Positive pole piece, electrochemical device and electronic device

Abstract

The invention provides a positive pole piece, an electrochemical device and an electronic device, the positive pole piece comprises 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, and the coating comprises an organic compound, the organic compound includes at least one functional group selected from a cyano group, an isonitrile group, an azinyl group, and an isocyanate group, and the thickness of the coating layer is 0.3 [mu] m to 3 [mu] m. The positive pole piece provided by the invention can improve the thermal safety, the high-temperature cycle performance, the high-temperature storage expansion rate and the 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] As portable chemical energy sources, electrochemical devices (such as lithium-ion batteries) 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 due to their high energy density, high operating voltage platform, low self-discharge, long service life and environmental friendliness.

[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) 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] A first aspect of the present application provides a positive electrode plate, which includes 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 of the positive electrode active material layer, and the coating includes an organic compound, wherein the organic compound includes at least one functional group selected from cyano, isonitrile, oxazine and isocyanate, and the thickness of the coating is 0.3 μm to 3 μm.

[0006] In the positive electrode plate provided by the present application, a coating containing an organic compound is arranged on the surface and / or inside of the positive electrode active material layer. The above-mentioned organic compound can react with the metal on the surface of the positive electrode active material layer to form a complex, which can reduce the phase change and oxygen release reaction of the positive electrode plate at high temperature, and is beneficial to improve the stability of the positive electrode plate, 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 bond energy of the carbon-nitrogen triple bond or double bond contained in the above-mentioned organic compound is relatively high and is not easily oxidized. The organic compound itself will have a strong antioxidant property and strong stability, which can improve the mechanical safety of the positive electrode plate used in the electrochemical device. Combined with the thickness range of the coating in this case, the inventor found that the thickness of the coating is within the above range, which can improve the thermal safety and high-temperature cycle performance of the electrochemical device on the one hand, and also help the electrochemical device maintain good energy density and high-temperature storage expansion performance.

[0007] Based on the first aspect, in some possible implementations, the thickness of the coating is 0.5 μm to 2.5 μm, which is beneficial to further improve 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 safety 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, which is beneficial to improving the electrolyte wettability of the positive electrode plate, further 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.

[0010] Based on the first aspect, in some embodiments, 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, which can improve the thermal safety and high temperature cycle performance of the electrochemical device while further improving 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 inside the positive electrode active material layer and the other is located on a surface of the positive electrode active material layer, which can improve the thermal safety and high temperature cycle performance of the electrochemical device while further improving the mechanical safety of the electrochemical device.

[0012] Based on the first aspect, in some embodiments, the positive electrode plate 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. The provision of multiple coatings can further improve the thermal stability of the positive electrode plate, and further improve the thermal safety and high temperature cycle performance of the electrochemical device.

[0013] Based on the first aspect, in some embodiments, the coating mass per unit area of ​​the coating 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, and also help to improve 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 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 is beneficial to increase the contact area between the organic compound and the positive electrode active material, and to further improve the stability of the positive electrode active material, thereby further improving the thermal safety and high temperature cycle 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 of D / d is 1:(1-20). The particles of the organic compound are evenly distributed in the coating, and the organic compound can fully act on the positive electrode active material, further improving the thermal safety and high temperature cycle 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 to further improve the thermal safety and high temperature cycle performance of the electrochemical device.

[0019] Based on the first aspect, in some embodiments, in the coating, the atomic percentage of nitrogen is 1% to 60%. The above suitable content of nitrogen allows the coating to contain a suitable content of organic compounds, which is beneficial to further improve the thermal safety, high temperature cycle 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 to the thickness of the positive electrode active material layer is 1:(5-50). This allows the electrochemical device to exert its thermal stability effect on the positive electrode active material layer while having a good volume energy density and a suitable 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 above-mentioned binder can fully bond the organic compound particles and bond them to the positive electrode active material layer, reduce the shedding of the coating, help improve the stability of the positive electrode sheet, and also improve the thermal safety and high temperature cycle 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 cobalt oxide, 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, 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 1 N / m to 60 N / m. The high bonding force between the coating and the positive electrode current collector is conducive to improving the mechanical safety of the electrochemical device.

