A method for preparing a positive electrode sheet of a polymer lithium battery

Abstract

The application provides a preparation method of a positive plate of a polymer lithium battery. The process realizes integrated optimization of electrode material-structure-process. The synergistic effect of a functional polymer conductive agent and Se-CeO2 doping significantly enhances the conductivity, structural stability and interface stability of the electrode. Fine slurry mixing and roll control ensure the uniformity and density of the coating under high load. Finally, while reducing the interface impedance and improving the utilization rate of active material, the high energy density and long cycle reliability are considered, thereby providing an effective electrode manufacturing process for high-performance lithium batteries.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of lithium battery positive plate, and particularly relates to a preparation process of a polymer lithium battery positive plate. BACKGROUND

[0002] Lithium ion batteries have become the focus of attention in the energy storage field due to their high working voltage, long cycle life, good safety performance, and no memory effect. In the composition of lithium ion batteries, the positive electrode material is a key factor that determines the energy density, power performance, and cycle stability of the battery, and its development is crucial for improving the overall performance of the battery.

[0003] The current mainstream positive electrode preparation process usually adopts a simple mechanical mixing mode of active material, conductive carbon black, and polymer binder (such as PVDF). However, this process has significant defects: the conductive agent is poorly dispersed, making it difficult to form an efficient and continuous three-dimensional conductive network; under high active material load, the electrode structure is prone to cracking due to stress concentration; the interfacial bonding force between the active material, conductive agent, and binder is weak, and peeling is likely to occur during long-term cycling or high-current charging and discharging. These defects limit the rate performance of the positive electrode active material under the background of increasing demand for high energy density.

[0004] The uniformity of slurry dispersion is the basis for solving the above problems. In the conventional lithium battery positive electrode slurry preparation process, the effective dispersion of active material, conductive agent, and binder is crucial. Poor dispersion can lead to imperfect conductive networks, increased battery resistance, and reduced rate performance; low active material utilization, affecting capacity performance; and insufficient adhesion, leading to the risk of electrode powdering. Therefore, ensuring that the slurry has good dispersion and quality is a prerequisite for achieving good adhesion and conductivity of the electrode.

[0005] The optimization of conductive agents is one of the core approaches to improve the performance of electrodes. Commonly used polymer conductive agents mainly include carbon black, conductive graphite and carbon fiber materials. However, these materials have limitations: materials such as carbon fiber are prone to agglomeration, difficult to disperse uniformly in the slurry, resulting in uneven conductive network, affecting the overall conductivity. Multi-walled carbon nanotubes (MWNTs) as a new type of nano-conductive material have extremely high aspect ratio and excellent conductivity, can build an efficient three-dimensional conductive network in the electrode, significantly improve the conductivity of the electrode, relieve the volume expansion effect and improve the cycle stability, and are an ideal candidate material to solve the problems of poor conductivity, high volume expansion rate and low cycle life. However, its surface has certain chemical inertness and lacks sufficient functional groups, which makes it difficult to disperse and process in a polymer matrix, and its compatibility with the active material matrix is poor, and the interface interaction is weak. Therefore, how to effectively functionalize the surface of MWNTs to improve its dispersibility, stability and interface compatibility with each component of the electrode is a research focus to improve its application effect and solve the problems of existing conductive agents.

[0006] At the same time, the development of new high-capacity positive active materials is another key to improve the energy density. The quinone polymer positive electrode material exhibits high theoretical specific capacity, excellent cycle performance, fast charging and discharging capacity and environmental friendliness, etc. Significant advantages have great application potential. How to effectively use high-performance active materials such as quinone polymers and synergize with optimized conductive agents (such as MWNTs) to build a high-performance composite electrode system is one of the important directions of this research.

