Positive electrode sheet, method for manufacturing the same, and battery

Abstract

The application discloses a positive electrode sheet, a preparation method thereof and a battery. The positive electrode sheet comprises a current collector and a positive active material layer, the positive active material layer is arranged on at least one side of the current collector, and the material of the positive active material layer comprises lithium nickel cobalt manganese oxide, lithium manganese oxide and lithium iron manganese phosphate. The positive electrode sheet has good low-temperature resistance, and can improve the cycle performance and capacity retention rate of the battery.

Description

Technical Field

[0001] This invention belongs to the field of battery technology, specifically relating to a positive electrode sheet and its preparation method, and a battery. Background Technology

[0002] As the popularity of new energy vehicles increases, the problems they expose are also becoming more apparent. Range and charging speed are two particularly prominent issues, especially range in the cold winters of northern regions. Lithium-ion batteries, with their advantages of high energy density, long cycle life, high operating voltage, and environmental friendliness, are gradually becoming the primary power source for new energy vehicles.

[0003] However, existing lithium-ion batteries have poor capacity retention and cycle performance at low temperatures, which limits their application. Summary of the Invention

[0004] This invention aims to at least partially solve one of the technical problems in related technologies. Therefore, one object of this invention is to provide a positive electrode sheet and its preparation method, as well as a battery. The positive electrode sheet of this application has good low-temperature resistance and can improve the cycle performance and capacity retention of the battery.

[0005] In a first aspect, the present invention provides a positive electrode sheet. According to an embodiment of the present invention, the positive electrode sheet includes a current collector and a positive active material layer. The positive active material layer is disposed on at least one side of the current collector. The material of the positive active material layer includes lithium nickel cobalt manganese oxide, lithium manganese oxide, and lithium iron manganese phosphate, wherein lithium nickel cobalt manganese oxide and lithium manganese oxide are polycrystalline materials.

[0006] According to the above embodiments of the present invention, the positive electrode sheet includes a current collector and a positive electrode active material layer, wherein the positive electrode active material layer is formed on the current collector. The material of the positive electrode active material layer includes lithium nickel cobalt manganese oxide, lithium manganese oxide, and lithium iron manganese phosphate. Lithium nickel cobalt manganese oxide provides capacity, which is beneficial for improving energy density and providing more electrical energy, thereby improving the battery's capacity retention rate. Both lithium nickel cobalt manganese oxide and lithium iron manganese phosphate have good cycle life, ensuring good cycle performance of the battery during use. The crystal structure of lithium manganese oxide maintains good stability at low temperatures and is not prone to structural changes, thus ensuring the normal progress of the internal reaction of the battery, and further improving the low-temperature resistance of the positive electrode sheet. Furthermore, polycrystalline lithium nickel cobalt manganese oxide and polycrystalline lithium manganese oxide have poor crystallinity, with irregular polyhedral grains, easily generating a large number of grain boundaries, thereby improving the conductivity of the positive electrode sheet. Therefore, the positive electrode of this application has good low-temperature resistance under the combined action of lithium nickel cobalt manganese oxide, lithium manganese oxide and lithium iron manganese phosphate, which can improve the cycle performance and capacity retention of the battery.

[0007] In addition, the positive electrode sheet according to the above embodiments of the present invention may have the following additional technical features:

[0008] In some embodiments of the present invention, the mass ratio of lithium manganese oxide, lithium nickel cobalt manganese oxide, and lithium iron manganese phosphate is 5:3:2. This improves the low-temperature capacity retention and safety performance of the battery.

[0009] In some embodiments of the present invention, the lithium manganese oxide, the lithium nickel cobalt manganese oxide, and the lithium iron manganese phosphate satisfy the following relationship: 24 ≤ (d1×S1×0.5+d2×S2×0.3+d3×S3×0.2)×PD ≤ 30, where d1 is the Dv50 particle size of lithium manganese oxide in μm; and S1 is the specific surface area of ​​lithium manganese oxide in m². 2 / g; d2 is the Dv50 particle size of lithium nickel cobalt manganese oxide, in μm; S2 is the specific surface area of ​​lithium nickel cobalt manganese oxide, in m². 2 / g; d3 is the Dv50 particle size of lithium manganese iron phosphate, in μm; S3 is the specific surface area of ​​lithium manganese iron phosphate, in m². 2 / g; PD is the compaction density of the positive electrode active material layer, in g / cm³. 3 The preferred value is 26≤(d1×S1×0.5+d2×S2×0.3+d3×S3×0.2)×PD≤28. This improves the battery's low-temperature capacity retention and safety performance.

