Positive electrode material and preparation method thereof, electrochemical device and electronic equipment

Abstract

The invention discloses a positive electrode material and a preparation method thereof, an electrochemical device and electronic equipment. The positive electrode material sequentially comprises an inner core, a first coating layer and a second coating layer from inside to outside, the inner core comprises lithium nickel manganese oxide doped with a phosphorus element; the first coating layer is in a film shape, and the first coating layer contains phosphate; the second coating layer is in an island shape or a chain shape, and the second coating layer contains phosphate. An electrochemical device (especially a lithium ion battery) prepared from the positive electrode material can slow down Mn dissolution and improve high-temperature cycling stability.

Description

Technical Field

[0001] The invention relates to a positive electrode material and a preparation method thereof, an electrochemical device and an electronic device. Background Art

[0002] Lithium-ion batteries (LIBs) are currently the mainstream energy storage technology and are widely used in electric vehicles (EVs), consumer electronics, and grid energy storage. However, traditional cathode materials (such as LiCoO2, LiFePO4, NCM / NCA) have limitations in energy density, cost, or safety, and there is an urgent need to develop higher performance cathode materials. 0.5 Mn 1.5 O4 (LNMO) has a voltage platform (~4.7 V) much higher than traditional cathode materials (such as LiCoO2 ~3.9 V, LiFePO4 ~3.4 V), which can significantly improve the energy density of the battery (theoretical energy density can reach ~650 Wh / kg, close to high nickel NCM). LNMO can be paired with high-capacity negative electrodes (such as silicon carbon, lithium metal) to construct a high-energy-density full battery. Therefore, due to the high operating voltage of LNMO (~4.7V vs. Li + / Li), low cost (cobalt-free), excellent thermal stability and rate performance, making it one of the important candidate materials for the next generation of high energy density lithium-ion batteries.

[0003] However, despite its numerous advantages, LNMO's practical application still faces challenges with electrolyte compatibility, cycle stability, and interfacial transport. When used with traditional carbonate-based electrolytes (such as EC / DMC), LNMO is easily oxidized at voltages above 4.3 V, leading to unstable CEI and reduced battery cycle stability. Furthermore, as a manganese-containing cathode material, battery charge and discharge cycles inevitably involve manganese dissolution and structural phase transitions, which can damage the electrode structure and significantly reduce the battery's cycle stability. This problem is particularly prominent at high temperatures. Summary of the Invention

[0004] The present invention aims to overcome the existing shortcomings of lithium nickel manganese oxide (LMNO) in lithium-ion batteries, such as severe Mn dissolution and poor high-temperature cycling performance. The present invention provides a positive electrode material, a preparation method thereof, an electrochemical device, and an electronic device. Electrochemical devices (particularly lithium-ion batteries) using this positive electrode material can mitigate Mn dissolution and improve high-temperature cycling stability.

[0005] The present invention solves the above technical problems through the following technical solutions:

[0006] The first aspect of the present invention provides a positive electrode material, which includes, from the inside to the outside, a core, a first coating layer and a second coating layer; the core includes lithium nickel manganese oxide doped with phosphorus; the first coating layer is film-shaped, and the first coating layer contains phosphate; the second coating layer is island-shaped or chain-shaped, and the second coating layer contains phosphate.

[0007] A second aspect of the present invention provides a method for preparing a positive electrode material, comprising the following steps:

[0008] S1. Performing a first sintering on a first mixed material to obtain a first precursor; wherein the first mixed material includes a lithium nickel manganese oxide precursor, γ-Li3PO4 and a lithium salt;

[0009] S2. performing a second sintering on the second mixed material to obtain a second precursor; wherein the second mixed material includes the first precursor and β-Li3PO4;

[0010] S3. Perform a third sintering on the third mixed material to obtain the positive electrode material; wherein the third mixed material includes the second precursor and amorphous Li3PO4.

[0011] A third aspect of the present invention provides a positive electrode material, which is prepared using the above-mentioned method for preparing the positive electrode material.

[0012] A fourth aspect of the present invention provides an electrochemical device, wherein the positive electrode sheet of the electrochemical device comprises the positive electrode material as described above.

[0013] A fifth aspect of the present invention provides an electronic device comprising the electrochemical device described above.

[0014] On the basis of conforming to the common sense in this field, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0015] The reagents and raw materials used in the present invention are commercially available.

[0016] The positive progress effect of the present invention is:

[0017] The positive electrode material provided in the present invention is prepared by doping lithium nickel manganese oxide with phosphorus and providing a double-layer coating containing phosphate on the surface of the lithium nickel manganese oxide, wherein the Mn element has good stability. The electrochemical device (especially lithium-ion battery) obtained by using this positive electrode material can slow down the dissolution of Mn and improve the high-temperature cycle stability of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is the SEM image of the first precursor in Example 1.

[0019] Figure 2 This is the SEM image of the second precursor in Example 1.

[0020] Figure 3 This is the SEM image of the positive electrode material obtained in Example 1. DETAILED DESCRIPTION

[0021] The present invention is further illustrated by way of examples below, but the present invention is not limited to the scope of the examples. Experimental methods in the following examples where specific conditions are not specified were performed according to conventional methods and conditions, or selected according to the product specifications.

[0022] The first aspect of the present invention provides a positive electrode material, which includes, from the inside to the outside, a core, a first coating layer and a second coating layer; the core includes lithium nickel manganese oxide doped with phosphorus; the first coating layer is film-shaped, and the first coating layer contains phosphate; the second coating layer is island-shaped or chain-shaped, and the second coating layer contains phosphate.

