Positive electrode sheet and battery

Abstract

The application discloses a positive plate and a battery, and relates to the technical field of secondary batteries. The positive plate comprises a positive current collector and a positive active material layer arranged on at least one side of the positive current collector. The positive active material layer comprises a first coating layer and a second coating layer arranged in sequence. The first coating layer is arranged on the surface of the positive current collector, and the second coating layer is arranged on the surface of the first coating layer away from the positive current collector. The problems of increased brittleness and degraded electrochemical performance of a conventional positive plate caused by high surface density in the prior art are solved.

Description

Technical Field

[0001] This invention relates to the field of secondary battery technology, and more specifically, to a positive electrode and a battery. Background Technology

[0002] Lithium-ion batteries are widely used in portable electronic devices, electric vehicles, and energy storage systems due to their advantages such as high power density, light weight, small size, and environmental friendliness. To improve battery energy density, current methods primarily focus on increasing the coating amount per unit area or volume of the positive electrode material. For example, increasing the thickness of the active material layer in the positive electrode sheet increases the areal density, thereby increasing the coating amount per unit area. However, as the thickness of the positive electrode sheet increases, it becomes prone to breakage during the rolling process and severe cracking occurs during the baking process, especially at high areal densities. Furthermore, with increasing positive electrode sheet thickness, Li... + The increased migration path not only raises ion transfer and diffusion resistance but also increases the internal resistance of the battery, severely impacting its cycle life. On the other hand, current methods primarily aim to increase the amount of cathode material coated per unit volume by increasing the compaction density of the cathode sheet. This can be achieved through methods such as grading large and small particles or strictly controlling the particle size distribution width. Larger particles contribute to higher compaction density, while smaller particles improve electrode performance. However, the presence of small particles increases the risk of side reactions between the cathode sheet and the electrolyte at high temperatures, directly leading to a decrease in battery cycle life. Furthermore, the preparation of high-density cathode materials often results in lower yield rates and increased material costs. Summary of the Invention

[0003] The main objective of this invention is to provide a positive electrode and a battery to solve the problems of increased brittleness and degraded electrochemical performance caused by the high areal density of traditional positive electrode in the prior art.

[0004] To achieve the above objectives, according to one aspect of the present invention, a positive electrode sheet is provided, the positive electrode sheet comprising a positive current collector and a positive active material layer disposed on at least one side of the positive current collector, the positive active material layer comprising a first coating layer and a second coating layer disposed sequentially, the first coating layer being disposed on the surface of the positive current collector, and the second coating layer being disposed on the surface of the first coating layer away from the positive current collector;

[0005] The first coating includes a first conductive agent and a first binder, and the second coating includes a second positive electrode material, a second conductive agent, and a second binder.

[0006] The mass content of the first conductive agent in the first coating is x, and the mass content of the first adhesive in the first coating is y, satisfying 10%≤x≤60% and 30%≤y≤70%; the mass content of the second conductive agent in the second coating is a, and the mass content of the second adhesive in the second coating is b, satisfying 0%≤a≤1.0% and 1.0%≤b≤2.0%.

[0007] Furthermore, the positive electrode active material layer also includes a third coating layer, which is disposed on the surface of the second coating layer away from the positive electrode current collector. The third coating layer includes a third positive electrode material, a third conductive agent, and a third binder. The mass content of the third conductive agent in the third coating layer is d, the mass content of the third binder in the third coating layer is e, and the mass content of the third positive electrode material in the third coating layer is f, satisfying: 0≤d≤0.8%, 0.1%≤e≤1%, and d+e+f=100%.

[0008] Furthermore, the thickness of the first coating is 0.2 μm to 10 μm; and / or,

[0009] The thickness of the second coating is 1μm~200μm; and / or,

[0010] The areal density of the first coating is 0.1 g / m³. 2 ~10g / m 2 ; and / or,

[0011] The surface density of the second coating is 1 g / m³. 2 ~260g / m 2 ; and / or,

[0012] The thickness of the third coating is 0.1 μm to 260 μm; and / or

[0013] The surface density of the third coating is 0.1 g / m³. 2 ~320g / m 2 ; and / or,

[0014] Furthermore, the areal density of the third coating is 0.1 to 10 times that of the second coating.

[0015] Furthermore, the softness of the first coating is 1 mN to 30 mN; and / or,

[0016] The second coating has a softness of 50mN~1400mN; and / or,

[0017] The softness of the third coating is 0.1 mN to 1400 mN; and / or,

[0018] The compaction density of the positive electrode is 2.5 g / cm³. 3 ~2.8g / cm 3 ; and / or,

[0019] The flexibility of the positive electrode sheet is 50mN~1400mN.

[0020] Furthermore, the porosity ε1 of the first coating is 20%~70%, the porosity ε2 of the second coating is 20%~40%, and the porosity ε3 of the third coating is 22%~32%. The electronic conductivity σ1 of the first coating, the electronic conductivity σ2 of the second coating, and the electronic conductivity σ3 of the third coating satisfy: σ1:σ2:σ3=(1-ε1) 1.5 : (1-ε2) 1.5 :(1-ε3) 1.5 .

[0021] Furthermore, the first coating also includes a first positive electrode material, the mass content of the first positive electrode material in the first coating is z, satisfying: 0≤z≤30%, x+y+z=100%, and the first positive electrode material includes at least one of lithium iron phosphate and lithium manganese iron phosphate;

[0022] The first conductive agent includes at least one of carbon black, graphite flakes, carbon nanotubes, and graphene; and / or,

[0023] The specific surface area of ​​the first conductive agent is 30 g / m². 2 ~1400g / m 2 ; and / or,

[0024] The first binder includes at least one of styrene-butadiene emulsion, polyacrylic acid, polymethyl methacrylate, polyimide, polyvinyl alcohol, polyacrylonitrile, polyvinylidene fluoride, polytetrafluoroethylene, polyamide-imide, and polyaniline.

[0025] Furthermore, the mass content of the second cathode material in the second coating is c, a+b+c=100%, and the second cathode material includes at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, lithium manganese oxide, and lithium-rich manganese-based materials.

[0026] The second conductive agent includes at least one of carbon black, graphite flakes, carbon nanotubes, and graphene; and / or,

[0027] The specific surface area of ​​the second conductive agent is 100 g / m². 2 ~1400g / m 2 ; and / or,

[0028] The second binder includes at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyimide, polyacrylic acid, and polymethyl methacrylate.

[0029] Furthermore, the third cathode material includes at least one of lithium iron phosphate, lithium manganese iron phosphate, ternary lithium nickel cobalt manganese oxide, lithium manganese oxide, and lithium-rich manganese-based materials.

[0030] The third conductive agent includes at least one of carbon black, graphite sheets, carbon nanotubes, and graphene;

[0031] The specific surface area of ​​the third conductive agent is 150 g / m². 2 ~1400g / m 2 ;

[0032] The third binder includes at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyimide, polyacrylic acid, and polymethyl methacrylate.

[0033] A second aspect of the present invention provides a battery comprising a positive electrode plate as described in the first aspect.

