Positive pole piece, preparation method thereof and battery

Abstract

The invention relates to the field of batteries, in particular to a positive pole piece, a preparation method thereof and a battery, the positive pole piece comprises a modified current collector and a positive active material layer arranged on at least one side surface of the modified current collector along the thickness direction; the positive active material layer comprises a positive active material; the positive electrode active material comprises a ternary positive electrode material and a coating layer coating at least part of the surface of the ternary positive electrode material; the coating layer comprises a first composite material, the first composite material comprises a lithium supplement agent and an MXene material, and the lithium supplement agent is adsorbed on at least part of the surface of the MXene material; the modified current collector comprises a positive current collector substrate and a coating arranged on at least one side surface of the positive current collector substrate along the thickness direction; the coating comprises a second composite material, and the second composite material comprises polypyrrole and graphene. The positive pole piece disclosed by the invention can remarkably improve the cycling stability of the battery.

Description

Technical Field

[0001] This invention relates to the field of batteries, specifically to a positive electrode sheet, a method for preparing the same, and a battery. Background Technology

[0002] With the increasing global demand for clean energy and sustainable development, lithium-ion batteries are widely used in daily life due to their high energy density, environmental friendliness, and lack of memory effect. As society progresses, people have higher requirements for the performance of lithium-ion batteries, such as higher energy density and better rate performance. Currently, high-nickel ternary cathode materials have significant advantages in terms of energy density (>250 Wh / kg) and cost. However, the residual Li2CO3 / LiOH on the surface of high-nickel materials can react with the electrolyte (such as LiPF6 / LiFSI) to generate CO / CO2 gas, leading to battery bulging and thermal runaway risks. Furthermore, the cathode particles and current collector only conduct electrons through physical contact, lacking a chemical bonding mechanism, resulting in interface contact degradation during cycling (capacity decay >20% after 500 cycles). Summary of the Invention

[0003] In view of this, the present invention aims to provide a positive electrode sheet, its preparation method and battery, to solve the problems of multiple side reactions at the interface between the positive electrode sheet and the electrolyte in the prior art, and the easy occurrence of residual lithium runaway and interface kinetic mismatch in high-nickel materials.

[0004] To solve the above-mentioned technical problems, this application is implemented as follows: A first aspect of the present invention provides a positive electrode sheet, the positive electrode sheet comprising a modified current collector and a positive active material layer disposed on at least one side surface of the modified current collector along the thickness direction; The positive electrode active material layer includes a positive electrode active material; the positive electrode active material includes a ternary positive electrode material and a coating layer covering at least a portion of the surface of the ternary positive electrode material; The coating layer includes a first composite material, which includes a lithium supplement and an MXene material, wherein the lithium supplement is adsorbed on at least a portion of the surface of the MXene material; The modified current collector includes a positive current collector substrate and a coating disposed on at least one side surface of the positive current collector substrate along the thickness direction; The coating comprises a second composite material, which includes polypyrrole and graphene.

[0005] Optionally, the mass ratio of the lithium replenishing agent to the MXene material is 3:1 to 5:1; Optionally, the lithium supplement includes at least one selected from Li₂ZrO₃, Li₂C₂O₄, Li₂MnO₃, Li₅FeO₄, Li₂NiO₂, and Li₂S; optionally, the MXene material includes Ti₃C₂T. x MXene, V2CT x Mxene, Zr2C2T x MXene and Nb4C3T x At least one of MXene.

[0006] Optionally, the thickness of the coating layer is 5-10 nm; and / or, the coating layer has a porous structure; optionally, the pore size of the porous structure in the coating layer is 4-10 nm; optionally, the porosity of the coating layer is 20%-40%; and / or, the particle size of the ternary cathode material is 50-80 nm; optionally, the ternary cathode material includes LiNi. 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.5 Co 0.3 Mn 0.2 O2 and LiNi 0.6 Co 0.2 Mn 0.2 At least one of O2.

[0007] Optionally, the mass ratio of the polypyrrole to the graphene is 10:1 to 4:1; and / or, the coating further includes a first binder; optionally, the mass ratio of the second composite material to the first binder is 5:1 to 15:1; optionally, the first binder includes polytetrafluoroethylene and / or acrylic resin; and / or, the thickness of the coating is 10 to 15 nm.

[0008] Optionally, the thickness of the positive electrode active material layer is 80~120μm; and / or, the positive electrode active material layer further includes a second binder and a conductive agent; optionally, the mass ratio of the positive electrode active material, the second binder and the conductive agent is (93~97):(2~5):(1~2); optionally, the second binder includes at least one of polytetrafluoroethylene, polyvinylidene fluoride and sodium carboxymethyl cellulose; optionally, the conductive agent includes at least one of conductive carbon black, acetylene black, graphene, conductive graphite, conductive carbon nanotubes and conductive carbon fibers.

[0009] A second aspect of the present invention provides a method for preparing a positive electrode sheet, comprising the following steps: S1. Prepare an MXene material dispersion; mix the first precursor, the second precursor, and the first solvent for a first dispersion treatment, adjust the pH to obtain a sol; mix the sol and the MXene material dispersion, perform a second dispersion, centrifugation, and washing treatment to obtain a first product; perform a first drying and annealing treatment on the first product to obtain a first composite material; mix the first composite material, the ternary cathode material, and the second solvent, perform a third dispersion and a second drying treatment to obtain the cathode active material; S2. Prepare a mixed solution containing graphene and polypyrrole, perform a third drying and heat treatment to obtain a second composite material; prepare a first slurry containing the second composite material, coat the slurry containing the second composite material onto at least one side of the positive electrode current collector matrix along the thickness direction, perform a fourth drying and a first pressing treatment to obtain a modified current collector. S3. The second slurry containing the positive electrode active material is coated on at least one side of the modified current collector along the thickness direction, and then subjected to the fifth drying and second tableting treatment.

