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 includes a positive electrode current collector, a positive electrode active material layer, and a coating. The coating is located on the surface and / or within the positive electrode active material layer. The coating includes an organic compound, the organic compound includes at least one functional group selected from cyano, isonitrile, oxazine, and isocyanate groups, and the thickness of the coating is 0.3 μm to 3 μm. The positive electrode sheet provided herein can improve the thermal safety, high-temperature cycling performance, high-temperature storage expansion rate, and mechanical safety of the electrochemical device.

Description

Technical Field

[0001] The present application relates to the field of electrochemical energy storage, and in particular to a positive electrode sheet, an electrochemical device using the positive electrode sheet, and an electronic device using the electrochemical device. Background Art

[0002] Electrochemical devices (such as lithium-ion batteries) are portable chemical energy sources. Due to their high energy density, high operating voltage platform, low self-discharge, long service life and environmental friendliness, they are widely used in consumer electronics (such as mobile phones, notebooks, cameras, etc.), energy storage products (such as home energy storage, energy storage power stations, UPS power supplies, etc.) and new energy vehicles and other fields and industries.

[0003] As the operating voltage and temperature of the electrochemical device increase, the positive electrode active materials in the positive electrode sheet (such as lithium cobalt oxide, nickel-cobalt-manganese ternary materials and lithium iron phosphate, etc.) become structurally unstable and easily react with the electrolyte, affecting the high-temperature cycle performance and safety performance of the electrochemical device. Summary of the Invention

[0004] The present application provides a positive electrode sheet, an electrochemical device, and an electronic device.

[0005] In a first aspect, the present application provides a positive electrode plate, which includes a positive electrode current collector, a positive electrode active material layer, and a coating. The coating is located on the surface and / or inside the positive electrode active material layer. The coating includes an organic compound, and the organic compound includes at least one functional group selected from cyano, isonitrile, oxazine, and isocyanate. The thickness of the coating is 0.3 μm to 3 μm.

[0006] In the positive electrode sheet provided in the present application, a coating containing an organic compound is provided on the surface and / or inside the positive electrode active material layer. The above-mentioned organic compound can undergo a complex reaction with the metal on the surface of the positive electrode active material layer, which can reduce the phase change and oxygen release reaction of the positive electrode sheet at high temperature, thereby improving the stability of the positive electrode sheet, thereby improving the thermal safety and high-temperature cycle performance of the electrochemical device, and reducing the high-temperature storage expansion rate of the electrochemical device. At the same time, the carbon-nitrogen triple bond or double bond contained in the above-mentioned organic compound has a high bond energy and is not easily oxidized. The organic compound itself has strong antioxidant properties and strong stability, which can improve the mechanical safety of the positive electrode sheet used in the electrochemical device. In combination with the thickness range of the coating in this case, the inventors found that when the thickness of the coating is within the above-mentioned range, on the one hand, it can improve the thermal safety and high-temperature cycle performance of the electrochemical device, and on the other hand, it is also conducive to maintaining good energy density and high-temperature storage expansion performance of the electrochemical device.

[0007] Based on the first aspect, in some possible implementations, the coating has a thickness of 0.5 μm to 2.5 μm, which is beneficial for further improving the high-temperature cycle performance and thermal safety performance of the electrochemical device.

[0008] 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.

[0009] 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 helps improve the electrolyte wettability of the positive electrode sheet, further improves the thermal safety and high-temperature cycling performance of the electrochemical device, and reduces the high-temperature storage expansion rate of the electrochemical device.

[0010] Based on the first aspect, in some embodiments, the coating is located within the positive electrode active material layer, and the coating divides the positive electrode active material layer into multiple layers 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.

[0011] Based on the first aspect, in some embodiments, the positive electrode sheet includes two coatings, one of which is located within the positive electrode active material layer and the other is 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.

[0012] Based on the first aspect, in some embodiments, the positive electrode plate includes three coating layers, one of which is located within the positive electrode active material layer, and the other two coating layers are located on opposite surfaces of the positive electrode active material layer. The provision of multiple coating layers can further improve the thermal stability of the positive electrode plate, further enhancing the thermal safety and high-temperature cycling performance of the electrochemical device.

[0013] Based on the first aspect, in some embodiments, the coating mass per unit area is 1 mg / 5000 mm 2 Up to 25mg / 5000mm 2 , so that the coating can fully cover the positive electrode active layer or the positive electrode current collector, and keep the impedance of the electrochemical device within an appropriate range, which is also beneficial to improving the mechanical safety, thermal safety and high-temperature cycle performance of the electrochemical device.

[0014] Based on the first aspect, in some embodiments, the particle size Dv50 of the organic compound is 100 nm to 1000 nm, which is beneficial to the uniformity of the coating and further improves the mechanical safety, thermal safety and high-temperature cycle performance of the electrochemical device.

[0015] Based on the first aspect, in some embodiments, the particle size Dv50 of the positive electrode active material is 5 μm to 30 μm. The particle size of the positive electrode active material within the above range can improve the uniformity of preparing the positive electrode slurry and help improve the rate performance of the electrochemical device.

[0016] 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 helps increase 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 improving the thermal safety and high-temperature cycling performance of the electrochemical device.

[0017] Based on the first aspect, in some embodiments, the particle size Dv50 of the organic compound is Dnm, the thickness of the coating is dμm, and the ratio D / d is 1:(1-20). This allows the organic compound particles to be evenly distributed in the coating, allowing the organic compound to fully interact with the positive electrode active material, further improving the thermal safety and high-temperature cycling performance of the electrochemical device.

[0018] Based on the first aspect, in some embodiments, the thickness of the positive electrode active material layer is 20 μm to 80 μm, which is beneficial for further improving the thermal safety and high-temperature cycle performance of the electrochemical device.

[0019] Based on the first aspect, in some embodiments, the coating comprises nitrogen in an atomic percentage of 1% to 60%. The above-mentioned suitable nitrogen content allows the coating to contain a suitable content of organic compounds, thereby further improving the thermal safety, high-temperature cycling performance, and high-temperature storage expansion rate of the electrochemical device.

[0020] Based on the first aspect, in some embodiments, the ratio of the thickness of the coating layer to the thickness of the positive electrode active material layer is 1:(5-50). This allows the coating layer to exert its thermal stability effect on the positive electrode active material layer while maintaining a good volumetric energy density and appropriate impedance, further improving the thermal safety of the electrochemical device.

[0021] 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.

[0022] Based on the first aspect, in some embodiments, the coating further comprises a binder, and the binder comprises 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. The binder can sufficiently bind the organic compound particles to the positive electrode active material layer, thereby reducing shedding of the coating, improving the stability of the positive electrode sheet, and enhancing the thermal safety and high-temperature cycling performance of the electrochemical device.

