Positive pole piece, preparation method thereof and lithium ion battery

Abstract

The invention discloses a positive pole piece, a preparation method of the positive pole piece and a lithium ion battery. The positive pole piece comprises a current collector and a positive pole material layer arranged on the current collector, the positive electrode material layer comprises a positive electrode active material, a binder, a conductive agent and an additive; the additive is a maleimide derivative with aromatic phosphate as a bridging group, and the molecular structure of the maleimide derivative comprises maleimide groups at two ends, a rigid aromatic skeleton in the middle and a bridged phosphate group. According to the invention, the maleimide derivative taking aromatic phosphate as a bridging group is introduced as an additive, a layer of stable interface film is constructed on the surface of the positive electrode, and the cross-linked network and flame retardant characteristics of the interface film can be utilized to enhance the safety and enhance the cycle stability and rate capability of the electrode so as to achieve the purpose and effect of high-power charging and discharging.

Description

Technical Field

[0001] This invention relates to the technical field of batteries, specifically to a positive electrode sheet and its preparation method, and a lithium-ion battery. Background Technology

[0002] Lithium-ion batteries have gained widespread attention due to their high energy density, long cycle life, and high output voltage. Currently, while ensuring battery safety, further improving the energy density, charge / discharge speed, and operating range of lithium-ion batteries has become a major research focus. In recent years, with the development of cathode materials moving towards higher energy density, higher power density, higher rate performance, lower cycle capacity loss, higher cycle stability, higher safety, and higher economic efficiency, high-nickel ternary layered oxide cathode materials such as Li[Ni] have become increasingly important. 1-x-y Co x Mn y O2, with its advantages such as high voltage and high capacity, is gradually becoming one of the preferred cathode materials for the next generation of high-energy lithium-ion batteries.

[0003] However, despite the numerous advantages mentioned above, high-nickel NCM cathode materials still face a series of key technological bottlenecks before achieving large-scale commercial application. These bottlenecks primarily include insufficient cycle stability, inadequate rate performance, and a pressing need to improve safety performance. These issues are closely related to the following factors: First, the inherent crystal structure instability of NCM materials is a significant factor limiting their performance. With increasing nickel content, the material undergoes more drastic volume changes and phase transitions during charge and discharge, leading to lattice stress accumulation and microcrack formation. This, in turn, causes the active material to pulverize and detach, resulting in irreversible capacity loss. Simultaneously, the high delithiation state of Ni... 4+ Thermodynamic instability can lead to oxygen release from the material surface, exacerbating structural collapse and deterioration.

[0004] Secondly, interfacial side reactions between the cathode material and the electrolyte are another key limiting factor. Under high-voltage charging conditions, the surface of high-nickel cathode materials exhibits strong oxidizing properties, easily catalyzing the oxidative decomposition of the electrolyte and generating harmful byproducts such as gases like HF and CO2, as well as insoluble precipitates. These side reactions not only consume active lithium but also form a high-resistivity solid electrolyte interphase (CEI) film on the cathode surface, significantly increasing interfacial resistance, hindering the rapid insertion and extraction of lithium ions, leading to increased polarization and accelerated capacity decay.

[0005] Furthermore, the problem of transition metal ions (especially Ni and Mn ions) dissolving from the cathode material and depositing on the anode surface also seriously affects the battery's cycle performance and safety. These dissolved transition metal ions catalyze the continuous growth of the SEI film on the anode, consume active lithium, and increase the battery's internal resistance.

[0006] To address the aforementioned issues, current research on optimizing the electrochemical performance of high-nickel NCM cathode materials focuses primarily on the regulation and improvement of the electrode-electrolyte interface. How to enhance interfacial stability, improve lithium-ion transport kinetics at the solid-liquid interface, effectively suppress interfacial side reactions, prevent the dissolution of transition metal ions, and enhance the structural and thermal stability of the cathode material through rational material design and interface engineering techniques, thereby comprehensively improving the electrochemical and safety performance of the battery, has become a current research hotspot and focus. Common modification strategies include elemental doping modification, surface coating technology, the use of electrolyte additives, and the morphology and microstructure control of the cathode material. However, existing technologies still suffer from limitations such as limited modification effects, complex processes, high costs, or difficulty in simultaneously achieving multiple performance indicators, necessitating the development of more effective, economical, and easily industrialized technical solutions. Summary of the Invention

[0007] The purpose of this invention is to overcome the shortcomings of the above-mentioned background technology and provide a positive electrode sheet and its preparation method, as well as a lithium-ion battery.

[0008] To achieve the above objectives, a first aspect of the present invention provides a positive electrode sheet, comprising a current collector and a positive electrode material layer disposed on the current collector; the positive electrode material layer comprises a positive electrode active material, a binder, a conductive agent, and an additive; The additive is a maleimide derivative with aromatic phosphate esters as bridging groups. The molecular structure of the maleimide derivative includes maleimide groups at both ends, a rigid aromatic skeleton in the middle, and bridging phosphate ester groups.

[0009] Furthermore, the additive is tris(4-maleimide phenyl) phosphate, with the following molecular structure: .

[0010] Furthermore, the positive electrode active material is lithium nickel cobalt manganese oxide; The adhesive is selected from at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyacrylic acid, polyacrylonitrile, polyimide, and sodium carboxymethyl cellulose; The conductive agent is selected from at least one of conductive carbon black, carbon nanotubes, graphene, conductive graphite, and carbon fiber. The current collector is selected from one of aluminum foil, carbon-coated aluminum foil, and aluminum alloy foil.

[0011] Furthermore, in the positive electrode sheet, by mass percentage, the positive electrode material layer contains: the positive electrode active material at a mass percentage of 94.2% to 96.7%, the binder at a mass percentage of 0.8% to 1.5%, the conductive agent at a mass percentage of 1.0% to 2.0%, and the additive at a mass percentage of 0.5% to 3%.

[0012] A second aspect of the present invention provides a method for preparing the above-mentioned positive electrode sheet, comprising the following steps: The adhesive is added to the solvent to make a glue solution; Add the conductive agent to the adhesive solution and stir until homogeneous to form a slurry; The positive electrode active material and additives are added to the slurry and stirred evenly to obtain the positive electrode slurry; wherein, the additive is a maleimide derivative with aromatic phosphate ester as the bridging group, and the molecular structure of the maleimide derivative includes maleimide groups at both ends, a rigid aromatic skeleton in the middle and bridging phosphate ester groups. The positive electrode slurry is coated onto the current collector and dried to obtain the positive electrode sheet.