[0010] Optionally, in step S1, the concentration of the MXene material dispersion is 0.5~2.5 mg / mL; and / or, the molar ratio of the first precursor to the second precursor is 1:1~5:1; and / or, the mass ratio of the sol to the MXene material dispersion is 3:1~8:1; and / or, the content of lithium supplementer in the sol is 5~10 wt%; and / or, the mass ratio of the ternary cathode material to the first composite material is 2:1~6:1; and / or, in step S2, the viscosity of the first slurry is 1000~2000 mPa·s; and / or, in step S3, the solid content of the second slurry is 60 wt%~70 wt%.

[0011] Optionally, in step S1, the first precursor includes one of LiNO3, Li2CO3, and LiOH; and / or, the second precursor includes at least one of ZrOCl2·8H2O, ZrO(NO3)2, ZrO2, Zr(SO4)2·H2O, NiO, CS2, MnO, and FeC2O4·2H2O; and / or, in step S2, the first slurry further includes a first binder and a third solvent; optionally, the third solvent includes at least one of ethanol, isopropanol, and tert-propanol; and / or, in step S3, the second slurry further includes a second binder, a conductive agent, and a fourth solvent; optionally, the fourth solvent includes at least one of N-methylpyrrolidone, N-ethylpyrrolidone, N,N-dimethylacetamide, and N,N-dimethylformamide.

[0012] Optionally, in step S1, the pH range is 8-9; and / or, in step S1, the second dispersion temperature is 60-100℃, the second dispersion time is 2-6 hours, and the second dispersion rotation speed is 300-600 rpm; and / or, the centrifugation speed is 8000-10000 rpm, the centrifugation time is 30-60 minutes, and the centrifugation temperature is 10-30℃; and / or, the first drying temperature is -50 to -30℃, and the first drying time is 16-32 hours; and / or, the annealing temperature is 400-600℃, and the annealing time is 1-3 hours. The atmosphere includes an inert atmosphere; and / or, the temperature of the third dispersion treatment is 10~30℃, the time of the third dispersion treatment is 6~10h, and the rotation speed of the third dispersion treatment is 600~800rpm; and / or, the temperature of the second drying treatment is 60~80℃, and the time of the second drying treatment is 12~20h; and / or, in step S2, the third drying includes vacuum drying; optionally, the temperature of the vacuum drying is 60~80℃, and the time of the vacuum drying is 24~30h; and / or, the temperature of the heat treatment is 300~450℃, the time of the heat treatment is 1~3h, and the atmosphere of the heat treatment includes an inert atmosphere.

[0013] A third aspect of the present invention provides a battery comprising a positive electrode, the positive electrode comprising the above-described positive electrode and / or a positive electrode prepared according to the above-described preparation method.

[0014] The beneficial technical effects of the present invention through the above technical solution are as follows: (1) The positive electrode active material in the positive electrode sheet of the present invention includes a ternary positive electrode material and a coating layer covering at least a portion of the surface of the ternary positive electrode material. The coating layer includes a first composite material, which includes a lithium supplement agent and an MXene material. The lithium supplement agent is adsorbed on at least a portion of the surface of the MXene material. The first composite material has a stable crystal structure and can reduce the direct contact between the high-nickel ternary positive electrode and the electrolyte, thereby reducing interfacial side reactions.

[0015] (2) This invention uses a modified current collector as the positive electrode current collector. The modified current collector includes a positive electrode current collector matrix and a coating disposed on at least one side surface of the positive electrode current collector matrix along the thickness direction. The coating includes a second composite material, which includes polypyrrole and graphene. The electrostatic self-assembly and hydrogen bonding interaction between the second composite material and MXene in the positive electrode active material coating layer can promote the formation of a three-dimensional conductive network and form Ti-OC covalent bonds, thereby solving the problems of residual lithium runaway and interfacial kinetic mismatch in high-nickel materials. At the same time, the N atoms in the polypyrrole form Al-N coordination bonds with the aluminum foil, which can effectively improve the bonding strength between the coating and the current collector.

[0016] Other features and advantages of the present invention will be described in detail in the following detailed description section. Detailed Implementation

[0017] This invention discloses a positive electrode sheet, its preparation method, and a battery. Those skilled in the art can refer to the content of this document and appropriately modify the process parameters to achieve the desired result. It is particularly important to note that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included in this invention. The methods and applications of this invention have been described through preferred embodiments. Those skilled in the art can clearly modify or appropriately change and combine the methods and applications described herein without departing from the content, spirit, and scope of this invention to realize and apply the technology of this invention.

[0018] In the description of this invention, the list of items connected by the term "at least one of" or other similar terms may mean any combination of the listed items. For example, if items A and B are listed, then the phrase "at least one of A and B" means only A; only B; or A and B. In another example, if items A, B, and C are listed, then the phrase "at least one of A, B, and C" means only A; or only B; only C; A and B (excluding C); A and C (excluding B); B and C (excluding A); or all of A, B, and C. Item A may contain a single element or multiple elements. Item B may contain a single element or multiple elements. Item C may contain a single element or multiple elements.

[0019] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges or individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0020] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0021] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0022] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0023] To address the problems of numerous side reactions at the interface between the positive electrode and the electrolyte in existing technologies, as well as the tendency for uncontrolled residual lithium and interfacial kinetic mismatch in high-nickel materials, the present invention adopts the following technical solution: A first aspect of the present invention provides a positive electrode sheet, the positive electrode sheet comprising a modified current collector and a positive active material layer disposed on at least one side surface of the modified current collector along the thickness direction; The positive electrode active material layer includes a positive electrode active material; the positive electrode active material includes a ternary positive electrode material and a coating layer covering at least a portion of the surface of the ternary positive electrode material; The coating layer includes a first composite material, which includes a lithium supplement and an MXene material, wherein the lithium supplement is adsorbed on at least a portion of the surface of the MXene material; The modified current collector includes a positive current collector substrate and a coating disposed on at least one side surface of the positive current collector substrate along the thickness direction; The coating comprises a second composite material, which includes polypyrrole (PPy) and graphene.

