Positive plate as well as electrochemical device and electronic equipment comprising positive plate

Abstract

The invention discloses a positive plate as well as an electrochemical device and electronic equipment comprising the positive plate. The positive plate comprises a positive current collector and a positive material layer arranged on at least one surface of the current collector, and the positive material layer sequentially comprises a first active material layer, a second active material layer and a third active material layer in the direction far away from the positive current collector; the first active material layer comprises a first nickel cobalt lithium manganate material; the second active material layer comprises a composite active material, the composite active material comprises an inner core and a coating layer arranged on the surface of the inner core, the inner core comprises a second nickel cobalt lithium manganate material, and the coating layer comprises a second lithium manganese iron phosphate material; and the third active material layer comprises a first lithium iron manganese phosphate material. An electrochemical device (especially a lithium ion battery) obtained by adopting the positive plate has excellent rate capability, capacity performance and cycle performance.

Description

Technical Field

[0001] The present invention provides a positive electrode and an electrochemical device and electronic device containing the same. Background Technology

[0002] Lithium-ion batteries, as the core of modern electrochemical energy storage systems, rely heavily on the development and application of cathode materials for their performance. The properties of cathode materials directly affect the battery's energy density, cycle life, and rate performance, thus influencing its application prospects in electric vehicles, energy storage systems, and other fields. In recent years, lithium manganese iron phosphate (LiMn) has become increasingly important. x Fe y Lithium iron phosphate (LiFePO4, x+y=1, LMFP) has attracted widespread attention as a promising new cathode material due to its superior voltage plateau and energy density compared to traditional lithium iron phosphate (LiFePO4, LFP). Compared to LFP (theoretical voltage plateau of approximately 3.45V), LMFP has a higher theoretical voltage plateau (approximately 4.1V), giving it greater energy output potential. However, the insufficient conductivity of LMFP significantly limits its applications.

[0003] To improve the conductivity and overall electrochemical performance of LMFP (Lithium Cobalt Phosphate Film), researchers have attempted to composite it with nickel cobalt manganese oxide (NCM). NCM, with its high electronic conductivity, high rate performance, and good energy density, can effectively address the conductivity deficiency of LMFP. Furthermore, the high voltage plateau of NCM complements the characteristics of LMFP, potentially improving the overall energy density of the composite material and thus enhancing the market competitiveness of lithium-ion batteries. However, although the LMFP-NCM composite scheme can theoretically improve the conductivity and energy density of the cathode material, existing LMFP-NCM composite systems still suffer from poor conductivity, failing to achieve excellent rate and capacity performance in lithium-ion batteries and thus not meeting the requirements of practical applications. Summary of the Invention

[0004] The technical problem this invention aims to solve is to overcome the shortcomings of existing lithium-ion batteries using LMFP and NCM composite systems, which cannot simultaneously achieve excellent rate performance and capacity performance. This invention provides a positive electrode and electrochemical and electronic devices incorporating it. Electrochemical devices (especially lithium-ion batteries) using this positive electrode exhibit both excellent rate performance and capacity performance, as well as excellent cycle performance.

[0005] The present invention solves the above-mentioned technical problems through the following technical solution:

[0006] A first aspect of the present invention provides a positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive electrode material layer disposed on at least one surface of the current collector, wherein, along a direction away from the positive current collector, the positive electrode material layer sequentially comprises a first active material layer, a second active material layer, and a third active material layer; the first active material layer comprises a first lithium nickel cobalt manganese oxide material; the second active material layer comprises a composite active material, the composite active material comprising a core and a coating layer disposed on its surface, wherein the core comprises a second lithium nickel cobalt manganese oxide material, the coating layer comprises a second lithium manganese iron phosphate material; and the third active material layer comprises a first lithium manganese iron phosphate material.

[0007] A second aspect of the present invention provides an electrochemical device comprising a positive electrode as described above.

[0008] A third aspect of the present invention provides an electronic device comprising the electrochemical device described above.

[0009] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0010] The reagents and raw materials used in this invention are all commercially available.

[0011] The positive and progressive effects of this invention are as follows:

[0012] This invention specifically designs a cathode sheet comprising a three-layer active material layer obtained by combining two types of cathode materials, NCM and LMFP. Along the direction away from the cathode current collector, this cathode sheet sequentially uses NCM, a composite active material (LMFP-coated NCM), and LMFP as the cathode material, overcoming the problem of poor electrochemical performance in existing LMFP and NCM composite systems. Electrochemical devices (especially lithium-ion batteries) using this cathode sheet simultaneously exhibit excellent rate performance, capacity performance, and cycle performance. Attached Figure Description

[0013] Figure 1 This is a schematic diagram of the structure of the composite active material in the positive electrode obtained in Examples 1-10.

[0014] Figure 2 This is a schematic diagram of the microstructure of the positive electrode material layer of the positive electrode sheet obtained in Examples 1-10.

[0015] Figure 3 The diagram shows the structure of the positive electrode obtained in Examples 1-10.

[0016] Figure 4 The graphs show a comparison of the cycle performance of lithium-ion batteries obtained using the positive electrode sheets in Examples 1-10 and Comparative Examples 1-5.

[0017] Figure 5 The image shown is a CPSEM-EDS image of the positive electrode sheet of Example 1.

[0018] Reference numerals: 1-Third active material layer; 2-Second active material layer; 20-Composite active material particles; 21-LMFP particles; 22-NCM particles; 3-First active material layer; 4-Positive electrode current collector. Detailed Implementation

[0019] The present invention is further illustrated below by way of embodiments, but the invention is not limited to the scope of the embodiments described herein. Experimental methods in the following embodiments that do not specify specific conditions were performed according to conventional methods and conditions, or as selected according to the product instructions.

[0020] A first aspect of the present invention provides a positive electrode sheet, the positive electrode sheet comprising a positive current collector and a positive electrode material layer disposed on at least one surface of the current collector, wherein, along a direction away from the positive current collector, the positive electrode material layer sequentially comprises a first active material layer, a second active material layer, and a third active material layer; the first active material layer comprises a first lithium nickel cobalt manganese oxide material; the second active material layer comprises a composite active material, the composite active material comprising a core and a coating layer disposed on its surface, wherein the core comprises a second lithium nickel cobalt manganese oxide material, the coating layer comprises a second lithium manganese iron phosphate material; and the third active material layer comprises a first lithium manganese iron phosphate material.

