Positive electrode sheet and its manufacturing method, secondary battery

Abstract

This invention relates to the field of energy storage technology, specifically to a positive electrode sheet and its manufacturing method, and a secondary battery. The positive electrode sheet includes a positive current collector, a first active layer disposed on the surface of the positive current collector, a second active layer disposed on the surface of the first active layer, and a third active layer disposed on the surface of the second active layer. The first active layer includes a first polycrystalline high-nickel material and a first monocrystalline high-nickel material; the second active layer includes a second polycrystalline high-nickel material and a second monocrystalline high-nickel material; and the third active layer includes a third monocrystalline high-nickel material and a porous carbon material. The nickel content in the first polycrystalline high-nickel material is higher than that in the second polycrystalline high-nickel material. The nickel content in the first, second, and third monocrystalline high-nickel materials decreases sequentially. The porosity of the first, second, and third active layers increases sequentially, while the areal density decreases sequentially. The electrode sheet of this invention can block the interference of gas generation from the negative electrode while ensuring the battery's capacity is utilized.

Description

Technical Field

[0001] This invention relates to the field of energy storage technology, specifically to a positive electrode sheet and its manufacturing method, and a secondary battery. Background Technology

[0002] Currently, high-nickel ternary cathode materials are the main cathode materials for high-energy-density batteries, offering a capacity increase of over 10% compared to medium-nickel ternary materials. However, high-nickel ternary cathode materials have extremely poor thermal stability. Below 200℃, they react violently with the electrolyte and negative electrode side inside the cell, generating heat and releasing oxygen, thus exacerbating the thermal runaway of the cell. Research shows that the onset temperature and heat generation of thermal runaway in high-nickel cathodes are closely related to factors such as nickel content, particle size, surface coating, internal doping, and the electrolyte and gas surrounding the material particles.

[0003] Therefore, how to improve the thermal runaway trigger temperature of the battery cell by designing high-nickel electrodes is an urgent problem to be solved in this field. Summary of the Invention

[0004] In view of this, the present invention aims to provide a positive electrode sheet and its manufacturing method, and a secondary battery, so as to solve the problems of side reactions and excessive heat generation of high-nickel electrode sheets in the prior art.

[0005] To solve the above-mentioned technical problems, the present invention is implemented as follows:

[0006] A first aspect of the present invention provides a positive electrode sheet, the positive electrode sheet comprising a positive current collector, a first active layer disposed on at least one side surface of the positive current collector along the thickness direction, a second active layer disposed on a side surface of the first active layer away from the positive current collector, and a third active layer disposed on a side surface of the second active layer away from the first active layer.

[0007] The first active layer comprises a first polycrystalline high-nickel material and a first single-crystal high-nickel material, the second active layer comprises a second polycrystalline high-nickel material and a second single-crystal high-nickel material, and the third active layer comprises a third single-crystal high-nickel material and a porous carbon material;

[0008] The content of the first polycrystalline high-nickel material in the first active layer material is higher than that of the second polycrystalline high-nickel material in the second active layer material; the content of the first single-crystal high-nickel material in the first active layer material is lower than that of the second single-crystal high-nickel material in the second active layer material; the nickel content in the first polycrystalline high-nickel material is higher than that in the second polycrystalline high-nickel material; and the nickel content in the first single-crystal high-nickel material, the second single-crystal high-nickel material, and the third single-crystal high-nickel material decreases sequentially.

[0009] The porosity of the first active layer, the second active layer, and the third active layer increases sequentially; the areal density of the first active layer, the second active layer, and the third active layer decreases sequentially.

[0010] Optionally, based on the total mass of the first active layer material, the content of the first polycrystalline high-nickel material is 54-64 wt%, and the content of the first single-crystal high-nickel material is 34-44 wt%; and / or, based on the total mass of the second active layer material, the content of the second polycrystalline high-nickel material is 44-54 wt%, and the content of the second single-crystal high-nickel material is 44-54 wt%; and / or, based on the total mass of the third active layer material, the content of the third single-crystal high-nickel material is 94-96 wt%, and the content of the porous carbon material is 2-4 wt%.

[0011] Optionally, the first polycrystalline high-nickel material includes LiNi. x1 Co y1 Mn 1-x1-y1 O2, wherein 0.84≤x1≤0.88, 0.06≤y1≤0.12, 1-x1-y1>0; the first polycrystalline high-nickel material is doped with a first metallic element, the first metallic element including at least one of Al, Zr, Cr, Sr, Mo, Sc, La, Nb and Y, the doping amount of the first metallic element being 2500~3500ppm; and / or, the first single-crystal high-nickel material including LiNi. n1 Co m1 Mn 1-n1-m1 O2, wherein 0.88≤n1≤0.92, 0.06≤m1≤0.12, 1-n1-m1>0; the first single-crystal high-nickel material is doped with a second metal element, the second metal element including at least one of Al, Zr, Cr, Sr, Mo, Sc, La, Nb and Y, the doping amount of the second metal element being 2000~3000ppm; and / or, the second polycrystalline high-nickel material including LiNi x2 Co y2 Mn 1-x2-y2 O2, wherein 0.80≤x2≤0.84, 0.06≤y2≤0.12, 1-x2-y2>0; the second polycrystalline high-nickel material is doped with a third metal element, wherein the third metal element includes at least one selected from Al, Zr, Cr, Sr, Mo, Sc, La, Nb, and Y, and the doping amount of the third metal element is 1500~2500ppm; and / or, the second single-crystal high-nickel material includes LiNi. n2 Co m2 Mn 1-n2-m2O2, wherein 0.84≤n2≤0.88, 0.06≤m2≤0.12, 1-n2-m2>0; the second single-crystal high-nickel material is doped with a fourth metal element, wherein the fourth metal element includes at least one selected from Al, Zr, Cr, Sr, Mo, Sc, La, Nb, and Y, and the doping amount of the fourth metal element is 1000~2000ppm; and / or, the third single-crystal high-nickel material includes LiNi. n3 Co m3 Mn 1-n3-m3 O2, wherein 0.80≤n3≤0.84, 0.06≤m3≤0.12, 1-n3-m3>0; the surface of the third single-crystal high-nickel material is coated with a coating layer, the coating layer comprising at least one of an oxide, phosphate, sulfate and hydroxide of a fifth metal element, wherein the fifth metal element is selected from at least one of Al, Zr, Ti, Zn, Sr, Y, V, Nb, Ce and La, and the coating layer thickness is 100~400nm.

[0012] Optionally, the particle size of the first polycrystalline high-nickel material is smaller than that of the second polycrystalline high-nickel material; the particle sizes of the first single-crystal high-nickel material, the second single-crystal high-nickel material, and the third single-crystal high-nickel material increase sequentially.

