Positive electrode sheet and preparation method therefor, battery and vehicle

Abstract

A positive electrode sheet (100) and a preparation method therefor, a battery, and a vehicle. The positive electrode sheet (100) comprises a current collector (11), a first positive electrode active material layer (12) and a second positive electrode active material layer (13). The first positive electrode active material layer (12) is arranged on at least one side of the current collector (11), the first positive electrode active material layer (12) comprises a first positive electrode active material, and the first positive electrode active material comprises LiNixCoyMn1-x-yO2, wherein 0.6≤x≤0.95, 0.03≤y≤0.1, and 0<x+y<1. The second positive electrode active material layer (13) is arranged on the side of the first positive electrode active material layer (12) facing away from the current collector (11), the second positive electrode active material layer (13) comprises a second positive electrode active material, and an electrochemical potential window of the second positive electrode active material is greater than that of the first positive electrode active material.

Description

Positive electrode sheet and preparation method thereof, battery and vehicle

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application is based on the Chinese patent application with application number 202410157406.4 and application date of February 4, 2024, and claims the priority of the above-mentioned Chinese patent application. The entire content of the above-mentioned Chinese patent application is hereby introduced into this application as a reference. Technical Field

[0003] The present application relates to, but is not limited to, the field of battery technology, and specifically to a positive electrode plate and a preparation method thereof, a battery, and a vehicle. Background Art

[0004] With the continuous expansion of the new energy vehicle market, the installed capacity of lithium-ion batteries has increased year by year, and higher requirements have been placed on lithium-ion batteries, such as higher energy density, faster charging speed and longer cycle life.

[0005] Ternary cathode materials (LiNixCoyMn1-x-yO2, 0<x, y<1, NCM) have high energy density and have been widely used in new energy vehicle power batteries. However, compared with lithium iron phosphate (LiFePO4), another mainstream cathode material on the market, the cycle life of NCM needs to be improved. The reasons for the cycle failure of NCM lithium-ion batteries at the positive end include the transformation of the internal structure of the NCM material under deep delithiation, side reactions on the surface of NCM particles, and the decomposition of the electrolyte after the generation of oxygen under high voltage.

[0006] The current mainstream improvement methods are all based on the intrinsic level of NCM materials, improving the structural stability and interface stability of NCM materials through doping, coating and other means. However, the fundamental reasons for the improvement are difficult to explore clearly, and there are problems such as high material costs and poor consistency.

[0007] At the electrode level, the voltage at different positions inside the electrode is different. This phenomenon is of particular concern when considering the problem of lithium plating in the negative electrode. In fact, during the charge and discharge process of lithium-ion batteries, there is also the problem of different voltages at different positions on the positive electrode end. In fact, what is detected is the voltage on the collector side, not the voltage on the positive electrode side close to the diaphragm. However, after a long cycle of the positive electrode, the voltage difference between the two ends of the positive electrode may increase to 100mV to 150mV, which will cause the positive electrode material close to the diaphragm side to withstand a higher voltage. Failure behavior occurs preferentially in the positive electrode active material close to the diaphragm side, affecting the cycle performance of the lithium-ion battery.

[0008] Summary of the Invention

[0009] The following is an overview of the subject matter described in detail in this article. This overview is not intended to limit the scope of protection of the claims.

[0010] An object of the present application is to provide a positive electrode plate. The positive electrode plate of the present application has good high-voltage resistance performance and can improve the cycle performance of the battery.

[0011] Another object of the present application is to provide a preparation method.

[0012] Another object of the present application is to provide a battery.

[0013] Another object of the present application is to provide a vehicle.

[0014] In the first aspect of the present application, a positive electrode plate is provided. According to an embodiment of the present application, the positive electrode plate includes a current collector, a first positive electrode active material layer, and a second positive electrode active material layer. The first positive electrode active material layer is disposed on at least one side of the current collector. The first positive electrode active material layer includes a first positive electrode active material, and the first positive electrode active material includes LiNi x Co y Mn 1-x-y O₂, where 0.6 ≤ x ≤ 0.95, 0.03 ≤ y ≤ 0.1, and 0 < x + y < 1; the second positive electrode active material layer is disposed on a side of the first positive electrode active material layer facing away from the current collector. The second positive electrode active material layer includes a second positive electrode active material, and the electrochemical potential window of the second positive electrode active material is greater than the electrochemical potential window of the first positive electrode active material.

[0015] According to the positive electrode plate of the above embodiment of the present application, it includes a current collector, a first positive electrode active material layer, and a second positive electrode active material layer, and the first positive electrode active material layer and the second positive electrode active material layer are sequentially formed on the current collector, that is, the first positive electrode active material layer is located between the current collector and the second positive electrode active material layer, and the electrochemical potential window of the second positive electrode active material in the second positive electrode active material layer is greater than the electrochemical potential window of the first positive electrode active material in the first positive electrode active material layer, so that the high-voltage resistance performance of the second positive electrode active material layer is better than that of the first positive electrode active material layer, which can improve the high-voltage resistance performance of the positive electrode plate, is beneficial to inhibiting the transformation of the internal structure of the second positive electrode active material, and the setting of the second positive electrode active material layer can also protect the first positive electrode active material and reduce the damage of high voltage to its structure, thereby improving the cycle performance of the battery. In addition, the first positive electrode active material includes LiNi x Co y Mn 1-x-yO2, where 0.6 ≤ x ≤ 0.95, 0.03 ≤ y ≤ 0.1, and 0 < x + y < 1. This material contains various active substances (such as Ni, Co, Mn) and has good chemical stability during the charge and discharge process of the battery, which can effectively extend the cycle performance of the battery. That is, the first positive electrode active material layer using the first positive electrode active material that meets the above chemical formula can maintain the high cycle performance of the battery. Thus, the positive electrode sheet of the present application has good high-voltage resistance performance and can improve the cycle performance of the battery.

[0016] In the second aspect of the present application, the present application proposes a method for preparing the above positive electrode sheet. According to an embodiment of the present application, the method includes: forming a first positive electrode active material layer including a first positive electrode active material on at least one side of a current collector; and forming a second positive electrode active material layer including a second positive electrode active material on a side of the first positive electrode active material layer away from the current collector to obtain a positive electrode sheet.

