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

Abstract

The application discloses a positive electrode material, a preparation method of the positive electrode material, a positive electrode sheet, an electrochemical device and electronic equipment, and the positive electrode material comprises a positive electrode active material and a metal element-containing substance, the metal element-containing substance comprises a metal oxide and / or a nano metal element; and the metal element-containing substance is at least partially attached to the surface of the positive electrode active material, wherein the metal element-containing substance attached to the surface of the positive electrode active material is at least partially in a rod shape. The positive electrode material has excellent electrical conductivity, and when the positive electrode material is applied to a battery, the battery has excellent rate performance.

Description

Technical Field

[0001] This invention relates to a positive electrode material and its preparation method, a positive electrode sheet, an electrochemical device, and an electronic device. Background Technology

[0002] Lithium-ion batteries are widely used due to their high energy density, high specific capacity, long cycle life, and fast response. Currently, lithium iron phosphate (LiFePO4, hereinafter referred to as LFP) is gaining increasing attention as a cathode material due to its advantages such as high theoretical capacity, stable charge / discharge voltage platform, stable material structure, excellent cycle performance, low cost, and environmental friendliness. However, it also suffers from drawbacks such as low conductivity, poor kinetic performance, and poor rate performance, which to some extent limits the further promotion and use of lithium iron phosphate batteries. Summary of the Invention

[0003] In order to overcome the shortcomings of poor conductivity of positive electrode active materials in the prior art, which result in poor rate performance of batteries when applied to them, this invention provides a positive electrode material and its preparation method, a positive electrode sheet, an electrochemical device, and an electronic device. The positive electrode material has excellent conductivity and excellent rate performance when applied to batteries.

[0004] The present invention solves the above-mentioned technical problems through the following technical solutions.

[0005] In a first aspect, the present invention provides a positive electrode material comprising a positive electrode active material and a substance containing a metal element, wherein the substance containing the metal element comprises a metal oxide and / or a nano-metal element; at least a portion of the substance containing the metal element is attached to the surface of the positive electrode active material, wherein at least a portion of the substance containing the metal element attached to the surface of the positive electrode active material is rod-shaped.

[0006] Secondly, the present invention provides a method for preparing the cathode material as described above, comprising the following steps:

[0007] The positive electrode material is obtained by subjecting a mixture containing a positive electrode active material to a metal plasma environment, where the metal plasma reacts in the mixture to form the metal-containing substance.

[0008] Thirdly, the present invention provides a positive electrode sheet comprising the positive electrode material as described above.

[0009] Fourthly, the present invention provides an electrochemical device comprising a positive electrode as described above.

[0010] Fifthly, the present invention provides an electronic device comprising the electrochemical device as described above.

[0011] 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.

[0012] The reagents and raw materials used in this invention are all commercially available.

[0013] The positive and progressive effects of this invention are as follows:

[0014] This invention utilizes a metal plasma environment to prepare cathode materials. Metal-containing substances are introduced into the cathode active material, and at least a portion of these substances are controlled to adhere to the surface of the cathode active material. Furthermore, the metal-containing substances adhering to the surface of the cathode active material are controlled to be rod-shaped, allowing them to provide good electrical contact and form a conductive network that significantly improves the material's conductivity. Additionally, the metal-containing substances also act as a support, facilitating lithium-ion transport, increasing its transport coefficient, and improving the rate performance of the cathode material.

[0015] Meanwhile, the method of the present invention also has the advantages of simple synthesis, low equipment requirements, simple process, green and environmentally friendly, rapid reaction and high material activity. Attached Figure Description

[0016] Figure 1 The image shows the XRD pattern of the cathode material prepared in Example 1.

[0017] Figure 2 The image shows a SEM image of the cathode material prepared in Example 1.

[0018] Figure 3 The first charge-discharge curves at 0.1C are for Example 1, Comparative Example 1, and Comparative Example 2.

[0019] Figure 4 The graphs show the cycling performance of Example 1, Comparative Example 1, and Comparative Example 2 at different scaling ratios.

[0020] Figure 5 The resistivity diagrams are for Example 1, Comparative Example 1, and Comparative Example 2. Detailed Implementation

[0021] The invention will be described in more detail below for a clearer understanding. It will be understood that the words or terms used in this specification and claims should not be construed as having the meanings defined in common dictionaries. It will be further understood that, based on the principle that the inventors can appropriately define the meanings of words or terms to best interpret the invention, the words or terms should be interpreted as having meanings consistent with their meanings in the relevant technical context and the technical concept of the invention.

[0022] cathode materials

[0023] The cathode material according to the first aspect of the present invention includes a cathode active material and a metal-containing material, wherein the metal-containing material includes metal oxides and / or nano-metal elements; at least a portion of the metal-containing material is attached to the surface of the cathode active material, wherein at least a portion of the metal-containing material attached to the surface of the cathode active material is rod-shaped.

[0024] In this invention, "attachment" means that a substance containing a metal element is attached to the surface of the positive electrode active material; or that one end of the substance containing a metal element is fixed to the surface of the positive electrode material, i.e., it grows out of the positive electrode material.

