Preparation method of polymer lithium battery positive plate

Abstract

The invention provides a preparation method of a polymer lithium battery positive plate. According to the process, integrated optimization of an electrode material, a structure and a process is realized. Through the synergistic effect of the functional polymer conductive agent and Se-CeO2 doping, the conductivity, structural stability and interface stability of the electrode are remarkably enhanced, and the uniformity and compactness of the coating under high load are guaranteed through fine slurry mixing and rolling control. And finally, the interface impedance is reduced, the utilization rate of active substances is improved, the high energy density and the long cycle reliability are considered, and an effective electrode manufacturing process is provided for a high-performance lithium battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium battery positive electrode sheets, and in particular relates to a preparation process of a polymer lithium battery positive electrode sheet. Background Art

[0002] Lithium-ion batteries have become a focus of attention in the energy storage field due to their significant advantages, including high operating voltage, long cycle life, good safety performance, and lack of memory effect. Among the components of lithium-ion batteries, the cathode material is a key factor in determining their energy density, power performance, and cycle stability. Its development is crucial to improving the overall performance of the battery.

[0003] The current mainstream cathode preparation process typically involves a simple mechanical mixing of active materials, conductive carbon black, and a polymer binder (such as PVDF). However, this process has significant drawbacks: poor dispersion of the conductive agent makes it difficult to form an efficient, continuous three-dimensional conductive network; high active material loadings can lead to stress concentration and cracking of the electrode structure; and weak interfacial bonding between the active material, conductive agent, and binder, making delamination likely during long-term cycling or high-current charge / discharge. These drawbacks limit the rate performance of cathode active materials, given the increasingly urgent demand for high energy density.

[0004] Uniform slurry dispersion is fundamental to solving these problems. Effective dispersion of the active material, conductive agent, and binder is crucial in the preparation of conventional lithium battery cathode slurries. Poor dispersion can lead to an imperfect conductive network, increased battery internal resistance, and reduced rate performance; low active material utilization, impacting capacity; and insufficient bonding, which can lead to electrode powder shedding. Therefore, ensuring excellent slurry dispersion and quality is a prerequisite for achieving good electrode bonding and conductivity.

[0005] Optimizing conductive agents is a key approach to improving electrode performance. Commonly used polymer conductive agents include carbon black, conductive graphite, and carbon fibers. However, these materials have limitations: carbon fibers and other materials tend to agglomerate, making them difficult to disperse uniformly in the slurry. This results in an uneven conductive network, which compromises overall conductivity. Multi-walled carbon nanotubes (MWNTs), a novel nanoconductive material, possess an extremely high aspect ratio and excellent conductivity. They can form efficient three-dimensional conductive networks within electrodes, significantly improving conductivity, mitigating volume expansion effects, and enhancing cycling stability. They are ideal candidates for addressing issues such as poor conductivity, high volume expansion, and low cycle life. However, their surface chemical inertness and lack of sufficient functional groups make them difficult to disperse and manipulate in polymer matrices. Furthermore, their compatibility with the active material matrix is ​​poor, resulting in weak interfacial interactions. Therefore, effective surface functionalization of MWNTs to improve their dispersibility, stability, and interfacial compatibility with electrode components is a key research priority to enhance their application and address the challenges of existing conductive agents.

[0006] The development of novel high-capacity cathode active materials is another key to improving energy density. Benzoquinone polymer cathode materials exhibit significant advantages, including high theoretical specific capacity, excellent cycling performance, rapid charge and discharge capabilities, and environmental friendliness, and possess enormous potential for application. One of the key research areas is the effective utilization of high-performance active materials such as benzoquinone polymers, and their synergistic effects with optimized conductive agents (such as MWNTs) to construct high-performance composite electrode systems.

[0007] In addition, doping and modification of the cathode active material itself is also an effective way to improve its overall performance. Research has shown that the introduction of doping elements can effectively enhance the material's electrical conductivity and structural stability. For example, selenium (Se) doping can, to a certain extent, alleviate the oxygen loss problem during cycling in lithium-rich manganese-based cathode materials. However, Se doping has limitations: a narrow effective doping concentration window, limited improvement in conductivity, and insufficient effectiveness in suppressing structural distortion (such as the transition from layered structure to spinel phase). Rare earth metals, due to their unique electronic structure and chemical properties, exhibit significant advantages in expanding lattice channels, stabilizing crystal structure, and enhancing interfacial stability, promising further optimization of material properties. Therefore, how to achieve efficient and controllable doping of cathode materials with elements such as rare earth metals to synergistically improve their conductivity, structural stability, and long-cycle performance is another core research focus of this invention. Summary of the Invention