[0025] The second aspect of the present application provides an electrochemical device, comprising a negative electrode sheet, a separator, an electrolyte and the positive electrode sheet, wherein the separator is located between the positive electrode sheet and the negative electrode sheet. The chemical device including the positive electrode sheet has excellent thermal safety, mechanical safety, high temperature cycle performance and high temperature storage expansion rate.

[0026] A third aspect of the present application provides an electronic device, including an electrochemical device, wherein the electronics comprising the electrochemical device have 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: 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.

[0028] Figure 2 for Figure 1 Enlarged schematic diagram of part A.

[0029] Figure 3 for Figure 2 Schematic diagram of the enlarged portion B.

[0030] Figure 4 This is a scanning electron microscope image of the coating surface prepared in Example 1-1 of the present application.

[0031] Figure 5 for Figure 4 Scanning electron micrograph at 2000x magnification. DETAILED DESCRIPTION

[0032] The technical scheme in the embodiment of the present application is described clearly and in detail below. Obviously, the described embodiment is a part of the embodiment of the present application, rather than all the embodiments. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally 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.

[0033] 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 range of variation 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 a range format is 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.

[0034] 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, 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 include a single element or multiple elements. Item B may include a single element or multiple elements. Item C may include a single element or multiple elements.

[0035] As used herein, amounts, ratios and other numerical values ​​are sometimes presented herein in a range format. It should be understood that such a range format is used for convenience and brevity, and should be flexibly construed to include not only the values ​​explicitly specified as range limits, but also all individual values ​​or sub-ranges encompassed within the range, as if each value and sub-range were explicitly specified.

[0036] 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.

[0037] The shell can be a packaging bag encapsulated by a packaging film (such as an aluminum-plastic film), such as 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, and the like.

[0038] The electrode assembly includes a positive electrode sheet, a negative electrode sheet and a separator, wherein the separator is disposed between the positive electrode sheet and the negative electrode sheet. The electrode assembly may be a laminated structure, which is formed by stacking the positive electrode sheet, the separator and the negative electrode sheet. In other embodiments, the electrode assembly may also be a wound structure, which is formed by stacking the positive electrode sheet, the separator and the negative electrode sheet and then winding them.

[0039] The present application provides a positive electrode plate, which includes a positive electrode collector, a positive electrode active material layer and a coating, wherein the coating is located on the surface and / or inside of the positive electrode active material layer, and the coating includes an organic compound, wherein the organic compound includes at least one functional group selected from cyano, isonitrile, oxazine and isocyanate, and the thickness of the coating is 0.3 μm to 3 μm.

[0040] In the positive electrode plate provided by the present application, a coating containing an organic compound is arranged on the surface or / and inside of the positive electrode active material layer. The above-mentioned organic compound can react with the metal on the surface or inside of the positive electrode active material layer to form a complex, which can reduce the phase change and oxygen release reaction of the positive electrode plate at high temperature, and is beneficial to improve the stability of the positive electrode plate, 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 bond energy of the carbon-nitrogen triple bond or double bond contained in the above-mentioned organic compound is relatively high and is not easily oxidized. The organic compound itself will have a strong antioxidant property and strong stability, which can improve the mechanical safety of the positive electrode plate used in the electrochemical device. Combined with the thickness range of the coating in this case, the inventor found that the thickness of the coating is within the above range, which can improve the thermal safety and high-temperature cycle performance of the electrochemical device on the one hand, and is also beneficial for the electrochemical device to maintain good energy density and high-temperature storage expansion performance.

[0041] In some embodiments, the thickness of the coating may 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 the range formed by any two of the above values.

[0042] 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 in 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.

[0043] In some embodiments, the coating has a thickness of 0.5 μm to 2.5 μm, which is beneficial to further improve the high temperature cycle performance and thermal safety performance of the electrochemical device.

[0044] 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 attenuation rate, and increase the passing temperature of the thermal safety test. The above 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.

[0045] 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 In the embodiment, 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.

[0046] In other embodiments, the positive electrode sheet includes two coatings, one coating is located between the positive electrode current collector and the positive electrode active material layer, and the other coating is located on the surface of the positive electrode active material layer away from the positive electrode current collector. The coatings are provided on both surfaces of the positive electrode active material layer, which can improve the thermal safety and high temperature cycle performance of the electrochemical device while also further improving the mechanical safety of the electrochemical device.

[0047] In some embodiments, the coating is located inside the positive electrode sheet, and along the thickness direction of the positive electrode sheet, the positive electrode active material layer is divided into multiple layers by the coating. 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 thickness layer 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.

