Positive electrode active material and preparation method and application thereof

Abstract

The invention provides a positive electrode active material and a preparation method and application thereof. The positive electrode active material comprises an active matrix; the first coating layer is arranged on at least part of the surface of the active matrix, and the first coating layer comprises an antimony compound; the second coating layer is arranged on at least part of the surface of the first coating layer, and the second coating layer comprises a single-walled carbon nanotube. According to the positive electrode active material as well as the preparation method and the application thereof, the structural stability and the conductivity of the positive electrode active material can be improved, and the rate capability and the cycle performance of a lithium ion battery can be improved.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, specifically to a positive electrode active material, its preparation method, and its application. Background Technology

[0002] With the rapid development of lithium-ion batteries in electric vehicles and large-scale energy storage, higher requirements have been placed on the performance stability of lithium-ion batteries. Among these, the performance of the positive electrode directly affects the performance of lithium-ion batteries. Currently, when preparing positive electrode sheets using a liquid-phase wet process, the positive active material, conductive agent, and binder are typically dispersed in an organic solvent to form a slurry, which is then coated and dried. The drying process requires organic solvent recovery, resulting in high costs, and it is difficult to control the uniformity and stability of the complex interfaces formed between the positive active material, conductive agent, and binder during the drying process. To avoid solvent issues and reduce costs, dry preparation technology has received increasing attention. However, simple dry mixing often fails to achieve highly uniform dispersion and close contact of components such as the positive active material, conductive agent, and binder, easily leading to discontinuous conductive networks and obstructed ion transport paths, thus affecting the battery's rate performance and cycle life. Summary of the Invention

[0003] This invention proposes a positive electrode active material, its preparation method, and its application, which can improve the structural stability and conductivity of the positive electrode active material and enhance the rate performance and cycle performance of lithium-ion batteries.

[0004] To solve the above-mentioned technical problems, the present invention is achieved through the following technical solution.

[0005] This invention proposes a positive electrode active material, comprising:

[0006] Active matrix;

[0007] A first coating layer, the first coating layer being disposed on at least a portion of the surface of the active substrate, the first coating layer comprising an antimony compound; and

[0008] A second coating layer is disposed on at least a portion of the surface of the first coating layer, and the second coating layer includes single-walled carbon nanotubes.

[0009] In one embodiment of the present invention, the antimony compound is selected from at least one of Sb2Se3, Sb2S3 or Sb2Te3; and / or, the mass ratio of the active matrix to the antimony compound is (98 to 99.99):(0.01 to 2).

[0010] In one embodiment of the present invention, the thickness of the first coating layer is 1 nm to 100 nm, and the coating rate of the first coating layer is 90% to 100%, wherein the coating rate of the first coating layer is the percentage of the coating area of ​​the first coating layer on the surface of the active substrate to the surface area of ​​the active substrate.

[0011] In one embodiment of the present invention, the second coating layer further includes a binder, wherein the content of the single-walled carbon nanotubes in the positive electrode active material is 0.01 wt% to 2 wt%, and the content of the binder in the positive electrode active material is 0.1 wt% to 7 wt%.

[0012] And / or, the adhesive is selected from one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyimide, or polyurethane.

[0013] In one embodiment of the present invention, the second coating layer is a three-dimensional mesh structure, and the coating rate of the second coating layer is 1% to 50%, wherein the coating rate of the second coating layer is the percentage of the coating area of ​​the second coating layer on the surface of the first coating layer to the surface area of ​​the first coating layer.

[0014] And / or, the single-walled carbon nanotubes have a diameter of 0.5 nm to 2.5 nm and an aspect ratio of 100 to 10000.

[0015] In one embodiment of the present invention, the thickness of the first coating layer is 10 nm to 50 nm;

[0016] And / or, the coverage of the second coating layer is 1% to 25%;

[0017] And / or, the diameter of the single-walled carbon nanotube is 1 nm to 2 nm, and the aspect ratio is 1000 to 5000.

[0018] In one embodiment of the present invention, the active matrix is ​​selected from one or more of lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, or lithium nickel cobalt aluminum oxide.

[0019] The present invention also provides a method for preparing a positive electrode active material, for preparing the above-mentioned positive electrode active material, comprising:

[0020] The active matrix and antimony compound are mixed evenly to obtain a mixture; the median particle size of the antimony compound is 1 nm to 100 nm.

[0021] The mixture is sintered to obtain an intermediate with a first coating layer; the sintering temperature is 610°C to 800°C and the sintering time is 1 hour to 24 hours.

[0022] The intermediate, single-walled carbon nanotubes, binder, and solvent are mixed evenly to obtain a mixed slurry; the solvent is selected from one or more of N-methylpyrrolidone, dimethylformamide, dimethylacetamide, triethyl phosphate, or cyclohexanone.

[0023] The mixed slurry is dried and ground to obtain the positive electrode active material.

[0024] The present invention also provides a lithium-ion battery, including a positive electrode sheet, wherein the positive electrode sheet includes a positive electrode active material, and the positive electrode active material is selected from the positive electrode active material described above or the positive electrode active material obtained by the preparation method described above.

[0025] In one embodiment of the present invention, the lithium-ion battery is an all-solid-state lithium-ion battery.

[0026] In summary, this invention proposes a positive electrode active material, its preparation method, and its application. Through double-layer coating, the first coating layer acts as a flexible buffer layer, absorbing stress and reducing mechanical damage to the positive electrode active material. Simultaneously, the first coating layer provides a more even and uniform lithium-ion (Li) ion distribution. + The insertion / extraction interface is designed to avoid excessively high local current density or uneven reaction, thereby optimizing the Li... + The first and second coating layers improve the utilization efficiency; simultaneously, the antimony compound in the first coating layer forms Sb-O bonds with the oxygen-containing active matrix, alleviating the escape of lattice oxygen and enhancing the thermal stability of the oxygen-containing cathode active material; the presence of single-walled carbon nanotubes on the surface of the cathode active material solves the dispersion problem of single-walled carbon nanotubes in dry cathode sheets, and the single-walled carbon nanotubes construct a highly efficient three-dimensional conductive network, forming a through-type ion diffusion channel, thereby ensuring that electrons can quickly reach every corner of the active matrix; and the fibrous three-dimensional network uniformly coats the surface of the active matrix, which can restrain the volume change of the active matrix during cycling. Therefore, the first and second coating layers together improve the structural stability and conductivity of the cathode active material, thereby improving the rate performance and cycle stability of the battery. Detailed Implementation

[0027] The following specific examples illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention.

[0028] It should be understood that the invention can be embodied in various forms and should not be construed as being limited to the embodiments set forth herein. Rather, providing these embodiments will make the disclosure thorough and complete, and will fully convey the scope of the invention to those skilled in the art.

[0029] The technical solution of the present invention will be further described in detail below with reference to several embodiments. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0030] This invention proposes a positive electrode active material comprising an active substrate, a first coating layer, and a second coating layer. The first coating layer is disposed on at least a portion of the surface of the active substrate and comprises an antimony compound. The second coating layer is disposed on at least a portion of the surface of the first coating layer and comprises single-walled carbon nanotubes (SWCNTs). This double-layer coating provides a three-dimensional conductive network, reduces interfacial impedance, and improves ion / electron transport efficiency. Both layers synergistically enhance the structural stability of the positive electrode active material, thereby improving the rate performance and cycle stability of the battery.