[0013] Optionally, the Dv50 of the first polycrystalline high-nickel material is 6~8μm; and / or, the Dv50 of the first single-crystal high-nickel material is 2~3.5μm; and / or, the Dv50 of the second polycrystalline high-nickel material is 8~10μm; and / or, the Dv50 of the second single-crystal high-nickel material is 3.5~4.5μm; and / or, the Dv50 of the third single-crystal high-nickel material is 4.5~6μm.

[0014] Optionally, the porous carbon material has a pore size of 2-5 nm and a porosity of 40-50%; and / or, the porous carbon material includes at least one of porous activated carbon, carbon molecular sieve, and porous carbon microspheres.

[0015] Optionally, the areal density of the first active layer is 55~65 g / m². 2 The porosity is 24-28%, and the thickness is 16-19 μm; and / or, the areal density of the second active layer is 45-55 g / m³. 2 The porosity is 28-32%, and the thickness is 13-16 μm; and / or, the areal density of the third active layer is 35-45 g / m³. 2 The porosity is 30-34% and the thickness is 11-14 μm.

[0016] Optionally, the first active layer further includes a first conductive agent and a first binder; based on the total mass of the first active layer material, the content of the first conductive agent is 1~3wt%, and the content of the first binder is 0.8~2.5wt%; the first conductive agent includes at least one of conductive graphite, conductive carbon black, conductive carbon fiber, carbon nanotubes and graphene, and the first binder includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, sodium alginate and polyacrylic acid; and / or, the second active layer further includes a second conductive agent and a second binder; based on the total mass of the second active layer material, the content of the second conductive agent is 1~3wt%, and the content of the second binder is 0.8~2.5wt%. The second conductive agent includes at least one of conductive graphite, conductive carbon black, conductive carbon fiber, carbon nanotubes, and graphene; the second binder includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, sodium alginate, and polyacrylic acid; and / or, the third active layer further includes a third conductive agent and a third binder; based on the total mass of the third active layer material, the content of the third conductive agent is 1~3wt%, and the content of the third binder is 0.8~2.5wt%; the third conductive agent includes at least one of conductive graphite, conductive carbon black, conductive carbon fiber, carbon nanotubes, and graphene; the third binder includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, sodium alginate, and polyacrylic acid.

[0017] A second aspect of the present invention provides a method for preparing a positive electrode sheet, the method comprising:

[0018] S1. The first slurry is coated on at least one side surface of the positive electrode current collector along the thickness direction, and a first drying process and a first rolling process are performed to obtain a first electrode sheet with a first active layer.

[0019] S2. The second slurry is coated on the surface of the first electrode sheet away from the positive current collector, and a second drying process and a second rolling process are performed to obtain a second electrode sheet with a first active layer and a second active layer.

[0020] S3. The third slurry is coated on the surface of the second electrode away from the first active layer, and then a third drying process and a third rolling process are performed.

[0021] The first slurry contains a first polycrystalline high-nickel material and a first single-crystal high-nickel material, the second slurry contains a second polycrystalline high-nickel material and a second single-crystal high-nickel material, and the third slurry contains a third single-crystal high-nickel material and a porous carbon material.

[0022] A third aspect of the present invention provides a battery comprising a positive electrode, wherein the positive electrode is the positive electrode described above or a positive electrode prepared according to the method described above.

[0023] Through the above technical solution, the beneficial technical effects of the present invention are as follows: The positive electrode sheet of the present invention includes a positive current collector, a first active layer disposed on at least one side surface of the positive current collector along the thickness direction, a second active layer disposed on the side surface of the first active layer away from the positive current collector, and a third active layer disposed on the side surface of the second active layer away from the first active layer. The outermost third active layer is made of a single-crystal material with the lowest nickel content, and the outer layer of the single-crystal material has a relatively thick coating layer, resulting in high thermal stability. This layer also contains porous carbon material capable of adsorbing a large amount of gas. The middle second active layer has a higher nickel content and incorporates some polycrystalline material, increasing capacity utilization. Simultaneously, by doping with other metal elements, it improves the bulk stability of the material, inhibits oxygen release, and mitigates thermal runaway. The bottommost first active layer has the lowest porosity and is furthest from the negative electrode, making it least prone to thermal runaway. Because the first active layer has the highest nickel content and polycrystalline proportion, its capacity utilization is significantly better than the upper layers. This layer can further improve bulk stability and mitigate thermal runaway by increasing the doping amount. This invention uses different active layers to block interference from negative electrode gas generation while ensuring the battery's capacity is fully utilized.

[0024] Other features and advantages of the present invention will be described in detail in the following detailed description section. Detailed Implementation

[0025] This invention discloses a positive electrode sheet and its manufacturing method, as well as a secondary battery. Those skilled in the art can refer to the content of this document and appropriately modify the process parameters to achieve the desired result. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this invention. The methods and applications of this invention have been described through preferred embodiments. Those skilled in the art can clearly modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit, and scope of this invention to realize and apply the technology of this invention.

[0026] In the description of this invention, the list of items connected by the term "at least one of" or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0027] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges or individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0028] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined with each other to form new technical solutions.

[0029] Unless otherwise specified, all technical features and optional technical features of this invention can be combined to form new technical solutions.

[0030] Unless otherwise specified, the terms "comprising" and "including" as used in this invention can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0031] To address the problems of excessive side reactions and heat generation in existing high-nickel electrode materials, the present invention adopts the following technical solution:

[0032] A first aspect of the present invention provides a positive electrode sheet, the positive electrode sheet comprising a positive current collector, a first active layer disposed on at least one side surface of the positive current collector along the thickness direction, a second active layer disposed on a side surface of the first active layer away from the positive current collector, and a third active layer disposed on a side surface of the second active layer away from the first active layer.

[0033] The first active layer comprises a first polycrystalline high-nickel material and a first single-crystal high-nickel material, the second active layer comprises a second polycrystalline high-nickel material and a second single-crystal high-nickel material, and the third active layer comprises a third single-crystal high-nickel material and a porous carbon material;

[0034] The content of the first polycrystalline high-nickel material in the first active layer material is higher than that of the second polycrystalline high-nickel material in the second active layer material; the content of the first single-crystal high-nickel material in the first active layer material is lower than that of the second single-crystal high-nickel material in the second active layer material; the nickel content in the first polycrystalline high-nickel material is higher than that in the second polycrystalline high-nickel material; and the nickel content in the first single-crystal high-nickel material, the second single-crystal high-nickel material, and the third single-crystal high-nickel material decreases sequentially.