[0023] In the present invention, different Li3PO4 structures are introduced into lithium nickel manganese oxide. Specifically, γ-Li3PO4 is used to replace some of the O sites in the lithium nickel manganese oxide with P, thereby doping phosphorus. β-Li3PO4 and amorphous Li3PO4 are used to form the first and second coating layers, respectively. The synergistic effect of the different Li3PO4 structures is used to slow down the dissolution of Mn and improve high-temperature cycling stability. The synergistic effect of the different Li3PO4 structures is specifically reflected in the following aspects:

[0024] (1) For doping γ-Li3PO4: γ-Li3PO4 has the characteristics of high temperature stability. Using γ-Li3PO4 as a doping phosphoric acid source can ensure that PO4 3- Replace O 2- While forming anion doping sites, it stabilizes the main spinel structure and inhibits the oxygen loss of the spinel material during charge and discharge cycles under high voltage conditions. At the same time, the doped PO4 3- Mn that can stabilize the system 4+ , reduce the Mn in the system 3+ content, thereby achieving the effect of reducing Mn dissolution;

[0025] (2) For the first coating layer: β-Li3PO4 is a thermodynamically stable phase with strong chemical inertness. β-Li3PO4 is used as a phosphate source for the coating intermediate layer to form a film-like coating layer on the surface of the material particles, which can block the direct contact between the spinel positive electrode material and the electrolyte. β-Li3PO4 can resist the corrosion of HF generated by the decomposition of the electrolyte and protect the LNMO surface from Mn 3+ dissolution, the lattice channel (~0.4 Å) of β-Li3PO4 allows Li +By blocking solvent molecules (such as EC, ~0.5 Å), the interfacial impedance is reduced, and the thermal expansion coefficient of β-Li3PO4 (~10 -6 / °C) and LNMO (~8×10 -6 / °C) is close, which can reduce the interface peeling during the cycle;

[0026] (3) For the second coating layer: Amorphous Li3PO4 can further form an island-shaped or chain-shaped discontinuous coating layer composed of tiny particles on the surface of the first coating layer, thereby further isolating the main metal material (nickel, manganese, etc.) from direct contact with the electrolyte; in the present invention, amorphous Li3PO4 is specifically used as the outermost coating phosphate source. The high density of this amorphous structure can effectively block Mn 3+ Mn produced by disproportionation 2+ react with the electrolyte;

[0027] In particular, by combining the two-layer coating structure obtained by using Li3PO4 and amorphous Li3PO4, in which the first coating layer β-Li3PO4 serves as the transition layer between the outermost second coating layer and the main spinel structure, the interface structure bridge can be made tighter. The combination of these two structures can improve the mechanical strength of the first coating layer and the second coating layer, reduce the occurrence of interface shedding of the second coating layer during long cycles, and thus permanently protect the main spinel structure from erosion by the electrolyte.

[0028] In the present invention, the "membrane-like" coating layer refers to a continuous and smooth coating layer on the surface of the material particles, which exhibits a substantially continuous and smooth surface structure when magnified 10-20K times under SEM.

[0029] In the present invention, the "island-like or chain-like" coating refers to a discontinuous coating composed of tiny particles on the surface of the material particles. When magnified 10-20K times under SEM, the surface of the material particles appears as discrete particles with a rough surface.

[0030] In some embodiments, the core does not contain any metal ions other than Ni, Li, and Mn, such as Fe, etc. Here, "does not contain" means that the content of other metal ions other than Ni, Li, and Mn is less than 500 ppm, which is considered to be free.

[0031] In some preferred embodiments, in the first coating layer, the cations of the phosphate are Ni, Mn and Li.

[0032] In some embodiments, the first coating layer does not contain any metal ions other than Ni, Li, and Mn, such as Fe, etc., wherein "does not contain" means that the content of other metal ions other than Ni, Li, and Mn is less than 500 ppm, which is considered to be absent.

[0033] In some preferred embodiments, in the second coating layer, the cation of the phosphate is Li.

[0034] In some embodiments, the second coating layer does not contain any metal ions other than Ni, Li, and Mn, such as Fe, etc., wherein "does not contain" means that the content of other metal ions other than Ni, Li, and Mn is less than 500 ppm, which is considered to be non-containing.

[0035] In the present invention, the positive electrode material is generally primary particles, and the average particle size of the positive electrode material may be 2.5-2.6 μm.

[0036] In some preferred embodiments, the average thickness of the first coating layer is 3-10 nm, preferably 3-8 nm, for example 5 nm.

[0037] In some preferred embodiments, the average thickness of the second coating layer is 3-10 nm, preferably 3-8 nm, for example 5 nm.

[0038] In some preferred embodiments, the average thickness ratio of the first coating layer to the second coating layer is 1:(0.5-2), for example, 1:1.

[0039] In some preferred embodiments, the raw material of the first coating layer includes β-Li3PO4.

[0040] The average particle size of the β-Li3PO4 is preferably 30-40 nm, for example, 35 nm.

[0041] In some preferred embodiments, the raw material of the second coating layer includes amorphous Li3PO4.

[0042] The average particle size of the amorphous Li3PO4 is preferably 0.1-0.2 μm, for example, 0.15 μm.

[0043] In some preferred embodiments, in the inner core, the raw material of the phosphorus element is γ-Li3PO4.

[0044] The average particle size of the γ-Li3PO4 is preferably 30-40 nm, for example, 35 nm.

[0045] In some more preferred embodiments, the mass ratio of the lithium nickel manganese oxide to the γ-Li3PO4 is 1:(0.001-0.005), for example, 1:0.003.

[0046] In some more preferred embodiments, the mass ratio of the γ-Li 3 PO 4 , the β-Li 3 PO 4 and the amorphous Li 3 PO 4 is 1:(0.5-1):(0.5-1), for example, 1:0.75:0.75.

[0047] In the present invention, the positive electrode material having the above composition, structure and performance can be prepared by the preparation method of the positive electrode material provided in the second aspect of the present invention.

[0048] A second aspect of the present invention provides a method for preparing a positive electrode material, comprising the following steps:

[0049] S1. Performing a first sintering on a first mixed material to obtain a first precursor; wherein the first mixed material includes a lithium nickel manganese oxide precursor, γ-Li3PO4 and a lithium salt;

[0050] S2. performing a second sintering on the second mixed material to obtain a second precursor; wherein the second mixed material includes the first precursor and β-Li3PO4;

[0051] S3. Perform a third sintering on the third mixed material to obtain the positive electrode material; wherein the third mixed material includes the second precursor and amorphous Li3PO4.

[0052] In some preferred embodiments, in step S1, the lithium salt is lithium carbonate.

[0053] In some preferred embodiments, in step S1, the lithium nickel manganese oxide precursor includes nickel hydroxide and / or manganese hydroxide.

[0054] In some preferred embodiments, in step S1, in the first mixture, the mass ratio of the lithium nickel manganese oxide precursor to the lithium salt is 1:(0.1-0.3).