[0008] The present invention discloses a process for preparing a positive electrode sheet for a polymer lithium battery to solve the above-mentioned and potential problems in the prior art. In order to solve the above-mentioned technical problems, the process of the present application is as follows: (1) Preparation of binder solution: dissolve PVDF in NMP to prepare a binder solution with a mass concentration of 8%-12%; (2) Dispersing the polymer conductive agent: Add 40% of the weight of polyethylene glycol to 15-18 parts by weight of the polymer conductive agent, and stir and disperse at 500 rpm for 10 minutes; (3) Preparing a positive electrode slurry: adding the dispersed polymer conductive agent obtained in step (2) to 7-10 parts by mass of the binder solution in step (1), and stirring at a speed of 1500-1800 rpm for 20-30 minutes; Add the positive electrode material in batches: first add 40-48 parts by mass of the positive electrode material, and stir and disperse at a speed of 2500-2800 rpm for 10 minutes; add 2-5% of the binder solution described in step (1); then add 48-52 parts by mass of the positive electrode material, and continue stirring and dispersing for 10 minutes; switch to a low speed of 200 rpm and stir for 15 minutes to defoam, to obtain a positive electrode slurry with a viscosity of 6500-8500 mPa·s; (4) Coating and drying: The slurry was coated on the carbon-coated aluminum foil current collector and baked at 120 °C for 6 hours; (5) Rolling: Roll the dried positive electrode sheet to a compaction density of 2.4-3.4 g / cm³ and an active material loading of 4.0-10.0 mg / cm²; (6) Cutting: Cut the rolled positive electrode sheet into the required size.

[0009] Among them, the positive electrode material is prepared by the following steps: adding 0.5-1.5 wt% of Se-CeO2 nanopowder and 0.5 wt% of stearic acid to the positive electrode active material, ball milling at 300 rpm for 2 hours; then heating to 700°C at 5°C / min in an O2 atmosphere and heat treating for 4 hours.

[0010] Among them, the preparation method of Se-CeO2 nanopowder is: Ce(NO3)3·6H2O and Na2SeO3 are mixed in a mass ratio of 1:9, ammonia water with pH=10 is slowly injected into the mixture at a solid-liquid ratio of 1:3, and the mixture is placed at 160°C for hydrothermal reaction for 12 hours. The product is centrifuged and washed, and calcined at 600°C for 2 hours to obtain Se-CeO2 nanopowder, which is then ball milled to obtain a particle size of 50-100nm.

[0011] The positive electrode active material is one or more of LiCoO2, NCM523 and NCM333.

[0012] Among them, the polymer conductive agent is 30 parts of MWCNTs and anthraquinone-2-carboxylic acid in a mass ratio of 1:2 in 200 parts of anhydrous DMF, ultrasonically treated for 10-30 minutes to form a uniform dispersion, 45-55 parts of triethylamine are added as a catalyst, and stirred at 80°C for 4 hours to obtain a product. The product is washed with ethanol, dialyzed, and dried.

[0013] Among them, MWCNTs also include a pretreatment process: 10-26 parts of MWCNTs are placed in 50-80 parts of 70% HNO3 and ultrasonically treated at 60-80°C for 2-4 hours, cooled to room temperature and then vacuum filtered, washed with deionized water until the filtrate pH is 6.8-7.3, and dried to obtain carboxylated MWCNTs. The carboxylated MWCNTs are dissolved in SOCl2 solution at a material-liquid ratio of 1:20, refluxed at 70°C for 6 hours, and further chlorinated.

[0014] The advantages and beneficial effects of the present invention are: 1. This application significantly improves the comprehensive performance of the electrode through multi-component synergistic modification and refined process control. First, the use of functional polymer conductive agents strengthens the mechanical stability of the electrode while building an efficient electronic network and reduces the proportion of inactive substances. Se-CeO2 nanopowders are used to in-situ dope the positive electrode material, and the rare earth element effect is used to effectively inhibit the degradation of the material structure and the dissolution of transition metals, thereby improving the cycle life and safety. The precisely controlled slurry mixing process ensures component uniformity and interface compatibility, avoiding agglomeration and pore defects at the source, and improving the corresponding electrochemical performance.