[0035] The porosity of the first active layer, the second active layer, and the third active layer increases sequentially; the areal density of the first active layer, the second active layer, and the third active layer decreases sequentially.

[0036] The positive electrode sheet of the present invention includes a positive current collector, a first active layer disposed on at least one side surface of the positive current collector along its thickness direction, a second active layer disposed on the side surface of the first active layer away from the positive current collector, and a third active layer disposed on the side surface of the second active layer away from the first active layer. The outermost third active layer is made of a single-crystal material with the lowest nickel content, exhibiting high thermal stability, and this layer contains porous carbon material capable of adsorbing a large amount of gas. The middle second active layer has a higher nickel content and incorporates some polycrystalline material, increasing capacity utilization. The bottommost first active layer has the lowest porosity and is furthest from the negative electrode, making it least susceptible to thermal runaway. Furthermore, the first active layer has the highest nickel content and polycrystalline proportion, resulting in significantly better capacity utilization compared to the upper layers. By designing different active layers, the present invention can block the interference of gas generation from the negative electrode on the gas-producing area while ensuring capacity utilization.

[0037] In this invention, if the content of the first polycrystalline high-nickel material in the first active layer material is too high, it may lead to poor thermal stability of the layer, thereby reducing the cell failure temperature; if the content of the first polycrystalline high-nickel material in the first active layer material is too low, it may lead to an excessively high capacity utilization of the layer, thereby affecting the cell energy density. According to this invention, based on the total mass of the first active layer material, the content of the first polycrystalline high-nickel material can be 54~64wt%, and the content of the first single-crystal high-nickel material can be 34~44wt%.

[0038] In this invention, if the content of the second polycrystalline high-nickel material in the second active layer material is too high, it may lead to poor thermal stability of the layer, thereby reducing the cell failure temperature; if the content of the second polycrystalline high-nickel material in the second active layer material is too low, it may lead to an excessively high capacity utilization of the layer, thereby affecting the cell energy density. According to this invention, based on the total mass of the second active layer material, the content of the second polycrystalline high-nickel material is 44~54wt%, and the content of the second single-crystal high-nickel material is 44~54wt%.

[0039] In this invention, if the content of the third single-crystal high-nickel material in the third active layer material is too high, it may lead to poor thermal stability of the layer and reduce the cell failure temperature. Based on the total mass of the third active layer material, the content of the third single-crystal high-nickel material is 94~96wt%, and the content of the porous carbon material is 2~4wt%.

[0040] In one embodiment of the present invention, the first polycrystalline high-nickel material may include LiNi. x1 Co y1 Mn 1-x1- y1 O2, wherein 0.84≤x1≤0.88, 0.06≤y1≤0.12, and 1-x1-y1>0. Preferably, the first polycrystalline high-nickel material may be doped with a first metal element, which may include at least one of Al, Zr, Cr, Sr, Mo, Sc, La, Nb, and Y. The doping amount of the first metal element may be 2500~3500ppm. By doping with the first metal element, the bulk stability of the first polycrystalline high-nickel material can be improved, thereby mitigating the degree of thermal runaway.

[0041] In one embodiment of the present invention, the first single-crystal high-nickel material may include LiNi. n1 Co m1 Mn 1-n1- m1 O2, wherein 0.88≤n1≤0.92, 0.06≤m1≤0.12, and 1-n1-m1>0. Preferably, the first single-crystal high-nickel material may be doped with a second metal element, which may include at least one of Al, Zr, Cr, Sr, Mo, Sc, La, Nb, and Y. The doping amount of the second metal element may be 2000~3000ppm. By doping with the second metal element, the bulk stability of the first single-crystal high-nickel material can be improved, thereby mitigating the degree of thermal runaway.

[0042] In one embodiment of the present invention, the second polycrystalline high-nickel material may include LiNi. x2 Co y2 Mn 1-x2- y2O2, wherein 0.80≤x2≤0.84, 0.06≤y2≤0.12, and 1-x2-y2>0. Preferably, the second polycrystalline high-nickel material may be doped with a third metal element, which may include at least one of Al, Zr, Cr, Sr, Mo, Sc, La, Nb, and Y. The doping amount of the third metal element may be 1500~2500ppm. By doping with the third metal element, the bulk stability of the material can be improved, oxygen release from the material can be suppressed, and the degree of thermal runaway can be slowed down.

[0043] In one embodiment of the present invention, the second single-crystal high-nickel material may include LiNi. n2 Co m2 Mn 1-n2- m2 O2, wherein 0.84≤n2≤0.88, 0.06≤m2≤0.12, and 1-n2-m2>0. Preferably, the second single-crystal high-nickel material may be doped with a fourth metal element, which may include at least one of Al, Zr, Cr, Sr, Mo, Sc, La, Nb, and Y. The doping amount of the fourth metal element may be 1000~2000ppm. By doping with the fourth metal element, the bulk stability of the material can be improved, oxygen release from the material can be suppressed, and the degree of thermal runaway can be mitigated.

[0044] In one embodiment of the present invention, the third single-crystal high-nickel material may include LiNi. n3 Co m3 Mn 1-n3- m3 O2, wherein 0.80≤n3≤0.84, 0.06≤m3≤0.12, and 1-n3-m3>0. Preferably, the surface of the third single-crystal high-nickel material may be coated with a coating layer, which may include at least one of an oxide, phosphate, sulfate, and hydroxide of a fifth metal element. The fifth metal element may be selected from at least one of Al, Zr, Ti, Zn, Sr, Y, V, Nb, Ce, and La. The thickness of the coating layer may be 100~400 nm. The coating layer of the present invention is beneficial to improving the thermal stability of the single-crystal material.

[0045] In a preferred embodiment of the present invention, the particle size of the first polycrystalline high-nickel material is smaller than that of the second polycrystalline high-nickel material; the particle sizes of the first single-crystal high-nickel material, the second single-crystal high-nickel material, and the third single-crystal high-nickel material increase sequentially. In this invention, a larger particle size of the high-nickel material results in a smaller specific surface area, fewer interfacial side reactions, and higher safety performance, but also a decrease in kinetic performance, leading to lower capacity utilization. The increasing particle size of the high-nickel material from bottom to top in this invention provides more capacity in the lower layer, where thermal runaway is less likely, while increasing the particle size in the upper layer, where thermal runaway is more likely, reduces side reactions and improves safety performance, thereby maximizing both capacity utilization and safety.

[0046] According to the present invention, the suitable particle size of the first polycrystalline high-nickel material, the first single-crystal high-nickel material, the second polycrystalline high-nickel material, the second single-crystal high-nickel material and the third single-crystal high-nickel material helps to keep the thermal stability of each layer at a similar level, and avoids the overall thermal runaway caused by a shortcoming in a certain layer.