[0021] In this invention, by specifically using a composite active material containing LMFP coated with NCM as an intermediate layer, a first active material layer containing NCM is placed close to the current collector, while a third active material layer containing LMFP is placed as the outermost layer away from the current collector, a positive electrode sheet with excellent conductivity and other properties is obtained, thereby improving the rate performance and energy density of the resulting battery.

[0022] In this invention, "particle size" refers to the average particle size, and the particle size of a single particle refers to the longest straight-line distance between any two points on the outer surface of the particle.

[0023] In some embodiments of the present invention, the particle size of the second lithium nickel cobalt manganese oxide material in the composite active material is 0.5~20 μm, more preferably 0.5~10 μm, and even more preferably 0.5~3 μm, for example 3 μm.

[0024] In some embodiments of the present invention, the particle size of the second lithium manganese iron phosphate material in the composite active material is 0.01~5 μm, more preferably 0.01~1 μm, and even more preferably 0.01~0.3 μm, for example 0.3 μm.

[0025] In some embodiments of the present invention, the particle size of the composite active material is 0.5~20 μm, preferably 4~15 μm, for example 5 μm or 12 μm.

[0026] In some embodiments of the present invention, the thickness of the coating layer in the composite active material is 10~500 nm, for example, 20 nm.

[0027] In some embodiments of the present invention, the second lithium nickel cobalt manganese oxide material in the composite active material is a single crystal or a polycrystalline material. The single crystal also includes a quasi-single crystal form.

[0028] In some embodiments of the present invention, the mass ratio of the second lithium nickel cobalt manganese oxide material and the second lithium manganese iron phosphate material in the composite active material is (1~99):(1~99), for example, 5:5, 9:1 or 1:9.

[0029] In some embodiments of the present invention, the preparation method of the composite active material includes the following steps: coating the second lithium nickel cobalt manganese oxide material with a second lithium manganese iron phosphate precursor solution, wherein the second lithium manganese iron phosphate precursor in the second lithium manganese iron phosphate precursor solution forms the second lithium manganese iron phosphate material, and the coating treatment is preferably a sol-gel method, a chemical vapor deposition method, or an impregnation method; the second lithium manganese iron phosphate precursor solution preferably includes lithium salt and manganese-based iron phosphate.

[0030] In some embodiments of the present invention, the content of the composite active material in the second active material layer is 70% to 90%, for example, 80%, where the percentage is the mass percentage of the composite active material in the second active material layer.

[0031] In some embodiments of the present invention, the second active material layer may also be doped with individual NCM particles and / or LMFP particles.

[0032] In some embodiments of the present invention, the thickness of the second active material layer is 20~200 μm, more preferably 20~100 μm, for example 50 μm.

[0033] In some embodiments of the present invention, the mass ratio of the first lithium nickel cobalt manganese oxide material, the composite active material and the first lithium manganese iron phosphate material is 1:(0.1~10):(0.1~10), for example 1:1:1, 1:0.25:0.25, 1:4:1, 1:0.4:1, 1:1:4 or 1:1:0.4.

[0034] In some embodiments of the present invention, the particle size of the first nickel cobalt manganese oxide lithium material in the first active material layer is 0.5~20 μm, more preferably 0.5~10 μm, for example 3 μm.

[0035] In some embodiments of the present invention, the thickness of the first active material layer is 20~200 μm, more preferably 20~100 μm, for example 50 μm.

[0036] In some optional embodiments of the present invention, the content of the first lithium nickel cobalt manganese oxide material in the first active material layer is 70% to 90%, for example, 80%, and the percentage is the mass percentage of the first lithium nickel cobalt manganese oxide material in the first active material layer.

[0037] In some embodiments of the present invention, the first lithium nickel cobalt manganese oxide material in the first active material layer is a single crystal or a polycrystalline material. The single crystal also includes a quasi-single crystal form.

[0038] In some embodiments of the present invention, in the third active material layer, the particle size of the first lithium manganese iron phosphate material is 0.01~5 μm, more preferably 0.01~1 μm, for example 0.3 μm.

[0039] In some embodiments of the present invention, the thickness of the third active material layer is 20~200 μm, more preferably 20~100 μm, for example 50 μm.

[0040] In some embodiments of the present invention, the content of the first lithium manganese iron phosphate material in the third active material layer is 70% to 90%, for example, 80%, and the percentage is the mass percentage of the first lithium manganese iron phosphate material in the third active material layer.

[0041] In some embodiments of the present invention, the positive electrode material layer further includes a conductive agent.

[0042] In some embodiments of the present invention, the first active material layer further includes a conductive agent. The content of the conductive agent may be 0-20%, for example 5%, where the percentage is the mass percentage of the conductive agent in the first active material layer.

[0043] In some embodiments of the present invention, the second active material layer further includes a conductive agent. The content of the conductive agent can be 0-20%, and the percentage is the mass percentage of the conductive agent in the second active material layer.

[0044] In some embodiments of the present invention, the third active material layer further includes a conductive agent. The content of the conductive agent can be 0-20%, and the percentage is the mass percentage of the conductive agent in the third active material layer.

[0045] In this invention, the conductive agent is a reagent used to ensure that the electrode has good charge and discharge performance. It can be selected from graphite materials such as natural graphite and artificial graphite; carbon black materials such as carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, and thermal cracking black; conductive fibers such as carbon fiber and metal fiber; metal powders such as fluorinated carbon powder, aluminum powder, and nickel powder; conductive whiskers such as zinc oxide and potassium titanate; and conductive metal oxides or polyphenylene derivatives such as titanium dioxide, for example, carbon black.

[0046] In some embodiments of the present invention, the positive electrode material layer further includes a binder.

[0047] In some embodiments of the present invention, the first active material layer further includes a binder. The content of the binder may be 0-20%, for example 5% or 10%, where the percentage is the mass percentage of the binder in the first active material layer.

[0048] In some embodiments of the present invention, the second active material layer further includes a binder. The content of the binder may be 0-20%, for example 5% or 10%, where the percentage is the mass percentage of the binder in the second active material layer.