[0031] In one embodiment of the present invention, the active matrix is ​​selected from one or more of lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, or lithium nickel cobalt aluminum oxide, preferably one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, or lithium nickel cobalt aluminum oxide. The active matrix may be, for example, spherical or irregularly shaped gravel particles.

[0032] In one embodiment of the present invention, the antimony compound is selected from at least one of Sb₂Se₃, Sb₂S₃, or Sb₂Te₃. The first coating layer, acting as a flexible buffer layer, can absorb stress and reduce mechanical damage to the positive electrode active material. Simultaneously, the first coating layer provides a more even and uniform lithium-ion (Li₂) surface. + The insertion / extraction interface is designed to avoid excessively high local current density or uneven reaction, thereby optimizing the Li... + This improves utilization efficiency. Simultaneously, after heat treatment, the antimony compound forms Sb-O bonds with the oxygen-containing active matrix, mitigating the escape of lattice oxygen and enhancing the thermal stability of the oxygen-containing cathode active material. When this cathode active material is used in dry-process cathode sheets, the interaction between the electrolyte and the cathode active material in the dry-process cathode sheet can be significantly reduced under the protection of the interfacial coating, enhancing the stability of the dry-process cathode sheet under high-temperature cycling.

[0033] In one embodiment of the present invention, the antimony compound is selected, for example, from Sb₂Se₃. Due to the chemical stability, low melting point, and volatility of Sb₂Se₃, Sb diffuses more easily during heat treatment and distributes uniformly on the surface of the active substrate. Furthermore, the presence of Se helps maintain Sb in a lower valence state, preventing the rapid formation of coarse Sb₂O₃ or Sb₂O₅ particles. This facilitates the formation of a uniform oxide layer, resulting in a dense and continuous first coating layer. This reduces the loss of the active substrate during subsequent cathode electrode fabrication, improves the high-temperature stability of the cathode active material, and ensures uniform lithium-ion transport, optimizing the Li₂O₃ content. + Utilization efficiency.

[0034] In one embodiment of the present invention, the mass ratio of the active matrix to the antimony compound is, for example, (98 to 99.99):(0.01 to 2). By controlling the mass ratio of the active matrix to the antimony compound, the energy density of the positive electrode active material is ensured.

[0035] In one embodiment of the present invention, the thickness of the first coating layer is, for example, 1 nm to 100 nm, preferably 10 nm to 50 nm, and the coverage of the first coating layer is, for example, 90% to 100%. The coverage of the first coating layer is the percentage of the surface area of ​​the active substrate covered by the first coating layer. By forming a first coating layer with high coverage, the first coating layer can provide a more flat and uniform Li₂ substrate. + The insertion / extraction interface avoids excessively high local current density or uneven reaction, thereby optimizing Li + Utilization efficiency.

[0036] In one embodiment of the present invention, the second coating layer further includes a binder, such as one or more selected from polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP), polyimide (PI), or polyurethane (PU), etc., and the binder content in the positive electrode active material is from 0.1 wt% to 7 wt%. When the positive electrode sheet is prepared by dry process using this positive electrode active material, single-walled carbon nanotubes exist on the surface of the positive electrode active material, which can solve the dispersion problem of single-walled carbon nanotubes in the dry process positive electrode sheet. Simultaneously, the binder in the second coating layer can improve the peel force between the positive electrode active layer and the current collector, reduce the shedding of the positive electrode active material, and improve the safety performance of the battery.

[0037] In one embodiment of the present invention, the diameter of the single-walled carbon nanotubes is, for example, 0.5 nm to 2.5 nm, preferably 1 nm to 2 nm, and the aspect ratio is, for example, 100 to 10000, preferably 1000 to 5000. The single-walled carbon nanotubes construct a highly efficient three-dimensional conductive network; that is, the second coating layer is a three-dimensional network structure, and the fibrous three-dimensional network of single-walled carbon nanotubes uniformly coats the surface of the active substrate, which can restrain the volume change of the active substrate during cycling. Therefore, the first and second coating layers together improve the structural stability of the positive electrode active material.

[0038] In one embodiment of the present invention, the content of the single-walled carbon nanotubes in the positive electrode active material is from 0.01 wt% to 2 wt%, and the coating rate of the second coating layer is from 1% to 50%, preferably from 1% to 25%. The coating rate of the second coating layer is the percentage of the surface area of ​​the second coating layer on the surface of the first coating layer. By controlling the diameter and aspect ratio of the single-walled carbon nanotubes, a highly efficient three-dimensional conductive network can be constructed with a relatively small coating amount, forming a through-type ion diffusion channel, thereby ensuring that electrons can quickly reach every corner of the active substrate. Therefore, the first and second coating layers together reduce the charge transfer impedance at the interface between the positive electrode active material and the solid electrolyte, improving the rate performance of the battery.

[0039] The present invention also proposes a method for preparing a positive electrode active material, which is used to prepare the above-mentioned positive electrode active material. The preparation method is as follows: the active matrix and antimony compound are mixed evenly to obtain a mixture; the mixture is sintered to obtain an intermediate with a first coating layer; the intermediate, single-walled carbon nanotubes, binder and solvent are mixed evenly to obtain a mixed slurry; the mixed slurry is dried and ground to obtain the positive electrode active material.

[0040] In one embodiment of the present invention, the active matrix and the antimony compound are mixed uniformly at a mass ratio of (98 to 99.99):(0.01 to 2), for example by ball milling, wherein the ball-to-material ratio is, for example, (30 to 1):1, the ball milling speed is, for example, 50 rpm / min to 300 rpm / min, and the ball milling time is, for example, 0.1 h to 24 h, to obtain a mixture. The active matrix is, for example, spherical or irregularly shaped crushed particles, with a median particle size D50 of, for example, 500 nm to 10 μm. The antimony compound is, for example, spherical or irregularly shaped crushed particles, with a median particle size D50 of, for example, 1 nm to 100 nm. In this application, the median particle size D50 refers to the particle size value corresponding to a cumulative volume distribution percentage of 50% in the volume distribution curve.

[0041] In one embodiment of the present invention, the mixture is sintered in a vacuum or inert gas atmosphere, and the sintering temperature is, for example, 610°C to 800°C, and the sintering time is, for example, 1h to 24h, to obtain an intermediate having a first coating layer.

[0042] In one embodiment of the present invention, an intermediate, single-walled carbon nanotubes, a binder, and a solvent are mixed uniformly. The intermediate, single-walled carbon nanotubes, and binder are mixed, for example, at a mass ratio of (90 to 99):(0.01 to 2):(0.1 to 7), and then the solvent is added and mixed uniformly to obtain a mixed slurry. The solvent is, for example, one or more of N-methylpyrrolidone (NMP), dimethylformamide (DMF), dimethylacetamide (DMAC), triethyl phosphate (TEP), or cyclohexanone (CYC).