[0023] Based on the first aspect, in some embodiments, the positive electrode active material includes at least one of lithium cobaltate, lithium nickel cobalt manganese oxide, lithium iron phosphate, lithium nickel cobalt aluminum oxide, lithium-rich manganese-based materials, lithium manganese oxide, lithium iron manganese phosphate, or lithium titanate.

[0024] 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. 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. The high bonding strength between the coating and the positive electrode current collector helps improve the mechanical safety of the electrochemical device.

[0025] A second aspect of the present application provides an electrochemical device comprising a negative electrode sheet, a separator, an electrolyte, and the aforementioned positive electrode sheet, wherein the separator is positioned between the positive and negative electrode sheets. The electrochemical device comprising the aforementioned positive electrode sheet exhibits excellent thermal safety, mechanical safety, high-temperature cycling performance, and high-temperature storage expansion ratio.

[0026] A third aspect of the present application provides an electronic device, including an electrochemical device, wherein the electronic device including the electrochemical device has excellent thermal safety and high-temperature universality. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] The above and / or additional aspects and advantages of the present application will become apparent and easily understood from the description of the embodiments in conjunction with the following drawings, in which:

[0028] Figure 1 This is a cross-sectional scanning electron microscope image of the positive electrode sheet prepared in Example 1-1 of the present application.

[0029] Figure 2 for Figure 1 Enlarged schematic diagram of part A.

[0030] Figure 3 for Figure 2 Schematic diagram of the enlarged portion B.

[0031] Figure 4 This is a scanning electron microscope image of the coating surface prepared in Example 1-1 of the present application.

[0032] Figure 5 for Figure 4 Scanning electron microscope image at a magnification of . DETAILED DESCRIPTION

[0033] The technical solutions in the embodiments of the present application are described clearly and in detail below. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all of the embodiments. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art of the present application. The terms used in the specification of the present application are only for the purpose of describing specific embodiments and are not intended to limit the present application.

[0034] As used herein, the term "about" is used to describe and illustrate small changes. When used in conjunction with an event or situation, the term may refer to an example in which the event or situation occurs precisely and an example in which the event or situation occurs very approximately. For example, when used in conjunction with a numerical value, the term may refer to a variation range of 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%. In addition, amounts, ratios, and other numerical values ​​are sometimes presented in this article in a range format. It should be understood that such range formats are for convenience and simplicity, and should be flexibly understood to include not only numerical values ​​explicitly designated as range limits, but also all individual numerical values ​​or subranges encompassed within the range, as if each numerical value and subrange were explicitly designated.

[0035] In the detailed description and claims, a list of items linked 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, 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, 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 consist of a single element or multiple elements. Item B may consist of a single element or multiple elements. Item C may consist of a single element or multiple elements.

[0036] As used herein, amounts, ratios, and other numerical values ​​are sometimes presented herein in a range format. It should be understood that such range format is used for convenience and brevity and should be interpreted flexibly to include not only the values ​​explicitly specified as limits of the range, but also all individual values ​​or sub-ranges encompassed within the range, as if each value and sub-range were explicitly specified.

[0037] An embodiment of the present application provides an electrochemical device, which includes a housing, an electrode assembly, and an electrolyte. The electrode assembly and the electrolyte are both located in the housing.

[0038] The housing can be a packaging bag encapsulated with a packaging film (such as an aluminum-plastic film), for example, if the electrochemical device is a soft-pack electrochemical device. In other embodiments, the electrochemical device can also be a steel-shell electrochemical device, an aluminum-shell electrochemical device, or the like.

[0039] The electrode assembly includes a positive electrode sheet, a negative electrode sheet, and a separator, with the separator being disposed between the positive and negative electrode sheets. The electrode assembly can be a laminated structure, formed by stacking the positive electrode sheet, separator, and negative electrode sheet. In other embodiments, the electrode assembly can also be a wound structure, formed by stacking the positive electrode sheet, separator, and negative electrode sheet and then winding them.

[0040] The present application provides a positive electrode plate, which includes a positive electrode current collector, a positive electrode active material layer, and a coating. The coating is located on the surface and / or inside the positive electrode active material layer. The coating includes an organic compound, which includes at least one functional group selected from cyano, isonitrile, oxazine, and isocyanate. The thickness of the coating is 0.3 μm to 3 μm.

[0041] In the positive electrode sheet provided in the present application, a coating containing an organic compound is provided on the surface or / and inside the positive electrode active material layer. The above-mentioned organic compound can undergo a complexation reaction with the metal on the surface or inside the positive electrode active material layer, which can reduce the phase change and oxygen release reaction of the positive electrode sheet at high temperature, thereby improving the stability of the positive electrode sheet, thereby improving the thermal safety and high-temperature cycle performance of the electrochemical device, and reducing the high-temperature storage expansion rate of the electrochemical device. At the same time, the carbon-nitrogen triple bond or double bond contained in the above-mentioned organic compound has a high bond energy and is not easily oxidized. The organic compound itself has strong antioxidant properties and strong stability, which can improve the mechanical safety of the positive electrode sheet used in the electrochemical device. In combination with the thickness range of the coating in this case, the inventors found that when the thickness of the coating is within the above-mentioned range, on the one hand, it can improve the thermal safety and high-temperature cycle performance of the electrochemical device, and on the other hand, it is also conducive to maintaining good energy density and high-temperature storage expansion performance of the electrochemical device.

[0042] In some embodiments, the thickness of the coating can be 0.3 μm, 0.5 μm, 0.8 μm, 1 μm, 1.2 μm, 1.5 μm, 1.7 μm, 2 μm, 2.2 μm, 2.5 μm, 2.7 μm, 2.9 μm, 3 μm, or any value within a range formed by any two of the above values.

[0043] If the thickness of the coating is small, such as less than 0.3μm, the setting of the coating has little room for improvement in the structure of the positive electrode plate, and has little improvement on the thermal safety and high-temperature cycle performance of the positive electrode plate; if the thickness of the coating is large, such as greater than 3μm, it will reduce the energy density of the electrochemical device, and at the same time 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.

[0044] In some embodiments, the coating has a thickness of 0.5 μm to 2.5 μm, which is beneficial for further improving the high-temperature cycle performance and thermal safety performance of the electrochemical device.

[0045] In some embodiments, the coating is located between the positive electrode current collector and the positive electrode active material layer. The coating is in contact with the positive electrode plate, which can improve the stability of the positive electrode plate, reduce the high-temperature storage expansion rate of the electrochemical device, reduce the high-temperature cycle capacity decay rate, and increase the passing temperature of the thermal safety test. The above-mentioned coating is also conducive to increasing the passing rate of the nail penetration test of the electrochemical device, thereby further improving the thermal safety 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 is coated on the positive electrode current collector coated with the coating, so that the coating is located between the positive electrode current collector and the positive electrode active material layer.

