Positive electrode sheet, electrochemical device, and electronic device

Abstract

The present application provides a positive electrode sheet, an electrochemical device, and an electronic device. The positive electrode sheet comprises a positive electrode current collector, a positive electrode active material layer, and a coating layer. The coating layer is located on the surface of and / or inside the positive electrode active material layer, the coating layer comprises an organic compound, the organic compound comprises at least one functional group of a cyano group, an isocyano group, an azine group, and an isocyanate group, and the thickness of the coating layer is 0.3 μm to 3 μm. The positive electrode sheet provided in the present application can improve the thermal safety, high-temperature cycle performance, high-temperature storage expansion rate, and mechanical safety of the electrochemical device.

Description

Positive electrode plate, electrochemical device and electronic device

[0001] This application claims priority to Chinese Patent Application No. 202411785140.4, filed on December 6, 2024, entitled "Positive Electrode, Electrochemical Device and Electronic Device", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of electrochemical energy storage, and in particular to a positive electrode, an electrochemical device using the positive electrode, and an electronic device using the electrochemical device. Background Technology

[0003] Electrochemical devices (such as lithium-ion batteries) are widely used in consumer electronics (such as mobile phones, laptops, cameras, etc.), energy storage products (such as home energy storage, energy storage power stations, UPS power supplies, etc.) and new energy vehicles as portable chemical energy sources due to their advantages such as high energy density, high operating voltage platform, low self-discharge, long service life and environmental friendliness.

[0004] As the operating voltage and temperature of electrochemical devices increase, the structure of the positive electrode active material (such as lithium cobalt oxide, nickel cobalt manganese ternary materials, and lithium iron phosphate) in the positive electrode plate becomes unstable and easily reacts with the electrolyte, affecting the high-temperature cycle performance and safety performance of the electrochemical device. Summary of the Invention

[0005] This application provides a positive electrode, an electrochemical device, and an electronic device.

[0006] The first aspect of this application provides a positive electrode sheet, which includes a positive current collector, a positive active material layer, and a coating. The coating is located on the surface and / or inside the positive active material layer. The coating includes an organic compound, which includes at least one functional group selected from cyano, isonitrile, aziryl, and isocyanate groups. The thickness of the coating is 0.3 μm to 3 μm.

[0007] In the positive electrode sheet provided in this application, a coating containing an organic compound is disposed on the surface and / or inside the positive electrode active material layer. This organic compound can undergo a complexation reaction with the metal on the surface of the positive electrode active material layer, reducing phase transitions and oxygen release reactions that occur at high temperatures. This improves the stability of the positive electrode sheet, thereby enhancing the thermal safety and high-temperature cycling performance of the electrochemical device and reducing the high-temperature storage expansion rate. Simultaneously, the organic compound contains high-energy carbon-nitrogen triple or double bonds, making it less susceptible to oxidation. The organic compound itself possesses strong antioxidant properties and high stability, improving the mechanical safety of the positive electrode sheet used in electrochemical devices. Furthermore, considering the coating thickness range in this application, the inventors have discovered that a coating thickness within the aforementioned range can improve the thermal safety and high-temperature cycling performance of the electrochemical device, while also helping the electrochemical device maintain good energy density and high-temperature storage expansion performance.

[0008] Based on the first aspect, in some possible implementations, the coating thickness is from 0.5 μm to 2.5 μm. This is beneficial for further improving the high-temperature cycling performance and thermal safety performance of the electrochemical device.

[0009] Based on the first aspect, in some embodiments, the coating is located between the positive electrode current collector and the positive electrode active material layer. The coating can further improve the thermal and mechanical safety of the electrochemical device.

[0010] Based on the first aspect, in some embodiments, the coating is located on the surface of the positive electrode active material layer facing away from the positive electrode current collector. This is beneficial for improving the electrolyte wettability of the positive electrode sheet, further enhancing the thermal safety and high-temperature cycling performance of the electrochemical device, and reducing the high-temperature storage expansion rate of the electrochemical device.

[0011] Based on the first aspect, in some embodiments, the coating is located inside the positive electrode active material layer, and the positive electrode active material layer is divided into multiple layers by the coating along the thickness direction of the positive electrode sheet. This can improve the thermal safety and high-temperature cycling performance of the electrochemical device, while also further enhancing the mechanical safety of the electrochemical device.

[0012] Based on the first aspect, in some embodiments, the positive electrode includes two coatings, one coating located inside the positive electrode active material layer and the other coating located on a surface of the positive electrode active material layer. This can improve the thermal safety and high-temperature cycling performance of the electrochemical device, while also further enhancing the mechanical safety of the electrochemical device.

[0013] Based on the first aspect, in some embodiments, the positive electrode includes three coatings, one of which is located inside the positive electrode active material layer, and the other two coatings are located on two surfaces of the positive electrode active material layer, respectively. The arrangement of multiple coatings can further improve the thermal stability of the positive electrode, and further improve the thermal safety and high-temperature cycling performance of the electrochemical device.

[0014] Based on the first aspect, in some embodiments, the coating mass per unit area is 1 mg / 5000 mm². 2 Up to 25mg / 5000mm 2 This ensures that the coating can fully cover the positive electrode active layer or the positive electrode current collector, and keeps the impedance of the electrochemical device within a suitable range. It also helps to improve the mechanical safety, thermal safety and high-temperature cycling performance of the electrochemical device.

[0015] Based on the first aspect, in some embodiments, the particle size Dv50 of the organic compound is between 100 nm and 1000 nm. This is beneficial for the uniformity of coating application and for further improving the mechanical safety, thermal safety, and high-temperature cycling performance of the electrochemical device.

[0016] Based on the first aspect, in some embodiments, the particle size Dv50 of the positive electrode active material is from 5 μm to 30 μm. A particle size within this range can improve the uniformity of the prepared positive electrode slurry, which is beneficial for improving the rate performance of the electrochemical device.

[0017] Based on the first aspect, in some embodiments, the ratio of the particle size Dv50 of the organic compound to the particle size Dv50 of the positive electrode active material is 1:(10-500). This is beneficial for increasing the contact area between the organic compound and the positive electrode active material, and for further improving the stability of the positive electrode active material, thereby further improving the thermal safety and high-temperature cycling performance of the electrochemical device.

[0018] Based on the first aspect, in some embodiments, the particle size Dv50 of the organic compound is Dnm, the coating thickness is dμm, and the D / d ratio is 1:(1~20). This ensures that the organic compound particles are uniformly distributed in the coating, allowing the organic compound to fully act on the positive electrode active material, further improving the thermal safety and high-temperature cycling performance of the electrochemical device.

[0019] Based on the first aspect, in some embodiments, the thickness of the positive electrode active material layer is 20 μm to 80 μm. This is beneficial for further improving the thermal safety and high-temperature cycling performance of the electrochemical device.

[0020] Based on the first aspect, in some embodiments, the atomic percentage of nitrogen in the coating is 1% to 60%. This suitable nitrogen content allows the coating to contain a suitable amount of organic compounds, thereby further improving the thermal safety, high-temperature cycling performance, and high-temperature storage expansion rate of the electrochemical device.

[0021] Based on the first aspect, in some embodiments, the ratio of the coating thickness to the thickness of the positive electrode active material layer is 1:(5-50). This allows the electrochemical device to exert the thermal stability effect of the coating on the positive electrode active material layer while maintaining good volumetric energy density and suitable impedance, thereby further improving the thermal safety of the electrochemical device.

[0022] Based on the first aspect, in some embodiments, the organic compound includes at least one of polyacrylonitrile, dicyandiamide, cyanuric acid, nitrile rubber, 1,3,5-triazine-2,4,6-triamine compounds, isocyanurate, and thiocyanate.