[0043] In one embodiment of the present invention, the mixed slurry is heated and dried at 25°C to 150°C for 0.1 h to 24 h to remove the solvent. The dried material is then ground into a uniform powder to obtain a positive electrode active material with a double-layer coating. In this application, a first coating layer containing an antimony compound is constructed on the surface of the active substrate by ball milling and high-temperature sintering. A second coating layer including single-walled carbon nanotubes is formed on at least a portion of the surface of the first coating layer by liquid-phase mixing and coating. The positive electrode active material has advantages such as continuous conductive network, low interfacial impedance, and high ion / electron transport efficiency, thereby improving the electrochemical performance of the battery.

[0044] This invention also proposes an all-solid-state lithium-ion battery, comprising a dry-process positive electrode, a negative electrode, and a separator layer, wherein the separator layer is disposed between the dry-process positive and negative electrode layers, and the separator layer is a solid electrolyte layer. In this invention, the all-solid-state lithium-ion battery is, for example, a primary battery or a secondary battery, and the secondary battery is, for example, a pouch battery, a prismatic battery, or a cylindrical battery, etc. This invention does not impose specific limitations on the type and category of all-solid-state lithium-ion batteries.

[0045] In one embodiment of the present invention, the dry-process positive electrode sheet includes a positive current collector and a positive active layer disposed on at least one surface of the positive current collector. The positive current collector is, for example, a foil formed by surface treatment of materials such as nickel, titanium, aluminum, silver, stainless steel, or carbon. Besides foil, the positive current collector can also be used in any one or more combinations of various forms such as film, mesh, porous, foam, or nonwoven fabric.

[0046] In one embodiment of the present invention, the positive electrode active layer includes a positive electrode active material, a positive electrode electrolyte, a positive electrode conductive agent, and a positive electrode binder. The positive electrode active material is selected from the above-mentioned positive electrode active materials, and the positive electrode electrolyte is selected from at least one of oxide solid electrolytes, sulfide solid electrolytes, and halide solid electrolytes, and for example, from Li7La3Zr2O. 12 Li 13 Al3Ti 17 (PO4)3, Li 10 GeP2S 12 At least one of Li6PS5Cl, Li3InCl6, or Li3YCl6. The positive electrode conductive agent is selected from at least one of graphite, graphene, conductive carbon black, carbon fiber, and carbon nanotubes. The positive electrode binder is selected from at least one or more of fibrous binders such as polytetrafluoroethylene, ethylene-tetrafluoroethylene copolymer, or fluorinated ethylene propylene copolymer.

[0047] In one embodiment of the present invention, the mass ratio of the positive electrode active material, the positive electrode electrolyte, the positive electrode conductive agent, and the positive electrode binder is, for example, (45 to 99.7):(0.1 to 40):(0.1 to 10):(0.1 to 5). When preparing the positive electrode sheet, the positive electrode active material, the positive electrode electrolyte, and the positive electrode conductive agent are mixed according to the mass ratio, for example, in a stirrer at a speed of 100 rpm / min to 2000 rpm / min for 0.5 min to 120 min to obtain a premix. The positive electrode binder is added to the premix, and the mixture is premixed at a temperature of -40°C to 15°C at a speed of 500 rpm / min to 3000 rpm / min for 0.5 min to 60 min to obtain a mixed dry material. The mixed dry materials are heated to 20°C to 140°C and held at this temperature for 0.1 to 24 hours. Then, they are subjected to fibrillation mixing at a speed of 2000 to 15000 rpm for 0.5 to 60 minutes, followed by kneading in an internal mixer for 0.5 to 60 minutes to strengthen the fibrillation of the mixed dry materials. After cooling to room temperature, such as 25°C to 30°C, the materials are crushed and granulated at a speed of 100 to 3000 rpm. The granulated powder is then fed into a differential roller mill for film formation to obtain the positive electrode active layer. The positive electrode active layer is then combined with the positive electrode current collector to obtain the dry-process positive electrode sheet.

[0048] In an embodiment of the present invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode active layer coated at least on one surface of the negative electrode current collector. Among them, the negative electrode current collector is, for example, a copper foil current collector, a composite copper foil current collector, a carbon current collector, a foam copper current collector or a stainless steel current collector, etc., and the negative electrode active layer includes a negative electrode active material, a negative electrode electrolyte, a negative electrode conductive agent and a negative electrode binder, etc. Among them, the mass ratio of the negative electrode active material, the negative electrode electrolyte, the negative electrode conductive agent and the negative electrode binder is, for example, (60 to 78):(20 to 30):(1 to 5):(1 to 5). In this embodiment, the negative electrode active material is selected from graphite-based materials, silicon materials or composite materials composed of a combination of the two. The graphite-based materials include at least one of natural graphite or artificial graphite. The natural graphite includes at least one of massive graphite, flake graphite or earthy graphite, etc. The artificial graphite includes at least one of single crystal graphite, polycrystalline graphite, pyrolytic graphite or graphite fiber, etc. The silicon materials include, but are not limited to, silicon, silicon-carbon materials and silicon-oxygen materials (SiO x , 0 < x < 2). The negative electrode electrolyte is, for example, selected from at least one of oxide solid electrolytes, sulfide solid electrolytes and halide solid electrolytes, etc., and is also, for example, selected from Li7La3Zr2O 12 , Li 13 Al3Ti 17 (PO4)3, Li 10 GeP2S 12 , Li6PS5Cl, Li3InCl6 or Li3YCl6, etc. The negative electrode conductive agent is, for example, selected from at least one of conductive carbon black, acetylene black, Ketjen black, carbon nanotubes or graphene, etc. The negative electrode binder is, for example, selected from at least one of polypropylene, polyacrylate, polyethylene ether, polymethyl methacrylate, polyhexafluoropropylene or styrene-butadiene rubber, etc.

[0049] In an embodiment of the present invention, the negative electrode active material is, for example, a composite of graphite and silicon-carbon materials, and the mass ratio of graphite and silicon-carbon materials is, for example, 1:1. The negative electrode active material, the negative electrode electrolyte, the negative electrode conductive agent and the negative electrode binder are fully stirred in a xylene solvent system according to a mass ratio of 70:25:2:3. After mixing evenly, it is coated on the copper foil, dried and cold-pressed to obtain the negative electrode sheet.

[0050] In an embodiment of the present invention, the solid electrolyte layer includes a solid electrolyte. The solid electrolyte is selected from at least one of oxide solid electrolytes, sulfide solid electrolytes and halide solid electrolytes, etc., and is also, for example, selected from Li7La3Zr2O 12 , Li 13 Al3Ti 17 (PO4)3, Li 10 GeP2S 12At least one of Li6PS5Cl, Li3InCl6, or Li3YCl6 is used. A solid electrolyte is pressed at, for example, 200 MPa to 350 MPa to obtain a 200 μm solid electrolyte layer. A dry-process positive electrode, the solid electrolyte layer, and the negative electrode are sequentially placed into a mold and pressed and sealed to obtain an all-solid-state lithium-ion battery. The assembly process is completed under an argon atmosphere or vacuum.

