Positive electrode material, pole piece, and electrochemical device and electric device comprising same

Abstract

The invention relates to a positive electrode material, a pole piece and an electrochemical device and an electric device comprising the same, and belongs to the technical field of electrochemical energy storage. The positive electrode material provided by the invention comprises a base material and a coating layer coating the surface of the base material, the coating layer comprises Li-doped Co3O4, and a value in lattice constants of the Li-doped Co3O4 is 8.085-8.09. According to the positive electrode material provided by the invention, the Li-doped Co3O4 coating layer structure is arranged on the surface of the base material, and the coating layer has characteristics similar to a fast ion conductor microcosmically and has excellent electronic conductivity and lithium ion conduction capability, so that the dynamic behavior of charges in a high-speed transmission process is promoted; the capacity retention ratio and platform voltage stability of the battery under the high-rate charge-discharge condition are effectively improved, the gas production behavior of the positive electrode material in the circulation process is effectively relieved, and particle fragmentation is inhibited, so that the overall performance and reliability of the battery are improved.

Description

Technical Field

[0001] This application belongs to the field of electrochemical energy storage technology, specifically relating to cathode materials, electrode sheets, and electrochemical devices and electrical devices including them. Background Technology

[0002] In lithium-ion rechargeable batteries, lithium nickel manganese cobalt oxide (NCM) cathode materials have become one of the most widely used cathode materials due to their high energy density and excellent lithium-ion intercalation / deintercalation kinetics. However, during repeated lithium-ion intercalation / deintercalation, the layered structure of the material undergoes significant lattice stress and volume changes, leading to microcracks and even breakage of the cathode particles. Simultaneously, lattice oxygen loss creates oxygen vacancies, further inducing the dissolution and migration of transition metal ions, exacerbating structural degradation. Furthermore, continuous interfacial side reactions between the cathode material and the electrolyte can cause surface phase transitions, interfacial film instability, and gas evolution, severely impairing the battery's cycle life and safety. These degradation phenomena are particularly pronounced under harsh conditions such as high temperature and high voltage, significantly limiting the actual lifespan of NCM-based lithium-ion batteries. Therefore, developing cathode materials that can effectively mitigate gas generation behavior and suppress particle breakage during cycling, thereby improving the overall performance and reliability of the battery, is of great significance. Summary of the Invention

[0003] The purpose of this application is to overcome the problems existing in the prior art and to provide a positive electrode material, an electrode sheet, and an electrochemical device and an electrical device including the same.

[0004] This application is implemented through the following technical solution: This application provides a cathode material, including a substrate material and a coating layer covering the surface of the substrate material. The coating layer includes Li-doped Co3O4, and the lattice constant α of the Li-doped Co3O4 is 8.085 Å to 8.09 Å.

[0005] In some embodiments, the Co2p of the Li-doped Co3O4 3 / 2 The binding energy of the main peak is 779.8 eV ~ 781.5 eV.

[0006] In some embodiments, the maximum thickness δmax and the minimum thickness δmin of the coating layer satisfy the following: δmax / δmin ≤ 2.0, 1 / 750μm≤δmax≤1 / 15μm, 1 / 1500μm≤δmin≤1 / 30μm.

[0007] In some embodiments, the amount of Li element n in the Li-doped Co3O4 is... Li The amount of substance n of Co element CoSatisfies: 0.01 ≤ n Li / n Co ≤ 0.1.

[0008] In some embodiments, the average thickness δ of the coating layer and the radius R of the substrate material satisfy: 0.0001 ≤ δ / R ≤ 0.1; the radius R of the substrate material is R = D / 2, where D is the radius of the substrate material. v50 Particle size.

[0009] In some embodiments, the average thickness δ of the coating layer is 0.001 μm to 0.05 μm.

[0010] In some embodiments, the matrix material D v50 The particle size D is 1μm~20μm.

[0011] In some embodiments, the average thickness δ of the coating layer, the radius R of the matrix material, and the amount of substance n of the Li element are specified. Li The amount of substance n of Co element Co Satisfies: 0.001 ≤ (n) Co / n Li )×(δ / R)≤10.

[0012] In some embodiments, the matrix material has the general chemical formula Li(Ni) x Co y Mn z O2, where 0≤x≤1, 0≤y≤1, 0≤z≤1, and x+y+z=1.

[0013] Another aspect of this application provides a positive electrode sheet, including the positive electrode material described in this application.

[0014] In another aspect, this application provides an electrochemical device including the positive electrode described in this application.

[0015] In another aspect, this application provides an electrical device, including the electrochemical device described in this application.

[0016] This application has the following beneficial effects: The cathode material of this application has a Li-doped Co3O4 coating layer on the surface of the substrate material, wherein the Li in the coating layer is... + Able to replace part of Co 2+ Site, producing Co 4+Furthermore, when the lattice constant α of Li-doped Co3O4 is between 8.085 Å and 8.09 Å, it exhibits microscopic characteristics similar to a fast ion conductor, significantly improving the conductivity of Co3O4 and compensating for capacity loss caused by the coating layer, while avoiding the high-pressure, high-temperature structural instability issues caused by Li doping. Lithium doping into the Co3O4 lattice generates a large number of hole carriers, enhancing the material's conductivity. This coating layer combines excellent electronic conductivity with lithium-ion conduction capability and high-temperature resistance, promoting the dynamic behavior of charge during high-speed transport and effectively improving the capacity retention and plateau voltage stability of lithium-ion batteries under high-rate charge-discharge conditions. Detailed Implementation

[0017] In the description of this application, the technical features described in an open-ended manner include both closed technical solutions consisting of the listed features and open technical solutions that include the listed features.