[0046] 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. Figure 1 , both sides of the positive electrode current collector are coated with positive electrode active material layers, wherein the surface of one positive electrode active material layer is coated with a coating layer, and the coating layer (the color is white compared to other areas) forms a protective layer on the surface of the positive electrode active material layer; Figure 1 The thickness of the positive electrode current collector is 7.995 μm, the thickness of the coating is 2.023 μm, the thickness of the positive electrode active material layer in contact with the coating is 32.61 μm, and the thickness of the other positive electrode active material layer is 36.93 μm. Figure 2 and Figure 3, the coating is evenly distributed on the surface of the positive electrode active material layer, and the organic compound particles in the coating are evenly dispersed. The above coating can reduce the phase change and oxygen release reaction of the positive electrode plate at high temperature, thereby improving the stability of the positive electrode plate, which is beneficial to improving the thermal safety and high-temperature cycle performance of the electrochemical device, and reducing the high-temperature storage expansion rate of the electrochemical device. At the same time, the thickness of the coating applied on the positive electrode active material layer is relatively thin, which can further reduce the impedance of the electrochemical device and improve the high-temperature cycle performance of the electrochemical device. In addition, the coating setting applied to the positive electrode active material layer is also beneficial to improving the electrolyte wettability of the positive electrode plate, which is beneficial to further improve the high-temperature cycle performance of the electrochemical device and reduce the high-temperature storage expansion rate.

[0047] In other embodiments, 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. 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 the mechanical safety of the electrochemical device.

[0048] 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 is located inside the positive electrode sheet, which can improve the thermal stability of the positive electrode sheet, reduce the collapse of the positive electrode active material under the high voltage of 4.5V, and further improve the thermal safety and high temperature cycle performance of the electrochemical device. When the thickness of the positive electrode active material layer is greater than 70μm, a layer of coating is provided every 45μm in the thickness direction of the positive electrode sheet, so that while the electrochemical device has good impedance, the thermal stability of the positive electrode sheet can be further improved, thereby improving the mechanical safety, thermal safety and high temperature cycle performance of the electrochemical device.

[0049] If the coating is located inside the positive electrode sheet, 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 sheet.

[0050] In some embodiments, if the positive electrode sheet includes two coatings, one coating is located within the positive electrode active material layer, and the other coating is located on any 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 facing 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 the mechanical safety of the electrochemical device.

[0051] In some embodiments, the positive electrode sheet includes three coatings: one coating located within the positive active material layer, and two coatings located on either surface of the positive active material layer. The remaining two coatings are located on the surface of the positive active material layer facing the positive current collector and the surface facing away from the positive current collector, respectively. This arrangement improves the thermal safety and high-temperature cycling performance of the electrochemical device while also further enhancing the mechanical safety of the electrochemical device.

[0052] In some embodiments, the coating mass per unit area is 1 mg / 5000 mm 2 Up to 25mg / 5000mm 2 The coating mass per unit area is within the above range so that the coating can fully cover the positive electrode active layer or the positive electrode current collector and keep the impedance of the electrochemical device within a suitable range, which is also beneficial to improving the mechanical safety, thermal safety and high temperature cycle performance of the electrochemical device. In some embodiments, the coating mass per unit area is 1 mg / 5000 mm 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 formed by any two of the above values. Preferably, the coating mass per unit area is 3 mg / 5000 mm 2 Up to 15mg / 5000mm 2 .

[0053] In some embodiments, the coating mass per unit area is 3 mg / 5000 mm 2 Up to 8mg / 5000mm 2 . Further improve the mechanical safety, thermal safety and high-temperature cycle performance of electrochemical devices.

[0054] In some embodiments, the particle size Dv50 of the organic compound is 100 nm to 1000 nm. The particle size of the organic compound within the above range is conducive to the application of a thinner coating, and can also improve the uniformity of the coating containing the organic compound, improve the density of the coating, so that the coating maintains a suitable density, improves the electrolyte infiltration and promotes the migration of active ions, thereby further improving the mechanical safety, thermal safety and high temperature cycle 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 formed by any two of the above values. Wherein, D V 50 is also called the "median particle size", which means that in the volume-based particle size distribution of the organic compound particles, the particle size measured from the small particle size reaches 50% of the cumulative volume, that is, the volume of the organic compound particles smaller than this particle size accounts for 50% of the total volume of the negative electrode material particles.

[0055] The particle size Dv50 of the positive electrode active material is 5μm to 30μm. The particle size of the positive electrode active material is within the above range, which is conducive to making the positive electrode active material layer have a suitable porosity, reducing the expansion rate, improving the cycle stability of the electrochemical device, and also improving the uniformity of preparing the positive electrode slurry, which is conducive to improving the rate performance of the electrochemical device. In some embodiments, the particle size Dv50 of the positive electrode active material can be 5μm, 7μm, 8μm, 9μm, 10μm, 12μm, 14μm, 15μm, 18μm, 20μm, 22μm, 24μm, 25μm, 27μm, 29μm, 30μm or any value within the range formed by any two of the above values.

[0056] In some embodiments, the ratio of the organic compound particle size Dv50 to the positive electrode active material particle size Dv50 is 1:(10-500). A ratio within this range helps increase the contact area between the organic compound and the positive electrode active material, 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. In some embodiments, the ratio of the organic compound particle size Dv50 to the positive electrode active material particle size Dv50 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 formed by any two of the above values.

[0057] In some embodiments, the organic compound has a particle size Dv50 of Dnm, the coating has a thickness of dμm, and the D / d ratio is 1:(1-20). Within this range, the organic compound particles are evenly distributed in the coating, allowing the organic compound to fully interact with 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 a range consisting of any two of the foregoing values. Preferably, the D / d ratio is 1:(3-10).

[0058] In some embodiments, the thickness of the positive electrode active material layer is 20 μm to 80 μm. This preferred thickness range for the positive electrode active material layer facilitates the electrochemical device to have both good energy density and high-temperature storage expansion performance, while also having 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 a range formed by any two of the aforementioned values.

[0059] In some embodiments, the atomic percentage of nitrogen in the coating is 1% to 60%. The above-mentioned suitable content of nitrogen allows the coating to contain a suitable content of organic compounds, which is conducive to further improving the thermal safety, high-temperature cycle 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 formed by any two of the above values.

[0060] In some embodiments, the ratio of the thickness of the coating layer to the thickness of the positive electrode active material layer is 1:(5-50). The thickness ratio of the coating layer to the positive electrode active material layer is within the above range so that the electrochemical device can exert its thermal stability effect on the positive electrode active material layer while having a good volumetric energy density and suitable impedance, further improving the thermal safety of the electrochemical device. If the coating thickness is too small, there may be problems such as missing coating or uneven coating, which is not conducive to the coating's role in thermally stabilizing the positive electrode active material layer. In some embodiments, the ratio of the thickness of the coating layer to the thickness of the positive electrode active material layer 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 formed by any two of the above values.