[0015] 2. First, the deeply functionalized MWNTs conductive agent is thoroughly dispersed in the binder solution to form a pre-wrapped structure, laying the foundation for subsequent uniform network construction. The positive electrode active material is then added in batches, and high-speed dispersion is used to ensure maximum initial uniformity and effectively prevent agglomeration. After adding a large amount of active material, the binder is replenished in a timely manner to effectively address the problem of localized insufficient coating caused by excessive active material, avoid direct contact between particles and the formation of weak bonding areas, and ensure good inter-particle bonding. Finally, a low-speed stirring phase is used to focus on defoaming and structural relaxation, releasing internal stress in the slurry and stabilizing the structure. This synergistic effect of orderly addition, dynamic viscosity adjustment, and intensity gradient control not only significantly promotes efficient material dispersion, sufficient coating of the active material, and the stable construction of the conductive network, but also minimizes the risk of mechanical damage to the formed conductive network and active material particles caused by prolonged high-speed stirring. The resulting slurry exhibits excellent viscosity stability, superior rheological properties, and structural uniformity, which is highly conducive to achieving highly uniform coating and stable wet film, laying the foundation for the production of high-quality electrode sheets. This microstructural optimization directly translates into better structural stability and superior electrochemical performance of the electrode during cycling.

[0016] 3. Deep functionalization of multi-walled carbon nanotubes (MWNTs) through surface carboxylation, acyl chloride activation, and covalent grafting of anthraquinone molecules imparts a unique "amphiphilic" structural advantage. The large π-conjugated backbone of the anthraquinone molecules interacts strongly with the carbon nanotube surface (e.g., π-π stacking), achieving strong anchoring. The modified MWNTs form an efficient "molecular wire" network between active particles, significantly reducing interfacial contact resistance and improving electron transfer efficiency. The exposed polar groups of anthraquinone form multiple strong hydrogen bonds and dipole interactions with the cathode active material and PVDF binder, greatly enhancing the interfacial compatibility and adhesion between the conductive agent and the matrix material. This strong interfacial interaction significantly improves the mechanical integrity and structural stability of the electrode, effectively resisting volumetric stress during charge and discharge, and reducing the risk of cracking and powdering in high-load electrodes. Polyethylene glycol pretreatment further optimizes the dispersion and rheological properties of the functionalized MWNTs in the slurry, laying a good foundation for subsequent processing. This functionalized conductive agent can build a more efficient conductive network at a lower addition amount, which helps reduce the proportion of inactive substances in the electrode and thus improve the electrochemical performance.

[0017] 4. Synergistic modification of positive electrode active materials using Se-CeO2 nanocomposite powders. During the heat treatment process, Se ions effectively enter the active material lattice, and the strong bonds formed significantly improve the stability of the lattice oxygen, fundamentally inhibiting harmful oxygen precipitation and the accompanying structural phase transition under high voltage. The nano-Se-CeO2 component forms a dynamic passivation layer in situ on the surface of the active material or at the grain boundary. The lattice oxygen fixation effect of Se and the stabilizing framework effect of CeO2 synergistically strengthen the integrity of the crystal structure, effectively resisting volume stress and structural distortion during charge and discharge. The passivation layer significantly reduces the dissolution of transition metal ions and protects the chemical stability of the electrode. This lattice doping, combined with nano-surface modification, achieves a simultaneous improvement in bulk structural stability and interface compatibility at the nanoscale, thereby significantly improving the overall electrochemical performance, cycle life and safety of the electrode. DETAILED DESCRIPTION

[0018] The present invention will be further described in detail below with reference to the examples. The specifications of multi-walled carbon nanotubes are diameter: 20~40nm, length: <2μm, purity: >97%, purchased from Shenzhen Nanoport Co., Ltd.; the positive electrode active materials LiCoO2, LiNi 0.5 Co 0.2 Mn 0.3 O2(NCM523) and LiN i0.3 Co 0.3 Mn 0.3 O2 (NCM333) was purchased from Guangdong Boyi New Energy Technology Co., Ltd.; the aluminum foil used was battery-grade aluminum foil.

[0019] Example 1 MWCNTs pretreatment: 18 parts of MWCNTs were placed in 65 parts of 70% HNO3 and ultrasonically treated at 70°C for 3 hours. After cooling to room temperature, vacuum filtration was performed and the filtrate was washed with deionized water until the pH of the filtrate was 7.0. The carboxylated MWCNTs were obtained by dissolving the carboxylated MWCNTs in SOCl2 solution at a solid-liquid ratio of 1:20 and refluxed at 70°C for 6 hours for further chlorination.