[0018] In the description of this application, the use of terms such as "first," "second," etc., is for the purpose of distinguishing technical features only and should not be construed as indicating or implying relative importance or implicitly indicating the number of technical features indicated or the order of the technical features indicated.

[0019] Throughout the description of this application, references to "some embodiments," "partial embodiments," "one embodiment," "another embodiment," "a specific embodiment," or "partial embodiment" mean that at least one embodiment or example in this application includes the specific features, structures, materials, or characteristics described in that embodiment or example.

[0020] In the description of this application, a list of items connected by the terms “one of,” “one of,” “a kind of,” or other similar terms may mean any one of the listed items; a list of items connected by the term “at least one of” may mean any combination of the listed items.

[0021] In the description of this application, numerical ranges are referred to. Unless otherwise specified, such numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Any lower limit can be combined with any upper limit to form a range not explicitly stated; and any lower limit can be combined with other lower limits to form a range not explicitly stated, just as any upper limit can be combined with any other upper limit to form a range not explicitly stated. Furthermore, each individually disclosed point or single value can itself serve as a lower or upper limit and can be combined with any other point or single value or with other lower or upper limits to form a range not explicitly stated.

[0022] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. The embodiments of this application may omit unnecessary detailed descriptions. For example, detailed descriptions of well-known matters and repeated descriptions of actually identical structures may be omitted. This is to avoid making the following description unnecessarily lengthy and to facilitate understanding by those skilled in the art.

[0023] This application provides a cathode material, including a substrate material and a coating layer covering the surface of the substrate material. The coating layer includes Li-doped Co3O4, and the lattice constant α of the Li-doped Co3O4 is 8.085 Å to 8.09 Å.

[0024] The cathode material provided in this application has a Li-doped Co3O4 coating layer structure on the surface of a substrate material (such as lithium nickel cobalt manganese oxide). Metal ions M at the interface between the coating layer and the substrate material form MO-Co chemical bonds with the Co in the coating layer. This material can significantly improve the stability of the NCM system during high-voltage, high-temperature cycling, and the Li in the coating layer... + Able to replace part of Co 2+ Site, producing Co 4+ Furthermore, when the lattice constant α of Li-doped Co3O4 is 8.085 Å to 8.09 Å, it exhibits characteristics similar to a fast ion conductor at the microscopic level. It combines excellent electronic conductivity with lithium-ion conduction capability and high-temperature resistance, promoting the dynamic behavior of charge during high-speed transport. This effectively improves the overall conductivity of the material, as well as the capacity retention rate and plateau voltage stability of the battery under high-rate charge and discharge conditions. It can also significantly improve the conductivity of Co3O4, compensate for the capacity loss caused by the coating layer, and avoid the structural instability caused by high-pressure and high-temperature Li doping. This effectively alleviates the gas generation behavior of the cathode material during cycling and suppresses particle fragmentation, thereby improving the overall performance and reliability of the battery.

[0025] Specifically, the method for testing the lattice constant 'a' value of Li-doped Co3O4 is as follows: The cladding layer structure is observed using HRTEM, then selected area electron diffraction (SEED) is used to obtain selected area diffraction spots. The interplanar spacing 'd' value is calculated from the spot pattern, and the interplanar spacing (h, k, l) values ​​are matched according to the 'd' value. Finally, the 'a' value is calculated using the interplanar spacing formula for cubic crystal systems and the Bragg diffraction equation. The average value of 'a' is taken from three different regions. The Bragg diffraction equation is: 2dsinθ = nλ; the interplanar spacing formula for cubic crystal systems is: (h...k...l ... 2+k 2 +l 2 ) / a 2 =1 / d 2 .

[0026] For example, the lattice constant α of the Li-doped Co3O4 may be 8.085 Å, 8.086 Å, 8.087 Å, 8.088 Å, 8.089 Å, or fall within the range of any two of the above values.

[0027] In some embodiments, the matrix material has the general chemical formula Li(Ni) x Co y Mn z O2, where 0≤x≤1, 0≤y≤1, 0≤z≤1, and x+y+z=1.

[0028] In some embodiments, the Co2p of the Li-doped Co3O4 3 / 2 The binding energy of the main peak is 779.8 eV ~ 781.5 eV.

[0029] In the Li-doped Co3O4, as the lithium (Li) doping concentration increases, the average oxidation state of Co increases, and the Co2p... 3 / 2 The main peak binding energy shifts towards higher binding energy directions when Co2p 3 / 2 When combined within the above range, sufficient Li can be ensured. + Entering the crystal lattice generates a large number of hole carriers, while avoiding excessive doping that could lead to structural distortion or the formation of impurity phases (such as Li2O).

