A high-performance positive electrode sheet, its preparation method and application

Abstract

This invention relates to a high-performance positive electrode sheet, its preparation method, and its application. The positive electrode sheet of this invention is prepared by the following method: preparing a single-crystal positive electrode slurry and a polycrystalline positive electrode slurry; spraying the single-crystal positive electrode slurry and the polycrystalline positive electrode slurry onto at least one side of a current collector; and drying and pressing to obtain the positive electrode sheet. The preparation method of the positive electrode sheet of this invention can specifically distribute more conductive agent around the single crystal where the conductive network requirement is high, which can significantly reduce impedance and improve dynamic performance.

Description

Technical Field

[0001] This invention belongs to the field of battery electrode technology and its preparation technology, and in particular refers to a high-performance positive electrode, its preparation method and application. Background Technology

[0002] Lithium-ion batteries are widely used in new energy vehicles and other products. Cathode materials are one of the most important components in lithium batteries, determining their key performance characteristics. Currently, mainstream cathode materials include polycrystalline lithium nickel cobalt manganese oxide (NCM), polycrystalline lithium nickel cobalt aluminum oxide (NCA), polycrystalline lithium manganese oxide (LMO), polycrystalline lithium iron phosphate (LFP), and LTO. Composite systems, which combine two or more cathode materials to form cathode sheets, can balance the characteristics of both materials. For example, blending LFP and NCM can improve energy density while maintaining safety performance; blending large-particle and small-particle cathode materials can improve compaction and reduce costs; blending monocrystalline and polycrystalline NCM can improve material compaction while also considering gas generation and rate capability.

[0003] In ternary materials, single-crystal structures are more complete, resulting in longer lithium-ion migration paths and relatively weaker conductivity. To reduce the impedance of single-crystal particles, a larger amount of conductive agents needs to be added to maintain a better conductive network and reduce reaction impedance. Polycrystalline particles have better conductivity and require less of a conductive network. To address the poor single-crystal kinetics in single-crystal-polycrystalline blends, many conductive agents such as CNTs and SPs need to be added. However, these conductive agents are uniformly distributed in the electrode and are difficult to specifically bind around the single crystal, making it difficult to maximize their effectiveness. Summary of the Invention

[0004] Therefore, the technical problem to be solved by the present invention is to overcome the technical problem that in the prior art, it is difficult for single crystals in the conductive agent to be uniformly and specifically combined around the single crystal ternary material, resulting in poor conductivity and high reaction impedance of the electrode.

[0005] To address the aforementioned technical problems, this invention provides a high-performance positive electrode sheet, its preparation method, and its applications. The preparation method of the positive electrode sheet of this invention enables the specific distribution of more conductive agent around the single crystal, which has a high requirement for conductive network, thus significantly reducing impedance and improving kinetic performance.

[0006] The first objective of this invention is to provide a method for preparing a high-performance positive electrode sheet, comprising the following steps: preparing a single-crystal positive electrode slurry and a polycrystalline positive electrode slurry, spraying the single-crystal positive electrode slurry and the polycrystalline positive electrode slurry onto the surface of a current collector, and drying and pressing the slurry to obtain the positive electrode sheet.

[0007] In one embodiment of the present invention, the monocrystalline cathode slurry and the polycrystalline cathode slurry are sprayed simultaneously or in stages.

[0008] In one embodiment of the present invention, spraying can be performed using a single-tube or multi-tube spraying method.

[0009] In one embodiment of the present invention, the spraying parameters include any of the following parameters:

[0010] (i) Spraying is carried out using single-pipe or multi-pipe spraying;

[0011] (ii) Spraying can be carried out in any order;

[0012] (iii) For two-tube spraying, the spraying rate formula is: V1=V2×j2 / j1×r1 / (1-r1); where r1 is the mass ratio of the monocrystalline cathode material to the sum of the masses of the polycrystalline cathode material and the monocrystalline cathode material, 1-r1 is the mass ratio of the polycrystalline cathode material to the sum of the masses of the polycrystalline cathode material and the monocrystalline cathode material; j1 is the mass ratio of the monocrystalline cathode material to the monocrystalline cathode slurry, j2 is the mass ratio of the polycrystalline cathode material to the polycrystalline cathode slurry; V1 is the spraying rate of the monocrystalline cathode slurry, and V2 is the spraying rate of the polycrystalline cathode slurry. For example, r1=20%; 1-r1=80%; j1=30%; j2=35%; V2=10L / s; then V1=10*35% / 30%*20% / 80%=2.92L / s.