[0024] The positive electrode active material in the positive electrode sheet of the present invention includes a ternary positive electrode material and a coating layer covering at least a portion of the surface of the ternary positive electrode material. The coating layer includes a first composite material, which includes a lithium replenishing agent and an MXene material. The lithium replenishing agent is adsorbed on at least a portion of the surface of the MXene material. The first composite material has a stable crystal structure and can reduce the direct contact between the high-nickel ternary positive electrode and the electrolyte, thereby reducing interfacial side reactions. The present invention uses a modified current collector as the positive electrode current collector. The modified current collector includes a positive electrode current collector matrix and a coating disposed on at least one side surface of the positive electrode current collector matrix along the thickness direction. The coating includes a second composite material, which includes polypyrrole and graphene. The second composite material forms covalent bonds with the MXene in the positive electrode active material coating layer, thereby solving the problems of residual lithium runaway and interfacial kinetic mismatch in high-nickel materials. At the same time, the N atoms in the polypyrrole form Al-N coordination bonds with the aluminum foil, which can effectively improve the bonding strength between the coating and the current collector.

[0025] In this invention, a suitable ratio of lithium replenisher to MXene material has a synergistic effect, compensating for active lithium while constructing a stable and efficient conductive network. However, if the lithium replenisher content is too high, excessive Li₂O or Li₂ may be released during electrochemical activation or cycling. + This can lead to excessively high local alkalinity and may damage Li2ZrO3. - The density and stability of the MXene coating layer lead to cracks or pores; the generated Li₂O is an insulator, and excessive presence may block the ion and electron transport channels in the coating layer, increasing interfacial impedance and deteriorating the rate performance of the battery; as cycling progresses, active lithium is continuously depleted and cannot be effectively replenished, leading to accelerated capacity decay and failing to realize the long-cycle potential of high-nickel materials; if the lithium replenisher content is too low, the initial active lithium is insufficient, the cathode material may not be fully activated, some high-capacity phases cannot be utilized, and the excellent conductive network constructed by PPy / graphene / MXene cannot perform effectively, and the interfacial kinetic mismatch problem still exists. According to the present invention, the mass ratio of the lithium replenisher to the MXene material is 3:1 to 5:1; exemplaryly, the mass ratio of the lithium replenisher to the MXene material can be any value among 3:1, 3.5:1, 4:1, 4.5:1, and 5:1, or any value within the range of any two of the above values.

[0026] For example, the lithium supplement includes at least one of Li2ZrO3, Li2C2O4, Li2MnO3, Li5FeO4, Li2NiO2 and Li2S.

[0027] For example, the MXene material includes Ti3C2T x MXene, V2CT x Mxene, Zr2C2T x MXene and Nb4C3T x At least one of MXene.

[0028] According to the present invention, if the coating layer is too thick, especially if the Li2ZrO3 layer is too thick, it may prolong the path of lithium ions diffusing from the bulk phase to the electrolyte, increase interfacial impedance, and lead to increased battery polarization and decreased rate performance, especially severe capacity loss during high-rate charge and discharge. Although MXene has excellent conductivity, if the insulating phase Li2ZrO3 is too thick, it may disrupt the continuous conductive network formed by MXene, affecting the rapid transport of electrons within the particles. If the coating layer is too thin, a continuous and dense protective layer may not be formed, resulting in numerous defects and voids, which cannot effectively prevent direct contact between the high-nickel material and the electrolyte, and interfacial side reactions (such as corrosion, gas generation, and residual lithium conversion) cannot be effectively suppressed. In the present invention, the thickness of the coating layer can be 5~10 nm; exemplaryly, the thickness of the coating layer can be any value among 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, and 10 nm, or any value within the range formed by any two of the above values.

[0029] In a preferred embodiment of the present invention, the coating layer has a porous structure.

[0030] The appropriate pore size of the porous structure enables the construction of high-speed, directional lithium-ion transport channels, achieving a synergistic optimization of interfacial side reaction suppression and ion conduction enhancement. Optionally, the pore size of the porous structure in the coating layer is 4~10 nm; for example, the pore size of the porous structure in the coating layer can be any value among 4 nm, 5 nm, 6 nm, 7 nm, 8 nm, 9 nm, and 10 nm, or any value within the range formed by any pair of the above values.

[0031] In this invention, a suitable porosity of the coating layer achieves an optimal balance between maximizing ion transport and maintaining structural integrity. Optionally, the porosity of the coating layer is 20% to 40%; exemplaryly, the porosity of the coating layer can be any value from 20%, 25%, 30%, 35%, and 40%, or any value within the range formed by any pair of the above values.

[0032] According to the present invention, if the particle size of the ternary cathode material is too large, the diffusion rate of lithium ions within the bulk phase of the cathode material particles may be slow. An excessively large particle size (e.g., much larger than 80 nm) will significantly prolong the diffusion path of lithium ions from the particle center to the surface, leading to increased polarization during charging and discharging, especially a significant reduction in capacity at high rates and deterioration of fast-charging performance. If the particle size of the ternary cathode material is too small (e.g., <30 nm), the specific surface area of ​​the material will increase several times, which means a significant increase in the reaction interface in contact with the electrolyte. Even with a coating layer, the large surface area will lead to an increased overall degree of side reactions, faster consumption of active lithium and electrolyte, and a decrease in cycle life and coulombic efficiency. In the present invention, the particle size of the ternary cathode material can be 50~80 nm; exemplaryly, the particle size of the ternary cathode material can be any value among 50 nm, 60 nm, 70 nm, and 80 nm, or any value within the range formed by any two of the above values.

[0033] For example, the ternary cathode material includes LiNi. 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.5 Co 0.3 Mn 0.2 O2 and LiNi 0.6 Co 0.2 Mn 0.2 At least one of O2.