[0023] Based on the first aspect, in some embodiments, the coating further includes a binder, which includes at least one selected from polyamide, polyacrylonitrile, polyvinyl alcohol, acrylate polymer, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, and styrene-butadiene rubber. The aforementioned binder can effectively bond and adhere organic compound particles to the positive electrode active material layer, reducing coating peeling, improving the stability of the positive electrode sheet, and also enhancing the thermal safety and high-temperature cycling performance of the electrochemical device.

[0024] Based on the first aspect, in some embodiments, the positive electrode active material includes at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate, lithium nickel cobalt aluminum oxide, lithium-rich manganese-based material, lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate.

[0025] Based on the first aspect, in some embodiments, the coating is located on at least one surface of the positive electrode current collector, for example, the coating is located between the positive electrode current collector and the positive electrode active material layer, and after the positive electrode sheet is stored at 85°C for 5 hours, the peel force between the coating and the positive electrode current collector is 1 N / m to 60 N / m. High adhesion between the coating and the positive electrode current collector is beneficial for improving the mechanical safety of the electrochemical device.

[0026] A second aspect of this application provides an electrochemical device comprising a negative electrode, a separator, an electrolyte, and a positive electrode, wherein the separator is located between the positive and negative electrode. The chemical device comprising the aforementioned positive electrode exhibits excellent thermal safety, mechanical safety, high-temperature cycling performance, and high-temperature storage expansion rate.

[0027] A third aspect of this application provides an electronic device, including an electrochemical device, wherein the electrons comprising the electrochemical device have excellent thermal safety and high-temperature versatility. Attached Figure Description

[0028] The above and / or additional aspects and advantages of this application will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0029] Figure 1 is a cross-sectional scanning electron microscope image of the positive electrode sheet prepared in Example 1-1 of this application.

[0030] Figure 2 is an enlarged schematic diagram of part A in Figure 1.

[0031] Figure 3 is an enlarged schematic diagram of part B in Figure 2.

[0032] Figure 4 is a scanning electron microscope image of the coating surface prepared in Example 1-1 of this application.

[0033] Figure 5 is a scanning electron microscope image at the magnification of Figure 4. Detailed Implementation

[0034] The technical solutions in the embodiments of this application are described clearly and in detail below. Obviously, the described embodiments are only some, not all, of the embodiments of this application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the specification of this application is for the purpose of describing particular embodiments only and is not intended to limit this application.

[0035] As used herein, the term "about" is used to describe and indicate small variations. When used in conjunction with an event or situation, the term may refer to examples in which the event or situation occurred precisely and examples in which the event or situation occurred very approximately. For example, when used in conjunction with numerical values, the term may refer to a range of variation less than or equal to ±10% of the numerical value, such as less than or equal to ±5%, less than or equal to ±4%, less than or equal to ±3%, less than or equal to ±2%, less than or equal to ±1%, less than or equal to ±0.5%, less than or equal to ±0.1%, or less than or equal to ±0.05%. Additionally, quantities, ratios, and other numerical values ​​are sometimes presented in range format herein. It should be understood that such range format is for convenience and brevity and should be interpreted flexibly to include not only numerical values ​​explicitly specified as range limits but also all individual numerical values ​​or subranges covered within the range, as if each numerical value and subrange were explicitly specified.

[0036] In the detailed description and claims, a list of items connected by the terms "at least one of," "at least one of," or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" or "at least one of A or B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" or "at least one of A, B, or C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0037] As used herein, quantities, ratios, and other numerical values ​​are sometimes presented in range format. It should be understood that such range format is for convenience and brevity and should be interpreted flexibly to include not only numerical values ​​explicitly specified as range limits, but also all individual numerical values ​​or subranges covered within the range, as if each numerical value and subrange were explicitly specified.

[0038] One embodiment of this application provides an electrochemical device, which includes a housing, an electrode assembly, and an electrolyte. Both the electrode assembly and the electrolyte are located within the housing.

[0039] The outer casing can be a packaging bag sealed with an encapsulating film (such as aluminum-plastic film), for example, the electrochemical device can be a flexible packaged electrochemical device. In other embodiments, the electrochemical device can also be a steel-cased electrochemical device, an aluminum-cased electrochemical device, etc.

[0040] The electrode assembly includes a positive electrode, a negative electrode, and a separator, with the separator disposed between the positive and negative electrode. The electrode assembly can be a stacked structure, formed by layering the positive electrode, separator, and negative electrode. In other embodiments, the electrode assembly can also be a wound structure, formed by winding the stacked positive electrode, separator, and negative electrode.

[0041] This application provides a positive electrode sheet, which includes a positive current collector, a positive active material layer, and a coating. The coating is located on the surface and / or inside the positive active material layer. The coating includes an organic compound, which includes at least one functional group selected from cyano, isonitrile, aziryl, and isocyanate groups. The thickness of the coating is 0.3 μm to 3 μm.

[0042] In the positive electrode sheet provided in this application, a coating containing an organic compound is disposed on the surface and / or interior of the positive electrode active material layer. This organic compound can undergo a complexation reaction with the metal on or inside the surface of the positive electrode active material layer, reducing phase transitions and oxygen release reactions occurring at high temperatures. This improves the stability of the positive electrode sheet, thereby enhancing the thermal safety and high-temperature cycling performance of the electrochemical device and reducing the high-temperature storage expansion rate. Simultaneously, the organic compound contains high-energy carbon-nitrogen triple or double bonds, making it less susceptible to oxidation. The organic compound itself possesses strong antioxidant properties and high stability, improving the mechanical safety of the positive electrode sheet used in electrochemical devices. Furthermore, considering the coating thickness range in this application, the inventors have discovered that a coating thickness within the aforementioned range can improve the thermal safety and high-temperature cycling performance of the electrochemical device, while also helping the electrochemical device maintain good energy density and high-temperature storage expansion performance.

[0043] In some embodiments, the thickness of the coating can be 0.3μm, 0.5μm, 0.8μm, 1μm, 1.2μm, 1.5μm, 1.7μm, 2μm, 2.2μm, 2.5μm, 2.7μm, 2.9μm, 3μm, or any value within the range of any two of the above values.

[0044] If the coating thickness is small, such as less than 0.3 μm, the coating provides little room for improvement in the structure of the positive electrode and little improvement in the thermal safety and high-temperature cycle performance of the positive electrode. If the coating thickness is large, such as greater than 3 μm, it will reduce the energy density of the electrochemical device, increase the impedance of the electrochemical device, reduce the high-temperature storage expansion performance of the electrochemical device, increase lithium plating, and reduce the cycle performance of the electrochemical device.

[0045] In some embodiments, the coating thickness is from 0.5 μm to 2.5 μm. This is beneficial for further improving the high-temperature cycling performance and thermal safety performance of the electrochemical device.

[0046] In some embodiments, the coating is located between the positive electrode current collector and the positive electrode active material layer. The coating, in contact with the positive electrode, can improve the stability of the positive electrode, reduce the high-temperature storage expansion rate of the electrochemical device, reduce the high-temperature cycle capacity decay rate, and increase the thermal safety test pass temperature. Furthermore, the coating also helps to increase the pass rate of the pin penetration test of the electrochemical device, thereby further improving the thermal and mechanical safety of the electrochemical device. In a specific preparation process, the coating can be first applied to the positive electrode current collector, and then the positive electrode active material layer can be coated onto the coated positive electrode current collector, so that the coating is located between the positive electrode current collector and the positive electrode active material layer.