[0013] (iii) Spraying can be done simultaneously or in any order to ensure that the proportion of single crystal and polycrystalline active material (i.e., j1) in the unit volume of the electrode remains unchanged.

[0014] In one embodiment of the present invention, the polycrystalline cathode slurry comprises a polycrystalline cathode material, a conductive agent, a binder, and a solvent. The polycrystalline cathode slurry is prepared by the following method: in a solvent, the polycrystalline cathode material, binder, and conductive agent are stirred and mixed to achieve a solid content of 5% to 70%, followed by vacuum stirring to remove bubbles, thereby obtaining the polycrystalline cathode slurry.

[0015] In one embodiment of the present invention, after stirring and mixing, the mixture is stirred at 1000 rpm to 3000 rpm for 1 to 2 hours.

[0016] In one embodiment of the present invention, the vacuum stirring conditions are: -40MPa to -80MPa, slow stirring, stirring speed of 10 rpm to 20 rpm, and stirring time of 30 min to 60 min.

[0017] In one embodiment of the present invention, the polycrystalline cathode material is selected from one or more of polycrystalline lithium nickel cobalt manganese oxide (NCM), polycrystalline lithium nickel cobalt aluminum oxide (NCA), polycrystalline lithium manganese oxide (LMO), polycrystalline lithium iron phosphate (LFP), polycrystalline lithium manganese iron phosphate (LFMP), polycrystalline lithium nickel manganese oxide (LNMO), polycrystalline lithium cobalt oxide (LCO), polycrystalline lithium nickel oxide (LNO), and polycrystalline lithium-rich manganese base oxides (LLOs).

[0018] In one embodiment of the present invention, the adhesive is selected from one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride, styrene rubber, nitrile rubber, styrene-butadiene rubber (SBR), polyacrylamide (PAA), polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), polyimide (PI), butadiene rubber, modified butadiene rubber, carboxyl-modified styrene-butadiene rubber, and modified polyorganosiloxane polymers.

[0019] In one embodiment of the present invention, the solvent is selected from one or more of N-methylpyrrolidone (NMP), ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl acetate (MA), ethyl acetate (EA), and ethyl propionate (EP).

[0020] In one embodiment of the present invention, the conductive agent is selected from one or more of Super P, carbon nanotubes (CNTs), carbon black, carbon fiber (VGCF), conductive polymers, graphene, acetylene black, Denka black, activated carbon, and conductive polymers.

[0021] In one embodiment of the present invention, the carbon nanotubes are multi-walled CNTs and / or single-walled CNTs.

[0022] In one embodiment of the present invention, the conductive polymer is selected from one or more of polyacetylene, polyaniline, polythiophene, and polypyrrole.

[0023] In one embodiment of the present invention, the binder accounts for 0.5 wt% to 10 wt% of the mass of the polycrystalline cathode slurry. More preferably, it is 0.5 wt%-1 wt%, 1 wt%-2 wt%, 2 wt%-3 wt%, 3 wt%-4 wt%, 4 wt%-5 wt%, 5 wt%-6 wt%, 6 wt%-7 wt%, 7 wt%-8 wt%, 8 wt%-9 wt%, or 9 wt%-10 wt%. For example, it is 0.5 wt%, 1 wt%, 1.5 wt%, 2 wt%, 2.5 wt%, 3 wt%, 3.5 wt%, 4 wt%, 4.5 wt%, 5 wt%, 5.5 wt%, 6 wt%, 6.5 wt%, 7 wt%, 7.5 wt%, 8 wt%, 8.5 wt%, 9 wt%, 9.5 wt%, or 10 wt%.

[0024] In one embodiment of the present invention, the polycrystalline cathode material accounts for 87% to 99.4% of the mass of the polycrystalline cathode slurry. More preferably, it is 84%-96.5%, 96.5%-97.5%, or 97.5%-99.4%.