[0017] According to the method for preparing the above positive electrode sheet according to the above embodiment of the present application, by forming a first positive electrode active material layer including a first positive electrode active material on at least one side of the current collector, the cycle performance of the battery can be improved. By forming a second positive electrode active material layer including a second positive electrode active material on the first positive electrode active material layer, that is, the first positive electrode active material layer is located between the current collector and the second positive electrode active material layer, and the electrochemical potential window of the second positive electrode active material is greater than that of the first positive electrode active material, the high-voltage resistance performance of the second positive electrode active material layer is better than that of the first positive electrode active material layer. During the charge and discharge cycle process, the voltage difference between the diaphragm side and the current collector side of the positive electrode sheet can be reduced, and further, the transformation of the internal structure of the positive electrode active material can be inhibited, improving the cycle performance of the battery.

[0018] In the third aspect of the present application, the present application proposes a battery. According to an embodiment of the present application, the battery includes the above positive electrode sheet or a positive electrode sheet prepared by using the above method.

[0019] According to the battery of the above embodiment of the present application, the battery has good comprehensive performance and can have good cycle performance.

[0020] In the fourth aspect of the present application, the present application proposes a vehicle. According to an embodiment of the present application, the vehicle includes the above battery.

[0021] According to the vehicle of the above embodiment of the present application, the vehicle has good stability and high market satisfaction.

[0022] The additional aspects and advantages of the present application will be partially given in the following description, partially become obvious from the following description, or be understood through the practice of the present application.

[0023] Other aspects will be apparent after reading and understanding the drawings and the detailed description. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] FIG. 1 shows a schematic structural view of a positive electrode sheet according to an embodiment of the present application;

[0025] FIG. 2 shows a schematic flow chart of preparing a positive electrode sheet according to an embodiment of the present application. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0026] Embodiments of the present application will be described in detail below. Examples of the embodiments are shown in the drawings, where the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below are exemplary and are intended to explain the present application and should not be construed as a limitation of the present application.

[0027] In a first aspect of the present application, the present application provides a positive electrode sheet 100. According to an embodiment of the present application, referring to FIG. 1, the positive electrode sheet 100 includes: a current collector 11, a first positive electrode active material layer 12, and a second positive electrode active material layer 13.

[0028] The current collector 11, as a carrier of the positive electrode active material, can carry and support the positive electrode active material and ensure stability during the charge and discharge process of the battery. As an example, the current collector 11 includes but is not limited to at least one of pure aluminum foil and composite aluminum foil.

[0029] According to an embodiment of the present application, referring to FIG. 1, the first positive electrode active material layer 12 is provided on at least one side of the current collector 11. The first positive electrode active material layer 12 includes a first positive electrode active material, and the first positive electrode active material includes LiNi x Co y Mn 1-x-y O2, where 0.6 ≤ x ≤ 0.95, 0.03 ≤ y ≤ 0.1, and 0 < x + y < 1. For example, x can be 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, etc.; y can be 0.03, 0.05, 0.08, 0.1, etc. By limiting the content of nickel element within the above range, the discharge specific capacity of the first positive electrode active material can be improved, and thus the cycle performance of the lithium battery can be enhanced; by limiting the content of cobalt element within the above range, it is beneficial to the formation of the layered structure of the first positive electrode active material, inhibits the Li / Ni mixing in the first positive electrode active material, and optimizes the electrochemical performance of the first positive electrode active material; by limiting the content of manganese element within the above range, the structure of the first positive electrode active material can be stabilized, and the stability of the first positive electrode active material can be improved. Therefore, by using the first positive electrode active material that satisfies the above chemical formula in the first positive electrode active material layer 12, the cycle stability of the battery can be further improved.

[0030] According to some specific embodiments of the present application, the first positive electrode active material includes at least one of material A, material B, and material C. Among them, the material A is a single crystal material with the chemical formula LiNi x1 Co y1 Mn 1-x1-y1 O2, where 0.6 ≤ x1 < 0.8, 0.03 ≤ y1 ≤ 0.1, and 0 < x1 + y1 < 1. For example, x1 can be 0.6, 0.65, 0.7, 0.75, 0.78, etc., and y1 can be 0.03, 0.05, 0.08, 0.1, etc.; the material B is a single crystal material with the chemical formula LiNi x2 Co y2 Mn 1-x2-y2 O2, where 0.8 ≤ x2 ≤ 0.95, 0.03 ≤ y2 ≤ 0.1, and 0 < x2 + y2 < 1. For example, x2 can be 0.8, 0.84, 0.88, 0.9, 0.95, etc., and y2 can be 0.03, 0.05, 0.08, 0.1, etc.; the material C is a polycrystalline material with the chemical formula LiNi x3 Co y3 Mn 1-x3-y3 O2, where 0.8 ≤ x3 ≤ 0.95, 0.03 ≤ y3 ≤ 0.1, and 0 < x3 + y3 < 1. For example, x3 can be 0.8, 0.84, 0.88, 0.9, 0.95, etc., and y3 can be 0.03, 0.05, 0.08, 0.1, etc. According to the content of nickel element in materials A, B, and C, material A is a single crystal nickel material composed of primary particles. Material B is a single crystal high-nickel material composed of primary particles. Material C is a polycrystalline high-nickel material composed of secondary particles formed by agglomeration of primary particles. On the one hand, the above first positive electrode active material contains multiple active substances (such as Ni, Co, Mn), enabling the battery to store more electrical energy in the same volume, ensuring the capacity of the positive electrode sheet 100 can be exerted, and being beneficial to improving the energy density of the battery. On the other hand, it can also provide a stable structure, reduce the generation of side reactions, inhibit gas generation during the cycling process of the first positive electrode active material, and be beneficial to improving the cycling performance of the battery.

[0031] Those skilled in the art will understand that single small crystals are usually called primary particles, and particles formed after agglomeration are called secondary particles. The particle size of primary particles refers to the average particle size of primary particles, which can be measured using a scanning electron microscope. The average particle size of secondary particles is a well-known meaning in the art and can be measured using instruments and methods well-known in the art. As an example, the average particle size of secondary particles can be measured using laser diffraction particle size analysis. Specifically, the average particle size of secondary particles can be measured using a laser particle size analyzer (e.g., Malvern Master Size 3000) with reference to standard GB / T 19077-2016.

[0032] It should be noted that medium nickel refers to the molar ratio A of nickel element to transition metal elements in medium nickel materials, 60%≤A<80%, and high nickel refers to the molar ratio of nickel element to transition metal elements in high nickel materials is not less than 80%.