[0047] In other embodiments, the coating is located on the surface of the positive electrode active material layer facing away from the positive electrode current collector. As shown in Figure 1, the positive electrode current collector is coated with positive electrode active material layers on both sides, with one surface of the positive electrode active material layer coated with a coating (white in color compared to other areas) forming a protective layer on the surface of the positive electrode active material layer. In Figure 1, the thickness of the positive electrode current collector is 7.995 μm, and the thickness of the coating is 2.023 μm, with the thickness of the positive electrode active material layer in contact with the coating being 32.61 μm and the thickness of the other positive electrode active material layer being 36.93 μm. As shown in Figures 2 and 3, the coating is uniformly distributed on the surface of the positive electrode active material layer, and the organic compound particles in the coating are uniformly dispersed. This coating can reduce the phase transition and oxygen release reaction occurring in the positive electrode at high temperatures, thereby improving the stability of the positive electrode, which is beneficial for improving the thermal safety and high-temperature cycling performance of the electrochemical device, and reducing the high-temperature storage expansion rate of the electrochemical device. Meanwhile, the thinner coating applied to the positive electrode active material layer can further reduce the impedance of the electrochemical device and improve its high-temperature cycling performance. Furthermore, the coating on the positive electrode active material layer also improves the electrolyte wettability of the positive electrode, further enhancing the high-temperature cycling performance of the electrochemical device and reducing high-temperature storage expansion.

[0048] In other embodiments, the positive electrode includes two coatings: one coating is located between the positive current collector and the positive active material layer, and the other coating is located on the surface of the positive active material layer facing away from the positive current collector. Having coatings on both surfaces of the positive active material layer can improve the thermal safety and high-temperature cycling performance of the electrochemical device, while also further enhancing its mechanical safety.

[0049] In some embodiments, the coating is located inside the positive electrode sheet, and the positive electrode active material layer is divided into multiple layers by the coating along the thickness direction of the positive electrode sheet. In the above-mentioned positive electrode sheet, the coating being located inside the positive electrode sheet can improve the thermal stability of the positive electrode sheet, reduce the collapse of the positive electrode active material under high voltage of 4.5V, and further improve the thermal safety and high-temperature cycling performance of the electrochemical device. When the thickness of the positive electrode active material layer is greater than 70μm, a coating layer is provided every 45μm along the thickness direction of the positive electrode sheet. This further improves the thermal stability of the positive electrode sheet while maintaining good impedance in the electrochemical device, thereby improving the mechanical safety, thermal safety, and high-temperature cycling performance of the electrochemical device.

[0050] If the coating is located inside the positive electrode, a conductive agent will be added to the coating to improve the conductivity of the coating and thus improve the overall conductivity of the positive electrode.

[0051] In some embodiments, the positive electrode includes two coatings, one coating located inside the positive electrode active material layer and the other coating located on either surface of the positive electrode active material layer. The other coating can be located on the surface of the positive electrode active material layer facing the positive electrode current collector or on the surface away from the positive electrode current collector. This can improve the thermal safety and high-temperature cycling performance of the electrochemical device while also further enhancing its mechanical safety.

[0052] In some embodiments, the positive electrode includes three coatings, one of which is located inside the positive electrode active material layer, and the other two coatings are located on two surfaces of the positive electrode active material layer, respectively. The other two coatings are located on the surface of the positive electrode active material layer facing the positive electrode current collector and the surface facing away from the positive electrode current collector, respectively. This arrangement can improve the thermal safety and high-temperature cycling performance of the electrochemical device, while also further enhancing the mechanical safety of the electrochemical device.

[0053] In some embodiments, the coating mass per unit area is 1 mg / 5000 mm². 2 Up to 25mg / 5000mm 2 The coating mass per unit area is within the above-mentioned range to ensure that the coating can fully cover the positive electrode active layer or the positive electrode current collector, and to maintain the impedance of the electrochemical device within a suitable range. This also helps to improve the mechanical safety, thermal safety, and high-temperature cycling performance of the electrochemical device. In some embodiments, the coating mass per unit area is 1 mg / 5000 mm². 2 2mg / 5000mm 2 3mg / 5000mm 2 5mg / 5000mm 2 7mg / 5000mm 2 8mg / 5000mm 2 9mg / 5000mm 2 10mg / 5000mm 2 12mg / 5000mm 2 13mg / 5000mm 2 15mg / 5000mm 2 20mg / 5000mm 2 25mg / 5000mm 2 Or any value within the range of any two of the above values. Preferably, the coating mass per unit area is 3 mg / 5000 mm². 2 Up to 15mg / 5000mm 2 .

[0054] In some embodiments, the coating mass per unit area is 3 mg / 5000 mm². 2Up to 8mg / 5000mm 2 Further improve the mechanical safety, thermal safety, and high-temperature cycling performance of electrochemical devices.

[0055] In some embodiments, the particle size Dv50 of the organic compound is between 100 nm and 1000 nm. A particle size within this range facilitates the application of thinner coatings, improves the uniformity of the coating containing the organic compound, enhances the coating's density, maintains suitable density, improves electrolyte wetting, and promotes the migration of active ions, thereby further improving the mechanical safety, thermal safety, and high-temperature cycling performance of the electrochemical device. In some embodiments, the particle size Dv50 of the organic compound can be 100 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1000 nm, or any value within the range of any two of the above values. Wherein, D... V 50, also known as "median particle size", represents the particle size that reaches 50% of the total volume of organic compound particles in the volume-based particle size distribution. In other words, the volume of organic compound particles smaller than this size accounts for 50% of the total volume of the negative electrode material particles.

[0056] The particle size Dv50 of the positive electrode active material is from 5 μm to 30 μm. A particle size within this range is beneficial for achieving suitable porosity in the positive electrode active material layer, reducing expansion rate, improving the cycle stability of the electrochemical device, and also improving the uniformity of the prepared positive electrode slurry, thus enhancing the rate performance of the electrochemical device. In some embodiments, the particle size Dv50 of the positive electrode active material can be 5 μm, 7 μm, 8 μm, 9 μm, 10 μm, 12 μm, 14 μm, 15 μm, 18 μm, 20 μm, 22 μm, 24 μm, 25 μm, 27 μm, 29 μm, 30 μm, or any value within the range of any two of the above values.

[0057] In some embodiments, the ratio of the particle size Dv50 of the organic compound to the particle size Dv50 of the positive electrode active material is 1:(10-500). A ratio within this range is beneficial for increasing the contact area between the organic compound and the positive electrode active material, further improving the stability of the positive electrode active material, and thus further enhancing the thermal safety and high-temperature cycling performance of the electrochemical device. In some embodiments, the ratio of the particle size Dv50 of the organic compound to the particle size Dv50 of the positive electrode active material can be 1:10, 1:20, 1:30, 1:50, 1:80, 1:100, 1:150, 1:200, 1:250, 1:300, 1:400, 1:450, 1:480, 1:500, or any value within the range of any two of the above values.

[0058] In some embodiments, the particle size Dv50 of the organic compound is Dnm, the coating thickness is dμm, and the D / d ratio is 1:(1-20). Within this range, the organic compound particles are uniformly distributed in the coating, allowing the organic compound to fully act on the positive electrode active material, further improving the thermal safety and high-temperature cycling performance of the electrochemical device. In some embodiments, the D / d ratio can be 1:1, 1:2, 1:3, 1:5, 1:7, 1:9, 1:10, 1:11, 1:12, 1:14, 1:16, 1:18, 1:20, or any value within the range of any two of the above values. Preferably, the D / d ratio is 1:(3-10).

[0059] In some embodiments, the thickness of the positive electrode active material layer is from 20 μm to 80 μm. This suitable thickness range of the positive electrode active material layer facilitates the electrochemical device to possess both good energy density and high-temperature storage expansion performance, while exhibiting low impedance. In some embodiments, the thickness of the positive electrode active material layer can be 20 μm, 30 μm, 40 μm, 50 μm, 60 μm, 70 μm, 80 μm, or any value within the range of any two of the above values.