[0013] Furthermore, the solvent is selected from one of N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide; The current collector is selected from one of aluminum foil, carbon-coated aluminum foil, and aluminum alloy foil; The temperature at which the positive electrode slurry is coated onto the current collector and dried is 80-120℃.

[0014] A third aspect of the present invention provides a lithium-ion battery comprising the above-described positive electrode.

[0015] A fourth aspect of the present invention provides a method for preparing a lithium-ion battery, comprising the following steps: Using the above-mentioned positive electrode sheet, small positive electrode sheets are obtained by rolling and slitting; The negative electrode sheet is prepared and then rolled and slit to obtain small negative electrode sheets. The positive electrode chip, the negative electrode chip, and the separator are stacked together and packaged to form a battery cell; The battery cell is then post-processed to obtain a lithium-ion battery.

[0016] Furthermore, the preparation of the negative electrode sheet includes: mixing and dispersing the negative electrode conductive agent, artificial graphite and silicon carbon material evenly, then adding polyacrylic acid and water and dispersing evenly, finally adding styrene-butadiene rubber and stirring evenly, coating the resulting slurry onto a copper current collector, and drying to obtain the negative electrode sheet.

[0017] Furthermore, by mass percentage, the negative electrode sheet comprises: 80-92% artificial graphite, 5-15% silicon carbon material, 1-4% polyacrylic acid, 0.5-2% negative electrode conductive agent, and 1-3% styrene-butadiene rubber; the separator is selected from one of polyethylene separator, polypropylene separator, ceramic-coated separator, and PVDF-coated separator.

[0018] Compared with the prior art, the present invention has the following advantages: Firstly, this invention adds an additive, a maleimide derivative with aromatic phosphate ester as a bridging group, during the preparation of the positive electrode slurry. The molecular structure consists of three parts: maleimide groups at both ends provide electrochemical stability; a rigid aromatic skeleton in the middle enhances high voltage stability; and bridging phosphate ester groups provide flame retardant function. The maleimide groups at both ends of the molecule possess excellent electrochemical polymerization ability and stability, enabling the formation of a dense and uniform solid electrolyte interface (CEI) film in situ on the cathode surface. This effectively physically isolates the electrolyte from the highly active cathode material, suppressing side reactions. The rigid aromatic skeleton in the middle endows the additive with extremely high oxidation stability, allowing it to withstand the high operating voltage of high-nickel materials. Simultaneously, the bridging phosphate groups have flame-retardant properties, releasing phosphorus-containing free radicals when the battery experiences thermal runaway, inhibiting chain combustion reactions and significantly improving the safety of high-energy-density batteries. Specific functional groups in the additive molecule (such as amine and phosphate groups) have a strong adsorption and neutralization effect on hydrofluoric acid (HF) produced by electrolyte decomposition, preventing HF from corroding the cathode active material, thereby inhibiting the dissolution of transition metal ions (Ni, Mn) and reducing the risk of cathode structure collapse.

[0019] Secondly, the additive in the cathode material layer of this invention has a mass percentage of 0.5% to 3%. This ensures sufficient additive participation in interfacial film formation and surface modification, achieving effective interfacial protection, while avoiding excessive addition that could negatively impact the electronic conductivity and lithium-ion transport efficiency of the cathode material layer, thus preventing adverse effects on battery energy density and rate performance. This addition range has been experimentally optimized and verified to achieve a good balance between interfacial protection and electrochemical performance. The additive can chemically react with residual alkaline lithium salts (LiOH, Li2CO3) on the surface of high-nickel ternary materials (NCM) to generate stable products such as Li3PO4. This not only lowers the pH value of the slurry, preventing gelation during preparation and improving coating consistency and yield, but also reduces battery gas generation at the source.

[0020] Thirdly, the preparation method of the positive electrode sheet of this invention adopts a coating process, which eliminates the need for complex post-processing equipment. The specific order of adding the adhesive, conductive agent, and finally active material and additives ensures the uniform dispersion of the additives in the slurry, allowing them to fully coat the surface of the positive electrode particles and maximize their interface modification function. The entire preparation process of this invention is carried out at room temperature and pressure, without the need for high-temperature sintering or special atmosphere protection, which helps to reduce production energy consumption and costs, while avoiding the decomposition or inactivation of additives under high-temperature conditions.

[0021] Fourth, the lithium-ion battery of this invention has excellent cycle stability. Because the additives in the positive electrode can form a stable protective layer on the surface of the positive electrode material, effectively suppressing interfacial side reactions and the dissolution of transition metal ions, the lithium-ion battery of this invention has significantly improved cycle stability and can maintain a high capacity retention rate during long-term charge-discharge cycles, extending the battery's service life. The interfacial protective layer formed by the additives has moderate lithium-ion conductivity and does not significantly increase interfacial impedance, enabling the battery to maintain good capacity performance and low polarization under high-rate charge-discharge conditions, meeting the application requirements of fast charging and fast discharging. The flame-retardant properties of the phosphate ester groups and the inhibitory effect of the stable interfacial layer on electrolyte decomposition jointly improve the thermal stability and safety performance of the battery, reducing the risk of thermal runaway under abuse conditions such as overcharging and overheating, and enhancing safety performance.

[0022] Fifth, the negative electrode sheet of this invention uses artificial graphite and silicon carbon materials as the negative electrode active materials, which can combine the cycle stability of artificial graphite and the high specific capacity of silicon carbon materials to effectively improve the specific capacity of the negative electrode, thereby improving the overall energy density of the lithium-ion battery. It uses polyacrylic acid and styrene-butadiene rubber as a composite binder system. Polyacrylic acid can form chemical bonds with the surface of silicon carbon materials through carboxyl groups, effectively alleviating the volume expansion of silicon carbon materials during charging and discharging, and improving the cycle stability of the negative electrode. Styrene-butadiene rubber provides good flexibility and bonding strength. The synergistic effect of the two can effectively maintain the integrity of the negative electrode structure. The high-capacity silicon-carbon composite negative electrode of this invention is matched with the high-capacity lithium nickel cobalt manganese oxide positive electrode. The positive and negative electrode capacities are rationally designed, which can fully utilize the capacity advantages of the positive and negative electrode materials and maximize the energy density of the lithium-ion battery. Attached Figure Description

[0023] Figure 1 The graphs show the room temperature cycling performance of lithium-ion batteries in Example 9 and Comparative Example 4. Figure 2 This is a graph showing the overcharge test curve of the lithium-ion battery in Example 9; Figure 3 The graph shows the overcharge test curve of the lithium-ion battery in Comparative Example 4. Detailed Implementation

[0024] The following describes in detail the positive electrode sheet of the present invention, its preparation method, and embodiments of the lithium-ion battery. This description is provided to enable those skilled in the art to fully understand the invention and is not intended to limit the subject matter described in the claims.

