Positive plate as well as preparation method and application thereof

Abstract

The invention relates to the technical field of batteries, in particular to a positive plate as well as a preparation method and application thereof. The positive plate comprises a current collector layer, a plasma spraying layer and a coating layer, the plasma spraying layer is located on the surface of at least one side of the current collector layer, and the coating layer is located on the surface, away from the current collector layer, of the plasma spraying layer; the plasma spraying layer comprises a first active material and a first conductive agent; the coating layer comprises a second active material, a binder and a second conductive agent; the mass content W of the binder in the coating layer meets the following conditions: 0 lt; w < = 1%. According to the positive plate, the use proportion of the binder can be remarkably reduced, and the positive plate has excellent structural stability, high energy density, high charge-discharge efficiency and good cycle stability.

Description

Technical Field

[0001] The present invention relates to the field of battery technology, and in particular to a positive electrode sheet, a preparation method thereof, and applications thereof. Background Art

[0002] Lithium-ion batteries have undergone over three decades of technological evolution, with their applications gradually expanding from portable consumer electronics to electric vehicles and large-scale energy storage systems. In recent years, with the accelerated transformation of the global energy structure and the explosive growth of the new energy vehicle market, the energy density, cycle life, and charging efficiency of power batteries have become the core drivers of technological innovation in the industry. In particular, users' urgent demand for fast charging is driving the evolution of battery systems towards high-rate charge and discharge performance.

[0003] However, the charging efficiency of new energy vehicles is still a major challenge. The new stage of fast charging cells prefers small particle size and large specific surface area materials, increases conductive agents, reduces coating weight and compaction methods, while improving charging and discharging capabilities at the expense of energy density. In addition, the electrode coating has insufficient adhesion, low peel strength, and active materials are easy to fall off. These problems have magnified the difficulty of developing fast charging cells and hindered the improvement of battery energy density.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] One object of the present invention is to provide a positive electrode sheet that can greatly reduce the proportion of binder by setting a composite layer (plasma spray layer and coating layer), and can significantly improve the charge and discharge efficiency and energy density while ensuring the bonding strength between the composite layer and the current collector layer.

[0006] Another object of the present invention is to provide a method for preparing a positive electrode sheet. This method combines plasma spraying technology and wet coating technology, which can significantly reduce the proportion of binder used and the amount of solvent used, so that the obtained positive electrode sheet has excellent structural stability and high charge and discharge efficiency.

[0007] Another object of the present invention is to provide a battery.

[0008] Another object of the present invention is to provide an electrical device.

[0009] In order to achieve the above-mentioned purpose of the present invention, the following technical solutions are adopted: A positive electrode sheet, comprising a current collector layer, a plasma sprayed layer, and a coating layer; the plasma sprayed layer is located on at least one side of the current collector layer, and the coating layer is located on a surface of the plasma sprayed layer away from the current collector layer; the plasma sprayed layer comprises a first active material and a first conductive agent; the coating layer comprises a second active material, a binder, and a second conductive agent; the mass content W of the binder in the coating layer satisfies: <W≤1%。

[0010] In some embodiments, the mass content A1 of the first conductive agent in the plasma sprayed layer and the mass content B1 of the second conductive agent in the coating layer satisfy the relationship: 1≤A1 / B1≤5.5.

[0011] In some embodiments, the first conductive agent and the second conductive agent each independently include at least one of conductive graphite, conductive carbon black, carbon nanotubes, carbon fibers, and metal conductive particles.

[0012] In some embodiments, the plasma sprayed layer has a thickness of 1 to 100 μm.

[0013] In some embodiments, the coating layer has a thickness of 100-200 μm.

[0014] In some embodiments, the mass content A2 of the first active material in the plasma sprayed layer is equal to the mass content B2 of the second active material in the coating layer, and A2≥B2.

[0015] In some embodiments, the first active material and the second active material each independently include at least one of lithium nickel cobalt manganese oxide, lithium nickel manganese oxide, lithium iron manganese oxide, lithium cobalt oxide, lithium iron phosphate, and lithium manganese oxide.

[0016] In some embodiments, the binder content in the plasma sprayed layer is zero.

[0017] In some embodiments, the mass content W of the binder in the coating layer satisfies: 0.5%≤W≤1%.