[0049] In some embodiments of the present invention, the third active material layer further includes a binder. The content of the binder may be 0-20%, for example 5% or 10%, where the percentage is the mass percentage of the binder in the third active material layer.

[0050] In this invention, the binder can be a component that facilitates the bonding between the positive electrode material and the conductive agent, and also facilitates the bonding between the positive electrode material and the positive electrode current collector. It can typically be selected from polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), sodium carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers, such as PVDF.

[0051] In some embodiments of the present invention, the first active material layer includes a first lithium nickel cobalt manganese oxide material, polyvinylidene fluoride, and conductive carbon black.

[0052] In some specific embodiments of the present invention, the mass ratio of the first lithium nickel cobalt manganese oxide material, polyvinylidene fluoride and conductive carbon black is 8:1:1 or 9:0.5:0.5.

[0053] In some embodiments of the present invention, the second active material layer includes a composite active material, polyvinylidene fluoride, and conductive carbon black.

[0054] In some specific embodiments of the present invention, the mass ratio of the composite active material, polyvinylidene fluoride and conductive carbon black is 8:1:1 or 9:0.5:0.5.

[0055] In some embodiments of the present invention, the third active material layer comprises a first lithium manganese iron phosphate material, polyvinylidene fluoride, and conductive carbon black.

[0056] In some specific embodiments of the present invention, the mass ratio of the first lithium manganese iron phosphate material, polyvinylidene fluoride and conductive carbon black is 8:1:1 or 9:0.5:0.5.

[0057] In this invention, the positive electrode current collector can be a conventional positive electrode current collector in the art. For the positive electrode current collector, materials that do not cause chemical changes and have high conductivity can be used without limitation. For example, commonly used materials include stainless steel, aluminum, nickel, titanium, or calcined carbon, or aluminum or stainless steel materials surface-treated with carbon, nickel, titanium, silver, etc. To enhance adhesion, micro-embossing can be formed on the surface of the positive electrode current collector. The positive electrode current collector can be used in various forms, such as films, sheets, foils, meshes, or porous bodies.

[0058] In some optional embodiments of the present invention, the positive current collector is aluminum foil.

[0059] In some optional embodiments of the present invention, the thickness of the positive current collector can be 5~20 μm, for example 15 μm or 13 μm.

[0060] In this invention, the positive electrode sheet can be prepared using methods conventional in the art.

[0061] In some optional embodiments of the present invention, the method for preparing the positive electrode sheet includes the following steps:

[0062] S1. Apply a first active slurry to at least one surface of the positive electrode current collector and dry it, wherein the first active slurry forms a first active material layer; wherein the first active slurry includes a first lithium nickel cobalt manganese oxide material;

[0063] S2. Apply a second active slurry to the first active material layer and dry it, thereby forming a second active material layer; wherein, the second active slurry includes the composite active material; the composite active material includes a second lithium nickel cobalt manganese oxide material coated with a second lithium manganese iron phosphate material;

[0064] S3. Apply a third active slurry to the second active material layer and dry it, wherein the third active slurry forms a third active material layer; wherein the third active slurry includes a first lithium manganese iron phosphate material.

[0065] A second aspect of the present invention provides an electrochemical device comprising a positive electrode as described above.

[0066] In this invention, the electrochemical device is preferably a battery.

[0067] In this invention, the electrochemical device is preferably a lithium-ion battery. The lithium-ion battery can be a liquid battery, a solid-state battery, or a semi-solid-state battery. For example, a liquid lithium-ion battery includes a positive electrode, a negative electrode, a separator, and an electrolyte; a solid lithium-ion battery includes a positive electrode, a negative electrode, and a solid electrolyte. The type of battery does not limit the scope of protection of this invention.

[0068] The following uses a liquid battery as a specific embodiment to illustrate the technical content of the present invention.

[0069] In one alternative embodiment, the electrochemical device is a lithium-ion battery; the lithium-ion battery includes a negative electrode, an electrolyte, a separator, and a positive electrode as described above.

[0070] negative electrode sheet

[0071] In some implementations, the negative electrode is a lithium electrode.

[0072] In other embodiments, the negative electrode sheet may include a negative electrode current collector and a negative electrode material layer, the negative electrode material layer being disposed on at least one surface of the negative electrode current collector, the negative electrode material layer comprising a negative electrode material.

[0073] In this invention, the negative electrode material in the negative electrode material layer can be a negative electrode material conventionally used in the art, such as graphite-based negative electrode material, silicon-oxygen-based negative electrode material, or silicon-carbon-based negative electrode material.

[0074] In some embodiments, the negative electrode material includes one or more of lithium titanate, artificial graphite, natural graphite, soft carbon, hard carbon, mesophase carbon microspheres, silicon suboxide, and silicon carbide.

[0075] In some implementations, the negative electrode material layer further includes a conductive agent.

[0076] The conductive agent is not particularly limited, as long as it is conductive and does not cause chemical changes in the battery. For example, specific materials that can be used include: graphite, such as natural or artificial graphite; carbon-based materials, such as conductive carbon black (Super P, abbreviated as SP), carbon nanotubes (CNT), acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, or carbon fiber; metal powders or metal fibers, such as copper, nickel, aluminum, or silver; conductive whiskers, such as zinc oxide whiskers or potassium titanate whiskers; conductive metal oxides, such as titanium dioxide; or conductive polymers, such as polyphenylene derivatives.

[0077] In some specific implementations, the conductive agent in the negative electrode material layer is carbon black Super P.

[0078] In some implementations, the negative electrode material layer further includes a binder.

[0079] The type of adhesive is not particularly limited and can be selected from polyvinylidene fluoride, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid (PAA), ethylene-propylene-diene terpolymer and its sulfonates, styrene-butadiene rubber (SBR), fluororubber and various copolymers, such as SBR.

[0080] In some implementations, the negative electrode material layer also includes a thickener.

[0081] The addition of the thickener can increase the viscosity of the system of each component in the negative electrode slurry. It can be a thickener commonly used in the art to prepare negative electrode sheets, such as sodium carboxymethyl cellulose (CMC).