[0025] The "scope" disclosed in this invention is defined in the form of a lower limit and an upper limit. A given scope is defined by selecting a lower limit and an upper limit, which define the boundaries of the specific scope. The scope defined in this way can include or exclude end values, and can be arbitrarily combined; that is, any lower limit can be combined with any upper limit to form a scope.

[0026] Unless otherwise specified, all embodiments and optional embodiments of the present invention can be combined to form new technical solutions. All technical features and optional technical features of the present invention can be combined to form new technical solutions. All steps of the present invention can be performed sequentially or randomly.

[0027] A positive electrode sheet of the present invention includes a current collector and a positive electrode material layer disposed on the current collector; the positive electrode material layer includes a positive electrode active material, a binder, a conductive agent and an additive.

[0028] The additive is a maleimide derivative with aromatic phosphate esters as bridging groups. The molecular structure of this maleimide derivative includes maleimide groups at both ends, a rigid aromatic skeleton in the middle, and bridging phosphate ester groups. The maleimide groups at both ends provide electrochemical stability; the rigid aromatic skeleton in the middle enhances high-voltage stability; and the bridging phosphate ester groups provide flame retardant properties. The CEI film formed by the amine groups contains polar —C—N— groups, which can react with HF, reducing the dissolution of Ni / Mn from the positive electrode. This group also has a strong affinity for HF, scavenging HF, promoting the dissociation of lithium salt ions, and inhibiting the phase transition caused by LiNi mixing at the positive electrode. Furthermore, it can form a redox couple, preventing battery overcharging and improving the cycle performance and safety of the NCM. The phosphate ester groups can adsorb onto the positive electrode surface and then oxidize to form a CEI film, preventing HF from damaging the positive electrode. The formed CEI film contains less LiF and polar P—F and P—O groups, which can balance the HF concentration, enhance Li+ conduction, and inhibit CEI damage and Ni… 4+ Reduction formation hinders Li + Migrating NiO; in addition, it reacts with strongly alkaline lithium compounds LiOH and Li2CO3 in the cathode slurry to generate Li3PO4 and LiF, which can remove the alkali that initiates side reactions in the electrolyte and improve the cycle performance and safety performance of NCM; —C6H x —The phenyl group has good stability and can form a stable interfacial film on the positive / negative electrode, thereby improving the cycle performance and electrical performance of NCM.

[0029] In some embodiments, the additive is tris(4-maleimide phenyl) phosphate, with the following molecular structure: .

[0030] In some embodiments, the positive electrode active material is lithium nickel cobalt manganese oxide; The adhesive is selected from at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyacrylic acid, polyacrylonitrile, polyimide, and sodium carboxymethyl cellulose; The conductive agent is selected from at least one of conductive carbon black, carbon nanotubes, graphene, conductive graphite, and carbon fiber. The current collector is selected from one of aluminum foil, carbon-coated aluminum foil, and aluminum alloy foil.

[0031] In some preferred embodiments, the binder is polyvinylidene fluoride; the conductive agent is conductive carbon black; and the current collector is aluminum foil.

[0032] In some embodiments, the temperature at which the positive electrode slurry is coated onto the current collector and dried is 80-120°C. For example, the drying temperature can be 80°C, 90°C, or 120°C, or other unlisted values ​​within the range of 80-120°C.

[0033] In some embodiments, the positive electrode material layer comprises a positive electrode active material, a binder, a conductive agent, and additives.

[0034] The positive electrode active material has a mass percentage of 94.2% to 96.7%. For example, the mass percentage of the positive electrode active material can be 94.2%, 95.5%, or 96.7%, or other unlisted values ​​within the range of 94.2% to 96.7%. The adhesive has a mass percentage of 0.8% to 1.5%, for example, the mass percentage of the adhesive can be 0.8%, 1.2% or 1.5%, or other unlisted values ​​within the range of 0.8% to 1.5%; The mass percentage of the conductive agent is 1.0% to 2.0%. For example, the mass percentage of the conductive agent can be 1.0%, 1.6%, or 2.0%, or other unlisted values ​​within the range of 1.0% to 2.0%. The additive is present in a mass percentage of 0.5% to 3%. For example, the mass percentage of the additive may be 0.5%, 1.5%, or 3%, or other unlisted values ​​within the range of 0.5% to 3%.

[0035] In some preferred embodiments, the positive electrode material layer comprises a positive electrode active material, a binder, a conductive agent, and an additive; wherein the positive electrode active material has a mass percentage of 95.7%, the binder has a mass percentage of 1.2%, the conductive agent has a mass percentage of 1.6%, and the additive has a mass percentage of 1.5%.

[0036] The method for preparing the positive electrode sheet of the present invention includes the following steps: The adhesive is added to the solvent to make a glue solution; Add the conductive agent to the adhesive solution and stir until homogeneous to form a slurry; The positive electrode active material and additives are added to the slurry and stirred evenly to obtain the positive electrode slurry; wherein, the additive is a maleimide derivative with aromatic phosphate ester as the bridging group, and the molecular structure of the maleimide derivative includes maleimide groups at both ends, a rigid aromatic skeleton in the middle and bridging phosphate ester groups. The positive electrode slurry is coated onto the current collector and dried to obtain the positive electrode sheet.

[0037] In some embodiments, the solvent is selected from one of N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide; The current collector is selected from one of aluminum foil, carbon-coated aluminum foil, and aluminum alloy foil.

[0038] In some preferred embodiments, the solvent is selected from N-methylpyrrolidone; the current collector is selected from aluminum foil.

[0039] The present invention provides a lithium-ion battery comprising the above-described positive electrode sheet.

[0040] The method for preparing the lithium-ion battery of the present invention includes the following steps: Using the above-mentioned positive electrode sheet, small positive electrode sheets are obtained by rolling and slitting; The negative electrode sheet is prepared and then rolled and slit to obtain small negative electrode sheets. The positive electrode chip, the negative electrode chip, and the separator are stacked together and packaged to form a battery cell; The battery cell is then post-processed to obtain a lithium-ion battery.