[0018] In some embodiments, the binder includes at least one of polyvinyl chloride, polyethylene, polyimide, polyether nitrile, polypropylene, polystyrene, polymethyl acrylate, polyamide, polyvinylidene fluoride, polytetrafluoroethylene, polyethylene terephthalate, and polytetrafluoroethylene.

[0019] In some embodiments, the peel strength of the positive electrode sheet is greater than or equal to 470 N / m.

[0020] In some embodiments, the charging or discharging time of the battery corresponding to the positive electrode sheet when the state of charge is between 20% and 80% is less than 28 minutes.

[0021] The method for preparing the positive electrode sheet as described above comprises the following steps: A dry mixture formed by the first active material and the first conductive agent is sprayed onto at least one surface of the current collector layer by plasma spraying to obtain a plasma sprayed layer.

[0022] A coating slurry formed by a second active material, a binder, a second conductive agent and a solvent is applied to the surface of the plasma sprayed layer to form a coating layer, thereby obtaining a positive electrode sheet.

[0023] In some embodiments, the plasma spraying specifically includes: heating the dry mixture to a semi-molten state or a molten state by a plasma arc, and then spraying the heated dry mixture onto the surface of the current collector using high-pressure gas.

[0024] In some embodiments, the interval time T between the plasma spraying and the coating is ≤ 60 s, preferably 5 to 15 s.

[0025] In some embodiments, during the plasma spraying process, the plasma arc is heated to a temperature of ≤400°C, preferably 50-200°C.

[0026] In some embodiments, the preparation of the dry mix specifically includes: stirring and dispersing the first active material and the first conductive agent at a stirring speed of 10-30 rpm, a dispersing speed of 500-2500 rpm, and a time of 0.5-2 h.

[0027] In some embodiments, the coating slurry is prepared by stirring and dispersing the second active material, the binder, the second conductive agent, and the solvent at a stirring speed of 10-40 rpm and a dispersing speed of 500-4500 rpm for 2-5 hours.

[0028] In some embodiments, the method further comprises drying the spray coating, wherein the drying temperature is 25-125° C. and the drying time is 0.5-2 minutes.

[0029] A battery comprises the positive electrode sheet or the positive electrode sheet prepared by the positive electrode sheet preparation method.

[0030] An electrical device comprises the battery.

[0031] Compared with the prior art, the present invention has the following beneficial effects: (1) The positive electrode sheet of the present invention has a plasma sprayed layer on the surface of the current collector layer, which can form a mechanical anchoring effect and chemical bonding, forming a more stable connection with the surface of the current collector, strengthening the interfacial binding energy, avoiding the use of binders, increasing the ratio of the first conductive agent to the first active material, improving the peel strength and increasing the energy density of the battery cell; the coating layer provides a fast ion channel, ensuring the bonding effect between the coating layer and the plasma sprayed layer while reducing the amount of binder applied, and increasing the charge and discharge efficiency. The positive electrode sheet of the present invention can significantly reduce the proportion of binders used, has excellent structural stability, high energy density, high charge and discharge efficiency, and good cycle stability.

[0032] (2) The preparation method of the positive electrode sheet of the present invention adopts a plasma spraying method combined with a wet coating method to construct a double-layer composite layer. The dry mixture is mechanically anchored and in-situ activated on the surface of the current collector layer by plasma spraying. The dry mixture can be embedded in the pits on the surface of the current collector. At the same time, the first conductive agent may form a chemical bond with the surface of the current collector layer, thereby forming a dense and continuous three-dimensional conductive network, thereby improving the electron transmission performance. The coating slurry is formed into a coating layer with a certain porous structure by wet coating, which can optimize ion diffusion and achieve the wetting balance of the electrolyte. The method of the present invention can achieve precise control of electron-ion transmission, improve the structural stability of the positive electrode sheet, and improve its fast charging performance, energy density and cycle performance.

[0033] (3) The battery of the present invention adopts the above-mentioned positive electrode sheet, which has high energy density, good fast charging performance and good cycle stability. DETAILED DESCRIPTION

[0034] The embodiments of the present invention will be described in detail below with reference to the examples, but it will be understood by those skilled in the art that the following examples are merely illustrative of the present invention and should not be construed as limiting the scope of the invention. Where specific conditions are not specified in the examples, the methods were performed according to conventional conditions or the conditions recommended by the manufacturer. Where the manufacturers of the reagents or instruments are not specified, they are all commercially available conventional products.