[0025] In this invention, "rod-shaped" refers to particles with an aspect ratio greater than 1, which can be elongated (aspect ratio greater than 2:1) or spherical (aspect ratio greater than 1:1 and less than 2:1), with elongated shape being preferred.

[0026] In some embodiments of the present invention, the positive electrode active material is one or more of lithium iron phosphate (LFP), lithium manganese iron phosphate, nickel manganese cobalt ternary material (NCM), lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, nickel cobalt aluminum material (NCA), and lithium-rich manganese-based material.

[0027] In some embodiments of the present invention, the positive electrode active material is one or more of lithium iron phosphate (LFP), lithium manganese iron phosphate, nickel manganese cobalt ternary material (NCM), lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, nickel cobalt aluminum material (NCA), and lithium-rich manganese-based material.

[0028] In some embodiments of the present invention, the metal oxide is one or more of zinc oxide, copper oxide, and titanium oxide.

[0029] In some embodiments of the present invention, the nano-metallic element is one or more of nano-gold, nano-platinum, and nano-palladium.

[0030] In some embodiments of the present invention, the rod-shaped metal-containing material has a length of 1-2 μm and a diameter of 50-100 nm.

[0031] In some embodiments of the present invention, the metal oxide is zinc oxide, wherein the rod-shaped zinc oxide is elongated and has an aspect ratio greater than 2:1, preferably greater than 10:1.

[0032] In some embodiments of the present invention, the mass ratio of the positive electrode active material to the metal-containing material is (10-999):1.

[0033] In some embodiments of the present invention, the mass ratio of the positive electrode active material to the metal-containing material is (10-200):1.

[0034] In some embodiments of the present invention, the mass ratio of the positive electrode active material to the metal-containing material is (19-999):1.

[0035] In some embodiments of the present invention, the mass ratio of the positive electrode active material to the metal-containing material is (19-190):1.

[0036] In some embodiments of the present invention, the mass ratio of the positive electrode active material to the metal-containing material is (10-20):1.

[0037] In some embodiments of the present invention, the mass ratio of the positive electrode active material to the metal-containing material is 10:1, 19:1, 39:1, 48.8:1, 100:1, 199:1, 200:1, 300:1, 400:1, 500:1, 600:1, 700:1, 800:1, 900:1, 999:1, or 1000:1.

[0038] In some embodiments of the present invention, another portion of the metal-containing material is embedded inside the positive electrode active material.

[0039] In some embodiments of the present invention, the positive electrode material further includes a conductive agent, which is coated on the surface of the positive electrode active material, and another portion of the metal-containing material is embedded inside the positive electrode active material and / or the conductive agent.

[0040] In certain embodiments of the present invention, the conductive agent is one or more of Ketjen black, carbon nanotubes (CNTs), and graphene.

[0041] In some specific embodiments of the present invention, the mass ratio of the positive electrode active material to the conductive agent is (19-999):1.

[0042] In some specific embodiments of the present invention, the mass ratio of the positive electrode active material to the conductive agent is (150-200):1, for example, 195:1.

[0043] Preparation method of positive electrode material

[0044] The method for preparing the cathode material according to the second aspect of the present invention includes the following steps:

[0045] The positive electrode material is obtained by subjecting a mixture containing a positive electrode active material to a metal plasma environment, where the metal plasma reacts in the mixture to form the metal-containing substance.

[0046] In this invention, due to the local temperature and pressure differences in the mixture, metal plasma diffuses into the solution to form metal oxides or nano-metal elements, which then attach to or embed into the positive electrode active material.

[0047] In some embodiments of the present invention, the mass concentration of the positive electrode active material in the mixture containing the positive electrode active material is 0.1%-90%, for example, 20%. Here, % means the percentage of the mass of the positive electrode active material to the mass of the mixture.

[0048] In some embodiments of the present invention, the preparation method of the mixture includes the following steps: mixing the positive electrode active material and water. The mixing may be performed by stirring, with a stirring speed of, for example, 50-1000 rpm and a stirring time of, for example, 5-30 minutes.

[0049] In some embodiments of the present invention, the D50 particle size of the positive electrode active material is 0.5-100 μm, for example, 1 μm or 1.1 μm.

[0050] In some embodiments of the present invention, the metal is one or more of zinc, copper, titanium, gold, platinum, and palladium. When the metal is one or more of zinc, copper, and titanium, it reacts to form one or more of zinc oxide, copper oxide, and titanium oxide in the cathode material; when the metal is one or more of gold, platinum, and palladium, it reacts to form one or more of nano-gold, nano-platinum, and nano-palladium in the cathode material.

[0051] In a specific embodiment of the present invention, the method for preparing the positive electrode material includes the following steps:

[0052] A mixture containing LFP is placed in a Zn plasma environment, where the Zn plasma reacts in the LFP-containing mixture to form ZnO, thereby obtaining the cathode material; wherein the cathode material comprises LFP and ZnO, and at least a portion of the ZnO is attached to the surface of the LFP, wherein at least a portion of the ZnO attached to the surface of the LFP is rod-shaped; wherein the rod-shaped ZnO is preferably elongated strip-shaped with an aspect ratio greater than 2:1, more preferably greater than 10:1.