[0034] In this invention, if the mass ratio of polypyrrole (PPy) to graphene is too high, it may lead to decreased electronic conductivity, insufficient structural stability, and inadequate mechanical strength. Graphene is the main component providing the two-dimensional long-range electronic conductive network. When its content is too low, the PPy particles will be isolated and unable to form a highly efficient conductive path throughout the entire coating, resulting in a significant decrease in the overall electronic conductivity of the coating and failing to meet the requirements of high-rate charge and discharge. The two-dimensional sheet structure of graphene has excellent mechanical strength and can act as a skeletal support in the coating. Too much PPy and too little graphene will make the coating more like a soft polymer film, with decreased mechanical strength and toughness, making it prone to cracking or damage during electrode rolling and cycling. If the mass ratio of polypyrrole (PPy) to graphene is too low, it may lead to insufficient bonding force between the coating and the current collector, poor graphene dispersion, and structural defects. In this invention, the N atoms in PPy form Al-N coordination bonds with the aluminum foil, which is a "chemical anchor" that ensures the coating adheres firmly to the current collector. Insufficient PPy content means insufficient "anchor points," resulting in poor adhesion between the coating and the current collector, making it prone to peeling off from the aluminum foil during processing or recycling. Simultaneously, PPy effectively inserts itself between graphene sheets during polymerization, preventing graphene recombination and acting as a "spacer" and "dispersant." Insufficient PPy leads to graphene sheet agglomeration, preventing the formation of a uniform, dense conductive network and potentially causing defects in the coating. According to the present invention, the mass ratio of polypyrrole to graphene is 10:1 to 4:1. Exemplarily, the mass ratio of polypyrrole to graphene can be any value from 10:1, 9:1, 8:1, 7:1, 6:1, 5:1, and 4:1, or any value within the range of any two of the above values.

[0035] In one embodiment of the present invention, the coating further includes a first adhesive; optionally, the mass ratio of the second composite material to the first adhesive is 5:1 to 15:1.

[0036] For example, the first adhesive comprises polytetrafluoroethylene and / or acrylic resin.

[0037] According to the present invention, if the coating thickness is too thick, it may lead to increased interfacial impedance and decreased energy density. Specifically, an excessively thick coating (especially the polymer binder) increases the path and resistance of lithium ions migrating from the electrolyte to the surface of the active material, resulting in increased battery polarization and reduced rate performance and capacity. In this invention, the coating (such as the PPy / graphene hybrid conductive layer and binder) is a non-active material; excessive thickness will reduce the mass proportion of the active material in the electrode, thereby directly lowering the battery's mass energy density and volumetric energy density. If the coating thickness is too thin, it may lead to an incomplete conductive network and insufficient bonding strength. In this invention, an excessively thin coating may prevent the formation of a continuous and uniform PPy / graphene conductive layer, resulting in a "blind zone" of electron transport between the current collector and the active material, causing some active material to be underutilized and overall conductivity to decrease. Simultaneously, an excessively thin coating means insufficient Al-N coordination bonds formed with the aluminum foil and insufficient contact area with the upper active material layer, resulting in poor adhesion between the coating and the current collector, making it prone to peeling during battery manufacturing (such as rolling and slitting) and cycling. In this invention, the thickness of the coating can be 10-15 nm. For example, the thickness of the coating can be any value among 10 nm, 11 nm, 12 nm, 13 nm, 14 nm, and 15 nm, or any value within the range formed by any two of the above values.

[0038] According to the present invention, if the thickness of the positive electrode active material layer is too thick, it may lead to ion transport restriction, increased polarization, and obstructed electron conduction. On the one hand, during charging and discharging, lithium ions need to migrate through the entire electrode thickness in the electrolyte. An excessively thick electrode will lengthen the ion transport path in the electrolyte, increase resistance, and lead to severe concentration polarization and voltage hysteresis, resulting in a sharp deterioration in rate performance and low capacity utilization at high rates. On the other hand, electrons need to be transported through a conductive agent network in a thicker electrode. An excessively thick electrode can easily lead to obstructed electron conduction paths and increase electrode internal resistance. If the thickness of the positive electrode active material layer is too thin, it may lead to a decrease in volumetric energy density and gravimetric energy density, and also increase the complexity and cost of the process. In the present invention, an excessively thin electrode means that the proportion of non-active components (current collectors, separators, etc.) in the battery is relatively increased, thereby significantly reducing the overall energy density of the battery and making the product uncompetitive. At the same time, in order to achieve the specified battery capacity, more current collectors and separators are needed to assemble more electrode sheets, which greatly increases the production process, cost, and difficulty of battery packaging. In this invention, the thickness of the positive electrode active material layer can be 80~120μm. For example, the thickness of the positive electrode active material layer can be any value among 80μm, 90μm, 100μm, 110μm, and 120μm, or any value within the range formed by any two of the above values.

[0039] In one embodiment of the present invention, the positive electrode active material layer further includes a second binder and a conductive agent; optionally, the mass ratio of the positive electrode active material, the second binder and the conductive agent is (93~97):(2~5):(1~2).

[0040] For example, the second adhesive includes at least one of polytetrafluoroethylene, polyvinylidene fluoride, and sodium carboxymethyl cellulose.

[0041] For example, the conductive agent includes at least one of conductive carbon black, acetylene black, graphene, conductive graphite, conductive carbon nanotubes, and conductive carbon fibers.

[0042] A second aspect of the present invention provides a method for preparing a positive electrode sheet, comprising the following steps: S1. Prepare an MXene material dispersion; mix the first precursor, the second precursor, and the first solvent for a first dispersion treatment, adjust the pH to obtain a sol; mix the sol and the MXene material dispersion, perform a second dispersion, centrifugation, and washing treatment to obtain a first product; perform a first drying and annealing treatment on the first product to obtain a first composite material; mix the first composite material, the ternary cathode material, and the second solvent, perform a third dispersion and a second drying treatment to obtain the cathode active material; S2. Prepare a mixed solution containing graphene and polypyrrole, perform a third drying and heat treatment to obtain a second composite material; prepare a first slurry containing the second composite material, coat the slurry containing the second composite material onto at least one side of the positive electrode current collector matrix along the thickness direction, perform a fourth drying and a first pressing treatment to obtain a modified current collector. S3. The second slurry containing the positive electrode active material is coated on at least one side of the modified current collector along the thickness direction, and then subjected to the fifth drying and second tableting treatment.