[0035] According to one aspect of the present invention, the present invention relates to a positive electrode sheet, comprising a current collector layer, a plasma sprayed layer and a coating layer; the plasma sprayed layer is located on at least one side surface of the current collector layer, and the coating layer is located on the surface of the plasma sprayed layer away from the current collector layer; the plasma sprayed layer comprises a first active material and a first conductive agent; the coating layer comprises a second active material, a binder and a second conductive agent; the mass content W of the binder in the coating layer satisfies: <W≤1%。

[0036] The positive electrode sheet of the present invention is provided with a plasma sprayed layer on the surface of the current collector layer, which can form a mechanical anchoring effect and a chemical bonding effect, forming a more stable connection with the surface of the current collector, strengthening the interfacial binding energy, and avoiding the use of a binder (i.e., the binder content in the plasma sprayed layer is 0), increasing the ratio of the first conductive agent to the first active material, improving the peel strength and increasing the energy density of the battery cell; the coating layer provides a fast ion channel, ensuring the bonding effect between the coating layer and the plasma sprayed layer while reducing the amount of binder applied, and increasing the charge and discharge efficiency. In some embodiments, the mass content W of the binder in the coating layer is 0.2%, 0.3%, 0.5%, 0.6%, 0.8%, 0.9% or 1%, etc. The positive electrode sheet of the present invention can significantly reduce the proportion of binder used, has excellent structural stability, high energy density, high charge and discharge efficiency, and good cycle stability.

[0037] In some embodiments, the mass content A1 of the first conductive agent in the plasma sprayed layer and the mass content B1 of the second conductive agent in the coating layer satisfy the relationship: 1≤A1 / B1≤5.5, and the value of A1 / B1 is, for example, 1, 1.5, 2, 3.5, 3, 3.5, 4, 5, etc., or a range of values ​​therebetween. The present invention achieves gradient matching and functional coordination of the conductive agent in the plasma sprayed layer and the coating layer by controlling 1≤A1 / B1≤5.5. The plasma sprayed layer can form an efficient electron pathway, and the coating layer can achieve rapid diffusion of lithium ions, that is, achieving a dynamic balance between electron transmission and ion transmission, thereby improving fast charging performance.

[0038] In some embodiments, the first conductive agent and the second conductive agent each independently include at least one of conductive graphite, conductive carbon black, carbon nanotubes, carbon fibers and metal conductive particles. The present invention adopts a combination of one or more of the above conductive agents, such as a mixture of conductive carbon black and carbon nanotubes, a mixture of conductive carbon black, carbon nanotubes and carbon fibers, etc. In some embodiments, the mass content of the first conductive agent in the plasma sprayed layer is 1.5% to 5.5%, such as 1.5%, 2%, 2.5%, 3%, 4% or 5.5%. In some embodiments, the mass content of the second conductive agent in the coating layer is 0.5% to 3%, such as 0.5%, 1%, 2%, 3%, etc. The first conductive agent and the second conductive agent of the present invention have a suitable mass content, and can work synergistically to ensure the electrochemical performance of the positive electrode composite layer.

[0039] In some embodiments, the plasma-sprayed layer has a thickness of 1 to 100 μm, such as 1 μm, 5 μm, 10 μm, 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, or 100 μm, or any range therebetween. A preferred thickness is 10 to 50 μm. The present invention utilizes a plasma-sprayed layer of suitable thickness to ensure interfacial bonding strength between the plasma-sprayed layer and the current collector layer, while also ensuring the conductive properties of the layer.

[0040] In some embodiments, the coating layer has a thickness of 100 to 200 μm, for example, 100 μm, 120 μm, 150 μm, 180 μm, 190 μm, 200 μm, etc. The present invention uses a coating layer of appropriate thickness to ensure synergy with the plasma sprayed layer and improve the overall mechanical and electrochemical properties of the positive electrode sheet.