[0048] If the coating is located inside the positive electrode plate, a conductive agent will be added to the coating to improve the conductivity of the coating and to improve the overall conductivity of the positive electrode plate.

[0049] In some embodiments, if the positive electrode sheet includes two coatings, one coating is located inside 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 the surface away from the positive electrode current collector. While improving the thermal safety and high temperature cycle performance of the electrochemical device, it is also beneficial to further improve the mechanical safety of the electrochemical device.

[0050] In some embodiments, the positive electrode sheet 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. 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 away from the positive electrode current collector. Such an arrangement can improve the thermal safety and high temperature cycle performance of the electrochemical device while also helping to further improve the mechanical safety of the electrochemical device.

[0051] 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, and also help improve 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 of ​​the coating is 3 mg / 5000 mm 2 Up to 15mg / 5000mm 2 .

[0052] 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.

[0053] In some embodiments, the particle size Dv50 of the organic compound is 100nm to 1000nm. 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, improve the electrolyte infiltration and promote 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 100nm, 200nm, 300nm, 400nm, 500nm, 600nm, 700nm, 800nm, 900nm, 1000nm 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.

[0054] 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, and improving the cycle stability of the electrochemical device. It can also improve 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 composed of any two of the above values.

[0055] 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). The ratio of the two within the above range is conducive to increasing the contact area between the organic compound and the positive electrode active material, and is conducive to further improving the stability of the positive electrode active material, thereby further improving the thermal safety and high temperature cycle 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 composed of any two of the above values.

[0056] In some embodiments, 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). Within this range, the particles of the organic compound are evenly distributed in the coating, and the organic compound can fully act on the positive electrode active material, further improving the thermal safety and high temperature cycle performance of the electrochemical device. In some embodiments, the ratio of D / d 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 ratio of D / d is 1:(3~10).

[0057] In some embodiments, the thickness of the positive electrode active material layer is 20 μm to 80 μm. The suitable thickness range of the positive electrode active material layer is conducive to making the electrochemical device have good energy density and high temperature storage expansion performance, and has a small 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.

[0058] In some embodiments, in the coating, the atomic percentage of nitrogen is 1% to 60%. The above suitable content of nitrogen is such that the coating contains a suitable content of organic compounds, which is beneficial to further improve the thermal safety, high temperature cycle performance and high temperature storage expansion rate of the electrochemical device. In some embodiments, in the coating, the atomic percentage of nitrogen 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.

[0059] In some embodiments, the ratio of the thickness of the coating to the thickness of the positive electrode active material layer is 1: (5~50). The thickness ratio of the coating and the positive electrode active material layer is within the above range, so that the electrochemical device can exert the thermal stability of the coating on the positive electrode active material layer under good volume energy density and suitable impedance, and further improve the thermal safety of the electrochemical device. If the thickness of the coating is small, there may be leakage or uneven coating, which is not conducive to the role of the coating on the thermal stability of the positive electrode active material layer. In some embodiments, the ratio of the thickness of the coating 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 composed of any two of the above values.

[0060] 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. 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, polyphosphate melamine, and cyanuric acid melamine. The above organic compounds can all 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 temperature, and can improve the thermal safety and high temperature cycle performance of the electrochemical device.

[0061] 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 above-mentioned binder can fully bond the organic compound particles and bond them to the positive electrode active material layer, reduce the shedding of the coating, help improve the stability of the positive electrode sheet, and also improve the thermal safety and high temperature cycle performance of the electrochemical device.

[0062] 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 iron manganese phosphate, or lithium titanate.

[0063] In some embodiments, the coating is located between the positive electrode current collector and the positive electrode active material layer, and the positive electrode sheet is stored at 85°C for 5 hours, and the peeling force between the coating and the positive electrode current collector is 1N / m to 60N / m. At this peeling force, the bonding force between the coating and the positive electrode current collector is high, which is beneficial to improve 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 composed of any two of the above values.

[0064] 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.

[0065] 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.

[0066] 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 such as natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, or carbon fiber; metal-based materials such as metal powder or metal fiber of copper, nickel, aluminum, silver, etc.; conductive polymers such as polyphenylene derivatives.

[0067] Negative electrode The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector.

[0068] 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.