[0034] By applying the technical solution of this invention, controlling the mass content of the first binder and the first conductive agent in the first coating not only helps to improve the adhesion between the positive electrode active material layer and the positive electrode current collector, but also helps to improve the conductivity of the first coating. At the same time, by controlling the content of the second binder in the second coating, it helps to reduce the proportion of inactive materials, increase the compaction density of the second coating and the porosity of the second coating. Due to the reduction of the second binder, it helps to reduce the brittleness caused by the curing effect, helps to reduce the breakage of the positive electrode sheet, promotes the transport of lithium ions, and thus helps to improve the battery capacity and cycle performance. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of the structure of the positive electrode sheet in one embodiment of the present invention.

[0036] Figure 2 This is a schematic diagram of the positive electrode sheet in another embodiment of the present invention.

[0037] Figure 3 This is a schematic diagram of the positive electrode sheet in another embodiment of the present invention.

[0038] Figure 4 This is a schematic diagram of the structure of the positive electrode sheet in one embodiment of the present invention.

[0039] Explanation of reference numerals in the attached figures:

[0040] 1-Positive current collector; 2-Positive active material layer; 201-First coating; 202-Second coating; 203-Third coating. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0042] As described in the background section of this invention, conventional cathode sheets in the prior art suffer from increased brittleness and degraded electrochemical performance due to their high areal density. To address these problems, in a typical embodiment of this invention, such as... Figure 1 and Figure 2 As shown, a positive electrode sheet is provided, comprising a positive current collector 1 and a positive active material layer 2 disposed on at least one side of the positive current collector 1. The positive active material layer 2 comprises a first coating layer 201 and a second coating layer 202 sequentially stacked. The first coating layer 201 is disposed on the surface of the positive current collector 1, and the second coating layer 202 is disposed on the surface of the first coating layer 201 away from the positive current collector 1. The first coating layer 201 comprises a first conductive agent and a first binder, and the second coating layer 202 comprises a second positive electrode material, a second conductive agent, and a second binder. The mass content of the first conductive agent in the first coating layer is x, and the mass content of the first binder in the first coating layer is y, satisfying 10%≤x≤60% and 30%≤y≤70%. The mass content of the second conductive agent in the second coating layer is a, and the mass content of the second binder in the second coating layer is b, satisfying 0%≤a≤1.0% and 1.0%≤b≤2.0%.

[0043] In this invention, the positive electrode sheet includes a positive current collector 1 and a positive active material layer 2 disposed on at least one side of the positive current collector 1. Specifically, the positive electrode sheet has two opposing surfaces, and the positive active material layer 2 can be disposed on one or both surfaces; this invention does not impose further limitations. For example, the positive electrode sheet has two opposing first and second surfaces, and the positive active material layer 2 can be disposed on the first surface, the second surface, or both surfaces simultaneously.

[0044] The present invention does not specifically limit the type of positive electrode current collector 1, as long as it is conductive and will not cause adverse chemical changes in the battery. For example, it can be aluminum foil; or aluminum foil that has been surface treated with one of carbon, nickel, titanium, silver, etc.

[0045] The positive electrode active material layer 2 includes a first coating layer 201 and a second coating layer 202 stacked sequentially. The first coating layer 201 includes a first conductive agent and a first binder. The first coating layer 201 is bonded to the positive electrode current collector 1. The first coating layer 201 contains a high content of the first conductive agent and the first binder, which is beneficial to forming a continuous and dense first coating layer 201, so that the first coating layer 201 has high adhesion, low porosity and strong interfacial bonding. By controlling the mass content of the first conductive agent in the first coating 201 to be 10%~60% and the mass content of the first binder in the first coating 201 to be 30%~70%, it helps to enhance the bonding force between the positive electrode active material layer 2 and the positive electrode current collector 1. Even under high compaction conditions, the positive electrode active material layer 2 can be stably attached to the positive electrode current collector 1, reducing the coating peeling problem caused by high compaction, thereby improving the structural stability and service life of the battery. Secondly, the high mass content of the first conductive agent in the first coating 201 is beneficial to provide good conductivity and promote the effective transfer of charge inside the positive electrode sheet, thereby helping to improve the electrochemical reaction rate and performance of the battery under high load conditions. In addition, by controlling the mass content of the first binder and the first conductive agent, it is beneficial to improve the conductivity of the first coating, enabling the first coating 201 to act as a stress buffer, effectively absorbing and dispersing the pressure generated by the second coating 202 during processing (such as rolling), reducing stress concentration inside the positive electrode sheet, and significantly reducing the probability of crack formation and propagation, thereby improving the mechanical strength and overall performance of the positive electrode sheet.

[0046] The second coating 202 is disposed on the side of the first coating 201 away from the positive electrode current collector 1, and includes a second positive electrode material and a second binder. The mass content of the second binder in the second coating 202 is ≤2%. Compared with the first coating 201, the lower proportion of binder in the second coating 202 helps to reduce the proportion of inactive materials, maximize the loading of the second positive electrode material, thereby helping to improve the areal density of the positive electrode sheet and the energy density of the battery, and thus helping to improve the battery capacity. By controlling the mass content of the second binder in the second coating 202, it also helps to reduce material costs and effectively reduce the problems of increased ion transport paths and decreased electrochemical performance caused by excessive binder, which helps to optimize Li + The migration path is improved, reducing the internal resistance of the battery and thus helping to improve the cycle performance of the battery. In addition, compared with traditional single-layer coated positive electrode sheets, the positive electrode sheet of the present invention improves the areal density while helping to improve the mechanical strength and processing performance of the positive electrode sheet. Especially during high-pressure rolling, it helps to reduce electrode sheet breakage and improve processing yield.

[0047] In traditional cathode plates, a high binder content is often used to ensure the bonding between the positive electrode active material and the positive electrode current collector 1. However, an excessively high binder ratio sacrifices porosity and hinders the bonding of Li.+ The migration path increases the battery's internal resistance, leading to electrochemical performance degradation, especially under high power and rapid charge / discharge conditions. This invention, by controlling the mass content of the first binder and the first conductive agent in the first coating 201, not only helps improve the adhesion between the positive electrode active material layer 2 and the positive electrode current collector 1, but also improves the conductivity of the first coating 201. Simultaneously, by controlling the content of the second binder in the second coating 202, it helps reduce the proportion of inactive materials, increase compaction density and porosity. The reduction in the second binder helps reduce the increased brittleness caused by the curing effect, helps reduce the breakage of the positive electrode sheet, and promotes lithium-ion transport, thereby helping to improve the battery's capacity and cycle performance.

[0048] Specifically, the mass content of the first conductive agent in the first coating 201 can be in the range of 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, 60%, or any two of these; and the mass content of the first adhesive in the first coating 201 can be in the range of 30%, 35%, 40%, 45%, 50%, 55%, 60%, 70%, or any two of these.