[0041] In some embodiments, the mass content A2 of the first active material in the plasma sprayed layer is equal to the mass content B2 of the second active material in the coating layer, satisfying the following: A2 ≥ B2. In some embodiments, the mass content of the second active material in the coating layer is 94.5% to 99%, preferably 96.5% to 98%. In some embodiments, the mass content of the first active material in the plasma sprayed layer is 94.5% to 99%, preferably 97.5% to 98.5%. In some embodiments, the first active material and the second active material each independently comprise a combination of one or more of lithium nickel cobalt manganese oxide, lithium nickel manganese oxide, lithium iron manganese oxide, lithium cobalt oxide, lithium iron phosphate, and lithium manganese oxide.

[0042] In some embodiments, the mass content W of the binder in the coating layer satisfies the following: 0.5% ≤ W ≤ 1%. In some embodiments, the binder comprises at least one of polyvinyl chloride, polyethylene, polyimide, polyether nitrile, polypropylene, polystyrene, polymethyl acrylate, polyamide, polyvinylidene fluoride, polytetrafluoroethylene, polyterephthalate, and polytetrafluoroethylene, for example, a combination of polyimide and polyether nitrile, or a combination of polystyrene and polymethyl acrylate. The present invention utilizes the aforementioned binder in an appropriate amount and ratio to ensure effective bonding between the coating layer and the plasma sprayed layer while also maintaining the coating layer's electrical conductivity.

[0043] In some embodiments, the current collector layer comprises aluminum foil and has a thickness of 8 to 20 μm.

[0044] In some embodiments, the positive electrode sheet has a peel strength greater than or equal to 470 N / m, for example, 470 to 580 N / m. In the positive electrode sheet of the present invention, the composite layer (plasma sprayed layer and coating layer) and the current collector layer have excellent bonding strength, which helps improve the structural stability of the positive electrode sheet.

[0045] In some embodiments, the battery corresponding to the positive electrode sheet has a charge or discharge time of less than 28 minutes, such as 15 to 28 minutes, at a state of charge of 20% to 80%. The battery obtained by the positive electrode sheet of the present invention has excellent charge and discharge efficiency.

[0046] The simplest and most common way to achieve fast charging of battery cells is to increase the proportion of conductive agent in battery materials. However, simply increasing the conductive agent material will affect the content of active materials and binders in the battery cell. Increasing the conductive agent at the expense of the proportion of active materials will lead to a decrease in energy density. Reducing the binder input and increasing the conductive agent proportion will lead to a series of problems after electrode coating, poor adhesion, reduced peel strength, and easy detachment of active materials. In terms of adhesion between active materials and current collectors, the demand for binder content is much greater than the demand for binders between active materials. For a single coating process, the binder ratio must first consider the peel strength requirement between active materials and current collectors. Therefore, the binder ratio in the overall slurry is much higher than that actually used. At this time, a double coating design is adopted. For the upper slurry where only the adhesion between active materials needs to be considered, the binder content can be greatly reduced, and the reduced binder ratio is replaced with a conductive agent. This can effectively improve its fast charging performance without changing the active material. As for the bottom layer (the material layer close to the current collector), plasma spraying technology is used to achieve high adhesion of the material to the surface of the substrate. This technology uses a plasma arc driven by direct current as a heat source to heat the metal material to a molten or semi-molten state, and sprays it at high speed onto the pre-treated current collector surface to form a firmly adhered surface layer. In essence, it does not require the use of additional adhesives, so only a premix of active materials and conductive agents is needed to produce the bottom structure of the battery cell, and the overall proportion of active materials and conductive agents can be increased. While improving the peel strength, it also increases the energy density and charge and discharge capacity of the battery cell.

[0047] According to another aspect of the present invention, the present invention relates to a method for preparing the positive electrode sheet as described above, comprising the following steps: A dry mixture formed by the first active material and the first conductive agent is sprayed onto at least one surface of the current collector layer by plasma spraying to obtain a plasma sprayed layer.

[0048] A coating slurry formed by a second active material, a binder, a second conductive agent and a solvent is applied to the surface of the plasma sprayed layer to form a coating layer, thereby obtaining a positive electrode sheet.