[0010] In some embodiments of the present invention, the average particle size of the primary lithium manganese oxide particles is 0.2 μm-2 μm. This allows for a suitable contact area between the lithium manganese oxide and the electrolyte, and shortens the diffusion path of lithium ions, thereby improving the cycle performance of the battery.

[0011] In some embodiments of the present invention, the Dv50 particle size of the lithium manganese oxide is 6μm-20μm. This allows for adjustment of the pore structure and distribution of the positive electrode active material, improving the wetting performance of the electrolyte and the lithium-ion shuttle efficiency, which is beneficial for improving the rate performance of the battery.

[0012] In some embodiments of the present invention, the specific surface area of ​​the lithium manganese oxide is 0.2 m². 2 / g-0.8m 2 / g. This can reduce interfacial side reactions, decrease gas production, and thus improve the cycle performance of the battery.

[0013] In some embodiments of the present invention, the average particle size of the primary nickel-cobalt-manganese oxide particles is 0.05 μm-0.2 μm. This allows for a suitable contact area between the lithium nickel-cobalt-manganese oxide and the electrolyte, and shortens the diffusion path of lithium ions, thereby improving the cycle performance of the battery.

[0014] In some embodiments of the present invention, the Dv50 particle size of the lithium nickel cobalt manganese oxide is 6μm-18μm. This is beneficial for improving the rate performance of the battery.

[0015] In some embodiments of the present invention, the specific surface area of ​​the lithium nickel cobalt manganese oxide is 0.2 m². 2 / g-0.8m 2 / g. This can reduce interfacial side reactions, decrease gas production, and thus improve the cycle performance of the battery.

[0016] In some embodiments of the present invention, the Dv50 particle size of the lithium manganese iron phosphate is 0.5 μm-2 μm. This is beneficial for improving the rate performance of the battery.

[0017] In some embodiments of the present invention, the specific surface area of ​​the lithium manganese iron phosphate is 10 m². 2 / g-30m 2 / g. This can reduce interfacial side reactions, decrease gas production, and thus improve the cycle performance of the battery.

[0018] In some embodiments of the present invention, the compaction density of the positive electrode active material layer is 2.5 g / cm³. 3 -3.4g / cm 3 This promotes better lithium-ion insertion and extraction, which helps increase battery discharge capacity, reduce internal resistance, reduce polarization loss, and improve battery cycle performance.

[0019] In a second aspect of the invention, this application proposes a method for preparing the above-mentioned positive electrode sheet. According to an embodiment of the invention, the method includes: forming a positive electrode active material layer comprising lithium nickel cobalt manganese oxide, lithium manganese oxide, and lithium iron manganese phosphate on at least one side of a current collector, thereby obtaining a positive electrode sheet. This results in a positive electrode sheet with good low-temperature performance, which is beneficial for improving the capacity retention and cycle performance of the battery at low temperatures.

[0020] In a third aspect of the invention, this application proposes a battery, according to an embodiment of the invention, comprising the above-described positive electrode sheet or a positive electrode sheet prepared by the above-described method. Therefore, the positive electrode sheet has better low-temperature resistance, which is beneficial for improving the low-temperature capacity retention rate and cycle performance of the battery, resulting in better overall performance of the battery.

[0021] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0022] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the description of the embodiments taken in conjunction with the following drawings, in which:

[0023] Figure 1 This invention shows a schematic diagram of the structure of a positive electrode sheet according to an embodiment of the present application;

[0024] Figure 2 The graph shows a comparison of the discharge curves of the batteries of Example 1, Comparative Example 1 and Comparative Example 4 of this application at -30°C.

[0025] Attached icon number

[0026] Positive electrode 100, current collector 11, positive electrode active material layer 12. Detailed Implementation

[0027] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein 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 intended to explain the present invention, and should not be construed as limiting the present invention.

[0028] In a first aspect, the present invention provides a positive electrode 100, according to an embodiment of the invention, with reference to... Figure 1 The positive electrode 100 includes a current collector 11 and a positive electrode active material layer 12.

[0029] The current collector 11 serves as a carrier for the positive electrode active material, enabling it to support and carry the positive electrode active material and ensure the stability of the battery during charging and discharging. As an example, the current collector 11 includes, but is not limited to, at least one of pure aluminum foil and composite aluminum foil.