[0020] Preparation of polymer conductive agent: 30 parts of pretreated MWCNTs and anthraquinone-2-carboxylic acid were added in a mass ratio of 1:2 in 200 parts of anhydrous DMF and ultrasonically treated for 20 minutes to form a uniform dispersion. 50 parts of triethylamine was added as a catalyst and stirred at 80°C for 4 hours to obtain the product. The product was washed with ethanol, dialyzed, and dried. After that, 40% of its mass of polyethylene glycol was added and the mixture was stirred and dispersed at 500 rpm for 10 minutes for later use.

[0021] Preparation method of Se-CeO2: Ce(NO3)3·6H2O and Na2SeO3 are mixed in a mass ratio of 1:9, and ammonia water with pH=10 is slowly injected into the mixture at a solid-liquid ratio of 1:3. The mixture is placed in a hydrothermal reaction at 160°C for 12 hours. The product is centrifuged and washed, calcined at 600°C for 2 hours, and ball milled to obtain Se-CeO2 powder with a particle size of 50-70nm.

[0022] Positive electrode material: 1.0 wt% Se-CeO2 nanopowder and 0.5 wt% stearic acid were added to the NCM523 positive electrode active material, ball milled at a speed of 300 rpm for 2 h, heated at a rate of 5 °C / min in an O2 atmosphere, and heat treated at 700 °C for 4 h to obtain the positive electrode material.

[0023] PVDF was dissolved in NMP to prepare a binder with a mass concentration of 10%; 16 parts of polymer conductive agent were added to 8 parts of the binder solution, stirred at 1650 rpm for 25 minutes, and the positive electrode material was added in batches. First, 44 parts of the positive electrode material were added, and the speed was 2650 rpm for stirring and dispersion for 10 minutes. 4% of the binder was added, and then 50 parts of the positive electrode material were added. The stirring and dispersion were continued for 10 minutes, and then the speed was changed to low speed 200 rpm and stirred for 15 minutes to defoam to form a uniform positive electrode slurry. The viscosity of the slurry was controlled at 7500 mPa·s. The mixed slurry was then coated on a carbon-coated aluminum foil current collector and dried at 120°C for 6 hours. The dried positive electrode sheet was compacted by a roller press to a compaction density of 2.8 g / cm³. The loading of the active material of the obtained positive electrode sheet was 7 mg / cm 2 The rolled positive electrode sheet is cut into small pieces of the required size by a slitting machine for subsequent battery assembly.

[0024] Example 2 MWCNTs pretreatment: 10 parts of MWCNTs were placed in 80 parts of 70% HNO3 and ultrasonically treated at 60°C for 2 hours. After cooling to room temperature, vacuum filtration was performed and the filtrate was washed with deionized water until the pH of the filtrate was 7.3. The carboxylated MWCNTs were obtained by dissolving the carboxylated MWCNTs in SOCl2 solution at a solid-liquid ratio of 1:20 and refluxed at 70°C for 6 hours for further chlorination.

[0025] Preparation of polymer conductive agent: 30 parts of pretreated MWCNTs and anthraquinone-2-carboxylic acid were added in a mass ratio of 1:2 in 200 parts of anhydrous DMF and ultrasonically treated for 10 minutes to form a uniform dispersion. 55 parts of triethylamine was added as a catalyst and stirred at 80°C for 4 hours to obtain a product. The product was washed with ethanol, dialyzed, and dried. After that, 40% of its mass of polyethylene glycol was added and the mixture was stirred and dispersed at 500 rpm for 10 minutes for use.

[0026] Preparation method of Se-CeO2: Ce(NO3)3·6H2O and Na2SeO3 are mixed in a mass ratio of 1:9, and ammonia water with pH=10 is slowly injected into the mixture at a solid-liquid ratio of 1:3. The mixture is placed in a hydrothermal reaction at 160°C for 12 hours. The product is centrifuged and washed, calcined at 600°C for 2 hours, and ball milled to obtain Se-CeO2 powder with a particle size of 60-80nm.

[0027] Positive electrode material: 1.5wt% Se-CeO2 nanopowder and 0.5wt% stearic acid were added to the LiCoO2 positive electrode active material, the ball milling speed was 300rpm, the time was 2h, the heating rate was 5℃ / min, and the positive electrode material was obtained by heat treatment at 700℃ for 4h.