[0049] The second coating 202 also includes a second conductive agent. The mass content of the second conductive agent in the second coating 202 is 'a', the mass content of the second binder in the second coating 202 is 'b', and the mass content of the second positive electrode material in the second coating 202 is 'c', satisfying: 0 ≤ a ≤ 1%, 1% ≤ b ≤ 2%, and a + b + c = 100%. Specifically, when a = 0, it means that the second coating 202 does not include the second conductive agent; when 0 < a ≤ 1%, it means that the mass content of the second conductive agent in the second coating 202 is > 0 and ≤ 1%. By controlling the mass content of the second conductive agent in the second coating 202 to be > 0 and ≤ 1%, it helps to improve the electronic conduction network inside the second coating 202, while minimizing the influence of the second conductive agent on the porosity of the second coating 202, which helps to further promote the Li... + The efficient migration of Li. When 1%≤b≤2%, it means that the mass content of the second binder in the second coating 202 is ≥1% and ≤2%, which further reduces the proportion of inactive materials in the second coating 202, helps to further increase the compaction density of the second coating 202, thereby further improving the energy density of the positive electrode. At the same time, it helps to reduce the coating hardening caused by excessive binder, so that the microstructure of the second coating 202 retains a moderate porosity, which is not only beneficial to promoting Li +The rapid migration of these materials can also absorb and disperse stress during processing, reducing crack formation and contributing to further improvements in the flexibility and processing performance of the cathode sheet. By controlling the mass content of the second conductive agent and the second binder to meet the above requirements, with the remainder being the second cathode material, it helps to increase the loading of active material and further improve the battery capacity.

[0050] Specifically, the mass content of the second conductive agent in the second coating 202 can be in the range of 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or any two of these. The mass content of the second adhesive in the second coating 202 can be in the range of 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2%, or any two of these.

[0051] In some embodiments, the first coating 201 further includes a first positive electrode material, the mass content of which is z, satisfying: 0 ≤ z ≤ 30%, x + y + z = 100%. Specifically, when z = 0, it means that the first coating 201 does not include the first positive electrode material; when 0 < z ≤ 30%, it means that the mass content of the first positive electrode material in the first coating 201 is > 0 and ≤ 30%. By controlling the mass content of the first positive electrode material in the first coating 201 to be > 0 and ≤ 30%, it helps to further improve the areal density of the positive electrode sheet and increase the energy output of the battery. In addition, by introducing the positive electrode material into the first coating 201 to form a multilayer structure with the second coating 202, it not only helps to uniformly disperse stress but also helps to form gradient porosity and conductivity, optimizing Li + The migration path helps to further reduce the internal impedance of the battery and improve the overall energy efficiency.

[0052] Specifically, the mass content of the first positive electrode material in the first coating 201 can be 0.01%, 0.1%, 1%, 3%, 5%, 10%, 15%, 20%, 25%, 30%, or any combination thereof.

[0053] like Figure 3 and Figure 4 As shown, in some embodiments, the positive electrode active material layer 2 further includes a third coating layer 203, which is disposed on the surface of the second coating layer 202 away from the first coating layer 201. The third coating layer 203 includes a third positive electrode material, a third conductive agent, and a third binder. The mass content of the third conductive agent in the third coating layer 203 is d, the mass content of the third binder in the third coating layer 203 is e, and the mass content of the third positive electrode material in the third coating layer 203 is f, satisfying: 0≤d≤0.8%, 0.1%≤e≤1%, and d+e+f=100%.

[0054] Specifically, the positive electrode active material layer 2 includes a first coating 201, a second coating 202, and a third coating 203 stacked sequentially. The first coating 201 is disposed on the surface of the positive electrode current collector 1, the second coating 202 is disposed on the surface of the first coating 201 away from the positive electrode current collector 1, and the third coating 203 is disposed on the surface of the second coating 202 away from the positive electrode current collector 1.

[0055] When d=0, it means that the third coating 203 does not contain a third conductive agent. When 0<d≤0.8%, it means that the mass content of the third conductive agent in the third coating 203 is >0 and ≤0.8%, which helps to reduce the rigid skeleton formed by the third conductive agent. When 0.1%≤e≤1%, it means that the mass content of the third binder in the third coating 203 is 0.1%~1%. The content of the third binder in the third coating 203 is extremely low, which helps to reduce the coating hardening caused by excessive binder, resulting in more pores in the microstructure of the third coating 203, providing space for physical deformation. In the manufacturing process of the positive electrode sheet, rolling is used to increase the compaction density of the positive electrode sheet. However, excessive stress will lead to increased brittleness of the positive electrode sheet, and even fracture. In this invention, the third coating 203 is the outermost layer of the positive electrode sheet, directly bearing the contact pressure of the rolling die. The third coating 203 has low hardness and good elasticity, which helps to absorb and disperse stress, reduce cracks or fractures in the positive electrode sheet caused by excessive pressure concentration, thereby helping to improve the structural integrity of the positive electrode sheet and improve the manufacturing yield. Furthermore, the low hardness and elasticity of the third coating 203 are beneficial for Li + Providing a smoother migration path helps reduce the electrochemical impedance inside the battery, thereby further improving the battery's efficiency and cycle life.

[0056] Specifically, the mass content of the third conductive agent in the third coating 203 can be within the range of 0.01%, 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, or any two of these. The mass content of the third binder in the third coating 203 can be within the range of 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, or any two of these. Further, the mass content of the third positive electrode material in the third coating 203 can be within the range of 98.2%, 98.5%, 98.8%, 99%, 99.1%, 99.2%, 99.5%, 99.8%, 99.9%, or any two of these.

[0057] This invention does not limit the specific types of conductive agents and binders. Conductive agents include, but are not limited to, carbon-based materials. The binder is used to bond the positive electrode material particles to facilitate the formation of a film layer. In some embodiments, the first conductive agent includes at least one of carbon black, graphite flakes, carbon nanotubes, and graphene; and / or, the specific surface area of ​​the first conductive agent is 30 g / m². 2 ~1400g / m 2 ; and / or, the first binder comprises at least one of styrene-butadiene emulsion, polyacrylic acid, polymethyl methacrylate, polyimide, polyvinyl alcohol, polyacrylonitrile, polyvinylidene fluoride, polytetrafluoroethylene, polyamide-imide, and polyaniline; and / or, the second binder comprises at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyimide, polyacrylic acid, and polymethyl methacrylate; and / or, the second conductive agent comprises at least one of carbon black, graphite flakes, carbon nanotubes, and graphene; and / or, the specific surface area of ​​the second conductive agent is 100 g / m². 2 ~1400g / m 2 ; and / or, the third conductive agent includes at least one of carbon black, graphite flakes, carbon nanotubes, and graphene; and / or, the specific surface area of ​​the third conductive agent is 150 g / m². 2 ~1400g / m 2 ; and / or, the third binder includes at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyimide, polyacrylic acid, and polymethyl methacrylate.

[0058] The cathode material includes compounds that can reversibly insert and deintercalate lithium ions. In some embodiments, the first cathode material, the second cathode material, and the third cathode material each independently include, but are not limited to, at least one of lithium iron phosphate, lithium manganese iron phosphate, ternary lithium nickel cobalt manganese oxide, lithium manganese oxide, and lithium-rich manganese-based materials.