[0030] According to an embodiment of the present invention, reference Figure 1 The positive electrode active material layer 12 is disposed on at least one side of the current collector 11. The material of the positive electrode active material layer includes lithium nickel cobalt manganese oxide, lithium manganese oxide, and lithium iron manganese phosphate, wherein lithium nickel cobalt manganese oxide and lithium manganese oxide are polycrystalline materials. Lithium nickel cobalt manganese oxide can provide capacity, which is beneficial to improving energy density and providing more electrical energy, thereby improving the battery's capacity retention rate. Both lithium nickel cobalt manganese oxide and lithium iron manganese phosphate have good cycle life, ensuring good cycle performance of the battery during use. The crystal structure of lithium manganese oxide maintains good stability at low temperatures and is not prone to structural changes, thus ensuring the normal progress of the internal reaction of the battery, which in turn helps improve the low-temperature resistance of the positive electrode sheet. Furthermore, polycrystalline lithium nickel cobalt manganese oxide and polycrystalline lithium manganese oxide have poor crystallinity, with irregular polyhedral grains, easily generating a large number of grain boundaries, thereby improving the conductivity of the positive electrode sheet. Therefore, the positive electrode of this application has good low-temperature resistance under the combined action of lithium nickel cobalt manganese oxide, lithium manganese oxide and lithium iron manganese phosphate, which can improve the cycle performance and capacity retention of the battery.

[0031] According to some specific embodiments of the present invention, the mass ratio of lithium manganese oxide, lithium nickel cobalt manganese oxide, and lithium iron manganese phosphate is 5:3:2. By limiting the mass ratio of lithium manganese oxide, lithium nickel cobalt manganese oxide, and lithium iron manganese phosphate to the above range, the proportion of lithium manganese oxide, lithium nickel cobalt manganese oxide, and lithium iron manganese phosphate in the positive electrode active material layer 12 can be adjusted, thereby improving the low-temperature capacity retention rate and safety performance of the battery.

[0032] According to some specific embodiments of the present invention, the lithium manganese oxide, the lithium nickel cobalt manganese oxide, and the lithium iron manganese phosphate satisfy the following relationship: 24 ≤ (d1×S1×0.5+d2×S2×0.3+d3×S3×0.2)×PD ≤ 30. For example, it can be 24, 25, 26, 27, 28, 30, etc., where d1 is the Dv50 particle size of lithium manganese oxide in μm; S1 is the specific surface area of ​​lithium manganese oxide in m². 2 / g; d2 is the Dv50 particle size of lithium nickel cobalt manganese oxide, in μm; S2 is the specific surface area of ​​lithium nickel cobalt manganese oxide, in m². 2 / g; d3 is the Dv50 particle size of lithium manganese iron phosphate, in μm; S3 is the specific surface area of ​​lithium manganese iron phosphate, in m². 2 / g; PD is the compaction density of the positive electrode active material layer, in g / cm³. 3 By limiting the relationship between the Dv50 particle size, specific surface area, and compaction density of the positive electrode active material layer of lithium manganese oxide, lithium nickel cobalt manganese oxide, and lithium iron manganese phosphate within the aforementioned range, on the one hand, a better range of particle matching for these three materials can be achieved, shortening the lithium-ion insertion and extraction paths and improving the conductivity of the positive electrode. On the other hand, the porosity of the positive electrode active material layer can be controlled, giving it suitable porosity that facilitates lithium-ion migration, thereby improving the low-temperature performance of the positive electrode. Furthermore, it can accommodate more electrolyte, forming a solid electrolyte interphase (SEI) film on the surface of the positive electrode, inhibiting Mn dissolution, and thus improving battery cycle performance and safety. Further, 26 ≤ (d1×S1×0.5+d2×S2×0.3+d3×S3×0.2)×PD ≤ 28.

[0033] According to some specific embodiments of the present invention, the average particle size of the primary particles of lithium manganese oxide is 0.2 μm-2 μm. For example, it can be 0.2 μm, 1 μm, 1.5 μm, 2 μm, etc. By limiting the average particle size of the primary particles of lithium manganese oxide to the above range, a certain porosity can be guaranteed, thereby improving the liquid retention capacity.

[0034] It should be noted that the average particle size of primary lithium manganese oxide refers to the average size of a single lithium manganese oxide particle. It reflects the overall average size of lithium manganese oxide particles and has a certain influence on particle shape, distribution, and quality. Typically, images of lithium manganese oxide particles are observed and captured using a scanning electron microscope, and then image processing software is used to calculate the average particle size of the primary lithium manganese oxide particles.