[0051] This invention also proposes a lithium-ion battery, such as a liquid lithium-ion battery or a semi-solid lithium-ion battery, comprising a positive electrode, a negative electrode, a separator, and an electrolyte. The separator is disposed between the dry-process positive and negative electrodes. When the lithium-ion battery is a liquid lithium-ion battery, the separator is a membrane; when the lithium-ion battery is a semi-solid lithium-ion battery, the separator is a solid electrolyte layer. In this invention, the lithium-ion battery is, for example, a primary battery or a secondary battery. A secondary battery is, for example, a pouch battery, a prismatic battery, or a cylindrical battery. This invention does not specifically limit the type or category of lithium-ion batteries. In this embodiment, a liquid lithium-ion battery is used as an example for illustration.

[0052] In one embodiment of the present invention, the positive electrode sheet includes a positive current collector and a positive active layer disposed on at least one surface of the positive current collector. The positive active layer includes a positive active material, a positive conductive agent, and a positive binder. The selection range of the positive current collector, positive active material, positive conductive agent, and positive binder is the same as that in the all-solid-state lithium-ion battery in the previous embodiment, and will not be elaborated further here.

[0053] In one embodiment of the present invention, the mass ratio of the positive electrode active material, the positive electrode conductive agent, and the positive electrode binder is, for example, (85 to 99.8):(0.1 to 10):(0.1 to 5). When preparing the positive electrode sheet, the positive electrode active material and the positive electrode binder are mixed according to the mass ratio and premixed at a temperature of -40°C to 15°C at a rotation speed of 500 rpm to 3000 rpm for 0.5 to 60 minutes to obtain a dry powder. The dry powder is then heated to 20°C to 140°C and held at this temperature for 0.1 to 24 hours. Then, it is subjected to fibrillation mixing at a rotation speed of 2000 rpm to 15000 rpm for 0.5 to 60 minutes, followed by kneading using an internal mixer for 0.5 to 60 minutes to strengthen the fiber structure of the dry powder. After cooling to room temperature, the material is crushed and granulated at speeds ranging from 100 rpm to 3000 rpm. The granulated powder is then fed into a differential roller mill to form a film, thereby obtaining the positive electrode active layer. The positive electrode active layer is then combined with the positive electrode current collector to obtain the positive electrode sheet.

[0054] In one embodiment of the present invention, the negative electrode sheet includes a negative current collector and a negative active layer coated at least on one surface of the negative current collector. The negative active layer includes a negative active material, a thickener, a negative conductive agent, and a negative binder, etc. The selection range of the negative current collector, negative active material, negative conductive agent, and negative binder is the same as that in the all-solid-state lithium-ion battery of the previous embodiment, and will not be elaborated further here. The thickener is, for example, selected from sodium carboxymethyl cellulose, etc.

[0055] In one embodiment of the present invention, the negative electrode active material is, for example, a composite of graphite and silicon oxide, and the mass ratio of graphite to silicon oxide is, for example, (90 to 95):(5 to 10). The negative electrode active material, acetylene black, sodium carboxymethyl cellulose, and styrene-butadiene rubber are mixed, for example, at a mass ratio of 96:2:1:1, and deionized water is added. The mixture is stirred thoroughly to obtain a negative electrode slurry. The negative electrode slurry is uniformly coated onto copper foil, and after drying, cold pressing, and slitting, a negative electrode sheet is obtained.

[0056] In one embodiment of the present invention, the electrolyte includes, for example, an organic solvent, a lithium salt, and additives. The organic solvent is selected from one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl acetate (EA), fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), or diethyl carbonate (DEC). The lithium salt is selected from, for example, one or more of lithium bis(fluorosulfonyl)imide (LiFSi), lithium difluorophosphate (LiPO2F2), lithium hexafluorophosphate (LiPF6), or lithium tetrafluoroborate (LiBF4). The additives are selected from one or more of vinylene carbonate (VC), lithium difluorooxalate borate (LiDFOB), or 1,3-propanesultone (1,3-PS). In this embodiment, in an argon atmosphere glove box with a water content of less than 10 ppm, ethylene carbonate, diethyl carbonate, and fluoroethylene carbonate are mixed, for example, at a mass ratio of 3:5:2. Thoroughly dried LiPF6, VC, and LiDFOB are dissolved in the mixed organic solvent and mixed thoroughly to obtain an electrolyte, wherein the content of LiPF6 is 12.5 wt%, the content of VC is 3 wt%, and the content of LiDFOB is 0.5 wt%.

[0057] In one embodiment of the present invention, the separator is, for example, a polyethylene membrane, a polypropylene membrane, a glass fiber membrane, or a composite membrane, and the thickness of the separator is, for example, 9 μm to 15 μm. In another embodiment of the present invention, the separator is, for example, an 8 μm to 10 μm polyethylene film as the base film, and a 2 μm to 4 μm thick nano-alumina coating is coated on at least one side of the base film. The above-mentioned positive electrode, separator, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrode to act as a separator, and the stacked or wound layers are used to obtain a bare cell. The bare cell is installed in a casing, baked at 80°C to remove water, injected with the above-mentioned electrolyte, and sealed. Afterwards, it undergoes processes such as settling, hot and cold pressing, formation, clamping, and capacity testing to obtain a lithium-ion battery.

[0058] The present invention will be explained in more detail below by referring to embodiments, which should not be construed as limiting. Appropriate modifications can be made within the scope of the present invention, and all such modifications fall within the technical scope of the present invention.

[0059] Example 1

[0060] Preparation of positive electrode active materials: Sb₂Se₃ with a median particle size D₅₀ of 30 nm and LiNi with a median particle size D₅₀ of 3 μm were selected. 0.9 Mn 0.05 Co 0.05 O2, 9.97g of LiNi 0.9 Mn 0.05 Co 0.05 O2 and 0.03g of Sb2Se3 were mixed and ball-milled at 200rpm / min for 5h. Then, the mixture was sintered at 700℃ for 10h under an argon atmosphere to obtain an active matrix with a first coating layer. The thickness of the first coating layer Sb2Se3 was 20nm.

[0061] Using SWCNTs with an aspect ratio of 2000 and a tube diameter of 1.4 nm, 9.899 g of LiNi with the first coating layer was coated. 0.9 Mn 0.05 Co 0.05 O2, 0.001g of SWCNT and 0.1g of PVDF were mixed with 10g of NMP solution at 1000rpm / min to form a uniform slurry. The slurry was then baked at 80℃ for 1h to obtain a mixed powder. The mixed powder was then ground and dispersed to obtain a positive electrode active material with a double-layer coating.

[0062] Preparation of the positive electrode sheet: 8.2g of the obtained positive electrode active material, 1.5g of Li6PS5Cl, and 0.2g of conductive carbon black were mixed evenly in a stirrer at 1000rpm / min for 5min. Then, 0.1g of PTFE was added to obtain a powder. The temperature was maintained at 7℃, and premixing was performed at 1500rpm / min for 5min. After uniform mixing, the powder was heated to 80℃ and held for 0.5h. Then, it was subjected to fibrillation mixing at 8000rpm / min for 3min, followed by kneading in a mixer for 3min to fibrillate the powder. The fibrillated powder was cooled to room temperature and crushed and granulated at 2500rpm / min. The granulated powder was then placed in a differential roller mill for film formation to obtain the positive electrode active layer. The areal capacity of the positive electrode active layer was 4mAh / cm². -2 It is then combined with aluminum foil to obtain a dry-process positive electrode sheet.