[0082] In this invention, the negative electrode current collector can be a conventional negative electrode current collector in the art. The negative electrode current collector, serving as the substrate supporting the negative electrode material layer, is typically a metal foil with a thickness of 3-500 μm. There are no particular limitations on the material, as long as it has high conductivity and does not produce a chemical reaction in the secondary battery system. For example, it can be a foil formed by surface treatment of nickel, titanium, aluminum, silver, stainless steel, carbon, etc. The negative electrode current collector usually has a smooth surface, but fine textures can also be formed on its surface to improve the adhesion between the negative electrode material layer and the negative electrode current collector. Besides foil, the negative electrode current collector can also be used in any one or more combinations of various forms such as film, mesh, porous, foam, or non-woven fabric. Generally, the negative electrode current collector is copper foil.

[0083] In some embodiments, the method for preparing the negative electrode sheet includes the following steps: coating the negative electrode slurry obtained by thoroughly mixing the components of the negative electrode material layer in a solvent onto at least one surface of the negative electrode current collector, drying, cold pressing, and slitting to obtain the final product.

[0084] electrolyte

[0085] In some embodiments, the electrolyte may be a conventional electrolyte used in batteries, typically including non-aqueous solvents and lithium salts.

[0086] In this invention, the non-aqueous solvent can be a conventional non-aqueous solvent in the art.

[0087] In some embodiments, the non-aqueous solvent preferably comprises ester solvents and / or dimethyl sulfoxide (DMSO), more preferably carbonate solvents. The carbonate solvent may optionally be one or more of ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), methyl ethyl carbonate (MEC), methyl ethyl carbonate (EMC), ethylene carbonate, propylene carbonate, and butyl carbonate (BC). The non-aqueous solvent may also include ethyl acetate.

[0088] In this invention, the lithium salt can be a conventional lithium salt in the art, preferably one or more of LiPF6, LiBF4, LiClO4, LiCF3SO3 and LiN(CF3SO2)2, for example, LiPF6.

[0089] In this invention, the electrolyte may include additives, which may be conventional additives in the art, such as fluoroethylene carbonate (FEC).

[0090] In some embodiments, the electrolyte includes LiPF6, ethylene carbonate, and ethyl methyl carbonate.

[0091] The volume ratio of ethylene carbonate to methyl ethyl carbonate is, for example, 7:3.

[0092] The concentration of the lithium salt is, for example, 1 mol / L.

[0093] In some embodiments, the electrolyte can be prepared by conventional methods in the art. Optionally, it can be prepared by the following method: mixing the various non-aqueous solvents and additives in proportion in an argon atmosphere glove box with a water content of <10 ppm, and then adding a fully dried lithium salt and mixing evenly to obtain the electrolyte.

[0094] diaphragm

[0095] In some alternative embodiments, the diaphragm may be a polypropylene membrane or a polyethylene membrane.

[0096] In one specific embodiment, the diaphragm is a polypropylene membrane; the thickness of the diaphragm is 11 μm.

[0097] In this invention, the method for preparing the lithium-ion battery can be a conventional method in the art. It can be that the positive electrode, separator, and negative electrode are wound in sequence to obtain the battery cell, which is then packaged in a packaging shell and injected with the electrolyte. Alternatively, the positive electrode, separator, and negative electrode are stacked in sequence to obtain the battery cell, which is then packaged in a packaging shell and injected with the electrolyte. After that, the lithium-ion battery is obtained through processes such as settling, hot and cold pressing, formation, clamping, and capacity testing.

[0098] A third aspect of the present invention provides an electronic device comprising the electrochemical device described above.

[0099] For example, the electronic devices described in this invention may be, but are not limited to, mobile devices (such as mobile phones, tablets, laptops, video recorders, portable printers / copiers, etc.), electric vehicles (such as pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems and backup power supplies, etc.

[0100] Based on common knowledge in the field, the above-mentioned preferred conditions can be combined arbitrarily to obtain various preferred embodiments of the present invention.

[0101] Example 1

[0102] (1) Preparation of composite active materials (impregnation method): Mn, a precursor of LMFP, is impregnated with LMFP. 0.5 Fe 0.5 The suspension prepared by ultrasonically dispersing PO4 in anhydrous ethanol solution is an LMFP precursor solution, and LiNi is selected. 0.8 Mn 0.1 Co 0.1 O2 micron-sized single crystal particles (NCM811) were immersed in an LMFP precursor solution, then dried and mixed with Li2CO3 lithium salt in the molar ratio corresponding to LMFP formation, and sintered at a high temperature of 300°C to form LMFP particles (LiMn). 0.5 Fe 0.5 PO4 (with a particle size of 500 nm) is used to coat NCM811 particles (i.e., second lithium manganese iron phosphate material) with LMFP particles (i.e., second lithium nickel cobalt manganese oxide material), and the particles are allowed to cool naturally to obtain a composite active material (where the mass ratio of NCM811 particles to LMFP particles is 5:5).

[0103] (2) Preparation of the positive electrode:

[0104] S1. NCM811 (i.e., the first nickel cobalt manganese lithium oxide material), PVDF binder and conductive carbon black are mixed in a mass ratio of 8:1:1 to prepare a first active slurry (solvent is N-methylpyrrolidone, solid content is 62%), which is then coated onto the surface of carbon-coated aluminum foil (single-sided coating, aluminum foil thickness is 15μm). The coating thickness of the first active slurry is 50μm. After drying, the first active slurry forms the first active material layer.

[0105] S2. The composite active material, PVDF binder and conductive carbon black prepared in step (1) are mixed in a mass ratio of 8:1:1 to form a second active slurry (the solvent is N-methylpyrrolidone and the solid content is 62%). The slurry is then uniformly coated onto the first active material layer. The coating thickness of the second active slurry is 50 μm. After drying, the second active slurry forms the second active material layer.

[0106] S3. Mix LMFP (i.e., lithium manganese iron phosphate), PVDF binder, and conductive carbon black in a mass ratio of 8:1:1 to prepare a third active slurry (solvent is N-methylpyrrolidone, solid content is 62%), and uniformly coat it above the second active material layer. The coating thickness of the third active slurry is 50μm. After drying, the third active slurry forms the third active material layer.

[0107] S4. Roll forming (rolling pressure is 10T) to cut into positive electrode sheets with a diameter of 12mm.