[0030] Specifically, the Co2p of the Li-doped Co3O4 3 / 2 The main peak binding energy was measured using X-ray photoelectron spectroscopy (XPS) to determine the Co 2p binding energy of the Li-doped Co3O4 nanocoating layer. 3 / 2 The binding energy of the main peak was used for characterization. First, a full-spectrum scan of 0-1350 eV was performed to confirm the presence of elements such as Co, O, and C. Then, a high-resolution scan was performed on the Co 2p region (770-795 eV), with a pass energy of 20-30 eV and a step size ≤0.1 eV for 2-5 accumulations to improve the signal-to-noise ratio. The charge shift was corrected using the C 1s peak (284.8 eV). The Co 2p spectrum was fitted using Advantage, and the spin-orbit splitting was fixed at Δ=15.1 eV with an intensity ratio of Co 2p. 3 / 2 :Co 2p 1 / 2 =2:1.

[0031] For example, the Co2p of the Li-doped Co3O4 3 / 2The main peak binding energy can be 779.8 eV, 779.9 eV, 780 eV, 780.1 eV, 780.2 eV, 780.3 eV, 780.4 eV, 780.5 eV, 780.6 eV, 780.7 eV, 780.8 eV, 780.9 eV, 781 eV, 781.1 eV, 781.2 eV, 781.3 eV, 781.4 eV, or 781.5 eV, or fall within the range of any two of the above values.

[0032] In some embodiments, the maximum thickness δmax and the minimum thickness δmin of the coating layer satisfy the following: δmax / δmin ≤ 2.0, 1 / 750μm≤δmax≤1 / 15μm, 1 / 1500μm≤δmin≤1 / 30μm.

[0033] Specifically, the maximum thickness δmax and minimum thickness δmin of the coating layer are obtained by measuring and statistically analyzing the coating layer thickness using a scanning electron microscope cross-section or ultrathin section. The coating layer thickness is the vertical distance from the outer surface of the coating layer to the surface of the substrate material. Twenty measurement points are randomly selected from the outermost edge of the coating layer, and the maximum thickness δmax and minimum thickness δmin of the coating layer are taken from these 20 points.

[0034] In some embodiments, the amount of Li element n in the Li-doped Co3O4 is... Li The amount of substance n of Co element Co Satisfies: 0.01 ≤ n Li / n Co ≤ 0.1.

[0035] When the amount of Li to Co in Li-doped Co3O4 satisfies the above-mentioned ratio, sufficient Li can be produced. + Entering the crystal lattice generates a large number of hole carriers, while avoiding excessive doping that could lead to structural distortion or the formation of impurity phases (such as Li₂O), thereby regulating Co₂p. 3 / 2 The main peak binding energy and the lattice constant of Li-doped Co3O4 are within the specified range, which gives the cathode material excellent ionic conductivity.

[0036] For example, the n Co / n Li It can be 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09 or 0.1, or fall within the range of any two of the above values.

[0037] In some embodiments, the average thickness δ of the coating layer and the radius R of the substrate material satisfy: 0.0001 ≤ δ / R ≤ 0.1; the radius R of the substrate material is R = D / 2, where D is the radius of the substrate material. v50 Particle size.

[0038] This study found that when δ / R satisfies the above relationship, the material has good conductivity and can effectively alleviate the gas generation behavior of the cathode material during cycling and suppress particle fragmentation. Excessive coating thickness affects the conductivity and specific capacity of the material, while too thin coating has little effect on structural stability.

[0039] In some embodiments, the matrix material D v50 The particle size D is 1μm~20μm.

[0040] D v50 This refers to the particle size corresponding to a cumulative particle distribution of 50%. For example, the D of the matrix material... v50 The particle size is 1μm, 1.5μm, 2μm, 2.5μm, 3μm, 3.5μm, 4μm, 4.5μm, 5μm, 5.5μm, 6μm, 6.5μm, 7μm, 7.5μm, 8μm, 8.5μm, 9μm, 9.5μm, 10μm, 10.5μm, 11μm, 11.5μm, 12μm, 12.5μm, 13μm, 13.5μm, 14μm, 14.5μm, 15μm, 15.5μm, 15μm, 16.5μm, 17μm, 17.5μm, 18μm, 18.5μm, 19μm, 19.5μm, or 20μm, or falls within the range of any two of the above values.

[0041] In some embodiments, the internal grains of the matrix material are single-crystal particles.

[0042] Specifically, the average thickness δ of the coating layer is obtained by measuring and statistically analyzing the coating layer thickness using a scanning electron microscope section or an ultrathin section. The coating layer thickness is the vertical distance from the outer surface of the coating layer to the surface of the substrate material. Twenty measurement points are arbitrarily selected on the outermost side of the coating layer, and the maximum thickness δmax and minimum thickness δmin of the coating layer at these 20 points are taken. The average thickness δ of the coating layer is defined as (δmax + δmin) / 2.

[0043] In some embodiments, the average thickness δ of the coating layer is 0.001 μm to 0.05 μm.

[0044] For example, the average thickness δ of the coating layer may be 0.001μm, 0.005μm, 0.01μm, 0.015μm, 0.02μm, 0.025μm, 0.03μm, 0.035μm, 0.04μm, 0.045μm, or 0.05μm, or fall within the range of any two of the above values.