[0063] Preparation of negative electrode sheet: Graphite and silicon carbon materials are mixed at a mass ratio of 1:1 to obtain negative electrode active material. The negative electrode active material, Li6PS5Cl, acetylene black and styrene-butadiene rubber are stirred thoroughly in a xylene solvent system at a mass ratio of 70:25:2:3. After being mixed evenly, the mixture is coated on copper foil, dried and cold pressed to obtain negative electrode sheet.

[0064] Preparation of solid electrolyte layer: Li6PS5Cl solid electrolyte was cold-pressed at 300MPa to obtain a solid electrolyte layer with a thickness of 200μm.

[0065] Preparation of all-solid-state lithium-ion batteries: In a glove box filled with dry argon gas, dry-process positive electrode, solid electrolyte layer and negative electrode are placed into a mold and pressed and sealed to obtain all-solid-state lithium-ion batteries.

[0066] Example 2

[0067] In the preparation of the positive electrode active material, the content of SWCNT in the positive electrode active material was changed to 0.02 wt%, and other operations were kept the same as those in Comparative Example 1.

[0068] Example 3

[0069] In preparing the positive electrode active material, the content of SWCNT in the positive electrode active material was changed to 0.05 wt%, and other operations were consistent with those in Example 1.

[0070] Example 4

[0071] In preparing the positive electrode active material, the content of SWCNT in the positive electrode active material was changed to 1 wt%, and other operations were kept the same as in Example 1.

[0072] Example 5

[0073] In preparing the positive electrode active material, the content of SWCNT in the positive electrode active material was changed to 2wt%, and other operations were kept the same as in Example 1.

[0074] Example 6

[0075] In preparing the positive electrode active material, the content of SWCNT in the positive electrode active material was changed to 0.005 wt%, and other operations were consistent with those in Example 1.

[0076] Example 7

[0077] In preparing the positive electrode active material, the content of SWCNT in the positive electrode active material was changed to 2.5 wt%, and other operations were kept the same as in Example 1.

[0078] Example 8

[0079] When preparing the positive electrode active material, the aspect ratio of SWCNT was selected to be 100, and other operations were consistent with those in Example 3.

[0080] Example 9

[0081] When preparing the positive electrode active material, the aspect ratio of SWCNT was selected to be 500, and other operations were consistent with those in Example 3.

[0082] Example 10

[0083] When preparing the positive electrode active material, the aspect ratio of SWCNT was selected to be 1000, and other operations were consistent with those in Example 3.

[0084] Example 11

[0085] When preparing the positive electrode active material, the aspect ratio of SWCNT was selected to be 5000, and other operations were consistent with those in Example 3.

[0086] Example 12

[0087] When preparing the positive electrode active material, the aspect ratio of SWCNT was selected to be 10000, and other operations were consistent with those in Example 3.

[0088] Example 13

[0089] When preparing the positive electrode active material, the aspect ratio of SWCNT was selected to be 80, and other operations were consistent with those in Example 3.

[0090] Example 14

[0091] When preparing the positive electrode active material, the aspect ratio of SWCNT selected was 12000, and other operations were consistent with those in Example 3.

[0092] Example 15

[0093] When preparing the positive electrode active material, the selected SWCNT diameter was 0.5 nm, and other operations were consistent with those in Example 3.

[0094] Example 16

[0095] When preparing the positive electrode active material, the selected SWCNT diameter was 1 nm, and other operations were consistent with those in Example 3.

[0096] Example 17

[0097] When preparing the positive electrode active material, the selected SWCNT diameter was 2 nm, and other operations were consistent with those in Example 3.

[0098] Example 18

[0099] When preparing the positive electrode active material, the selected SWCNT diameter was 2.5 nm, and other operations were consistent with those in Example 3.

[0100] Example 19

[0101] When preparing the positive electrode active material, the selected SWCNT diameter was 0.4 nm, and other operations were consistent with those in Example 3.

[0102] Example 20

[0103] When preparing the positive electrode active material, the selected SWCNT diameter was 3 nm, and other operations were consistent with those in Example 3.

[0104] Example 21

[0105] When preparing the positive electrode active material, the median particle size D50 of Sb2Se3 was selected to be 1 nm, and other operations were consistent with those in Example 3.

[0106] Example 22

[0107] When preparing the positive electrode active material, the median particle size D50 of Sb2Se3 was selected to be 10 nm, and other operations were consistent with those in Example 3.

[0108] Example 23

[0109] When preparing the positive electrode active material, the median particle size D50 of Sb2Se3 was selected to be 50 nm, and other operations were consistent with those in Example 3.

[0110] Example 24

[0111] When preparing the positive electrode active material, the median particle size D50 of Sb2Se3 was selected to be 100 nm, and other operations were consistent with those in Example 3.

[0112] Example 25

[0113] When preparing the positive electrode active material, the median particle size D50 of Sb2Se3 was selected to be 120 nm, and other operations were consistent with those in Example 3.

[0114] Example 26

[0115] When preparing the positive electrode active material, the sintering temperature was 615℃, and other operations were consistent with those in Example 3.

[0116] Example 27

[0117] When preparing the positive electrode active material, the sintering temperature was 800℃, and other operations were consistent with those in Example 3.

[0118] Example 28

[0119] When preparing the positive electrode active material, the sintering temperature was 850°C, and other operations were consistent with those in Example 3.

[0120] Example 29

[0121] When preparing the positive electrode active material, the sintering temperature was 600℃, and other operations were consistent with those in Example 3.

[0122] Example 30

[0123] When preparing positive electrode active materials, LiNi 0.9 Mn 0.05 Co 0.05 The mass ratio of O2 to Sb2Se3 was 99.99:0.01, and the thickness of the first coating layer was 1 nm. Other operations were the same as in Example 3.

[0124] Example 31

[0125] When preparing positive electrode active materials, LiNi 0.9 Mn 0.05 Co 0.05 The mass ratio of O2 to Sb2Se3 was 99.9:0.1, and the thickness of the first coating layer was 10 nm. Other operations were the same as in Example 3.

[0126] Example 32

[0127] When preparing positive electrode active materials, LiNi 0.9 Mn 0.05 Co 0.05 The mass ratio of O2 to Sb2Se3 was 99.1:0.9, and the thickness of the first coating layer was 50 nm. Other operations were the same as in Example 3.

[0128] Example 33

[0129] When preparing positive electrode active materials, LiNi 0.9 Mn 0.05 Co 0.05 The thickness of the first coating layer obtained by using an O2 to Sb2Se3 mass ratio of 98:2 was 100 nm, and other operations were consistent with those in Example 3.