[0053] In a specific embodiment of the present invention, the method for preparing the positive electrode material includes the following steps:

[0054] The cathode material is obtained by reacting a mixture containing LFP in a Cu plasma environment to form CuO. The cathode material comprises LFP and CuO, wherein at least a portion of the CuO is attached to the surface of the LFP, and the CuO attached to the surface of the LFP is at least partially rod-shaped.

[0055] In a specific embodiment of the present invention, the method for preparing the positive electrode material includes the following steps:

[0056] A mixture containing LFP is placed in a gold plasma environment, where the gold plasma reacts in the LFP-containing mixture to form gold nanoparticles, thereby obtaining the cathode material; wherein the cathode material comprises LFP and gold nanoparticles, at least a portion of the gold nanoparticles are attached to the surface of the LFP, and at least a portion of the gold nanoparticles attached to the surface of the LFP are rod-shaped.

[0057] In a specific embodiment of the present invention, the method for preparing the positive electrode material includes the following steps:

[0058] A mixture containing LFP is placed in a platinum plasma environment, where the platinum plasma reacts in the LFP-containing mixture to form platinum nanoparticles, thereby obtaining the cathode material; wherein the cathode material comprises LFP and platinum nanoparticles, at least a portion of the platinum nanoparticles are attached to the surface of the LFP, and at least a portion of the platinum nanoparticles attached to the surface of the LFP are rod-shaped.

[0059] In some embodiments of the present invention, the mixture further includes a metal chloride, which preferably includes potassium chloride and / or sodium chloride. The metal chloride serves as a conductive medium.

[0060] In some specific embodiments of the present invention, the concentration of metal chloride in the mixture is 0.05-1 mol / L.

[0061] In some specific embodiments of the present invention, the concentration of metal chloride in the mixture is 0.05-0.5 mol / L.

[0062] In some specific embodiments of the present invention, the concentration of metal chloride in the mixture is 0.5 mol / L.

[0063] In some embodiments of the present invention, the preparation method of the mixture includes: mixing an aqueous solution of a positive electrode active material and a metal chloride to obtain the mixture.

[0064] The mixing can be carried out by stirring, with the stirring speed being, for example, 50-1000 rpm and the stirring time being, for example, 5-30 minutes.

[0065] In some embodiments of the present invention, the mixture further contains a conductive agent.

[0066] In certain specific embodiments of the present invention, the conductive agent is one or more of Ketjen Black, CNT, and graphene.

[0067] In certain specific embodiments of the present invention, the mass concentration of the conductive agent in the mixture is 0.1%-2%. Here, % represents the percentage of the mass of the conductive agent relative to the mass of the mixture.

[0068] In certain embodiments of the present invention, the preparation method of the mixture includes the following steps: mixing the positive electrode active material, the conductive agent, and the aqueous solution of the metal chloride. The mixing may be performed by stirring, with a stirring speed of, for example, 50-1000 rpm and a stirring time of, for example, 5-30 minutes.

[0069] In some specific embodiments of the present invention, the mass concentration of the conductive agent in the mixture is 0.5%.

[0070] In some embodiments of the present invention, the formation of the metal plasma environment includes the following steps: two electrodes, each connected to the two poles of a high-voltage pulsed DC power supply, are immersed in the mixture at opposite positions and with a distance maintained, to form a discharge circuit, wherein the electrodes are the elemental metal.

[0071] Among them, the high-voltage pulsed DC power supply provides pulsed current to excite the metal elemental electrode, and high-energy electrons or free radicals bombard the metal surface to obtain metal atoms or atomic clusters, forming metal plasma.

[0072] In some specific embodiments of the present invention, the metallic element is a metal wire, the diameter of which is, for example, 0.1-5 mm; and the length of which is, for example, 200 mm.

[0073] In certain specific embodiments of the present invention, the mass ratio of the positive electrode active material and the metal-containing material is controlled by controlling the length of the metal element immersed in the mixture.

[0074] In some specific embodiments of the present invention, the spacing is 0.05-1 mm.

[0075] In some specific embodiments of the present invention, the spacing is 0.3 mm.

[0076] In some specific embodiments of the present invention, the discharge repetition frequency of the high-voltage pulsed DC power supply is 15-30kHz, and the pulse width of the high-voltage pulsed DC power supply is 1-5μs.

[0077] In some specific embodiments of the present invention, the discharge repetition frequency of the high-voltage pulsed DC power supply is 20kHz, and the pulse width of the high-voltage pulsed DC power supply is 3μs.

[0078] In some specific embodiments of the present invention, the discharge repetition frequency of the high-voltage pulsed DC power supply is 20kHz, and the pulse width of the high-voltage pulsed DC power supply is 1μs.

[0079] In some specific embodiments of the present invention, the discharge repetition frequency of the high-voltage pulsed DC power supply is 20kHz, and the pulse width of the high-voltage pulsed DC power supply is 5μs.

[0080] In some specific embodiments of the present invention, the discharge repetition frequency of the high-voltage pulsed DC power supply is 15kHz, and the pulse width of the high-voltage pulsed DC power supply is 3μs.