[0035] According to some specific embodiments of the present invention, the Dv50 particle size of the lithium manganese oxide is 6μm-20μm. For example, it can be 6μm, 10μm, 15μm, 20μm, etc. By controlling the Dv50 of the lithium manganese oxide within the above range, the pore structure and distribution of the positive electrode active material can be adjusted, the wetting performance of the electrolyte and the lithium ion shuttle efficiency can be improved, which is beneficial to improving the rate performance of the battery.

[0036] It should be noted that Dv50 particle size refers to the particle size at which the cumulative distribution of lithium manganese oxide particles reaches 50%. That is, lithium manganese oxide particles smaller than this size account for 50% of the total volume of all positive electrode active material particles, and lithium manganese oxide particles larger than this size also account for 50% of the total volume of all positive electrode active material particles. The Dv50 particle size is measured using a laser particle size analyzer.

[0037] According to some specific embodiments of the present invention, the specific surface area of ​​the lithium manganese oxide is 0.2 m². 2 / g-0.8m 2 / g. For example, it can be 0.2m. 2 / g, 0.5m 2 / g, 0.8m 2 / g etc. By limiting the specific surface area of ​​lithium manganese oxide within the above range, on the one hand, the electrochemical reactivity of the positive electrode active material can be controlled, which is beneficial to improving the energy density of the positive electrode 100. On the other hand, it can also reduce interfacial side reactions and reduce gas production, thereby improving the cycle performance of the battery.

[0038] It should be noted that the specific surface area of ​​lithium manganese oxide can be determined by the following method: The specific surface area of ​​solid substances is determined using the gas adsorption BET method, with nitrogen as the adsorbent. The specific surface area of ​​the sample is characterized by the number of nitrogen molecules closely packed (adsorbed) on its surface and the maximum cross-sectional area of ​​the molecules. The equilibrium saturation adsorption capacity (V) of nitrogen molecules on the sample surface is measured. The monolayer saturation adsorption capacity (Vm) is calculated using different theoretical models, thus determining the number of molecules. The equivalent maximum cross-sectional area (Am) of nitrogen molecules is calculated using a hexagonal close-packed model, thereby determining the specific surface area of ​​the sample. The calculation formula is as follows: S g =V m NA m / 22400W, S g The specific surface area of ​​the sample being tested (m²)2 / g), V m A represents the saturated adsorption capacity (mL) of nitrogen molecules in a monolayer under standard conditions. m The equivalent maximum cross-sectional area of ​​a nitrogen molecule (theoretical value of hexagonal close-packed structure Am = 0.162 nm) 2 W is the mass of the sample being tested (g), and N is Avogadro's constant (6.02 x 10⁻⁶). 23 ).

[0039] According to some specific embodiments of the present invention, the average particle size of the primary particles of the lithium nickel cobalt manganese oxide is 0.05 μm-0.2 μm. For example, it can be 0.05 μm, 0.1 μm, 0.2 μm, etc. By limiting the average particle size of the primary particles of lithium nickel cobalt manganese oxide to the above range, the contact area between lithium nickel cobalt manganese oxide and electrolyte can be moderate, and the diffusion path of lithium ions can be shortened, thereby improving the cycle performance of the battery.

[0040] According to some specific embodiments of the present invention, the Dv50 particle size of the lithium nickel cobalt manganese oxide is 6μm-18μm. For example, it can be 6μm, 10μm, 15μm, 18μm, etc. By controlling the Dv50 of the lithium nickel cobalt manganese oxide within the above range, the pore structure and distribution of the positive electrode active material can be adjusted, the wetting performance of the electrolyte and the lithium ion shuttle efficiency can be improved, which is beneficial to improving the rate performance of the battery.

[0041] According to some specific embodiments of the present invention, the specific surface area of ​​the lithium nickel cobalt manganese oxide is 0.2 m². 2 / g-0.8m 2 / g. For example, it can be 0.2m. 2 / g, 0.5m 2 / g, 0.8m 2 / g etc. By limiting the specific surface area of ​​lithium nickel cobalt manganese oxide within the above-mentioned range, on the one hand, the electrochemical reactivity of the positive electrode active material can be controlled, which is beneficial to improving the energy density of the positive electrode 100. On the other hand, it can also reduce interfacial side reactions and reduce gas production, thereby improving the cycle performance of the battery.