[0055] In some preferred embodiments, in step S1, the average particle size of the first precursor is 2.5-2.6 μm.

[0056] In some preferred embodiments, in step S1, the temperature of the first sintering is 850-950°C, for example, 900°C.

[0057] In some preferred embodiments, in step S1, the first sintering time is 8-12 hours, for example, 10 hours.

[0058] In some preferred embodiments, the average particle size of the γ-Li3PO4 is 30-40 nm, for example, 35 nm.

[0059] In some preferred embodiments, the mass ratio of the lithium nickel manganese oxide to the γ-Li3PO4 is 1:(0.001-0.005), for example, 1:0.003.

[0060] In some preferred embodiments, the mass ratio of γ-Li3PO4, β-Li3PO4 and amorphous Li3PO4 is 1:(0.73-0.76):(0.73-0.76).

[0061] In some preferred embodiments, in step S2, the average particle size of the second precursor is 2.5-2.6 μm.

[0062] In some preferred embodiments, in step S2, the average particle size of the β-Li3PO4 is 30-40 nm, for example, 35 nm.

[0063] In some preferred embodiments, in step S3, the average particle size of the amorphous Li3PO4 is 0.1-0.2 μm, for example, 0.15 μm.

[0064] In some preferred embodiments, in step S2, the temperature of the second sintering is 350-450°C, for example, 400°C.

[0065] In some preferred embodiments, in step S2, the second sintering time is 5-8 h, for example, 6 h.

[0066] In some preferred embodiments, in step S2, in the second mixture, the mass ratio of the first precursor to β-Li3PO4 is 1:(0.0023-0.0026).

[0067] In some preferred embodiments, in step S3, the temperature of the third sintering is 300-400°C, for example, 350°C.

[0068] In some preferred embodiments, in step S3, the third sintering time is 5-8 h, for example, 6 h.

[0069] In some preferred embodiments, in step S3, in the third mixture, the mass ratio of the second precursor to amorphous Li3PO4 is 1:(0.0023-0.0026).

[0070] A third aspect of the present invention provides a positive electrode material, which is prepared using the above-mentioned method for preparing the positive electrode material.

[0071] In the present invention, the composition, structure and performance of the positive electrode material are the same as those of the positive electrode material described in the first aspect.

[0072] A fourth aspect of the present invention provides an electrochemical device, wherein the positive electrode sheet of the electrochemical device comprises the positive electrode material as described above.

[0073] In the present invention, the electrochemical device is preferably a battery.

[0074] In the present 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 sheet, a negative electrode sheet, a separator, and an electrolyte; a solid-state lithium-ion battery includes a positive electrode, a negative electrode, and a solid electrolyte. The battery type does not limit the scope of protection of the present invention.

[0075] The following uses a liquid battery as a specific embodiment to illustrate the technical content of the present invention.

[0076] In an optional embodiment, the electrochemical device is a lithium-ion battery; the lithium-ion battery comprises a negative electrode sheet, a positive electrode sheet, an electrolyte and a separator, and the positive electrode sheet comprises the positive electrode material described above.

[0077] positive electrode

[0078] In the present invention, the positive electrode sheet may include a positive electrode current collector and a positive electrode material layer, wherein the positive electrode material layer is disposed on at least one surface of the positive electrode current collector; the positive electrode material layer includes the positive electrode material as described above.

[0079] In some embodiments, the positive electrode material layer further includes a conductive agent. The conductive agent is an agent used to ensure that the electrode has good charge and discharge performance. The conductive agent can be selected from graphite materials such as natural graphite and artificial graphite, carbon black, acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black and other carbon black materials, conductive fibers such as carbon fibers and metal fibers, metal powders such as carbon fluoride powder, aluminum powder, nickel powder and other metal powders, conductive whiskers such as zinc oxide and potassium titanate, and conductive metal oxides such as titanium dioxide or polyphenylene derivatives, such as carbon black.

[0080] In some embodiments, the positive electrode material layer further includes a binder. The binder can be a component that facilitates bonding between the positive electrode material and the conductive agent, and also facilitates bonding between the positive electrode material and the positive electrode current collector. Typically, the binder can be selected from polyvinylidene fluoride (PVDF), polyvinyl alcohol (PVA), carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene terpolymer (EPDM), sulfonated EPDM, styrene-butadiene rubber, fluororubber, and various copolymers, such as PVDF.

[0081] In some embodiments, the positive electrode material layer includes a positive electrode material, polyvinylidene fluoride, and conductive carbon black.

[0082] In some specific embodiments, the mass ratio of the positive electrode material, polyvinylidene fluoride and conductive carbon black is 90:5:5.

[0083] In the present invention, the positive electrode current collector may be a conventional positive electrode current collector in the art. For the positive electrode current collector, any material that does not cause chemical changes and has high conductivity may be used without restriction. For example, stainless steel, aluminum, nickel, titanium, or calcined carbon, or aluminum or stainless steel materials that have been surface-treated with carbon, nickel, titanium, silver, or the like may be commonly used. To enhance adhesion, micro-embossing may be formed on the surface of the positive electrode current collector. The positive electrode current collector may be used in various forms, such as a film, sheet, foil, mesh, or porous body.

[0084] In some optional embodiments, the positive electrode current collector is aluminum foil.

[0085] In some optional embodiments, the thickness of the positive electrode current collector may be 8-16 μm, for example, 15 μm.

[0086] In the present invention, the positive electrode sheet can be prepared by conventional methods in the art.

[0087] In some optional embodiments, the method for preparing the positive electrode sheet includes the following steps:

[0088] After the positive electrode material, binder and conductive agent are mixed in a certain mass ratio, a solvent is added and mixed evenly to obtain a positive electrode slurry; the positive electrode slurry is then evenly coated on at least one surface of the positive electrode current collector; and then the positive electrode sheet is prepared through processes such as drying, rolling, and slitting.

[0089] In some embodiments, the coating area density of the positive electrode slurry is 8.6-8.7 mg / cm 2 .

[0090] negative electrode

[0091] In some embodiments, the negative electrode sheet is lithium foil.

[0092] In other embodiments, the negative electrode sheet may include a negative electrode current collector and a negative electrode material layer, wherein the negative electrode material layer is disposed on at least one surface of the negative electrode current collector, and the negative electrode material layer includes a negative electrode material.