[0081] In some specific embodiments of the present invention, the discharge repetition frequency of the high-voltage pulsed DC power supply is 30kHz, and the pulse width of the high-voltage pulsed DC power supply is 3μs.

[0082] In some alternative embodiments of the present invention, the apparatus used for the reaction is a beaker, a large reaction vessel, or a chemical reactor.

[0083] Positive electrode film

[0084] The positive electrode sheet described in the third aspect of the present invention comprises the positive electrode material as described above.

[0085] In some embodiments of the present invention, the positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, the positive active material layer including the positive electrode material as described above.

[0086] In some alternative embodiments, the positive electrode active material layer further includes a binder, a dispersant, and a conductive agent.

[0087] For the positive electrode current collector, materials that do not cause chemical changes and have high conductivity can be used without restriction. Commonly used materials include stainless steel, aluminum, nickel, titanium, or calcined carbon, or aluminum or stainless steel surface-treated with carbon, nickel, titanium, silver, etc. To enhance the adhesion of the positive electrode active material, micro-embossing can be formed on the surface of the positive electrode current collector. Positive electrode current collectors can be used in various forms, such as films, sheets, foils, meshes, or porous bodies.

[0088] In some alternative implementations, the thickness of the positive current collector is 8-16 μm.

[0089] In some specific implementations, the positive current collector is an aluminum foil with a thickness of 16 μm.

[0090] Depending on actual needs, the conductive agent may also include other conventional conductive agents in the art, such as: graphite, such as natural graphite or artificial graphite; carbon-based materials, such as acetylene black, Ketjen black, channel black, furnace black, lamp black, thermal black and carbon fiber; metal powder or metal fiber, such as copper, nickel, aluminum and silver; conductive whiskers, such as zinc oxide whiskers and potassium titanate whiskers; conductive metal oxides, such as titanium dioxide; or conductive polymers, such as polyphenylene derivatives, etc., and any one of them or a mixture of two or more of them may be used.

[0091] The binder serves to improve the adhesion between positive electrode materials and the adhesion between the positive electrode material and the positive electrode current collector. There are no particular limitations on the type of binder. Specific examples of binders may include polyvinylidene fluoride (PVDF), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-co-HFP), polyvinyl alcohol, polyacrylonitrile, carboxymethyl cellulose (CMC), starch, hydroxypropyl cellulose, regenerated cellulose, polyvinylpyrrolidone, tetrafluoroethylene, polyethylene, polypropylene, ethylene-propylene-diene monomer (EPDM), sulfonated EPDM, styrene-butadiene rubber (SBR), fluororubber or various copolymers thereof, and any one or a mixture of two or more thereof may be used.

[0092] The dispersant may be a dispersant conventionally used in the art, such as a modified styrene-maleic anhydride copolymer.

[0093] In some alternative embodiments, the positive electrode sheet can be prepared using conventional methods in the art, such as the following method: mixing positive electrode material, binder, conductive agent and dispersant in a certain mass ratio, adding solvent and mixing evenly to obtain a positive electrode slurry; then uniformly coating the positive electrode slurry onto the positive electrode current collector; and then drying, cold pressing and slitting to obtain the positive electrode sheet.

[0094] In one specific embodiment, the solvent is NMP.

[0095] In some alternative embodiments, the positive electrode sheet can be prepared using conventional methods in the art, such as the following method: mixing the positive electrode material, binder and conductive agent in a certain mass ratio, adding a solvent and mixing evenly to obtain a positive electrode slurry; then uniformly coating the positive electrode slurry onto the positive electrode current collector; and then drying, cold pressing and slitting to obtain the positive electrode sheet.

[0096] In one specific implementation, the mass ratio of the positive electrode material, binder, and conductive agent is 97%:2%:1%.

[0097] Electrochemical device

[0098] The electrochemical device described in the fourth aspect of the present invention includes a positive electrode as described above.

[0099] In some embodiments of the present invention, the electrochemical device may be a sodium-ion battery or a lithium-ion battery.

[0100] In some alternative implementations, the lithium-ion battery further includes a negative electrode, a separator, and an electrolyte.

[0101] The electrolyte can be an organic liquid electrolyte, an inorganic liquid electrolyte, a solid polymer electrolyte, a gel polymer electrolyte, an inorganic solid electrolyte, a molten inorganic electrolyte, etc., such as LiPF6.

[0102] The battery preparation method can be a conventional battery preparation method in the art. For example, it can be: winding the negative electrode, the separator and the positive electrode to obtain a battery cell, placing the battery cell into a packaging shell and injecting the electrolyte, and then sequentially going through processes such as sealing, standing, hot and cold pressing, formation, venting and capacity testing to obtain the battery.

[0103] negative electrode sheet

[0104] In this invention, the negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector.

[0105] In some embodiments, the negative electrode active material layer includes a negative electrode material, a conductive agent, a binder, and a thickener.

[0106] In some specific embodiments, the mass ratio of the negative electrode material, the conductive agent, the binder, and the thickener is 97:0.7:1.8:0.5.

[0107] The negative electrode material can be any negative electrode material conventionally used in the art to prepare negative electrode sheets, and can be one or more of artificial graphite, natural graphite, soft carbon, hard carbon, mesophase carbon microspheres, silicon suboxide and silicon carbide.