[0059] In some embodiments, the thickness of the first coating 201 is 0.2 μm to 10 μm; and / or, the thickness of the second coating 202 is 1 μm to 200 μm; and / or, the thickness of the third coating 203 is 0.1 μm to 260 μm. By controlling the thicknesses of the first coating 201, the second coating 202, and the third coating 203 within the above ranges, the functions of the first coating 201, the second coating 202, and the third coating 203 are maximized, which helps to further improve the energy density and manufacturing yield of the positive electrode.

[0060] In some embodiments, the areal density of the third coating is 0.1 to 10 times that of the second coating, which is beneficial to further improve the energy density of the battery.

[0061] In some embodiments, the areal density of the first coating 201 is 0.1 g / m³. 2 ~10g / m2 ; and / or, the areal density of the second coating 202 is 1 g / m³. 2 ~260g / m 2 ; and / or, the areal density of the third coating 203 is 0.1~320 g / m³. 2 By controlling the areal density of the first coating 201, the second coating 202, and the third coating 203 within the aforementioned range, it is beneficial to promote the uniform distribution of active materials in the positive electrode sheet, which helps to increase the compaction density of the positive electrode sheet and thus further improve the energy density of the battery. In some embodiments, the compaction density of the positive electrode sheet is 2.5 g / cm³. 3 ~2.8g / cm 3 For example, 2.5g / cm 3 2.55g / cm 3 2.6g / cm 3 2.65g / cm 3 2.7g / cm 3 2.75g / cm 3 2.8g / cm 3 or a range consisting of any two of them.

[0062] In some embodiments, the porosity ε1 of the first coating 201 is 20%~70%, the porosity ε2 of the second coating 202 is 20%~40%, and the porosity ε3 of the third coating 203 is 22%~32%. The electronic conductivity σ1 of the first coating 201, the electronic conductivity σ2 of the second coating 202, and the electronic conductivity σ3 of the third coating 203 satisfy: σ1 : σ2 : σ3 = (1 - ε1) 1.5 : (1-ε2) 1.5 :(1-ε3) 1.5 By controlling the porosity of the first coating 201, the second coating 202, and the third coating 203 to meet the above requirements, and ensuring that the electronic conductivity σ1, σ2, and σ3 of the first coating 201, the second coating 202, and the third coating 203 satisfy the above relationship, it helps to further optimize the synergistic effect between the coatings, effectively promote the thermal management and electrolyte wetting balance inside the battery, and thus further improve the overall stability and cycle life of the battery.

[0063] Specifically, the porosity ε1 of the first coating 201 can be in the range of 20%, 30%, 40%, 50%, 60%, 70%, or any two of these. The porosity ε2 of the second coating 202 can be in the range of 20%, 25%, 30%, 35%, 40%, or any two of these. The porosity ε3 of the third coating 203 can be in the range of 22%, 25%, 28%, 30%, 32%, or any two of these.

[0064] In some embodiments, the flexibility of the first coating 201 is 1 mN to 30 mN; and / or, the flexibility of the second coating 202 is 50 mN to 1400 mN; and / or, the flexibility of the third coating 203 is 0.1 to 1400 mN. The flexibility is tested according to GB / T 8942-2016, using a microcomputer flexibility tester, model: PN-RT1000F. Controlling the flexibility of the first coating 201 within a lower range helps enhance the adhesion between the first coating 201 and the positive electrode current collector 1, reducing the risk of detachment in subsequent processes. Controlling the flexibility of the second coating 202 within the above range helps to improve conductivity while maintaining sufficient mechanical flexibility to adapt to deformation during the rolling process, reducing cracks or breakage. Controlling the flexibility of the third coating 203 within the above range effectively alleviates the stress distribution of the third coating 203 under higher pressure, reducing coating structure damage and further improving the structural stability of the positive electrode sheet.

[0065] In some embodiments, the flexibility of the positive electrode sheet is 50 mN to 1400 mN. By controlling the flexibility of the positive electrode sheet within the above range, it is helpful to improve the processing performance of the positive electrode sheet under high compaction density, thereby further improving the energy density and cycle life of the battery.

[0066] In some embodiments, the method for preparing the positive electrode sheet of the present invention includes the following steps: physically mixing a first positive electrode material, a first conductive agent, and a first binder in proportion, adding a first solvent for high-speed dispersion, and stirring to form a first paste mixture; or physically mixing a first conductive agent and a first binder in proportion, adding a first solvent for high-speed dispersion, and stirring to form a first paste mixture; coating the first paste mixture onto the positive electrode current collector 1 using a gravure coating machine or a transfer coating machine, or co-extruding it using a multi-die extruder, and drying it to form a first coating 201; physically mixing a second positive electrode material, a second conductive agent, and a second binder in proportion, adding a second solvent for high-speed dispersion, and stirring to form a second paste mixture; coating the second paste mixture onto the surface of the first coating 201 using a gravure coating machine or a transfer coating machine, or co-extruding it using a multi-die extruder, and drying it to form a second coating 202; and obtaining the positive electrode sheet by roll pressing.

[0067] In other embodiments, the preparation method of the positive electrode sheet of the present invention includes the following steps: physically mixing a first positive electrode material, a first conductive agent, and a first binder in proportion, adding a first solvent for high-speed dispersion, and stirring to form a first paste mixture; or physically mixing a first conductive agent and a first binder in proportion, adding a first solvent for high-speed dispersion, and stirring to form a first paste mixture; coating the first paste mixture onto the positive electrode current collector 1 using a gravure coating machine or a transfer coating machine, or co-extruding it using a multi-die extruder, and forming a first coating 201 after drying; physically mixing a second positive electrode material, a second conductive agent, and a second binder in proportion. A second solvent is added and dispersed at high speed to form a second paste mixture. The second paste mixture is coated onto the surface of the first coating 201 using a gravure coating machine or a transfer coating machine, or co-extruded using a multi-die extruder, and dried to form the second coating 202. A third positive electrode material, a third conductive agent, and a third binder are physically mixed in proportion, and a third solvent is added and dispersed at high speed to form a third paste mixture. The third paste mixture is coated onto the surface of the second coating 202 using a gravure coating machine or a transfer coating machine, or co-extruded using a multi-die extruder, and dried to form the third coating 203. A positive electrode sheet is obtained by roll pressing.

[0068] In the above embodiments, the first solvent, the second solvent, and the third solvent can be at least one of water, NMP (N-methylpyrrolidone), DMF (dimethylformamide), and DMSO (dimethyl sulfoxide). The solid content of the paste mixture can be 5% to 75%, and the viscosity can be 5 cp to 20000 cp.

[0069] A second aspect of the present invention provides a battery comprising the positive electrode of the first aspect.

[0070] Thanks to the inclusion of the aforementioned high-performance cathode, this secondary battery combines high capacity with excellent cycle performance.