[0061] 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, isocyanurates, and thiocyanates. Among them, the 1,3,5-triazine-2,4,6-triamine compound may include at least one of 1,3,5-triazine-2,4,6-triamine, polyacrylonitrile, melamine, cyanuric acid, melamine polyphosphate, and melamine cyanurate. All of the above organic compounds can react with the metal on the surface of the positive electrode active material layer to reduce the phase change and oxygen release reaction of the positive electrode at high temperatures, thereby improving the thermal safety and high-temperature cycling performance of the electrochemical device.

[0062] In some embodiments, the coating further comprises a binder, and the binder comprises 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. The binder can sufficiently bind the organic compound particles to the positive electrode active material layer, thereby reducing shedding of the coating, improving the stability of the positive electrode sheet, and enhancing the thermal safety and high-temperature cycling performance of the electrochemical device.

[0063] In some embodiments, the positive electrode active material includes at least one of lithium cobaltate, lithium nickel cobalt manganese oxide, lithium iron phosphate, lithium nickel cobalt aluminum oxide, lithium-rich manganese-based materials, lithium manganese oxide, lithium iron manganese phosphate, or lithium titanate.

[0064] In some embodiments, 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 peeling force between the coating and the positive electrode current collector is 1N / m to 60N / m. At this peeling force, the adhesion between the coating and the positive electrode current collector is high, which is beneficial to improving the mechanical safety of the electrochemical device. In some embodiments, under the above conditions, the peeling force between the coating and the positive electrode current collector can be 1N / m, 5N / m, 7N / m, 10N / m, 12N / m, 15N / m, 20N / m, 22N / m, 27N / m, 30N / m, 35N / m, 38N / m, 40N / m, 45N / m, 50N / m, 53N / m, 55N / m, 60N / m or any value within the range of any two of the above values.

[0065] According to some embodiments of the present application, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil or nickel foil may be used. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver, silver alloy, etc.) on a polymer substrate.

[0066] The positive electrode material layer also includes a binder and a conductive agent. The binder is used to bond the positive electrode active material particles to facilitate the formation of a film layer, and can also improve the bonding force between the positive electrode active layer and the positive electrode current collector. In some embodiments, the binder may include but is not limited to a binder polymer, such as polyvinylidene fluoride, polytetrafluoroethylene, polyolefins, sodium carboxymethyl cellulose, lithium carboxymethyl cellulose, modified polyvinylidene fluoride, modified SBR rubber or polyurethane. In some embodiments, the polyolefin binder includes at least one of polyethylene, polypropylene, polyolefin ester, polyolefin alcohol or polyacrylic acid.

[0067] In some embodiments, the conductive agent includes a carbon-based material, a metal-based material, a conductive polymer, or a mixture thereof. Carbon-based materials include natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, or carbon fiber; metal-based materials include metal powders or metal fibers of copper, nickel, aluminum, silver, etc.; and conductive polymers include polyphenylene derivatives.

[0068] Negative electrode

[0069] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector.

[0070] The negative electrode current collector includes copper foil, aluminum foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, a polymer substrate coated with a conductive metal, or any combination thereof.

[0071] The negative electrode active material includes a material that reversibly intercalates / deintercalates lithium ions. In some embodiments, the material that reversibly intercalates / deintercalates lithium ions includes a carbon material. 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 a mixture thereof. Crystalline carbon can be amorphous, flaky, platelet-shaped, spherical, or fibrous natural graphite or artificial graphite. Amorphous carbon can be soft carbon, hard carbon, mesophase pitch carbide, calcined coke, etc.

[0072] In some embodiments, the negative electrode active material layer includes a negative electrode active material. The specific types of negative electrode active materials are not subject to specific restrictions and can be selected according to needs. 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 beads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel structured lithiated TiO2-Li4Ti5O 12 , Li-Al alloy or any combination thereof. The silicon-carbon composite refers to a composite containing at least about 5 wt% silicon based on the weight of the silicon-carbon negative electrode active material.

[0073] 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.

[0074] When the negative electrode includes a silicon-carbon compound, based on the total weight of the negative electrode active material, silicon:carbon=about 1:10-10:1, the median particle size Dv of the silicon-carbon compound is about 1:10-10:1. 50 The negative electrode active material layer may be formed using a method such as evaporation, sputtering, or plating. When the negative electrode comprises lithium metal, the negative electrode active material layer may be formed using, for example, a spherical, twisted conductive skeleton and metal particles dispersed within the conductive skeleton. In some embodiments, the spherical, twisted conductive skeleton 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.

[0075] In some embodiments, the negative electrode active material layer may include a binder and, optionally, a conductive material. The binder improves 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 binder includes, but is not limited to: polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0076] In some embodiments, the conductive material includes, but is not limited to, a carbon-based material, a metal-based material, a conductive polymer, 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, and silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0077] 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, a polymer substrate coated with a conductive metal, and any combination thereof.

[0078] 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 on a current collector. In some embodiments, the solvent may include water, etc., but is not limited thereto.

[0079] Isolation film

[0080] The material and shape of the separator used in the electrochemical device of the present application are not particularly limited and can be any technology disclosed in the prior art. In some embodiments, the separator includes a polymer or inorganic substance formed of a material that is stable to the electrolyte of the present application.

[0081] For example, the separator may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, film, or composite film having a porous structure, and the material of the substrate layer is selected from at least one of polyethylene, polypropylene, polyethylene terephthalate, and polyimide. Specifically, polypropylene porous film, polyethylene porous film, polypropylene non-woven fabric, polyethylene non-woven fabric, or polypropylene-polyethylene-polypropylene porous composite film may be used.

[0082] A surface treatment layer is provided on at least one surface of the substrate layer. The surface treatment layer may be a polymer layer, an inorganic layer, or a layer formed by a mixture of a polymer and an inorganic material. The inorganic layer includes inorganic particles and a binder. The inorganic particles are selected from at least one of aluminum oxide, 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.

[0083] The binder is selected from at least one of polyvinylidene fluoride, a copolymer of vinylidene fluoride and hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate salt, polyvinylpyrrolidone, polyethylene alkoxy, polymethyl methacrylate, polytetrafluoroethylene, and polyhexafluoropropylene. The polymer layer comprises a polymer, and the polymer material is selected from at least one of polyamide, polyacrylonitrile, an acrylate polymer, polyacrylic acid, polyacrylate salt, polyvinylpyrrolidone, polyethylene alkoxy, polyvinylidene fluoride, and poly(vinylidene fluoride-hexafluoropropylene).

[0084] electrolyte

[0085] According to some embodiments of the present application, the electrolyte includes an organic solvent, a lithium salt, and optional additives.

[0086] The organic solvent in the electrolyte of the present application can be any organic solvent known in the prior art as a solvent for an electrolyte. The electrolyte used in the electrolyte of the present application is not limited and can be any electrolyte known in the prior art. The additive in the electrolyte of the present application can be any additive known in the prior art as an electrolyte additive. 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).