[0108] In one specific implementation, the negative electrode material is artificial graphite.

[0109] 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).

[0110] 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 carbon black (Super P), 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, etc.

[0111] 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, ethylene-propylene-diene terpolymer and its sulfonates, styrene-butadiene rubber (SBR), fluororubber and various copolymers.

[0112] In one specific embodiment, the adhesive is styrene-butadiene rubber.

[0113] For the negative electrode current collector, the negative electrode current collector can be a current collector conventionally used for negative electrodes in the art, and can be a common current collector or a composite current collector. The negative electrode current collector can be made of a non-chemically reactive and conductive material without restriction. For example, copper, stainless steel, aluminum, nickel, titanium, calcined carbon, or aluminum-cadmium alloys can be used, or copper, stainless steel, or aluminum-cadmium alloys surface-treated with carbon, nickel, titanium, or silver. Furthermore, to enhance the adhesion of the negative electrode material, micro-embossing can be formed on the surface of the negative electrode current collector. The negative electrode current collector can be used in various forms, such as a film, sheet, foil, mesh, or porous body.

[0114] In some alternative implementations, the thickness of the negative electrode current collector is 5-10 μm.

[0115] In some specific implementations, the negative electrode current collector is a copper foil with a thickness of 6 μm.

[0116] In some alternative embodiments, the negative electrode sheet can be prepared using conventional methods in the art, such as the following method: mixing the negative electrode material, conductive agent, binder and thickener in a certain mass ratio, adding solvent and mixing evenly to obtain a negative electrode slurry; then uniformly coating the negative electrode slurry onto the negative electrode current collector; and then preparing the negative electrode sheet through processes such as drying, rolling, and cutting.

[0117] In one specific implementation, the solvent is water.

[0118] diaphragm

[0119] The diaphragm can be a diaphragm conventionally used in the art, such as a porous polymer membrane, wherein the porous polymer membrane is, for example, a porous polymer membrane made of polyolefin polymers such as ethylene homopolymer, propylene homopolymer, ethylene / butene copolymer, ethylene / hexene copolymer, ethylene / methacrylate copolymer, etc.; or, a typical porous nonwoven fabric can be used, wherein the porous nonwoven fabric is, for example, a nonwoven fabric made of high melting point glass fiber, polyethylene terephthalate fiber, etc.

[0120] electronic devices

[0121] The electronic device described in the fifth aspect of the present invention includes the electrochemical device as described above.

[0122] 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.

[0123] 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.

[0124] The reagents and raw materials used in this invention are all commercially available.

[0125] Example 1

[0126] The preparation of cathode materials includes the following steps:

[0127] A mixture was prepared by stirring lithium iron phosphate powder with a D50 particle size of 1.1 μm and a 0.5 mol / L potassium chloride aqueous solution at a speed of 500 rpm for 10 min. The mass concentration of lithium iron phosphate powder in the mixture was 20%, that is, the mass percentage of lithium iron phosphate powder in the mixture was 20%. The concentration of potassium chloride in the mixture was 0.5 mol / L.

[0128] Two Zn elemental metal wires, each 200 mm long and 1 mm in diameter, were used as electrodes. These two electrodes were immersed in the aforementioned mixture with a 0.3 mm gap between them and the electrodes. The two electrodes were connected to the two poles of a high-voltage pulsed DC power supply to form a discharge circuit. The discharge repetition frequency was 20 kHz and the pulse width was 3 μs, creating a Zn plasma environment. The Zn plasma reacted in the mixture to form zinc oxide. Once a certain mass of Zn elemental metal wires was consumed, the discharge was stopped. The resulting solution was filtered, washed with deionized water, and dried to obtain the positive electrode material.

[0129] The preparation of the positive electrode includes the following steps:

[0130] The above-mentioned positive electrode material, binder, and conductive agent are mixed in a mass ratio of 97%:2%:1%, and NMP is added as a solvent to mix evenly to obtain a positive electrode slurry. The positive electrode slurry is then uniformly coated on a 16 μm thick positive electrode current collector aluminum foil. After drying, cold pressing, and slitting, a positive electrode sheet is obtained.

[0131] Example 2-31

[0132] Except for the parameters in Table 1, the parameters for the preparation process of the cathode materials in Examples 2-31 are the same as those in Example 1.

[0133] The preparation of the positive electrode is the same as in Example 1.

[0134] The mixtures in Examples 4 and 16 also include a conductive agent. The specific preparation method of the mixtures in Examples 4 and 16 is as follows: the positive electrode active material, the conductive agent and the potassium chloride aqueous solution are stirred at a speed of 500 rpm for 10 min to obtain the mixture.