[0069] 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, flake-shaped, spherical or fibrous natural graphite or artificial graphite. Amorphous carbon can be soft carbon, hard carbon, mesophase pitch carbide, calcined coke, etc.

[0070] 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.

[0071] 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.

[0072] 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, and the median particle size Dv of the silicon-carbon compound is 50 The negative electrode active material layer may be formed by evaporation, sputtering, plating, or the like. When the negative electrode comprises lithium metal, the negative electrode active material layer may be formed by, for example, a spherical, twisted conductive skeleton and metal particles dispersed in the conductive skeleton. In some embodiments, the spherical, twisted conductive skeleton may have a porosity of about 5% to about 85%. In some embodiments, a protective layer may be further provided on the lithium metal negative electrode active material layer.

[0073] 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, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene 1,1-difluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0074] In some embodiments, the conductive material includes, but is not limited to: a carbon-based material, a metal-based material, a conductive polymer, or a mixture 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, silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0075] 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.

[0076] The negative electrode can be prepared by a preparation method 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 coating the active material composition on a current collector. In some embodiments, the solvent may include water, etc., but is not limited thereto.

[0077] Isolation film 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.

[0078] For example, the isolation film may include a substrate layer and a surface treatment layer. The substrate layer is a non-woven fabric, a film or a 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, a polypropylene porous film, a polyethylene porous film, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite film may be selected.

[0079] A surface treatment layer is provided on at least one surface of the substrate layer, and the surface treatment layer may be a polymer layer or an inorganic layer, or a layer formed by a mixed polymer and an inorganic substance. The inorganic layer includes inorganic particles and a binder, and 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.

[0080] The binder is selected from at least one of polyvinylidene fluoride, copolymer of vinylidene fluoride-hexafluoropropylene, polyamide, polyacrylonitrile, polyacrylate, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene alkoxy, polymethyl methacrylate, polytetrafluoroethylene and polyhexafluoropropylene. The polymer layer contains a polymer, and the material of the polymer is selected from at least one of polyamide, polyacrylonitrile, acrylate polymer, polyacrylic acid, polyacrylate, polyvinylpyrrolidone, polyethylene alkoxy, polyvinylidene fluoride and poly(vinylidene fluoride-hexafluoropropylene).

[0081] Electrolyte According to some embodiments of the present application, the electrolyte includes an organic solvent, a lithium salt, and optional additives.

[0082] The organic solvent in the electrolyte of the present application may be any organic solvent known in the prior art that can be used as a solvent for the electrolyte. The electrolyte used in the electrolyte according to the present application is not limited, and it can be any electrolyte known in the prior art. The additive of the electrolyte according to the present application can be any additive known in the prior art that can be used 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).

[0083] In some embodiments, the organic solvent includes an ether solvent, for example, 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 trifluoromethanesulfonyl imide LiN(CF3SO2)2 (LiTFSI), lithium bis(fluorosulfonyl)imide Li(N(SO2F)2) (LiFSI), lithium bis(oxalatoborate) LiB(C2O4)2 (LiBOB) or lithium di(oxalatoborate) LiBF2(C2O4) (LiDFOB). In some embodiments, the additive includes at least one of fluoroethylene carbonate and adiponitrile.

[0084] 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.

[0085] The electronic device of the present application is not particularly limited. In some embodiments, the electronic device of the present application includes, but is not limited to, a laptop computer, a pen-input computer, a mobile computer, an electronic book player, a portable phone, a portable fax machine, a portable copier, a portable printer, a head-mounted stereo headset, a video recorder, an LCD TV, a portable cleaner, a portable CD player, a mini-disc, a transceiver, an electronic notepad, a calculator, a memory card, a portable recorder, a radio, a backup power supply, a motor, a car, a motorcycle, a power-assisted bicycle, a bicycle, a lighting fixture, a toy, a game console, a clock, an electric tool, a flashlight, a camera, a large household battery and a lithium-ion capacitor, etc.

[0086] The present application is described below by specific examples and comparative examples. Those skilled in the art should understand that the preparation methods described in the present application are only examples, and any other suitable preparation methods are within the scope of the present application.