[0033] According to some specific embodiments of the present application, the average particle size of the primary particles of the material A is 2 μm to 6 μm. For example, the average particle size of the primary particles can be 2 μm, 3 μm, 4 μm, 5 μm, 6 μm, etc. By limiting the average particle size of the primary particles of the material A to the above range, the contact area between the nickel material in the single crystal and the electrolyte can be moderate, and the diffusion path of lithium ions can be shortened, which can reduce capacity decay and thus improve the cycle performance of the battery.

[0034] According to some specific embodiments of the present application, the volume average particle size Dv50 of the material A is 1 μm to 6 μm. For example, the volume average particle size Dv50 can be 1 μm, 2 μm, 3 μm, 5 μm, 6 μm, etc. By controlling the volume average particle size Dv50 of the material A within the above range, the pore structure and distribution of the first positive electrode active material can be adjusted, the electrolyte infiltration performance and the lithium ion shuttle efficiency can be improved, which is conducive to improving the rate performance of the battery and thus the cycle performance of the battery.

[0035] It should be noted that the volume average particle size Dv50 refers to the particle size at which the cumulative distribution of Material A particles reaches 50%. That is, the volume content of Material A particles smaller than this particle size accounts for 50% of the total positive electrode active material particles, and the volume content of Material A particles larger than this particle size also accounts for 50% of the total positive electrode active material particles. The volume average particle size Dv50 is measured using a laser particle size analyzer.

[0036] According to some specific embodiments of the present application, the BET specific surface area of ​​the material A is 0.5 m 2 / g to 1.5m 2 / g. For example, it can be 0.5m 2 / g,1m 2 / g,1.5m2 By limiting the BET specific surface area of ​​material A to within the above range, on the one hand, the electrochemical reaction activity of the first positive electrode active material can be controlled, which is beneficial for improving the energy density of the positive electrode sheet 100. On the other hand, it can also reduce interfacial side reactions and reduce gas production, thereby improving the cycle performance of the battery.

[0037] Specifically, the BET specific surface area of ​​material A can be measured by the following method: the BET specific surface area of ​​the solid material is measured by the gas adsorption BET method, with nitrogen as the adsorbent. The BET specific surface area of ​​the sample is characterized by the number of nitrogen molecules densely packed (adsorbed) on its surface and the maximum cross-sectional area of ​​the molecules. The equilibrium saturated adsorption capacity (V) of nitrogen molecules on the sample surface is actually measured, and the monolayer saturated adsorption capacity (Vm) is calculated through different theoretical models, and then the number of molecules is obtained. The equivalent maximum cross-sectional area (Am) of the nitrogen molecules is calculated using the surface close-packed hexagonal model, and the BET specific surface area of ​​the measured sample can be calculated. The calculation formula is as follows: S g =V m NA m / 22400W,S g is the BET specific surface area of ​​the sample being tested (m 2 / g), V m is the saturated adsorption capacity of nitrogen molecules monolayer under standard conditions (mL), A m The equivalent maximum cross-sectional area of ​​nitrogen molecules (close-packed hexagonal theoretical value Am = 0.162nm 2 ), W is the mass of the sample being tested (g), N is the Avogadro constant (6.02x10 23 ).

[0038] According to some specific embodiments of the present application, the average particle size of the primary particles of Material B is 1 μm to 3 μm. For example, it can be 1 μm, 2 μm, 3 μm, etc. By limiting the average particle size of the primary particles of Material B to the above range, the contact area between Material B and the electrolyte can be moderate, and the diffusion path of lithium ions can be shortened, which can reduce capacity decay and thus improve the cycle performance of the battery.

[0039] According to some specific embodiments of the present application, the volume average particle size Dv50 of the material B is 1 μm to 5 μm. For example, it can be 1 μm, 3 μm, 4 μm, 5 μm, etc. By controlling the D50 of material B within the above range, the pore structure and distribution of the first positive electrode active material can be adjusted, improving the electrolyte infiltration performance and lithium ion shuttle efficiency, which is conducive to improving the battery's rate performance and thus the battery's cycle performance.

[0040] According to some specific embodiments of the present application, the BET specific surface area of ​​the material B is 0.5 m 2 / g to 1.5m 2 / g. For example, it can be 0.5m 2 / g,1m 2 / g,1.5m 2 By limiting the BET specific surface area of ​​material B to the above range, on the one hand, the electrochemical reaction activity of the first positive electrode active material can be controlled, which is beneficial for improving the energy density of the positive electrode sheet 100. On the other hand, it can also reduce interfacial side reactions and reduce gas production, thereby improving the cycle performance of the battery.

[0041] According to some specific embodiments of the present application, the average particle size of the primary particles of the material C is 50 nm to 1000 nm. For example, it can be 50 nm, 100 nm, 300 nm, 600 nm, 800 nm, 1000 nm, etc. Material C is a polycrystalline material, that is, composed of secondary particles formed by the agglomeration of primary particles. By limiting the average particle size of the primary particles of material C to the above range, the structural parameters of material C, such as the pore size and BET specific surface area, can be controlled, which can shorten the diffusion path of ions, improve ionic conductivity, and thus improve the rate performance of the battery.

[0042] According to some specific embodiments of the present application, the average particle size of the secondary particles of the material C is 5 μm to 20 μm. For example, it can be 5 μm, 10 μm, 15 μm, 20 μm, etc. By limiting the average particle size of the primary particles of the material C to the above range, the contact area between the material C and the electrolyte can be moderate, and the diffusion path of lithium ions can be shortened, which can reduce capacity decay and thus improve the cycle performance of the battery.

[0043] According to some specific embodiments of the present application, the volume average particle size Dv50 of the material C is 7 μm to 18 μm. For example, it can be 7 μm, 10 μm, 15 μm, 18 μm, etc. By limiting the volume average particle size Dv50 of the material C to the above range, the pore structure and distribution of the first positive electrode active material can be adjusted, the electrolyte infiltration performance and the lithium ion shuttle efficiency can be improved, which is conducive to improving the rate performance of the battery and thus the cycle performance of the battery.

[0044] According to some specific embodiments of the present application, the BET specific surface area of ​​the material C is 0.2 m 2 / g to 1m 2 / g. For example, it can be 0.2m 2 / g,0.5m 2 / g,0.8m 2 / g,1m 2By limiting the BET specific surface area of ​​material C to the above range, on the one hand, the electrochemical reaction activity of the first positive electrode active material can be controlled, which is beneficial for improving the energy density of the positive electrode sheet 100. On the other hand, it can also reduce interfacial side reactions and reduce gas production, thereby improving the cycle performance of the battery.