[0071] Specifically, the secondary battery includes a casing, an electrode assembly, and an electrolyte. Both the electrode assembly and the electrolyte are located inside the casing. The casing can be a packaging bag encapsulated with an encapsulation film (such as an aluminum-plastic film), for example, a pouch battery. In other embodiments, it can also be a steel-cased battery, an aluminum-cased battery, etc.

[0072] The electrode assembly includes a positive electrode, a negative electrode, and a separator, with the separator disposed between the positive and negative electrode. The negative electrode includes a negative current collector and a layer of negative active material disposed on at least one surface of the negative current collector. The negative current collector can be at least one of copper foil, nickel foil, stainless steel foil, titanium foil, or carbon-based current collector. The negative active material layer includes a negative electrode material, a conductive material, and a binder material. The separator includes a membrane layer with a porous structure, and its material includes, but is not limited to, at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide, or aramid. The electrolyte acts as a conductor of active ions between the positive and negative electrode. In some embodiments, the electrolyte includes a lithium salt and an organic solvent. The lithium salt includes, but is not limited to, at least one of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), and lithium perchlorate (LiClO4). Organic solvents include carbonate compounds, such as at least one of diethyl carbonate (DEC), dimethyl carbonate (DMC), methyl ethyl carbonate (MEC), ethylene carbonate (EC), and propylene carbonate (PC).

[0073] The present application will be further described in detail below with reference to specific embodiments, which should not be construed as limiting the scope of protection claimed in the present application.

[0074] Example 1

[0075] The preparation of the positive electrode in this embodiment includes the following steps:

[0076] S1, add conductive carbon black (BET 70m) in a mass ratio of 60%:40%. 2 Mix (g) and polyacrylic acid PAA, add water and disperse at high speed, and stir to form a first paste mixture with a solid content of 15%;

[0077] Lithium iron phosphate (LFP) and conductive carbon black (BET 200m) were mixed in a mass ratio of 97%:1.0%:2.0%. 2 / g), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP, HFP copolymerization ratio is 10%), water is added for high-speed dispersion, and stirred into a second paste mixture with a solid content of 65%;

[0078] S2, the first paste mixture is transferred onto aluminum foil using a gravure printing process, and dried to form a first coating; the second paste mixture is then transferred onto the first coating, dried to form a second coating, and rolled to achieve a compaction density of 2.5 g / cm³. 3 The positive electrode has a first coating thickness of 1 μm, a second coating thickness of 210 μm, and a first coating surface density of 1 g / m³. 2 The areal density of the second coating is 260 g / m³.2 .

[0079] Example 2

[0080] The preparation of the positive electrode in this embodiment includes the following steps:

[0081] S1, mix conductive carbon black (BET 140m) in a mass ratio of 30%:20%:50% (BET 140m). 2 / g), styrene-butadiene emulsion (SBR) and polyacrylic acid (PAA) are mixed, water is added and dispersed at high speed, and stirred to form a first paste mixture with a solid content of 18%;

[0082] Lithium iron phosphate (LFP) and conductive carbon black (BET 200m) were mixed in a mass ratio of 97.4%:1.0%:1.6%. 2 / g), polyvinylidene fluoride (PVDF) is mixed, water is added and dispersed at high speed, and stirred to form a second paste mixture with a solid content of 67%;

[0083] Lithium iron phosphate (LFP) and conductive carbon black (BET 200m) were mixed in a mass ratio of 98.5%:0.5%:1.0%. 2 Mix / g), polyvinylidene fluoride (PVDF), add water and disperse at high speed, and stir to form a third paste-like mixture with a solid content of 70%;

[0084] S2, the first paste mixture is transferred onto aluminum foil using a gravure printing process, and dried to form a first coating; the second paste mixture is transferred onto the first coating, and dried to form a second coating; the third paste mixture is transferred onto the second coating, and dried to form a third coating. The final compaction density is 2.6 g / cm³. 3 The positive electrode has a first coating thickness of 2 μm, a second coating thickness of 110 μm, a third coating thickness of 90 μm, and a first coating surface density of 1.5 g / m³. 2 The areal density of the second coating is 140 g / m³. 2 The areal density of the third coating is 120 g / m³. 2 .

[0085] Example 3

[0086] The preparation of the positive electrode in this embodiment includes the following steps:

[0087] S1, mix conductive carbon black (BET 140m) in a mass ratio of 40%:20%:40% (BET 140m). 2 / g), styrene-butadiene emulsion (SBR) and polyacrylic acid (PAA) are mixed, water is added and dispersed at high speed, and stirred to form a first paste mixture with a solid content of 18%;

[0088] Lithium iron phosphate (LFP) and conductive carbon black (BET 200m) were mixed in a mass ratio of 97.8%:0.8%:1.4%. 2 / g), polyvinylidene fluoride (PVDF) is mixed, water is added and dispersed at high speed, and stirred to form a second paste mixture with a solid content of 67%;

[0089] Lithium iron phosphate (LFP) and conductive carbon black (BET 200m) were mixed in a mass ratio of 98.6%:0.6%:0.8%. 2 Mix / g), polyvinylidene fluoride (PVDF), add water and disperse at high speed, and stir to form a third paste-like mixture with a solid content of 70%;

[0090] S2, the first paste mixture is transferred onto aluminum foil using a gravure printing process, and dried to form a first coating; the second paste mixture is transferred onto the first coating, and dried to form a second coating; the third paste mixture is transferred onto the second coating, and dried to form a third coating. The final compaction density is 2.65 g / cm³. 3 The positive electrode has a first coating thickness of 2 μm, a second coating thickness of 90 μm, a third coating thickness of 110 μm, and a first coating surface density of 1.5 g / m³. 2 The areal density of the second coating is 120 g / m³. 2 The areal density of the third coating is 140 g / m³. 2 .

[0091] Example 4

[0092] The preparation of the positive electrode in this embodiment includes the following steps:

[0093] S1, add conductive carbon black (BET 70m) in a mass ratio of 60%:40%. 2 Mix (g) and polyacrylic acid PAA, add water and disperse at high speed, and stir to form a first paste mixture with a solid content of 15%;

[0094] Lithium iron phosphate (LFP) and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 98%:2%, and water was added for high-speed dispersion and stirring to form a second paste-like mixture with a solid content of 60%.

[0095] Lithium iron phosphate (LFP) and polyvinylidene fluoride (PVDF) were mixed in a mass ratio of 99%:1%, and water was added for high-speed dispersion and stirring to form a third paste-like mixture with a solid content of 70%.

[0096] S2, the first paste mixture is transferred onto aluminum foil using a gravure printing process, and dried to form a first coating; the second paste mixture is transferred onto the first coating, and dried to form a second coating; the third paste mixture is transferred onto the second coating, and dried to form a third coating. The final compaction density is 2.55 g / cm³. 3 The positive electrode has a first coating thickness of 0.5 μm, a second coating thickness of 100 μm, a third coating thickness of 100 μm, and a first coating surface density of 0.5 g / m³. 2 The areal density of the second coating is 130 g / m³. 2 The areal density of the third coating is 130 g / m³. 2 .