[0108] Example 2

[0109] (1) Preparation of composite active materials (sol-gel method): LiNi was selected 0.9 Mn 0.05 Co 0.05 O2 polycrystalline secondary particles (NCM955) were thoroughly dried and immersed in a surface tension agent solution, followed by ultrasonic dispersion to obtain suspension 1. Nanoscale LMFP powder was added to suspension 1 and stirred, allowing the LMFP particles to self-assemble on the NCM955 surface, forming coated particles. This was then ultrasonically dispersed to obtain suspension 2. Polyvinyl alcohol was then added to suspension 2 to form a stable, transparent sol system, resulting in sol 1. Through slow polymerization, a three-dimensional network structure gel was formed, with the spaces between the gel networks filled with solvent that had lost its flowability. The gel was sintered and cured at 300℃ to prepare a coating material, achieving the coating of NCM955 particles (i.e., lithium manganese iron phosphate) by LMFP particles (i.e., lithium nickel cobalt manganese oxide). The particles were then allowed to cool naturally to obtain a composite active material (where the mass ratio of NCM955 particles to LMFP particles was 5:5).

[0110] (2) Preparation of the positive electrode:

[0111] S1. A first active slurry (solvent: N-methylpyrrolidone, solid content: 62%) is prepared by mixing NCM955 (i.e., the first nickel-cobalt-manganese lithium oxide material), PVDF binder, and conductive carbon black in a mass ratio of 9:0.5:0.5. This slurry is then applied to the surface of a carbon-coated aluminum foil (single-sided coating, aluminum foil thickness: 13 μm). The surface density of the first active slurry is 1 mg / cm³. 2 After drying, the first active slurry forms the first active material layer.

[0112] S2. The composite active material, PVDF binder, and conductive carbon black prepared in step (1) are mixed in a mass ratio of 9:0.5:0.5 to form a second active slurry (solvent is NMP, solid content is 62%), and uniformly coated onto the first active material layer. The surface density of the second active slurry is 0.5 mg / cm³. 2 After drying, the second active slurry forms the second active material layer.

[0113] S3. A third active slurry (solvent: N-methylpyrrolidone, solid content: 62%) is prepared by mixing LMFP (i.e., lithium manganese iron phosphate), PVDF binder, and conductive carbon black in a mass ratio of 9:0.5:0.5 and uniformly coated above the second active material layer. The surface density of the third active slurry is 0.5 mg / cm³. 2 After drying, the third active slurry forms the third active material layer.

[0114] S4. Roll forming (rolling pressure is 10T) to cut into positive electrode sheets with a diameter of 12mm.

[0115] Example 3

[0116] The difference between this embodiment and Embodiment 1 is that in step (2) of the preparation of the positive electrode sheet, in step S1, the coating thickness of the first active slurry is 200 μm, and the other conditions and steps are the same as in Embodiment 1. The mass ratio of the positive electrode material in the first active material layer, the second active material layer and the third active material layer of the obtained positive electrode sheet is 1:0.25:0.25.

[0117] Example 4

[0118] The difference between this embodiment and Embodiment 1 is that in step (2) of the preparation of the positive electrode sheet, in step S1, the coating thickness of the first active slurry is 20 μm, and the other conditions and steps are the same as in Embodiment 1. The mass ratio of the positive electrode material in the first active material layer, the second active material layer and the third active material layer of the obtained positive electrode sheet is 1:2.5:2.5.

[0119] Example 5

[0120] The difference between this embodiment and Embodiment 1 is that in step (2) of the preparation of the positive electrode sheet, the coating thickness of the second active slurry in step S2 is 200 μm, and the other conditions and steps are the same as in Embodiment 1. The mass ratio of the positive electrode material in the first active material layer, the second active material layer and the third active material layer of the obtained positive electrode sheet is 1:4:1.

[0121] Example 6

[0122] The difference between this embodiment and Embodiment 1 is that in step (2) of the preparation of the positive electrode sheet, the coating thickness of the second active slurry in step S2 is 20 μm, and the other conditions and steps are the same as in Embodiment 1. The mass ratio of the positive electrode material in the first active material layer, the second active material layer and the third active material layer of the obtained positive electrode sheet is 1:0.4:1.

[0123] Example 7

[0124] The difference between this embodiment and Embodiment 1 is that in step (2) of the preparation of the positive electrode sheet, in step S3, the coating thickness of the third active slurry is 200 μm, and the other conditions and steps are the same as in Embodiment 1. The mass ratio of the positive electrode material in the first active material layer, the second active material layer and the third active material layer of the obtained positive electrode sheet is 1:1:4.

[0125] Example 8

[0126] The difference between this embodiment and Embodiment 1 is that in step (2) of the preparation of the positive electrode sheet, in step S3, the coating thickness of the third active slurry is 20 μm, and the other conditions and steps are the same as in Embodiment 1. The mass ratio of the positive electrode material in the first active material layer, the second active material layer and the third active material layer of the obtained positive electrode sheet is 1:1:0.4.

[0127] Example 9

[0128] The difference between this embodiment and embodiment 1 is that in step (1) the preparation of the composite active material, the mass ratio of NCM811 particles to LMFP particles is NCM811:LMFP=1:9, and the other conditions and steps are the same as in embodiment 1.

[0129] Example 10

[0130] The difference between this embodiment and embodiment 1 is that in step (1) the preparation of the composite active material, the mass ratio of NCM811 particles to LMFP particles is NCM811:LMFP=9:1, and the other conditions and steps are the same as in embodiment 1.

[0131] Schematic diagrams of the composite active materials in the positive electrode sheets obtained in Examples 1-10 are shown below. Figure 1 As shown.

[0132] The microstructure diagrams of the positive electrode material layer of the positive electrode sheets obtained in Examples 1-10 are shown below. Figure 2 As shown.

[0133] The structural schematic diagrams of the positive electrode sheets obtained in Examples 1-10 are shown below. Figure 3 As shown.

[0134] Comparative Example 1

[0135] The difference between this comparative example and Example 1 is that step (1) is omitted, and step S2 is omitted in step (2). In step S3, the third active slurry (LMFP, PVDF binder and conductive carbon black in a mass ratio of 8:1:1) is uniformly coated on top of the first active material layer (NCM811, PVDF binder and conductive carbon black in a mass ratio of 8:1:1). The remaining conditions and steps are the same as in Example 1.