[0041] In some embodiments, the preparation of the negative electrode sheet includes: mixing and dispersing a negative electrode conductive agent, artificial graphite and silicon carbon material evenly, then adding polyacrylic acid and water and dispersing evenly, finally adding styrene-butadiene rubber and stirring evenly, coating the resulting slurry onto a copper current collector, and drying to obtain the negative electrode sheet.

[0042] In some embodiments, the artificial graphite has a mass percentage of 80-92%, the silicon carbon material has a mass percentage of 5-15%, the polyacrylic acid has a mass percentage of 1-4%, the negative electrode conductive agent has a mass percentage of 0.5-2%, and the styrene-butadiene rubber has a mass percentage of 1-3%; the diaphragm is selected from one of polyethylene diaphragm, polypropylene diaphragm, ceramic-coated diaphragm, and PVDF-coated diaphragm.

[0043] In some preferred embodiments, the artificial graphite has a mass percentage of 85.86%, the silicon-carbon material has a mass percentage of 9.54%, the polyacrylic acid has a mass percentage of 2.0%, the negative electrode conductive agent has a mass percentage of 1.1%, and the styrene-butadiene rubber has a mass percentage of 1.5%; the diaphragm is selected from polyethylene diaphragms.

[0044] Example The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0045] Example 1: The method for preparing the positive electrode sheet in this embodiment includes the following steps: Weigh out 95.7% lithium nickel cobalt manganese oxide, 1.2% polyvinylidene fluoride (PVDF) as the positive electrode binder, 1.6% conductive carbon black as the positive electrode conductive agent, and 1.5% positive electrode additive by weight. First, add PVDF to N-methylpyrrolidone solvent to prepare a slurry. Then, add the conductive carbon black to the slurry and stir until uniform. Next, add the lithium nickel cobalt manganese oxide and additive to the slurry and stir until uniform. Finally, coat the slurry onto an aluminum current collector and dry it at 90°C to prepare the positive electrode sheet.

[0046] Example 2: The method for preparing the positive electrode sheet in this embodiment includes the following steps: Weigh out 96.7% lithium nickel cobalt manganese oxide, 1.2% polyvinylidene fluoride (PVDF) as the positive electrode binder, 1.6% conductive carbon black as the positive electrode conductive agent, and 0.5% positive electrode additive by weight. First, add PVDF to N-methylpyrrolidone solvent to prepare a slurry. Then, add the conductive carbon black to the slurry and stir until uniform. Next, add the lithium nickel cobalt manganese oxide and additive to the slurry and stir until uniform. Finally, coat the slurry onto an aluminum current collector and dry it at 80°C to prepare the positive electrode sheet.

[0047] Example 3: The method for preparing the positive electrode sheet in this embodiment includes the following steps: Weigh out 94.2% lithium nickel cobalt manganese oxide, 1.2% polyvinylidene fluoride (PVDF) as the positive electrode binder, 1.6% conductive carbon black as the positive electrode conductive agent, and 3% positive electrode additive by weight. First, add PVDF to N-methylpyrrolidone solvent to prepare a slurry. Then, add the conductive carbon black to the slurry and stir until uniform. Next, add the lithium nickel cobalt manganese oxide and additive to the slurry and stir until uniform. Finally, coat the slurry onto an aluminum current collector and dry it at 120°C to prepare the positive electrode sheet.

[0048] Examples 4-8: The preparation methods of Examples 4-8 below are basically the same as those of Example 1, except that the positive electrode components and formulation contents are shown in Table 1 below.

[0049] Table 1 Example 9: The method for preparing a lithium-ion battery in this embodiment includes the following steps: S1. Preparation of positive electrode sheet: The positive electrode sheet prepared in Example 1 is rolled and slit to obtain small positive electrode sheets.

[0050] S2. Preparation of negative electrode sheet: Weigh out 85.86% artificial graphite negative electrode material, 9.54% silicon-carbon negative electrode material, 2.0% negative electrode binder polyacrylic acid, 1.1% negative electrode conductive agent conductive carbon black and 1.5% styrene-butadiene rubber by mass. First, mix and disperse the conductive carbon black, graphite and silicon-carbon evenly. Then, add polyacrylic acid and deionized water to the above mixture and disperse evenly. Finally, add styrene-butadiene rubber and stir until uniform. After mixing, coat the above slurry onto the copper current collector and dry it to prepare the negative electrode sheet. After rolling and slitting, obtain small negative electrode sheets.

[0051] S3. Cell preparation: The positive and negative electrode pieces are vacuum baked, stacked to form a cell, and then packaged in an aluminum-plastic film.

[0052] S4. Battery preparation: After baking, the battery cell undergoes post-processing: liquid injection, formation, aging, and capacity testing to obtain a lithium-ion battery.

[0053] Example 10: The method for preparing a lithium-ion battery in this embodiment includes the following steps: S1. Preparation of positive electrode sheet: The positive electrode sheet prepared in Example 2 is rolled and slit to obtain small positive electrode sheets.

[0054] S2. Preparation of negative electrode sheet: Weigh out 85.86% artificial graphite negative electrode material, 9.54% silicon-carbon negative electrode material, 2.0% negative electrode binder polyacrylic acid, 1.1% negative electrode conductive agent conductive carbon black and 1.5% styrene-butadiene rubber by mass. First, mix and disperse the conductive carbon black, graphite and silicon-carbon evenly. Then, add polyacrylic acid and deionized water to the above mixture and disperse evenly. Finally, add styrene-butadiene rubber and stir until uniform. After mixing, coat the above slurry onto the copper current collector and dry it to prepare the negative electrode sheet. After rolling and slitting, obtain small negative electrode sheets.

[0055] S3. Cell preparation: The positive and negative electrode pieces are vacuum baked, stacked to form a cell, and then packaged in an aluminum-plastic film.

[0056] S4. Battery preparation: After baking, the battery cell undergoes post-processing: liquid injection, formation, aging, and capacity testing to obtain a lithium-ion battery.

[0057] Example 11: The method for preparing a lithium-ion battery in this embodiment includes the following steps: S1. Preparation of positive electrode sheet: The positive electrode sheet prepared in Example 3 is rolled and slit to obtain small positive electrode sheets.