[0135] Table 1

[0136] New number Types of metal chlorides Concentration of metal chlorides in the mixed solution (mol / L) Types of conductive agents Mass concentration of conductive agent in the mixture Types of metal wires Diameter of the metal wire (mm) Spacing (mm) The discharge repetition frequency (kHz) of the high-voltage pulsed DC power supply. Pulse width (μs) of high-voltage pulsed DC power supply Example 1 Potassium chloride 0.5 / / Zinc 1 0.3 20 3 Example 2 Potassium chloride 0.5 / / Zinc 1 0.3 20 3 Example 3 Potassium chloride 0.5 / / Zinc 1 0.3 20 3 Example 4 Potassium chloride 0.5 Kochen Black 0.5% Zinc 1 0.3 20 3 Example 5 Potassium chloride 0.5 / / copper 1 0.3 20 3 Example 6 Potassium chloride 0.5 / / Zinc 1 0.3 20 3 Example 7 Potassium chloride 0.5 / / Zinc 1 0.3 20 3 Example 8 Potassium chloride 0.5 / / Zinc 1 0.3 20 3 Example 9 Potassium chloride 0.5 / / gold 1 0.3 20 3 Example 10 Potassium chloride 0.5 / / platinum 1 0.3 20 3 Example 11 Sodium chloride 0.5 / / Zinc 1 0.3 20 3 Example 12 Potassium chloride 0.05 / / Zinc 1 0.3 20 3 Example 13 Potassium chloride 1 / / Zinc 1 0.3 20 3 Example 14 Potassium chloride 0.5 graphene 0.5% Zinc 1 0.3 20 3 Example 15 Potassium chloride 0.5 / / Zinc 0.1 0.3 20 3 Example 16 Potassium chloride 0.5 / / Zinc 5 0.3 20 3 Example 17 Potassium chloride 0.5 / / Zinc 1 0.05 20 3 Example 18 Potassium chloride 0.5 / / Zinc 1 1 20 3 Example 19 Potassium chloride 0.5 / / Zinc 1 0.3 15 3 Example 20 Potassium chloride 0.5 / / Zinc 1 0.3 30 3 Example 21 Potassium chloride 0.5 / / Zinc 1 0.3 20 1 Example 22 Potassium chloride 0.5 / / Zinc 1 0.3 20 5 Example 23 Potassium chloride 0.5 / / Zinc 1 0.3 20 3 Example 24 Potassium chloride 0.5 / / Zinc 1 0.3 20 3 Example 25 Potassium chloride 0.5 / / Zinc 1 0.3 20 3 Example 26 Potassium chloride 0.5 / / Zinc 1 0.3 20 3 Example 27 Potassium chloride 0.5 / / Zinc 1 0.3 20 3 Example 28 Potassium chloride 0.5 / / Zinc 1 0.3 20 3 Example 29 Potassium chloride 0.5 / / Zinc 1 0.3 20 3 Example 30 Potassium chloride 0.5 / / Zinc 1 0.3 20 3 Example 31 Potassium chloride 0.5 / / Zinc 1 0.3 20 3

[0137] Note: " / " in the table indicates that the substance is not present.

[0138] Comparative Example 1

[0139] Comparative Example 1 did not use a high-voltage pulsed DC power supply to form a discharge circuit, and the other preparation processes were the same as in Example 1. Unrecombined lithium iron phosphate was obtained in the comparative example.

[0140] The preparation method of the positive electrode is the same as in Example 1.

[0141] Comparative Example 2

[0142] Comparative Example 2 uses the preparation method of patent CN102244242A, specifically the following steps:

[0143] (1) Take 10 mL of 1.5 mol / L LiOH solution, and slowly add 10 mL of 0.5 mol / L H3PO4 solution dropwise into the LiOH solution. Stir thoroughly for 1 hour to obtain a white colloidal solution A.

[0144] (2) Take 1 mL of 0.5 mol / L Zn(Ac)2 solution and 1 mL of 1.5 mol / L lithium hydroxide solution, mix them in an ice-water bath and continue stirring for 2 hours to obtain a white precipitate solution B;

[0145] (3) While stirring vigorously, slowly add solution B to solution A and continue stirring thoroughly for 2 hours to form a mixed solution C;

[0146] (4) Dissolve 0.005 mol of FeSO4 in 20 ml of deionized water to form a ferrous sulfate solution. Quickly add the ferrous sulfate solution to the mixed solution C and stir for 1 min to form a dark green mixed solution D.

[0147] (5) Transfer the mixed solution D into the reactor and react at 180°C for 16 hours. After natural cooling, take a sample, wash with a large amount of deionized water, and dry at 80°C for 12 hours to obtain ZnO / LiFePO4 powder.

[0148] The preparation method of the positive electrode is the same as in Example 1.

[0149] Example 1

[0150] The cathode materials prepared in Examples 1-31 above include lithium iron phosphate as the cathode active material and a substance containing metal elements, which includes metal oxides or nano-metal elements. At least a portion of the substance containing metal elements is attached to the surface of the cathode active material, and the other portion is embedded in the interior of the cathode active material. The substance containing metal elements attached to the surface of the cathode active material is at least a long rod-shaped material. The length of the long rod-shaped substance containing metal elements is 1-2 μm and the diameter is 50-100 nm.

[0151] The length and diameter of the rod-shaped metallic substance were determined using SEM images.

[0152] In the positive electrode materials prepared in Examples 1-31, the composition of the positive electrode material was obtained by XRD pattern analysis. The mass ratio of positive electrode active material to metal-containing material and the mass ratio of positive electrode active material to conductive agent were calculated by the amount of positive electrode active material, metal-containing material and conductive agent added, or obtained by ICP or EDS testing.