[0042] According to some specific embodiments of the present invention, the Dv50 particle size of the lithium manganese iron phosphate is 0.5 μm-2 μm. For example, it can be 0.5 μm, 0.1 μm, 1.5 μm, 2 μm, etc. By limiting the Dv50 particle size of the lithium manganese iron phosphate within the above range, the pore structure and distribution of the positive electrode active material can be adjusted, the wetting performance of the electrolyte and the shuttle efficiency of lithium ions can be improved, which is beneficial to improving the rate performance of the battery.

[0043] According to some specific embodiments of the present invention, the specific surface area of ​​the lithium manganese iron phosphate is 10 m². 2 / g-30m2 / g. For example, it can be 10m. 2 / g, 15m 2 / g, 20m 2 / g, 30m 2 / g etc. By limiting the specific surface area of ​​lithium manganese iron phosphate within the above range, on the one hand, the electrochemical reactivity of the positive electrode active material can be controlled, which is beneficial to improving the energy density of the positive electrode 100. On the other hand, it can also reduce interfacial side reactions and reduce gas production, thereby improving the cycle performance of the battery.

[0044] According to some specific embodiments of the present invention, the compaction density of the positive electrode active material layer is 2.5 g / cm³. 3 -3.4g / cm 3 For example, it could be 2.5 g / cm³. 3 3.0g / cm 3 3.4g / cm 3 By limiting the compaction density of the positive electrode active material layer in the positive electrode sheet 100 to the above range, lithium ions can be better inserted 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.

[0045] It should be noted that the positive electrode active material layer 12 can be formed on one side of the current collector 11, or it can be formed on both sides of the current collector 11. Those skilled in the art can choose according to actual needs.

[0046] In a second aspect, the present invention provides a method for preparing the positive electrode 100. According to an embodiment of the present invention, the method includes: forming a positive electrode active material layer 12 comprising lithium nickel cobalt manganese oxide, lithium manganese oxide, and lithium iron manganese phosphate on at least one side of a current collector 11, thereby obtaining a positive electrode.

[0047] In this step, a positive electrode active material layer 12 is formed by mixing lithium nickel cobalt manganese oxide, lithium manganese oxide, and lithium iron manganese phosphate on at least one side of the current collector 11. This improves the battery's capacity retention and cycle performance at low temperatures.

[0048] According to a specific embodiment of the present invention, the formation of a positive electrode active material layer 12 comprising lithium nickel cobalt manganese oxide, lithium manganese oxide, and lithium iron manganese phosphate on at least one side of the current collector 11 is performed by the following steps:

[0049] S10. Lithium nickel cobalt manganese oxide, lithium manganese oxide and lithium iron manganese phosphate are mixed to obtain the positive electrode active material.

[0050] In this step, the positive electrode active material is prepared by mixing and stirring lithium nickel cobalt manganese oxide, lithium manganese oxide, and lithium iron manganese phosphate. Lithium nickel cobalt manganese oxide has a high energy density, providing more electrical energy and thus improving the battery's capacity retention rate. Both lithium nickel cobalt manganese oxide and lithium iron manganese phosphate have good cycle life, ensuring good cycle performance during battery use. The crystal structure of lithium manganese oxide maintains good stability at low temperatures, is not prone to structural changes, and ensures the normal progress of internal battery reactions, thereby improving the low-temperature resistance of the positive electrode. Furthermore, polycrystalline lithium nickel cobalt manganese oxide and polycrystalline lithium manganese oxide have poor crystallinity, with irregular polyhedral grains, easily generating numerous grain boundaries, which can improve the conductivity of the positive electrode. Therefore, the positive electrode of this application, under the combined action of lithium nickel cobalt manganese oxide, lithium manganese oxide, and lithium iron manganese phosphate, has good low-temperature resistance, improving the battery's cycle performance and capacity retention rate.

[0051] S20. Mix the positive electrode active material, conductive agent, binder and solvent to obtain a slurry.

[0052] In this step, a slurry is obtained by mixing and stirring the positive electrode active material, conductive agent, binder and solvent. Specifically, the positive electrode active material, conductive agent and binder are mixed in a mass ratio of 94:3:3, and then the solvent is added in a high-speed mixer and mixed evenly to form a slurry with a solid content of 45% to 80%.

[0053] As an example, the binder includes, but is not limited to, polyvinylidene fluoride (PVDF). The conductive agent includes, but is not limited to, at least one of conductive carbon black and carbon nanotubes. The solvent includes, but is not limited to, N-methylpyrrolidone (NMP).