[0058] S2. Preparation of negative electrode sheet: Weigh out 85.86% artificial graphite negative electrode material, 9.54% silicon-carbon negative electrode material, 2.0% negative electrode binder polyacrylic acid, 1.1% negative electrode conductive agent conductive carbon black and 1.5% styrene-butadiene rubber by mass. First, mix and disperse the conductive carbon black, graphite and silicon-carbon evenly. Then, add polyacrylic acid and deionized water to the above mixture and disperse evenly. Finally, add styrene-butadiene rubber and stir until uniform. After mixing, coat the above slurry onto the copper current collector and dry it to prepare the negative electrode sheet. After rolling and slitting, obtain small negative electrode sheets.

[0059] S3. Cell preparation: The positive and negative electrode pieces are vacuum baked, stacked to form a cell, and then packaged in an aluminum-plastic film.

[0060] S4. Battery preparation: After baking, the battery cell undergoes post-processing: liquid injection, formation, aging, and capacity testing to obtain a lithium-ion battery.

[0061] Example 12: The method for preparing a lithium-ion battery in this embodiment includes the following steps: S1. Preparation of positive electrode sheet: The positive electrode sheet prepared in Example 4 is rolled and slit to obtain small positive electrode sheets.

[0062] S2. Preparation of the negative electrode sheet: Weigh out 80% artificial graphite negative electrode material, 15% silicon-carbon negative electrode material, 2.0% negative electrode binder polyacrylic acid, 1.0% negative electrode conductive agent conductive carbon black, and 2.0% styrene-butadiene rubber by weight. First, mix and disperse the conductive carbon black, graphite, and silicon-carbon evenly. Then, add polyacrylic acid and deionized water to the above mixture and disperse evenly. Finally, add styrene-butadiene rubber and stir until uniform. After mixing, coat the above slurry onto a copper current collector, dry it, and prepare the negative electrode sheet. Obtain small negative electrode sheets by rolling and slitting.

[0063] S3. Cell preparation: The positive and negative electrode pieces are vacuum baked, stacked with a ceramic-coated separator to form a cell, and then encapsulated in an aluminum-plastic film.

[0064] S4. Battery preparation: After baking, the battery cell undergoes post-processing: liquid injection, formation, aging, and capacity testing to obtain a lithium-ion battery.

[0065] Example 13: The method for preparing a lithium-ion battery in this embodiment includes the following steps: S1. Preparation of positive electrode sheet: The positive electrode sheet prepared in Example 5 is rolled and slit to obtain small positive electrode sheets.

[0066] S2. Preparation of the negative electrode sheet: Weigh out 92% artificial graphite negative electrode material, 5% silicon-carbon negative electrode material, 1.0% negative electrode binder polyacrylic acid, 1.0% negative electrode conductive agent conductive carbon black, and 1.0% styrene-butadiene rubber by weight. First, mix and disperse the conductive carbon black, graphite, and silicon-carbon evenly. Then, add polyacrylic acid and deionized water to the above mixture and disperse evenly. Finally, add styrene-butadiene rubber and stir until uniform. After mixing, coat the above slurry onto a copper current collector, dry it, and prepare the negative electrode sheet. After rolling and slitting, obtain small negative electrode sheets.

[0067] S3. Cell preparation: The positive and negative electrode pieces are vacuum baked, stacked with a polyethylene (PE) separator to form a cell, and then encapsulated in an aluminum-plastic film.

[0068] S4. Battery preparation: After baking, the battery cell undergoes post-processing: liquid injection, formation, aging, and capacity testing to obtain a lithium-ion battery.

[0069] Example 14: The method for preparing a lithium-ion battery in this embodiment includes the following steps: S1. Preparation of positive electrode sheet: The positive electrode sheet prepared in Example 6 is rolled and slit to obtain small positive electrode sheets.

[0070] S2. Preparation of the negative electrode sheet: Weigh out 81% artificial graphite negative electrode material, 10% silicon-carbon negative electrode material, 4.0% negative electrode binder polyacrylic acid, 2.0% negative electrode conductive agent conductive carbon black, and 3.0% styrene-butadiene rubber by weight. First, mix and disperse the conductive carbon black, graphite, and silicon-carbon evenly. Then, add polyacrylic acid and deionized water to the above mixture and disperse evenly. Finally, add styrene-butadiene rubber and stir until uniform. After mixing, coat the above slurry onto a copper current collector, dry it, and prepare the negative electrode sheet. After rolling and slitting, obtain small negative electrode sheets.

[0071] S3. Cell preparation: The positive and negative electrode small pieces are vacuum baked, stacked with PVDF coated separator to form a cell, and then packaged in an aluminum-plastic film.

[0072] S4. Battery preparation: After baking, the battery cell undergoes post-processing: liquid injection, formation, aging, and capacity testing to obtain a lithium-ion battery.

[0073] Example 15: The method for preparing a lithium-ion battery in this embodiment includes the following steps: S1. Preparation of positive electrode sheet: The positive electrode sheet prepared in Example 7 is rolled and slit to obtain small positive electrode sheets.

[0074] S2. Preparation of the negative electrode sheet: Weigh out 87.5% artificial graphite negative electrode material, 10% silicon-carbon negative electrode material, 1.0% negative electrode binder polyacrylic acid, 0.5% negative electrode conductive agent conductive carbon black, and 1.0% styrene-butadiene rubber by weight. First, mix and disperse the conductive carbon black, graphite, and silicon-carbon evenly. Then, add polyacrylic acid and deionized water to the above mixture and disperse evenly. Finally, add styrene-butadiene rubber and stir until uniform. After mixing, coat the above slurry onto a copper current collector, dry it, and prepare the negative electrode sheet. Obtain small negative electrode sheets by rolling and slitting.

[0075] S3. Cell preparation: The positive and negative electrode pieces are vacuum baked, stacked with a polypropylene (PP) separator to form a cell, and then encapsulated in an aluminum-plastic film.

[0076] S4. Battery preparation: After baking, the battery cell undergoes post-processing: liquid injection, formation, aging, and capacity testing to obtain a lithium-ion battery.

[0077] Example 16: The method for preparing a lithium-ion battery in this embodiment includes the following steps: S1. Preparation of positive electrode sheet: The positive electrode sheet prepared in Example 8 is rolled and slit to obtain small positive electrode sheets.