[0043] The preparation method of this invention achieves a uniform, dense, and firmly bonded coating layer. Step S1 employs a "sol-gel method + in-situ annealing": by forming a sol from the precursor and mixing it with an MXene dispersion, uniform mixing and adhesion of the Li2ZrO3 precursor and MXene sheets can be achieved at the nanoscale. Subsequent annealing allows the amorphous precursor to crystallize in-situ into Li2ZrO3, forming a strong interaction with MXene. Compared to simple mechanical mixing and coating, this process yields a more uniform, defect-free, and more strongly bonded composite coating layer. Furthermore, this invention prioritizes the construction of a stable and highly conductive current collector-active material interface. Step S2 first prepares a "modified current collector," on which a robust PPy / graphene conductive underlayer is constructed. This layer forms stable Al-N coordination bonds with the current collector through heat treatment, resulting in strong adhesion and preventing coating detachment during cycling. This lays the foundation for subsequent interfacial bonding: This pre-laid conductive layer provides a reaction interface for MXene in the subsequently coated cathode material coating layer, ensuring that the two can form covalent bonds with the highest probability, thereby systematically solving the problem of interfacial kinetic mismatch.

[0044] The preparation method of the present invention effectively protects the structure of the active material. In the entire preparation process, the ternary cathode material is introduced only in the second half of S1, which avoids direct exposure to high temperature during the high temperature annealing process (first step drying and annealing), prevents adverse phase transition and lithium loss on the surface of the high nickel material due to high temperature, and preserves the integrity of its bulk structure.

[0045] In one embodiment of the present invention, in step S1, the concentration of the MXene material dispersion is 0.5~2.5 mg / mL; exemplaryly, the concentration of the MXene material dispersion can be any value among 0.5 mg / mL, 1 mg / mL, 1.5 mg / mL, 2 mg / mL and 2.5 mg / mL or any value within the range of any two of the above values.

[0046] The molar ratio of the first precursor to the second precursor of the present invention can be 1:1 to 5:1; for example, the molar ratio of the first precursor to the second precursor can be any value among 1:1, 2:1, 3:1, 4:1 and 5:1 or any value within the range of any two of the above values.

[0047] The mass ratio of the sol to the MXene material dispersion of the present invention can be 3:1 to 8:1; for example, the mass ratio of the sol to the MXene material dispersion can be any value among 3:1, 4:1, 5:1, 6:1, 7:1 and 8:1 or any value within the range of any two of the above values.

[0048] The lithium supplement content in the sol of the present invention can be 5 to 10 wt%; for example, the lithium supplement content in the sol can be any value among 5 wt%, 6 wt%, 8 wt%, 9 wt% and 10 wt% or any value within the range of any two of the above values.

[0049] The mass ratio of the ternary cathode material to the first composite material of the present invention can be 2:1 to 6:1; for example, the mass ratio of the ternary cathode material to the first composite material can be any value among 2:1, 3:1, 4:1, 5:1, and 6:1 or any value within the range of any two of the above values.

[0050] In one embodiment of the present invention, in step S2, the viscosity of the first slurry can be 1000~2000 mPa·s; exemplaryly, the viscosity of the first slurry can be any value among 1000 mPa·s, 1250 mPa·s, 1500 mPa·s, 1750 mPa·s and 2000 mPa·s or any value within the range of any two of the above values.

[0051] In one embodiment of the present invention, in step S3, the solid content of the second slurry can be 60wt% to 70wt%. For example, the solid content of the second slurry can be any value selected from 60wt%, 62wt%, 65wt%, 67wt%, and 70wt%, or any value within the range formed by any pair of the above values.

[0052] For example, in step S1, the first precursor includes one of LiNO3, Li2CO3 and LiOH.

[0053] For example, the second precursor includes at least one of ZrOCl2·8H2O, ZrO(NO3)2, ZrO2, Zr(SO4)2·H2O, NiO, CS2, MnO and FeC2O4·2H2O.

[0054] In one embodiment of the present invention, in step S2, the first slurry further includes a first binder and a third solvent; exemplarily, the third solvent includes at least one of ethanol, isopropanol and tert-propanol.

[0055] In one embodiment of the present invention, in step S3, the second slurry further includes a second binder, a conductive agent, and a fourth solvent; exemplarily, the fourth solvent includes at least one of N-methylpyrrolidone, N-ethylpyrrolidone, N,N-dimethylacetamide, and N,N-dimethylformamide.

[0056] In one embodiment of the present invention, in step S1, the pH range is 8-9; and / or, in step S1, the second dispersion temperature is 60-100℃, the second dispersion time is 2-6h, and the second dispersion rotation speed is 300-600rpm; and / or, the centrifugation rotation speed is 8000-10000rpm, the centrifugation time is 30-60min, and the centrifugation temperature is 10-30℃; and / or, the first drying temperature is -50 to -30℃, and the first drying time is 16-32h; and / or, the annealing temperature is 400-600℃, the annealing time is 1-3h, and the annealing atmosphere includes an inert atmosphere; and / or, the third dispersion temperature is 10-30℃, the third dispersion time is 6-10h, and the third dispersion rotation speed is 600-800rpm; and / or, the second drying temperature is 60-80℃, and the second drying time is 12-20h.

[0057] In one embodiment of the present invention, in step S2, the third drying includes vacuum drying; optionally, the temperature of the vacuum drying is 60~80℃, and the time of the vacuum drying is 24~30h; and / or, the temperature of the heat treatment is 300~450℃, the time of the heat treatment is 1~3h, and the atmosphere of the heat treatment includes an inert atmosphere.