[0045] In some embodiments, the average thickness δ of the coating layer, the radius R of the matrix material, and the amount of substance n of the Li element are specified. Li The amount of substance n of Co element Co Satisfies: 0.001 ≤ (n) Co / n Li )×(δ / R)≤10.

[0046] δ / R can be used to measure the relative thickness of the coating layer for particles of different sizes. The smaller the δ / R, the thinner the relative thickness of the coating; the larger the δ / R, the thicker the relative thickness of the coating. In this application, the amount of Li doping in the coating layer is related to the relative thickness of the coating layer. Under the above relationship, it is possible to: avoid structural instability and side reactions caused by excessive doping; and at the same time provide sufficient conductivity to reduce polarization, ensuring efficient ion / electron transport in the bulk phase and at the interface, thereby synergistically suppressing particle fragmentation and gas generation, and comprehensively improving the overall electrochemical performance of the battery.

[0047] In some embodiments, the average thickness δ of the coating layer, the radius R of the matrix material, and the amount of substance n of the Li element are specified. Li The amount of substance n of Co element Co Satisfies: 0.06 ≤ (n Co / n Li )×(δ / R)≤1.

[0048] When (n) Co / n Li With δ / R in the range of 0.06 to 1, dynamic matching between coating thickness and Li doping amount can be achieved, which can prevent interface instability caused by overdoping and ensure that the coating has a sufficient conductive network, suppressing particle fragmentation and reducing gas generation, thereby improving cycle stability and rate performance.

[0049] For example, the (n) Co / n Li)×(δ / R) can be 0.001, 0.005, 0.01, 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5, 5.5, 6, 6.5, 7, 7.5, 8, 8.5, 9, 9.5 or 10, or fall within the range of any two of the above values.

[0050] Another aspect of this application provides a positive electrode sheet, including the positive electrode material described in this application.

[0051] In some embodiments, the positive electrode sheet may include a positive current collector and a positive electrode material layer disposed on at least one side of the positive current collector, wherein the positive electrode material layer includes the positive electrode material described in this application.

[0052] In some embodiments, the positive current collector is a metal foil or a composite current collector. In some embodiments, the metal foil is an aluminum foil. The composite current collector may include a metal foil substrate and a conductive layer disposed on at least one side of the metal foil substrate.

[0053] In some embodiments, the conductive layer may include at least one of carbon, carbon black, graphite, expanded graphite, graphene, graphene nanosheets, carbon fiber, carbon nanofiber, graphitized carbon sheet, carbon tube, carbon nanotube, activated carbon, and mesoporous carbon.

[0054] In some embodiments, the positive electrode material layer further includes a positive electrode binder and a positive electrode conductive agent.

[0055] In some embodiments, the positive electrode binder includes at least one of polyvinylidene fluoride (PVDF), poly(vinylidene fluoride)-hexafluoropropylene (PVDF-HFP), polytetrafluoroethylene (PTFE), vinylidene fluoride-tetrafluoroethylene-propylene terpolymer, vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, fluorinated acrylate resin, polyacrylic acid, polyacrylonitrile, polyimide, polyurethane, polyvinyl butyral, polyvinylpyrrolidone (PVP), acrylic acid-acrylonitrile-acrylamide copolymer, and acrylic acid-acrylonitrile-acrylate copolymer. The positive electrode binder of this application is not limited to the above materials, but also includes other materials that can be used as battery positive electrode binders.

[0056] In some embodiments, the positive electrode conductive agent may include at least one of carbon, carbon black, graphite, expanded graphite, graphene, graphene nanosheets, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon fibers, carbon nanofibers, graphitized carbon sheets, carbon nanotubes, carbon nanotubes, activated carbon, and mesoporous carbon. The positive electrode conductive agent in this application is not limited to the above materials, but also includes other materials that can be used as positive electrode conductive agents in batteries.

[0057] This application also provides an electrochemical device, including any device in which an electrochemical reaction occurs to interconvert chemical energy and electrical energy, including, but not limited to, all types of primary batteries, secondary batteries, fuel cells, solar cells, or capacitors. In particular, the electrochemical device is a lithium secondary battery, including lithium metal secondary batteries, lithium-ion secondary batteries, lithium polymer secondary batteries, or lithium-ion polymer secondary batteries.

[0058] In some embodiments, the electrochemical device includes the positive electrode described in this application.

[0059] In some embodiments, the electrochemical device further includes a negative electrode.

[0060] In some embodiments, the negative electrode sheet may include a negative electrode current collector and a negative electrode active material layer disposed on at least one side of the negative electrode current collector.

[0061] In some embodiments, the negative current collector is a metal foil or a composite current collector. In some embodiments, the metal foil is a copper foil. The composite current collector may include a metal foil substrate and a conductive layer disposed on at least one side of the metal foil substrate. In some embodiments, the conductive layer may include at least one of carbon, carbon black, graphite, expanded graphite, graphene, graphene nanosheets, carbon fibers, carbon nanofibers, graphitized carbon sheets, carbon nanotubes, activated carbon, and mesoporous carbon.

[0062] In some embodiments, the negative electrode active material layer includes a negative electrode active material, a negative electrode binder, and a negative electrode conductive agent.