[0087] Example 1-1 Preparation method of polyacrylonitrile (PAN) particles: Using the aqueous phase precipitation copolymerization method of acrylonitrile and itaconic acid, 3kg of deionized water was added to a 5L reactor under a nitrogen atmosphere, and then acrylonitrile AN after distillation treatment, comonomer itaconic acid IA, initiator ammonium persulfate APS and molecular weight regulator isopropanol IPA or n-dodecyl mercaptan were added in a certain ratio of 99:1, and the stirring rate was adjusted. The polymerization reaction was promoted by heating at 60°C in a water bath. The generated PAN was insoluble in water. After a certain reaction time of 12h~18h, a polymer slurry was obtained. The polymer slurry was filtered and washed with deionized water for multiple times, and then vacuum dried at a high temperature of 50~60°C for 6~8 hours to obtain a white PAN polymer powder. The PAN white powder was ground to obtain polyacrylonitrile particles with a Dv50 of 0.5μm.

[0088] Preparation of positive electrode sheet: 8μm aluminum foil is selected as the current collector, and the positive electrode active material lithium cobalt oxide, conductive agent conductive carbon black (Super P), and binder polyvinylidene fluoride (PVDF) are 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. Among them, the particle size Dv50 of the positive electrode active material lithium cobalt oxide is 16μm, and the positive electrode active slurry is evenly coated on one side of the positive electrode current collector aluminum foil, dried, and then the above steps are repeated on the other side of the aluminum foil to obtain a positive electrode sheet coated with a positive electrode active material layer on both sides, wherein the thickness of the positive electrode active material layer is 40μm.

[0089] 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 sheet are evenly distributed.

[0090] Preparation of negative electrode sheet: 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 collector copper foil, dried, and 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, which is then cold pressed and cut to obtain a cut negative electrode sheet.

[0091] Preparation of lithium-ion batteries: The prepared positive electrode sheet, separator, and negative electrode sheet are stacked in order, with the separator being between the positive electrode sheet and the negative electrode sheet, to obtain a stacked electrode assembly. After welding the electrode ears, 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.

[0092] Example 1-2 Isocyanate compounds: Place a certain amount of 1,3,5-triazine-2,4,6-triamine compound into a 3L three-necked round-bottom flask equipped with a mechanical stirrer, a thermometer and a cooler, then add an appropriate amount of water and sodium hydroxide solution to make the solution pH 9-11. Start the stirrer and heat until it is completely dissolved to a temperature of 70-90°C, add a crystal growth inducer of melamine cyanurate, mix well, and then gradually and slowly add cyanuric acid in 3 batches until the solution is weakly acidic and the pH value is 5-7. Maintain the required reaction temperature of 80°C-110°C and continue stirring for 3-6 hours to obtain a viscous white granular material. The mass ratio of 1,3,5-triazine-2,4,6-triamine compound to cyanuric acid is 50 parts:50 parts. The white particles are then filtered, washed and dried by vacuum filtration, and finally the product is subjected to ultrafine grinding to obtain melamine cyanurate particles, wherein the particle size Dv50 of the melamine cyanurate particles is 0.5 μm.

[0093] Preparation of positive electrode sheet: The steps and conditions for preparing the positive electrode sheet coated with positive electrode active material layers on both sides are the same as those in Example 1-1.

[0094] The above-mentioned melamine cyanurate particles and binder polyvinylidene fluoride (PVDF) were added to N-methylpyrrolidone (NMP) at a weight ratio of 95:5, and stirred evenly to form a coating slurry, and the coating slurry was evenly coated on the surface of the positive electrode active material layer, dried, and cut to obtain a composite positive electrode sheet. The remaining preparation steps are the same as those in Example 1-1.

[0095] Example 1-3 to Example 1-5 The type of organic compound or the type of binder is changed, and the other steps and conditions are the same as those of Example 1-1.

[0096] Examples 1-6 The difference between Example 1-6 and Example 1-1 is that the coating is applied to the surface of the isolation film. Melamine cyanurate particles and adhesive polyacrylate are added to deionized water at a weight ratio of 95:5, stirred evenly to form an isolation film coating slurry, and the coating slurry is evenly applied to the surface of the isolation film, dried, and coated with a polyacrylate adhesive layer to obtain a composite spacer layer. The preparation parameters and conditions in Table 1 are implemented. The other steps are the same as those in Example 1-1.

[0097] Example 1-7 to Example 1-14 The thickness of the coating was changed, and the remaining steps and conditions were the same as those of Example 1-2.