[0087] In some embodiments, the organic solvent includes an ether solvent, such as at least one of 1,3-dioxolane (DOL) and ethylene glycol dimethyl ether (DME). In some embodiments, the lithium salt includes at least one of an organic lithium salt or an inorganic lithium salt. In some embodiments, the lithium salt includes, but is not limited to, lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium difluorophosphate (LiPO2F2), lithium bis(trifluoromethanesulfonyl)imide (LiN(CF3SO2)2) (LiTFSI), lithium bis(fluorosulfonyl)imide (Li(N(SO2F)2)) (LiFSI), lithium bis(oxalatoborate) (LiB(C2O4)2) (LiBOB), or lithium difluorooxalatoborate (LiBF2(C2O4)) (LiDFOB). In some embodiments, the additive includes at least one of fluoroethylene carbonate and adiponitrile.

[0088] According to some embodiments of the present application, the electrochemical device of the present application includes, but is not limited to: a lithium-ion battery. In some embodiments, the electrochemical device includes a lithium-ion battery.

[0089] The electronic devices of the present application are not particularly limited. In some embodiments, the electronic devices of the present application include, but are not limited to, laptop computers, pen-type computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD televisions, portable cleaners, portable CD players, mini-discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries, and lithium-ion capacitors.

[0090] The present application is described below by way of specific examples and comparative examples. It should be understood by those skilled in the art that the preparation methods described in this application are merely examples, and any other suitable preparation methods are within the scope of this application.

[0091] Example 1-1

[0092] Preparation method of polyacrylonitrile (PAN) particles:

[0093] Using an aqueous precipitation copolymerization method involving acrylonitrile and itaconic acid, 3 kg of deionized water was added to a 5 L reactor under a nitrogen atmosphere. Then, in a 99:1 ratio, distilled acrylonitrile (AN), the comonomer itaconic acid (IA), the initiator ammonium persulfate (APS), and the molecular weight modifiers isopropyl alcohol (IPA) or n-dodecyl mercaptan were added. The polymerization reaction was accelerated by heating in a water bath at 60°C under controlled stirring. The resulting PAN (polyacrylonitrile) was insoluble in water. After a reaction time of 12–18 hours, a polymer slurry was obtained. The polymer slurry was filtered and washed with deionized water multiple times, then vacuum-dried at 50–60°C for 6–8 hours to obtain a white PAN polymer powder. The white PAN powder was then ground to obtain polyacrylonitrile particles with a Dv50 of 0.5 μm.

[0094] Preparation of the positive electrode sheet: 8μm aluminum foil was used as the current collector. The positive electrode active material, lithium cobalt oxide, the conductive agent, conductive carbon black (Super P), and the binder, polyvinylidene fluoride (PVDF), were added to N-methylpyrrolidone (NMP) in a weight ratio of 96:2.5:1.5 and stirred evenly to form a positive electrode active slurry. The positive electrode active material, lithium cobalt oxide, had a particle size (Dv50) of 16μm. The positive electrode active slurry was evenly coated on one side of the positive electrode current collector aluminum foil and dried. The above steps were then repeated on the other side of the foil to obtain a positive electrode sheet coated on both sides with a positive electrode active material layer. The thickness of the positive electrode active material layer was 40μm.

[0095] The PAN particles and the binder polyvinylidene fluoride (PVDF) 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 evenly coated on the surface of the positive electrode active material layer, dried, and cut to obtain a composite positive electrode sheet. Figure 4 and Figure 5 , the surface particles of the composite positive electrode are evenly distributed.

[0096] Preparation of negative electrode sheet:

[0097] The negative electrode active material artificial graphite, thickener sodium carboxymethyl cellulose (CMC) and binder styrene-butadiene rubber (SBR) are added to deionized water in a weight ratio of 96:2:2, and stirred evenly to form a negative electrode slurry. The negative electrode slurry is evenly coated on one side of the negative electrode current collector copper foil and dried. Then, the above steps are repeated on the other side of the copper foil to obtain a negative electrode sheet coated with a negative electrode active layer on both sides. The negative electrode sheet is then cold pressed and cut to obtain a cut negative electrode sheet.

[0098] Preparation of lithium-ion batteries:

[0099] The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order with the separator placed between the positive electrode sheet and the negative electrode sheet to obtain a laminated electrode assembly. After welding the tabs, the electrode assembly is placed in an aluminum-plastic film packaging bag, heat-sealed on all sides, leaving a liquid injection port, and the above-mentioned electrolyte is injected. After vacuum packaging, standing, formation, degassing and other processes, a lithium-ion battery is obtained.

[0100] Example 1-2

[0101] Isocyanate Compounds: Place a predetermined amount of 1,3,5-triazine-2,4,6-triamine in a 3L, three-necked round-bottom flask equipped with a mechanical stirrer, thermometer, and cooler. Add an appropriate amount of water and sodium hydroxide solution to a pH of 9-11. Start the stirrer and heat until completely dissolved at 70-90°C. Add a crystal growth inducer (melamine cyanurate) and mix thoroughly. Then, gradually and slowly add cyanuric acid in three batches until the solution becomes slightly acidic and reaches a pH of 5-7. Maintain the desired reaction temperature of 80-110°C and stir continuously for 3-6 hours to obtain a viscous, white granular product. The mass ratio of 1,3,5-triazine-2,4,6-triamine to cyanuric acid is 50 parts:50 parts. The white particles are then vacuum filtered, washed and dried, and finally the product is ultrafinely pulverized to obtain melamine cyanurate particles, wherein the particle size Dv50 of the melamine cyanurate particles is 0.5 μm.

[0102] Preparation of positive electrode sheet: The steps and conditions for preparing the positive electrode sheet coated with the positive electrode active material layer on both sides are the same as those in Example 1-1.

[0103] The melamine cyanurate particles and the binder polyvinylidene fluoride (PVDF) were added to N-methylpyrrolidone (NMP) in a weight ratio of 95:5 and stirred to form a coating slurry. The coating slurry was evenly applied to the surface of the positive electrode active material layer, dried, and cut into pieces to obtain a composite positive electrode sheet. The remaining preparation steps were the same as in Example 1-1.

[0104] Example 1-3 to Example 1-5

[0105] The type of the organic compound or the type of the binder was changed, and the other steps and conditions were the same as those in Example 1-1.

[0106] Examples 1-6

[0107] Example 1-6 differs from Example 1-1 in that the coating is applied to the surface of the separator. Melamine cyanurate particles and a polyacrylate binder were added to deionized water at a weight ratio of 95:5 and stirred evenly to form a separator coating slurry. The coating slurry was evenly applied to the surface of the separator, dried, and then coated with a polyacrylate adhesive layer to form a composite spacer layer. Preparation parameters and conditions were followed in accordance with Table 1. All other steps were the same as in Example 1-1.