[0049] The preparation method of the positive electrode sheet of the present invention adopts a plasma spraying method combined with a wet coating method to construct a double-layer composite layer. The dry mixture is mechanically anchored and in-situ activated on the surface of the current collector layer by plasma spraying. The dry mixture can be embedded in the pits on the surface of the current collector. At the same time, the first conductive agent may form a chemical bond with the surface of the current collector layer, thereby forming a dense and continuous three-dimensional conductive network, thereby improving the electron transmission performance. The coating slurry is formed into a coating layer with a certain porous structure by a wet coating method, which can optimize ion diffusion and achieve the wetting balance of the electrolyte. The method of the present invention can achieve precise control of electron-ion transmission, improve the structural stability of the positive electrode sheet, and improve its fast charging performance, energy density and cycle performance.

[0050] In some embodiments, the dry blend is prepared by mixing the first active material and the first conductive agent at a stirring speed of 10 to 30 rpm and a dispersion speed of 500 to 2500 rpm for 0.5 to 2 hours. Suitable dry blend preparation conditions are employed to ensure that the materials are thoroughly mixed.

[0051] In some embodiments, the plasma spraying process specifically includes placing the dry mix into a powder feeder within a plasma spraying mechanism, heating the dry mix to a semi-molten or molten state via a plasma arc, and then spraying the heated dry mix onto the surface of the current collector using high-pressure gas, thereby forming a primary, firm surface layer and thereby improving the adhesion of the underlying layer. The present invention utilizes plasma spraying technology under suitable conditions, eliminating the need for solvent in the underlying material; only pre-mixing the powder is required for spraying. This reduction in solvent not only reduces material costs but also shortens the drying time of the coating.

[0052] High-pressure gas is used as both a power source for spraying and a protective agent to prevent the material from being oxidized while not reacting with the material. Inert gases are used, including but not limited to helium (He), neon (Ne), argon (Ar), krypton (Kr), xenon (Xe), radon (Rn, radioactive), and Og (radioactive, artificial element), preferably one of helium or argon. In some embodiments, the equipment used for plasma spraying includes but is not limited to high temperature and high pressure plasma, low temperature and low pressure plasma, and high temperature and low pressure plasma equipment.

[0053] In some embodiments, the interval time T between the plasma spraying and the coating is ≤ 60s, such as 5s, 10s, 15s, 20s, 30s, 50s or 60s, and preferably 5 to 15s. The present invention ensures the preparation effect of the coating layer by limiting the interval time between plasma spraying and coating. Within a suitable time after plasma spraying, the plasma sprayed layer still has a certain temperature, and the solvent and binder in the coating slurry form a good bonding effect with the surface of the sprayed layer, thereby ensuring the uniformity of the coating layer and the ion transmission performance, which can effectively improve the comprehensive performance of the above composite layer.

[0054] In some embodiments, during the plasma spraying process, the plasma arc is heated to a temperature ≤ 400°C, such as 250°C, 300°C, or 400°C; preferably 50-200°C.

[0055] In some embodiments, the coating method includes transfer coating, micro-dimple coating, extrusion coating, dip coating, curtain coating, preferably extrusion coating.

[0056] In some embodiments, the preparation of the coating slurry includes: stirring and dispersing the second active material, the binder, the second conductive agent, and the solvent. The stirring speed is 10-40 rpm, the dispersion speed is 500-4500 rpm, and the time is 2-5 hours. Specifically, the binder and the solvent are first pre-dispersed to prepare a premixed glue, the stirring speed is 10-30 rpm, the dispersion speed is 2500-4500 rpm, and the time is 1-3 hours; then the premixed glue, the second conductive agent, and the second active material are stirred at high speed to disperse into a uniform slurry, the stirring speed is 20-40 rpm, the dispersion speed is 500-3000 rpm, and the time is 1-2 hours.

[0057] In some embodiments, the process further comprises drying the spray coating at a temperature of 25 to 125° C. (e.g., 25° C., 50° C., 80° C., 100° C., or 125° C.), preferably 80 to 120° C. The drying time is 0.5 to 2 minutes (e.g., 0.5 minutes, 1 minute, 1.5 minutes, or 2 minutes), preferably 0.8 to 1.5 minutes.

[0058] In some embodiments, the equipment used for drying includes but is not limited to a hot air oven, an infrared drying oven, a laser drying oven, a microwave drying oven, etc., preferably a hot air oven or an infrared drying oven.