[0093] In the present invention, the negative electrode material in the negative electrode material layer may be a negative electrode material conventionally used in the art, such as a graphite-based negative electrode material, a silicon-oxygen-based negative electrode material, or a silicon-carbon-based negative electrode material.

[0094] In some embodiments, the negative electrode material includes one or more of lithium titanate, artificial graphite, natural graphite, soft carbon, hard carbon, mesocarbon microbeads, silicon monoxide, and silicon-carbon materials.

[0095] In some embodiments, the negative electrode material layer further includes a conductive agent.

[0096] The conductive agent is not particularly limited, as long as it is conductive and does not cause chemical changes in the battery. Examples include: graphite, such as natural graphite or artificial graphite; carbon-based materials, such as conductive carbon black (Super P, abbreviated SP), carbon nanotubes (CNTs), acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black, or carbon fiber; metal powder or metal fiber, 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.

[0097] In some specific embodiments, the conductive agent in the negative electrode material layer is carbon black Super P.

[0098] In some embodiments, the negative electrode material layer further includes a binder.

[0099] The type of the binder is not particularly limited, and can be selected from polyvinylidene fluoride, polyvinylidene fluoride, polyvinyl alcohol, carboxymethyl cellulose, starch, hydroxypropyl cellulose, regenerated cellulose, polyvinyl pyrrolidone, polytetrafluoroethylene, polyethylene, polypropylene, polyacrylic acid (PAA), ethylene-propylene-diene terpolymer and its sulfonate, styrene-butadiene rubber (SBR), fluororubber and various copolymers, for example, SBR.

[0100] In some embodiments, the negative electrode material layer further includes a thickener.

[0101] The addition of the thickener can increase the system viscosity of the components in the negative electrode slurry, and the thickener can be a thickener conventionally used in the art for preparing negative electrode sheets, such as sodium carboxymethyl cellulose (CMC).

[0102] In the present invention, the negative electrode current collector may be a conventional negative electrode current collector in the art. The negative electrode current collector serves as a substrate supporting the negative electrode material layer, and is generally a metal foil having a thickness of 3-500 μm. There is no particular restriction on the material, as long as it has high electrical conductivity and does not produce chemical reactions in the secondary battery system. For example, it can be a foil formed by surface treatment of nickel, titanium, aluminum, nickel, silver, stainless steel, carbon, etc. The negative electrode current collector generally has a smooth surface, but fine lines may also be formed on its surface to increase the adhesion between the negative electrode material layer and the current collector. In addition to foil, the negative electrode current collector may also be in the form of a film, mesh, porous, foam or non-woven fabric, or any one or more combinations thereof. Generally, the negative electrode current collector is copper foil.

[0103] In some embodiments, the preparation method of the negative electrode sheet includes the following steps: thoroughly stirring and mixing the components of the negative electrode material layer in a solvent to obtain a negative electrode slurry, coating it on at least one surface of the negative electrode current collector, drying, cold pressing, and cutting.

[0104] electrolyte

[0105] In some embodiments, the electrolyte may be an electrolyte conventionally used for batteries in the art, generally including a non-aqueous solvent and a lithium salt.

[0106] In the present invention, the non-aqueous solvent may be a conventional non-aqueous solvent in the art.

[0107] In some embodiments, the non-aqueous solvent preferably includes an ester solvent and / or dimethyl sulfoxide (DMSO), and more preferably includes a carbonate solvent. The carbonate solvent can 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), ethyl methyl carbonate (EMC), ethylene carbonate, propylene carbonate, and butylene carbonate (BC). The non-aqueous solvent may also include ethyl acetate.

[0108] In the present invention, the lithium salt may be a conventional lithium salt in the art, preferably one or more of LiPF6, LiBF4, LiClO4, LiCF3SO3 and LiN(CF3SO2)2, for example, LiPF6.

[0109] In the present invention, the electrolyte may include an additive, and the additive may be a conventional additive in the art, such as fluoroethylene carbonate (FEC).

[0110] In some embodiments, the electrolyte includes LiPF6, ethylene carbonate, dimethyl carbonate, and ethyl methyl carbonate.

[0111] The volume ratio of ethylene carbonate, dimethyl carbonate and ethyl methyl carbonate is, for example, 1:2:1.

[0112] The concentration of the lithium salt is, for example, 1 mol / L.

[0113] In some embodiments, the electrolyte can be prepared by conventional methods in the art. Optionally, it can be prepared by the following method: in an argon atmosphere glove box with a water content of <10 ppm, various non-aqueous solvents and additives are mixed according to a proportion, and then fully dried lithium salt is added and mixed uniformly to obtain the electrolyte.

[0114] diaphragm

[0115] In some optional embodiments, the separator may be a polypropylene film or a polyethylene film.

[0116] In a specific embodiment, the separator is a polypropylene film; the thickness of the separator is 11 μm.

[0117] In the present invention, the preparation method of the lithium-ion battery can be a conventional preparation method in the field, which can be a process of winding a positive electrode sheet, a separator, and a negative electrode sheet in this order to obtain a battery cell, then packaging the battery cell in a packaging shell and injecting the electrolyte; or a process of stacking a positive electrode sheet, a separator, and a negative electrode sheet in this order to obtain a battery cell, then packaging the battery cell in a packaging shell and injecting the electrolyte; and then undergoing processes such as standing, hot and cold pressing, formation, clamping, and capacity separation to obtain a lithium-ion battery.

[0118] A fifth aspect of the present invention provides an electronic device comprising the electrochemical device described above.

[0119] Illustratively, the electronic devices described in the present invention may be, but are not limited to, mobile devices (such as mobile phones, tablet computers, laptop computers, 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.

[0120] On the basis of conforming to the common sense in this field, the above-mentioned preferred conditions can be arbitrarily combined to obtain the preferred embodiments of the present invention.

[0121] Example 1

[0122] The preparation method of the positive electrode material in this embodiment includes the following steps:

[0123] S1. First sintering: nickel manganese hydroxide precursor and lithium carbonate (the mass ratio of nickel manganese hydroxide precursor to lithium carbonate is 1:0.2) and γ-Li3PO4 (average particle size of 35nm, content of 2000ppm) are mixed in a high-speed mixer and then put into a box furnace for the first sintering. The sintering temperature is 900℃ and the sintering time is 10h. After being taken out of the furnace, the powder material is crushed and sieved to obtain the average particle size of 2.5-2.6μm, which is the first precursor.