[0060] In some embodiments, the atomic percentage of nitrogen in the coating is between 1% and 60%. This suitable nitrogen content ensures that the coating contains a suitable amount of organic compounds, thereby further improving the thermal safety, high-temperature cycling performance, and high-temperature storage expansion rate of the electrochemical device. In some embodiments, the atomic percentage of nitrogen in the coating can be 1%, 2%, 3%, 5%, 7%, 10%, 12%, 15%, 17%, 20%, 22%, 25%, 27%, 30%, 32%, 35%, 37%, 40%, 45%, 50%, 55%, 60%, or any value within the range of any two of the above values.

[0061] In some embodiments, the ratio of the coating thickness to the thickness of the positive electrode active material layer is 1:(5-50). This ratio ensures that the electrochemical device, with good volumetric energy density and suitable impedance, leverages the coating's role in stabilizing the positive electrode active material layer, further improving the device's thermal safety. If the coating thickness is too small, there may be missed areas or uneven coating, which is detrimental to the coating's role in stabilizing the positive electrode active material layer. In some embodiments, the ratio of the coating thickness to the positive electrode active material layer thickness can be 1:5, 1:7, 1:8, 1:10, 1:11, 1:12, 1:14, 1:18, 1:20, 1:25, 1:30, 1:35, 1:40, 1:42, 1:45, 1:48, 1:50, or any value within the range of any two of the above values.

[0062] In some embodiments, the organic compound includes at least one selected from polyacrylonitrile, dicyandiamide, cyanuric acid, nitrile rubber, 1,3,5-triazine-2,4,6-triamine compounds, isocyanurate, and thiocyanate. The 1,3,5-triazine-2,4,6-triamine compounds may include at least one selected from 1,3,5-triazine-2,4,6-triamine, polyacrylonitrile, melamine, cyanuric acid, melamine polyphosphate, and melamine cyanurate. All of the above organic compounds can undergo complexation reactions with the metals on the surface of the positive electrode active material layer, reducing phase transitions and oxygen release reactions at high temperatures, thereby improving the thermal safety and high-temperature cycling performance of the electrochemical device.

[0063] In some embodiments, the coating further includes a binder, which includes at least one selected from polyamide, polyacrylonitrile, polyvinyl alcohol, acrylate polymers, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, and styrene-butadiene rubber. The above-mentioned binders can effectively bond organic compound particles to the positive electrode active material layer, reduce coating peeling, improve the stability of the positive electrode sheet, and also enhance the thermal safety and high-temperature cycling performance of the electrochemical device.

[0064] In some embodiments, the positive electrode active material includes at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate, lithium nickel cobalt aluminum oxide, lithium-rich manganese-based materials, lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate.

[0065] In some embodiments, the coating is located between the positive electrode current collector and the positive electrode active material layer. After the positive electrode sheet is stored at 85°C for 5 hours, the peel force between the coating and the positive electrode current collector is 1 N / m to 60 N / m. At this peel force, the adhesion between the coating and the positive electrode current collector is high, which is beneficial for improving the mechanical safety of the electrochemical device. In some embodiments, under the above conditions, the peel force between the coating and the positive electrode current collector can be 1 N / m, 5 N / m, 7 N / m, 10 N / m, 12 N / m, 15 N / m, 20 N / m, 22 N / m, 27 N / m, 30 N / m, 35 N / m, 38 N / m, 40 N / m, 45 N / m, 50 N / m, 53 N / m, 55 N / m, 60 N / m, or any value within the range of any two of the above values.

[0066] According to some embodiments of this application, the positive current collector can be a metal foil or a composite current collector. For example, aluminum foil or nickel foil can be used. The composite current collector can be formed by forming a metallic material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate.

[0067] The positive electrode material layer also includes an adhesive and a conductive agent. The adhesive is used to bond the positive electrode active material particles, thereby facilitating the formation of the film layer, and also improves the bonding force between the positive electrode active layer and the positive electrode current collector. In some embodiments, the adhesive may include, but is not limited to, an adhesive polymer, such as at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyolefins, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, modified polyvinylidene fluoride, modified SBR rubber, or polyurethane. In some embodiments, the polyolefin adhesive includes at least one of polyethylene, polypropylene, polyolefin ester, polyolefin alcohol, or polyacrylic acid.

[0068] In some embodiments, the conductive agent includes carbon-based materials, metal-based materials, conductive polymers, or mixtures thereof. Examples of carbon-based materials include natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, or carbon fibers; examples of metal-based materials include metal powders or fibers of copper, nickel, aluminum, silver, etc.; and examples of conductive polymers include polyphenylene derivatives.

[0069] Negative electrode sheet

[0070] The negative electrode sheet includes a negative current collector and a negative active material layer disposed on the negative current collector.

[0071] Negative current collectors include copper foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrates coated with conductive metal, or any combination thereof.

[0072] Negative electrode active materials include materials that reversibly insert / deintercalate lithium ions. In some embodiments, the materials that reversibly insert / deintercalate lithium ions include carbon materials. In some embodiments, the carbon material can be any carbon-based negative electrode active material commonly used in lithium-ion rechargeable batteries. In some embodiments, the carbon material includes, but is not limited to: crystalline carbon, amorphous carbon, or mixtures thereof. Crystalline carbon can be amorphous, flake-shaped, flake-shaped, spherical, or fibrous natural or artificial graphite. Amorphous carbon can be soft carbon, hard carbon, mesophase pitch carbides, calcined coke, etc.

[0073] In some embodiments, the negative electrode active material layer includes a negative electrode active material. The specific type of negative electrode active material is not limited and can be selected according to requirements. In some embodiments, the negative electrode active material includes, but is not limited to: lithium metal, structured lithium metal, natural graphite, artificial graphite, mesophase microcarbon spheres (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composites, Li-Sn alloys, Li-Sn-O alloys, Sn, SnO, SnO2, and spinel-structured lithiated TiO2-Li4Ti5O. 12 Li-Al alloys or any combination thereof. The silicon-carbon composite refers to a silicon-carbon anode active material containing at least about 5 wt% silicon by weight.

[0074] In some embodiments, the negative electrode active material comprises at least one of artificial graphite, natural graphite, hard carbon, soft carbon, silicon alloy, or silicon oxide.

[0075] When the negative electrode includes silicon-carbon compounds, based on the total weight of the negative electrode active material, the silicon:carbon ratio is approximately 1:10-10:1, and the median particle size Dv of the silicon-carbon compounds is... 50 The micrometer size ranges from approximately 0.1 micrometers to 20 micrometers. When the negative electrode comprises an alloy material, the negative electrode active material layer can be formed using methods such as vapor deposition, sputtering, or plating. When the negative electrode comprises lithium metal, the negative electrode active material layer is formed, for example, using a conductive framework with a spherical twisted structure and metal particles dispersed within the conductive framework. In some embodiments, the spherical twisted conductive framework may have a porosity of approximately 5% to approximately 85%. In some embodiments, a protective layer may also be provided on the lithium metal negative electrode active material layer.

[0076] In some embodiments, the negative electrode active material layer may include an adhesive and optionally a conductive material. The adhesive enhances the bonding between the negative electrode active material particles and the bonding between the negative electrode active material and the current collector. In some embodiments, the adhesive includes, but is not limited to: polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0077] In some embodiments, the conductive material includes, but is not limited to, carbon-based materials, metal-based materials, conductive polymers, or mixtures thereof. In some embodiments, the carbon-based material is selected from natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material is selected from metal powder, metal fiber, copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0078] In some embodiments, the current collector includes, but is not limited to: copper foil, nickel foil, stainless steel foil, titanium foil, nickel foam, copper foam, polymer substrate coated with a conductive metal, and any combination thereof.