[0136] The resulting positive electrode does not contain a second active material layer. Along the direction away from the positive current collector, the positive material layer of the resulting positive electrode sequentially includes a first active material layer and a third active material layer.

[0137] Comparative Example 2

[0138] The difference between this comparative example and Example 1 is that step (1) of preparing the composite active material is not performed; instead, only LiNi in a mass ratio of 5:5 is used. 0.8 Mn 0.1 Co 0.1 O2 micron-sized single crystal particles (NCM811) and nano-sized LMFP particles are simply mixed (ground and mixed thoroughly in an agate mortar for 20 minutes) to obtain a simple mixture of NCM811 particles and LMFP particles, rather than LMFP particles coating NCM811 particles.

[0139] In step (2) the preparation of the positive electrode sheet, in step S2, a simple mixture of NCM811 particles and LMFP particles prepared by the above method, PVDF binder and conductive carbon black are mixed in a mass ratio of 8:1:1 to form the second active slurry; the remaining conditions and steps are the same as in Example 1.

[0140] Comparative Example 3

[0141] The difference between this comparative example and Example 1 is that in the preparation of the positive electrode, in step S1, single-crystal lithium manganese oxide LiMn2O4 (particle size of 50μm) is used instead of NCM811, and the other conditions and steps are the same as in Example 1.

[0142] Comparative Example 4

[0143] The difference between this comparative example and Example 1 is that in the preparation of the positive electrode, in step S1, the composite active material obtained in step (1) is used to replace NCM811, and the other conditions and steps are the same as in Example 1.

[0144] Comparative Example 5

[0145] The difference between this comparative example and Example 1 is that in the preparation of the positive electrode, steps S1 and S3 are performed using the following steps:

[0146] S1. Mix LMFP, PVDF binder and conductive carbon black in a mass ratio of 8:1:1 to prepare a third active slurry (solvent is N-methylpyrrolidone, solid content is 62%), and apply it to the surface of carbon-coated aluminum foil (single-sided coating, aluminum foil thickness is 15μm). The coating thickness of the first active slurry is 50μm. Dry it to form the first active material layer.

[0147] S3. Mix NCM811, PVDF binder, and conductive carbon black in a mass ratio of 8:1:1 to prepare the first active slurry (solvent is N-methylpyrrolidone, solid content is 62%), and uniformly coat it on top of the second active material layer. The coating thickness of the third active slurry is 50μm. After drying, the third active slurry forms the third active material layer.

[0148] The remaining conditions and steps are the same as in Example 1. Essentially, the positions of the first and third active material layers in the resulting positive electrode are interchanged.

[0149] Example 1

[0150] (1) Resistivity of the positive electrode

[0151] The resistivity of the positive electrode sheets prepared in Examples 1-10 and Comparative Examples 1-5 was tested respectively. The specific testing method was as follows: four tungsten wire probes were arranged in a straight line with equal spacing of 3 mm to contact the sample surface. A constant current I was applied to the two outer probes, and the voltage drop V was collected by the two inner probes. The resistivity was calculated using the formula ρ = R * (A / L), where ρ is the resistivity; R is the measured resistance value; A is the cross-sectional area through which the current passes in the measurement direction (for the electrode sheet, it is usually thickness × width); and L is the distance between the voltage probes in the measurement direction. The test results are shown in Table 3.

[0152] (2) Thickness of each layer in the positive electrode plate

[0153] The positive electrode sheets prepared in Examples 1-10 and Comparative Examples 1-5 were subjected to cross-section polishing (CP) ion beam profiling. The cross-sections were then analyzed using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). The SEM analysis was performed using a JSM-7610FPlus SEM (equipped with an EDS accessory) manufactured by NEC (Japan Electronics Corporation). The test voltage was 5.0 kV, and the magnification was 2000x. The resulting CPSEM-EDS images of the positive electrode sheets were obtained. The CPSEM-EDS image of the positive electrode sheet in Example 1 is shown below. Figure 5As shown in the CPSEM-EDS diagram of the positive electrode, the boundaries of each active material layer can be clearly seen, and the thickness of each active material layer can be measured.

[0154] (3) Particle size of positive electrode active material in each layer

[0155] Cross-sectional images of each active material layer (i.e., the first active material layer, the second active material layer, and the third active material layer) in the positive electrode sheets prepared in Examples 1-10 and Comparative Examples 1-5 were obtained using a TEM (manufacturer: JEOL, model JEM-200cx, Nippon Electronics Co., Ltd.). Particle size data of the active materials in each active material layer were measured. Taking the positive electrode sheet prepared in Example 1 as an example, the specific testing method is as follows:

[0156] The test voltage was set to 200kV and the magnification was set to 2000x. A TEM image of the cross-section of the three-layer positive electrode active material layer was obtained. Twenty particles were randomly selected from each layer, and the particle size (the longest straight-line distance between any two points on the outer surface of the particle) was measured one by one. The largest 5% and the smallest 5% were removed, and the average value of the remaining 90% of the particles was taken as the particle size of the positive electrode active material (i.e., the first lithium nickel cobalt manganese oxide material, the composite active material, and the first lithium manganese iron phosphate material) in each active material layer.

[0157] Furthermore, in the tests of the coating thickness, the second lithium manganese iron phosphate material in the coating layer, and the core (i.e., the second lithium nickel cobalt manganese oxide material) size of the composite active material in the second active material layer, the obtained TEM cross-sectional images of the second active material layer were magnified based on 20 selected composite active material particles at a test voltage of 200kV and a magnification of 100kV to obtain cross-sectional TEM images of the 20 selected composite active material particles. Based on the cross-sectional TEM image of each composite active material particle, the following measurements were performed:

[0158] ① Measure the thickness of the coating layer, and take the data at the point of maximum coating layer thickness as the coating layer thickness value;

[0159] ② Measure the particle size (the longest straight-line distance between any two points on the outer surface of the particle) of the core (i.e., the second nickel cobalt manganese oxide material).

[0160] ③ Measure the particle size of the second lithium manganese iron phosphate material in the coating layer: Randomly select 20 small particles in the coating layer, measure the particle size (the longest straight-line distance between any two points on the outer surface of the particle) one by one, and take the average value.