[0059] According to another aspect of the present invention, the present invention also relates to a battery, comprising the positive electrode sheet or the positive electrode sheet prepared by the positive electrode sheet preparation method.

[0060] The battery of the present invention adopts the above-mentioned positive electrode sheet, has high energy density, good fast charging performance and good cycle stability.

[0061] According to another aspect of the present invention, the present invention also relates to an electric device comprising the battery. The electric device of the present invention includes electric vehicles, electric tools, etc.

[0062] The following is further explained with reference to specific embodiments and comparative examples.

[0063] Example 1 A method for preparing a positive electrode sheet comprises the following steps: (a) The first active material and the first conductive agent were dispersed in a stirring apparatus at a high speed of 20 rpm and a dispersion speed of 2000 rpm for 1 hour to form a dry blend. The first active material was lithium nickel cobalt manganese oxide (NCM), and the first conductive agent was conductive carbon black, with a mass ratio of 97.5%:2.5%. This dry blend was heated to 200°C and sprayed onto both sides of a current collector layer (aluminum foil) using a helium atmosphere. The resulting plasma-sprayed coating had a thickness of 25 μm.

[0064] (b) Ten seconds after the plasma spraying, a coating slurry was applied to the surface of the plasma sprayed layer through an extrusion die at a speed of 5 m / min to form a coating layer. The coating slurry preparation method: The binder (polyvinylidene fluoride) and solvent were pre-dispersed, and then the second active material (lithium nickel cobalt manganese oxide) and the second conductive agent (conductive carbon black) were added. The mass ratio of the second active material, the second conductive agent, and the binder was 97%:2.5%:0.5%. The stirring speed was 30 rpm and the dispersion speed was 2000 rpm. High-speed dispersion was carried out for 5 hours to form a stable suspension to obtain the coating slurry. The coating slurry was then dried in a hot air oven at a constant speed at 100°C for 1 minute to form a coating layer (150 μm), thus obtaining the positive electrode sheet.

[0065] Example 2 A method for preparing a positive electrode sheet comprises the following steps: (a) The first active material and the first conductive agent were dispersed in a stirring apparatus at a high speed of 20 rpm and a dispersion speed of 2000 rpm for 1 hour to form a dry mix. The first active material was lithium nickel cobalt manganese oxide, and the first conductive agent was conductive carbon black, with a mass ratio of 98.8%:1.2%. The dry mix was heated to 200°C and sprayed onto both surfaces of the current collector layer using a helium atmosphere using plasma spraying to produce a plasma sprayed coating with a thickness of 25 μm.

[0066] (b) Ten seconds after the plasma spraying, a coating slurry was applied to the surface of the plasma sprayed layer through an extrusion die at a speed of 5 m / min to form a coating layer. The coating slurry preparation method: The binder (polyvinylidene fluoride) and solvent were pre-dispersed, and then the second active material (lithium nickel cobalt manganese oxide) and the second conductive agent (conductive carbon black) were added. The mass ratio of the second active material, the second conductive agent, and the binder was 97.3%:1.2%:1.5%. The stirring speed was 30 rpm and the dispersion speed was 2000 rpm. High-speed dispersion was carried out for 5 hours to form a stable suspension to obtain the coating slurry. The coating slurry was then dried in a hot air oven at a constant speed at 100°C for 1 minute to form a coating layer (150 μm), thus obtaining the positive electrode sheet.

[0067] Example 3 A method for preparing a positive electrode sheet comprises the following steps: (a) The first active material and the first conductive agent were dispersed in a stirring apparatus at a high speed of 20 rpm and a dispersion speed of 2000 rpm for 1 hour to form a dry mix. The first active material was lithium nickel cobalt manganese oxide, and the first conductive agent was conductive carbon black, with a mass ratio of 97.5%:2.5%. The dry mix was heated to 200°C and sprayed onto both surfaces of the current collector layer using a helium atmosphere using plasma spraying to produce a plasma sprayed coating with a thickness of 45 μm.