[0079] The negative electrode can be prepared by methods known in the art. For example, the negative electrode can be obtained by mixing an active material, a conductive material, and a binder in a solvent to prepare an active material composition, and then coating the active material composition onto a current collector. In some embodiments, the solvent may include, but is not limited to, water.

[0080] Separating membrane

[0081] The material and shape of the separator used in the electrochemical device of this application are not particularly limited, and can be any technology disclosed in the prior art. In some embodiments, the separator comprises a polymer or inorganic material formed from a material stable to the electrolyte of this application.

[0082] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a nonwoven fabric, membrane, or composite membrane with a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene nonwoven fabric, a polyethylene nonwoven fabric, or a polypropylene-polyethylene-polypropylene porous composite membrane may be selected.

[0083] A surface treatment layer is disposed on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixture of polymer and inorganic materials. The inorganic layer includes inorganic particles and a binder. The inorganic particles are selected from at least one of alumina, silicon oxide, magnesium oxide, titanium oxide, hafnium dioxide, tin oxide, cerium dioxide, nickel oxide, zinc oxide, calcium oxide, zirconium oxide, yttrium oxide, silicon carbide, boehmite, aluminum hydroxide, magnesium hydroxide, calcium hydroxide, and barium sulfate.

[0084] The binder is selected from at least one of polyvinylidene fluoride, a copolymer of polyvinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer contains a polymer, the polymer material of which is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyvinyl alkoxy, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0085] electrolyte

[0086] According to some embodiments of this application, the electrolyte includes an organic solvent, a lithium salt, and optional additives.

[0087] The organic solvent in the electrolyte of this application may be any organic solvent known in the prior art that can be used as an electrolyte solvent. There are no limitations on the electrolyte used in the electrolyte according to this application; it may be any electrolyte known in the prior art. The additives in the electrolyte according to this application may be any additives known in the prior art that can be used as electrolyte additives. In some embodiments, the organic solvent includes, but is not limited to: ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl methyl carbonate (EMC), dimethyl carbonate (DMC), or ethyl propionate (EP).

[0088] In some embodiments, the organic solvent includes ether solvents, such as at least one selected from 1,3-dioxapentane (DOL) and dimethyl glycol ether (DME). In some embodiments, the lithium salt includes at least one selected from organic lithium salts or inorganic lithium salts. In some embodiments, the lithium salt includes, but is not limited to: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(fluoromethanesulfonyl)imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalatoborate)borate LiB(C2O4)2 (LiBOB), or lithium difluorooxalatoborate LiBF2(C2O4) (LiDFOB). In some embodiments, the additive includes at least one selected from fluoroethylene carbonate and adiponitrile.

[0089] According to some embodiments of this application, the electrochemical device of this application includes, but is not limited to, a lithium-ion battery. In some embodiments, the electrochemical device includes a lithium-ion battery.

[0090] The electronic devices described in this application are not particularly limited. In some embodiments, the electronic devices described in this application include, but are not limited to, laptops, pen-based computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors, etc.

[0091] The present application will be described below through specific embodiments and comparative examples. Those skilled in the art should understand that the preparation methods described in this application are merely examples, and any other suitable preparation methods are within the scope of this application.

[0092] Example 1-1

[0093] Preparation method of polyacrylonitrile (PAN) particles:

[0094] Acrylonitrile and itaconic acid were copolymerized in an aqueous phase under a nitrogen atmosphere. 3 kg of deionized water was added to a 5 L reactor, followed by distilled acrylonitrile (AN), itaconic acid (IA), ammonium persulfate (APS) as an initiator, and isopropanol (IPA) or n-dodecyl mercaptan as a molecular weight regulator, in a 99:1 ratio. The stirring rate was controlled, and the polymerization reaction was accelerated by heating in a water bath at 60 °C. The resulting PAN was insoluble in water. After a reaction time of 12–18 h, a polymer slurry was obtained. The polymer slurry was filtered multiple times and washed with deionized water, then vacuum dried at 50–60 °C for 6–8 h to obtain white PAN polymer powder. The white PAN powder was then ground to obtain polyacrylonitrile particles with a Dv50 of 0.5 μm.

[0095] Preparation of the positive electrode sheet: An 8μm aluminum foil was selected as the current collector. Lithium cobalt oxide (LCO), conductive carbon black (Super P), and polyvinylidene fluoride (PVDF) were added to N-methylpyrrolidone (NMP) in a weight ratio of 96:2.5:1.5 and stirred until homogeneous to form a positive electrode active slurry. The particle size (Dv50) of the lithium cobalt oxide was 16μm. The positive electrode active slurry was uniformly coated onto one side of the aluminum foil and dried. The above steps were repeated on the other side of the aluminum foil to obtain a positive electrode sheet with a double-sided coating of positive electrode active material layers, the thickness of which was 40μm.

[0096] The PAN particles and the binder polyvinylidene fluoride (PVDF) were added to N-methylpyrrolidone (NMP) at a weight ratio of 95:5 and stirred until homogeneous to form a coating slurry. The coating slurry was then uniformly coated onto the surface of the positive electrode active material layer, dried, and cut to obtain the composite positive electrode sheet. Referring to Figures 4 and 5, the surface particles of the composite positive electrode sheet are uniformly distributed.

[0097] Preparation of negative electrode sheet:

[0098] Artificial graphite (anode active material), sodium carboxymethyl cellulose (CMC) (thickener), and styrene-butadiene rubber (SBR) (binder) are added to deionized water in a weight ratio of 96:2:2 and stirred evenly to form a cathode slurry. The cathode slurry is then uniformly coated onto one side of a copper foil current collector and dried. The above steps are repeated on the other side of the copper foil to obtain a cathode sheet with a cathode active layer coated on both sides. After cold pressing and cutting, the cut cathode sheet is obtained.

[0099] The fabrication of lithium-ion batteries:

[0100] The prepared positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrode to obtain a stacked electrode assembly. After welding the tabs, the electrode assembly is placed in an aluminum-plastic film packaging bag, heat-sealed around the perimeter, leaving an injection port, and the electrolyte is injected. After vacuum sealing, settling, formation, and degassing, a lithium-ion battery is obtained.

[0101] Examples 1-2

[0102] Isocyanate compounds: A certain amount of 1,3,5-triazine-2,4,6-triamine compound is placed in a 3L three-necked round-bottom flask equipped with a mechanical stirrer, thermometer, and cooler. Then, appropriate amounts of water and sodium hydroxide solution are added to bring the pH of the solution to 9-11. The stirrer is started, and the mixture is heated until completely dissolved to a temperature of 70-90°C. A crystal growth inducer for melamine cyanurate is added and mixed thoroughly. Then, cyanuric acid is gradually and slowly added in three batches until the solution becomes weakly acidic, with a measured pH of 5-7. The desired reaction temperature is maintained at 80-110°C, and stirring is continued for 3-6 hours to obtain a viscous white granular substance. The mass ratio of 1,3,5-triazine-2,4,6-triamine compound to cyanuric acid is 50 parts:50 parts. The white particles were then vacuum filtered, washed, and dried. Finally, the product was subjected to ultrafine pulverization to obtain melamine cyanurate particles, wherein the particle size Dv50 of the melamine cyanurate particles was 0.5 μm.

[0103] Preparation of positive electrode sheet: The steps and conditions for preparing a positive electrode sheet coated with a positive active material layer on both sides are the same as in Example 1-1.