[0028] PVDF was dissolved in NMP to prepare a binder with a mass concentration of 12%; 15 parts of polymer conductive agent were added to 10 parts of the binder solution, stirred at 1500 rpm for 30 minutes, and the positive electrode material was added in batches. First, 40 parts of the positive electrode material were added, and the speed was 2800 rpm and stirred for 10 minutes. 5% of the binder was added, and then 52 parts of the positive electrode material were added. The stirring and dispersion were continued for 10 minutes, and then the speed was changed to 200 rpm. The mixture was stirred for 15 minutes to defoam and form a uniform positive electrode slurry. The viscosity of the slurry was controlled at 6500 mPa·s. The mixed slurry was then coated on a carbon-coated aluminum foil current collector and dried at 120 ° C for 6 hours. The dried positive electrode sheet was compacted by a roller press to a compaction density of 3.4 g / cm³. The loading of the active material of the obtained positive electrode sheet was 10.0 mg / cm 2 The rolled positive electrode sheet is cut into small pieces of the required size by a slitting machine for subsequent battery assembly.

[0029] Example 3 MWCNTs pretreatment: 26 parts of MWCNTs were placed in 50 parts of 70% HNO3 and ultrasonically treated at 80°C for 4 hours. After cooling to room temperature, vacuum filtration was performed and the filtrate was washed with deionized water until the pH of the filtrate was 6.8. The carboxylated MWCNTs were obtained by dissolving the carboxylated MWCNTs in SOCl2 solution at a solid-liquid ratio of 1:20 and refluxed at 70°C for 6 hours for further chlorination.

[0030] Preparation of polymer conductive agent: 30 parts of pretreated MWCNTs and anthraquinone-2-carboxylic acid were added in a mass ratio of 1:2 in 200 parts of anhydrous DMF and ultrasonically treated for 30 minutes to form a uniform dispersion. 45 parts of triethylamine was added as a catalyst and stirred at 80°C for 4 hours to obtain a product. The product was washed with ethanol, dialyzed, and dried. After that, 40% of its mass of polyethylene glycol was added and the mixture was stirred and dispersed at 500 rpm for 10 minutes for use.

[0031] Preparation method of Se-CeO2: Ce(NO3)3·6H2O and Na2SeO3 are mixed in a mass ratio of 1:9, and ammonia water with pH=10 is slowly injected into the mixture at a solid-liquid ratio of 1:3. The mixture is placed in a hydrothermal reaction at 160°C for 12 hours, the product is centrifuged and washed, calcined at 600°C for 2 hours, and ball milled to obtain Se-CeO2 powder with a particle size of 80-100nm.

[0032] Positive electrode material: 0.5wt% Se-CeO2 nanopowder and 0.5wt% stearic acid were added to the NCM333 positive electrode active material, and the ball milling speed was 300rpm for 2h. In an O2 atmosphere, the heating rate was 5℃ / min, and the positive electrode material was obtained by heat treatment at 700℃ for 4h.

[0033] PVDF was dissolved in NMP to prepare a binder with a mass concentration of 8%; 18 parts of polymer conductive agent were added to 7 parts of the binder solution, stirred at 1800 rpm for 20 minutes, and the positive electrode material was added in batches. First, 48 parts of the positive electrode material were added, and the speed was 2500 rpm and stirred and dispersed for 10 minutes. 2% of the binder was added, and then 48 parts of the positive electrode material were added. The stirring and dispersion continued for 10 minutes, and then the speed was changed to low speed 200 rpm. The stirring was carried out for 15 minutes to defoam to form a uniform positive electrode slurry. The viscosity of the slurry was controlled at 8500 mPa·s. The mixed slurry was then coated on a carbon-coated aluminum foil current collector and dried at 120 ° C for 6 hours. The dried positive electrode sheet was compacted by a roller press to a compaction density of 2.4 g / cm³. The loading of the active material of the obtained positive electrode sheet was 4.0 mg / cm 2 The rolled positive electrode sheet is cut into small pieces of the required size by a slitting machine for subsequent battery assembly.

[0034] Comparative Example 1 Preparation of polymer conductive agent: 30 parts of MWCNTs and anthraquinone-2-carboxylic acid in a mass ratio of 1:2 were dissolved in 200 parts of anhydrous DMF and ultrasonically treated for 20 minutes to form a uniform dispersion. 50 parts of triethylamine was added as a catalyst and stirred at 80°C for 4 hours to obtain the product. The product was washed with ethanol, dialyzed, and dried. After that, 40% of its mass of polyethylene glycol was added and the mixture was stirred and dispersed at 500 rpm for 10 minutes for later use.