[0130] Example 34

[0131] When preparing positive electrode active materials, LiNi 0.9 Mn 0.05 Co 0.05 The first coating layer, obtained by using an O2 to Sb2Se3 mass ratio of 97.5:2.5, has a thickness of 110 nm, and other operations are consistent with those in Example 3.

[0132] Example 35

[0133] The preparation method of the positive electrode active material is the same as that in Example 3.

[0134] Preparation of the positive electrode sheet: 9.7g of the obtained positive electrode active material and 0.2g of conductive carbon black were mixed evenly in a stirrer at 1000rpm / min for 5min. Then, 0.1g of PTFE was added to obtain powder. The temperature was maintained at 7℃, and premixing was performed at 1500rpm / min for 5min. After uniform mixing, the powder was heated to 80℃ and held for 0.5h. Then, it was subjected to fibrillation mixing at 8000rpm / min for 3min, followed by kneading in a mixer for 3min to fibrillate the powder. The fibrillated powder was cooled to room temperature and crushed and granulated at 2500rpm / min. The granulated powder was then placed in a differential roller mill for film formation to obtain the positive electrode active layer. The areal capacity of the positive electrode active layer was 4mAh / cm². -2 It is then combined with aluminum foil to obtain a positive electrode sheet.

[0135] Preparation of the negative electrode sheet: Graphite and silicon oxide materials are mixed at a mass ratio of, for example, 90:10 to serve as the negative electrode active material. The negative electrode active material, acetylene black, sodium carboxymethyl cellulose, and styrene-butadiene rubber are mixed at a mass ratio of 96:2:1:1. Deionized water is added, and the mixture is thoroughly stirred to obtain a negative electrode slurry. The negative electrode slurry is uniformly coated onto copper foil, and after drying, cold pressing, and slitting, the negative electrode sheet is obtained.

[0136] Membrane selection: 9μm polyethylene was selected as the base membrane, and a 3μm thick nano-alumina coating was applied to both sides of the base membrane.

[0137] Preparation of electrolyte: In an argon atmosphere glove box with a water content of less than 10 ppm, ethylene carbonate, diethyl carbonate and fluoroethylene carbonate were mixed in a mass ratio of 3:5:2. LiPF6, VC and LiDFOB were dissolved in the mixed organic solvent and mixed evenly to obtain the electrolyte, wherein the content of LiPF6 was 12.5 wt%, the content of VC was 3 wt%, and the content of LiDFOB was 0.5 wt%.

[0138] Preparation of lithium-ion batteries: The above-mentioned positive electrode, separator, and negative electrode are stacked sequentially, with the separator positioned between the positive and negative electrodes to provide insulation. The stacked or wound electrodes yield a bare cell. The bare cell is then installed in a casing, baked at 80°C to remove moisture, injected with the above-mentioned electrolyte, and sealed. Following this, it undergoes standing, hot and cold pressing, formation, clamping, and capacity testing processes to obtain a lithium-ion battery.

[0139] Comparative Example 1

[0140] In preparing the positive electrode active material, no first coating layer is set, and other operations are consistent with those in Example 3.

[0141] Comparative Example 2

[0142] In preparing the positive electrode active material, no second coating layer is set, and other operations are consistent with those in Example 3.

[0143] Comparative Example 3

[0144] LiNi was directly selected as the positive electrode active material. 0.9 Mn 0.05 Co 0.05 O2, without setting the first and second coating layers, other operations are consistent with Example 3.

[0145] Comparative Example 4

[0146] In the preparation of the positive electrode active material, the sintering step is omitted, and other operations are consistent with those in Example 3.

[0147] Comparative Example 5

[0148] LiNi was directly selected as the positive electrode active material. 0.9 Mn 0.05 Co 0.05 O2, without setting a first coating layer and a second coating layer, other operations are consistent with Example 35.

[0149] In this invention, lithium-ion batteries were prepared using different positive electrode active materials in Examples 1 to 35 and Comparative Examples 1 to 5, and the performance of the lithium-ion batteries was tested. The test results are shown in Tables 1 to 3.

[0150] In one embodiment of the present invention, the thickness of the coating layer can be characterized by transmission electron microscopy (TEM). By observing the positive electrode active material using TEM, the first and second coating layers coated on the core surface can be clearly observed based on the differences in lattice fringes. Five locations within the coating layer are randomly selected for testing, and the thicknesses of the first and second coating layers are obtained. The average values ​​are calculated as the thicknesses of the first and second coating layers, respectively.

[0151] In one embodiment of the present invention, the coating rate can be determined using methods known in the art. As an example, the coating rate can be determined by first analyzing the positive electrode active material using energy-dispersive X-ray spectroscopy (TEM-EDX) with a transmission electron microscope. Specifically, elemental analysis is performed on the periphery of the positive electrode active material particles in the TEM image using EDX. When an intermediate with a first coating layer is obtained, antimony is analyzed to determine the antimony compounds coating the surface of the active substrate. The coating portion can be identified based on the distribution of antimony. Based on the entire periphery of the observed active substrate, the proportion of the coating portion is calculated to obtain the coating rate of the first coating layer. When the positive electrode active material is obtained, carbon is analyzed to determine the SWCNTs coating the positive electrode active material. The location of the SWCNTs can be defined as the coating portion. For the entire periphery of the observed positive electrode active material, the proportion of the coating portion is calculated to obtain the coating rate of the second coating layer. For example, measurements are performed on 10 positive electrode active material particles, and their average values ​​are used as the coating rates of the first and second coating layers, respectively.

[0152] In one embodiment of the present invention, the median particle size D50 was obtained by dry testing using a HELOS-RODOS type dry laser particle size analyzer.

[0153] In one embodiment of the present invention, when testing the cycle performance of lithium-ion batteries, the lithium-ion batteries prepared in the examples and comparative examples are operated at a voltage range of 2.5V to 4.3V, and at a charge / discharge rate of 1C / 1C. The discharge capacity of the battery in the first cycle is recorded as the 1C discharge capacity. The test ends when the battery capacity reaches 80% of the first cycle capacity (80% State of Health, 80% SOH), and the number of cycle cycles is obtained. When the test temperature is 25°C (room temperature) and 80°C (80°C), the number of cycle cycles at room temperature and the number of cycle cycles at 80°C are obtained.

[0154] In one embodiment of the present invention, to test the rate performance of lithium-ion batteries, the lithium-ion batteries obtained in the examples and comparative examples were sequentially charged at different rates (0.33C, 0.5C, 1C, 2C) to 4.3V at 25°C, then charged at a constant voltage of 4.3V until the current was less than 0.05C. After resting for 10 minutes, they were discharged at a constant current of 0.33C to 2.5V. The charging capacity of the lithium-ion batteries at 0.33C and the high rate of 2C was tested, and the fast charging capacity retention rate at the high rate of 2C was calculated according to the following formula:

[0155] Fast charging capacity retention rate (%) = (2C charging capacity / 0.33C charging capacity) × 100%.

[0156] Table 1. Partial characteristics of the positive electrode active materials in Examples 1 to 7 and performance test results of lithium-ion batteries.