[0025] In one embodiment of the present invention, the conductive agent accounts for 0% to 5 wt% of the mass of the polycrystalline cathode slurry. More preferably, it is 0-1 wt%, 1 wt%-2 wt%, or 2 wt%-3 wt%. For example, it is 1.0 wt%, 1.1 wt%, 1.1 wt%, 1.1 wt%, 1.1 wt%, 1.1 wt%, 1.1 wt%, 2.0 wt%, 2.1 wt%, 2.2 wt%, 2.3 wt%, 2.4 wt%, 2.5 wt%, 2.6 wt%, 2.7 wt%, 2.8 wt%, 2.9 wt%, or 3.0 wt%.

[0026] In one embodiment of the present invention, the viscosity of the polycrystalline cathode slurry is less than or equal to 6000 mPa·s. More preferably, it is 500 mPa·s to 2000 mPa·s; even more preferably, it is 500 mPa·s to 1000 mPa·s, or 100 mPa·s to 2000 mPa·s. Examples include: 500 mPa·s, 600 mPa·s, 700 mPa·s, 800 mPa·s, 900 mPa·s, 1000 mPa·s, 1100 mPa·s, 1200 mPa·s, 1300 mPa·s, 1400 mPa·s, 1500 mPa·s, 1600 mPa·s, 1700 mPa·s, 1800 mPa·s, 1900 mPa·s, 2000 mPa·s, etc.

[0027] In one embodiment of the present invention, the single-crystal cathode slurry includes a single-crystal cathode material, a conductive agent, a binder, and a solvent.

[0028] In one embodiment of the present invention, the single-crystal cathode material is selected from one or more of single-crystal lithium nickel cobalt manganese oxide (NCM), single-crystal lithium nickel cobalt aluminum oxide (NCA), single-crystal lithium manganese oxide (LMO), single-crystal lithium iron phosphate (LFP), single-crystal lithium manganese iron phosphate (LFMP), single-crystal lithium nickel manganese oxide (LNMO), single-crystal lithium cobalt oxide (LCO), single-crystal lithium nickel oxide (LNO), and single-crystal lithium-rich manganese-based layered oxides (LLOs). Further, it is preferably one or more of single-crystal lithium nickel cobalt manganese oxide (NCM), single-crystal lithium nickel cobalt aluminum oxide (NCA), and single-crystal lithium manganese oxide (LMO).

[0029] In one embodiment of the present invention, the conductive agent is selected from one or more of Super P (SP), carbon nanotubes (CNT), carbon black, carbon fiber (VGCF), conductive polymer, graphene, acetylene black, Denka black, activated carbon, and conductive polymer. More preferably, it is selected from one or more of Super P, carbon nanotubes (CNT), carbon black, and carbon fiber (VGCF).

[0030] In one embodiment of the present invention, the adhesive is selected from one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride, styrene rubber, nitrile rubber, styrene-butadiene rubber (SBR), polyacrylamide (PAA), polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), polyimide (PI), butadiene rubber, modified butadiene rubber, carboxyl-modified styrene-butadiene rubber, and modified polyorganosiloxane polymers. More preferably, it is selected from one or more of polyvinylidene fluoride (PVDF), polyvinylidene fluoride, styrene rubber, nitrile rubber, styrene-butadiene rubber (SBR), polyacrylamide (PAA), polytetrafluoroethylene (PTFE), polyacrylonitrile (PAN), polyimide (PI), and butadiene rubber. More preferably, it is selected from one or more of polyvinylidene fluoride (PVDF), polyacrylamide (PAA), polytetrafluoroethylene (PTFE), and polyvinylidene fluoride.

[0031] In one embodiment of the present invention, the solvent is selected from one or more of N-methylpyrrolidone (NMP), ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), dimethyl carbonate (DMC), ethyl methyl carbonate (EMC), methyl acetate (MA), ethyl acetate (EA), and ethyl propionate (EP).

[0032] In one embodiment of the present invention, the single-crystal cathode material accounts for 84% to 99.35% of the mass of the single-crystal cathode slurry. More preferably, it is 87%-94.5%, 94.5%-95.5%, 95.5%-96.5%, 96.5%-98%, 98%-99.4%, etc.