[0063] In some embodiments, the negative electrode active material may include natural graphite particles, synthetic graphite particles, hard carbon, soft carbon, mesophase carbon microspheres (MCMB), Sn, SnO2, SnO, or Li4Ti5O. 12 The negative electrode active material is selected from at least one of LTO, Si material, silicon-carbon (Si-C) composite material, silicon-nitrogen (Si-N) composite material, and silicon-oxygen (Si-O) composite material. The negative electrode active material of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as negative electrode active materials for batteries.

[0064] In some embodiments, the negative electrode binder may include at least one of the following: polyacrylic acid, polymethacrylic acid, polyacrylate, polymethacrylate, polyacrylamide, styrene-butadiene rubber, acrylic styrene-butadiene rubber, acrylic acid-acrylonitrile-acrylamide copolymer, acrylic acid-acrylonitrile-acrylate copolymer, acrylonitrile-butadiene rubber, nitrile rubber, acrylonitrile-styrene-butadiene copolymer, acryloyl rubber, butyl rubber, fluororubber, polytetrafluoroethylene, polyvinyl alcohol, polyvinyl acetate, polyepoxychloropropane, polyphosphazene, polyacrylonitrile, polystyrene, latex, acrylic resin, phenolic resin, epoxy resin, carboxymethyl cellulose, hydroxypropyl cellulose, cellulose acetate, cellulose acetate butyrate, cellulose acetate propionate, cyanoethyl cellulose, carboxymethyl chitosan, polyester, polyamide, polyether, polyimide, polycarboxylic acid ester, polycarboxylic acid, polyurethane, alginate, fluorinated polymer, chlorinated polymer, polyvinylidene fluoride, and poly(vinylidene fluoride)-hexafluoropropylene. The negative electrode binder of this application is not limited to the above-mentioned materials, but also includes other materials that can be used as battery negative electrode binders.

[0065] In some embodiments, the negative electrode conductive agent may include at least one of carbon, carbon black, graphite, expanded graphite, graphene, graphene nanosheets, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon fibers, carbon nanofibers, graphitized carbon sheets, carbon nanotubes, activated carbon, and mesoporous carbon. The negative electrode conductive agent of this application is not limited to the above materials, but also includes other materials that can be used as battery negative electrode conductive agents.

[0066] In another aspect, this application provides an electrical device, including the electrochemical device described in this application.

[0067] The electrical device used in this application is not particularly limited and can be any electrical device known in the prior art. According to some embodiments of this application, the electrical device includes, but is not limited to, mobile phones, smartphones, laptops, tablets, wearable devices, smartwatches, smart bracelets, smart glasses, power banks, televisions, game consoles, game controllers, digital cameras, smart speakers, headphones, keyboards, mice, monitors, drones, audio equipment, home appliances, toys, power tools, automobiles, motorcycles, electric bicycles, bicycles, robots, robot dogs, industrial robots, and embodied intelligent robots.

[0068] To better illustrate the purpose, technical solution, and advantages of this application, the following detailed description will be provided in conjunction with specific embodiments. Those skilled in the art should understand that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.

[0069] Unless otherwise specified, the experimental methods used in the examples are conventional methods; the materials and reagents used are commercially available unless otherwise specified.

[0070] Example 1 A positive electrode material, the preparation method of which is as follows: (1) Precursor preparation NiSO4·6H2O, CoSO4·7H2O, and MnSO4·H2O were dissolved in deionized water at a molar ratio of 0.8:0.1:0.1. Ammonia was added to the reaction vessel as a complexing agent. After the reaction was completed, the precipitate was washed until neutral, filtered, and dried to obtain spherical Ni 0.8 Co 0.1 Mn 0.1 (OH)2 precursor; (2) Preparation of matrix materials The precursor and LiOH·H2O were mixed at a molar ratio of Li / (Ni+Co+Mn) = 1.05, ball-milled until homogeneous, and then subjected to a two-stage calcination in an oxygen atmosphere: the first stage was pre-calcination at 500℃ for 4 hours to remove moisture and organic matter; the second stage was heating to 900℃ and holding for 12 hours. After calcination, the product was crushed and sieved to obtain a layered LiNi structure. 0.8 Co 0.1 Mn 0.1 O2 cathode substrate material, D obtained through sieving v50 =5μm matrix material; (3) Preparation of Li-doped Co3O4 coating layer Dissolve LiNO3 and Co(NO3)2·6H2O in ethanol, n Li / n Co =0.02, add citric acid as a complexing agent, stir to form a homogeneous sol, and control the sol concentration to 0.2M. Then, react this sol with LiNi 0.8 Co 0.1 Mn 0.1 O2 powder was mixed at a liquid-to-solid ratio of 2 mL / g, and the solvent was evaporated at 80°C to form a gel. Then, it was calcined in air at 500°C for 4 hours and then calcined in air at 700°C for 6 hours to form a Li-doped Co3O4 coating layer on the surface of the substrate material, thus obtaining the cathode material.

[0071] Example 2 This embodiment provides a cathode material, which differs from Embodiment 1 in that, in step (1) of this embodiment, the molar ratio of NiSO4·6H2O, CoSO4·7H2O, and MnSO4·H2O is 0.85:0.08:0.07, and the matrix material is LiNi. 0.85 Co 0.08 Mn0.07 O2; D is obtained by sieving in step (2) v50 =1.4μm matrix material; in step (3), n Li / n Co =0.05, sol concentration is 0.05M, liquid-to-solid ratio is 1mL / g, and everything else is the same as in Example 1.