[0047] According to the present invention, the Dv50 of the first polycrystalline high-nickel material can be 6~8 μm; exemplarily, the Dv50 of the first polycrystalline high-nickel material can be any value selected from 6 μm, 6.5 μm, 7 μm, 7.5 μm, and 8 μm, or any value within the range formed by any pair of the above values. The Dv50 of the first single-crystal high-nickel material can be 2~3.5 μm; exemplarily, the Dv50 of the first single-crystal high-nickel material can be any value selected from 2 μm, 2.5 μm, 3 μm, and 3.5 μm, or any value within the range formed by any pair of the above values. The Dv50 of the second polycrystalline high-nickel material can be 8~10 μm; exemplarily, the Dv50 of the second polycrystalline high-nickel material can be any value selected from 8 μm, 8.5 μm, 9 μm, 9.5 μm, and 10 μm, or any value within the range formed by any pair of the above values. The Dv50 of the second single-crystal high-nickel material can be 3.5~4.5μm; exemplarily, the Dv50 of the second single-crystal high-nickel material can be any value among 3.5μm, 3.8μm, 4μm, and 4.5μm, or any value within the range formed by any two of the above values. The Dv50 of the third single-crystal high-nickel material can be 4.5~6μm. Exemplarily, the Dv50 of the third single-crystal high-nickel material can be any value among 4.5μm, 4.8μm, 5μm, 5.5μm, and 6μm, or any value within the range formed by any two of the above values.

[0048] According to the present invention, the addition of porous carbon material to the third active layer can adsorb the gas produced by the negative electrode and delay the reaction of the gas with the positive electrode active material. In this invention, the porous carbon material has a pore size of 2-5 nm and a porosity of 40-50%. Exemplarily, the pore size of the porous carbon material can be any value selected from 2 nm, 3 nm, 4 nm, and 5 nm, or any value within the range formed by any two of the above values; the porosity of the porous carbon material can be any value selected from 40%, 42%, 47%, and 50%, or any value within the range formed by any two of the above values.

[0049] For example, the porous carbon material includes at least one of porous activated carbon, carbon molecular sieve, and porous carbon microspheres.

[0050] According to the present invention, the first active layer, located in the lower layer least prone to thermal runaway, uses a high-capacity material to maximize the areal density and minimize porosity, thereby achieving the technical effect of increasing the capacity utilization of this layer. In this invention, the areal density of the first active layer can be 55~65 g / m³. 2 The porosity can be 24-28%, and the thickness can be 16-19 μm; for example, the areal density of the first active layer can be 55 g / m³. 2 57 g / m 2 60 g / m 2 62 g / m 2 and 65 g / m 2 The porosity of the first active layer can be any value in the range of 24%, 25%, 26%, 27%, and 28%, or any value within the range of any two of the above values; the thickness of the first active layer can be any value in the range of 16μm, 17μm, 18μm, and 19μm, or any value within the range of any two of the above values.

[0051] According to the present invention, the second active layer has a slightly reduced areal density, reducing the proportion of low-specific-capacity materials while maintaining overall energy density, and its higher porosity accelerates ion transport efficiency within the layer. In this invention, the areal density of the second active layer can be 45~55 g / m³. 2 The porosity can be 28-32%, and the thickness can be 13-16 μm. For example, the areal density of the second active layer can be 45 g / m³. 2 47 g / m 2 50 g / m 2 52 g / m 2 and 55 g / m 2The porosity of the second active layer can be any value in the range of 28%, 29%, 30%, 31%, and 32%, or any value within the range of any two of the above values; the thickness of the second active layer can be any value in the range of 13μm, 14μm, 15μm, and 16μm, or any value within the range of any two of the above values.

[0052] According to the present invention, the third active layer has the lowest specific capacity. This areal density range can improve safety. Increasing the areal density has no significant effect and will reduce the overall capacity utilization. Greater porosity can ensure the overall wetting of the electrolyte, thereby accelerating lithium-ion transport. In the present invention, the areal density of the third active layer can be 35~45 g / m³. 2 The porosity can be 30-34%, and the thickness can be 11-14 μm. For example, the areal density of the third active layer can be 35 g / m³. 2 37 g / m 2 40 g / m 2 42 g / m 2 and 45 g / m 2 The porosity of the third active layer can be any value from 30%, 31%, 32%, 33%, and 34%, or any value from any pair of values ​​above; the thickness of the third active layer can be any value from 11μm, 12μm, 13μm, and 14μm, or any value from any pair of values ​​above.

[0053] In one embodiment of the present invention, the first active layer may further include a first conductive agent and a first binder; based on the total mass of the first active layer material, the content of the first conductive agent may be 1 to 3 wt%, and the content of the first binder may be 0.8 to 2.5 wt%.

[0054] For example, the first conductive agent includes at least one of conductive graphite, conductive carbon black, conductive carbon fiber, carbon nanotubes and graphene.

[0055] For example, the first adhesive includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, sodium alginate, and polyacrylic acid.

[0056] In one embodiment of the present invention, the second active layer may further include a second conductive agent and a second binder; based on the total mass of the second active layer material, the content of the second conductive agent may be 1 to 3 wt%, and the content of the second binder may be 0.8 to 2.5 wt%.

[0057] For example, the second conductive agent includes at least one of conductive graphite, conductive carbon black, conductive carbon fiber, carbon nanotubes and graphene.

[0058] For example, the second adhesive includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, sodium alginate, and polyacrylic acid.

[0059] In one embodiment of the present invention, the third active layer may further include a third conductive agent and a third binder; based on the total mass of the third active layer material, the content of the third conductive agent may be 1~3wt%, and the content of the third binder may be 0.8~2.5wt%.

[0060] For example, the third conductive agent includes at least one of conductive graphite, conductive carbon black, conductive carbon fiber, carbon nanotubes and graphene.

[0061] For example, the third adhesive includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, sodium alginate, and polyacrylic acid.

[0062] A second aspect of the present invention provides a method for preparing a positive electrode sheet, the method comprising:

[0063] S1. The first slurry is coated on at least one side surface of the positive electrode current collector along the thickness direction, and a first drying process and a first rolling process are performed to obtain a first electrode sheet with a first active layer.

[0064] S2. The second slurry is coated on the surface of the first electrode sheet away from the positive current collector, and a second drying process and a second rolling process are performed to obtain a second electrode sheet with a first active layer and a second active layer.

[0065] S3. The third slurry is coated on the surface of the second electrode away from the first active layer, and then a third drying process and a third rolling process are performed.