[0033] In one embodiment of the present invention, the viscosity of the single-crystal cathode slurry is less than or equal to 6000 mPa·s. More preferably, it is between 500 mPa·s and 2000 mPa·s. Examples include: 500 mPa·s, 600 mPa·s, 700 mPa·s, 800 mPa·s, 900 mPa·s, 1000 mPa·s, 1100 mPa·s, 1200 mPa·s, 1300 mPa·s, 1400 mPa·s, 1500 mPa·s, 1600 mPa·s, 1700 mPa·s, 1800 mPa·s, 1900 mPa·s, and 2000 mPa·s.

[0034] In one embodiment of the present invention, the conductive agent accounts for 0 wt% to 5 wt% of the mass of the single-crystal positive electrode paste. More preferably, it is 1 wt% to 3 wt%, or 3 wt% to 5 wt%; more preferably, it is 0-1 wt%, 1 wt% to 2 wt%, 2 wt% to 3 wt%, 3 wt% to 4 wt%, or 4 wt% to 5 wt%. More preferably, it is 0-1 wt%, 1 wt% to 2 wt%, 2 wt% to 3 wt%, or 3 wt% to 4 wt%. For example, 1.0wt%, 1.1wt%, 1.1wt%, 1.1wt%, 1.1wt%, 1.1wt%, 1.1wt%, 2.0wt%, 2.1wt%, 2.2wt%, 2.3wt%, 2.4wt%, 2.5wt%, 2.6wt%, 2.7wt%, 2.8wt%, 2.9wt%, 3.0wt%, 3.1wt%, 3.2wt%, 3.3wt%, 3.4wt%, 3.5wt%, 3.6wt%, 3.7wt%, 3.8wt%, 3.9wt%, 4.0wt%, etc.

[0035] In one embodiment of the present invention, the preparation of the single-crystal cathode slurry includes the following steps: in a solvent, the single-crystal cathode material is stirred and mixed with a binder and a conductive agent to make the solid content 5% to 70%, and the mixture is vacuum stirred to remove bubbles to obtain the single-crystal cathode slurry.

[0036] In one embodiment of the present invention, after stirring and mixing, the mixture is stirred at 1000 rpm to 3000 rpm for 1 to 2 hours.

[0037] In one embodiment of the present invention, the vacuum stirring conditions are: -40MPa to -80MPa, slow stirring, stirring speed of 10 rpm to 20 rpm, and stirring time of 30 min to 60 min.

[0038] A second objective of the present invention is to provide a high-performance positive electrode sheet with a thickness of 10 μm to 150 μm.

[0039] A third objective of the present invention is to provide a lithium-ion battery comprising the aforementioned high-performance positive electrode.

[0040] In this invention, the polycrystalline cathode slurry and the monocrystalline cathode slurry are stirred separately and sprayed from different nozzles. Therefore, by adding more and better conductive agents to the monocrystalline cathode slurry, the conductive agents, such as long-range conductive agents multi-walled CNTs, single-walled CNTs, and VGCF, will accumulate around the monocrystalline cathode material after drying during the electrode preparation process.

[0041] The technical solution of the present invention has the following advantages compared with the prior art:

[0042] This invention can specifically adjust the distribution of conductive agents and other additives in the electrode; for example, CNTs are distributed around the positive electrode single crystal to achieve a good conductive network. The spraying device of this invention allows for free combination and specific arrangement of components, resulting in electrodes with different functional characteristics.

[0043] In existing technologies, traditional preparation methods involve blending CNTs, SPs, etc., with polycrystalline and single-crystal materials. However, CNTs and SPs are less distributed around the single crystal. In contrast, the electrode preparation method described in this invention allows for the directional distribution of conductive agents around the single-crystal NCM material. It is well known in the art that the quality of the conductive network is a key factor in the optimal performance of the positive electrode active material. In this invention, a spray coating method is used to separately coat the single-crystal and polycrystalline components. The conductive agent is compounded with the single-crystal components, which allows for the directional distribution of CNTs, SPs, etc., around the ternary single-crystal particles. This ensures that the single crystal achieves good conductivity, significantly reduces impedance, and improves kinetic performance. Attached Figure Description

[0044] To make the content of this invention easier to understand, the invention will be further described in detail below with reference to specific embodiments and accompanying drawings, wherein...

[0045] Figure 1 This is a diagram of the coating process in the preparation of the electrode sheet according to the present invention.