[0124] S2, second sintering: the first precursor and β-Li3PO4 (average particle size of 35 nm, content of 1000 ppm) were mixed in a high-speed mixer and then placed in a box furnace for second sintering at a sintering temperature of 400°C for 6 h. The second precursor (average particle size of 2.5-2.6 μm) was obtained after sieving after being taken out of the furnace.

[0125] S3, third sintering: the second precursor and amorphous Li3PO4 (average particle size of 0.15 μm, content of 1000 ppm) are mixed in a high-speed mixer and then put into a box furnace for the third sintering. The sintering temperature is 350 ° C and the sintering time is 6 h to obtain the positive electrode material;

[0126] Among them, the hydroxide precursor of nickel manganese and lithium carbonate form lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O4, namely LNMO), lithium nickel manganese oxide and γ-Li3PO4 form a core (ie, lithium nickel manganese oxide doped with phosphorus), β-Li3PO4 participates in forming the first coating layer, and amorphous Li3PO4 participates in forming the second coating layer.

[0127] Example 2

[0128] The only difference between this embodiment and embodiment 1 is that in step S2, the content of β-Li3PO4 is 2000 ppm, and the other conditions are the same as those in embodiment 1.

[0129] Example 3

[0130] The only difference between this embodiment and embodiment 1 is that in step S3, the content of amorphous Li3PO4 is 2000 ppm, and the other conditions are the same as those in embodiment 1.

[0131] Example 4

[0132] The only difference between this embodiment and embodiment 1 is that in step S1, the content of γ-Li3PO4 is 100 ppm, and the other conditions are the same as those in embodiment 1.

[0133] Example 5

[0134] The only difference between this embodiment and embodiment 1 is that in step S1, the content of γ-Li3PO4 is 4000 ppm, and the other conditions are the same as those in embodiment 1.

[0135] Example 6

[0136] The only difference between Example 6 and Example 1 is that in step S1 , the temperature of the first sintering is 850° C., and the other conditions are the same as those in Example 1.

[0137] Example 7

[0138] The only difference between Example 7 and Example 1 is that in step S1 , the temperature of the first sintering is 950° C., and the other conditions are the same as those in Example 1.

[0139] Example 8

[0140] The only difference between Example 8 and Example 1 is that in step S2, the temperature of the second sintering is 350°C, and the other conditions are the same as Example 1.

[0141] Example 9

[0142] The only difference between Example 9 and Example 1 is that in step S2, the temperature of the second sintering is 450°C, and the other conditions are the same as Example 1.

[0143] Example 10

[0144] The only difference between Example 10 and Example 1 is that in step S3, the temperature of the third sintering is 300° C., and the other conditions are the same as those in Example 1.

[0145] Example 11

[0146] The only difference between Example 11 and Example 1 is that in step S3, the temperature of the third sintering is 400° C., and the other conditions are the same as those in Example 1.

[0147] Comparative Example 1

[0148] The only difference between this comparative example and Example 1 is that in step S1, γ-Li3PO4 is not added; steps S2 and S3 are not performed, and the remaining conditions are the same as in Example 1. The obtained positive electrode material corresponds to the lithium nickel manganese oxide in Example 1.

[0149] Comparative Example 2

[0150] The only difference between this comparative example and Example 1 is that steps S2 and S3 are not performed, and the remaining conditions are the same as those in Example 1. The obtained positive electrode material corresponds to the core in Example 1 (ie, phosphorus-doped lithium nickel manganese oxide).

[0151] Comparative Example 3

[0152] The only difference between this comparative example and Example 1 is that step S3 is not performed, and the other conditions are the same as those in Example 1. Compared with the positive electrode material in Example 1, the obtained positive electrode material does not have the second coating layer.

[0153] Comparative Example 4

[0154] This comparative example differs from Example 1 in that step S2 is omitted. In step S3, the first precursor obtained in step S1 and amorphous Li3PO4 are subjected to a third sintering step (sintering temperature: 350°C, sintering time: 6 h). All other conditions are the same as in Example 1. The resulting positive electrode material, unlike the positive electrode material in Example 1, lacks the first coating layer.

[0155] Comparative Example 5

[0156] The only difference between this comparative example and Example 1 is that γ-Li3PO4 is not added in step S1, step S3 is not performed, and the remaining conditions are the same as in Example 1. Compared with the positive electrode material in Example 1, the obtained positive electrode material does not have a second coating layer, and the core is not doped with phosphorus.

[0157] Comparative Example 6

[0158] This comparative example differs from Example 1 in that: in step S1, γ-Li₃PO₄ is not added; step S2 is not performed; and in step S3, the first precursor obtained in step S1 and amorphous Li₃PO₄ are subjected to a third sintering step (sintering temperature 350°C, sintering time 6 hours). All other conditions are the same as in Example 1. The resulting positive electrode material, unlike the positive electrode material in Example 1, lacks the first coating layer, and the core is not doped with phosphorus.

[0159] Comparative Example 7

[0160] The difference between this comparative example and Example 1 is that: in step S2, the first precursor and amorphous Li3PO4 (average particle size of 0.15 μm, content of 1000 ppm) are subjected to a third sintering (sintering temperature of 350°C, sintering time of 6 h), and the particles are sieved after being taken out of the furnace until the average particle size of the particles is 2.5-2.6 μm; in step S3, the material obtained in step S2 and β-Li3PO4 are subjected to a second sintering (sintering temperature of 400°C, sintering time of 6 h), and the other conditions are the same as in Example 1.

[0161] Comparative Example 8

[0162] The difference between this comparative example and Example 1 is that in step S2, the first precursor and amorphous Li3PO4 (average particle size of 0.15 μm, content of 1000 ppm) are subjected to a third sintering (sintering temperature of 350°C, sintering time of 6 h) to obtain a second precursor (average particle size of 2.5-2.6 μm); the other conditions are the same as in Example 1.