[0045] According to some specific embodiments of the present application, the first positive electrode active material includes material B and material C. Material B is a single crystal high nickel material, and material C is a polycrystalline high nickel material. By mixing the single crystal high nickel material and the polycrystalline high nickel material as the first positive electrode active material, on the one hand, the polycrystalline material has better processing fluidity, and the single crystal material has better mechanical strength. By mixing these two materials, better processing performance can be obtained. On the other hand, the polycrystalline material has a higher energy density and good cycle stability, while the single crystal material has a higher cycle performance and fast charge and discharge capability. By mixing these two materials, their advantages can be comprehensively utilized to improve the cycle performance of the battery.

[0046] According to some specific embodiments of the present application, the mass ratio of material B to material C is (2-3):(7-8). For example, it can be 2:8, 3:7, etc. By limiting the mass ratio of material B to material C to the above range, the proportion of material B and material C in the first positive electrode active material layer 12 can be adjusted, which is beneficial to improving the cycle performance of the battery.

[0047] According to some specific embodiments of the present application, when the first positive electrode active material includes material B and material C, the volume average particle size Dv50 of the first positive electrode active material is 5 μm to 15 μm. For example, it can be 5 μm, 8 μm, 10 μm, 12 μm, 15 μm, etc. By limiting the mixed volume average particle size Dv50 of material B and material C to the above range, the contact area between the first positive electrode active material and the electrolyte can be moderate, and the diffusion path of lithium ions can be shortened, which can reduce capacity attenuation, thereby improving the cycle performance of the battery.

[0048] According to an embodiment of the present application, referring to FIG. 1, the second positive electrode active material layer 13 is provided on a side of the first positive electrode active material layer 12 facing away from the current collector 11. The second positive electrode active material layer 13 includes a second positive electrode active material, and an electrochemical potential window of the second positive electrode active material is greater than an electrochemical potential window of the first positive electrode active material. Thus, by forming the second positive electrode active material layer 13 including the second positive electrode active material on the first positive electrode active material layer 12, that is, the first positive electrode active material layer 12 is located between the current collector 11 and the second positive electrode active material layer 13, and the electrochemical potential window of the second positive electrode active material is greater than the electrochemical potential window of the first positive electrode active material, the high-voltage resistance performance of the second positive electrode active material layer 13 is better than that of the first positive electrode active material layer 12. During the charge-discharge cycle process, the second positive electrode active material layer 13 can resist the high voltage on the separator side, and thus can reduce the voltage difference between the separator side and the current collector 11 side of the positive electrode plate 100, which is beneficial to suppressing the transformation of the internal structure of the second positive electrode active material. Moreover, the setting of the second positive electrode active material layer can also protect the first positive electrode active material, reduce the damage to its structure caused by the high voltage, and improve the cycle performance of the battery.

[0049] The electrochemical potential window refers to the interval between the most positive potential and the most negative potential when the electrode material stably exists and does not decompose between a highest potential and a most negative potential. This interval between the most positive potential and the most negative potential is the electrochemical potential window of the electrode material.

[0050] According to some specific embodiments of the present application, the second positive electrode active material includes at least one of a lithium-rich manganese-based material and lithium iron manganese phosphate. Among them, the chemical formula of the lithium-rich manganese-based material is aLi2MnO3·(1 - a)LiNi x4 Co y4 Mn 1-x4-y4 O2, 0 ≤ a ≤ 1, 0.2 ≤ x4 ≤ 1, 0 ≤ y4 ≤ 0.5, 0 < x4 + y4 < l. For example, a can be 0.2, 0.5, 0.8, etc., x4 can be 0.33, 0.5, 0.6, 0.7, 0.8, etc., and y4 can be 0, 0.1, 0.2, 0.3, 0.33, 0.4, etc.; the chemical formula of the lithium iron manganese phosphate is LiMn x5 Fe 1-x5 PO4, 0.2 ≤ x5 ≤ 0.8. For example, x5 can be 0.2, 0.4, 0.5, 0.6, 0.8, etc. The above-mentioned second positive electrode active material has a relatively high electrochemical potential window, can effectively resist the situation of a relatively high voltage on the separator side during the charge and discharge of the positive electrode plate, improve the structural stability of the positive electrode plate near the separator side and the internal structural stability of the positive electrode active material, and thus is beneficial to improving the cycle performance of the battery.

[0051] According to some specific embodiments of the present application, the first positive electrode active material includes material A, and the second positive electrode active material includes a lithium-rich manganese-based material. When medium nickel material A is selected as the first positive electrode active material, the second positive electrode active material can be selected from a lithium-rich manganese-based material, wherein the medium nickel material contains a variety of active substances (such as Ni, Co, Mn), so that the battery can store more electrical energy in the same volume, which can ensure the full utilization of the capacity of the positive electrode plate 100, and is beneficial to improving the energy density of the battery. Moreover, Ni, Co and Mn also have good chemical stability during the battery charging and discharging process, which can effectively extend the cycle performance of the battery. The lithium-rich manganese-based material has a higher electrochemical potential window (4.6V), which can effectively resist the situation where the voltage on the diaphragm side is higher during the charging and discharging of the positive electrode plate, improve the structural stability of the positive electrode plate close to the diaphragm side and the structural stability inside the positive electrode active material, thereby helping to improve the cycle performance of the battery.

[0052] According to some specific embodiments of the present application, the first positive electrode active material includes at least one of material B and material C, and the second positive electrode active material includes lithium iron manganese phosphate. When a high-nickel material is selected as the first positive electrode active material, the second positive electrode active material can be selected from lithium iron manganese phosphate, wherein the high-nickel material contains a variety of active substances (such as Ni, Co, Mn), so that the battery can store more electrical energy in the same volume, which can ensure the full utilization of the capacity of the positive electrode plate 100, and Ni, Co and Mn also have good chemical stability during the battery charge and discharge process, which can effectively extend the cycle performance of the battery. Lithium iron manganese phosphate has a higher electrochemical potential window (>4.2V), which can effectively resist the situation where the voltage on the diaphragm side is high during the charge and discharge of the positive electrode plate, improve the structural stability of the positive electrode plate close to the diaphragm side and the structural stability inside the positive electrode active material, thereby helping to improve the cycle performance of the battery.