[0078] S2. Preparation of the negative electrode sheet: Weigh out 85% artificial graphite negative electrode material, 10% silicon-carbon negative electrode material, 2.5% negative electrode binder polyacrylic acid, 1.0% negative electrode conductive agent conductive carbon black, and 1.5% styrene-butadiene rubber by weight. First, mix and disperse the conductive carbon black, graphite, and silicon-carbon evenly. Then, add polyacrylic acid and deionized water to the above mixture and disperse evenly. Finally, add styrene-butadiene rubber and stir until uniform. After mixing, coat the above slurry onto a copper current collector, dry it, and prepare the negative electrode sheet. After rolling and slitting, obtain small negative electrode sheets.

[0079] S3. Cell preparation: The positive and negative electrode pieces are vacuum baked, stacked with a ceramic-coated separator to form a cell, and then encapsulated in an aluminum-plastic film.

[0080] S4. Battery preparation: After baking, the battery cell undergoes post-processing: liquid injection, formation, aging, and capacity testing to obtain a lithium-ion battery.

[0081] Comparative Example Comparative Example 1: The preparation method of the positive electrode sheet in this comparative example includes the following steps: Weigh out 97.2% lithium nickel cobalt manganese oxide, 1.2% polyvinylidene fluoride (PVDF) as the positive electrode binder, and 1.6% conductive carbon black as the positive electrode conductive agent according to the mass ratio. First, add PVDF to N-methylpyrrolidone solvent to prepare a slurry. Then, add the conductive carbon black to the slurry and stir until uniform. Next, add lithium nickel cobalt manganese oxide to the slurry and stir until uniform. Finally, coat the slurry onto an aluminum current collector and dry it to prepare the positive electrode sheet of Comparative Example 1.

[0082] Comparative Example 2: The preparation method of the positive electrode sheet in this comparative example differs from that in Example 1 only in the type of additives, and includes the following steps: 95.7% lithium nickel cobalt manganese oxide, 1.2% polyvinylidene fluoride (PVDF) as the positive electrode binder, 1.6% conductive carbon black as the positive electrode conductor, and 1.5% triphenyl phosphate (TPP) as the comparative additive are weighed according to mass. First, PVDF is added to N-methylpyrrolidone solvent to prepare a slurry. Then, conductive carbon black is added to the above slurry and stirred until uniform. Next, lithium nickel cobalt manganese oxide and the comparative additive are added to the above slurry and stirred until uniform. Finally, the slurry is coated on an aluminum current collector and dried to prepare the positive electrode sheet of Comparative Example 2.

[0083] Comparative Example 3: The preparation method of the positive electrode sheet in this comparative example differs from that in Example 1 only in the type of additives, and includes the following steps: 95.7% lithium nickel cobalt manganese oxide, 1.2% polyvinylidene fluoride (PVDF) as the positive electrode binder, 1.6% conductive carbon black as the positive electrode conductor, and 1.5% N,N'-1,3-phenylene bismaleimide (BMI) as the comparative additive are weighed by mass. First, PVDF is added to N-methylpyrrolidone solvent to prepare a slurry. Then, conductive carbon black is added to the above slurry and stirred until uniform. Next, lithium nickel cobalt manganese oxide and the comparative additive are added to the above slurry and stirred until uniform. Finally, the slurry is coated on an aluminum current collector and dried to prepare the positive electrode sheet of Comparative Example 3.

[0084] Comparative Example 4: The preparation method of the lithium-ion battery in this comparative example includes the following steps: S1. Preparation of positive electrode sheet: The positive electrode sheet prepared in Comparative Example 1 is rolled and slit to obtain small positive electrode sheets.

[0085] S2. Preparation of negative electrode sheet: Weigh out 85.86% artificial graphite negative electrode material, 9.54% silicon-carbon negative electrode material, 2.0% negative electrode binder polyacrylic acid, 1.1% negative electrode conductive agent conductive carbon black and 1.5% styrene-butadiene rubber by mass. First, mix and disperse the conductive carbon black, graphite and silicon-carbon evenly. Then, add polyacrylic acid and deionized water to the above mixture and disperse evenly. Finally, add styrene-butadiene rubber and stir until uniform. After mixing, coat the above slurry onto the copper current collector and dry it to prepare the negative electrode sheet. After rolling and slitting, obtain small negative electrode sheets.

[0086] S3. Cell preparation: The positive and negative electrode pieces are vacuum baked, stacked to form a cell, and then packaged in an aluminum-plastic film.

[0087] S4. Battery preparation: After baking, the battery cells undergo post-processing: liquid injection, formation, aging, and capacity testing to obtain the lithium-ion battery of Comparative Example 2.

[0088] Comparative Example 5: The preparation method of the lithium-ion battery in this comparative example includes the following steps: S1. Preparation of positive electrode sheet: The positive electrode sheet prepared in Comparative Example 2 is rolled and slit to obtain small positive electrode sheets.

[0089] S2. Preparation of negative electrode sheet: Same as in Example 9, using a formula of 85.86% artificial graphite and 9.54% silicon carbon.

[0090] S3. Cell preparation: The positive and negative electrode pieces are vacuum baked, stacked to form a cell, and then packaged in an aluminum-plastic film.

[0091] S4. Battery preparation: After baking, the battery cells undergo post-processing: liquid injection, formation, aging, and capacity testing to obtain the lithium-ion battery of Comparative Example 5.

[0092] Comparative Example 6: The preparation method of the lithium-ion battery in this comparative example includes the following steps: S1. Preparation of positive electrode sheet: The positive electrode sheet prepared in Comparative Example 3 is rolled and slit to obtain small positive electrode sheets.

[0093] S2. Preparation of negative electrode sheet: Same as in Example 9, using a formula of 85.86% artificial graphite and 9.54% silicon carbon.

[0094] S3. Cell preparation: The positive and negative electrode pieces are vacuum baked, stacked to form a cell, and then packaged in an aluminum-plastic film.

[0095] S4. Battery preparation: After baking, the battery cells undergo post-processing: liquid injection, formation, aging, and capacity testing to obtain the lithium-ion battery of Comparative Example 6.

[0096] Performance testing: I. Physical Performance Testing of Positive Electrode To verify the effect of the additive (aromatic phosphate-bridged maleimide derivative) described in this invention on the electrode structure, the positive electrode sheets prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to the following physical performance tests.

[0097] (a) Testing methods (1) Electrode peel strength test (adhesion): Test objective: To characterize the adhesion strength between the cathode material layer and the current collector, as well as the cohesive force within the material layer. Stronger adhesion results in a more stable battery structure during cycling, making it less prone to delamination or pulverization.