[0035] Preparation method of Se-CeO2: Ce(NO3)3·6H2O and Na2SeO3 are mixed in a mass ratio of 1:9, and ammonia water with pH=10 is slowly injected into the mixture at a solid-liquid ratio of 1:3. The mixture is placed in a hydrothermal reaction at 160°C for 12 hours. The product is centrifuged and washed, calcined at 600°C for 2 hours, and ball milled to obtain Se-CeO2 powder with a particle size of 60-80nm.

[0036] Positive electrode material: 1.0 wt% Se-CeO2 nanopowder and 0.5 wt% stearic acid were added to the NCM523 positive electrode active material, ball milled at a speed of 300 rpm for 2 h, heated at a rate of 5 °C / min in an O2 atmosphere, and heat treated at 700 °C for 4 h to obtain the positive electrode material.

[0037] PVDF was dissolved in NMP to prepare a binder with a mass concentration of 10%; 16 parts of polymer conductive agent were added to 8 parts of the binder solution, stirred at 1650 rpm for 25 minutes, and the positive electrode material was added in batches. First, 44 parts of the positive electrode material were added, and the speed was 2650 rpm for stirring and dispersion for 10 minutes. 4% of the binder was added, and then 50 parts of the positive electrode material were added. The stirring and dispersion were continued for 10 minutes, and then the speed was changed to low speed 200 rpm and stirred for 15 minutes to defoam to form a uniform positive electrode slurry. The viscosity of the slurry was controlled at 7500 mPa·s. The mixed slurry was then coated on a carbon-coated aluminum foil current collector and dried at 120°C for 6 hours. The dried positive electrode sheet was compacted by a roller press to a compaction density of 2.8 g / cm³. The loading of the active material of the obtained positive electrode sheet was 7 mg / cm 2 The rolled positive electrode sheet is cut into small pieces of the required size by a slitting machine for subsequent battery assembly.

[0038] Comparative Example 2 Preparation of polymer conductive agent: 18 parts of MWCNTs were placed in 65 parts of 70% HNO3 and ultrasonically treated at 70°C for 3 hours. After cooling to room temperature, vacuum filtration was performed, and the filtrate was washed with deionized water until the pH of the filtrate reached 7.0. The carboxylated MWCNTs were then dried to obtain carboxylated MWCNTs. The carboxylated MWCNTs were dissolved in SOCl2 solution at a material-liquid ratio of 1:20, refluxed at 70°C for 6 hours, and further chlorinated to obtain a polymer conductive agent. 40% of the weight of polyethylene glycol was added, and the mixture was stirred and dispersed at 500 rpm for 10 minutes for later use. Preparation method of Se-CeO2: Ce(NO3)3·6H2O and Na2SeO3 are mixed in a mass ratio of 1:9, and ammonia water with pH=10 is slowly injected into the mixture at a solid-liquid ratio of 1:3. The mixture is placed in a hydrothermal reaction at 160°C for 12 hours. The product is centrifuged and washed, calcined at 600°C for 2 hours, and ball milled to obtain Se-CeO2 powder with a particle size of 50-80nm.

[0039] Positive electrode material: 1.0 wt% Se-CeO2 nanopowder and 0.5 wt% stearic acid were added to the NCM523 positive electrode active material, ball milled at a speed of 300 rpm for 2 h, heated at a rate of 5 °C / min in an O2 atmosphere, and heat treated at 700 °C for 4 h to obtain the positive electrode material.

[0040] PVDF was dissolved in NMP to prepare a binder with a mass concentration of 10%; 16 parts of polymer conductive agent were added to 8 parts of the binder solution, stirred at 1650 rpm for 25 minutes, and the positive electrode material was added in batches. First, 44 parts of the positive electrode material were added, and the speed was 2650 rpm for stirring and dispersion for 10 minutes. 4% of the binder was added, and then 50 parts of the positive electrode material were added. The stirring and dispersion were continued for 10 minutes, and then the speed was changed to low speed 200 rpm and stirred for 15 minutes to defoam to form a uniform positive electrode slurry. The viscosity of the slurry was controlled at 7500 mPa·s. The mixed slurry was then coated on a carbon-coated aluminum foil current collector and dried at 120°C for 6 hours. The dried positive electrode sheet was compacted by a roller press to a compaction density of 2.8 g / cm³. The loading of the active material of the obtained positive electrode sheet was 7 mg / cm 2 The rolled positive electrode sheet is cut into small pieces of the required size by a slitting machine for subsequent battery assembly.

[0041] Comparative Example 3 The difference between this comparative example and Example 1 is that anthraquinone-2-carboxylic acid is replaced by pyrrole in this comparative example; the rest is the same as Example 1.