[0108] Example 1-7 to Example 1-14

[0109] The thickness of the coating was changed, and the remaining steps and conditions were the same as those in Example 1-2.

[0110] Examples 1-15

[0111] Polyacrylonitrile particles, binder polyacrylic acid (PAA), and conductive carbon black (conductive agent) were added to deionized water in a weight ratio of 90:5:5 and stirred evenly to form a positive electrode coating slurry. The positive electrode coating slurry was evenly applied to the surface of the positive electrode current collector, dried, and vacuum-dried to obtain a composite positive electrode current collector. The positive electrode active slurry was then applied to the composite positive electrode current collector, dried, cold-pressed three times, and cut into sheets to obtain composite positive electrode sheets. The remaining preparation steps and conditions were the same as those in Example 1-1.

[0112] Examples 1-16

[0113] Melamine cyanurate particles, polyacrylic acid (PAA) binder, and conductive carbon black (conductive carbon black) were added to deionized water in a weight ratio of 90:5:5 and stirred to form a positive electrode coating slurry. The positive electrode coating slurry was evenly applied to the surface of the positive electrode current collector, dried, and vacuum-dried to obtain a composite positive electrode current collector. The positive electrode active slurry was then applied to the composite positive electrode current collector, dried, cold-pressed three times, and cut into sheets to obtain composite positive electrode sheets. The remaining preparation steps and conditions were the same as those in Example 1-1.

[0114] Example 1-17 to Example 1-19

[0115] The types of organic compounds were changed, and the other steps and conditions were the same as those in Example 1-15.

[0116] Example 1-20 to Example 1-23

[0117] The thickness of the coating was changed, and the other steps and conditions were the same as those of Example 1-15.

[0118] Examples 1-24

[0119] The coatings prepared in Examples 1-1 and 1-17 were applied to both surfaces of the positive electrode active material layer. The specific steps were as follows: first, a positive electrode spacer slurry was applied to aluminum foil. Cyanuric acid particles, a binder polyacrylic acid adhesive (PAA), and a conductive carbon black were added to deionized water in a weight ratio of 90:5:5, and stirred evenly to form a positive electrode spacer slurry. The positive electrode spacer slurry was evenly applied to the surface of the positive electrode current collector and dried. The positive electrode active material was then applied, followed by the coating prepared in Example 1-1, resulting in a double-sided coated positive electrode sheet. All other steps and conditions were the same as in Example 1-1.

[0120] Examples 1-25

[0121] The coatings prepared in Examples 1-2 and 1-17 were applied to both surfaces of the positive electrode active material layer. The specific steps were as follows: first, a positive electrode spacer slurry was applied to aluminum foil. Cyanuric acid particles, a binder polyacrylic acid adhesive (PAA), and a conductive carbon black were added to deionized water in a weight ratio of 90:5:5, and stirred evenly to form a positive electrode spacer slurry. The positive electrode spacer slurry was evenly applied to the surface of the positive electrode current collector, dried, and then the positive electrode active material was applied. Finally, the coating prepared in Example 1-2 was applied, resulting in a double-sided coated positive electrode sheet. Other steps and conditions were the same as in Example 1-1.

[0122] Example 1-26 to Example 1-27

[0123] The type of binder was changed, and the other steps and conditions were the same as those in Example 1-4.

[0124] Examples 1-28

[0125] The type of binder was changed, and the other steps and conditions were the same as those in Example 1-18.

[0126] Comparative Example 1

[0127] There is no coating on the positive electrode plate, and other steps and conditions are the same as those in Example 1-1.

[0128] Comparative Example 2

[0129] A ceramic layer is coated on the surface of the active material layer. The preparation method of the ceramic layer is as follows: alumina powder particles and binder PVDF are added to N-methylpyrrolidone (NMP) solution in a weight ratio of 95:5, and stirred evenly to form a ceramic coating slurry. The coating slurry is evenly coated on the surface of the positive electrode active material layer, dried, and cut to obtain a composite positive electrode sheet.

[0130] Comparative Examples 3 to 5

[0131] The thickness of the coating was adjusted, and the other steps and conditions were the same as those in Example 1-6.

[0132] Comparative Example 6

[0133] A ceramic coating is applied to the surface of the positive electrode current collector. The preparation method of the ceramic coating is as follows: alumina powder particles and binder acrylic acid PAA are added to a deionized water solution in a weight ratio of 95:5, and the mixture is stirred evenly to form a ceramic coating slurry. The ceramic coating slurry is evenly applied to the surface of the positive electrode current collector, dried to obtain a composite positive electrode current collector, and then the positive electrode active material is applied to the composite positive electrode current collector, dried, and cut to obtain a composite positive electrode sheet.

[0134] Comparative Example 7 and Comparative Example 8

[0135] The thickness of the coating was adjusted, and the other steps and conditions were the same as those in Example 1-20.

[0136] Comparative Example 9

[0137] The two surfaces of the positive electrode active material layer were coated with the ceramic layer of Comparative Example 2 and the ceramic coating of Comparative Example 6, respectively. The other steps and conditions were the same as those of Comparative Example 2.

[0138] Example 2-1 to Example 2-7

[0139] The particle size Dv50 of the organic compound was adjusted, and the other steps and conditions were the same as those in Example 1-2.

[0140] Example 2-8 to Example 2-13

[0141] The particle size Dv50 of the positive electrode active material was adjusted, and other steps and conditions were the same as those in Example 1-2.

[0142] Example 2-14 to Example 2-19

[0143] The atomic ratio of nitrogen in the coating and the components in the coating were adjusted, and the other steps and conditions were the same as those in Example 1-2.

[0144] Example 2-20 to Example 2-24

[0145] The thickness of the positive electrode active material in the coating layer was adjusted, and other steps and conditions were the same as those in Example 1-2.

[0146] Example 3-1

[0147] The coating is performed multiple times to obtain a composite positive electrode with a coating layer in the intermediate layer. The positive electrode active slurry is applied to the surface of the positive electrode current collector and dried to a thickness of 40 μm. The slurry is dried to obtain a single-coated positive electrode sheet. Melamine cyanurate particles and a binder, vinylidene fluoride (PVDF), are added to an NMP solution in a weight ratio of 95:5 and stirred to form a coating slurry. The coating slurry is evenly applied to the primary positive electrode sheet and dried to obtain a secondary coated positive electrode sheet. The positive electrode active slurry is then applied to the secondary coated positive electrode sheet to obtain a composite triple-coated positive electrode sheet.

[0148] Other steps and conditions are the same as those in Example 1-1.

[0149] Example 3-2 to Example 3-4

[0150] The thickness of the coating layer located inside the positive electrode active material layer was changed, and the other steps and conditions were the same as those in Example 3-1.