[0072] Example 3 This embodiment provides a cathode material, which differs from Embodiment 1 in that, in step (1) of this embodiment, the molar ratio of NiSO4·6H2O, CoSO4·7H2O, and MnSO4·H2O is 0.9:0.05:0.05, and the matrix material is LiNi. 0.9 Co 0.05 Mn 0.05 O2; D is obtained by sieving in step (2) v50 The matrix material has a thickness of 3.6 μm; in step (3), n Li / n Co =0.08, sol concentration was 0.1M, liquid-to-solid ratio was 2mL / g, and everything else was the same as in Example 1.

[0073] Example 4 This embodiment provides a cathode material, which differs from Embodiment 1 in that, in step (1) of this embodiment, the molar ratio of NiSO4·6H2O, CoSO4·7H2O, and MnSO4·H2O is 0.7:0.2:0.1, and the matrix material is LiNi. 0.7 Co 0.2 Mn 0.1 O2; D is obtained by sieving in step (2) v50 The matrix material has a thickness of 6.4 μm; in step (3), n Li / n Co =0.03, sol concentration was 0.05M, liquid-to-solid ratio was 1.2mL / g, and everything else was the same as in Example 1.

[0074] Example 5 This embodiment provides a cathode material, which differs from Embodiment 1 in that n in step (3) of this embodiment... Li / n Co Unlike Example 1, n Li / n Co =0.01, and all other parameters are the same as in Example 1, to obtain the cathode material; the parameters of this example are shown in Table 1.

[0075] Example 6 This embodiment provides a cathode material, which differs from Embodiment 1 in that n in step (3) of this embodiment... Li / n CoUnlike Example 1, n Li / n Co =0.1, and all other parameters are the same as in Example 1, to obtain the positive electrode material; the parameters of this example are shown in Table 1.

[0076] Example 7 This embodiment provides a cathode material, which differs from Embodiment 1 in that, in step (2) of this embodiment, D is obtained by sieving. v50 The substrate material was 20 μm thick, and all other parameters were the same as in Example 1, to obtain the cathode material; the parameters of this example are shown in Table 1.

[0077] Example 8 This embodiment provides a positive electrode material. The difference from Embodiment 1 is that in step (3) of this embodiment, the sol concentration is 0.4 M and the liquid-solid ratio is 2 mL / g, so that the thickness of the coating layer is different from that of Embodiment 1. All other aspects are the same as those of Embodiment 1, and a positive electrode material is obtained. The parameters of this embodiment are shown in Table 1.

[0078] Example 9 This embodiment provides a positive electrode material. The difference from Embodiment 1 is that in step (3) of this embodiment, the sol concentration is 0.01 M and the liquid-solid ratio is 1 mL / g, so that the thickness of the coating layer is different from that of Embodiment 1. All other parameters are the same as those of Embodiment 1, and a positive electrode material is obtained. The parameters of this embodiment are shown in Table 1.

[0079] Example 10 This embodiment provides a cathode material, which differs from Embodiment 1 in that, in step (2) of this embodiment, D is obtained by sieving. v50 The substrate material was 1 μm thick, and all other parameters were the same as in Example 1 to obtain the cathode material; the parameters of this example are shown in Table 1.

[0080] Example 11 This embodiment provides a cathode material, which differs from Embodiment 1 in that, in step (2) of this embodiment, D is obtained by sieving. v50 =20μm matrix material; n in step (3) Li / n Co =0.1, sol concentration is 0.01 M, liquid-solid ratio is 1 mL / g, and other parameters are the same as in Example 1, to obtain the positive electrode material; the parameters of this example are shown in Table 1.

[0081] Example 12 This embodiment provides a cathode material, which differs from Embodiment 1 in that, in step (2) of this embodiment, D is obtained by sieving. v50 =1μm matrix material; n in step (3) Li / n Co=0.01, sol concentration was 0.4 M, liquid-to-solid ratio was 2 mL / g, and all other parameters were the same as in Example 1, to obtain the positive electrode material; the parameters of this example are shown in Table 1.

[0082] Comparative Example 1 This comparative example provides a cathode material whose preparation method differs from that of Example 1 in that LiNO3 is not added in step (3), while all other steps are the same as in Example 1, and a cathode material is obtained; that is, the cathode material obtained in this comparative example has a Co3O4 coating layer and is not doped with lithium.

[0083] Comparative Example 2 This comparative example provides a cathode material whose preparation method differs from that of Example 1 in that it does not contain step (3). All other steps are the same as in Example 1 to obtain the cathode material; that is, the cathode material obtained in this comparative example does not contain a coating layer.

[0084] Comparative Example 3 This embodiment provides a cathode material, which differs from Embodiment 1 in that n in step (3) of this embodiment... Li / n Co Unlike Example 1, n Li / n Co =0.005, and all other parameters are the same as in Example 1, to obtain the cathode material; the parameters of this example are shown in Table 1.

[0085] Comparative Example 4 This embodiment provides a cathode material, which differs from Embodiment 1 in that n in step (3) of this embodiment... Li / n Co Unlike Example 1, n Li / n Co =0.15, and all other parameters are the same as in Example 1, to obtain the cathode material; the parameters of this example are shown in Table 1.