[0097] Example 5

[0098] The preparation of the positive electrode in this embodiment includes the following steps:

[0099] S1, mix conductive carbon black (BET 70m) in a 50%:50% mass ratio. 2 Mix (g) and polyacrylic acid PAA, add water and disperse at high speed, and stir to form a first paste mixture with a solid content of 15%;

[0100] Lithium iron phosphate (LFP) and conductive carbon black (BET 200m) were mixed in a mass ratio of 98.4%:0.5% and 1.1%. 2 Mix / g) and polyvinylidene fluoride (PVDF), add water and disperse at high speed, and stir to form a second paste mixture with a solid content of 60%;

[0101] Lithium iron phosphate (LFP) and conductive carbon black (BET 200m) were mixed in a mass ratio of 99.4%:0.5%:0.1%. 2 Mix / g), polyvinylidene fluoride (PVDF), add water and disperse at high speed, and stir to form a third paste-like mixture with a solid content of 70%;

[0102] S2, the first paste mixture is transferred onto aluminum foil using a gravure printing process, and dried to form a first coating; the second paste mixture is transferred onto the first coating, and dried to form a second coating; the third paste mixture is transferred onto the second coating, and dried to form a third coating. The final compaction density is 2.70 g / cm³. 3 The positive electrode has a first coating thickness of 1 μm, a second coating thickness of 140 μm, a third coating thickness of 60 μm, and a first coating surface density of 1.5 g / m³. 2 The areal density of the second coating is 180 g / m³. 2 The areal density of the third coating is 80 g / m³.2 .

[0103] Example 6

[0104] The preparation of the positive electrode in this embodiment includes the following steps:

[0105] S1, lithium iron phosphate (LFP) and conductive carbon black (BET 140m) are mixed in a mass ratio of 20%:40%:10%:30%. 2 / g), styrene-butadiene emulsion (SBR) and polyacrylic acid (PAA) are mixed, water is added and dispersed at high speed, and stirred to form a first paste mixture with a solid content of 30%;

[0106] Lithium iron phosphate (LFP) and conductive carbon black (BET 200m) were mixed in a mass ratio of 97%:1%:2%. 2 / g), polyvinylidene fluoride (PVDF) is mixed, water is added and dispersed at high speed, and stirred to form a second paste mixture with a solid content of 67%;

[0107] Lithium iron phosphate (LFP) and conductive carbon black (BET 200m) were mixed in a mass ratio of 98.2%:0.8%:1.0%. 2 Mix / g), polyvinylidene fluoride (PVDF), add water and disperse at high speed, and stir to form a third paste-like mixture with a solid content of 70%;

[0108] S2, the first paste mixture is transferred onto aluminum foil using a gravure printing process, and dried to form a first coating; the second paste mixture is transferred onto the first coating, and dried to form a second coating; the third paste mixture is transferred onto the second coating, and dried to form a third coating. The final compaction density is 2.60 g / cm³. 3 The positive electrode has a first coating thickness of 1.5 μm, a second coating thickness of 80 μm, a third coating thickness of 120 μm, and a first coating surface density of 0.7 g / m³. 2 The areal density of the second coating is 100 g / m³. 2 The areal density of the third coating is 160 g / m³. 2 .

[0109] Example 7

[0110] The preparation of the positive electrode in this embodiment includes the following steps:

[0111] S1, lithium iron phosphate (LFP) and conductive carbon black (BET 70m) are mixed in a mass ratio of 10%:50%:40%. 2 Mix (g) and polyacrylic acid PAA, add water and disperse at high speed, and stir to form a first paste mixture with a solid content of 30%;

[0112] Lithium iron phosphate (LFP) and conductive carbon black (BET 200m) were mixed in a mass ratio of 97%:1%:2%. 2 Mix / g) and polyvinylidene fluoride (PVDF), add water and disperse at high speed, and stir to form a second paste mixture with a solid content of 60%;

[0113] Lithium iron phosphate (LFP) and conductive carbon black (BET 200m) were mixed in a mass ratio of 98.2%:0.8%:1%. 2 Mix / g), polyvinylidene fluoride (PVDF), add water and disperse at high speed, and stir to form a third paste-like mixture with a solid content of 70%;

[0114] S2, the first paste mixture is transferred onto aluminum foil using a gravure printing process, and dried to form a first coating; the second paste mixture is transferred onto the first coating, and dried to form a second coating; the third paste mixture is transferred onto the second coating, and dried to form a third coating. The final compaction density is 2.60 g / cm³. 3 The positive electrode has a first coating thickness of 0.5 μm, a second coating thickness of 150 μm, a third coating thickness of 50 μm, and a first coating surface density of 0.5 g / m³. 2 The areal density of the second coating is 200 g / m³. 2 The areal density of the third coating is 60 g / m³. 2 .

[0115] Example 8

[0116] The preparation of the positive electrode in this embodiment includes the following steps:

[0117] S1, lithium iron phosphate (LFP) and conductive carbon black (BET 70m) are mixed in a mass ratio of 30%:10%:60%. 2 (g) and polyacrylic acid PAA are mixed, water is added and dispersed at high speed, and stirred to form a first paste mixture with a solid content of 40%;

[0118] Lithium iron phosphate (LFP) and conductive carbon black (BET 200m) were mixed in a mass ratio of 97%:1%:2%. 2 Mix / g) and polyvinylidene fluoride (PVDF), add water and disperse at high speed, and stir to form a second paste mixture with a solid content of 60%;

[0119] Lithium iron phosphate (LFP) and conductive carbon black (BET 200m) were mixed in a mass ratio of 98.2%:0.8%:1%. 2 Mix / g), polyvinylidene fluoride (PVDF), add water and disperse at high speed, and stir to form a third paste-like mixture with a solid content of 70%;

[0120] S2, the first paste mixture is transferred onto aluminum foil using a gravure printing process, and dried to form a first coating; the second paste mixture is transferred onto the first coating, and dried to form a second coating; the third paste mixture is transferred onto the second coating, and dried to form a third coating. The final compaction density is 2.60 g / cm³. 3 The positive electrode has a first coating thickness of 3 μm, a second coating thickness of 100 μm, a third coating thickness of 100 μm, and a first coating surface density of 1 g / m³. 2 The areal density of the second coating is 130 g / m³. 2 The areal density of the third coating is 130 g / m³. 2 .