[0042] Comparative Example 4 The difference between this comparative example and Example 1 is that in this comparative example, 1.0 wt% of Se nanopowder and 0.5 wt% of stearic acid are added to the NCM523 positive electrode active material, the ball milling speed is 300 rpm, the time is 2 h, the heating rate is 5 ° C / min, and the positive electrode material is obtained by heat treatment at 700 ° C for 4 hours in an O2 atmosphere; the rest is the same as Example 1.

[0043] Comparative Example 5 The difference between this comparative example and Example 1 is that in this comparative example, 1.0 wt% of CeO2 nanopowder and 0.5 wt% of stearic acid are added to the NCM52 positive electrode active material, the ball milling speed is 300 rpm, the time is 2 h, the heating rate is 5 ° C / min, and the positive electrode material is obtained by heat treatment at 700 ° C for 4 hours in an O2 atmosphere; the rest is the same as Example 1.

[0044] Comparative Example 6 The difference between this comparative example and Example 1 is that the Se-CeO2 preparation method in this comparative example is as follows: Ce(NO3)3·6H2O and Na2SeO3 are mixed in a mass ratio of 3:7, and ammonia water with a pH value of 10 is slowly injected into the mixture at a solid-liquid ratio of 1:3, and the mixture is subjected to hydrothermal reaction at 160°C for 12 hours. The product is centrifuged and washed, calcined at 600°C for 2 hours, and ball-milled to obtain Se-CeO2 nanopowder with a particle size of 50-80nm; the rest is the same as Example 1.

[0045] Comparative Example 7 The difference between this comparative example and Example 1 is that the Se-CeO2 preparation method in this comparative example is as follows: Ce(NO3)3·6H2O and Na2SeO3 are mixed in a mass ratio of 1:1, and ammonia water with a pH value of 10 is slowly injected into the mixture at a solid-liquid ratio of 1:3, and the mixture is subjected to hydrothermal reaction at 160°C for 12 hours. The product is centrifuged and washed, calcined at 600°C for 2 hours, and ball-milled to obtain Se-CeO2 nanopowder with a particle size of 60-90nm; the rest is the same as Example 1.

[0046] Comparative Example 8 MWCNTs pretreatment: 18 parts of MWCNTs were placed in 65 parts of 70% HNO3 and ultrasonically treated at 70°C for 3 hours. After cooling to room temperature, vacuum filtration was performed and the filtrate was washed with deionized water until the pH of the filtrate was 7.0. The carboxylated MWCNTs were obtained by dissolving the carboxylated MWCNTs in SOCl2 solution at a solid-liquid ratio of 1:20 and refluxed at 70°C for 6 hours for further chlorination.

[0047] Preparation of polymer conductive agent: 30 parts of pretreated MWCNTs and anthraquinone-2-carboxylic acid were added in a mass ratio of 1:2 in 200 parts of anhydrous DMF and ultrasonically treated for 20 minutes to form a uniform dispersion. 50 parts of triethylamine was added as a catalyst and stirred at 80°C for 4 hours to obtain the product. The product was washed with ethanol, dialyzed, and dried. After that, 40% of its mass of polyethylene glycol was added and the mixture was stirred and dispersed at 500 rpm for 10 minutes for later use.

[0048] Preparation method of Se-CeO2: Ce(NO3)3·6H2O and Na2SeO3 are mixed in a mass ratio of 1:9, and ammonia water with pH=10 is slowly injected into the mixture at a solid-liquid ratio of 1:3. The mixture is placed in a hydrothermal reaction at 160°C for 12 hours, the product is centrifuged and washed, calcined at 600°C for 2 hours, and ball milled to obtain Se-CeO2 powder with a particle size of 90-100nm.

[0049] Positive electrode material: 1.0 wt% Se-CeO2 nanopowder and 0.5 wt% stearic acid were added to the NCM523 positive electrode active material, ball milled at a speed of 300 rpm for 2 h, heated at a rate of 5 °C / min in an O2 atmosphere, and heat treated at 700 °C for 4 h to obtain the positive electrode material.

[0050] PVDF was dissolved in NMP to prepare a binder with a mass concentration of 10%. 8 parts of binder, 16 parts of polymer conductive agent, and 94 parts of positive electrode material were stirred and dispersed at a speed of 2650 rpm for 10 minutes, and then 4% of binder was added. The speed was maintained and the stirring was continued for 15 minutes to form a uniform positive electrode slurry. The viscosity of the slurry was controlled at 7000 mPa·s. The mixed slurry was then coated on a carbon-coated aluminum foil current collector and dried at 120°C for 6 hours. The dried positive electrode sheet was compacted by a roller press to a compaction density of 2.8 g / cm³. The active material loading of the obtained positive electrode sheet was 7 mg / cm 2 The rolled positive electrode sheet is cut into small pieces of the required size by a slitting machine for subsequent battery assembly.