[0066] The first slurry contains a first polycrystalline high-nickel material and a first single-crystal high-nickel material, the second slurry contains a second polycrystalline high-nickel material and a second single-crystal high-nickel material, and the third slurry contains a third single-crystal high-nickel material and a porous carbon material.

[0067] A third aspect of the present invention provides a battery comprising a positive electrode, wherein the positive electrode is the positive electrode described above or a positive electrode prepared according to the method described above.

[0068] In some embodiments of the present invention, the battery further includes a negative electrode, an electrolyte, and a separator. That is, the battery includes a positive electrode, a negative electrode, an electrolyte, and a separator.

[0069] In this embodiment, the specific material or type of the negative electrode sheet is not limited, and any negative electrode sheet known in the art can be used.

[0070] In this embodiment, the specific material or type of the separator is not limited, and any separator known in the art that can be used in secondary batteries can be selected.

[0071] It should also be noted that the battery of the present invention does not limit the specific material or type of electrolyte, and can use any components and types known in the art that can be used in secondary batteries, as long as the purpose of the present invention can be achieved.

[0072] Since the battery provided in this embodiment of the invention adopts all the technical solutions of the above embodiments, it has at least all the beneficial effects brought about by the technical solutions of the above embodiments, and will not be described in detail here.

[0073] The present invention will be further described in detail below through examples. All raw materials used in the examples are commercially available.

[0074] Example 1

[0075] The positive current collector used in this embodiment is aluminum foil with a thickness of 10 μm.

[0076] A first slurry is prepared by dissolving a first polycrystalline high-nickel material, a first single-crystal high-nickel material, a first conductive agent, and a first binder in NMP at a mass ratio of 59:39:1.1:0.9. The first slurry is coated onto the surface of the positive electrode current collector and dried and rolled to obtain a first electrode sheet with a first active layer. A second slurry is prepared by dissolving a second polycrystalline high-nickel material, a second single-crystal high-nickel material, a second conductive agent, and a second binder in NMP at a mass ratio of 49:49:1.1:0.9. The second slurry is coated onto the surface of the first electrode sheet and dried and rolled to obtain a second electrode sheet with a first active layer and a second active layer. A third slurry is prepared by dissolving a third single-crystal high-nickel material, a porous carbon material, a third conductive agent, and a third binder in NMP at a mass ratio of 95:3:1.1:0.9. The third slurry is coated onto the surface of the second electrode sheet and dried and rolled to obtain the positive electrode sheet of this embodiment.

[0077] In this embodiment, the first polycrystalline high-nickel material is LiNi. 0.86 Co 0.08 Mn 0.06 O2, with a particle size range of 7μm, was the first polycrystalline high-nickel material doped with Al at a doping level of 3000ppm. The first single-crystal high-nickel material was LiNi. 0.9 Co 0.06 Mn 0.04O2, with a particle size range of 3μm. The first single-crystal high-nickel material is doped with Al element, with a doping amount of 2500ppm. The second polycrystalline high-nickel material is LiNi. 0.82 Co 0.1 Mn 0.08 O2, with a particle size range of 9 μm, is used in the second polycrystalline high-nickel material, which is doped with Al element at a doping level of 2000 ppm. The second single-crystal high-nickel material is LiNi. 0.86 Co 0.08 Mn 0.06 The first single-crystal high-nickel material contains O2 with a particle size range of 4 μm. The second single-crystal high-nickel material is doped with Al at a doping level of 1500 ppm. The third single-crystal high-nickel material is LiNi. 0.82 Co 0.1 Mn 0.08 O2, with a particle size range of 5μm, and the surface of the third single crystal high-nickel material is coated with an Al2O3 coating layer with a thickness of 300nm.

[0078] In this embodiment, the porous carbon material is porous activated carbon with a pore size of 5 nm and a porosity of 45%. The first conductive agent is conductive carbon black, the first binder is polyvinylidene fluoride, the second conductive agent is conductive carbon black, the second binder is polyvinylidene fluoride, the third conductive agent is conductive carbon black, and the third binder is polyvinylidene fluoride.

[0079] In this embodiment, the areal density of the first active layer is 60 g / m². 2 The porosity is 26% and the thickness is 18 μm; the areal density of the second active layer is 50 g / m³. 2 The porosity is 30% and the thickness is 15 μm; the areal density of the third active layer is 40 g / m³. 2 It has a porosity of 32% and a thickness of 13μm.

[0080] Example 2

[0081] The positive current collector used in this embodiment is aluminum foil with a thickness of 10 μm.

[0082] A first slurry is prepared by dissolving a first polycrystalline high-nickel material, a first single-crystal high-nickel material, a first conductive agent, and a first binder in NMP at a mass ratio of 64:34:1.1:0.9. The first slurry is coated onto the surface of the positive electrode current collector and dried and rolled to obtain a first electrode sheet with a first active layer. A second slurry is prepared by dissolving a second polycrystalline high-nickel material, a second single-crystal high-nickel material, a second conductive agent, and a second binder in NMP at a mass ratio of 44:54:1.1:0.9. The second slurry is coated onto the surface of the first electrode sheet and dried and rolled to obtain a second electrode sheet with a first active layer and a second active layer. A third slurry is prepared by dissolving a third single-crystal high-nickel material, a porous carbon material, a third conductive agent, and a third binder in NMP at a mass ratio of 94:4:1.1:0.9. The third slurry is coated onto the surface of the second electrode sheet and dried and rolled to obtain the positive electrode sheet of this embodiment.

[0083] In this embodiment, the first polycrystalline high-nickel material is LiNi. 0.84 Co 0.08 Mn 0.08 O2, 8μm in diameter, internally doped with Al at a doping concentration of 3500ppm. The first single-crystal high-nickel material was LiNi. 0.88 Co 0.06 Mn 0.06 O2, with a particle size of 3.5 μm, is internally doped with Al element at a doping concentration of 3000 ppm. The second polycrystalline high-nickel material is LiNi. 0.84 Co 0.1 Mn 0.06 O2, with a particle size of 10 μm, is doped with Al element at a doping concentration of 2500 ppm. The second single-crystal high-nickel material is LiNi. 0.88 Co 0.08 Mn 0.88 O2, with a particle size of 4.5 μm, is internally doped with Al element at a doping concentration of 2000 ppm. The third single-crystal high-nickel material is LiNi. 0.84 Co 0.1 Mn 0.06 O2, with a particle size range of 6μm, and the surface of the third single crystal high-nickel material is coated with an Al2O3 coating layer with a thickness of 100nm.

[0084] In this embodiment, the porous carbon material is porous activated carbon with a pore size of 2 nm and a porosity of 40%. The first conductive agent is conductive carbon black, the first binder is polyvinylidene fluoride, the second conductive agent is conductive carbon black, the second binder is polyvinylidene fluoride, the third conductive agent is conductive carbon black, and the third binder is polyvinylidene fluoride.