[0161] Based on the above measurements, the thickness of the coating layer, the particle size of the core, and the particle size of the second lithium manganese iron phosphate material in the coating layer were obtained in 20 composite active material particles, for a total of 20 sets of measurement results.

[0162] For the 20 sets of measurement results obtained, the following calculations were performed: the largest 5% and the smallest 5% were removed, and the average value of the corresponding parameters of the remaining 90% of the particles was taken to obtain the thickness of the coating layer in the composite active material, the particle size of the second nickel cobalt manganese oxide material, and the particle size of the second manganese iron phosphate material.

[0163] The testing methods for other embodiments and comparative examples are similar, and can be adjusted accordingly based on the order of the active material layers and the type of active material in the positive electrode sheet.

[0164] The test results are shown in Tables 1 and 2.

[0165] Example 2

[0166] Battery manufacturing

[0167] Lithium-ion coin cells were prepared using the positive electrode sheets obtained in Examples 1-10 and Comparative Examples 1-5, respectively. The specific preparation methods are as follows:

[0168] A lithium-ion battery was used as the counter electrode. The electrolyte consisted of ethylene carbonate (EC) and ethyl methyl carbonate (EMC) in a volume ratio of 7:3, with LiPF6 as the solute at a concentration of 1 mol / L. A Celgard 2400 polypropylene (PP) membrane with a thickness of 11 μm was used as the separator, and 35 µL of electrolyte was added to each side of the membrane. A CR2016 coin cell was assembled in a glove box. The electrolyte was prepared as follows: EC and EMC were mixed in the specified ratio in an argon atmosphere glove box with a water content of <10 ppm, and then thoroughly dried LiPF6 was added and mixed thoroughly.

[0169] Electrochemical performance testing

[0170] The electrochemical performance of the lithium-ion coin cells prepared above was tested, and the specific testing methods are as follows:

[0171] (1) Cycling performance: Capacity retention rate after 100 and 300 cycles at 0.33C / 1C

[0172] The newly prepared battery was activated by charging and discharging at 0.1C for 3 cycles at 25°C, with a charge / discharge range of 2.5~4.3V.

[0173] The activated batteries were subjected to a 0.33C / 1C cycle test at 25°C. Specifically, they were charged at 0.33C and discharged at 1C. The discharge capacity at the first cycle, the 100th cycle, and the 300th cycle were recorded. The capacity retention rate after 100 and 300 cycles was calculated using the following formula:

[0174] Capacity retention rate after 100 cycles at 0.33C / 1C = Discharge capacity at 100th cycle / Discharge capacity at first cycle × 100%;

[0175] Capacity retention rate after 300 cycles at 0.33C / 1C = Discharge capacity at 300th cycle / Discharge capacity at first cycle × 100%;

[0176] The charge / discharge rate is determined based on the actual NCM and LMFP ratios (NCM811: 200 mAh / g, NCM955: 210 mAh / g, LMFP: 160 mAh / g).

[0177] The test results are shown in Table 3.

[0178] The comparison charts of the cycle performance tests of lithium-ion batteries obtained from the positive electrode sheets in Examples 1-10 and Comparative Examples 1-5 are shown below. Figure 4 As shown.

[0179] (2) Discharge capacity

[0180] At 25℃, the newly prepared battery was activated by charging and discharging at 0.1C for 3 cycles, with a charge / discharge range of 2.5~4.3V. After activation, it was charged and discharged at 0.33C / 0.33C for 3 cycles, and the average discharge capacity was recorded as C0. The actual weight m of the positive electrode active material was calculated based on the mass ratio of the positive electrode active material and the actual coating weight. Based on the actual discharge energy E and discharge capacity C0, the energy density = E / m and the discharge specific capacity = C0 / m were calculated.

[0181] The test results are shown in Table 3.

[0182] (3) Ratio performance

[0183] At 25℃, the newly prepared battery was activated by charging and discharging at 0.1C for 3 cycles, with a charge / discharge range of 2.5~4.3V. After activation, it was charged and discharged at 0.33C / 0.33C for 3 cycles, and the average discharge capacity was recorded as C0; then, it was charged and discharged at 1C / 1C for 3 cycles, and the average discharge capacity was recorded as C1; finally, it was charged and discharged at 3C / 3C for 3 cycles, and the average discharge capacity was recorded as C2. The rate performance was calculated as RDC1=C1 / C0, RDC2=C2 / C0. RDC1 and RDC2 were defined as the rate performance of the Diane performance. The larger the RDC1 and RDC2, the better the rate performance.

[0184] The charge / discharge rate is determined based on the actual NCM and LMFP ratios (NCM811: 200 mAh / g, NCM955: 210 mAh / g, LMFP: 160 mAh / g).

[0185] The test results are shown in Table 3.

[0186] Table 1

[0187]

[0188] In Table 1, " / " indicates that the parameter is not involved.

[0189] Table 2

[0190]

[0191] Table 3

[0192]

[0193] The positive electrode sheets obtained in Examples 1-10 of this invention sequentially comprise a first active material layer containing NCM, a second active material layer containing composite active material (LMFP-coated NCM), and a third active material layer containing LMFP along the direction away from the positive electrode current collector. Lithium-ion batteries prepared based on this positive electrode sheet exhibit excellent rate performance, while also achieving excellent capacity and cycle performance. Specifically, RDC2 can reach over 93%, even exceeding 95%, while RDC1 can reach over 98%, the discharge specific capacity can reach over 170 mAh / g, the capacity retention rate after 300 cycles at 0.33C / 1C can reach over 91%, and the capacity retention rate after 100 cycles at 0.33C / 1C can reach over 96.30%. In composite active materials, coating LMFP particles onto the NCM surface reduces the expansion of NCM due to the minimal expansion of LMFP itself during lithium insertion / extraction. Simultaneously, the reduced termination voltage difference between the two materials due to internal charge compensation allows LMFP to operate at a lower voltage, thus improving electrical performance. Placing the first active material layer containing NCM close to the current collector improves the conductivity of the cathode. Using the third active material layer containing LMFP as the outermost layer addresses the issues of poor conductivity and ion conduction, thereby enhancing the interaction between the cathode material particles and the electrolyte.