[0163] Comparative Example 9

[0164] The difference between this comparative example and Example 1 is that in step S3, the second precursor and β-Li3PO4 (average particle size of 35 nm, content of 1000 ppm) are subjected to a third sintering (sintering temperature of 350°C, sintering time of 6 h); the other conditions are the same as in Example 1.

[0165] Comparative Example 10

[0166] The only difference between this embodiment and embodiment 1 is that in step S1, γ-Li3PO4 is not added, and the other conditions are the same as those in embodiment 1. The core of the obtained positive electrode material is not doped with phosphorus.

[0167] Effect Example 1

[0168] SEM tests were performed on the γ-Li3PO4, β-Li3PO4, amorphous Li3PO4 and the resulting positive electrode materials, the first precursor, and the second precursor in Examples 1-11 and Comparative Examples 1-10. TEM and TEM-EDS tests were performed on the resulting positive electrode materials. The specific test methods are as follows:

[0169] 1. SEM test

[0170] The SEM test was performed using a scanning electron microscope (SEM) model JSM-7610FPlus manufactured by JEOL Ltd.

[0171] (1) Characterize the surface morphology of the first precursor, the second precursor, and the cathode material:

[0172] The surface morphologies of the first precursor, the second precursor and the cathode material were characterized and SEM images were obtained at a voltage of 5 kV and a magnification of 10 K. The SEM images of the first precursor, the second precursor and the cathode material in Example 1 are shown in FIG. Figure 1 、 Figure 2 and Figure 3 As shown. Figure 2 It can be seen that after the second sintering, a continuous and smooth film layer (the first coating layer) is formed on the surface of the particles. The SEM image is affected by the changes in the light and dark fields and the angle. Figure 2 Taking the particle in the lower right corner as an example, there are light and dark layers on the surface, and the dark layer is the first coating layer. Figure 3 The SEM image of the positive electrode material particles obtained after the third sintering is compared with Figure 2 The smooth film-like coating is clearly visible Figure 3 The outer surface of the medium particles is rougher, with discrete granular protrusions distributed in an island-like coating (i.e., the third coating).

[0173] (2) Characterization of the average particle size of γ-Li3PO4, β-Li3PO4, amorphous Li3PO4, the first precursor, the second precursor and the cathode material:

[0174] SEM images were obtained for the γ-Li3PO4, β-Li3PO4, amorphous Li3PO4, first precursor, second precursor, and cathode material in each example and comparative example. The voltage was 5 kV and the magnification was 5K. At least 200 particles were randomly selected from each SEM image, and the particle size (the maximum straight-line distance between any two points on the particle edge) was measured using a Nanomeasurer. Three SEM images were obtained for each sample, and the particle size of at least 600 particles was measured and averaged to obtain the average particle size. The average particle size test results for the cathode material are shown in Table 1.

[0175] 2. TEM test

[0176] TEM tests were performed using a transmission electron microscope (TEM, manufactured by Hitachi, model HT7800).

[0177] For the positive electrode materials obtained in the above embodiment and comparative example, a focused ion beam (FIB) was used to obtain particle slice cross sections, and TEM tests were performed. The average thickness of the first coating layer and the second coating layer was obtained based on the obtained TEM images. Specifically:

[0178] At a magnification of 200,000 times, 10 sites were randomly selected in the TEM image (20nm×20nm) of the same positive electrode material, and the thickness values ​​of the first coating layer and the second coating layer were measured respectively with the help of Digital Micrograph. The average value was taken after removing the maximum and minimum values ​​to obtain the average thickness of the first coating layer and the second coating layer.

[0179] Then, 10 positive electrode material particles are randomly selected, and the thickness of the first coating layer and the second coating layer of each positive electrode material is calculated. The average thickness of the first coating layer and the average thickness of the second coating layer of the 10 positive electrode materials are calculated as the average thickness of the first coating layer and the second coating layer of the positive electrode material.

[0180] It can be seen from the TEM image that the positive electrode material prepared by the preparation method of the positive electrode material in Example 1 includes a core, a first coating layer and a second coating layer from the inside to the outside; wherein the average thickness of the first coating layer is 5 nm, and the average thickness of the second coating layer is 5 nm.

[0181] The positive electrode material prepared by the preparation method of the positive electrode material in Example 3 includes a core, a first coating layer and a second coating layer from the inside to the outside; wherein the average thickness of the first coating layer is 10 nm, and the average thickness of the second coating layer is 5 nm.

[0182] The positive electrode material prepared by the preparation method of the positive electrode material in Example 4 includes a core, a first coating layer and a second coating layer from the inside to the outside; wherein the average thickness of the first coating layer is 5 nm, and the average thickness of the second coating layer is 10 nm.

[0183] The above test results are shown in Table 1.

[0184] 3. TEM-EDS test

[0185] TEM-EDS tests were performed using a transmission electron microscope (TEM, manufactured by Hitachi, model HT7800) equipped with an EDS accessory (manufacturer: Hitachi, model: EMAX Evolution).

[0186] TEM-EDS tests were performed on the positive electrode materials of Examples 1-11 and Comparative Examples 1-10, respectively. According to the characterization results, the core of the positive electrode materials obtained in Examples 1-11 is distributed with P, O, Ni, Mn and Li, the first coating layer is distributed with P, O, Ni, Mn and Li, and the second coating layer is distributed with P, O and Li, indicating that the first coating layer of the positive electrode materials obtained in the examples contains phosphate and the second coating layer contains phosphate. Based on this, it should be understood by those skilled in the art that the P in the first coating layer will also bond with the Ni, Mn, Li and O elements on the surface; and with the help of XPS, it can be further characterized that the P element in the core replaces the O element in part of the LNMO structure, thereby forming phosphorus-doped lithium nickel manganese oxide.