[0098] Examples 1-15 Add polyacrylonitrile particles, binder polyacrylic acid (PAA) and conductive agent conductive carbon black to deionized water in a weight ratio of 90:5:5, stir evenly to form a positive electrode coating slurry, evenly apply the positive electrode coating slurry on the surface of the positive electrode collector, dry, and vacuum dehydrate to obtain a composite positive electrode collector. Apply the positive electrode active slurry to the composite positive electrode collector, dry, cold press 3 times, and cut into pieces to obtain a composite positive electrode sheet. The remaining preparation steps and conditions are the same as those in Example 1-1.

[0099] Examples 1-16 Melamine cyanurate particles, binder polyacrylic acid (PAA) and conductive agent conductive carbon black are 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 is evenly coated on the surface of the positive electrode collector, dried, and vacuum-dehydrated to obtain a composite positive electrode collector. The positive electrode active slurry is coated on the composite positive electrode collector, dried, cold pressed 3 times, and cut into pieces to obtain a composite positive electrode sheet. The remaining preparation steps and conditions are the same as those in Example 1-1.

[0100] Example 1-17 to Example 1-19 The type of organic compound was changed, and the other steps and conditions were the same as those of Example 1-15.

[0101] Example 1-20 to Example 1-23 The thickness of the coating was changed, and the other steps and conditions were the same as those of Example 1-15.

[0102] Examples 1-24 The coatings prepared in Example 1-1 and Example 1-17 are coated on the two surfaces of the positive electrode active material layer, respectively. The specific steps are: first, the positive electrode spacer slurry is coated on the aluminum foil, cyanuric acid particles, binder polyacrylic acid adhesive (PAA) and conductive agent conductive carbon black are added to deionized water in a weight ratio of 90:5:5, and stirred evenly to form a positive electrode spacer slurry, and the positive electrode spacer slurry is evenly coated on the surface of the positive electrode current collector, dried, and then coated with the positive electrode active material, and then coated with the coating prepared in Example 1-1, so as to obtain a positive electrode sheet covered with a coating on both sides. The other steps and conditions are the same as those in Example 1-1.

[0103] Examples 1-25 The coatings prepared in Examples 1-2 and 1-17 are coated on the two surfaces of the positive electrode active material layer, respectively. The specific steps are: firstly, the positive electrode spacer slurry is coated on the aluminum foil, and the cyanuric acid particles, the binder polyacrylic acid adhesive (PAA) and the conductive agent conductive carbon black are added to the deionized water in a weight ratio of 90:5:5, and stirred evenly to form the positive electrode spacer slurry, and the positive electrode spacer slurry is evenly coated on the surface of the positive electrode current collector, dried, and then coated with the positive electrode active material, and then coated with the coating prepared in Example 1-2, so as to obtain a positive electrode sheet covered with a coating on both sides. The other steps and conditions are the same as those in Example 1-1.

[0104] Example 1-26 to Example 1-27 The type of binder was changed, and the other steps and conditions were the same as those of Example 1-4.

[0105] Examples 1-28 The type of binder was changed, and the other steps and conditions were the same as those of Example 1-18.

[0106] Comparative Example 1 There is no coating on the positive electrode plate, and other steps and conditions are the same as those in Example 1-1.

[0107] Comparative Example 2 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 a binder PVDF are added to an N-methylpyrrolidone (NMP) solution in a weight ratio of 95:5, and the mixture is stirred evenly to form a ceramic coating slurry. The coating slurry is evenly coated on the surface of the positive electrode active material layer, and the composite positive electrode sheet is obtained after drying and cutting.

[0108] Comparative Examples 3 to 5 The thickness of the coating was adjusted, and the other steps and conditions were the same as those of Example 1-6.

[0109] Comparative Example 6 A ceramic coating is coated on the surface of the positive electrode current collector. The preparation method of the ceramic coating is as follows: alumina powder particles and a binder acrylic acid PAA are added to a deionized water solution in a weight ratio of 95:5, and stirred evenly to form a ceramic coating slurry. The ceramic coating slurry is evenly coated on 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 coated on the composite positive electrode current collector, dried, and cut to obtain a composite positive electrode sheet.

[0110] Comparative Example 7 and Comparative Example 8 The thickness of the coating was adjusted, and the other steps and conditions were the same as those of Example 1-20.