[0007] In addition, doping modification of the positive active material itself is also an effective way to improve its comprehensive performance. Studies have shown that by introducing doping elements, the electrical conductivity of the material can be effectively improved and the structural stability can be enhanced. For example, selenium (Se) doping can to some extent alleviate the problem of oxygen loss during the cycle of lithium-rich manganese-based positive electrode materials. However, selenium doping has limitations: the effective doping concentration window is narrow, the improvement of electrical conductivity is limited, and the effect of inhibiting structural distortion (such as the transformation of layered structure to spinel phase) is insufficient. Rare earth metal elements have shown significant advantages in expanding lattice channels, stabilizing crystal structure and enhancing interface stability due to their unique electronic structure and chemical properties, and are expected to further optimize the performance of the material. Therefore, how to realize the efficient and controllable doping of rare earth metals and other elements to the positive electrode material to synergistically improve its electrical conductivity, structural stability and long cycle performance is another core research focus of the invention. SUMMARY

[0008] The application discloses a preparation process of a polymer lithium battery positive electrode sheet to solve the above and any potential problems in the prior art. In order to solve the above technical problems, the process of the present application is as follows:

[0009] (1) Preparing binder solution: dissolving PVDF in NMP to prepare a binder solution with a mass concentration of 8%-12%;

[0010] (2) Dispersing polymer conductive agent: adding polyethylene glycol with a mass of 40% of the polymer conductive agent to 15-18 parts by mass, and stirring and dispersing for 10 minutes at a speed of 500 rpm;

[0011] (3) Preparing positive electrode slurry: adding the polymer conductive agent after dispersion in step (2) to 7-10 parts by mass of the binder solution in step (1), and stirring for 20-30 minutes at a speed of 1500-1800 rpm;

[0012] Batch adding positive electrode material: first adding 40-48 parts by mass of positive electrode material, and stirring and dispersing for 10 minutes at a speed of 2500-2800 rpm; supplementing 2-5% of the binder solution in step (1); then adding 48-52 parts by mass of positive electrode material, and continuing to stir and disperse for 10 minutes; switching to low-speed stirring at 200 rpm for 15 minutes to defoam, to obtain a positive electrode slurry with a viscosity of 6500-8500 mPa·s;

[0013] (4) Coating and drying: coating the slurry on a carbon-coated aluminum foil current collector, and baking at 120°C for 6 hours;

[0014] (5) Rolling: rolling 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;

[0015] (6) Slitting: slitting the rolled positive electrode sheet into the desired size.

[0016] The positive electrode material is prepared by the following steps: adding Se-CeO2 nano-powder with a mass of 0.5-1.5 wt% and 0.5 wt% of stearic acid to the positive electrode active material, and ball milling at 300 rpm for 2 hours; then heating to 700°C at a rate of 5°C / min in an O2 atmosphere, and heat treating for 4 hours.

[0017] The Se-CeO2 nano-powder is prepared by the following method: mixing Ce(NO3)3·6H2O and Na2SeO3 in a mass ratio of 1:9, slowly injecting ammonia water with a pH of 10 into the mixture at a solid-liquid ratio of 1:3, and placing it in a hydrothermal reaction at 160°C for 12 hours; centrifuging and washing the product, and calcining at 600°C for 2 hours to obtain Se-CeO2 nano-powder, and ball milling to obtain a particle size of 50-100 nm.

[0018] The positive electrode active material is one or more of LiCoO2, NCM523, and NCM333.

[0019] The polymer conductive agent is 30 parts of MWCNTs and anthraquinone-2-carboxylic acid with a mass ratio of 1:2 in 200 parts of anhydrous DMF, ultrasonic treatment for 10-30 min to form a uniform dispersion, 45-55 parts of triethylamine is added as a catalyst, stirring at 80 DEG C for 4 h to obtain the product, the product is washed with ethanol, dialysis and drying to obtain.

[0020] The MWCNTs also include a pretreatment process: 10-26 parts of MWCNTs are placed in 50-80 parts of 70% concentrated HNO3 and ultrasonic treated at 60-80 DEG C for 2-4 hours, cooled to room temperature, vacuum filtration, washed with deionized water until the filtrate pH is 6.8-7.3, dried to obtain carboxylated MWCNTs, and the carboxylated MWCNTs are dissolved in SOCl2 solution according to the solid-liquid ratio of 1:20, refluxed at 70 DEG C for 6 hours for further acyl chloride.

[0021] The advantages and beneficial effects of the present application are:

[0022] 1. The present application significantly improves the comprehensive performance of the electrode through multi-component synergistic modification and fine process control. First, the functional polymer conductive agent is used to build an efficient electronic network while strengthening the mechanical stability of the electrode and reducing the proportion of non-active substances; in-situ doping of the positive electrode material with Se-CeO2 nano powder utilizes the rare earth element effect to effectively inhibit material structure degradation and transition metal dissolution, improving the cycle life and safety; precise control of the slurry mixing process ensures component uniformity and interface compatibility, avoiding agglomeration and pore defects from the source, and improving the corresponding electrochemical performance.