[0104] The above-mentioned melamine cyanurate particles and polyvinylidene fluoride (PVDF) binder were added to N-methylpyrrolidone (NMP) at a weight ratio of 95:5, and stirred evenly to form a coating slurry. The coating slurry was then uniformly coated onto the surface of the positive electrode active material layer, dried, and cut to obtain the composite positive electrode sheet. The remaining preparation steps were the same as in Examples 1-1.

[0105] Examples 1-3 to Examples 1-5

[0106] The type of organic compound or the type of binder may be changed, but the other steps and conditions are the same as in Examples 1-1.

[0107] Examples 1-6

[0108] The difference between Examples 1-6 and Example 1-1 is that the coating is applied to the surface of the separator. Melamine cyanurate particles and polyacrylate binder are added to deionized water at a weight ratio of 95:5, and stirred until homogeneous to form a separator coating slurry. This slurry is then uniformly coated onto the surface of the separator, dried, and a polyacrylate adhesive layer is applied to obtain the composite spacer layer. The preparation parameters and conditions in Table 1 are followed. Other steps are the same as in Example 1-1.

[0109] Examples 1-7 to Examples 1-14

[0110] The thickness of the coating was changed, but the remaining steps and conditions were the same as in Examples 1-2.

[0111] Examples 1-15

[0112] Polyacrylonitrile particles, polyacrylic acid (PAA) binder, and conductive carbon black conductive agent were added to deionized water in a weight ratio of 90:5:5 and stirred until homogeneous to form a positive electrode coating slurry. This slurry was then uniformly coated onto the surface of the positive electrode current collector, dried, and vacuum-dehydrated to obtain a composite positive electrode current collector. The positive electrode active slurry was then coated onto the composite positive electrode current collector, dried, cold-pressed three times, and cut into sheets to obtain the composite positive electrode sheet. The remaining preparation steps and conditions were the same as in Examples 1-1.

[0113] Examples 1-16

[0114] Melamine cyanurate particles, polyacrylic acid (PAA) binder, and conductive carbon black conductive agent were added to deionized water in a weight ratio of 90:5:5 and stirred until homogeneous to form a positive electrode coating slurry. This slurry was then uniformly coated onto the surface of the positive electrode current collector, dried, and vacuum-dehydrated to obtain a composite positive electrode current collector. The positive electrode active slurry was then coated onto the composite positive electrode current collector, dried, cold-pressed three times, and cut into sheets to obtain the composite positive electrode sheet. The remaining preparation steps and conditions were the same as in Examples 1-1.

[0115] Examples 1-17 to Examples 1-19

[0116] The type of organic compound was changed, but the other steps and conditions were the same as in Examples 1-15.

[0117] Examples 1-20 to Examples 1-23

[0118] The coating thickness was varied, but other steps and conditions were the same as in Examples 1-15.

[0119] Examples 1-24

[0120] The coatings prepared in Examples 1-1 and 1-17 were respectively applied to the two surfaces of the positive electrode active material layer. The specific steps were as follows: First, a positive electrode spacer slurry was applied to an aluminum foil. Cyanuric acid particles, polyacrylic acid adhesive (PAA), and conductive carbon black were added to deionized water in a weight ratio of 90:5:5 and stirred until homogeneous to form the positive electrode spacer slurry. The positive electrode spacer slurry was then uniformly coated onto the surface of the positive electrode current collector and dried. Next, the positive electrode active material was coated, followed by the coating prepared in Example 1-1, thus obtaining a positive electrode sheet with coatings on both sides. Other steps and conditions were the same as in Example 1-1.

[0121] Examples 1-25

[0122] The coatings prepared in Examples 1-2 and 1-17 were respectively applied to the two surfaces of the positive electrode active material layer. The specific steps were as follows: First, a positive electrode spacer slurry was applied to an aluminum foil. Cyanuric acid particles, polyacrylic acid adhesive (PAA), and conductive carbon black were added to deionized water in a weight ratio of 90:5:5 and stirred until homogeneous to form the positive electrode spacer slurry. The positive electrode spacer slurry was then uniformly coated onto the surface of the positive electrode current collector and dried. Next, the positive electrode active material was coated, followed by the coating prepared in Examples 1-2, thus obtaining a positive electrode sheet with coatings on both sides. Other steps and conditions were the same as in Example 1-1.

[0123] Examples 1-26 to 1-27

[0124] The type of adhesive was changed, but the other steps and conditions were the same as in Examples 1-4.

[0125] Examples 1-28

[0126] The type of adhesive was changed, but the other steps and conditions were the same as in Examples 1-18.

[0127] Comparative Example 1

[0128] The positive electrode sheet has no coating, and the other steps and conditions are the same as in Example 1-1.

[0129] Comparative Example 2

[0130] A ceramic layer is coated on the surface of the active material layer. The ceramic layer is prepared by adding alumina powder particles and binder PVDF to a solution of N-methylpyrrolidone (NMP) in a weight ratio of 95:5, stirring evenly to form a ceramic coating slurry, coating the slurry evenly on the surface of the positive electrode active material layer, drying, and cutting to obtain a composite positive electrode sheet.

[0131] Comparative Examples 3 to 5

[0132] Adjust the coating thickness, and follow the same steps and conditions as in Examples 1-6.

[0133] Comparative Example 6

[0134] A ceramic coating is applied to the surface of the positive electrode current collector. The ceramic coating is prepared by adding alumina powder particles and binder PAA in a weight ratio of 95:5 to a deionized water solution and stirring until uniform to form a ceramic coating slurry. The ceramic coating slurry is then uniformly coated onto the surface of the positive electrode current collector and dried to obtain a composite positive electrode current collector. The positive electrode active material is then coated onto the composite positive electrode current collector, dried, and cut to obtain a composite positive electrode sheet.

[0135] Comparative Examples 7 and 8

[0136] Adjust the coating thickness, and follow the same steps and conditions as in Examples 1-20.

[0137] Comparative Example 9

[0138] A ceramic layer, as shown in Comparative Example 2, and a ceramic coating, as shown in Comparative Example 6, were respectively coated on the two surfaces of the positive electrode active material layer. Other steps and conditions were the same as in Comparative Example 2.

[0139] Examples 2-1 to 2-7

[0140] The particle size Dv50 of the organic compound was adjusted, and other steps and conditions were the same as in Examples 1-2.

[0141] Examples 2-8 to Examples 2-13

[0142] Adjust the particle size Dv50 of the positive electrode active material, and the other steps and conditions are the same as in Examples 1-2.

[0143] Examples 2-14 to 2-19

[0144] Adjust the atomic ratio of nitrogen in the coating and the composition of the coating, while keeping other steps and conditions the same as in Examples 1-2.

[0145] Examples 2-20 to 2-24

[0146] Adjust the thickness of the positive electrode active material in the coating, and the other steps and conditions are the same as in Examples 1-2.

[0147] Example 3-1

[0148] Multiple coating processes were used to obtain a composite positive electrode with an intermediate coating layer. Positive electrode active slurry was coated onto the surface of the positive electrode current collector, dried to a thickness of 40 μm, and then dried again to obtain a single-coated positive electrode sheet. Melamine cyanurate particles and vinylidene fluoride (PVDF) binder were added to an NMP solution at a weight ratio of 95:5 and stirred until homogeneous to form a coating slurry. This coating slurry was uniformly coated onto the single-coated positive electrode sheet and dried to obtain a double-coated positive electrode sheet. The positive electrode active slurry was then coated onto the double-coated positive electrode sheet to obtain a composite positive electrode sheet with three coatings.

[0149] The other steps and conditions are the same as in Example 1-1.

[0150] Examples 3-2 to 3-4

[0151] The thickness of the coating located inside the positive electrode active material layer was changed, while other steps and conditions were the same as in Example 3-1.