[0054] S30. The slurry is coated on at least one side of the current collector 11 and dried to obtain a positive electrode active material layer 12, thus obtaining a positive electrode sheet.

[0055] In this step, by coating the slurry onto at least one side of the current collector 11 and drying it, a positive electrode active material layer 12 is obtained, which is the positive electrode sheet 100. Specifically, a transfer coating machine is used to coat the slurry onto one side of an aluminum foil with a thickness of 12 μm, and then dried to ensure that the areal density of the positive electrode active material layer per unit area after drying is 17.5 mg / cm³. 2 Then, the same process is applied to the other side of the aluminum foil and dried to obtain a positive electrode semi-finished product. The positive electrode semi-finished product is then rolled to obtain the positive electrode sheet.

[0056] In a third aspect, the present invention provides a battery. According to an embodiment of the present invention, the battery includes the above-described positive electrode 100 or a positive electrode 100 prepared by the above-described method. The positive electrode 100 has good low-temperature resistance, which is beneficial to improving the low-temperature capacity retention rate and cycle performance of the battery, resulting in better overall performance of the battery.

[0057] A battery is a device that can be recharged after being discharged, allowing its active materials to be reactivated and continue to be used.

[0058] Typically, a battery includes a positive electrode 100, a negative electrode, a separator, and an electrolyte. During charging and discharging, active ions (lithium ions) move back and forth between the positive and negative electrode 100, inserting and extracting. The separator, positioned between the positive and negative electrode 100, serves as a barrier. The electrolyte, acting as a conductor between the positive and negative electrode 100, facilitates ion exchange.

[0059] According to some specific embodiments of the present invention, the battery can be a lithium-ion rechargeable battery.

[0060] The embodiments of this application do not impose any particular restrictions on the shape of the battery, which can be cylindrical, square, or any other arbitrary shape.

[0061] The present disclosure will be explained below with reference to embodiments. Those skilled in the art will understand that the following embodiments are for illustrative purposes only and should not be construed as limiting the scope of the disclosure. Where specific techniques or conditions are not specified in the embodiments, they are performed in accordance with the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0062] Example 1

[0063] 1. Preparation of the positive electrode sheet:

[0064] 1) Raw material selection: The Dv50 particle size of lithium nickel cobalt manganese oxide is 15.99 μm, and the specific surface area of ​​lithium nickel cobalt manganese oxide is 0.55 m². 2 / g; the Dv50 particle size of lithium manganese oxide is 12μm, and the specific surface area of ​​lithium manganese oxide is 0.542m². 2 / g; the Dv50 particle size of lithium manganese iron phosphate is 0.8μm, and the specific surface area of ​​lithium manganese iron phosphate is 20m². 2 / g.

[0065] 2) Lithium manganese oxide, lithium nickel cobalt manganese oxide, and lithium manganese iron phosphate are mixed in a mass ratio of 5:3:2 to obtain the positive electrode active material;

[0066] 3) Mix the positive electrode active material, conductive carbon black, carbon nanotubes and polyvinylidene fluoride in a mass ratio of 94:2:1:3, then mix with an appropriate amount of N-methylpyrrolidone and stir evenly to obtain a slurry with a solid content of 60%.

[0067] 4) Use a transfer coating machine to coat the slurry onto one side of an aluminum foil with a thickness of 12 μm, and dry it, maintaining a surface density of 17.5 mg / cm³ for the dried positive electrode active material layer per unit area. 2 Then, the same process is repeated on the other side of the aluminum foil, followed by drying to obtain a positive electrode semi-finished product. This positive electrode semi-finished product is then rolled to obtain a compacted density of 3.0 g / cm³. 3 The positive electrode sheet.

[0068] 2. Preparation of the negative electrode sheet: Artificial graphite powder, conductive carbon black, carbon nanotubes, CMC, and SBR were mixed in a mass ratio of 93:2:2:3. Deionized water was then added to a high-speed mixer and the mixture was uniformly mixed to form a slurry with a solid content of 48%. This slurry was then coated onto one side of an 8μm thick copper foil using a transfer coater and dried, ensuring that the areal density of the dried negative electrode active material layer was 8.5 mg / cm³. 2 Then, the same process is applied to the other side of the copper foil and dried to obtain a negative electrode semi-finished product. The negative electrode semi-finished product is then rolled to obtain the negative electrode sheet.