[0085] In this embodiment, the areal density of the first active layer is 55 g / m². 2The porosity is 24% and the thickness is 16 μm; the areal density of the second active layer is 45 g / m³. 2 The porosity is 28% and the thickness is 13 μm; the areal density of the third active layer is 45 g / m³. 2 It has a porosity of 30% and a thickness of 14μm.

[0086] Example 3

[0087] The positive current collector used in this embodiment is aluminum foil with a thickness of 10 μm.

[0088] A first slurry is prepared by dissolving a first polycrystalline high-nickel material, a first single-crystal high-nickel material, a first conductive agent, and a first binder in NMP at a mass ratio of 64:34:1.1:0.9. The first slurry is coated onto the surface of the positive electrode current collector and dried and rolled to obtain a first electrode sheet with a first active layer. A second slurry is prepared by dissolving a second polycrystalline high-nickel material, a second single-crystal high-nickel material, a second conductive agent, and a second binder in NMP at a mass ratio of 54:44:1.1:0.9. The second slurry is coated onto the surface of the first electrode sheet and dried and rolled to obtain a second electrode sheet with a first active layer and a second active layer. A third slurry is prepared by dissolving a third single-crystal high-nickel material, a porous carbon material, a third conductive agent, and a third binder in NMP at a mass ratio of 96:2:1.1:0.9. The third slurry is coated onto the surface of the second electrode sheet and dried and rolled to obtain the positive electrode sheet of this embodiment.

[0089] In this embodiment, the first polycrystalline high-nickel material is LiNi. 0.88 Co 0.08 Mn 0.04 O2, with a particle size range of 6 μm, was the first polycrystalline high-nickel material doped with Al at a doping level of 2500 ppm. The first single-crystal high-nickel material was LiNi. 0.92 Co 0.06 Mn 0.02 O2, with a particle size range of 2μm. The first single-crystal high-nickel material is doped with Al element, with a doping amount of 2000ppm. The second polycrystalline high-nickel material is LiNi. 0.8 Co 0.1 Mn 0.1 O2, with a particle size range of 8 μm, is used in the second polycrystalline high-nickel material, which is doped with Al element at a doping level of 1500 ppm. The second single-crystal high-nickel material is LiNi. 0.84 Co 0.08 Mn 0.08 The first single-crystal high-nickel material contains O2 with a particle size range of 3.5 μm. The second single-crystal high-nickel material is doped with Al at a doping level of 1000 ppm. The third single-crystal high-nickel material is LiNi. 0.8 Co 0.1 Mn 0.1O2, with a particle size range of 4.5μm, and the surface of the third single-crystal high-nickel material is coated with an Al2O3 coating layer with a thickness of 400nm.

[0090] In this embodiment, the porous carbon material is porous activated carbon with a pore size of 5 nm and a porosity of 50%. The first conductive agent is conductive carbon black, the first binder is polyvinylidene fluoride, the second conductive agent is conductive carbon black, the second binder is polyvinylidene fluoride, the third conductive agent is conductive carbon black, and the third binder is polyvinylidene fluoride.

[0091] In this embodiment, the areal density of the first active layer is 65 g / m². 2 The porosity is 28% and the thickness is 19 μm; the areal density of the second active layer is 55 g / m³. 2 The porosity is 32% and the thickness is 16 μm; the areal density of the third active layer is 35 g / m³. 2 It has a porosity of 34% and a thickness of 11μm.

[0092] Example 4

[0093] The preparation method of the positive electrode in this embodiment is generally the same as in Example 1, except that the density of the first active layer is 50 g / m². 2 The density of the second active layer is 40 g / m³. 2 The density of the second active layer is 30 g / m³. 2 .

[0094] Example 5

[0095] The preparation method of the positive electrode in this embodiment is the same as that in Embodiment 1, except that: the first polycrystalline high-nickel material has a particle size of 5 μm, the first single-crystal high-nickel material has a particle size of 1.5 μm, the second polycrystalline high-nickel material has a particle size of 7 μm, the second single-crystal high-nickel material has a particle size of 3 μm, and the third single-crystal high-nickel material has a particle size of 4 μm.

[0096] Example 6

[0097] The preparation method of the positive electrode in this embodiment is the same as that in Embodiment 1, except that: the first polycrystalline high-nickel material has a particle size of 8.5 μm, the first single-crystal high-nickel material has a particle size of 4 μm, the second polycrystalline high-nickel material has a particle size of 10.5 μm, the second single-crystal high-nickel material has a particle size of 5 μm, and the third single-crystal high-nickel material has a particle size of 6.5 μm.

[0098] Example 7

[0099] The preparation method of the positive electrode in this embodiment is the same as that in Embodiment 1, except that: the Al doping amount in the first polycrystalline high-nickel material is 1000ppm, the Al doping amount in the first single-crystal high-nickel material is 1500ppm, the Al doping amount in the second polycrystalline high-nickel material is 1000ppm, the Al doping amount in the second single-crystal high-nickel material is 500ppm, and the thickness of the Al2O3 coating layer in the third single-crystal high-nickel material is 50nm.

[0100] Example 8

[0101] The preparation method of the positive electrode in this embodiment is the same as that in Embodiment 1, except that: the Al doping amount in the first polycrystalline high-nickel material is 4000ppm, the Al doping amount in the first single-crystal high-nickel material is 3500ppm, the Al doping amount in the second polycrystalline high-nickel material is 3000ppm, the Al doping amount in the second single-crystal high-nickel material is 2500ppm, and the thickness of the Al2O3 coating layer in the third single-crystal high-nickel material is 500nm.

[0102] Comparative Example 1

[0103] The preparation method of the positive electrode in this comparative example is the same as that in Example 1, except that the mass ratio of the first polycrystalline high-nickel material, the first single-crystal high-nickel material, the first conductive agent and the first binder in the first slurry is 66:32:1.1:0.9.

[0104] In the second slurry, the mass ratio of the second polycrystalline high-nickel material, the second single-crystal high-nickel material, the second conductive agent, and the second binder is 56:42:1.1:0.9.

[0105] No porous carbon material is added to the third slurry. The mass ratio of the third single-crystal high-nickel material, the third conductive agent, and the third binder is 98:1.1:0.9.

[0106] Comparative Example 2

[0107] The preparation method of the positive electrode in this comparative example is the same as that in Example 1, except that the first polycrystalline high-nickel material in the first active layer is replaced with the first single-crystal high-nickel material; and the second polycrystalline high-nickel material in the second active layer is replaced with the second single-crystal high-nickel material.