[0046] Figure 2 This is a structural diagram of the electrode sheet obtained in an embodiment of the present invention. Detailed Implementation

[0047] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, so that those skilled in the art can better understand and implement the present invention. However, the embodiments described are not intended to limit the present invention.

[0048] The first objective of this invention is to provide a method for preparing a high-performance positive electrode sheet, comprising the following steps: preparing a single-crystal positive electrode slurry and a polycrystalline positive electrode slurry, spraying the single-crystal positive electrode slurry and the polycrystalline positive electrode slurry onto the surface of a current collector, and drying and pressing the slurry to obtain the positive electrode sheet.

[0049] In one embodiment of the present invention, the monocrystalline cathode slurry and the polycrystalline cathode slurry are sprayed simultaneously or in stages.

[0050] In one embodiment of the present invention, spraying can be performed using a single-tube or multi-tube spraying method.

[0051] In one embodiment of the present invention, the spraying parameters include any of the following parameters:

[0052] (i) Spraying is carried out using single-pipe or multi-pipe spraying;

[0053] (ii) Spraying can be carried out in any order;

[0054] (iii) For two-tube spraying, the spraying rate formula is: V1=V2×j2 / j1×r1 / (1-r1); where r1 is the mass ratio of the monocrystalline cathode material to the sum of the masses of the polycrystalline cathode material and the monocrystalline cathode material, 1-r1 is the mass ratio of the polycrystalline cathode material to the sum of the masses of the polycrystalline cathode material and the monocrystalline cathode material; j1 is the mass ratio of the monocrystalline cathode material to the monocrystalline cathode slurry, j2 is the mass ratio of the polycrystalline cathode material to the polycrystalline cathode slurry; V1 is the spraying rate of the monocrystalline cathode slurry, and V2 is the spraying rate of the polycrystalline cathode slurry. For example, r1=20%; 1-r1=80%; j1=30%; j2=35%; V2=10L / s; then V1=10*35% / 30%*20% / 80%=2.92L / s.

[0055] A second objective of the present invention is to provide a high-performance positive electrode sheet with a thickness of 10 μm to 150 μm.

[0056] A third objective of the present invention is to provide a lithium-ion battery comprising the aforementioned high-performance positive electrode.

[0057] Examples 1-5

[0058] Examples 1-5 provide a method for preparing a high-performance positive electrode and a battery, as detailed below:

[0059] (1) Preparation of single crystal cathode slurry (component 2): Take 1 part of single crystal, PVDF, multi-walled CNT, SP, and NMP; and prepare single crystal cathode slurry by mixing with a mixer. The solid content of the obtained single crystal cathode slurry is 30%, the active material accounts for 29% of the total slurry, and the viscosity is 600 mPa·S.

[0060] (2) Preparation of polycrystalline cathode slurry (component 1): Take polycrystalline PVDF, SP and NMP; mix them with a mixer to form component 1 to obtain polycrystalline cathode slurry. The solid content of the obtained polycrystalline cathode slurry is 35%, the active material accounts for 34.1% of the total slurry, and the viscosity is 500 mPa·S.

[0061] (3) Spray the single-crystal cathode slurry obtained in step (1) and the polycrystalline cathode slurry obtained in step (2) onto the surface of the electrode: spray simultaneously from two nozzles, with a spray rate ratio of component one to component two of 2.05:1; wherein, the mass of the active material is controlled by the spray rate:

[0062] For example, r2 = 30%; 1 - r2 = 70%; j2 = 30%; j1 = 34.1%; V1 is the polycrystalline injection rate;

[0063] Then V1 = 30% / 34.1% * 70% / 30% * V2 = 2.05V2.

[0064] (4) After spraying, the positive electrode is obtained by drying and pressing. The mass ratio of single crystal and polycrystalline particles after drying is shown in Table 1 and Table 2. The electrode is then cut into a certain shape.

[0065] (5) After stirring the negative electrode active materials such as graphite and Si materials with binders PVDF, SP and CNT, they are coated into corresponding negative electrode sheets and then cold-pressed and cut into matching shapes.

[0066] (6) The positive and negative electrode sheets are separated by a PE separator and are then processed into soft-pack, square, cylindrical and other full cells through stacking, winding and other methods.