[0069] 3. Preparation of lithium-ion batteries: The above-mentioned positive electrode sheet and the exposed metal foil part of the above-mentioned positive electrode sheet are processed and welded into electrode tabs, and then wound with the separator to form a core. The core is wrapped with aluminum-plastic film to make a semi-finished cell, and then the electrolyte is injected. After formation and capacity testing, the finished lithium-ion battery is obtained.

[0070] Example 2

[0071] 1. Preparation of the positive electrode sheet:

[0072] 1) Raw material selection: The Dv50 particle size of lithium nickel cobalt manganese oxide is 15.99 μm, and the specific surface area of ​​lithium nickel cobalt manganese oxide is 0.55 m². 2 / g; the Dv50 particle size of lithium manganese oxide is 12μm, and the specific surface area of ​​lithium manganese oxide is 0.542m². 2 / g; the Dv50 particle size of lithium manganese iron phosphate is 0.8μm, and the specific surface area of ​​lithium manganese iron phosphate is 20m². 2 / g.

[0073] 2) Lithium manganese oxide, lithium nickel cobalt manganese oxide, and lithium manganese iron phosphate are mixed in a mass ratio of 5:3:2 to obtain the positive electrode active material;

[0074] 3) Mix the positive electrode active material, conductive carbon black, carbon nanotubes and polyvinylidene fluoride in a mass ratio of 94:2:1:3, then mix with an appropriate amount of N-methylpyrrolidone and stir evenly to obtain a slurry with a solid content of 60%.

[0075] 4) Use a transfer coating machine to coat the slurry onto one side of an aluminum foil with a thickness of 12 μm, and dry it, maintaining a surface density of 17.5 mg / cm³ for the dried positive electrode active material layer per unit area. 2 Then, the same process is repeated on the other side of the aluminum foil, followed by drying to obtain a positive electrode semi-finished product. This positive electrode semi-finished product is then rolled to obtain a compacted density of 3.2 g / cm³. 3 The positive electrode sheet.

[0076] The preparation methods for the negative electrode sheet and the lithium-ion battery are the same as in Example 1.

[0077] The batteries of Examples 3-14 and Comparative Examples 1-3 are the same as those of Example 1, except that the parameters of the positive electrode are different (see Table 1).

[0078] Comparative Example 4

[0079] A positive electrode sheet was prepared using existing lithium iron phosphate (LFP) as the positive electrode active material.

[0080] The preparation methods for the negative electrode sheet and the lithium-ion battery are the same as in Example 1.

[0081] The experimental parameters of the positive electrode sheets of Examples 1-14 and Comparative Examples 1-3 of this application are shown in Table 1.

[0082] Table 1

[0083]

[0084] " / " indicates no.

[0085] Testing and Analysis

[0086] Under the same conditions, the batteries prepared in Examples 1-14 and Comparative Examples 1-4 were tested for low-temperature capacity retention and cycle performance. The specific test methods are as follows:

[0087] Low-temperature capacity retention test: First, set the capacity at room temperature: 1) Let stand for 5 minutes; 2) Discharge at 1C to 2.5V; 3) Let stand for 5 minutes; 4) Charge at 1C constant current and constant voltage to 4.2V, with the constant voltage cutoff current at 0.05C; 5) Let stand for 5 minutes; 6) Discharge at 1C to 2.5V; 7) Let stand for 5 minutes; The discharge capacity in step 6 is defined as C0.

[0088] Low temperature test: 1) Stand at room temperature for 5 minutes; 2) Discharge 1C0 to 2.5V at room temperature; 3) Stand at room temperature for 5 minutes; 4) Charge 1C0 at room temperature with constant current and constant voltage until the constant voltage cutoff current is 0.05C; 5) Stand at room temperature for 5 minutes; 6) Discharge 1C0 to 2.5V at room temperature; 7) Stand at room temperature for 5 minutes; 8) Charge 1C0 at room temperature with constant current and constant voltage until the constant voltage cutoff current is 0.05C; 9) Stand at -30℃ for 240 minutes; 10) Discharge 1C0 to 2.5V at -30℃; 11) Stand for 30 minutes.

[0089] Under low-temperature testing, step 6 discharge represents a 1C room-temperature discharge capacity, and step 10 represents a 1C low-temperature discharge capacity.

[0090] Capacity retention rate = (1C low-temperature discharge capacity / 1C room-temperature discharge capacity) × 100%

[0091] Figure 2 The graph shows a comparison of the discharge curves of the batteries in Example 1, Comparative Example 1, and Comparative Example 4 at -30°C. It can be seen from the graph that, under the same design capacity, the capacity of the pure LFP battery at low temperature is only 0.5 Ah, while that of Comparative Example 1 is 2.0 Ah. Example 1 can achieve a capacity of 2.5 Ah.