[0187] Effect Example 2

[0188] The positive electrode materials prepared in Examples 1-11 and Comparative Examples 1-10 were used to prepare positive electrode sheets, and the button batteries (lithium-ion batteries) obtained were assembled respectively. Specifically:

[0189] The method for preparing the positive electrode sheet comprises the following steps:

[0190] The prepared positive electrode material, conductive agent carbon black Super P, and binder PVDF were mixed in a mass ratio of 90:5:5. The carbon black Super P and PVDF were first added to an appropriate amount of N-methylpyrrolidone (NMP) solvent to form a conductive paste. The positive electrode material was then added to the conductive paste in proportion, mixed evenly using a homogenizer, and then coated onto one surface of aluminum foil (thickness 240μm). The mixture was dried, rolled (rolling pressure 19T), and cut into positive electrode sheets with a diameter of 16mm. The mass loading of the positive electrode active material was 8.6-8.7 mg·cm −2 ;

[0191] A lithium foil with a diameter of 19 mm and a thickness of 0.6 mm was used as the negative electrode;

[0192] The electrolyte was prepared by dissolving LiPF6 in a mixed solvent (EC / DC / EMC = 1 / 1 / 1, volume ratio), and the concentration of LiPF6 was 1 mol / L;

[0193] Separator: Celgard 2400 polypropylene (PP) film with a thickness of 11 μm was used as the separator. 35 μL of electrolyte was added to each side of the separator.

[0194] The positive electrode sheet, negative electrode sheet, separator and electrolyte are used to assemble a CR2430 button battery.

[0195] The electrochemical performance tests of the CR2430 button batteries assembled above were performed as follows:

[0196] The electrochemical performance test was conducted using a battery tester (CT-2001A, Wuhan LAND) with a charge and discharge voltage range of 3.5 V (discharge cut-off voltage) to 4.95 V (charge cut-off voltage). The following tests were performed:

[0197] (1) Capacity retention rate after 100 cycles at 45°C

[0198] At 45°C, a freshly prepared button cell was activated at 0.1 C for two cycles and then cycled at 1 C for 100 cycles. The first cycle discharge capacity (the first cycle of 100 cycles after activation) and the 100th cycle discharge capacity were obtained, respectively. 1 C = 140 mAh / g.

[0199] The 100-cycle capacity retention rate at 45°C is calculated based on the first-cycle discharge capacity and the 100th-cycle discharge capacity. The specific calculation formula is:

[0200] 100-cycle capacity retention rate (45°C) = 100th-cycle discharge capacity in grams / first-cycle discharge capacity in grams (after activation) × 100%.

[0201] (2) Manganese dissolution after 100 cycles at 45°C

[0202] The button cells that were cycled 100 times at 45°C were disassembled to obtain negative electrode sheets, and 10 mg of powder was scraped from the surface of the negative electrode. After digestion, the ICP was measured to obtain the manganese dissolution amount. Among them, due to the deviation of the measurement itself between 15-25 ppm, the manganese dissolution amount of the batteries obtained in Examples 3-11 after 100 cycles at 45°C was within an acceptable range. Taking Examples 5 and 6 as examples, the manganese dissolution amount of the batteries obtained from the positive electrode materials after 100 cycles at 45°C was 88 ppm and 66 ppm, respectively. Overall, the manganese dissolution situation was relatively similar.

[0203] (3) Mn 3+ content

[0204] At 25°C, the newly prepared button battery was charged at a constant current and constant voltage rate of 0.1C to a cut-off voltage of 4.95V, and then discharged at a rate of 0.1C to a voltage of 3.5V. The charge and discharge curves were obtained.3+ The content is the ratio of the platform capacity in the voltage range of 4.1-4.2V in the charge and discharge curve to the total discharge capacity in grams.

[0205] (4) First cycle discharge capacity

[0206] At 25°C, the newly prepared button battery was charged at a constant current and constant voltage rate of 0.1C to a cut-off voltage of 4.95V, and then discharged at a rate of 0.1C to a voltage of 3.5V, and the discharge capacity in grams at 0.1C was obtained.

[0207] (5) First-cycle Coulomb efficiency

[0208] At 25°C, the newly prepared button battery was charged at a constant current and constant voltage rate of 0.1C to a cut-off voltage of 4.95V, and then discharged at a rate of 0.1C to a voltage of 3.5V. The charging gram capacity and discharge gram capacity at 0.1C were obtained, and then the first-cycle coulombic efficiency was calculated according to "discharge gram capacity / charge gram capacity × 100%".

[0209] The above test results are shown in Table 2.

[0210]

[0211]

[0212] Note: “ / ” in Table 1 indicates that the parameter is not involved in the specific experiment.

[0213]

[0214] The positive electrode material of the present invention adopts Li3PO4 of different configurations, specifically by doping γ-Li3PO4, and sequentially adopting β-Li3PO4 and amorphous Li3PO4 to form the first coating layer and the second coating layer from the inside out outside the core, thereby slowing down the dissolution of Mn and improving the high-temperature cycle stability based on the synergistic effect of Li3PO4 of different configurations. According to Table 2, the manganese dissolution amount of the lithium ion battery obtained by using the positive electrode material in Examples 1-11 after 100 cycles at 45°C can be less than 150 ppm, or even less than 90 ppm; the capacity retention rate of 100 cycles at 45°C can reach more than 94%. In addition, the Mn content of the lithium ion battery obtained by using the positive electrode material is less than 150 ppm, or even less than 90 ppm, after 100 cycles at 45°C. 3+ The content is only less than 11%, the first-cycle discharge capacity can reach more than 134 mAh / g, and the first-cycle coulombic efficiency can reach more than 91%, or even up to 95%.

[0215] Compared with Example 1, the positive electrode material in Comparative Example 1 is not provided with a first coating layer and a second coating layer based on β-Li3PO4 and amorphous Li3PO4, respectively, and the core does not use γ-Li3PO4. The lithium ion battery obtained based on this positive electrode material has a significantly higher manganese dissolution amount after 100 cycles at 45°C, and the capacity retention rate of 100 cycles at 45°C is significantly reduced, which cannot effectively slow down the dissolution of Mn, and the high-temperature cycle stability is poor. In addition, the Mn content of the lithium ion battery is 3+ The content is obviously higher, and the first-cycle discharge capacity and the first-cycle coulombic efficiency are also poor.

[0216] Compared with Example 1, the positive electrode material in Comparative Example 2 is not provided with the first coating layer and the second coating layer. The manganese dissolution amount of the lithium ion battery obtained by using this positive electrode material after 100 cycles at 45°C is significantly higher, and the capacity retention rate after 100 cycles at 45°C is significantly reduced.