[0086] The cathode materials of the embodiments and comparative examples were characterized as follows: (1) XRD test XRD (X-ray diffraction) testing is used to analyze the crystal structure and phase composition of materials. It is performed using an X-ray diffractometer with Cu-Kα rays as the radiation source. The scanning angle range is generally 10°-90° with a step size of 0.02°. The tube voltage and current are 40 kV and 40 mA, respectively. The sample needs to be ground into a fine powder and evenly spread on a sample slide for testing. Finally, the phase structure of the material is determined by comparing the obtained XRD pattern with a standard PDF card.

[0087] (2) SEM and TEM tests SEM (Scanning Electron Microscopy) is used to observe the surface morphology and particle distribution of materials. During testing, the sample is dispersed on a conductive tape. If the sample has poor conductivity, it needs to be sputtered with gold or carbon. The sample is then placed in the SEM sample chamber and its morphology is observed under vacuum using an accelerating voltage of 5-15 kV. Images are taken at different magnifications to analyze the microstructure characteristics of the material. TEM (Transmission Electron Microscopy) is used to further analyze the microstructure and lattice arrangement of materials. Before testing, the sample is ultrasonically dispersed in ethanol or acetone and then dropped onto a copper grid on a carbon support film. After natural drying, it is placed in the TEM for observation. High-resolution images show lattice fringes, and combined with electron diffraction patterns, the crystal structure can be analyzed. Elemental analysis of local areas can be performed using EDS to confirm the elemental distribution.

[0088] In the cathode materials of the examples and comparative examples, n Li / n Co The matrix material radius R, the maximum thickness of the coating layer δmax, the minimum thickness of the coating layer δmin, the average thickness of the coating layer δ, the lattice constant α of the Li-doped Co3O4 coating layer, and Co2p 3 / 2 The main peak binding energies are shown in Table 1. The radius R of the matrix material was statistically determined using scanning electron microscopy (SEM). The maximum and minimum thicknesses of the coating layer, δmax and δmin, were also determined using SEM. The average thickness of the coating layer, δ = (δmax + δmin) / 2. The lattice constant α of the Li-doped Co3O4 coating layer was determined using selected area electron diffraction (SEM). The Co2p of the Li-doped Co3O4 coating layer... 3 / 2 The binding energy of the main peak was measured using photoelectron spectroscopy.

[0089] Table 1. Parameter table of cathode materials in the examples and comparative examples. The cathode materials of the examples and comparative examples were subjected to thermogravimetric analysis and ionic conductivity testing. The testing methods were as follows: (1) TG-DSC During testing, a small sample (approximately 5-10 mg) is placed in a crucible and heated from room temperature to 800 °C at a heating rate of 5-10 °C / min under nitrogen or air atmosphere. Thermogravimetric (TG) curves are recorded to observe the mass change, and differential scanning calorimetry (DSC) curves are recorded to identify endothermic or exothermic peaks, thereby determining the thermal decomposition temperature and phase transition behavior of the material. (2) Ionic conductivity test Ionic conductivity was measured using an electrochemical workstation with alternating current impedance (EIS) to evaluate the ionic conductivity of the material. The test frequency range was 1 MHz to 1 Hz, and the amplitude was 5 mV. The sample was pressed into a sheet and sandwiched between two stainless steel electrodes. During the test, the impedance behavior in the high-frequency region was analyzed using Nyquist plots. Combined with the sample thickness and electrode area, the ionic conductivity was calculated using the formula σ = L / (R × A), where σ is the ionic conductivity (S / cm), L is the sample thickness (cm), R is the bulk resistance (Ω), and A is the electrode area (cm²).

[0090] (3) Impedance test Charge transfer resistance (R) CT The impedance was measured using an electrochemical workstation (EIS) with a frequency range of 1 MHz to 0.01 Hz and an AC voltage amplitude of 5 mV. The impedance data are represented by a Nyquist plot; the semicircle appearing in the mid-frequency region corresponds to the charge transfer process, and its diameter is R. CT The impedance spectrum was fitted using an equivalent circuit model to extract R0. CT parameter.

[0091] The cathode materials used in the examples and comparative examples were respectively used to prepare lithium-ion secondary batteries for electrochemical devices. The preparation methods of the batteries are as follows: (1) Preparation of positive electrode The positive electrode material conductive agent acetylene black and binder polyvinylidene fluoride (PVDF) obtained in each embodiment and comparative example were thoroughly mixed in an N-methylpyrrolidone solvent system at a mass ratio of 95:3:2. The mixture was then coated onto the positive electrode current collector Al foil, and after drying, cold pressing and slitting, the positive electrode sheet was obtained. (2) Preparation of negative electrode The negative electrode active material artificial graphite, conductive agent acetylene black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) are thoroughly mixed in a deionized water solvent system at a mass ratio of 96:1:1.5:1.5. The mixture is then coated onto the negative electrode current collector Cu foil, and after drying, cold pressing, and slitting, the negative electrode sheet is obtained. (3) Preparation of the separating membrane Polyethylene (PE) porous polymer film is used as the separator; (4) Preparation of electrolyte A solution prepared by mixing lithium salt LiPF6 with a non-aqueous organic solvent (ethylene carbonate (EC): diethyl carbonate (DEC): propylene carbonate (PC): propyl propionate (PP): ethylene carbonate (VC) = 20:30:20:28:2, mass ratio) at a mass ratio of 8:92 is used as the electrolyte for lithium-ion secondary batteries. (5) Battery assembly The positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to provide safety isolation. The electrode assembly is then wound up, placed in a packaging shell, injected with electrolyte, and sealed to obtain a lithium-ion secondary battery.