[0153] The product parameters of the cathode materials prepared in Examples 1-31 are listed in Table 2:

[0154] Table 2

[0155]

[0156]

[0157] The cathode material prepared in Example 1 was subjected to XRD testing, and the obtained XRD pattern is shown below. Figure 1 As shown.

[0158] The cathode material prepared in Example 1 was subjected to SEM testing, and the obtained SEM images are shown below. Figure 1 As shown.

[0159] Example 2

[0160] Preparation of lithium-ion batteries

[0161] The positive electrode, separator and negative electrode prepared in Examples 1-24 and Comparative Examples 1 and 2 are wound to obtain a battery cell, which is then packaged in a packaging shell and injected with electrolyte to obtain a soft-pack battery.

[0162] The preparation of the negative electrode sheet includes the following steps: the obtained graphite material, conductive agent (SP), binder (PAA and SBR, with a mass ratio of 1.3:0.5) and thickener carboxymethyl cellulose (CMC) are mixed in a mass ratio of 97.2:0.5:1.8:0.5 (100 parts by mass in total), and then 82 parts by mass of deionized water are added and mixed evenly to obtain a negative electrode slurry; then the negative electrode slurry is evenly coated on copper foil; and then the negative electrode sheet is prepared by drying, rolling, cutting and other processes.

[0163] The diaphragm is a polyethylene film with a thickness of 11 μm, an air permeability of 230 s / 100 mL, and a porosity of 40%.

[0164] The electrolyte used is a commercially available electrolyte (manufacturer: Xinya Shanshan New Material Technology (Quzhou) Co., Ltd., model: E3).

[0165] The following tests were performed on the lithium-ion batteries prepared using the positive electrode sheets of Examples 1-24 and Comparative Examples 1 and 2:

[0166] 1. Initial discharge capacity and initial charge / discharge efficiency test: Connect the activated lithium-ion battery to the Blue Electric charge / discharge tester and perform its first long-cycle charge / discharge test to measure its charging capacity and discharge capacity. The working voltage range of the battery test is 2.5V (discharge cut-off voltage) to 3.65V (charge cut-off voltage), and the test rate is 0.1C.

[0167] First-time efficiency = (First discharge capacity / First charge capacity) × 100%.

[0168] The initial charge-discharge curves at 0.1C for Example 1 (ZnO / LiFePO4), Comparative Example 1 (LiFePO4), and Comparative Example 2 (ZnO / LiFePO4 control group) are shown below. Figure 3 As shown.

[0169] 2. Cyclic performance test at different rates: 5 cycles each of 0.1C, 0.5C, 1C, 2C, 5C, and 10C charge and discharge at different rates within the 2.5V-3.65V range. The specific capacity was calculated by dividing the capacity by the lithium iron phosphate content.

[0170] The cycling performance graphs of Example 1 (ZnO / LiFePO4), Comparative Example 1 (LiFePO4), and Comparative Example 2 (ZnO / LiFePO4 control group) at different rate ratios are shown below. Figure 4 As shown.

[0171] 3. Resistivity test: The four-probe method of a powder resistance tester is used for testing.

[0172] The resistivity diagrams of Example 1 (ZnO / LiFePO4), Comparative Example 1 (LiFePO4), and Comparative Example 2 (ZnO / LiFePO4 control group) are shown below. Figure 5 As shown.

[0173] The results of test 1 above are listed in Table 3:

[0174] Table 3

[0175] New number Initial discharge capacity (mAh / g) First charge / discharge efficiency Example 1 156.54 95.88% Example 2 155.87 95.47% Example 3 156.83 96.06% Example 4 156.91 96.11% Example 5 155.38 95.17% Example 6 157.76 96.63% Example 7 155.65 95.33% Example 8 156.03 95.57% Example 9 156.89 96.09% Example 10 156.67 95.96% Example 11 156.37 95.78% Example 12 156.9 96.10% Example 13 153.63 94.10% Example 14 157.01 96.17% Example 15 156.92 96.11% Example 16 155.86 95.46% Example 17 156.21 95.68% Example 18 156.78 96.03% Example 19 156.84 96.06% Example 20 156.12 95.62% Example 21 156.63 95.94% Example 22 156.32 95.75% Example 23 154.87 94.86% Example 24 153.66 94.12% Example 25 152.12 93.17% Example 26 151.01 92.49% Example 27 149.73 91.71% Example 28 149.34 91.47% Example 29 149.23 91.40% Example 30 149.15 91.35% Example 31 149.18 91.37% Comparative Example 1 139.1 88.60% Comparative Example 2 144.66 91.70%

[0176] As can be seen from the above data, the cathode material prepared in the embodiments of the present invention, when applied in a battery, can exhibit an initial discharge capacity of over 149 mAh / g and an initial charge-discharge efficiency of over 91%, indicating excellent conductivity and rate performance. This is likely because the rod-shaped metal-containing material prepared in the present invention is embedded in or attached to the surface of the cathode active material, providing good electrical contact and forming a conductive network that significantly improves the conductivity of the material. Furthermore, the metal-containing material also acts as a support, facilitating lithium-ion transport, increasing its transport coefficient, and thus improving the rate performance of the cathode material.