[0053] According to some specific embodiments of the present application, the average particle size of the primary particles of the lithium-rich manganese-based material is 50nm to 800nm. For example, it can be 50nm, 100nm, 300nm, 500nm, 800nm, etc. The lithium-rich manganese-based material is a polycrystalline material, which is composed of secondary particles formed by the agglomeration of primary particles. By limiting the average particle size of the primary particles of the lithium-rich manganese-based material to the above range, on the one hand, the pore size, BET specific surface area and other structural parameters of the polycrystalline material can be controlled, which can shorten the diffusion path of lithium ions and improve the ionic conductivity, thereby improving the charge and discharge performance of the battery. On the other hand, the mechanical strength and thermal stability of the second positive electrode active material can be increased, thereby improving the cycle performance of the battery.

[0054] According to some specific embodiments of the present application, the average particle size of the secondary particles of the lithium-rich manganese-based material is 10 μm to 20 μm. For example, it can be 10 μm, 12 μm, 15 μm, 18 μm, 20 μm, etc. By limiting the average particle size of the secondary particles of the lithium-rich manganese-based material to the above range, the contact area between the lithium-rich manganese-based material and the electrolyte can be moderate, and the diffusion path of lithium ions can be shortened, which can reduce capacity decay, thereby improving the cycle performance of the battery.

[0055] According to some specific embodiments of the present application, the volume average particle size Dv50 of the lithium-rich manganese-based material is 10 μm to 20 μm. For example, it can be 10 μm, 12 μm, 15 μm, 17 μm, 20 μm, etc. By limiting the volume average particle size Dv50 of the lithium-rich manganese-based material to the above range, the pore structure and distribution of the second positive electrode active material can be adjusted, the electrolyte infiltration performance and the lithium ion shuttle efficiency can be improved, which is conducive to improving the rate performance of the battery, and thus can improve the cycle performance of the battery.

[0056] According to some specific embodiments of the present application, the BET specific surface area of ​​the lithium-rich manganese-based material is 0.2 m 2 / g to 1m 2 / g. For example, it can be 0.2m 2 / g,0.5m 2 / g,0.7m 2 / g,0.9m 2 / g,1m 2 By limiting the BET specific surface area of ​​the lithium-rich manganese-based material to the above range, on the one hand, the electrochemical reaction activity of the second positive electrode active material can be controlled, which is conducive to improving the energy density of the positive electrode sheet 100. On the other hand, it can also reduce interfacial side reactions and reduce gas production, thereby improving the cycle performance of the battery.

[0057] According to some specific embodiments of the present application, the average primary particle size of the lithium manganese iron phosphate is 20 nm to 300 nm. For example, it can be 20 nm, 50 nm, 100 nm, 200 nm, 300 nm, etc. On the one hand, the structural parameters of the lithium manganese iron phosphate, such as the pore size and BET specific surface area, can be controlled, which can shorten the diffusion path of lithium ions and increase ionic conductivity, thereby improving the charge and discharge performance of the battery. On the other hand, it can increase the mechanical strength and thermal stability of the second positive electrode active material, thereby improving the cycle performance of the battery.

[0058] According to some specific embodiments of the present application, the volume average particle size Dv50 of the lithium manganese iron phosphate is 0.2 μm to 1.5 μm. For example, it can be 0.2 μm, 0.5 μm, 1 μm, 1.5 μm, etc. By controlling the D50 of the lithium manganese iron phosphate within the above range, the pore structure and distribution of the second positive electrode active material can be adjusted, improving the electrolyte infiltration performance and lithium ion shuttle efficiency, which is conducive to improving the battery's rate performance and thus the battery's cycle performance.

[0059] According to some specific embodiments of the present application, the BET specific surface area of ​​the lithium manganese iron phosphate is 10m 2 / g to 30m 2 / g. For example, it can be 10m 2 / g,20m 2 / g,30m 2 By limiting the BET specific surface area of ​​lithium manganese iron phosphate to the above range, on the one hand, the electrochemical reaction activity of the second positive electrode active material can be controlled, which is conducive to improving the energy density of the positive electrode sheet 100. On the other hand, it can also reduce interfacial side reactions and reduce gas production, thereby improving the cycle performance of the battery.

[0060] According to some specific embodiments of the present application, the lithium manganese iron phosphate further includes a carbon coating layer, which is coated on at least a portion of the surface of the lithium manganese iron phosphate. By providing the carbon coating layer on at least a portion of the surface of the lithium manganese iron phosphate, on the one hand, it can prevent the lithium manganese iron phosphate from directly contacting the electrolyte, thereby reducing the occurrence of side reactions and reducing gas production, which can further improve the cycle stability of the battery. On the other hand, it can also improve the conductivity of the material, which can further improve the rate performance of the battery.

[0061] According to some specific embodiments of the present application, the mass percentage of the carbon coating layer is 0.2% to 3% based on the total mass of the lithium manganese iron phosphate. For example, it can be 0.2%, 0.5%, 1%, 2%, 3%, etc. By limiting the mass percentage of the carbon coating layer to the above range, direct contact between the lithium manganese iron phosphate and the electrolyte can be avoided, thereby reducing the occurrence of side reactions and gas production, and further improving the cycle stability of the battery.

[0062] According to some specific embodiments of the present application, based on the total mass of the first positive electrode active material layer 12 and the second positive electrode active material layer 13, the mass proportion of the first positive electrode active material layer 12 is 70% to 90%. For example, it can be 70%, 80%, 90%, etc. By limiting the mass proportion of the first positive electrode active material layer 12 to the above range, it is possible to ensure that the first positive electrode active material layer 12 meets the requirements of high energy density and stability, while also ensuring that the second positive electrode active material layer 13 has high voltage resistance, which can withstand the high voltage on the diaphragm side during charging and discharging of the positive electrode sheet 100, which is beneficial to improving the cycle performance of the battery.

[0063] According to some specific embodiments of the present application, the compaction density of the positive active material layer in the positive electrode sheet 100 is 3.2 g / cm 3 to 3.7g / cm 3 , for example, can be 3.2 g / cm 3 , 3.5g / cm 3 , 3.7g / cm 3 By limiting the compaction density of the positive active material layer in the positive electrode sheet 100 to the above range, lithium ions can be better embedded and extracted, which is beneficial to increasing the discharge capacity of the battery, reducing internal resistance, reducing polarization loss, and improving the cycle performance of the battery.

[0064] It should be noted that the positive electrode active material layer is a general term for the first positive electrode active material layer 12 and the second positive electrode active material layer 13 .

[0065] According to some specific embodiments of the present application, the surface density of the positive active material layer in the positive electrode sheet 100 can be 100 g / m 2 Up to 400g / m 2 , for example, it can be 100g / m 2 , 250g / m 2 , 400g / m 2 By adjusting the density of the positive electrode active material layer, the lithium ion transmission path can be optimized, the internal resistance can be reduced, and the cycle performance of the battery can be improved.