[0092] The lithium-ion secondary batteries obtained in the examples and comparative examples were subjected to performance testing. The testing method was as follows: (1) Cyclic performance: First, in an environment of 45°C, the first charge and discharge were performed. Constant current and constant voltage charging were performed at a charging current of 1C until the upper limit voltage was 4.5. Then, constant current discharge was performed at a discharge current of 1C until the final voltage was 3V. The discharge capacity of the first cycle was recorded. Then, 500 charge and discharge cycles were performed, and the discharge capacity of the 500th cycle was recorded.

[0093] Cycle capacity retention = (Discharge capacity of the 500th cycle / Discharge capacity of the first cycle) × 100%.

[0094] (2) Thermal runaway temperature: The thermal safety of a single lithium-ion full battery was assessed using an extended volumetric accelerated calorimeter (EV-ARC) manufactured by THT Corporation, USA. Before testing, the battery was charged to 4.5 V at a constant current and constant voltage rate of 0.5 C to ensure it was fully charged. Subsequently, a K-type thermocouple was tightly attached to the center area of ​​the battery surface and fixed with high-temperature tape to improve temperature measurement accuracy. The test adopted the thermal waiting method, with a heating step size of 5℃, a waiting time of 45 min per step, and a self-heating rate trigger threshold of 0.02℃·min. -1 Within each temperature step, the system monitors in real time whether the battery exhibits self-heating behavior. Once dT / dt ≥ 0.02 ℃ / min is detected, thermal runaway is identified as initiation, and the system transitions to the adiabatic tracking phase, recording the dynamic evolution of temperature and temperature rise rate under adiabatic conditions. The thermal runaway initiation temperature is determined by analyzing the dT / dt-T curve.

[0095] The test results are shown in Table 2 below.

[0096] Table 2. Performance test results of the cathode materials and batteries in the examples and comparative examples. As shown in Table 2, appropriate Li doping and a uniform and moderate coating layer can significantly improve the capacity retention, ionic conductivity, and thermal stability of the material. However, excessively high doping ratios or uneven coating may have a negative impact on performance. Furthermore, a comparison between undoped and uncoated materials shows that the unoptimized material is significantly inferior in terms of electrochemical performance and thermal safety. Therefore, by reasonably controlling the doping ratio and coating layer parameters, the overall performance of the material can be effectively improved, providing a feasible path for the design of high-performance batteries.

[0097] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application and are not intended to limit the scope of protection of this application. Although this application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of this application without departing from the substance and scope of the technical solutions of this application.

Claims

1. A positive electrode material, characterized in that, It includes a matrix material and a coating layer covering the surface of the matrix material, wherein the coating layer includes Li-doped Co3O4, and the lattice constant α of the Li-doped Co3O4 is 8.085 Å to 8.09 Å.

2. The cathode material according to claim 1, characterized in that, At least one of the following must be met: (1) The Co2p of the Li-doped Co3O4 3 / 2 The binding energy of the main peak is 779.8 eV ~ 781.5 eV; (2) The maximum thickness δmax and the minimum thickness δmin of the coating layer satisfy the following conditions: δmax / δmin≤ 2.0, 1 / 750μm≤δmax≤1 / 15μm, 1 / 1500μm≤δmin≤1 / 30μm.

3. The cathode material according to claim 1, characterized in that, In the Li-doped Co3O4, the amount of Li element n Li The amount of substance n of Co element Co Satisfies: 0.01 ≤ n Li / n Co ≤ 0.

1.

4. The cathode material according to claim 1 or 2, characterized in that, The average thickness δ of the coating layer and the radius R of the matrix material satisfy the following condition: 0.0001 ≤ δ / R ≤ 0.1; the radius R of the matrix material is R = D / 2, where D is the radius of the matrix material. v50 Particle size.

5. The positive electrode material according to claim 4, characterized in that, The average thickness δ of the coating layer is 0.001 μm to 0.05 μm; and / or, the D of the matrix material... v50 The particle size D is 1μm~20μm.

6. The positive electrode material according to claim 5, characterized in that, The average thickness δ of the coating layer, the radius R of the matrix material, and the amount of Li element n Li The amount of substance n of Co element Co Satisfies: 0.001 ≤ (n) Co / n Li )×(δ / R)≤10.

7. The cathode material according to claim 1, characterized in that, The general chemical formula of the matrix material is Li(Ni) x Co y Mn z O2, where 0≤x≤1, 0≤y≤1, 0≤z≤1, and x+y+z=1.

8. A positive electrode plate, characterized in that, Includes the cathode material as described in any one of claims 1-7.

9. An electrochemical device, characterized in that, Includes the positive electrode sheet as described in claim 8.

10. An electrical appliance, characterized in that, Includes the electrochemical device as described in claim 9.

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