[0177] Compared with the Example, Comparative Example 1 is a non-recombined lithium iron phosphate, and its first discharge capacity is reduced to 139.1 mAh / g and its first charge-discharge efficiency is reduced to 88.6%. Compared with the Example, Comparative Example 2 uses a conventional hydrothermal synthesis method to prepare the cathode material. Not only is the preparation process more complicated, requiring high temperature and high pressure reaction, and large-scale production is difficult and risky, but its first discharge capacity and first charge-discharge efficiency are also worse than those of the Example.

[0178] Based on the results of Examples 1, 14 and 15, it can be seen that if the concentration of metal chloride in the mixture is 0.05-0.5 mol / L, it is more conducive to further increasing the initial discharge capacity to 156 mAh / g or more and the initial charge-discharge efficiency to 95% or more.

[0179] Based on the results of Examples 1-3, 6-8, and 23-31, it is evident that a mass ratio of positive electrode active material to metal-containing material of (10-999):1 is beneficial for simultaneously improving the initial discharge capacity and initial charge-discharge efficiency. Furthermore, a mass ratio of positive electrode active material to metal-containing material of (10-200):1 can increase the initial discharge capacity to 155 mAh / g or higher and the initial charge-discharge efficiency to 95% or higher. Even further, a mass ratio of positive electrode active material to metal-containing material of (10-20):1 is more beneficial for further increasing the initial discharge capacity to 156.8 mAh / g or higher and the initial charge-discharge efficiency to 96% or higher.

[0180] 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 material, characterized in that, It includes a positive electrode active material and a metal-containing material, wherein the metal-containing material includes metal oxides and / or nano-metal elements; at least a portion of the metal-containing material is attached to the surface of the positive electrode active material, wherein at least a portion of the metal-containing material attached to the surface of the positive electrode active material is rod-shaped, thereby forming a conductive network. Another portion of the metal-containing substance is embedded inside the positive electrode active material; The method for preparing the cathode material includes the following steps: The positive electrode material is obtained by subjecting a mixture containing a positive electrode active material to a metal plasma environment, where the metal plasma reacts in the mixture to form the metal-containing substance.

2. The cathode material as described in claim 1, characterized in that, The cathode material satisfies one or more of the following conditions (a)-(e): (a) The positive electrode active material is one or more of lithium iron phosphate, lithium manganese iron phosphate, nickel-manganese-cobalt ternary materials, lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, nickel-cobalt-aluminum materials, and lithium-rich manganese-based materials; (b) The metal oxide is one or more of zinc oxide, copper oxide, and titanium oxide; (c) The nano-metallic element is one or more of nano-gold, nano-platinum, and nano-palladium; (d) The length of the rod-shaped metallic substance is 1-2 μm and the diameter is 50-100 nm; (e) The mass ratio of the positive electrode active material to the metal-containing material is (10-999):

1.

3. The positive electrode material as described in claim 1, characterized in that, The positive electrode material further includes a conductive agent, and the positive electrode material satisfies one or more of the following conditions (a)-(c): (a) The conductive agent is coated on the surface of the positive electrode active material, and another part of the metal-containing material is embedded inside the positive electrode active material and / or the conductive agent; (b) The conductive agent is one or more of Ketjen black, carbon nanotubes, and graphene; (c) The mass ratio of the positive electrode active material to the conductive agent is (19-999):

1.

4. A method for preparing a positive electrode material as described in any one of claims 1-3, characterized in that, It includes the following steps: The positive electrode material is obtained by subjecting a mixture containing a positive electrode active material to a metal plasma environment, where the metal plasma reacts in the mixture to form the metal-containing substance.

5. The method for preparing the cathode material as described in claim 4, characterized in that, The method for preparing the cathode material satisfies one or both of the following conditions (a)-(b): (a) The D50 particle size of the positive electrode active material is 0.5-100 μm; (b) The metal is one or more of zinc, copper, titanium, gold, platinum and palladium.

6. The method for preparing the cathode material as described in claim 4, characterized in that, The method for preparing the cathode material satisfies one or more of the following conditions (a)-(c): (a) The mixture further includes a metal chloride, which includes potassium chloride and / or sodium chloride; (b) The formation of the metal plasma environment includes the following steps: two electrodes, each connected to the two poles of a high-voltage pulsed DC power supply, are immersed in the mixture at opposite positions and with a distance maintained, to form a discharge circuit, wherein the electrodes are the metal element; (c) The mixture also contains a conductive agent.

7. The method for preparing the cathode material as described in claim 6, characterized in that, The method for preparing the cathode material satisfies one or more of the following conditions (a)-(d): (a) The metallic element is a metal wire with a diameter of 0.1-5 mm; (b) The concentration of metal chloride in the mixture is 0.05-1 mol / L; (c) The spacing is 0.05-1 mm; (d) The discharge repetition frequency of the high-voltage pulsed DC power supply is 15-30kHz, and the pulse width of the high-voltage pulsed DC power supply is 1-5μs.

8. A positive electrode plate, characterized in that, It includes the cathode material as described in any one of claims 1-3.

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

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

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