[0058] A third aspect of the present invention provides a battery comprising a positive electrode, the positive electrode comprising the above-described positive electrode and / or a positive electrode prepared according to the above-described preparation method.

[0059] The present invention will be further described in detail below through examples. All raw materials used in the examples are commercially available.

[0060] Example 1 1. Preparation of the positive electrode sheet: (1) Preparation of the first composite material: Lithium nitrate (LiNO3) and zirconium oxychloride (ZrOCl2·8H2O) were dissolved in deionized water at a Li:Zr molar ratio of 2:1, and ammonia was added to adjust the pH to 8 to form a transparent sol; MXene dispersion: 0.3g Ti3C3T xMXene powder was ultrasonically dispersed in 120 ml of anhydrous ethanol (concentration 1.5 mg / mL) for 40 min to ensure monolayer dispersion. Li₂ZrO₃ sol and MXene dispersion were mixed at a mass ratio of 5:1 and stirred in an 80℃ water bath (500 rpm) for 4 h. Li₂ZrO₃ nanoparticles were electrostatically adsorbed onto the surface of the MXene sheets. The mixture was centrifuged at 90,000 rpm for 45 min and washed three times sequentially with ethanol and deionized water to remove unreacted ions, yielding the first product. The first product was freeze-dried (-40℃, 24 h) to form a porous composite powder, which was then annealed at 500℃ for 2 h under an argon atmosphere to obtain the first composite material (Li₂ZrO₃-MXene coating).

[0061] (2) Preparation of positive electrode active material: High-nickel ternary positive electrode material (chemical formula: LiNi) 0.8 Co 0.1 Mn 0.1 O2) and Li2ZrO3-MXene coating were dispersed in ethanol (at a mass ratio of 4:1) to form a suspension. The suspension was magnetically stirred at 700 rpm for 8 hours, then centrifuged at 9000 rpm for 45 min. The suspension was washed three times with ethanol and deionized water, and then dried in a vacuum oven at 60°C for 18 h to obtain the positive electrode active material.

[0062] (3) Aluminum foil interface treatment: First, dissolve 8 ml of pyrrole monomer in 80 ml of ethanol aqueous solution (1:2 volume ratio), place it in an ice bath at 3℃, and add 2.8 g of APS (ammonium persulfate) oxidant. React for 18 h to obtain nano-sized PPy particles; ultrasonically treat 0.1 g of graphene (GO) in ethanol aqueous solution (1:1 volume ratio) for 2 h to ensure the sheet dispersion. Mix the synthesized PPy with graphene (ratio of 6:1) and ultrasonically disperse for 2 h to fully combine them. The mixture was vacuum dried at 70°C for 26 h to remove the solvent, and then heat-treated for 2 h (heated to 400°C in an inert gas atmosphere) to further improve its structural stability, thus obtaining a second composite material. The second composite material and the binder were dispersed in a solvent (deionized water or ethanol) at a mass ratio of 10:1 and stirred at high speed (1000-2000 rpm) to obtain a first slurry containing the second composite material. This slurry was then coated onto an aluminum foil current collector, and after drying and cold pressing, a modified aluminum foil current collector was obtained.

[0063] (4) Sheet making: The positive electrode active material, conductive agent (conductive carbon black) and binder (PVDF) are mixed in a mass ratio of 94:5:1 to obtain a mixed material. The mixed material is thoroughly stirred at high speed in NMP to obtain a positive electrode slurry. The positive electrode slurry is coated on a modified aluminum foil current collector. After drying and pressing, a positive electrode sheet is obtained.

[0064] 2. Preparation of negative electrode sheet: The negative electrode active material (graphite), conductive agent (conductive carbon black) and binder (CMC) are mixed in a mass ratio of 75:2:23 to obtain a mixed material. The mixed material is stirred evenly in deionized water at high speed to obtain a negative electrode slurry. The negative electrode slurry is coated on conventional copper foil, and after drying and pressing, a negative electrode sheet is obtained.

[0065] 3. Separating membrane: PP porous film is used as the separating membrane.

[0066] 4. Electrolyte: Ethylene carbonate (EC), dimethyl carbonate (DMC), and diethyl carbonate (DEC) are mixed in a volume ratio of 1:1:1. Then, fully dried lithium salt LiPF6 is dissolved in the mixed organic solvent at a ratio of 1 mol / L to prepare the electrolyte.

[0067] 5. Preparation of lithium battery: After weighing, the electrode sheet is directly used as the negative electrode of the lithium-ion battery. The 2032 coin cell is assembled in a glove box filled with Ar. The assembly sequence of the battery from top to bottom is: negative electrode shell, gasket, pad, lithium sheet, separator, self-supporting electrode sheet, positive electrode shell, to obtain the coin cell of this embodiment.

[0068] Example 2 The preparation method of the positive electrode sheet in this embodiment is the same as that in Example 1, except that the mass ratio of Li2ZrO3 sol to MXene dispersion is 8:1, thus obtaining the positive electrode active material of this embodiment.

[0069] The preparation methods of the negative electrode sheet, separator, electrolyte and lithium battery in this embodiment are the same as in Embodiment 1.

[0070] Example 3 The preparation method of the positive electrode sheet in this embodiment is the same as that in Example 1, except that the mass ratio of Li2ZrO3 sol to MXene dispersion is 3:1, thus obtaining the positive electrode active material of this embodiment.

[0071] The preparation methods of the negative electrode sheet, separator, electrolyte and lithium battery in this embodiment are the same as in Embodiment 1.

[0072] Example 4 The preparation method of the positive electrode sheet in this embodiment is the same as that in Example 1, except that the mass ratio of the ternary positive electrode material to the first composite material (Li2ZrO3-MXene) is 6:1, thus obtaining the positive electrode active material of this embodiment.

[0073] The preparation methods of the negative electrode sheet, separator, electrolyte and lithium battery in this embodiment are the same as in Embodiment 1.