[0152] Examples 3-6

[0153] Melamine cyanurate particles and polyacrylic acid adhesive (PAA) were added to deionized water at a weight ratio of 95:5 and stirred evenly to form a positive electrode coating slurry. The positive electrode coating slurry was then evenly coated onto the surface of the positive electrode current collector, dried, and dehydrated under vacuum to obtain a composite positive electrode current collector.

[0154] The positive electrode active slurry is coated onto the positive electrode coating of the composite positive electrode current collector and dried to form a first positive electrode active material layer with a thickness of 40 μm on the surface of the composite positive electrode current collector. The aforementioned melamine cyanurate particles, polyvinylidene fluoride (PVDF) binder, and carbon black conductive agent are added to N-methylpyrrolidone (NMP) in a weight ratio of 90:7:3 and stirred evenly to form a coating slurry. This coating slurry is uniformly coated onto the surface of the first positive electrode active material layer and dried to obtain the first composite positive electrode sheet. The positive electrode active slurry is then coated onto the coating of the first composite positive electrode sheet and dried to a thickness of 40 μm to obtain the second composite positive electrode sheet.

[0155] Melamine cyanurate particles and polyvinylidene fluoride (PVDF) binder are added to N-methylpyrrolidone (NMP) in a weight ratio of 95:5 and stirred evenly to form a coating slurry. The coating slurry is then uniformly coated onto the surface of the positive active material layer of the second composite positive electrode sheet, dried, and cut to obtain a three-layer coated positive electrode sheet.

[0156] The other steps and conditions are the same as in Example 1-1.

[0157] Examples 3-5, 3-7, and 3-8

[0158] Adjust the type of organic compound in the coating, or change the thickness of the coating located within the positive electrode active material layer, while keeping other steps and conditions the same as in Examples 3-6.

[0159] Performance testing of the positive electrode:

[0160] (1) Nitrogen content test in coating

[0161] The coating was separated from the lithium-ion battery, washed three times with NMP, centrifuged to remove electrolyte, adhesive, and residual lithium salt, and then dried. Elemental analysis was used to determine the quantitative nitrogen content in the coating.

[0162] (2) Particle size Dv50 of organic compounds and particle size Dv50 of positive electrode active materials

[0163] The coating and positive electrode active material were separated from the lithium-ion battery, washed three times with NMP, centrifuged to remove electrolyte, adhesive, and residual lithium salt, and then dried. The volumetric particle size distribution was measured using a laser particle size analyzer.

[0164] (3) Coating thickness and positive electrode active material layer thickness testing

[0165] The composite positive electrode in the lithium-ion battery was disassembled into a structure of separator + composite positive electrode + separator. The interface was plasma-cut, and the cross-sectional morphology of the composite positive electrode was obtained by scanning electron microscopy (SEM). The thickness of the coating and positive active material layer was measured.

[0166] (4) Peel force test between coating and positive current collector

[0167] After storing the lithium-ion battery at 85°C for 5 hours, the coated positive electrode current collector is separated from the lithium-ion battery. High-adhesion adhesive tape is then applied to the coating surface, and a tensile testing machine is used to test the adhesion between the coating and the current collector, i.e., the peel force.

[0168] Performance testing of lithium-ion batteries:

[0169] (1) High-temperature cycling performance

[0170] The lithium-ion battery was placed in a 45°C constant temperature test chamber and left to stand for 30 minutes to allow it to reach a constant temperature. It was then charged at a constant current of 0.5C to 4.45V, followed by constant voltage charging to a current of 0.05C. After standing for 1 minute, it was discharged at a constant current of 0.5C to 3.0V, and this was recorded as the initial discharge capacity C0. This process was repeated 100 times, and the discharge capacity C1 after 100 cycles was recorded. The cycle capacity retention rate of the lithium-ion battery was then calculated.

[0171] High-temperature cycling capacity retention rate = C1 / C0 × 100%.

[0172] (2) High-temperature storage expansion rate test

[0173] At 25℃, the lithium-ion battery was left to stand for 5 minutes, then charged at a constant current rate of 0.5C to 4.45V, and then charged at a constant voltage rate of 0.05C to 4.45V. After standing for 5 minutes, the thickness D1 of the lithium-ion battery was measured. The fully charged lithium-ion battery was stored at 80℃ for 24 hours, and the thickness D2 of the lithium-ion battery was measured. The high-temperature storage expansion rate of the lithium-ion battery was calculated using the following formula:

[0174] High-temperature storage expansion rate = (D2-D1) / D1*100%.

[0175] (3) Thermal safety test

[0176] At 25°C, let the lithium-ion battery stand for 5 minutes, then charge it at a constant current rate of 0.5C to 4.45V, and then charge it at a constant voltage of 4.5V to 0.05C, and let it stand for 5 minutes. Then place the lithium-ion battery in a constant temperature chamber and continuously heat it at a rate of 10°C / min to the set temperature (e.g., 130°C), and maintain this temperature for 60 minutes. If the lithium-ion battery does not explode or catch fire, it has passed the temperature test.

[0177] Take another lithium-ion battery of the same type, increase the temperature of the constant temperature chamber by 1℃ (to 131℃), and maintain this temperature for 60 minutes. If the battery cell does not explode or catch fire, it has passed the temperature test. Continue this process until the battery cell can no longer pass the thermal safety test at this temperature, and obtain the thermal safety passing temperature that the battery cell can pass.

[0178] (4) Mechanical safety testing

[0179] At 25℃, let the lithium-ion battery stand for 5 minutes, then charge it at a constant current rate of 0.5C to 4.45V, and then charge it at a constant voltage of 4.45V to 0.05C, and let it stand for 5 minutes. Drive a 3mm diameter steel nail into the center of the lithium-ion battery at a speed of 30mm / s, hold it for 10 minutes, and then pull it out. If the lithium-ion battery does not explode or catch fire, it is considered to have passed the test.

[0180] (5) Impedance of lithium-ion batteries

[0181] At 25°C, the lithium-ion battery was left to stand for 5 minutes, then charged at a constant current rate of 0.5C to 4.45V, and then charged at a constant voltage of 4.45V to 0.05C. After standing for 5 minutes, the DC impedance of the lithium-ion battery (cell) under full charge was measured.

[0182] In this application, the "I" surface and the "II" surface are used to distinguish the different positions of the coating in the electrochemical device. When the coating is located between the positive electrode current collector and the positive electrode active material layer, it is named the I surface. When the coating is located between the positive electrode plate and the separator, it is named the II surface. When two coatings exist at the same time, and the two coatings exist between the positive electrode current collector and the positive electrode active material layer and between the positive electrode plate and the separator, respectively, it is named the I+II surface.

[0183] Table 1

[0184] Table 2

[0185] Table 3

[0186] As can be seen from Tables 1 and 2 above, compared with Comparative Examples 1 to 5, in Examples 1-1 to 1-6, when the coating is located between the positive electrode and the separator, and different types of organic compounds are used, the corresponding lithium-ion batteries have excellent high-temperature cycle performance and high-temperature storage expansion rate, as well as good thermal safety pass temperature and mechanical safety performance.

[0187] Referring to Table 3, in Examples 1-2, 1-6 to 1-14, when the coating thickness is between 0.3 μm and 3 μm, the corresponding lithium-ion batteries can simultaneously achieve excellent high-temperature cycling performance, high-temperature storage expansion rate, and thermal safety pass temperature.

[0188] Table 4

[0189] Table 5

[0190] As can be seen from Tables 4 and 5 above, compared with Comparative Examples 1 and 6 to 8, in Examples 1-15 to 1-19, when the coating is located between the positive electrode current collector and the active material layer, and different types of organic compounds are used, the corresponding lithium-ion batteries have excellent high-temperature cycle performance and high-temperature storage expansion rate, as well as good thermal safety pass temperature and mechanical safety performance.