[0157]

[0158] Please refer to Table 1. Comparing Examples 1 to 7, it can be seen that when preparing the positive electrode active material, only changing the SWCNT content, as the SWCNT content increases, the coating rate of the second coating layer increases, and the performance of the lithium-ion battery first increases and then decreases. This is because if the coating rate of the second coating layer is too small, the conductive network in the positive electrode active material is incomplete, the second coating layer is not uniform enough, and it is difficult to form an effective continuous conductive network on the surface of the active substrate, affecting the electrical connection between adjacent particles and resulting in high contact resistance. When the SWCNT content increases, the coating rate of the second coating layer becomes too large, which hinders the diffusion and transport of lithium ions on the surface of the positive electrode active material particles. Therefore, controlling the SWCNT content range can improve the performance of the lithium-ion battery.

[0159] Table 2, partial characteristics of the positive electrode active materials and performance test results of lithium-ion batteries in Examples 3, 8 to 34 and Comparative Examples 1 to 4.

[0160]

[0161] Please refer to Table 2. Comparing Examples 3, 8 to 14, it can be seen that when preparing the positive electrode active material, only changing the aspect ratio of SWCNTs leads to an initial increase followed by a decrease in lithium-ion battery performance as the aspect ratio of SWCNTs increases. This is because if the aspect ratio of SWCNTs in the second coating layer is too small, it is difficult to leverage the advantages of SWCNTs as efficient network builders, potentially limiting conductivity and thus reducing battery performance. Conversely, if the aspect ratio of SWCNTs in the second coating layer is too large, it can lead to difficulties in dispersion, uneven coating, and blocked channels, negatively impacting electron and ion transport, which is also detrimental to the performance of the positive electrode active material in the battery. Therefore, by controlling the aspect ratio of SWCNTs to ensure the formation of a three-dimensional conductive network and improve coating uniformity, the performance of the lithium-ion battery can be improved.

[0162] Please refer to Table 2. Comparing Examples 3, 15 to 20, it can be seen that when preparing the positive electrode active material, only changing the diameter of the SWCNT tubes results in an initial increase followed by a decrease in lithium-ion battery performance as the SWCNT diameter increases. This is because when the SWCNT diameter in the second coating layer is too small, the SWCNT has an extremely high specific surface area, which significantly increases the contact area with the positive electrode electrolyte, thereby inducing a large number of side reactions and severely affecting the battery's cycle performance. When the SWCNT diameter in the second coating layer is too large, the rigidity of the SWCNT increases, making it difficult to bend. During the coating process, it is difficult to tightly adhere to the curved surface of the active substrate particles, which may lead to poor contact or large gaps between the coating layer and the particles, affecting the interfacial electron transfer efficiency. Therefore, by controlling the SWCNT diameter, the performance of the formed positive electrode active material can be improved, thereby improving the performance of the lithium-ion battery.

[0163] Please refer to Table 2. Comparing Examples 3, 21 to 25, it can be seen that when preparing the positive electrode active material, only the median particle size of the Sb₂Se₃ particles is changed. As the median particle size of the Sb₂Se₃ particles increases, the coating thickness of the first coating layer first increases and then decreases, and the performance of the lithium-ion battery first increases and then decreases. The particle size of the Sb₂Se₃ particles affects the electrochemical performance of the coated positive electrode active material. This is because when the median particle size of Sb₂Se₃ is too small, agglomeration easily occurs during ball milling. Agglomerated particles may cause the local coating layer to be too thick or too thin, resulting in defects. When the median particle size of Sb₂Se₃ is too large, it is difficult to melt and form a thin and uniform nano-coating layer. Therefore, by controlling the median particle size of Sb₂Se₃ particles, a thin and uniform nano-coating layer can be formed, improving the stability of the positive electrode active material and providing a flat and uniform Li₂O₃ coating. + Intercalation / deintercalation interfaces are optimized to avoid excessively high local current densities or uneven reactions, thus improving Li... + This improves the utilization efficiency, thereby enhancing the performance of lithium-ion batteries.

[0164] Please refer to Table 2. Comparing Examples 3, 26 to 29, it can be seen that when preparing the positive electrode active material, only the sintering temperature is changed. As the sintering temperature increases, the coating rate of the first coating layer increases, and the performance of the lithium-ion battery first increases and then decreases. This is because the melting point of Sb₂Se₃ is approximately 611°C. When the sintering temperature is too low or sintering is not performed, it is insufficient for Sb₂Se₃ to fully melt on the surface of the active substrate, making it difficult to form good chemical bonds and achieve uniform coating on the active substrate. When the sintering temperature is too high, it may cause structural changes, oxygen loss, grain growth, or phase transitions in the active substrate itself. Therefore, controlling the sintering temperature to form a uniform first coating layer without affecting the performance of the active substrate improves the performance of the lithium-ion battery.

[0165] Please refer to Table 2. Comparing Examples 3, 30 to 34, it can be seen that when preparing the positive electrode active material, only changing the mass ratio of the active matrix to Sb₂Se₃, the coating thickness of the first coating layer increases with the increase of Sb₂Se₃ content. The performance of the lithium-ion battery first increases and then decreases. This is because when the coating thickness is too small, it cannot effectively suppress the volume expansion / contraction of the active matrix during charge-discharge cycles, leading to the destruction of the material structure of the active matrix and the loss of active sites. When the coating thickness is too large, it will significantly increase the Li₂Se₃ content. + The diffusion and electron transport pathways within the first coating layer increase the battery's internal resistance. Therefore, a suitable mass ratio of active substrate to Sb₂Se₃ and an appropriate coating thickness of the first coating layer are necessary to improve the stability of the active substrate while ensuring lithium-ion transport in the cathode active material, thereby enhancing the performance of the lithium-ion battery.

[0166] Please refer to Table 2. Comparing Example 3 and Comparative Examples 1 to 4, it can be seen that the performance of the lithium-ion battery is poor when neither the first nor the second coating layer is provided. When only the first and second coating layers are provided, or when the first coating layer is not sintered during preparation, the performance of the lithium-ion battery is slightly improved compared to the absence of both coating layers, but the overall performance is still poor. This is because Sb₂Se₃, as the first coating layer, can provide tighter and more uniform chemical and mechanical protection with the active substrate. It can form a stable passivation layer, effectively suppressing side reactions and buffering the initial volume change of the internal active substrate. In addition, it can alleviate the release of oxygen from the active substrate during cycling. SWCNT, as the second coating layer, further enhances the conductivity of the coating layer and provides additional mechanical support and flexibility. Without the SWCNT coating layer, the electron transport rate slows down, the utilization rate of the positive electrode active material at high current densities decreases, resulting in a significant deterioration in rate performance and the inability to achieve rapid charge and discharge. Similarly, the volume expansion constraint of the active substrate is also weakened. Without the Sb₂Se₃ coating layer, the active substrate comes into direct contact with the electrolyte, leading to more severe side reactions. Furthermore, the lack of an Sb₂Se₃ stress-absorbing layer makes the active substrate susceptible to mechanical damage during cycling. In addition, the absence of Sb-O bonds in the positive electrode active material means that the escape of lattice oxygen cannot be effectively limited, significantly deteriorating its cycle performance and high-temperature performance. Therefore, the synergistic effect of the first and second coating layers in the positive electrode active material improves its structural stability and conductivity, thereby enhancing the performance of lithium-ion batteries, including the positive electrode active material.