[0111] Comparative Example 9 The ceramic layer of Comparative Example 2 and the ceramic coating of Comparative Example 6 were coated on both surfaces of the positive electrode active material layer. The other steps and conditions were the same as those of Comparative Example 2.

[0112] Example 2-1 to Example 2-7 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.

[0113] Example 2-8 to Example 2-13 The particle size Dv50 of the positive electrode active material was adjusted, and the other steps and conditions were the same as those in Example 1-2.

[0114] Example 2-14 to Example 2-19 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.

[0115] Example 2-20 to Example 2-24 The thickness of the positive electrode active material in the coating layer was adjusted, and the other steps and conditions were the same as those in Example 1-2.

[0116] Example 3-1 Apply the coating several times to obtain a composite positive electrode with a coating in the middle layer. Apply the positive electrode active slurry to the surface of the positive electrode collector, dry it to a thickness of 40um, and dry it to obtain a single-coated positive electrode sheet. Add cyanuric acid melamine ester particles and binder polyvinylidene fluoride (PVDF) to the NMP solution at a weight ratio of 95:5, stir evenly to form a coating slurry, apply the coating slurry evenly to the primary positive electrode sheet, dry it to obtain a secondary coated positive electrode sheet, and then apply the positive electrode active slurry to the secondary coated positive electrode sheet to obtain a composite 3-coated composite positive electrode sheet.

[0117] The other steps and conditions are the same as those in Example 1-1.

[0118] Example 3-2 to Example 3-4 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.

[0119] Embodiment 3-6 Melamine cyanurate particles and a 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.

[0120] The positive electrode active slurry is 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 40um on the surface of the composite positive electrode current collector. The above-mentioned melamine cyanurate particles, binder polyvinylidene fluoride (PVDF), and conductive agent carbon black are added to N-methylpyrrolidone (NMP) in a weight ratio of 90:7:3, stirred evenly to form a coating slurry, and the coating slurry is evenly applied to the surface of the first positive electrode active material layer, dried to obtain a first composite positive electrode sheet. The positive electrode active slurry is then applied to the coating of the first composite positive electrode sheet and dried to a thickness of 40um to obtain a second composite positive electrode sheet.

[0121] 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 plate, dried, and cut to obtain a three-layer coated positive electrode plate.

[0122] The other steps and conditions are the same as those in Example 1-1.

[0123] Example 3-5, Example 3-7 and Example 3-8 The type of organic compound in the coating layer is adjusted, or the thickness of the coating layer located within the positive electrode active material layer is changed. Other steps and conditions are the same as those of Example 3-6.

[0124] Performance test of positive electrode: (1) Test of nitrogen content in coating The coating was separated from the lithium-ion battery, washed with NMP three times, centrifuged to remove the electrolyte, glue and residual lithium salt, and dried. The quantitative nitrogen content in the coating was obtained using an elemental analyzer.

[0125] (2) Particle size Dv50 of organic compound and particle size Dv50 of positive electrode active material The coating and the positive electrode active material were separated from the lithium-ion battery, washed with NMP three times, centrifuged to remove the electrolyte, glue and residual lithium salt, and dried. The volume particle size distribution of the particles was measured using a laser particle size tester.

[0126] (3) Coating thickness and positive electrode active material layer thickness test The composite positive electrode sheet in the lithium-ion battery is disassembled into the structure of isolation membrane + composite positive electrode sheet + isolation membrane, 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.

[0127] (4) Peel force test between coating and positive electrode current collector After the lithium-ion battery was stored at 85°C for 5 h, 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 between the coating and the current collector, i.e., the peeling force, was tested using a 180° tensile test machine.

[0128] Performance test of lithium-ion battery: (1) High temperature cycle performance Place the lithium-ion battery in a 45°C constant temperature test box and let it stand for 30 minutes to allow the lithium-ion battery to reach a constant temperature. Charge it to 4.45V at a constant current of 0.5C, charge it to a current of 0.05C at a constant voltage, let it stand for 1 minute, and discharge it to 3.0V at a constant current of 0.5C, and record it as the initial discharge capacity C0. Repeat this step for 100 cycles, record the discharge capacity C1 after 100 cycles, and calculate the cycle capacity retention rate of the lithium-ion battery.

[0129] High temperature cycle capacity retention rate = C1 / C0×100%.