[0066] It should be noted that the first positive electrode active material layer 12 can be formed on one side of the current collector 11 or on both sides of the current collector 11 . Those skilled in the art can make the selection according to actual needs.

[0067] In a second aspect of the present application, the present application proposes a method for preparing the positive electrode sheet 100. According to an embodiment of the present application, referring to FIG2 , the method includes:

[0068] S1 . Forming a first positive electrode active material layer 12 including a first positive electrode active material on at least one side of a current collector 11 .

[0069] In this step, the first positive electrode active material layer 12 is formed on at least one side of the current collector 11 using the first positive electrode active material. Thus, by forming the first positive electrode active material layer 12 including the first positive electrode active material on at least one side of the current collector 11, the cycle performance of the battery can be improved.

[0070] According to a specific embodiment of the present application, forming the first positive electrode active material layer 12 including the first positive electrode active material on at least one side of the current collector 11 is performed by the following steps:

[0071] S11 , mixing a first positive electrode active material, a first conductive agent, and a first solvent to obtain a first slurry.

[0072] In this step, the first positive electrode active material, the first conductive agent, and the first solvent are mixed and stirred to obtain the first slurry.

[0073] According to some specific embodiments of the present application, the first slurry also includes a first binder, and the mass ratio of the first positive electrode active material, the first binder, and the first conductive agent is (0.95-0.98): (0-0.3): (0.02-0.05). For example, it can be 0.95:0.1:0.02, 0.98:0.3:0.05, 0.96:0.2:0.04, etc. The first positive electrode active material can improve the cycle performance of the battery. The first binder and the second conductive agent play the role of connecting the first positive electrode active material and strengthening the electrode structure in the positive electrode sheet 100. By limiting the mass ratio of the first positive electrode active material, the first binder, and the first conductive agent to the above range, the high energy density of the battery can be ensured, and the cycle performance of the battery can also be improved.

[0074] As an example, the first binder includes but is not limited to polyvinylidene fluoride. The first conductive agent includes but is not limited to at least one of conductive carbon black, carbon nanotubes, and carbon nanofibers. The first solvent includes but is not limited to N-methylpyrrolidone.

[0075] S12 , coating the first slurry on at least one side of the current collector 11 , and drying it for the first time to obtain a first positive electrode active material layer 12 .

[0076] In this step, the first positive electrode active material layer 12 is obtained by coating the first slurry on at least one side of the current collector 11 and performing a first drying.

[0077] According to some specific embodiments of the present application, the temperature of the first drying is 60°C to 80°C. For example, it can be 60°C, 70°C, 80°C, etc. By limiting the temperature of the first drying to the above range, on the one hand, the evaporation rate of water can be controlled to avoid cracks on the material surface. On the other hand, it can promote the curing process of the binder, so that the positive electrode sheet 100 has good mechanical strength and stability.

[0078] According to some specific embodiments of the present application, the first drying time is 3 minutes to 10 minutes. For example, it can be 3 minutes, 5 minutes, 7 minutes, etc. By limiting the first drying time to the above range, the solidification of the positive electrode sheet 100 structure can be promoted, and the stability and consistency of the positive electrode sheet 100 can be improved.

[0079] S2 . Forming a second positive electrode active material layer 13 including a second positive electrode active material on a side of the first positive electrode active material layer 12 away from the current collector 11 .

[0080] In this step, a second positive electrode active material layer 13 including a second positive electrode active material is formed on the first positive electrode active material layer 12, that is, the first positive electrode active material layer 12 is located between the current collector 11 and the second positive electrode active material layer 13, and the electrochemical potential window of the second positive electrode active material is larger than the electrochemical potential window of the first positive electrode active material, so that the high voltage resistance of the second positive electrode active material layer 13 is better than that of the first positive electrode active material layer 12. During the charge and discharge cycle, the voltage difference between the positive electrode sheet 100 on the diaphragm side and the current collector 11 side can be reduced, thereby suppressing the transformation of the internal structure of the positive electrode active material and improving the cycle performance of the battery.

[0081] According to a specific embodiment of the present application, forming the second positive electrode active material layer 13 including the second positive electrode active material on the side of the first positive electrode active material layer 12 away from the current collector 11 is performed by the following steps:

[0082] S21 , mixing a second positive electrode active material, a second conductive agent, and a second solvent to obtain a second slurry.

[0083] In this step, the first slurry can be obtained by mixing and stirring the second positive electrode active material, the second conductive agent, and the second solvent.

[0084] According to some specific embodiments of the present application, the first slurry also includes a second binder, and the mass ratio of the second positive electrode active material, the second binder, and the second conductive agent is (0.95-0.98): (0-0.3): (0.02-0.05). For example, it can be 0.95:0.1:0.02, 0.98:0.3:0.05, 0.96:0.2:0.04, etc. The second positive electrode active material can improve the high voltage resistance and cycle performance of the positive electrode plate 100. The second binder and the second conductive agent play the role of connecting the second positive electrode active material and strengthening the structure of the positive electrode plate 100 in the positive electrode plate 100. By limiting the mass ratio of the second positive electrode active material, the second binder, and the second conductive agent to the above range, it can resist the situation where the voltage on the diaphragm side is high during charging and discharging of the positive electrode plate 100, which is beneficial to improving the cycle performance of the battery.

[0085] As an example, the second binder includes but is not limited to polyvinylidene fluoride. The second conductive agent includes but is not limited to at least one of conductive carbon black, carbon nanotubes, and carbon nanofibers. The second solvent includes but is not limited to N-methylpyrrolidone.

[0086] S22 , coating the second slurry on the side of the first positive electrode active material layer 12 away from the current collector 11 , and drying it for the second time to obtain a second positive electrode active material layer 13 .

[0087] In this step, the second slurry is applied to the side of the first positive electrode active material layer 12 away from the current collector 11 , dried for a second time, and then rolled to obtain the second positive electrode active material layer 13 , that is, the positive electrode sheet 100 .

[0088] According to some specific embodiments of the present application, the second drying temperature is between 110°C and 130°C. For example, it can be 110°C, 120°C, 130°C, etc. By limiting the second drying temperature to the above range, on the one hand, the evaporation rate of water can be controlled, thereby preventing cracks on the material surface. On the other hand, it can promote the curing process of the binder, so that the positive electrode sheet 100 has good mechanical strength and stability.

