V) in the SEM image of Figure 1. Figure 2(B) is an image showing the results of mapping the framed part in Figure 2(A) with S, Mo, and V respectively. From the mapping results in Figure 2, it was confirmed that in the LS-VMS obtained in Example 1, S, Mo, and V were uniformly distributed throughout the positive electrode active material.

[0078] Figure 3 shows the X-ray diffraction measurement (XRD) results of the LS-VMS obtained in Example 1. For the X-ray diffraction measurement, "SmartLab" manufactured by Rigaku was used, and the measurement was carried out using a Cu-Kα (λ = 1.540 Å) radiation source in the range of 2θ = 10 to 100°.

[0079] As can be seen from the XRD spectrum in Figure 3, diffraction peaks were clearly observed at 2θ = 14.6°, 2θ = 32.9°, 2θ = 39.5°, and 2θ = 58.3°. These diffraction peaks belonged to the (002), (100), (103), and (110) planes of 2H-MoS2 respectively (refer to JCPDS NO. 37-1492). On the other hand, it was found that no structure indicating VS2 was seen in the XRD spectrum of Figure 3.

[0080] As a result, as shown in Figure 4, it can be seen that the LS-VMS obtained in Example 1 has a structure in which the vanadium element (V) penetrates into the framework of molybdenum disulfide (MoS2).

[0081] Figure 5(A) shows the results of a constant current charge-discharge test using the battery assembled in Preparation Example 1, and Figure 5(B) shows the results of a constant current charge-discharge test using the battery assembled in Preparation Example 2. These measurements were made using a LAND Battery Test System "CT2001A" (Wuhan LAND electronics Co., Ltd. China). Here, the measurement temperature was 30 °C and the applied voltage was 1.5 - 3.5 V.

[0082] As shown in Figure 5(A), in the battery of Preparation Example 1 having the LS-VMS obtained in Example 1 as the positive electrode active material, after 1000 cycles, at a high current density of 1 A / g -1 the Coulomb efficiency was about 100%, and it was also found that a specific capacity of 118 mAh / g -1 could be provided after 1000 cycles. In contrast, as shown in Figure 5(B), in the battery of Preparation Example 2 having commercially available LiFePO4 as the positive electrode active material, after 1000 cycles, at a low current density of 0.17 A / g -1 the Coulomb efficiency remained at about 96.7%, and the specific capacity after 1000 cycles also remained at 109 mAh / g -1 as well.

[0083] From the above, it was found that the secondary battery having the LS-VMS obtained in Example 1 as the positive electrode active material has excellent cycle characteristics.

Claims

1. A method for producing a positive electrode active material containing a sulfide of a transition metal element M1 and at least one transition metal element M2 other than the transition metal element M1, wherein the transition metal element M1 is Mo, W or V, the transition metal element M2 is at least one selected from the group consisting of Mo, W and V, the transition metal element M1 and the transition metal element M2 are different from each other, the positive electrode active material forms a laminated structure, a step A of obtaining a product by heat-treating a raw material containing a transition metal element M1 source, a transition metal element M2 source, a sulfur source, and a solvent; a step B of firing the product obtained in the step A; A method for producing a positive electrode active material, comprising:

2. The production method according to claim 1, wherein the temperature of the heat treatment in the step A is 100 to 400°C.

3. The production method according to claim 1 or 2, wherein the temperature of the firing in the step B is 200 to 1000°C.

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