[0098] Method: Cut the positive electrode sheet into strips of 20mm×100mm, attach them to the surface of the electrode sheet with special 3M tape, and use a tensile testing machine to stretch the electrode sheet at a peel angle of 180° and a speed of 50mm / min. Record the average peel force (N / m).

[0099] (2) Electrode and diaphragm resistance test (interface resistance): Test objective: To characterize the overall electronic conductivity of the electrode and the uniformity of the conductive agent dispersion. Lower resistance indicates a better conductive network structure, which corresponds to better rate performance (3C charging) of the subsequent battery.

[0100] Method: A four-probe resistance tester was used to perform multi-point tests on the rolled positive electrode sheet under constant pressure (e.g., 10 MPa), and the average value (Ω·cm) was taken.

[0101] (3) Electrode flexibility test (round rod bending method): Test objective: To verify whether the "phosphate ester flexible bridging group" in the additive improves the brittleness of the electrode. The more flexible the electrode, the less likely it is to develop microcracks during winding and breathing.

[0102] Method: Bend the electrode sheet 180° around a 3mm diameter round steel rod and observe whether the coating at the bend is cracked or powdered.

[0103] Evaluation criteria: No cracks (excellent), minor cracks (good), obvious breakage / material loss (poor).

[0104] (II) Test results of physical and mechanical properties of the positive electrode sheet The positive electrode sheets prepared in Examples 1-3 and Comparative Examples 1-3 were subjected to the following physical property tests, and the results are shown in Table 1 below: Table 1 (III) Results Analysis 1. Structural stability analysis (peel strength): Examples 1-3 and Comparative Example 1: After adding the additive of the present invention, the peel strength of the electrode was significantly improved (from 14.2 N / m to 40+ N / m). This is because the additive of the present invention contains bismaleimide groups, which undergo in-situ cross-linking polymerization during the drying process to form a three-dimensional network structure, which firmly locks the active particles together like "glue".

[0105] Examples 1-3 and Comparative Examples 2 and 3: Comparative Example 2 uses TPP, a small molecule liquid with no cross-linking function, resulting in only a slight improvement in adhesion; Comparative Example 3 uses BMI, which has good adhesion (35.4 N / m), but its excessive structural rigidity causes the electrode to become brittle. This invention, by introducing flexible phosphate ester bridging groups, achieves a balance of rigidity and flexibility, ensuring high adhesion while passing flexibility tests.

[0106] 2. Conductive network analysis (diaphragm resistance): The resistivity of Example 1 (18.6 Ω·cm) was significantly lower than that of Comparative Example 1 (35.8 Ω·cm). This indicates that the polar additive of the present invention improves the dispersibility of conductive carbon black in the positive electrode slurry, reduces agglomeration, and constructs a more efficient electron transport channel.

[0107] 3. Relationship with battery performance: The high peel strength and cross-linked structure of Example 1 prevent the positive electrode coating from peeling off and causing short-circuit expansion during needle penetration, while the phosphate groups also provide flame retardancy, resulting in excellent needle penetration test results. In contrast, Comparative Example 1, due to its loose structure (low peel strength), experienced coating collapse during needle penetration, leading to thermal runaway.

[0108] 4. Energy density correlation: In Example 3, the addition amount reached 3%, resulting in the highest peel strength, but the increased proportion of organic matter led to a decrease in compaction density (3.58 g / cm³). 3 The resistance increased slightly.

[0109] II. Battery Performance Testing To further test the performance of the positive electrode sheets prepared in the above embodiments and comparative examples after they were made into batteries, the lithium-ion batteries prepared in Examples 9-11 and Comparative Examples 4-6 were subjected to the following performance tests.

[0110] (a) Testing methods: Energy density test: At 25℃, charge at a constant current of 0.33C to 4.3V, and then charge at a constant voltage to 0.05C. After standing for 5 minutes, discharge at a constant current of 0.33C to 3.0V and calculate the gravimetric energy density (Wh / kg) of the battery.

[0111] Cyclic performance test: At 25℃, charge and discharge cycles were performed at a 1C / 1C rate within a voltage range of 3.0V-4.3V, and the discharge capacity retention rate was recorded after the 500th cycle.

[0112] Rate charging performance test: At 25℃, the ratio of constant current charging capacity to total charging capacity (CCRatio) of the battery under 3C constant current charging conditions is tested to characterize fast charging capability.

[0113] Needle penetration safety test: Under full charge (4.3V), use a 5mm diameter high-temperature resistant steel needle to vertically pierce the center of the battery at a speed of 25mm / s, and observe whether it catches fire or explodes. Five batteries are tested in each group, and the number of batteries that pass is recorded (no fire or explosion is considered a pass).

[0114] (II) Test Results 1. The performance test results of the lithium-ion batteries prepared in Examples 9-11 and Comparative Examples 4-6 are as follows: Table 2 2. Overcharge tests were conducted on the batteries of Example 9 and Comparative Example 4. After a full charge of 0.33C, the batteries were charged at a constant current of 1C to 126% SOC, then charging was stopped, and the results were observed for 1 hour. The test results are as follows: Figure 2 and Figure 3 As shown.

[0115] (III) Results Analysis and Conclusions: 1. Safety Analysis (Needle Penetration Test): Example 9 (5 / 5 pass) vs. Comparative Example 4 (0 / 5 pass): Example 9 used the additive of the present invention, which contains phosphate ester groups in its molecule. When the local high temperature is generated by needle puncture, it decomposes to produce phosphorus-containing free radicals, capturing H· and OH· free radicals in the combustion chain reaction, thus playing a significant flame-retardant role. Simultaneously, its special cross-linking structure prevents large-area peeling and short-circuit diffusion of the electrode coating at the moment of needle puncture. In contrast, the blank group (Comparative Example 4) completely failed the needle puncture test.

[0116] Effect of dosage: Example 11 (3.0% dosage) also maintained a high pass rate of 5 / 5, but Example 10 (0.5% dosage) only had a pass rate of 2 / 5, indicating that the additive needs to reach a certain concentration threshold to form a complete flame retardant and structural protection network.

[0117] Structural Advantage Analysis: Although the TPP used in Comparative Example 5 contains phosphorus and has a certain degree of flame retardancy (3 / 5 pass), its electrode structure is prone to collapse under mechanical abuse due to the lack of cross-linking groups. Although the BMI used in Comparative Example 6 has a cross-linked structure, it lacks the chemical flame retardancy of phosphorus, resulting in a low pass rate (1 / 5 pass). This invention achieves optimal safety through the synergistic effect of "phosphate ester + maleimide".