[0130] (2) High temperature storage expansion rate test At 25°C, the lithium-ion battery was left to stand for 5 minutes, then charged to 4.45V at a constant current rate of 0.5C, and charged to 0.05C at a constant voltage rate of 4.45V, and left to stand for 5 minutes, and 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 by the following formula: High temperature storage expansion rate = (D2-D1) / D1*100%.

[0131] (3) Thermal safety test 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 of 4.5V, and let it stand for 5 minutes. Then put the lithium-ion battery in a constant temperature box, and continue to heat it to a set temperature (such as 130°C) at a rate of 10°C / min, and maintain this temperature for 60 minutes. The lithium-ion battery passes this temperature if it does not explode or catch fire.

[0132] Take the same type of lithium-ion battery, increase the temperature of the thermostat by 1°C (131°C), maintain this temperature for 60 minutes, and the battery cell will pass the temperature if it does not explode or catch fire. Until the battery cell fails to pass the thermal safety test at this temperature, the thermal safety passing temperature at which the battery cell can pass is obtained.

[0133] (4) Mechanical safety testing 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 of 4.45V, and let it stand for 5 minutes. A 3mm diameter steel nail is inserted into the center of the lithium-ion battery at a speed of 30mm / s, maintained for 10 minutes, and then pulled out. The lithium-ion battery passes if it does not explode or catch fire.

[0134] (5) Impedance of lithium-ion batteries At 25°C, the lithium-ion battery was allowed to stand for 5 minutes, then charged to 4.45V at a constant current rate of 0.5C, and charged to 0.05C at a constant voltage rate of 4.45V, and allowed to stand for 5 minutes. The DC impedance of the lithium-ion battery (cell) in the fully charged state was measured.

[0135] In the present application, "I" surface and "II" surface 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 as I surface, and when the coating is located between the positive electrode plate and the isolation membrane, it is named as II surface. 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 isolation membrane, and they are named as I+II surfaces.

[0136] Table 1 Table 2 Table 3 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 isolation membrane, 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.

[0137] Combined with Table 3, in Examples 1-2 and 1-6 to 1-14, 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 and thermal safety pass temperature.

[0138] Table 4 Table 5 It can be seen from Table 4 and Table 5 above that, compared with Comparative Example 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.

[0139] From Table 4 and Table 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 under low cell impedance.

[0140] Table 6 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.

[0141] Table 7 Table 8 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 passing temperature and mechanical safety performance.

[0142] Table 9 Table 10 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, as well as good thermal safety pass temperature and mechanical safety performance.

[0143] Table 11 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.

[0144] Table 12 From the above Table 12, 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.

[0145] Table 13 From the above Table 13, 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 passing temperature and mechanical safety performance.

[0146] Table 14 Table 15 From Table 14 and Table 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.

[0147] Table 16 Table 17 From Tables 16 and 17 above, when the coating comprises three coatings, two of which are located on the two surfaces of the positive electrode active material layer and the other 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, as well as good thermal safety passing temperature and mechanical safety performance.

[0148] The above disclosure is only a preferred implementation mode of the present application, and certainly cannot be used to limit the present application. Therefore, equivalent changes made according to the present application are still within the scope covered by the present application.

Claims

1. A positive electrode sheet, 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 of the positive electrode active material layer, the coating comprises an organic compound, the organic compound comprises at least one functional group selected from cyano, isonitrile, oxazine and isocyanate, and the thickness of the coating is 0.3 μm to 3 μm.

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

3. The positive electrode sheet according to claim 1, characterized in that: 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, characterized in that: 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, characterized in that: The positive electrode plate includes two coating layers, one of which is located between the positive electrode current collector and the positive electrode active material layer, and the other of which is located on a 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, characterized in that: The coating layer 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 layer.

7. The positive electrode sheet according to claim 1, characterized in that: The positive electrode plate includes two coatings, 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, characterized in that: The positive electrode plate includes three coatings, one of which is located inside the positive electrode active material layer, and the other two coatings are respectively located on two surfaces of the positive electrode active material layer.

9. The positive electrode sheet according to claim 1, characterized in that: 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 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 9, 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 layer 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 9, 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 according to any one of claims 1 to 9, characterized in that: The coating also includes a binder, and the binder 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.

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, lithium iron manganese phosphate or lithium titanate.

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 as claimed in 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 as claimed in claim 16.

Images