[0051] Test 1: Battery performance test The button-type batteries were assembled in an argon-filled glove box, and the charge-discharge cycle test was performed on the tester with a voltage window of 2.75-4.3V. The first efficiency at a current density of 2C and the cycle performance at different 2C temperatures were tested; the different temperatures included room temperature (25°C) and high temperature (60°C).

[0052] The results are shown in Table 1 below: Table 1

Claims

1. A method for preparing a positive electrode sheet of a polymer lithium battery, characterized in that: The specific process is as follows: (1) Preparation of binder solution: dissolve PVDF in NMP to prepare a binder solution with a mass concentration of 8%-12%; (2) Dispersing the polymer conductive agent: Add 40% of the weight of polyethylene glycol to 15-18 parts by weight of the polymer conductive agent, and stir and disperse at 500 rpm for 10 minutes; (3) Preparing a positive electrode slurry: Add the dispersed polymer conductive agent obtained in step (2) to 7-10 parts by mass of the binder solution, and stir at a speed of 1500-1800 rpm for 20-30 minutes; Add the positive electrode material in batches: first add 40-48 parts by mass of the positive electrode material and stir and disperse at 2500-2800 rpm for 10 minutes; add 2-5% of the binder solution; then add 48-52 parts by mass of the positive electrode material and continue stirring and dispersing for 10 minutes; then switch to a low speed of 200 rpm and stir for 15 minutes to defoam, to obtain a positive electrode slurry with a viscosity of 6500-8500 mPa·s; (4) Coating and drying: The slurry was coated on the carbon-coated aluminum foil current collector and baked at 120 °C for 6 hours; (5) Rolling: Roll the dried positive electrode sheet to a compaction density of 2.4-3.4 g / cm³ and an active material loading of 4.0-10.0 mg / cm²; (6) Cutting: Cut the rolled positive electrode sheet into the required size.

2. The method for preparing a positive electrode sheet for a polymer lithium battery according to claim 1, wherein: The positive electrode material is prepared by the following steps: adding 0.5-1.5 wt% of Se-CeO2 nanopowder and 0.5 wt% of stearic acid to the positive electrode active material, ball milling at 300 rpm for 2 hours; then heating to 700°C at 5°C / min in an O2 atmosphere and heat treating for 4 hours.

3. The method for preparing a positive electrode sheet for a polymer lithium battery according to claim 2, wherein: The preparation method of the Se-CeO2 nanopowder is as follows: Ce(NO3)3·6H2O and Na2SeO3 are mixed in a mass ratio of 1:9, ammonia water with a pH value of 10 is slowly injected into the mixture at a solid-liquid ratio of 1:3, and the mixture is subjected to a hydrothermal reaction at 160°C for 12 hours. The product is centrifuged and washed, and calcined at 600°C for 2 hours to obtain Se-CeO2 nanopowder, which is then ball-milled to obtain a particle size of 50-100 nm.

4. The method for preparing a positive electrode sheet for a polymer lithium battery according to claim 2, wherein: The positive electrode active material is one or more of LiCoO2, NCM523 and NCM333.

5. The method for preparing a positive electrode sheet for a polymer lithium battery according to claim 1, wherein: The polymer conductive agent is 30 parts of MWCNTs and anthraquinone-2-carboxylic acid in a mass ratio of 1:2 in 200 parts of anhydrous DMF, ultrasonically treated for 10-30 minutes to form a uniform dispersion, 45-55 parts of triethylamine is added as a catalyst, and stirred at 80°C for 4 hours to obtain a product, which is washed with ethanol, dialyzed, and dried.

6. The method for preparing a positive electrode sheet for a polymer lithium battery according to claim 5, wherein: The MWCNTs also include a pretreatment process: placing 10-26 parts of MWCNTs in 50-80 parts of 70% HNO3 and ultrasonically treating them at 60-80°C for 2-4 hours, cooling to room temperature and vacuum filtering, washing with deionized water until the filtrate has a pH of 6.8-7.3, and drying to obtain carboxylated MWCNTs, dissolving the carboxylated MWCNTs in a SOCl2 solution at a material-liquid ratio of 1:20, refluxing at 70°C for 6 hours, and further chlorinating.

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