[0108] Comparative Example 3

[0109] The preparation method of the positive electrode in this comparative example is the same as that in Example 1, except that the first single-crystal high-nickel material in the first active layer is replaced with the first polycrystalline high-nickel material; and the second single-crystal high-nickel material in the second active layer is replaced with the second polycrystalline high-nickel material.

[0110] Comparative Example 4

[0111] The preparation method of the positive electrode in this comparative example is generally the same as that in Example 1, except that the single-crystal high-nickel material in the third active layer is replaced with polycrystalline high-nickel material LiNi. 0.82 Co 0.1 Mn 0.08 O2.

[0112] Comparative Example 5

[0113] The preparation method of the positive electrode in this comparative example is the same as that in Example 1, except that the polycrystalline high-nickel material used for both the first and second active layers is LiNi. 0.82 Co 0.1 Mn 0.08 O2, with a particle size range of 9μm, and the single-crystal high-nickel material used in the first, second, and third active layers is LiNi. 0.82 Co 0.1 Mn 0.08 O2.

[0114] Comparative Example 6

[0115] The preparation method of the positive electrode in this comparative example is the same as that in Example 1, except that the polycrystalline high-nickel material used for both the first and second active layers is LiNi. 0.86 Co 0.08 Mn 0.06 O2, with a particle size range of 9μm, and the single-crystal high-nickel material used in the first, second, and third active layers is LiNi. 0.9 Co 0.06 Mn 0.04 O2.

[0116] Test Example 1

[0117] The positive electrode sheets prepared in each embodiment and comparative example were used to prepare batteries. The performance of each group of batteries was tested, and the test results are shown in Table 1.

[0118] The battery manufacturing methods include:

[0119] (1) The negative electrode active material graphite, conductive agent conductive carbon black (SP), thickener sodium carboxymethyl cellulose and binder styrene-butadiene rubber are mixed in a mass ratio of 96.5:1:1:1.5, deionized water is added and stirred to form a uniform and stable negative electrode slurry with a solid content of 50%. The negative electrode slurry is uniformly coated on copper foil, and then dried, cold pressed and cut to obtain the negative electrode sheet.

[0120] (2) In a glove box filled with inert gas, ethylene carbonate, methyl ethyl carbonate and diethyl carbonate are mixed in a mass ratio of 1:1:1. Then, lithium salt LiPF6 is dissolved in an organic solvent with a concentration of 1.2 mol / L to obtain an electrolyte.

[0121] (3) A 9μm thick polypropylene film is selected as the substrate of the isolation film, and Al2O3 ceramic is coated on one side to form a ceramic coating.

[0122] (4) Arrange and assemble the positive electrode, separator, and negative electrode in sequence, using a winding method. Inject the electrolyte into the dry cell, soak for 24 hours, and then perform formation at 45°C with a formation rate of 0.05-0.2C and a cutoff voltage of 3.75V. After aging at room temperature for 24 hours, the cell fabrication is complete.

[0123] Capacity test: Charge the battery to 4.25V at 0.05C, let it stand for 30 minutes, then discharge it to 2.5V at 1C. Measure the cell discharge energy. Energy density = discharge energy / cell mass. The larger this value, the greater the cell energy density.

[0124] Hot box test: The battery is heated in a heating box from 25°C to 130°C at a rate of 5°C / min, held at that temperature for 30 minutes, then the temperature is stopped and the battery is observed for 1 hour. If the battery does not fail, it passes the national standard. The ambient temperature is then heated again to 130°C at a rate of 5°C / min and held at that temperature for 30 minutes. Then the temperature is increased in increments of 5°C and held at that temperature for 30 minutes. This process is repeated until the battery fails. The failure temperature of each battery is recorded. The higher the temperature, the higher the thermal stability of the cell and the better the safety performance.

[0125] Table 1

[0126]

[0127] As can be seen from Table 1, Examples 1 to 8 are preferred solutions, with all parameters within specifications and good performance in terms of energy density and thermal box failure stability. In Comparative Example 1, the polycrystalline ratio of the first and second active layers is higher than the ideal specification, and the third active layer removes porous material. The polycrystalline material has a large specific surface area and low thermal stability, and the absence of porous material adsorbs reactive gases, resulting in a decrease in the overall thermal stability of the electrode and a thermal runaway temperature far lower than that of the embodiment. In Comparative Example 2, all materials are single crystals, resulting in a lower overall capacity utilization of the electrode and a specific capacity far lower than that of the embodiment. In Comparative Example 3, all high-nickel materials in the first and second active layers are polycrystalline, leading to an intensified side reaction at high temperatures and a thermal runaway temperature far higher than that of the group using single crystal materials. In Comparative Example 4, the third active layer is replaced with a polycrystalline material, resulting in a significant decrease in thermal stability. This layer undergoes severe side reactions at lower temperatures, leading to a significant decrease in the overall runaway temperature. In Comparative Example 5, the Ni content in the high-nickel material is not optimized for different positions and is consistently low, resulting in no significant improvement in the cell thermal runaway temperature and a significant decrease in capacity utilization, with an overall energy density far lower than that of the embodiment. In Comparative Example 5, the Ni content in the high-nickel material is not optimized for different positions and is consistently high, resulting in a significant decrease in electrode thermal stability and a cell thermal runaway temperature far lower than that of the embodiment.

[0128] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered 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, a first active layer disposed on at least one side surface of the positive current collector along the thickness direction, a second active layer disposed on one side surface of the first active layer away from the positive current collector, and a third active layer disposed on one side surface of the second active layer away from the first active layer. The first active layer comprises a first polycrystalline high-nickel material and a first single-crystal high-nickel material, the second active layer comprises a second polycrystalline high-nickel material and a second single-crystal high-nickel material, and the third active layer comprises a third single-crystal high-nickel material and a porous carbon material; The content of the first polycrystalline high-nickel material in the first active layer material is higher than that of the second polycrystalline high-nickel material in the second active layer material; the content of the first single-crystal high-nickel material in the first active layer material is lower than that of the second single-crystal high-nickel material in the second active layer material; the nickel content in the first polycrystalline high-nickel material is higher than that in the second polycrystalline high-nickel material; and the nickel content in the first single-crystal high-nickel material, the second single-crystal high-nickel material, and the third single-crystal high-nickel material decreases sequentially. The porosity of the first active layer, the second active layer, and the third active layer increases sequentially; the areal density of the first active layer, the second active layer, and the third active layer decreases sequentially.