[0074] Example 5 The preparation method of the positive electrode sheet in this embodiment is the same as that in Embodiment 1, except that the mass ratio of the ternary positive electrode material to the first composite material (Li2ZrO3-MXene) is 2:1 to obtain the positive electrode active material of this embodiment.

[0075] The preparation methods of the negative electrode sheet, separator, electrolyte and lithium battery in this embodiment are the same as in Embodiment 1.

[0076] Example 6 The preparation method of the positive electrode sheet in this embodiment is the same as that in Embodiment 1, except that the mass ratio of PPy to graphene is 10:1 to obtain the second composite material of this embodiment.

[0077] The preparation methods of the negative electrode sheet, separator, electrolyte and lithium battery in this embodiment are the same as in Embodiment 1.

[0078] Example 7 The preparation method of the positive electrode sheet in this embodiment is the same as that in Embodiment 1, except that the mass ratio of PPy to graphene is 4:1 to obtain the second composite material of this embodiment.

[0079] The preparation methods of the negative electrode sheet, separator, electrolyte and lithium battery in this embodiment are the same as in Embodiment 1.

[0080] Comparative Example 1 The preparation method of the positive electrode sheet in this comparative example is generally the same as that in Example 1, except that a high-nickel ternary positive electrode material (chemical formula: LiNi) is used. 0.8 Co 0.1 Mn 0.1 O2 was used as the positive electrode active material in this comparative example.

[0081] The preparation methods of the negative electrode sheet, separator, electrolyte and lithium battery in this comparative example are the same as in Example 1.

[0082] Comparative Example 2 The preparation method of the positive electrode sheet in this comparative example is the same as that in Example 1, except that ordinary aluminum foil is used as the positive current collector in this comparative example.

[0083] The preparation methods of the negative electrode sheet, separator, electrolyte and lithium battery in this comparative example are the same as in Example 1.

[0084] Comparative Example 3 The preparation method of the positive electrode sheet in this comparative example is generally the same as that in Example 1, except that a high-nickel ternary positive electrode material (chemical formula: LiNi) is used. 0.8 Co 0.1 Mn 0.1 O2 was used as the positive electrode active material in this comparative example; ordinary aluminum foil was used as the positive electrode current collector in this comparative example.

[0085] The preparation methods of the negative electrode sheet, separator, electrolyte and lithium battery in this comparative example are the same as in Example 1.

[0086] Test Example 1 The batteries prepared in Examples 1-7 and Comparative Examples 1-3 were subjected to performance tests, and the test results are shown in Table 1.

[0087] (1) Internal resistance test: The internal resistance of different groups of batteries is obtained by using a battery internal resistance meter.

[0088] (2) Battery cycle performance test: At 25℃, the battery was charged at a constant current of 0.33C to a voltage of 3.65V, and then charged at a constant voltage to a current of 0.05C. After standing for 5 minutes, the battery was discharged at a constant current of 0.33C to 2.0V, and the discharge capacity at this time was recorded, which is the discharge capacity C0 of the first cycle. The cycle test was performed according to this procedure, and the capacity at the 200th cycle was recorded. It is denoted as C, and the capacity retention rate after 200 cycles is obtained by using the formula C / C0×100%.

[0089] (3) Peel strength test: Core equipment – ​​tensile testing machine. Sample preparation: The sample width is 25mm and the length is at least 200mm. At least 3 samples should be tested for each material. Attach one end of the sample to the standard test plate and roll it with a roller to ensure adhesion. The other end of the sample needs to be folded and fixed to the fixture to ensure that the peel line is in the position of minimum stress.

[0090] Table 1 As shown in Table 1, the batteries prepared in the embodiments of the present invention exhibit significantly reduced internal resistance, and significantly increased capacity retention and peel strength. Specifically, Example 1 demonstrates superior performance in all three key indicators: internal resistance (11.5 Ω), cycle capacity retention (96.5%), and coating peel strength (101 N / m). This proves that the synergistic system of "Li2ZrO3-MXene coating layer" and "PPy / graphene modified current collector" constructed by precisely controlling the proportions of each material can simultaneously achieve low impedance, long lifespan, and high interfacial stability. Examples 2 and 3 show that when the ratio of Li2ZrO3 to MXene deviates from the optimal value, it leads to increased internal resistance (~14.0 Ω) and decreased peel strength (~65-68 N / m). This indicates that excessive insulating Li2ZrO3 or insufficient conductive MXene will impair the overall performance of the coating layer. Examples 4 and 5 show that when the ratio of ternary material to coating material deviates from the optimal value, i.e., the coating layer is too thin or too thick, it also leads to increased internal resistance and poor adhesion. This verifies that the coating layer needs to be within a suitable thickness range to balance protection and conductivity. Examples 6 and 7 show that when the PPy to graphene ratio is unbalanced (10:1 or 4:1), the performance is also not optimal. Too much PPy (Example 6) may weaken the overall conductivity; while too little PPy (Example 7) may affect the dispersion of graphene and the bonding strength with the current collector, leading to a slight deterioration in internal resistance and cycling performance.

[0091] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A positive electrode plate, characterized in that, The positive electrode sheet includes a modified current collector and a positive active material layer disposed on at least one side surface of the modified current collector along the thickness direction. The positive electrode active material layer includes a positive electrode active material; the positive electrode active material includes a ternary positive electrode material and a coating layer covering at least a portion of the surface of the ternary positive electrode material; The coating layer includes a first composite material, which includes a lithium supplement and an MXene material, wherein the lithium supplement is adsorbed on at least a portion of the surface of the MXene material; The modified current collector includes a positive current collector substrate and a coating disposed on at least one side surface of the positive current collector substrate along the thickness direction; The coating comprises a second composite material, which includes polypyrrole and graphene.