[0023] 2. First, the deeply functionalized modified MWNTs conductive agent is fully dispersed in the binder solution to form a "pre-wrapped" structure, laying the foundation for subsequent uniform network construction. Then, the positive active material is added in batches, and high-speed dispersion is used to ensure maximum uniformity of the initial mixture, effectively preventing agglomeration. After adding a large amount of active material, the binder is supplemented in a timely manner to effectively solve the problem of insufficient local coating caused by excessive active material, avoiding direct contact between particles and the formation of weakly bonded areas, ensuring good particle-to-particle bonding. Finally, the low-speed stirring stage focuses on defoaming and structure relaxation, allowing internal stress to be released and the structure to be stabilized. The synergistic effect of this ordered feeding, dynamic viscosity adjustment, and strength gradient control not only significantly promotes efficient dispersion of the material, full coating of the active material, and stable construction of the conductive network, but also minimizes the risk of mechanical damage to the conductive network and active material particles caused by high-speed stirring for a long time. The final slurry has good viscosity stability, excellent rheological properties, and structural uniformity, which is very beneficial for achieving high uniformity coating and wet film stability, laying the foundation for the preparation of high-quality electrode sheets. This optimization of microstructure directly translates into better structural stability and more excellent electrochemical performance of the electrode during the cycling process.

[0024] 3. By deeply functionalizing the multi-walled carbon nanotubes (MWNTs) through surface carboxylation, acyl chloride activation, and covalent grafting of anthraquinone molecules, a unique "amphiphilic" structural advantage is achieved. The large π-conjugated backbone of the anthraquinone molecule interacts strongly with the carbon nanotube surface (such as π-π stacking), achieving strong anchoring. The modified MWNTs can construct an efficient "molecular wire" network between active particles, significantly reducing the interfacial contact resistance and improving the electron transport efficiency. The exposed polar groups of anthraquinone can form multiple strong hydrogen bonds and dipole interactions with the positive active material and PVDF binder, greatly enhancing the interfacial compatibility and bonding force between the conductive agent and the matrix material. This strong interfacial force significantly improves the mechanical integrity and structural stability of the electrode, effectively resisting the volume change stress during charging and discharging, reducing the risk of electrode cracking and powdering under high load. Polyethylene glycol pretreatment further optimizes the dispersion state and rheological properties of the functionalized MWNTs in the slurry, laying a good foundation for subsequent processes. This functionalized conductive agent can construct a more efficient conductive network at a lower addition amount, which helps to reduce the proportion of non-active material in the electrode, thereby improving the electrochemical performance.

[0025] 4. The positive active material is synergistically modified by Se-CeO2 nanocomposite powder. During the heat treatment process, Se ions effectively enter the active material lattice, and the strong bond formed by Se ions significantly improves the stability of lattice oxygen, fundamentally inhibiting the harmful oxygen precipitation and accompanying structural phase transition at high voltage. The nano Se-CeO2 component forms a dynamic passivation layer in situ at the surface or grain boundary of the active material. The lattice oxygen storage effect of Se and the stable framework effect of CeO2 synergistically strengthen the integrity of the crystal structure, effectively resisting the volume stress and structural distortion during the charging and discharging process. The passivation layer significantly reduces the dissolution of transition metal ions, protecting the chemical stability of the electrode. This combination of lattice doping and nano surface modification simultaneously improves the 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

[0026] The application will be further described in detail below in conjunction with examples. The multi-walled carbon nanotubes have a specification of diameter: 20-40 nm, length: <2 μm, and purity: >97%, and are purchased from Shenzhen Nanohop Co., Ltd.; the positive 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) are all purchased from Guangdong Boyi New Energy Technology Co., Ltd.; and the aluminum foil used is a battery-grade aluminum foil.