2. The positive electrode sheet according to claim 1, characterized in that, Based on the total mass of the first active layer material, the content of the first polycrystalline high-nickel material is 54~64wt%, and the content of the first single-crystal high-nickel material is 34~44wt%; and / or, Based on the total mass of the second active layer material, the content of the second polycrystalline high-nickel material is 44~54wt%, and the content of the second single-crystal high-nickel material is 44~54wt%; and / or, Based on the total mass of the third active layer material, the content of the third single-crystal high-nickel material is 94~96wt%, and the content of the porous carbon material is 2~4wt%.

3. The positive electrode sheet according to claim 1, characterized in that, The first polycrystalline high-nickel material includes LiNi x1 Co y1 Mn 1-x1-y1 O2, wherein 0.84≤x1≤0.88, 0.06≤y1≤0.12, 1-x1-y1>0; the first polycrystalline high-nickel material is doped with a first metallic element, the first metallic element including at least one of Al, Zr, Cr, Sr, Mo, Sc, La, Nb and Y, the doping amount of the first metallic element being 2500~3500ppm; and / or, The first single-crystal high-nickel material includes LiNi n1 Co m1 Mn 1-n1-m1 O2, wherein 0.88≤n1≤0.92, 0.06≤m1≤0.12, 1-n1-m1>0; the first single-crystal high-nickel material is doped with a second metallic element, the second metallic element including at least one of Al, Zr, Cr, Sr, Mo, Sc, La, Nb and Y, the doping amount of the second metallic element being 2000~3000ppm; and / or, The second polycrystalline high-nickel material includes LiNi x2 Co y2 Mn 1-x2-y2 O2, wherein 0.80≤x²≤0.84, 0.06≤y²≤0.12, 1-x²-y²>0; the second polycrystalline high-nickel material is doped with a third metal element, wherein the third metal element includes at least one selected from Al, Zr, Cr, Sr, Mo, Sc, La, Nb, and Y, and the doping amount of the third metal element is 1500~2500ppm; and / or, The second single-crystal high-nickel material includes LiNi n2 Co m2 Mn 1-n2-m2 O2, wherein 0.84≤n2≤0.88, 0.06≤m2≤0.12, 1-n2-m2>0; the second single-crystal high-nickel material is doped with a fourth metallic element, wherein the fourth metallic element includes at least one selected from Al, Zr, Cr, Sr, Mo, Sc, La, Nb, and Y, and the doping amount of the fourth metallic element is 1000~2000ppm; and / or, The third single-crystal high-nickel material includes LiNi. n3 Co m3 Mn 1-n3-m3 O2, wherein 0.80≤n3≤0.84, 0.06≤m3≤0.12, 1-n3-m3>0; the surface of the third single-crystal high-nickel material is coated with a coating layer, the coating layer comprising at least one of an oxide, phosphate, sulfate and hydroxide of a fifth metal element, wherein the fifth metal element is selected from at least one of Al, Zr, Ti, Zn, Sr, Y, V, Nb, Ce and La, and the coating layer thickness is 100~400nm.

4. The positive electrode sheet according to claim 1, characterized in that, The particle size of the first polycrystalline high-nickel material is smaller than the particle size of the second polycrystalline high-nickel material; The particle size of the first single-crystal high-nickel material, the second single-crystal high-nickel material, and the third single-crystal high-nickel material increases sequentially.

5. The positive electrode sheet according to claim 4, characterized in that, The Dv50 of the first polycrystalline high-nickel material is 6~8 μm; and / or, The Dv50 of the first single-crystal high-nickel material is 2~3.5μm; and / or, The Dv50 of the second polycrystalline high-nickel material is 8~10 μm; and / or, The Dv50 of the second single-crystal high-nickel material is 3.5~4.5μm; and / or, The Dv50 of the third single-crystal high-nickel material is 4.5~6μm.

6. The positive electrode sheet according to claim 1, characterized in that, The porous carbon material has a pore size of 2-5 nm and a porosity of 40-50%; and / or, The porous carbon material includes at least one of porous activated carbon, carbon molecular sieve, and porous carbon microspheres.

7. The positive electrode sheet according to claim 1, characterized in that, The areal density of the first active layer is 55~65 g / m². 2 Porosity of 24-28%, thickness of 16-19 μm; and / or, The areal density of the second active layer is 45~55 g / m². 2 Porosity of 28-32%, thickness of 13-16 μm; and / or, The areal density of the third active layer is 35~45 g / m². 2 The porosity is 30-34% and the thickness is 11-14 μm.

8. The positive electrode sheet according to claim 1, characterized in that, The first active layer further includes a first conductive agent and a first binder; based on the total mass of the first active layer material, the content of the first conductive agent is 1~3wt%, and the content of the first binder is 0.8~2.5wt%; the first conductive agent includes at least one of conductive graphite, conductive carbon black, conductive carbon fiber, carbon nanotubes, and graphene; the first binder includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, sodium alginate, and polyacrylic acid; and / or, The second active layer further includes a second conductive agent and a second binder; based on the total mass of the second active layer material, the content of the second conductive agent is 1~3wt%, and the content of the second binder is 0.8~2.5wt%; the second conductive agent includes at least one of conductive graphite, conductive carbon black, conductive carbon fiber, carbon nanotubes, and graphene; the second binder includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, sodium alginate, and polyacrylic acid; and / or, The third active layer further includes a third conductive agent and a third binder; based on the total mass of the third active layer material, the content of the third conductive agent is 1~3wt%, and the content of the third binder is 0.8~2.5wt%; the third conductive agent includes at least one of conductive graphite, conductive carbon black, conductive carbon fiber, carbon nanotubes and graphene, and the third binder includes at least one of polyvinylidene fluoride, sodium carboxymethyl cellulose, styrene-butadiene rubber, sodium alginate and polyacrylic acid.

9. A method for preparing the positive electrode sheet according to any one of claims 1 to 8, characterized in that, The method includes: S1. The first slurry is coated on at least one side surface of the positive electrode current collector along the thickness direction, and a first drying process and a first rolling process are performed to obtain a first electrode sheet with a first active layer. S2. The second slurry is coated on the surface of the first electrode sheet away from the positive current collector, and a second drying process and a second rolling process are performed to obtain a second electrode sheet with a first active layer and a second active layer. S3. The third slurry is coated on the surface of the second electrode away from the first active layer, and then a third drying process and a third rolling process are performed. The first slurry contains a first polycrystalline high-nickel material and a first single-crystal high-nickel material, the second slurry contains a second polycrystalline high-nickel material and a second single-crystal high-nickel material, and the third slurry contains a third single-crystal high-nickel material and a porous carbon material.

10. A battery, characterized in that, The battery includes a positive electrode sheet, which is the positive electrode sheet according to any one of claims 1 to 8 or the positive electrode sheet prepared according to the method of claim 9.

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