[0217] Compared to Example 1, lithium-ion batteries produced from cathode materials without a second coating layer (Comparative Example 3) or without a first coating layer (Comparative Example 4) exhibited significantly higher manganese dissolution after 100 cycles at 45°C, and significantly poorer capacity retention after 100 cycles at 45°C. Comparative Example 5, based on Comparative Example 3, further omitted γ-Li₃PO₄, exhibited even higher manganese dissolution after 100 cycles at 45°C. Comparative Example 6, based on Comparative Example 4, further omitted γ-Li₃PO₄, exhibited even higher manganese dissolution after 100 cycles at 45°C.

[0218] Although the obtained positive electrode materials are all provided with a double-layer coating, compared with Example 1, the double-layer coating obtained by using only amorphous Li3PO4 or β-Li3PO4 (Comparative Examples 8-9) or the double-layer coating obtained by using amorphous Li3PO4 and β-Li3PO4 in sequence (Comparative Example 7) has more severe Mn dissolution and poor high-temperature cycle stability.

[0219] Compared with Example 1, in Comparative Example 10, the core does not use γ-Li3PO4, and the manganese dissolution amount of the obtained lithium ion battery after 100 cycles at 45°C is significantly improved, and the capacity retention rate of 100 cycles at 45°C is lower.

[0220] In some optional embodiments (Examples 1, 6-7, 9, and 11), lithium-ion batteries using the cathode materials can achieve significantly lower manganese dissolution (the manganese dissolution amount after 100 cycles at 45°C can be no more than 70 ppm) while also maintaining excellent high-temperature cycling stability (capacity retention rate after 100 cycles at 45°C can reach over 94%). To achieve these excellent results, the following conditions were further optimized: the first sintering temperature was 850-950°C, the second sintering temperature was 400-450°C, and the third sintering temperature was 350-400°C.

[0221] Although specific embodiments of the present invention have been described above, those skilled in the art will appreciate that these are merely illustrative and that the scope of the present invention is defined by the appended claims. Those skilled in the art may make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, and such changes and modifications are intended to fall within the scope of the present invention.

Claims

1. A positive electrode material, characterized in that It includes a core, a first coating layer and a second coating layer from the inside to the outside; the core includes lithium nickel manganese oxide doped with phosphorus; the first coating layer is film-shaped and contains phosphate; the second coating layer is island-shaped or chain-shaped and contains phosphate.

2. The positive electrode material according to claim 1, wherein The positive electrode material satisfies one or more of the following conditions ad: a. In the first coating layer, the cations of the phosphate are Ni, Mn and Li; b. In the second coating layer, the cation of the phosphate is Li; c. The average thickness ratio of the first coating layer to the second coating layer is 1:(0.5-2); d. The average particle size of the positive electrode material is 2.5-2.6 μm.

3. The positive electrode material according to claim 1, wherein The positive electrode material satisfies one or more of the following conditions ac: a. In the core, the raw material of the phosphorus element is γ-Li3PO4; b. The raw material of the first coating layer includes β-Li3PO4; c. The raw material of the second coating layer includes amorphous Li3PO4.

4. The positive electrode material according to claim 3, wherein The positive electrode material satisfies one or more of the following conditions ae: a. The average particle size of the γ-Li3PO4 is 30-40 nm; b. The average particle size of β-Li3PO4 in the raw material of the first coating layer is 30-40nm; c. The average particle size of amorphous Li3PO4 in the raw material of the second coating layer is 0.1-0.2 μm; d. The mass ratio of the lithium nickel manganese oxide to the γ-Li3PO4 is 1: (0.001-0.005); e. The mass ratio of the γ-Li3PO4, the β-Li3PO4 and the amorphous Li3PO4 is 1:(0.5-1):(0.5-1).

5. A method for preparing a positive electrode material, characterized in that: It includes the following steps: S1. Performing a first sintering on a first mixed material to obtain a first precursor; wherein the first mixed material includes a lithium nickel manganese oxide precursor, γ-Li3PO4 and a lithium salt; S2. performing a second sintering on the second mixed material to obtain a second precursor; wherein the second mixed material includes the first precursor and β-Li3PO4; S3. Perform a third sintering on the third mixed material to obtain the positive electrode material; wherein the third mixed material includes the second precursor and amorphous Li3PO4.

6. The method for preparing the positive electrode material according to claim 5, wherein: It satisfies one or more of the following conditions al: a. In step S1, the lithium salt is lithium carbonate; b. In step S1, the lithium nickel manganese oxide precursor includes nickel hydroxide and / or manganese hydroxide; c. In step S1, in the first mixture, the mass ratio of the lithium nickel manganese oxide precursor to the lithium salt is 1:(0.1-0.3); d. In step S1, the average particle size of the γ-Li3PO4 is 30-40 nm; e. In step S1, the mass ratio of the lithium nickel manganese oxide to the γ-Li3PO4 is 1: (0.001-0.005); f. In step S1, the average particle size of the first precursor is 2.5-2.6 μm; g. In step S2, the average particle size of the β-Li3PO4 is 30-40 nm; h. In step S2, in the second mixture, the mass ratio of the first precursor to β-Li3PO4 is 1:(0.0023-0.0026); i. In step S2, the average particle size of the second precursor is 2.5-2.6 μm; j. In step S3, the average particle size of the amorphous Li3PO4 is 0.1-0.2 μm; k. In step S3, in the third mixture, the mass ratio of the second precursor to amorphous Li3PO4 is 1:(0.0023-0.0026); 1. The mass ratio of γ-Li3PO4, β-Li3PO4 and amorphous Li3PO4 is 1: (0.73-0.76): (0.73-0.76).

7. The method for preparing the positive electrode material according to claim 5, wherein: It satisfies one or more of the following conditions af: a. In step S1, the first sintering temperature is 850-950°C; b. In step S1, the first sintering time is 8-12 hours; c. In step S2, the temperature of the second sintering is 350-450°C; d. In step S2, the second sintering time is 5-8 hours; e. In step S3, the temperature of the third sintering is 300-400°C; f. In step S3, the third sintering time is 5-8 hours.

8. A positive electrode material, characterized in that The cathode material is prepared by the method for preparing the cathode material according to any one of claims 5 to 7.

9. An electrochemical device, characterized in that The positive electrode sheet of the electrochemical device comprises the positive electrode material according to any one of claims 1 to 4 and 8.

10. An electronic device, characterized in that: It comprises the electrochemical device according to claim 9.

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