[0027] Example 1

[0028] MWCNTs pretreatment: 18 parts of MWCNTs are placed in 65 parts of HNO3 with a concentration of 70% for ultrasonic treatment at 70°C for 3 hours. After cooling to room temperature, vacuum filtration is performed, and washing with deionized water is performed until the pH of the filtrate is 7.0. After drying, carboxylated MWCNTs are obtained. The carboxylated MWCNTs are dissolved in an SOCl2 solution according to a solid-liquid ratio of 1:20, and refluxing is performed at 70°C for 6 hours to further perform acyl chloride treatment.

[0029] Polymer conductive agent preparation: 30 parts of pretreated MWCNTs are ultrasonically treated in 200 parts of anhydrous DMF with anthraquinone-2-carboxylic acid at a mass ratio of 1:2 for 20 min to form a uniform dispersion liquid. 50 parts of triethylamine is added as a catalyst, and stirring is performed at 80°C for 4 h to obtain a product. The product is washed with ethanol, dialyzed, and dried. Then, 40% of polyethylene glycol by mass is added, and stirring is performed at 500 rpm for 10 min for standby use.

[0030] Se-CeO2 preparation method: Ce(NO3)3·6H2O and Na2SeO3 were mixed according to a mass ratio of 1:9, and ammonia water with a pH of 10 was slowly injected into the mixture according to a solid-liquid ratio of 1:3, and placed in a hydrothermal reaction at 160°C for 12 hours. The product was centrifuged, washed, calcined at 600°C for 2 hours, and ball milled to obtain Se-CeO2 powder with a particle size of 50-70 nm.

[0031] Positive electrode material: 1.0wt% of Se-CeO2 nano-powder and 0.5wt% of stearic acid were added to NCM523 positive electrode active material, ball milled at a speed of 300 rpm for 2h, heated at a rate of 5°C / min in an O2 atmosphere, and heat treated at 700°C for 4h to obtain the positive electrode material.

[0032] PVDF was dissolved in NMP to prepare a binder with a mass concentration of 10%; 16 parts of a polymer conductive agent were added to 8 parts of the binder solution, stirred at 1650 rpm for 25 min, and the positive electrode material was added in batches: first, 44 parts of the positive electrode material was added and stirred at a speed of 2650 rpm for 10 min, 4% of the binder was supplemented, and then 50 parts of the positive electrode material was added and continued to be stirred and dispersed for 10 min, and then the speed was reduced to 200 rpm and stirred for 15 min to defoam to form a uniform positive electrode slurry. The viscosity of the slurry was controlled at 7500 mPa·s, and then the mixed slurry was coated on a carbon-coated aluminum foil current collector, dried at 120°C for 6h, and the dried positive electrode sheet was compacted by a rolling machine to a compacted density of 2.8g / cm³, and the active material loading of the obtained positive electrode sheet was 7mg / cm 2 The rolled positive electrode sheet was cut into small pieces of the required size by a slitting machine for subsequent battery assembly.

[0033] Example 2

[0034] MWCNTs pretreatment: 10 parts of MWCNTs were placed in 80 parts of 70% concentrated HNO3 and ultrasonically treated at 60°C for 2 hours, cooled to room temperature, vacuum filtered, washed with deionized water until the filtrate pH was 7.3, and dried to obtain carboxylated MWCNTs. The carboxylated MWCNTs were dissolved in SOCl2 solution according to a solid-liquid ratio of 1:20, and refluxed at 70°C for 6 hours for further acyl chloride treatment.

[0035] Polymer conductive agent preparation: 30 parts of pretreated MWCNTs were ultrasonically treated in 200 parts of anhydrous DMF for 10 min to form a uniform dispersion liquid, 55 parts of triethylamine was added as a catalyst, and stirred at 80°C for 4h to obtain the product. The product was washed with ethanol, dialyzed, and dried, and then 40% of polyethylene glycol by mass was added and stirred and dispersed at 500 rpm for 10 min for standby use.

[0036] Se-CeO2 preparation method: Ce(NO3)3·6H2O and Na2SeO3 were mixed according to a mass ratio of 1:9, and ammonia water with a pH of 10 was slowly injected into the mixture according to a solid-liquid ratio of 1:3, and then placed in a hydrothermal reaction at 160°C for 12 hours. The product was centrifuged, washed, calcined at 600°C for 2 hours, and then ball-milled to obtain Se-CeO2 powder with a particle size of 60-80 nm.