[0068] (b) Ten seconds after the plasma spraying, the coating slurry was applied to the surface of the plasma sprayed layer through an extrusion die at a speed of 5 m / min to form a coating layer. The coating slurry preparation method involves pre-dispersing the binder (polyvinylidene fluoride) and solvent. The second active material (lithium nickel cobalt manganese oxide) and the second conductive agent (conductive carbon black) are then added in a mass ratio of 97%:2.5%:0.5% for the second active material, the second conductive agent, and the binder. The stirring speed is 30 rpm, the dispersion speed is 2000 rpm, and the high-speed dispersion is continued for 5 hours to form a stable suspension, thus obtaining the coating slurry. The slurry is then dried in a hot air oven at a constant speed at 100°C for 1 minute to form a coating layer (150 μm), thus obtaining the positive electrode sheet.

[0069] Comparative Example 1 A method for preparing a positive electrode sheet comprises the following steps: The binder (polyvinylidene fluoride) and solvent were pre-dispersed, and then the second active material (lithium nickel cobalt manganese oxide) and the second conductive agent (conductive carbon black) were added. The mass ratio of the second active material, the second conductive agent, and the binder was 97.3%:1.2%:1.5%. The stirring speed was 30 rpm, the dispersion speed was 2000 rpm, and high-speed dispersion was carried out for 5 hours to form a stable suspension to obtain a coating slurry. The coating slurry was applied to both surfaces of the current collector layer through an extrusion die at a speed of 5 m / min to form a coating layer. The thickness of the coating layer in this comparative example was the total thickness of the plasma sprayed layer and the coating layer in Example 1. The positive electrode sheet was then dried in a hot air oven at a constant speed at 100°C for 1 minute.

[0070] Comparative Example 2 A method for preparing a positive electrode sheet comprises the following steps: (1) The binder (polyvinylidene fluoride) and the solvent were pre-dispersed, and then the second active material (lithium nickel cobalt manganese oxide) and the second conductive agent (conductive carbon black) were added. The mass ratio of the second active material, the second conductive agent, and the binder was 96.8%:1.5%:1.7%. The stirring speed was 30 rpm, the dispersion speed was 2000 rpm, and the high-speed dispersion was performed for 5 hours to form a stable suspension to obtain the first coating slurry (primer coating).

[0071] (2) The binder (polyvinylidene fluoride) and the solvent were pre-dispersed, and then the second active material (lithium nickel cobalt manganese oxide) and the second conductive agent (conductive carbon black) were added. The mass ratio of the second active material, the second conductive agent, and the binder was 97.7%:1.2%:1.1%. The stirring speed was 30 rpm, the dispersion speed was 2000 rpm, and the high-speed dispersion was carried out for 5 hours to form a stable suspension to obtain the second coating slurry (upper coating).

[0072] (3) The first coating slurry and the second coating slurry were uniformly coated on the current collector layer at a speed of 5 m / min through a double-layer die head at a mass ratio of 7:3 for the upper and lower coating surface densities to form a double coating layer; then dried in a hot air oven at a temperature of 100 ° C for 1 min to obtain a positive electrode sheet.

[0073] Experimental example 1. Positive electrode performance test The positive electrode sheets obtained in each embodiment and comparative example were subjected to peel strength tests respectively, using the test method of B / T 2792 for adhesive tape peel strength.

[0074] The test results are shown in Table 1.

[0075] Table 1 Test results of positive electrode

[0076] 2. Battery performance test The positive electrode sheets of each embodiment and comparative example were used to make button cells and perform rate charging tests. The charging time from 20% to 80% SOC was calculated. The specific test data are shown in Table 2.

[0077] Table 2 Battery performance test

[0078] As can be seen from the above, the positive electrode sheets obtained by the methods of each embodiment of the present invention have high interfacial bonding strength between the composite layer and the current collector layer, that is, high peel strength, and good structural stability of the positive electrode sheets. The batteries prepared in each embodiment have excellent fast charging performance.

[0079] The peeling strength between the coating layer and the current collector layer of the positive electrode sheet obtained in Comparative Examples 1 and 2 is low, the interface bonding strength is low, and the fast charging performance of the obtained battery is relatively poor.