[0151] Examples 3-6

[0152] Melamine cyanurate particles and binder polyacrylic acid adhesive (PAA) are added to deionized water in a weight ratio of 95:5, and stirred evenly to form a positive electrode coating slurry. The positive electrode coating slurry is evenly coated on the surface of the positive electrode current collector, dried, and vacuum-dehydrated to obtain a composite positive electrode current collector.

[0153] The positive electrode active slurry was applied to 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, binder polyvinylidene fluoride (PVDF), and conductive agent carbon black were added to N-methylpyrrolidone (NMP) in a weight ratio of 90:7:3 and stirred evenly to form a coating slurry. The coating slurry was evenly applied to the surface of the first positive electrode active material layer and dried to obtain a first composite positive electrode sheet. The positive electrode active slurry was then applied to the coating of the first composite positive electrode sheet and dried to a thickness of 40 μm to obtain a second composite positive electrode sheet.

[0154] Melamine cyanurate particles and binder polyvinylidene fluoride (PVDF) are added to N-methylpyrrolidone (NMP) in a weight ratio of 95:5, stirred evenly to form a coating slurry, and the coating slurry is evenly coated on the surface of the positive electrode active material layer of the second composite positive electrode sheet, dried, and cut to obtain a three-layer coated positive electrode sheet.

[0155] Other steps and conditions are the same as those in Example 1-1.

[0156] Example 3-5, Example 3-7 and Example 3-8

[0157] The type of the organic compound in the coating layer is adjusted, or the thickness of the coating layer within the positive electrode active material layer is changed. Other steps and conditions are the same as those of Examples 3-6.

[0158] Performance test of positive electrode:

[0159] (1) Test of nitrogen content in coating

[0160] The coating was separated from the lithium-ion battery, washed three times with NMP, centrifuged to remove the electrolyte, glue, and residual lithium salts, and then dried. An elemental analyzer was used to determine the quantitative nitrogen content of the coating.

[0161] (2) Particle size Dv50 of organic compound and particle size Dv50 of positive electrode active material

[0162] The coating and cathode active material were separated from the lithium-ion battery, washed three times with NMP, centrifuged to remove the electrolyte, gel, and residual lithium salt, and dried. The volume particle size distribution of the particles was measured using a laser particle size analyzer.

[0163] (3) Coating thickness and positive electrode active material layer thickness test

[0164] The composite positive electrode sheet in the lithium-ion battery is disassembled into the structure of separator + composite positive electrode sheet + separator, the interface is plasma cut, the cross-sectional morphology of the composite positive electrode sheet is obtained by scanning electron microscopy (SEM), and the thickness of the coating and the positive electrode active material layer is measured.

[0165] (4) Peeling force test between coating and positive electrode current collector

[0166] After the lithium-ion battery was stored at 85°C for 5 hours, the coated positive electrode current collector was separated from the lithium-ion battery, and a high-adhesion tape was covered on the coating surface. The adhesion strength between the coating and the current collector, i.e., the peeling strength, was tested using a 180° tensile testing machine.

[0167] Performance test of lithium-ion batteries:

[0168] (1) High temperature cycle performance

[0169] Place the lithium-ion battery in a 45°C constant temperature test chamber and let it rest for 30 minutes to allow the lithium-ion battery to reach a constant temperature. Charge it at a constant current of 0.5C to 4.45V, then charge it at a constant voltage to a current of 0.05C. Let it rest for 1 minute, and then discharge it at a constant current of 0.5C to 3.0V. Record this as the initial discharge capacity C0. Repeat this process for 100 cycles, and record the discharge capacity C1 after 100 cycles to calculate the lithium-ion battery cycle capacity retention rate.

[0170] High temperature cycle capacity retention rate = C1 / C0×100%.

[0171] (2) High temperature storage expansion rate test

[0172] At 25°C, the lithium-ion battery was allowed to rest for 5 minutes, then charged to 4.45V at a constant current rate of 0.5C. It was then charged to 0.05C at a constant voltage rate of 4.45V and allowed to rest for 5 minutes. The thickness D1 of the lithium-ion battery was measured. The fully charged lithium-ion battery was stored at 80°C 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:

[0173] High temperature storage expansion rate = (D2-D1) / D1*100%.

[0174] (3) Thermal safety test

[0175] At 25°C, let the lithium-ion battery rest for 5 minutes, then charge it to 4.45V at a constant current rate of 0.5C, charge it to 0.05C at a constant voltage rate of 4.5V, and let it rest for 5 minutes. Then, place the lithium-ion battery in a constant temperature box and continuously increase the temperature at a rate of 10°C / min to the set temperature (such as 130°C). Maintain this temperature for 60 minutes. The lithium-ion battery passes the test if it does not explode or catch fire.

[0176] Take another lithium-ion battery of the same type and raise the temperature of the thermostat by 1°C (131°C). Maintain this temperature for 60 minutes. If the battery cell does not explode or catch fire, it is considered to have passed the test. The battery cell will fail the thermal safety test at this temperature, and the thermal safety pass temperature is determined.

[0177] (4) Mechanical safety testing

[0178] At 25°C, allow the lithium-ion battery to rest for 5 minutes. Then, charge it to 4.45V at a constant current rate of 0.5C. Then, charge it to 0.05C at a constant voltage rate of 4.45V and allow it to rest for 5 minutes. A 3mm diameter steel nail is driven into the center of the lithium-ion battery at a speed of 30mm / s. The nail is held in the center for 10 minutes before being removed. The lithium-ion battery passes the test if it does not explode or catch fire.

[0179] (5) Impedance of lithium-ion batteries

[0180] At 25°C, let the lithium-ion battery stand for 5 minutes, then charge it to 4.45V at a constant current rate of 0.5C, charge it to 0.05C at a constant voltage rate at 4.45V, let it stand for 5 minutes, and measure the DC impedance of the lithium-ion battery (cell) in the fully charged state.

[0181] In this application, "I" side and "II" side are used to distinguish 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 I side, and when the coating is located between the positive electrode plate and the separator, it is named II side. When two coatings exist at the same time, the two coatings are respectively located between the positive electrode current collector and the positive electrode active material layer and between the positive electrode plate and the separator, and they are named I+II sides.

[0182] Table 1

[0183]

[0184]

[0185] Table 2

[0186]

[0187] Table 3

[0188]

[0189] It can be seen from Table 1 and Table 2 above that, compared with Comparative Examples 1 to 5, in Examples 1-1 to 1-6, when the coating is located between the positive electrode plate and the separator, when 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.

[0190] Combined with Table 3, in Examples 1-2, 1-6 to 1-14, when the thickness of the coating is 0.3 μm to 3 μm, the corresponding lithium-ion batteries can simultaneously take into account excellent high-temperature cycle performance, high-temperature storage expansion rate and thermal safety pass temperature.

[0191] Table 4

[0192]

[0193] Table 5

[0194]

[0195] It can be seen from Tables 4 and 5 above that, compared with Comparative Examples 1 and Comparative Examples 6 to 8, in Examples 1-15 to Examples 1-19, when the coating is located between the positive electrode current collector and the active material layer, when 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.