[0089] According to some specific embodiments of the present application, the second drying time is 5 minutes to 20 minutes. For example, it can be 5 minutes, 10 minutes, 20 minutes, etc. By limiting the second drying time to the above range, the solidification of the positive electrode sheet 100 structure can be promoted, and the stability and consistency of the positive electrode sheet 100 can be improved.

[0090] In a third aspect of the present application, a battery is provided. According to an embodiment of the present application, the battery includes the aforementioned positive electrode sheet 100 or the positive electrode sheet 100 prepared using the aforementioned method. The positive electrode sheet 100 has a long cycle performance, which makes the battery have good overall performance and can also have good cycle performance.

[0091] A battery is a battery that can be recharged to activate the active materials after discharge and continue to be used.

[0092] Typically, a battery includes a positive electrode sheet 100, a negative electrode sheet, a separator, and an electrolyte. During the battery's charge and discharge process, active ions (lithium ions) are inserted and removed between the positive electrode sheet 100 and the negative electrode sheet. The separator is provided between the positive electrode sheet 100 and the negative electrode sheet to isolate them. The electrolyte conducts ions between the positive electrode sheet 100 and the negative electrode sheet.

[0093] According to some specific embodiments of the present application, the battery may be a lithium-ion secondary battery.

[0094] The embodiment of the present application has no particular limitation on the shape of the battery, which may be cylindrical, square, or any other shape.

[0095] In a fourth aspect, this application provides a vehicle. According to embodiments of this application, the vehicle includes the aforementioned battery, which exhibits high cycle performance. Consequently, compared to existing technologies, the vehicle has improved stability and higher market satisfaction. For example, the vehicle may include, but is not limited to, pure electric vehicles and hybrid electric vehicles.

[0096] The scheme of the present disclosure will be explained below in conjunction with the examples. Those skilled in the art will understand that the following examples are only used to illustrate the present disclosure and should not be considered to limit the scope of the present disclosure. Where specific techniques or conditions are not specified in the examples, they are carried out according to the techniques or conditions described in the literature in this area or according to the product instructions. Where the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be obtained commercially.

[0097] Example 1

[0098] 1. Preparation of the first positive electrode active material layer:

[0099] (1) Selection of raw materials: The first positive electrode active material is material A (nickel material in single crystal), with the chemical formula LiNi 0.68 Co 0.07 Mn 0.25 O2, the average particle size of the primary particles of material A is 5 μm, the volume average particle size Dv50 of material A is 3.52 μm, and the BET specific surface area of ​​material A is 0.85 m 2 / g; the first binder is polyvinylidene fluoride; the first conductive agent is conductive carbon black and carbon nanotubes, and the first solvent is N-methylpyrrolidone.

[0100] (2) Preparation of the first slurry: Material A, conductive carbon black, carbon nanotubes and polyvinylidene fluoride were mixed in a mass ratio of 97.3:1.2:0.5:1, and then mixed with an appropriate amount of N-methylpyrrolidone and stirred evenly to obtain the first slurry.

[0101] (3) The first slurry is evenly coated on a composite aluminum current collector, which is composed of two layers of aluminum foil with a thickness of 1.5 μm and a polypropylene sandwich with a thickness of 10 μm. The composite current collector is then dried at 60° C. for 10 minutes to obtain a first positive electrode active material layer.

[0102] 2. Preparation of the second positive electrode active material layer:

[0103] (1) Selection of raw materials: The second positive electrode active material is a lithium-rich manganese-based material with a chemical formula of 0.5Li2MnO3·0.5LiNi 0.33 Co 0.34 Mn 0.33 O2, the average particle size of the primary particles of the lithium-rich manganese-based material is 400nm, the average particle size of the lithium-rich manganese-based material is 14μm, the volume average particle size Dv50 of the lithium-rich manganese-based material is 13.38μm, and the BET specific surface area of ​​the lithium-rich manganese-based material is 0.44m 2 / g; the first binder is polyvinylidene fluoride; the first conductive agent is conductive carbon black and carbon nanotubes, and the first solvent is N-methylpyrrolidone.

[0104] (2) Preparation of the second slurry: The lithium-rich manganese-based material, conductive carbon black, carbon nanotubes and polyvinylidene fluoride were mixed in a mass ratio of 97.3:1.2:0.5:1, and then mixed with an appropriate amount of N-methylpyrrolidone and stirred evenly to obtain the second slurry.

[0105] (3) The second slurry is evenly coated on the dried first positive electrode active material layer, dried at 110°C for 15 minutes, and then rolled to obtain a second positive electrode active material layer, thereby obtaining a positive electrode sheet. The mass ratio of the first positive electrode active material layer to the second positive electrode active material layer is 7:3.

[0106] 3. Preparation of battery: The positive electrode sheet prepared above is assembled with the graphite negative electrode sheet, the separator and the electrolyte into a soft-pack battery for subsequent performance testing. The separator is a PP / PE composite film material, the electrolyte uses a mixed solvent with a mass ratio of EC:DEC:DMC = 1:1:1, and the electrolyte is 1M lithium hexafluorophosphate.

[0107] The batteries of Examples 2-8 and Comparative Examples 1-4 are the same as those of Example 1 except for the parameters of the positive electrode sheets (see Table 1).

[0108] The experimental parameters of the positive electrode sheets of Examples 1-8 and Comparative Examples 1-4 of the present application are shown in Table 1.

[0109] Table 1 “ / ” means none.

[0110] Testing and Analysis

[0111] Under the same conditions, the cycle performance of the soft-pack batteries prepared in Examples 1-8 and Comparative Examples 1-4 was tested. The specific test method is as follows:

[0112] When the first positive electrode active material in the first positive electrode active material layer is material A, the electrochemical test voltage is 2.8V to 4.4V; when the first positive electrode active material in the first positive electrode active material layer is a mixture of material B and material C, the electrochemical test voltage is 2.8V to 4.25V.

[0113] Cycling performance test: Under charge and discharge cycles, the charge and discharge rate was set to 0.33C and the test temperature was 25°C. The capacity retention rate after 1000 cycles was calculated. Capacity retention rate after 1000 cycles (%) = capacity after 1000 cycles / initial capacity.

[0114] The test results are shown in Table 2.