[0167] Table 3. Performance test results of lithium-ion batteries in Example 35 and Comparative Example 5

[0168]

[0169] Please refer to Table 3. Comparing Example 35 and Comparative Example 5, it can be seen that when the double-layer coated positive electrode active material of this application is used in liquid lithium-ion batteries, it can significantly improve the room temperature cycle performance and fast charging performance of lithium-ion batteries. However, the high-temperature cycle performance of liquid lithium-ion batteries is generally worse than that of all-solid-state lithium-ion batteries. This is because at high temperatures, there are side reactions between the electrolyte and the positive electrode active material, electrolyte decomposition, and interface film damage. Therefore, the improvement in high-temperature cycle performance is worse than that of all-solid-state lithium-ion batteries. Therefore, the double-layer coated positive electrode active material obtained in this application can be used in liquid lithium-ion batteries or semi-solid-state lithium-ion batteries to improve the performance of lithium-ion batteries.

[0170] This invention also provides an electronic device comprising at least one of the aforementioned lithium-ion batteries, which provides electrical energy. The electronic device can be a vehicle, mobile phone, portable device, laptop computer, ship, spacecraft, electric toy, or power tool, etc. In one embodiment of this invention, the vehicle is, for example, a new energy vehicle, which can be a pure electric vehicle, a hybrid electric vehicle, or a range-extended electric vehicle, etc. Spacecraft include airplanes, rockets, space shuttles, and spacecraft, etc. Electric toys include stationary or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, etc. Power tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers, etc. The electronic device includes the aforementioned lithium-ion battery, and therefore the advantages of including the aforementioned lithium-ion battery are not elaborated here.

[0171] In summary, this invention proposes a positive electrode active material, its preparation method, and its application. Through double-layer coating, the first coating layer acts as a flexible buffer layer, absorbing stress and reducing mechanical damage to the positive electrode active material. Simultaneously, the first coating layer provides a more even and uniform lithium-ion (Li) ion distribution. + The insertion / extraction interface is designed to avoid excessively high local current density or uneven reaction, thereby optimizing the Li... +The first and second coating layers improve the utilization efficiency; simultaneously, the antimony compound in the first coating layer forms Sb-O bonds with the oxygen-containing active matrix, alleviating the escape of lattice oxygen and enhancing the thermal stability of the oxygen-containing cathode active material; the presence of single-walled carbon nanotubes on the surface of the cathode active material solves the dispersion problem of single-walled carbon nanotubes in dry cathode sheets, and the single-walled carbon nanotubes construct a highly efficient three-dimensional conductive network, forming a through-type ion diffusion channel, thereby ensuring that electrons can quickly reach every corner of the active matrix; and the fibrous three-dimensional network uniformly coats the surface of the active matrix, which can restrain the volume change of the active matrix during cycling. Therefore, the first and second coating layers together improve the structural stability and conductivity of the cathode active material, thereby improving the rate performance and cycle stability of the battery.

[0172] The above description is merely a preferred embodiment of this application and an explanation of the technical principles used. Those skilled in the art should understand that the scope of the invention involved in this application is not limited to the technical solutions formed by a specific combination of the above-mentioned technical features, but should also cover other technical solutions formed by any combination of the above-mentioned technical features or their equivalent features without departing from the inventive concept. For example, technical solutions formed by replacing the above-mentioned features with technical features with similar functions disclosed in this application (but not limited to) each other.

[0173] Apart from the technical features described in the specification, the other technical features are known to those skilled in the art. To highlight the innovative features of this invention, the other technical features will not be described in detail here.

Claims

1. A positive electrode active material, characterized in that, include: Active matrix; A first coating layer is disposed on at least a portion of the surface of the active substrate, the first coating layer comprising an antimony compound; as well as A second coating layer is disposed on at least a portion of the surface of the first coating layer, and the second coating layer includes single-walled carbon nanotubes.

2. The positive electrode active material according to claim 1, characterized in that, The antimony compound is selected from at least one of Sb2Se3, Sb2S3 or Sb2Te3; and / or, the mass ratio of the active matrix to the antimony compound is (98 to 99.99):(0.01 to 2).

3. The positive electrode active material according to claim 1, characterized in that, The thickness of the first coating layer is 1 nm to 100 nm, and the coating rate of the first coating layer is 90% to 100%, wherein the coating rate of the first coating layer is the percentage of the coating area of ​​the first coating layer on the surface of the active substrate to the surface area of ​​the active substrate.

4. The positive electrode active material according to claim 1, characterized in that, The second coating layer further includes a binder, wherein the content of the single-walled carbon nanotubes in the positive electrode active material is from 0.01 wt% to 2 wt%, and the content of the binder in the positive electrode active material is from 0.1 wt% to 7 wt%. And / or, the adhesive is selected from one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyimide, or polyurethane.

5. The positive electrode active material according to claim 1, characterized in that, The second coating layer has a three-dimensional mesh structure, and the coating rate of the second coating layer is 1% to 50%, wherein the coating rate of the second coating layer is the percentage of the coating area of ​​the second coating layer on the surface of the first coating layer to the surface area of ​​the first coating layer; And / or, the diameter of the single-walled carbon nanotube is 0.5 nm to 2.5 nm, and the aspect ratio is 100 to 10000.

6. The positive electrode active material according to claim 5, characterized in that, The thickness of the first coating layer is 10 nm to 50 nm; And / or, the coverage of the second coating layer is 1% to 25%; And / or, the diameter of the single-walled carbon nanotube is 1 nm to 2 nm, and the aspect ratio is 1000 to 5000.

7. The positive electrode active material according to claim 1, characterized in that, The active matrix is ​​selected from one or more of lithium iron phosphate, lithium manganese iron phosphate, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, or lithium nickel cobalt aluminum oxide.

8. A method for preparing a positive electrode active material, used for preparing the positive electrode active material according to any one of claims 1 to 7, characterized in that, include: The active matrix and antimony compound are mixed evenly to obtain a mixture; the median particle size of the antimony compound is 1 nm to 100 nm. The mixture is sintered to obtain an intermediate with a first coating layer; the sintering temperature is 610°C to 800°C and the sintering time is 1 hour to 24 hours. The intermediate, single-walled carbon nanotubes, binder, and solvent are mixed evenly to obtain a mixed slurry; the solvent is selected from one or more of N-methylpyrrolidone, dimethylformamide, dimethylacetamide, triethyl phosphate, or cyclohexanone. The mixed slurry is dried and ground to obtain the positive electrode active material.

9. A lithium-ion battery, characterized in that, It includes a positive electrode sheet, wherein the positive electrode sheet includes a positive electrode active material, and the positive electrode active material is selected from the positive electrode active material of any one of claims 1 to 7 or the positive electrode active material obtained by the preparation method of claim 8.

10. The lithium-ion battery according to claim 9, characterized in that, The lithium-ion battery is an all-solid-state lithium-ion battery.

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