[0194] Compared with Example 1, the positive electrode obtained in Comparative Example 1 does not contain a second active material layer. Along the direction away from the positive current collector, the positive electrode material layer of the obtained positive electrode includes a first active material layer and a third active material layer in sequence. The resistivity of the positive electrode is increased. The rate performance RDC2 of the lithium-ion battery obtained based on the positive electrode is significantly worse, and the RDC1, the capacity retention rate after 300 cycles at 0.33C / 1C and the capacity retention rate after 100 cycles at 0.33C / 1C are all low.

[0195] Compared with Example 1, in the positive electrode obtained in Comparative Example 2, the second active material layer only uses a simple mixture of NCM811 and LMFP, instead of a composite active material of NCM coated with LMFP. The resistivity of the positive electrode is significantly increased, the rate performance RDC2 of the lithium-ion battery obtained based on the positive electrode is significantly reduced, and the RDC1, the capacity retention rate after 300 cycles at 0.33C / 1C, and the capacity retention rate after 100 cycles at 0.33C / 1C are poor.

[0196] Compared with Example 1, the positive electrode active material in the first active material layer of the positive electrode obtained in Comparative Example 3 is replaced by lithium manganese oxide instead of NCM811. The resistivity of the positive electrode is increased, and the rate performance RDC2 of the lithium-ion battery obtained based on the positive electrode is significantly reduced. Furthermore, RDC1, the capacity retention rate after 300 cycles at 0.33C / 1C, and the capacity retention rate after 100 cycles at 0.33C / 1C are significantly worse.

[0197] Compared with Example 1, in the positive electrode sheet obtained in Comparative Example 4, the positive electrode active material in the first active material layer was replaced with the prepared composite active material, which significantly reduced the resistivity of the positive electrode sheet. The rate performance RDC2 of the lithium-ion battery obtained based on this positive electrode sheet was greatly reduced, and the RDC1, the capacity retention rate after 300 cycles at 0.33C / 1C, and the capacity retention rate after 100 cycles at 0.33C / 1C were also significantly reduced.

[0198] Compared with Example 1, the positions of the first active material layer and the third active material layer in the positive electrode obtained in Comparative Example 5 were interchanged, resulting in a significant increase in the resistivity of the positive electrode. The rate performance RDC2 of the lithium-ion battery obtained based on this positive electrode was significantly reduced, and the RDC1, the capacity retention rate after 300 cycles at 0.33C / 1C, and the capacity retention rate after 100 cycles at 0.33C / 1C were significantly worse.

[0199] In some alternative implementations, the mass ratio of the positive electrode active material in the first active material layer, the second active material layer and the third active material layer of the obtained positive electrode sheet is 1:(0.4~2.5):(0.4~2.5), and the mass ratio of LMFP and NCM in the composite active material is between (1~5):(5~9). The lithium-ion battery obtained based on this positive electrode sheet has better rate performance. Specifically, RDC2 can reach more than 95.50%, and RDC1 can reach more than 99.40%.

[0200] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of the present invention is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but all such changes and modifications fall within the scope of protection of the present invention.

Claims

1. A positive electrode plate, characterized in that, The positive electrode sheet includes a positive current collector and a positive electrode material layer disposed on at least one surface of the current collector. Along the direction away from the positive current collector, the positive electrode material layer sequentially includes a first active material layer, a second active material layer and a third active material layer. The first active material layer includes a first lithium nickel cobalt manganese oxide material; The second active material layer includes a composite active material, which includes a core and a coating layer disposed on its surface. The core includes a second lithium nickel cobalt manganese oxide material, and the coating layer includes a second lithium manganese iron phosphate material. The third active material layer includes a first lithium manganese iron phosphate material.

2. The positive electrode sheet as described in claim 1, characterized in that, In the composite active material, the mass ratio of the second lithium nickel cobalt manganese oxide material to the second lithium manganese iron phosphate material is (1~99):(1~99).

3. The positive electrode sheet as described in claim 1, characterized in that, The mass ratio of the first lithium nickel cobalt manganese oxide material, the composite active material, and the first lithium manganese iron phosphate material is 1:(0.1~10):(0.1~10).

4. The positive electrode sheet as described in claim 1, characterized in that, The positive electrode material layer satisfies one or more of the following conditions a to c: a. In the first active material layer, the content of the first lithium nickel cobalt manganese oxide material is 70%~90%, and the percentage is the mass percentage of the first lithium nickel cobalt manganese oxide material in the first active material layer; b. In the second active material layer, the content of the composite active material is 70%~90%, and the percentage is the mass percentage of the composite active material in the second active material layer; c. In the third active material layer, the content of the first lithium manganese iron phosphate material is 70%~90%, and the percentage is the mass percentage of the first lithium manganese iron phosphate material in the third active material layer.

5. The positive electrode sheet as described in claim 1, characterized in that, The first lithium nickel cobalt manganese oxide material is either monocrystalline or polycrystalline; And / or, the second lithium nickel cobalt manganese oxide material is monocrystalline or polycrystalline.

6. The positive electrode sheet as described in claim 1, characterized in that, The positive electrode material layer satisfies one or more of the following conditions a to c: a. The thickness of the first active material layer is 20~200 μm; b. The thickness of the second active material layer is 20~200 μm; c. The thickness of the third active material layer is 20~200 μm.

7. The positive electrode sheet as described in claim 1, characterized in that, The composite active material satisfies one or more of the following conditions a to d: a. The particle size of the second lithium manganese iron phosphate material is 0.01~5μm; b. The particle size of the second lithium nickel cobalt manganese oxide material is 0.5~20 μm; c. The particle size of the composite active material is 0.5~20 μm; d. In the composite active material, the thickness of the coating layer is 10~500 nm.

8. The positive electrode sheet as described in claim 1, characterized in that, The positive electrode material layer satisfies one or two of the following conditions a to b: a. The particle size of the first lithium nickel cobalt manganese oxide material is 0.5~20 μm; b. The particle size of the first lithium manganese iron phosphate material is 0.01~5μm.

9. An electrochemical device, characterized in that, It includes the positive electrode sheet as described in any one of claims 1 to 8.

10. An electronic device, characterized in that, It includes the electrochemical device as described in claim 9.

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