[0121] Example 9

[0122] S1, mix lithium manganese iron phosphate (LMFP) and conductive carbon black (BET 200m) in a mass ratio of 10%:45%:45%. 2 Mix (g) and polyacrylic acid PAA, add water and disperse at high speed, and stir to form a first paste mixture with a solid content of 10%;

[0123] A mixture of ternary nickel-cobalt-manganese lithium oxide (NCM) and conductive carbon black (BET 800m) in a mass ratio of 98%:1%:1% was prepared. 2 Mix / g) and polyvinylidene fluoride (PVDF), add water and disperse at high speed, and stir to form a second paste mixture with a solid content of 75%;

[0124] Lithium iron phosphate (LFP) and conductive carbon black (BET 200m) were mixed in a mass ratio of 99.8%:0.2%:0.6%. 2 Mix / g), polyvinylidene fluoride (PVDF-HFP), add water and disperse at high speed, and stir to form a third paste-like mixture with a solid content of 72%;

[0125] S2, the first paste mixture is transferred onto aluminum foil using a gravure printing process, and dried to form a first coating; the second paste mixture is transferred onto the first coating, and dried to form a second coating; the third paste mixture is transferred onto the second coating, and dried to form a third coating. The final compaction density is 2.75 g / cm³. 3 The positive electrode has a first coating thickness of 5 μm, a second coating thickness of 140 μm, a third coating thickness of 150 μm, and a first coating surface density of 2.5 g / m³. 2 The areal density of the second coating is 230 g / m³. 2 The areal density of the third coating is 200 g / m³. 2 .

[0126] Comparative Example 1

[0127] The preparation of the positive electrode in this embodiment includes the following steps:

[0128] S1, lithium iron phosphate (LFP) and conductive carbon black (BET 200m) are mixed in a mass ratio of 96%:2.0%:2.0%. 2 / g), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP, HFP copolymerization ratio is 10%), water is added and dispersed at high speed, and stirred into a first paste mixture with a solid content of 65%;

[0129] Lithium iron phosphate (LFP) and conductive carbon black (BET 200m) were mixed in a mass ratio of 97%:1.0%:2.0%. 2 / g), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP, HFP copolymerization ratio is 10%), water is added for high-speed dispersion, and stirred into a second paste mixture with a solid content of 65%;

[0130] S2, the first paste mixture is transferred onto aluminum foil using a gravure printing process, and dried to form a first coating; the second paste mixture is then transferred onto the first coating, dried to form a second coating, and rolled to achieve a compaction density of 2.6 g / cm³. 3 The positive electrode has a first coating thickness of 20 μm, a second coating thickness of 145 μm, and a first coating surface density of 30 g / m³. 2 The areal density of the second coating is 190 g / m³. 2 .

[0131] Comparative Example 2

[0132] The preparation of the positive electrode in this embodiment includes the following steps:

[0133] S1, lithium iron phosphate (LFP) and conductive carbon black (BET 200m) are mixed in a mass ratio of 96%:2.0%:2.0%. 2 / g), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP, HFP copolymerization ratio is 10%), water is added and dispersed at high speed, and stirred into a first paste mixture with a solid content of 65%;

[0134] Lithium iron phosphate (LFP) and conductive carbon black (BET 200m) were mixed in a mass ratio of 97.4%:1.0%:1.6%. 2 / g), polyvinylidene fluoride (PVDF) is mixed, water is added and dispersed at high speed, and stirred to form a second paste mixture with a solid content of 67%;

[0135] Lithium iron phosphate (LFP) and conductive carbon black (BET 200m) were mixed in a mass ratio of 98.5%:0.5%:1.0%. 2 Mix / g), polyvinylidene fluoride (PVDF), add water and disperse at high speed, and stir to form a third paste-like mixture with a solid content of 70%;

[0136] S2, the first paste mixture is transferred onto aluminum foil using a gravure printing process, and dried to form a first coating; the second paste mixture is transferred onto the first coating, and dried to form a second coating; the third paste mixture is transferred onto the second coating, and dried to form a third coating. The final compaction density is 2.55 g / cm³. 3 The positive electrode has a first coating thickness of 10 μm, a second coating thickness of 160 μm, a third coating thickness of 120 μm, and a first coating surface density of 10 g / m³. 2 The areal density of the second coating is 200 g / m³. 2 The areal density of the third coating is 150 g / m³. 2 .

[0137] Comparative Example 3

[0138] The preparation of the positive electrode in this embodiment includes the following steps:

[0139] S1, lithium iron phosphate (LFP) and conductive carbon black (BET 200m) are mixed in a mass ratio of 96%:2.0%:2.0%. 2 / g), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP, HFP copolymerization ratio is 10%), water is added and dispersed at high speed, and stirred into a first paste mixture with a solid content of 65%;

[0140] S2, the first paste mixture is transferred onto aluminum foil using a gravure printing process, dried to form the first coating, and then rolled to obtain a compacted density of 2.5 g / cm³. 3 The positive electrode has a first coating with a thickness of 185 μm and a surface density of 230 g / m³. 2 .

[0141] Comparative Example 4

[0142] The preparation of the positive electrode in this embodiment includes the following steps:

[0143] S1, add conductive carbon black (BET 200m) at a mass ratio of 70%:30% (BET is 200m). 2 / g), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP, HFP copolymerization ratio is 10%), water is added and dispersed at high speed, and stirred into a first paste mixture with a solid content of 65%;

[0144] Lithium iron phosphate (LFP) and conductive carbon black (BET 200m) were mixed in a mass ratio of 97.4%:1.0%:1.6%. 2 / g), polyvinylidene fluoride (PVDF) is mixed, water is added and dispersed at high speed, and stirred to form a second paste mixture with a solid content of 67%;

[0145] Lithium iron phosphate (LFP) and conductive carbon black (BET 200m) were mixed in a mass ratio of 98.5%:0.5%:1.0%. 2 Mix / g), polyvinylidene fluoride (PVDF), add water and disperse at high speed, and stir to form a third paste-like mixture with a solid content of 70%;

[0146] S2, the first paste mixture is transferred onto aluminum foil using a gravure printing process, and dried to form a first coating; the second paste mixture is transferred onto the first coating, and dried to form a second coating; the third paste mixture is transferred onto the second coating, and dried to form a third coating. The final coating is then rolled to achieve a compaction density of 2.5 g / cm³. 3 The positive electrode has a first coating thickness of 0.5 μm, a second coating thickness of 105 μm, a third coating thickness of 105 μm, and a first coating surface density of 1 g / m³. 2 The areal density of the second coating is 130 g / m³. 2 The areal density of the third coating is 130 g / m³. 2 .

[0147] Comparative Example 5

[0148] The preparation of the positive electrode in this embodiment includes the following steps:

[0149] S1, add conductive carbon black (BET 200m) at a mass ratio of 20%:80% (BET 200m). 2 / g), polyvinylidene fluoride-hexafluoropropylene copolymer (PVDF-HFP, HFP copolymerization ratio is 10%), water is added and dispersed at high speed, and stirred into a first paste mixture with a solid content of 65%;

[0150] Lithium iron phosphate (LFP) and conductive carbon black (BET 200m) were mixed in a mass ratio of 97.4%:1.0%:1.6%. 2 / g), polyvinylidene fluoride (PVDF) is mixed, water is added and dispersed at high speed, and stirred to form a second paste mixture with a solid content of 67%;

[0151] Lithium iron phosphate (LFP) and conductive carbon black (BET 200m) were mixed in a mass ratio of 98.5%:0.5%:1.0%. 2Mix / g), polyvinylidene fluoride (PVDF), add water and disperse at high speed, and stir to form a third paste-like mixture with a solid content of 70%;

[0152] S2, a first paste mixture is transferred onto aluminum foil using a gravure printing process, and dried to form a first coating; a second paste mixture is transferred onto the first coating, and dried to form a second coating; a third paste mixture is transferred onto the second coating, and dried to form a third coating. The mixture is then rolled to achieve a compaction density of 2.45 g / cm³. 3 The positive electrode has a first coating thickness of 1 μm, a second coating thickness of 145 μm, a third coating thickness of 95 μm, and a first coating surface density of 2 g / m³. 2 The areal density of the second coating is 180 g / m³. 2 The areal density of the third coating is 120 g / m³. 2 .