[0080] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A positive electrode sheet, characterized in that: The invention comprises a current collector layer, a plasma sprayed layer and a coating layer; the plasma sprayed layer is located on at least one side surface of the current collector layer, and the coating layer is located on the surface of the plasma sprayed layer away from the current collector layer; The plasma sprayed layer includes a first active material and a first conductive agent; The coating layer includes a second active material, a binder, and a second conductive agent, and the mass content W of the binder in the coating layer satisfies: <W≤1%。 2. The positive electrode sheet according to claim 1, characterized in that Contains at least one of the following features (1) to (2): (1) The mass content A1 of the first conductive agent in the plasma sprayed layer and the mass content B1 of the second conductive agent in the coating layer satisfy the relationship: 1≤A1 / B1≤5.5; (2) The first conductive agent and the second conductive agent each independently include at least one of conductive graphite, conductive carbon black, carbon nanotubes, carbon fibers, and metal conductive particles.

3. The positive electrode sheet according to claim 1, characterized in that Contains at least one of the following features (1) to (2): (1) The thickness of the plasma sprayed layer is 1 to 100 μm; (2) The thickness of the coating layer is 100-200 μm.

4. The positive electrode sheet according to claim 1, characterized in that Contains at least one of the following features (1) to (5): (1) The mass content A2 of the first active material in the plasma sprayed layer is equal to the mass content B2 of the second active material in the coating layer, and the following conditions are satisfied: A2 ≥ B2; (2) The first active material and the second active material each independently include at least one of lithium nickel cobalt manganese oxide, lithium nickel manganese oxide, lithium iron manganese oxide, lithium cobalt oxide, lithium iron phosphate, and lithium manganese oxide; (3) The binder content in the plasma sprayed layer is 0; (4) The mass content W of the binder in the coating layer satisfies: 0.5%≤W≤1%; (5) The binder includes at least one of polyvinyl chloride, polyethylene, polyimide, polyether nitrile, polypropylene, polystyrene, polymethyl acrylate, polyamide, polyvinylidene fluoride, polytetrafluoroethylene, polyethylene terephthalate and polytetrafluoroethylene.

5. The positive electrode sheet according to claim 1, characterized in that: Contains at least one of the following features (1) to (2): (1) The peel strength of the positive electrode sheet is greater than or equal to 470 N / m; (2) The charging or discharging time of the battery corresponding to the positive electrode sheet is less than 28 minutes when the state of charge is between 20% and 80%.

6. The method for preparing a positive electrode sheet according to any one of claims 1 to 5, wherein: The following steps are involved: Spraying a dry mixture of the first active material and the first conductive agent onto at least one surface of the current collector layer by plasma spraying to obtain a plasma sprayed layer; A coating slurry formed by a second active material, a binder, a second conductive agent and a solvent is applied to the surface of the plasma sprayed layer to form a coating layer, thereby obtaining a positive electrode sheet.

7. The method for preparing a positive electrode sheet according to claim 6, wherein: Contains at least one of the following features (1) to (4): (1) The plasma spraying specifically includes: heating the dry mixture to a semi-molten state or a molten state by a plasma arc, and then spraying the heated dry mixture onto the surface of the current collector using high-pressure gas; (2) The interval between the plasma spraying and the coating is T≤60s, preferably 5-15s; (3) During the plasma spraying process, the plasma arc is heated to a temperature of ≤400°C, preferably 50-200°C; (4) The preparation of the dry mix specifically includes: stirring and dispersing the first active material and the first conductive agent at a stirring speed of 10 to 30 rpm and a dispersing speed of 500 to 2500 rpm for 0.5 to 2 hours.

8. The method for preparing a positive electrode sheet according to claim 6, wherein: Contains at least one of the following features (1) to (2): (1) The coating slurry is prepared by stirring and dispersing the second active material, the binder, the second conductive agent, and the solvent at a stirring speed of 10 to 40 rpm and a dispersion speed of 500 to 4500 rpm for 2 to 5 hours; (2) The method further includes drying the spray coating, wherein the drying temperature is 25 to 125° C., and the drying time is 0.5 to 2 minutes.

9. A battery, characterized in that: A positive electrode sheet comprising the positive electrode sheet according to any one of claims 1 to 5 or a positive electrode sheet prepared by the preparation method of the positive electrode sheet according to any one of claims 6 to 8.

10. An electrical device, characterized in that: A battery comprising the battery of claim 9.

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