[0118] 2. Cyclic and rate performance analysis: Optimal overall performance: Battery cycle performance tests at room temperature for Example 9 and Comparative Example 4 are shown in the following results. Figure 1 As shown. Example 9 achieved the highest cycle retention rate (88.72%) while maintaining a high energy density (301 Wh / kg). This is attributed to the additives improving the dispersibility of the conductive agent (reducing polarization) and enhancing the adhesion of the electrode (preventing particle shedding during cycling).

[0119] Side effects of excessive addition: Example 11 (3.0% addition) showed a significant decrease in cycle retention (76.82%) and 3C rate performance (75.51%). This is because organic additives are inherently insulating, and excessive addition increases the battery's internal resistance, leading to increased polarization, and also occupies space of the active material, reducing the overall energy density (down to 297Wh / kg).

[0120] Comparative analysis: Although Comparative Example 4 (blank) had the highest energy density (305 Wh / kg, due to the absence of inactive additives), its cycle life was poor. Comparative Example 5 (TPP) showed limited benefit in long-term cycling due to the fact that TPP is a small liquid molecule that is easily consumed by side reactions in the electrolyte.

[0121] 3. Overcharge test analysis: According to the overcharge test curves of Example 9 and Comparative Example 4, when the battery in Example 9 was overcharged to 126% SOC, it did not catch fire or explode; when the battery in Comparative Example 4 was overcharged to 126% SOC, it caught fire and exploded after 3 minutes of observation.

[0122] In summary, the positive electrode and lithium-ion battery provided by this invention introduce a specific amount (preferably 0.5%~3%, most preferably 1.5%) of maleimide derivatives with aromatic phosphate esters as bridging groups as additives. This molecule, under high voltage (>4.5V), captures free radicals through the maleimide groups, stabilizing the electrolyte interface; at high temperatures (>150℃), the phosphate ester groups decompose to form a stable carbonized layer, isolating the electrode from the electrolyte. The molecular design utilizes the π-π stacking effect between aromatic structures to form a stable interface film. Simultaneously, the phosphorus groups release phosphorus-oxygen free radicals before thermal runaway, inhibiting chain reactions and improving the battery's electrical and safety performance. Furthermore, the formation of a stable interface film on the positive electrode surface enhances safety while simultaneously improving electrode cycle stability and rate performance to achieve high-power charging and discharging. Without sacrificing energy density, it significantly improves the safety (especially needle penetration safety) and cycle stability of the high-nickel ternary system, solving the problem of achieving both high energy density and high safety in existing technologies.

[0123] The above are merely specific embodiments of the present invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should be included within the protection scope of the present invention. All other details not described in detail belong to the prior art.

Claims

1. A positive electrode plate, characterized in that, It includes a current collector and a positive electrode material layer disposed on the current collector; the positive electrode material layer includes a positive electrode active material, a binder, a conductive agent, and additives; The additive is a maleimide derivative with aromatic phosphate esters as bridging groups. The molecular structure of the maleimide derivative includes maleimide groups at both ends, a rigid aromatic skeleton in the middle, and bridging phosphate ester groups.

2. The positive electrode sheet according to claim 1, characterized in that, The additive is tris(4-maleimide-phenyl) phosphate, and its molecular structure is as follows: 。 3. The positive electrode sheet according to claim 2, characterized in that: The positive electrode active material is lithium nickel cobalt manganese oxide; The adhesive is selected from at least one of polyvinylidene fluoride, polytetrafluoroethylene, polyacrylic acid, polyacrylonitrile, polyimide, and sodium carboxymethyl cellulose; The conductive agent is selected from at least one of conductive carbon black, carbon nanotubes, graphene, conductive graphite, and carbon fiber. The current collector is selected from one of aluminum foil, carbon-coated aluminum foil, and aluminum alloy foil.

4. The positive electrode sheet according to claim 3, characterized in that, By mass percentage, the positive electrode material layer comprises: 94.2% to 96.7% of the positive electrode active material, 0.8% to 1.5% of the binder, 1.0% to 2.0% of the conductive agent, and 0.5% to 3% of the additive.

5. A method for preparing a positive electrode sheet according to any one of claims 1 to 4, characterized in that, Includes the following steps: The adhesive is added to the solvent to make a glue solution; Add the conductive agent to the adhesive solution and stir until homogeneous to form a slurry; The positive electrode active material and additives are added to the slurry and stirred evenly to obtain the positive electrode slurry; wherein, the additive is a maleimide derivative with aromatic phosphate ester as the bridging group, and the molecular structure of the maleimide derivative includes maleimide groups at both ends, a rigid aromatic skeleton in the middle and bridging phosphate ester groups. The positive electrode slurry is coated onto the current collector and dried to obtain the positive electrode sheet.

6. The preparation method according to claim 5, characterized in that: The solvent is selected from one of N-methylpyrrolidone, N,N-dimethylformamide, and N,N-dimethylacetamide; The current collector is selected from one of aluminum foil, carbon-coated aluminum foil, and aluminum alloy foil; The temperature at which the positive electrode slurry is coated onto the current collector and dried is 80-120℃.

7. A lithium-ion battery, characterized in that, It includes the positive electrode sheet as described in any one of claims 1 to 4.

8. A method for preparing a lithium-ion battery, characterized in that, Includes the following steps: Using any one of the positive electrode sheets according to claims 1 to 4, small positive electrode sheets are obtained by rolling and slitting. The negative electrode sheet is prepared and then rolled and slit to obtain small negative electrode sheets. The positive electrode chip, the negative electrode chip, and the separator are stacked together and packaged to form a battery cell; The battery cell is then post-processed to obtain a lithium-ion battery.

9. The preparation method according to claim 8, characterized in that, The preparation of the negative electrode sheet includes: mixing and dispersing the negative electrode conductive agent, artificial graphite and silicon carbon material evenly, then adding polyacrylic acid and water and dispersing evenly, finally adding styrene-butadiene rubber and stirring evenly, coating the resulting slurry onto a copper current collector, and drying to obtain the negative electrode sheet.

10. The preparation method according to claim 9, characterized in that, By mass percentage, the negative electrode sheet comprises: 80-92% artificial graphite, 5-15% silicon carbon material, 1-4% polyacrylic acid, 0.5-2% negative electrode conductive agent, and 1-3% styrene-butadiene rubber; the separator is selected from one of polyethylene separator, polypropylene separator, ceramic-coated separator, and PVDF-coated separator.

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