[0115] Table 2

[0116] Combining Table 1 and Table 2, it can be seen that compared with the batteries obtained in Comparative Examples 1-4, the batteries obtained in Examples 1-8 have better cycle performance, wherein Example 1 is a first positive electrode active material layer containing material A and a second positive electrode active material layer containing a lithium-rich manganese-based material, the mass fraction ratio of the first positive electrode active material layer to the second positive electrode active material layer is 7:3, and the charge and discharge voltage window is 2.8V to 4.4V. Since the voltage at the end of charging is high, a high-voltage material, a lithium-rich manganese-based material, is selected as the second positive electrode active material layer; Comparative Example 1 is a soft-pack battery prepared by using only a positive electrode plate made of material A. There is no surface high-voltage resistant layer, resulting in the late charge and discharge cycle. The voltage of the positive electrode plate near the diaphragm is higher than the voltage near the current collector, so the positive electrode material near the diaphragm of the positive electrode plate undergoes structural transformation first, and side reactions are more likely to occur, affecting the cycle performance of the battery.

[0117] Example 1 has a surface high-voltage resistant layer. Compared with Comparative Example 1, the discharge capacity of the soft-pack battery is slightly reduced. This is because in the charge and discharge voltage range of material A (2.8V to 4.4V), the lithium-rich manganese-based material cannot fully exert the capacity of the material itself; and the capacity retention rate of Example 1 after 1000 cycles is much higher than that of Comparative Example 1. This is because in the later stage of the cycle, the lithium-rich manganese-based material of the second positive electrode active material layer can withstand higher voltages and can exert higher capacity. By replenishing the capacity, the capacity attenuation of the soft-pack battery is suppressed, and excellent cycle performance is exerted. At the same time, the lithium-rich manganese-based material is a large polycrystalline particle, and a larger pore can be formed in the second positive electrode active material layer. The tortuosity of the pore is low, which can provide a fast transmission channel for lithium ions, which is beneficial to improving the rate performance of the battery.

[0118] Therefore, the present application divides the positive electrode active material coating of the positive electrode plate into a first positive electrode active material layer and a second positive electrode active material layer, and after preparing the slurries according to different mass fractions, applies them layer by layer on the current collector, dries and rolls them to make a positive electrode plate with excellent cycle performance, so as to achieve high voltage resistance of the positive electrode active material layer, and at the same time optimize the internal gap structure of the positive electrode plate, which can further improve the cycle performance of the battery.

[0119] In the description of this specification, the reference terms "one embodiment", "some embodiments", "example", "specific example", "some implementation plans" or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0120] Although the embodiments of the present application have been shown and described above, it can be understood that the above embodiments are exemplary and cannot be understood as limitations on the present application. Ordinary technicians in this field can change, modify, replace and modify the above embodiments within the scope of the present application.

Claims

1. A positive electrode sheet, wherein: include: current collector; The first positive electrode active material layer is provided on at least one side of the current collector, and the first positive electrode active material layer includes a first positive electrode active material, and the first positive electrode active material includes LiNi x Co y Mn 1-x-y O2,0.6≤x≤0.95,0.03≤y≤0.1,0 <x+y<1; The second positive electrode active material layer is arranged on a side of the first positive electrode active material layer away from the current collector, and the second positive electrode active material layer includes a second positive electrode active material, and the electrochemical potential window of the second positive electrode active material is larger than the electrochemical potential window of the first positive electrode active material.

2. The positive electrode sheet according to claim 1, wherein: The first positive electrode active material includes at least one of material A, material B and material C, wherein: The material A is a single crystal material with the chemical formula LiNi x1 Co y1 Mn 1-x1-y1 O2,0.6≤x1<0.8,0.03≤y1≤0.1,0 <x1+y1<1; The material B is a single crystal material with the chemical formula LiNi x2 Co y2 Mn 1-x2-y2 O2,0.8≤x2≤0.95,0.03≤y2≤0.1,0 <x2+y2<1; The material C is a polycrystalline material with the chemical formula LiNi x3 Co y3 Mn 1-x3-y3 O2,0.8≤x3≤0.95,0.03≤y3≤0.1,0 <x3+y3<1。 3. The positive electrode sheet according to claim 2, wherein: The volume average particle size Dv50 of the material A is 1 μm to 6 μm; and / or, The BET specific surface area of the material A is 0.5 m 2 / g to 1.5m 2 / g.

4. The positive electrode sheet according to claim 2 or 3, wherein: The volume average particle size Dv50 of the material B is 1 μm to 5 μm; and / or, The BET specific surface area of the material B is 0.5 m 2 / g to 1.5m 2 / g.

5. The positive electrode sheet according to any one of claims 2 to 4, wherein: The volume average particle size Dv50 of the material C is 7 μm to 18 μm; and / or, The BET specific surface area of the material C is 0.2 m 2 / g to 1m 2 / g.

6. The positive electrode sheet according to any one of claims 1 to 5, wherein: The second positive electrode active material includes at least one of a lithium-rich manganese-based material and lithium iron manganese phosphate, wherein: The chemical formula of the lithium-rich manganese-based material is aLi2MnO3·(1-a)LiNi x4 Co y4 Mn 1-x4-y4 O2, 0≤a≤1, 0.2≤x4≤1, 0≤y4≤0.5, 0 <x4+y4<1; The chemical formula of the lithium manganese iron phosphate is LiMn x5 Fe 1-x5 PO4, 0.2≤x5≤0.

8.

7. The positive electrode sheet according to claim 6, wherein: The first positive electrode active material includes material A, and the second positive electrode active material includes a lithium-rich manganese-based material.

8. The positive electrode sheet according to claim 6, wherein: The first positive electrode active material includes at least one of material B and material C, and the second positive electrode active material includes lithium manganese iron phosphate.

9. The positive electrode sheet according to claim 6, wherein: The volume average particle size Dv50 of the lithium-rich manganese-based material is 10 μm to 20 μm; and / or, The BET specific surface area of the lithium-rich manganese-based material is 0.2 m 2 / g to 1m 2 / g.

10. The positive electrode sheet according to claim 6, wherein: The volume average particle size Dv50 of the lithium manganese iron phosphate is 0.2 μm to 1.5 μm; and / or, The BET specific surface area of the lithium manganese iron phosphate is 10m 2 / g to 30m 2 / g.

11. A method for preparing the positive electrode sheet according to any one of claims 1 to 10, wherein: include: forming a first positive electrode active material layer including a first positive electrode active material on at least one side of the current collector; A second positive electrode active material layer including a second positive electrode active material is formed on a side of the first positive electrode active material layer away from the current collector to obtain a positive electrode sheet.

12. A battery, wherein: The battery comprises the positive electrode sheet according to any one of claims 1 to 10 or the positive electrode sheet prepared by the method according to claim 11.

13. A vehicle, wherein The vehicle includes the battery of claim 12.

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