[0153] Test methods

[0154] Softness test: Refer to GB / T 8942-2016, test instrument - microcomputer softness tester, model: PN-RT1000F.

[0155] Electronic conductivity test: Refer to GB / T 1551-2021 "Method for Determination of Resistivity of Single Crystal Silicon", four-probe method, model: RTS-8 four-probe tester.

[0156] Electrode breakage test: Bend 180° and observe the light transmission of the electrode. Bend repeatedly until it breaks completely and record the number of folds.

[0157] Capacity test: Electrode installation and tethering test, 0.33C capacity.

[0158] Cyclic performance testing: 1C / 1C charge / discharge test, number of cycles at 80% cutoff capacity. Graphite anode sheet, separator 7+2CCS+1PCS, commonly using LFP electrolyte.

[0159] The test results are shown in Table 1.

[0160] Table 1

[0161]

[0162] Table 2

[0163]

[0164] As shown in Tables 1 and 2, compared with Comparative Examples 1 to 5, Examples 1 to 9, by controlling the content of each component in the coating, help to improve the compaction density of the positive electrode, reduce the breakage of the positive electrode, and promote the transport of lithium ions, thereby helping to improve the battery capacity and cycle performance.

[0165] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A positive electrode plate, characterized in that, The positive electrode sheet includes a positive current collector and a positive active material layer disposed on at least one side of the positive current collector. The positive active material layer includes a first coating layer and a second coating layer disposed in sequence. The first coating layer is disposed on the surface of the positive current collector, and the second coating layer is disposed on the surface of the first coating layer away from the positive current collector. The first coating comprises a first conductive agent and a first binder, and the second coating comprises a second positive electrode material, a second conductive agent, and a second binder. The mass content of the first conductive agent in the first coating is x, and the mass content of the first adhesive in the first coating is y, satisfying 10%≤x≤60% and 30%≤y≤70%; the mass content of the second conductive agent in the second coating is a, and the mass content of the second adhesive in the second coating is b, satisfying 0%≤a≤1.0% and 1.0%≤b≤2.0%.

2. The positive electrode sheet according to claim 1, characterized in that, The positive electrode active material layer further includes a third coating layer, which is disposed on the surface of the second coating layer away from the positive electrode current collector. The third coating layer includes a third positive electrode material, a third conductive agent, and a third binder. The mass content of the third conductive agent in the third coating layer is d, the mass content of the third binder in the third coating layer is e, and the mass content of the third positive electrode material in the third coating layer is f, satisfying: 0≤d≤0.8%, 0.1%≤e≤1%, and d+e+f=100%.

3. The positive electrode sheet according to claim 2, characterized in that, The thickness of the first coating is 0.2 μm to 10 μm; and / or, The thickness of the second coating is 1 μm to 200 μm; and / or, The areal density of the first coating is 0.1 g / m³. 2 ~10g / m 2 ; and / or, The areal density of the second coating is 1 g / m³. 2 ~260g / m 2 ; and / or, The thickness of the third coating is 0.1 μm to 260 μm; and / or The surface density of the third coating is 0.1 g / m³. 2 ~320g / m 2 .

4. The positive electrode sheet according to claim 2, characterized in that, The areal density of the third coating is 0.1 to 10 times that of the second coating.

5. The positive electrode sheet according to claim 2, characterized in that, The first coating has a softness of 1 mN to 30 mN; and / or, The second coating has a softness of 50 mN to 1400 mN; and / or, The softness of the third coating is 0.1 mN to 1400 mN; and / or, The compaction density of the positive electrode is 2.5 g / cm³. 3 ~2.8g / cm 3 ; and / or, The flexibility of the positive electrode sheet is 50mN~1400mN.

6. The positive electrode sheet according to claim 2, characterized in that, The porosity ε1 of the first coating is 20%~70%, the porosity ε2 of the second coating is 20%~40%, and the porosity ε3 of the third coating is 22%~32%. The electronic conductivity σ1 of the first coating, the electronic conductivity σ2 of the second coating, and the electronic conductivity σ3 of the third coating satisfy: σ1:σ2:σ3=(1-ε1) 1.5 : (1-ε2) 1.5 :(1-ε3) 1.5 .

7. The positive electrode sheet according to any one of claims 1 to 6, characterized in that, The first coating further includes a first positive electrode material, wherein the mass content of the first positive electrode material in the first coating is z, satisfying: 0≤z≤30%, x+y+z=100%, and the first positive electrode material includes at least one of lithium iron phosphate and lithium manganese iron phosphate. The first conductive agent includes at least one of carbon black, graphite flakes, carbon nanotubes, and graphene; and / or, The specific surface area of ​​the first conductive agent is 30 g / m². 2 ~1400g / m 2 ; and / or, The first adhesive includes at least one of styrene-butadiene emulsion, polyacrylic acid, polymethyl methacrylate, polyimide, polyvinyl alcohol, polyacrylonitrile, polyvinylidene fluoride, polytetrafluoroethylene, polyamide-imide, and polyaniline.

8. The positive electrode sheet according to any one of claims 1 to 6, characterized in that, The mass content of the second positive electrode material in the second coating is c, a+b+c=100%, and the second positive electrode material includes at least one of lithium iron phosphate, lithium manganese iron phosphate, lithium nickel cobalt manganese oxide, lithium manganese oxide, and lithium-rich manganese-based materials. The second conductive agent includes at least one of carbon black, graphite flakes, carbon nanotubes, and graphene; and / or, The specific surface area of ​​the second conductive agent is 100 g / m². 2 ~1400g / m 2 ; and / or, The second adhesive includes at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyimide, polyacrylic acid, and polymethyl methacrylate.

9. The positive electrode sheet according to any one of claims 2 to 6, characterized in that, The third cathode material includes at least one of lithium iron phosphate, lithium manganese iron phosphate, ternary materials such as lithium nickel cobalt manganese oxide, lithium manganese oxide, and lithium-rich manganese-based materials. The third conductive agent includes at least one of carbon black, graphite sheets, carbon nanotubes, and graphene. The specific surface area of ​​the third conductive agent is 150 g / m². 2 ~1400g / m 2 ; The third adhesive includes at least one of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene copolymer, polyimide, polyacrylic acid, and polymethyl methacrylate.

10. A battery, characterized in that, The battery includes the positive electrode sheet according to any one of claims 1 to 9.

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