[0067] (7) After the battery is vacuum baked at 95°C for 10 hours, electrolyte is injected; after formation, capacity testing and other steps, a full cell is obtained.

[0068] Comparative Example 1

[0069] This comparative example uses a conventional preparation method to prepare the positive electrode sheet and the battery. The difference between this example and Example 2 is that the preparation method of the positive electrode sheet is different; the other parts are the same as in Example 1, as detailed below:

[0070] 28.8 wt% monocrystalline NCM, 68.25 wt% polycrystalline NCM, 1 wt% SP, and 1.5 wt% PVDF were directly blended, and NMP was added to prepare a slurry. This slurry was then coated onto an electrode to obtain a positive electrode. The same negative electrode was then matched to prepare a full cell.

[0071] The raw material components involved in the above embodiments and comparative examples are shown in Tables 1 and 2.

[0072] Table 1. Raw material composition and dosage for Examples 1-5 and Comparative Example 1

[0073]

[0074] Table 2 shows the total amount of paint used and performance test results after spraying in Examples 1-5 and Comparative Example 1.

[0075]

[0076]

[0077] Note: a represents the mass ratio of polycrystalline / monocrystalline particles to the sum of the masses of monocrystalline particles, conductive agent, polycrystalline particles, and binder. b represents the mass ratio of monocrystalline particles to the sum of the masses of (monocrystalline particles + polycrystalline particles).

[0078] Performance testing

[0079] The batteries obtained in Examples 1-5 and Comparative Example 1 were subjected to performance tests:

[0080] (1) Method for detecting the capacity retention rate of 3C discharge equivalent to 0.33C: Charge at 0.33C constant current to 100% SOC (e.g., NCM to 4.2V), then charge at constant voltage to 0.05C (e.g., 0.5A for 10Ah) and cut off, then discharge at 0.33C constant current to 0% SOC (2.5V) to obtain capacity C1; let stand for 10 minutes, then discharge at 3C (e.g., 30A for 10AH) to 0% SOC (2.5V) to obtain capacity C2; then the 3C capacity retention rate is C2 / C1;

[0081] (2) Detection method for DCR growth at 80% capacity retention: Fresh battery, adjust SOC to 50% SOC and let stand for 2h to obtain V1, discharge with 3C(I) for 10s to obtain V2; calculate DCR1: (V1-V2) / I; in an environment of 25℃, use 0.5C / 0.5C charge and discharge cycle until the capacity retention is 80%; then use the above DCR test method to measure DCR2 at 80% SOH; DCR growth rate = (DCR2-DCR1) / DCR1.

[0082] The experimental test results are shown in Table 2.

[0083] As shown in Table 2, compared with Comparative Example 1, in Example 1, with the addition of 1 wt% CNT to Component 2 (single crystal), and the total component being only 0.3 wt%, the 3C rate discharge capacity retention increased from 90.3 wt% to 95.1 wt%; the DCR growth decreased from 51.2% to 44.6%. This further demonstrates that, with the same amount of raw material components, the spraying method yields superior results.

[0084] In Example 2, compared with Comparative Example 1, CNT was further increased to 3% in component two, and the total component was 0.9%, consistent with Comparative Example 1. However, the rate performance was improved from 90.3% to 96.4%; the DCR growth was reduced from 51.2% to 41.5%.

[0085] In Example 3, compared with Example 1, 1% CNT was added to the polycrystalline component, but the rate performance only increased from 95.1% to 95.3%, with no significant difference; the DCR growth also showed no significant difference, indicating that CNT in the polycrystalline component did not significantly improve the rate performance and DCR growth.

[0086] In Example 4, compared with Example 3, no CNTs were added to the single crystal composition, the capacity retention rate decreased to 88.6%, and the DCR growth increased significantly to 54.8%.

[0087] Compared with Example 1, Example 5 showed that the addition of 1% SP improved the rate performance and DCR performance, indicating that the conductive agents such as SP and CNT are oriented around the single crystal and have a good improvement effect.