[0092] Cyclic performance test: First, set the capacity at room temperature: 1) Let stand for 5 minutes; 2) Discharge at 1C to 2.5V; 3) Let stand for 5 minutes; 4) Charge at 1C constant current and constant voltage to 4.2V, with the constant voltage cutoff current at 0.05C; 5) Let stand for 5 minutes; 6) Discharge at 1C to 2.5V; 7) Let stand for 5 minutes; The discharge capacity in step 6 is defined as C0.

[0093] Cyclic test: 1) Rest for 5 minutes; 2) Discharge 1C0 to 2.5V; 3) Rest for 5 minutes; 4) Charge 1C0 with constant current and constant voltage to 4.2V, with the constant voltage cutoff current at 0.05C; 5) Rest for 5 minutes; 6) Discharge 1C to 2.5V; 7) Rest for 5 minutes; 8) Cycle through steps 4 to 7 until the capacity decays to 80%.

[0094] The test results are shown in Table 2.

[0095] Table 2

[0096]

[0097] Combining Tables 1 and 2, it can be seen that, compared with the batteries obtained in Comparative Examples 1-4, the batteries obtained in Examples 1-14 have both better cycle performance and low-temperature capacity retention.

[0098] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," "some implementations," or "some examples," etc., indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments or examples. Moreover, without contradiction, those skilled in the art can combine and integrate the different embodiments or examples described in this specification, as well as the features of different embodiments or examples.

[0099] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention.

Claims

1. A positive electrode plate, characterized in that, The positive electrode sheet includes: current collector; A positive electrode active material layer is disposed on at least one side of the current collector, and the material of the positive electrode active material layer includes lithium nickel cobalt manganese oxide, lithium manganese oxide and lithium iron manganese phosphate, wherein lithium nickel cobalt manganese oxide and lithium manganese oxide are polycrystalline materials; The mass ratio of lithium manganese oxide, lithium nickel cobalt manganese oxide, and lithium iron manganese phosphate is 5:3:2; The lithium manganese oxide, lithium nickel cobalt manganese oxide, and lithium iron manganese phosphate satisfy the following relationship: 24 ≤ (d1×S1×0.5+d2×S2×0.3+d3×S3×0.2)×PD ≤ 30, where d1 is the Dv50 particle size of lithium manganese oxide in μm; S1 is the specific surface area of ​​lithium manganese oxide in m². 2 / g; d2 is the Dv50 particle size of lithium nickel cobalt manganese oxide, in μm; S2 is the specific surface area of ​​lithium nickel cobalt manganese oxide, in m². 2 / g; d3 is the Dv50 particle size of lithium manganese iron phosphate, in μm; S3 is the specific surface area of ​​lithium manganese iron phosphate, in m². 2 / g; PD is the compaction density of the positive electrode active material layer, in g / cm³. 3 ; The average particle size of the primary particles of the lithium manganese oxide is 0.2 μm-2 μm; The Dv50 particle size of the lithium manganese oxide is 6μm-20μm; The specific surface area of ​​the lithium manganese oxide is 0.2 m². 2 / g-0.8m 2 / g; The average particle size of the primary lithium nickel cobalt manganese oxide particles is 0.05 μm-0.2 μm; The Dv50 particle size of the lithium nickel cobalt manganese oxide is 6μm-18μm; The specific surface area of ​​the lithium nickel cobalt manganese oxide is 0.2 m². 2 / g-0.8m 2 / g; The Dv50 particle size of the lithium manganese iron phosphate is 0.5μm-2μm; The specific surface area of ​​the lithium manganese iron phosphate is 10 m². 2 / g-30m 2 / g; The compaction density of the positive electrode active material layer is 2.5 g / cm³. 3 -3.4g / cm 3 .

2. The positive electrode sheet according to claim 1, characterized in that, 26≤(d1×S1×0.5+d2×S2×0.3+d3×S3×0.2)×PD≤28.

3. A method for preparing the positive electrode sheet according to claim 1, characterized in that, include: A positive electrode active material layer comprising lithium nickel cobalt manganese oxide, lithium manganese oxide, and lithium iron manganese phosphate is formed on at least one side of the current collector to obtain a positive electrode sheet.

4. A battery, characterized in that, The battery includes the positive electrode sheet as described in claim 1 or 2, or the positive electrode sheet prepared by the method described in claim 3.

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