2. The positive electrode sheet according to claim 1, characterized in that, The mass ratio of the lithium supplement to the MXene material is 3:1 to 5:1; Optionally, the lithium supplement includes at least one of Li2ZrO3, Li2C2O4, Li2MnO3, Li5FeO4, Li2NiO2 and Li2S; Optionally, the MXene material includes Ti3C2T x MXene, V2CT x Mxene, Zr2C2T x MXene and Nb4C3T x At least one of MXene.

3. The positive electrode sheet according to claim 1, characterized in that, The thickness of the coating layer is 5~10 nm; and / or, The coating layer has a porous structure; Optionally, the pore size of the porous structure in the coating layer is 4~10 nm; Optionally, the porosity of the coating layer is 20% to 40%; and / or, The particle size of the ternary cathode material is 50~80nm; Optionally, the ternary cathode material includes LiNi. 0.8 Co 0.1 Mn 0.1 O2, LiNi 0.5 Co 0.3 Mn 0.2 O2 and LiNi 0.6 Co 0.2 Mn 0.2 At least one of O2.

4. The positive electrode sheet according to claim 1, characterized in that, The mass ratio of the polypyrrole to the graphene is 10:1 to 4:1; and / or, The coating also includes a first adhesive; Optionally, the mass ratio of the second composite material to the first adhesive is 5:1 to 15:1; Optionally, the first adhesive comprises polytetrafluoroethylene and / or acrylic resin; and / or, The thickness of the coating is 10~15nm.

5. The positive electrode sheet according to claim 1, characterized in that, The thickness of the positive electrode active material layer is 80~120μm; and / or, The positive electrode active material layer also includes a second binder and a conductive agent; Optionally, the mass ratio of the positive electrode active material, the second binder, and the conductive agent is (93~97):(2~5):(1~2); Optionally, the second adhesive includes at least one of polytetrafluoroethylene, polyvinylidene fluoride, and sodium carboxymethyl cellulose; Optionally, the conductive agent includes at least one of conductive carbon black, acetylene black, graphene, conductive graphite, conductive carbon nanotubes, and conductive carbon fibers.

6. A method for preparing a positive electrode sheet, characterized in that, Includes the following steps: S1. Prepare MXene material dispersion; mix the first precursor, the second precursor and the first solvent for the first dispersion treatment, adjust the pH to obtain a sol; The sol and MXene material dispersion were mixed, and then subjected to a second dispersion, centrifugation, and washing to obtain the first product. The first product is subjected to a first drying and annealing treatment to obtain a first composite material; the first composite material, the ternary cathode material, and the second solvent are mixed and subjected to a third dispersion and second drying treatment to obtain the cathode active material; S2. Prepare a mixed solution containing graphene and polypyrrole, perform a third drying and heat treatment to obtain a second composite material; prepare a first slurry containing the second composite material, coat the slurry containing the second composite material onto at least one side of the positive electrode current collector matrix along the thickness direction, perform a fourth drying and a first pressing treatment to obtain a modified current collector. S3. The second slurry containing the positive electrode active material is coated on at least one side of the modified current collector along the thickness direction, and then subjected to the fifth drying and second tableting treatment.

7. The method for preparing the positive electrode sheet according to claim 6, characterized in that, In step S1, the concentration of the MXene material dispersion is 0.5~2.5 mg / mL; and / or, The molar ratio of the first precursor to the second precursor is 1:1 to 5:1; and / or, The mass ratio of the sol to the MXene material dispersion is 3:1 to 8:1; and / or, The lithium supplement in the sol is 5-10 wt%; and / or, The mass ratio of the ternary cathode material to the first composite material is 2:1 to 6:1; and / or, In step S2, the viscosity of the first slurry is 1000~2000 mPa·s; and / or, In step S3, the solid content of the second slurry is 60wt%~70wt%.

8. The method for preparing the positive electrode sheet according to claim 7, characterized in that, In step S1, the first precursor includes one of LiNO3, Li2CO3, and LiOH; and / or, The second precursor includes at least one of ZrOCl2·8H2O, ZrO(NO3)2, ZrO2, Zr(SO4)2·H2O, NiO, CS2, MnO, and FeC2O4·2H2O; and / or, In step S2, the first slurry further includes a first binder and a third solvent; optionally, the third solvent includes at least one of ethanol, isopropanol, and tert-propanol; and / or, In step S3, the second slurry further includes a second binder, a conductive agent, and a fourth solvent; optionally, the fourth solvent includes at least one of N-methylpyrrolidone, N-ethylpyrrolidone, N,N-dimethylacetamide, and N,N-dimethylformamide.

9. The method for preparing the positive electrode sheet according to claim 6, characterized in that, In step S1, the pH range is 8-9; and / or, In step S1, the temperature of the second dispersion is 60~100℃, the dispersion time is 2~6h, and the dispersion rotation speed is 300~600rpm; and / or, The centrifugation speed is 8000~10000 rpm, the centrifugation time is 30~60 min, and the centrifugation temperature is 10~30℃; and / or, The first drying temperature is -50~-30℃, and the first drying time is 16~32h; and / or, The annealing treatment temperature is 400~600℃, the annealing treatment time is 1~3 hours, and the annealing treatment atmosphere includes an inert atmosphere; and / or, The temperature of the third dispersion treatment is 10~30℃, the time of the third dispersion treatment is 6~10h, and the rotation speed of the third dispersion treatment is 600~800rpm; and / or, The temperature of the second drying treatment is 60~80℃, and the time of the second drying treatment is 12~20h; and / or, In step S2, the third drying includes vacuum drying; optionally, the vacuum drying temperature is 60~80℃, and the vacuum drying time is 24~30h; and / or, The heat treatment temperature is 300~450℃, the heat treatment time is 1~3h, and the heat treatment atmosphere includes an inert atmosphere.

10. A battery, characterized in that, The battery includes a positive electrode sheet, which includes the positive electrode sheet according to any one of claims 1 to 5 and / or the positive electrode sheet prepared by the preparation method according to any one of claims 6 to 9.

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