[0196] From Tables 4 and 5, in Examples 1-17 and Examples 1-20 to 1-23, when the thickness of the coating is between 0.3 μm and 3 μm, the corresponding lithium-ion batteries can simultaneously have excellent high-temperature cycle performance, high-temperature storage expansion rate, good thermal safety pass temperature and mechanical safety performance at low cell impedance.

[0197] Table 6

[0198]

[0199] It can be seen from Table 6 above that, compared with Comparative Example 9, in Examples 1-24 to 1-25, two coatings are provided, which are respectively located between the positive electrode current collector and the active material layer and between the positive electrode plate and the separator. 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.

[0200] Table 7

[0201]

[0202] Table 8

[0203]

[0204] It can be seen from Tables 7 and 8 above that by adjusting the type of binder in the coating, the corresponding lithium-ion battery also has excellent high-temperature cycle performance and high-temperature storage expansion rate, as well as good thermal safety pass temperature and mechanical safety performance.

[0205] Table 9

[0206]

[0207] Table 10

[0208]

[0209] From Tables 9 and 10 above, the particle size Dv50 of the organic compound is adjusted. When the particle size of the organic compound is within an appropriate range, the corresponding lithium-ion battery also has excellent high-temperature cycle performance and high-temperature storage expansion rate, while also having good thermal safety pass temperature and mechanical safety performance.

[0210] Table 11

[0211]

[0212] From the above Table 11, by adjusting the particle size Dv50 of the positive electrode active material, the corresponding lithium-ion battery also has excellent high-temperature cycle performance and high-temperature storage expansion rate, as well as good thermal safety passing temperature and mechanical safety performance.

[0213] Table 12

[0214]

[0215] From Table 12 above, by adjusting the atomic ratio of nitrogen in the coating, the corresponding lithium-ion battery also has excellent high-temperature cycle performance and high-temperature storage expansion rate, as well as good thermal safety passing temperature and mechanical safety performance.

[0216] Table 13

[0217]

[0218] From Table 13 above, by adjusting the thickness of the positive electrode active material layer, the corresponding lithium-ion battery also has excellent high-temperature cycle performance and high-temperature storage expansion rate, as well as good thermal safety pass temperature and mechanical safety performance.

[0219] Table 14

[0220]

[0221] Table 15

[0222]

[0223] From Tables 14 and 15 above, the thickness of the coating is adjusted. When the coating is located inside the positive electrode active material layer, the corresponding lithium-ion battery also has excellent high-temperature cycle performance and high-temperature storage expansion rate, and also has a good thermal safety pass temperature.

[0224] Table 16

[0225]

[0226] Table 17

[0227]

[0228] From Tables 16 and 17 above, when the coating layer includes three coating layers, two of which are located on the two surfaces of the positive electrode active material layer and the other coating layer is located inside the positive electrode active material layer, the corresponding lithium-ion battery also has excellent high-temperature cycle performance and high-temperature storage expansion rate, as well as good thermal safety pass temperature and mechanical safety performance.

[0229] The above disclosure is only a preferred embodiment of the present application and certainly cannot be used to limit the present application. Therefore, equivalent changes made based on the present application are still within the scope covered by the present application.

Claims

1. A positive electrode plate, characterized in that: The invention comprises a positive electrode current collector, a positive electrode active material layer and a coating, wherein the coating is located on the surface and / or inside the positive electrode active material layer, the coating comprises an organic compound, the organic compound comprises one functional group selected from the group consisting of an isocyanate group, an oxazine group and an isocyanate group, or at least two functional groups selected from the group consisting of a cyanate group, an isocyanate group, an oxazine group and an isocyanate group, and the thickness of the coating is 0.3 μm to 3 μm; 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); the ratio of the thickness of the coating to the thickness of the positive electrode active material layer is 1:(5~50), and the ratio of the particle size Dv50 of the organic compound to the particle size Dv50 of the positive electrode active material in the positive electrode active material layer is 1:(10~60).

2. The positive electrode sheet according to claim 1, wherein: The coating has a thickness of 0.5 μm to 2.5 μm.

3. The positive electrode sheet according to claim 1, wherein: The coating layer is located between the positive electrode current collector and the positive electrode active material layer.

4. The positive electrode sheet according to claim 1, wherein: The coating layer is located on a surface of the positive electrode active material layer facing away from the positive electrode current collector.

5. The positive electrode sheet according to claim 1, wherein: The positive electrode sheet includes two coating layers, one coating layer is located between the positive electrode current collector and the positive electrode active material layer, and the other coating layer is located on the surface of the positive electrode active material layer facing away from the positive electrode current collector.

6. The positive electrode sheet according to claim 1, wherein: The coating layer is located inside the positive electrode active material layer. Along the thickness direction of the positive electrode sheet, the positive electrode active material layer is divided into multiple layers by the coating layer.

7. The positive electrode sheet according to claim 1, wherein: The positive electrode plate includes two coating layers, one of which is located inside the positive electrode active material layer, and the other is located on a surface of the positive electrode active material layer.

8. The positive electrode sheet according to claim 1, wherein: The positive electrode plate includes three coating layers, one of which is located inside the positive electrode active material layer, and the other two coating layers are respectively located on two surfaces of the positive electrode active material layer.

9. The positive electrode sheet according to claim 1, wherein: The coating mass per unit area is 1 mg / 5000 mm 2 Up to 25mg / 5000mm 2 .

10. The positive electrode sheet according to any one of claims 1 to 9, characterized in that: 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.

11. The positive electrode sheet according to any one of claims 1 to 9, wherein: 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%.

12. The positive electrode sheet according to any one of claims 1 to 9, wherein: The organic compound includes at least one of 1,3,5-triazine-2,4,6-triamine compounds and isocyanurate.

13. The positive electrode sheet according to any one of claims 1 to 9, characterized in that: The coating further comprises a binder, and the binder comprises at least one of polyamide, polyacrylonitrile, polyvinyl alcohol, acrylate polymer, polyacrylic acid, polyacrylate, sodium carboxymethyl cellulose, polyvinyl pyrrolidone, polyvinyl ether, polyvinylidene fluoride, and styrene-butadiene rubber.

14. The positive electrode sheet according to any one of claims 1 to 9, 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 or lithium iron manganese phosphate.

15. The positive electrode sheet according to any one of claims 1 to 9, characterized in that: The coating layer 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 peeling force between the coating layer and the positive electrode current collector is 1 N / m to 60 N / m.

16. An electrochemical device comprising a negative electrode sheet, a separator and an electrolyte, characterized in that: The electrochemical device further comprises a positive electrode sheet according to any one of claims 1 to 15, wherein the separator is located between the positive electrode sheet and the negative electrode sheet.

17. An electronic device, characterized in that: Comprising the electrochemical device of claim 16.

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