[0191] From Tables 4 and 5, in Examples 1-17 and Examples 1-20 to 1-23, when the coating thickness is between 0.3 μm and 3 μm, the corresponding lithium-ion batteries can simultaneously achieve excellent high-temperature cycle performance, high-temperature storage expansion rate, good thermal safety pass temperature, and mechanical safety performance under low cell impedance.

[0192] Table 6

[0193] As can be seen from Table 6 above, compared with Comparative Example 9, in Examples 1-24 to 1-25, there are two coatings, located between the positive electrode current collector and the active material layer and between the positive electrode sheet and the separator, respectively. The corresponding lithium-ion batteries have excellent high-temperature cycle performance and high-temperature storage expansion rate, as well as good thermal safety passage temperature and mechanical safety performance.

[0194] Table 7

[0195] Table 8

[0196] As can be seen from Tables 7 and 8 above, by adjusting the type of binder in the coating, the corresponding lithium-ion battery still has excellent high-temperature cycle performance and high-temperature storage expansion rate, as well as good thermal safety passing temperature and mechanical safety performance.

[0197] Table 9

[0198] Table 10

[0199] From Tables 9 and 10 above, by adjusting the particle size Dv50 of the organic compounds, the corresponding lithium-ion batteries, while maintaining excellent high-temperature cycle performance and high-temperature storage expansion rate, also exhibit good thermal safety passing temperature and mechanical safety performance.

[0200] Table 11

[0201] As shown in Table 11 above, by adjusting the particle size Dv50 of the positive electrode active material, the corresponding lithium-ion battery still has excellent high-temperature cycle performance and high-temperature storage expansion rate, as well as good thermal safety passing temperature and mechanical safety performance.

[0202] Table 12

[0203] As shown in Table 12 above, by adjusting the atomic ratio of nitrogen in the coating, the corresponding lithium-ion battery still has excellent high-temperature cycle performance and high-temperature storage expansion rate, as well as good thermal safety passing temperature and mechanical safety performance.

[0204] Table 13

[0205] As shown in Table 13 above, by adjusting the thickness of the positive electrode active material layer, the corresponding lithium-ion battery still has excellent high-temperature cycle performance and high-temperature storage expansion rate, as well as good thermal safety passing temperature and mechanical safety performance.

[0206] Table 14

[0207] Table 15

[0208] From Tables 14 and 15 above, by adjusting the coating thickness, when the coating is located inside the positive electrode active material layer, the corresponding lithium-ion battery also has excellent high-temperature cycle performance, high-temperature storage expansion rate, and good thermal safety passage temperature.

[0209] Table 16

[0210] Table 17

[0211] From Tables 16 and 17 above, when the coating consists of three layers, with two layers located on the two surfaces of the positive electrode active material layer and the other layer located inside the positive electrode active material layer, the corresponding lithium-ion battery also exhibits excellent high-temperature cycle performance, high-temperature storage expansion rate, good thermal safety pass temperature, and mechanical safety performance.

[0212] The above-disclosed embodiments are merely preferred embodiments of this application and should not be construed as limiting the scope of this application. Therefore, any equivalent variations made in accordance with this application are still within the scope of this application.

Claims

1. A positive electrode plate, characterized in that, The device includes a positive current collector, a positive active material layer, and a coating. The coating is located on the surface and / or inside the positive active material layer. The coating includes an organic compound, which includes at least one functional group selected from cyano, isonitrile, aziryl, and isocyanate groups. The thickness of the coating is from 0.3 μm to 3 μm.

2. The positive electrode sheet as described in claim 1, characterized in that, The coating thickness is from 0.5 μm to 2.5 μm.

3. The positive electrode sheet as described in claim 1, characterized in that, The coating is located between the positive electrode current collector and the positive electrode active material layer.

4. The positive electrode sheet as described in claim 1, characterized in that, The coating is located on the surface of the positive electrode active material layer that is away from the positive electrode current collector.

5. The positive electrode sheet as described in claim 1, characterized in that, The positive electrode sheet includes two coatings, one coating located between the positive current collector and the positive active material layer, and the other coating located on the surface of the positive active material layer facing away from the positive current collector.

6. The positive electrode sheet as described in claim 1, characterized in that, The coating is located inside the positive electrode active material layer, and along the thickness direction of the positive electrode sheet, the positive electrode active material layer is divided into multiple layers by the coating.

7. The positive electrode sheet as described in claim 1, characterized in that, The positive electrode sheet includes two coatings, one of which is located inside the positive active material layer, and the other of which is located on a surface of the positive active material layer.

8. The positive electrode sheet as described in claim 1, characterized in that, The positive electrode sheet includes three coatings, one of which is located inside the positive active material layer, and the other two coatings are located on two surfaces of the positive active material layer, respectively.

9. The positive electrode sheet as described in any one of claims 1 to 8, characterized in that, The coating mass per unit area is 1 mg / 5000 mm². 2 Up to 25mg / 5000mm 2 .

10. The positive electrode sheet according to any one of claims 1 to 9, characterized in that, The positive electrode sheet satisfies at least one of the following conditions: (1) The particle size Dv50 of the organic compound is 100 nm to 1000 nm, and the particle size Dv50 of the positive electrode active material is 5 μm to 30 μm; (2) The ratio of the particle size Dv50 of the organic compound to the particle size Dv50 of the positive electrode active material is 1:(10~500); (3) The particle size Dv50 of the organic compound is Dnm, the thickness of the coating is dμm, and the ratio of D / d is 1:(1~20).

11. The positive electrode sheet according to any one of claims 1 to 10, characterized in that, The positive electrode sheet satisfies at least one of the following conditions: (1) The thickness of the positive electrode active material layer is 20 μm to 80 μm; (2) In the coating, the atomic percentage of nitrogen is 1% to 60%; (3) The ratio of the thickness of the coating to the thickness of the positive electrode active material layer is 1:(5~50).

12. The positive electrode sheet according to any one of claims 1 to 11, characterized in that, The organic compound includes at least one of polyacrylonitrile, dicyandiamide, cyanuric acid, nitrile rubber, 1,3,5-triazine-2,4,6-triamine compounds, isocyanurate, and thiocyanate.

13. The positive electrode sheet as described in claim 4, characterized in that, The coating comprises the organic compound, which includes melamine cyanurate.

14. The positive electrode sheet according to any one of claims 1 to 13, characterized in that, The coating further includes an adhesive, which includes at least one of polyamide, polyacrylonitrile, polyvinyl alcohol, acrylate polymer, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinylpyrrolidone, polyvinyl ether, polyvinylidene fluoride, and styrene-butadiene rubber.

15. The positive electrode sheet according to any one of claims 1 to 14, characterized in that, The positive electrode active material includes at least one of lithium cobalt oxide, lithium nickel cobalt manganese oxide, lithium iron phosphate, lithium nickel cobalt aluminum oxide, lithium-rich manganese-based materials, lithium manganese oxide, lithium manganese iron phosphate, or lithium titanate.

16. The positive electrode sheet according to any one of claims 1 to 15, characterized in that, The coating is located between the positive current collector and the positive active material layer. After the positive electrode sheet is stored at 85°C for 5 hours, the peel force between the coating and the positive current collector is 1 N / m to 60 N / m.

17. An electrochemical device comprising a negative electrode, a separating membrane, and an electrolyte, characterized in that, The electrochemical device further includes a positive electrode as described in any one of claims 1 to 16, wherein the separator is located between the positive electrode and the negative electrode.

18. An electronic device, characterized in that, Includes the electrochemical device as described in claim 17.

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