[0088] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A method for preparing a high-performance positive electrode sheet, characterized in that, Includes the following steps: Prepare monocrystalline cathode slurry and polycrystalline cathode slurry, spray the monocrystalline cathode slurry and polycrystalline cathode slurry onto the surface of the current collector, and obtain the cathode sheet by drying and pressing; the polycrystalline cathode slurry includes polycrystalline cathode material, conductive agent, binder and solvent; the monocrystalline cathode slurry includes monocrystalline cathode material, conductive agent, binder and solvent. In the polycrystalline cathode slurry, the conductive agent accounts for 1 wt% to 2 wt% of the mass of the polycrystalline cathode slurry; In the single-crystal cathode slurry, the conductive agent accounts for 1.1 wt% to 4 wt% of the mass of the single-crystal cathode slurry; The monocrystalline cathode slurry and polycrystalline cathode slurry are sprayed simultaneously. The spraying is carried out using a two-pipe spraying method, and the spraying speed formula is: V1=V2×j2 / j1×r1 / (1-r1); where r1 is the mass ratio of monocrystalline cathode material to the sum of the masses of polycrystalline cathode material and monocrystalline cathode material, 1-r1 is the mass ratio of polycrystalline cathode material to the sum of the masses of polycrystalline cathode material and monocrystalline cathode material; j1 is the mass ratio of monocrystalline cathode material to monocrystalline cathode slurry, j2 is the mass ratio of polycrystalline cathode material to polycrystalline cathode slurry; V1 is the spraying speed of monocrystalline cathode slurry, and V2 is the spraying speed of polycrystalline cathode slurry.

2. The preparation method according to claim 1, characterized in that, The polycrystalline cathode slurry is prepared by the following method: in a solvent, the polycrystalline cathode material is stirred and mixed with a binder and a conductive agent to make the solid content between 5% and 70%, and then vacuum stirred to remove bubbles to obtain the polycrystalline cathode slurry.

3. The preparation method according to claim 1, characterized in that, The polycrystalline cathode material is selected from one or more of the following: polycrystalline lithium nickel cobalt manganese oxide (NCM), polycrystalline lithium nickel cobalt aluminum oxide (NCA), polycrystalline lithium manganese oxide (LMO), polycrystalline lithium iron phosphate (LFP), polycrystalline lithium manganese iron phosphate (LFMP), polycrystalline lithium nickel manganese oxide (LNMO), polycrystalline lithium cobalt oxide (LCO), polycrystalline lithium nickel oxide (LNO), and polycrystalline lithium-rich manganese-based morphological oxides (LLOs).

4. The preparation method according to claim 1, characterized in that, The polycrystalline cathode slurry meets at least one of the following conditions: The binder accounts for 0.5% to 10% of the mass of the polycrystalline cathode slurry; The polycrystalline cathode material accounts for 87% to 99.4% of the mass of the polycrystalline cathode slurry; The viscosity of the polycrystalline cathode slurry is less than 6000 mPa·S.

5. The preparation method according to claim 1, characterized in that, The preparation of the single-crystal cathode slurry includes the following steps: in a solvent, the single-crystal cathode material is stirred and mixed with a binder and a conductive agent to make the solid content between 5% and 70%, and then vacuum stirred to remove bubbles to obtain the single-crystal cathode slurry.

6. The preparation method according to claim 1, characterized in that, The single-crystal cathode material is selected from one or more of the following: single-crystal lithium nickel cobalt manganese oxide (NCM), single-crystal lithium nickel cobalt aluminum oxide (NCA), single-crystal lithium manganese oxide (LMO), single-crystal lithium iron phosphate (LFP), single-crystal lithium manganese iron phosphate (LFMP), single-crystal lithium nickel manganese oxide (LNMO), single-crystal lithium cobalt oxide (LCO), single-crystal lithium nickel oxide (LNO), and single-crystal lithium-rich manganese-based layered oxides (LLOs).

7. The preparation method according to claim 1, characterized in that, The single-crystal cathode slurry meets at least one of the following conditions: The binder accounts for 0.5% to 10% of the mass of the single-crystal cathode slurry; The single-crystal cathode material accounts for 84% to 99.35% of the mass of the single-crystal cathode slurry; The viscosity of the single-crystal cathode slurry is less than 6000 mPa·S.

8. A high-performance positive electrode obtained by the preparation method according to any one of claims 1-7, wherein the thickness of the positive electrode is 10 μm to 150 μm.

9. A lithium-ion battery, characterized in that, Includes the high-performance positive electrode sheet as described in claim 8.

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