[0037] Positive electrode material: 1.5wt% of Se-CeO2 nano-powder and 0.5wt% of stearic acid were added to LiCoO2 positive electrode active material, ball-milled at a speed of 300 rpm for 2 hours, heat-treated at 700°C for 4 hours in an O2 atmosphere at a heating rate of 5°C / min, to obtain the positive electrode material.

[0038] PVDF was dissolved in NMP to prepare a binder with a mass concentration of 12%; 15 parts of a polymer conductive agent were added to 10 parts of the binder solution, stirred at 1500 rpm for 30 min, and the positive electrode material was added in batches. First, 40 parts of the positive electrode material were added, stirred and dispersed at a speed of 2800 rpm for 10 min, 5% of the binder was supplemented, and then 52 parts of the positive electrode material were added, and the stirring and dispersion was continued for 10 min. The speed was then reduced to 200 rpm, and the mixture was stirred for 15 min to remove bubbles to form a uniform positive electrode slurry. The viscosity of the slurry was controlled at 6500 mPa·s. Then, the mixed slurry was coated on a carbon-coated aluminum foil current collector, dried at 120°C for 6 h, and the dried positive electrode sheet was compacted by a rolling machine to a compacted density of 3.4 g / cm³. The active material loading of the obtained positive electrode sheet was 10.0 mg / cm 2 The rolled positive electrode sheet was cut into small pieces of the required size by a slitting machine for subsequent battery assembly.

[0039] Example 3

[0040] MWCNTs pretreatment: 26 parts of MWCNTs were placed in 50 parts of 70% concentrated 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 was 6.8. After drying, carboxylated MWCNTs were obtained. The carboxylated MWCNTs were dissolved in an SOCl2 solution according to a solid-liquid ratio of 1:20, and refluxed at 70°C for 6 hours for further acyl chloride treatment.

[0041] Polymer conductive agent preparation: 30 parts of pretreated MWCNTs were ultrasonically treated in 200 parts of anhydrous DMF for 30 min to form a uniform dispersion liquid according to a mass ratio of 1:2 of anthraquinone-2-carboxylic acid. Then, 45 parts of triethylamine were added as a catalyst, and the mixture was stirred at 80°C for 4 h to obtain the product. The product was washed with ethanol, dialyzed, and dried. Then, 40% of polyethylene glycol by mass was added to the product, and the mixture was stirred and dispersed at 500 rpm for 10 min for standby use.

[0042] Se-CeO2 preparation method: Ce(NO3)3·6H2O and Na2SeO3 were mixed in a mass ratio of 1:9, and ammonia water with pH=10 was slowly injected into the mixture at a solid-liquid ratio of 1:3, and then placed in a hydrothermal reactor at 160°C for 12 hours. The product was centrifuged, washed, calcined at 600°C for 2 hours, and then ball milled to obtain Se-CeO2 powder with a particle size of 80-100 nm.

[0043] Positive electrode material: 0.5wt% Se-CeO2 nano powder and 0.5wt% stearic acid were added to the NCM333 positive electrode active material, ball milled at a speed of 300 rpm for 2h, heated at a rate of 5°C / min in an O2 atmosphere, and then heat treated at 700°C for 4h to obtain the positive electrode material.

[0044] PVDF was dissolved in NMP to prepare a binder with a mass concentration of 8%; 18 parts of a polymer conductive agent were added to 7 parts of the binder solution, stirred at 1800 rpm for 20 min, and then the positive electrode material was added in batches. First, 48 parts of the positive electrode material were added and stirred at a speed of 2500 rpm for 10 min. Then, 2% of the binder was supplemented, and another 48 parts of the positive electrode material was added and stirred for another 10 min. The stirring speed was then reduced to 200 rpm, and the mixture was stirred for 15 min to remove bubbles and form a uniform positive electrode slurry. The viscosity of the slurry was controlled at 8500 mPa·s. Then, the mixed slurry was coated on a carbon-coated aluminum foil current collector, dried at 120°C for 6h, and then the dried positive electrode sheet was compacted by a rolling machine to a compaction density of 2.4g / cm³. The active material loading of the obtained positive electrode sheet was 4.0mg / cm 2 The rolled positive electrode sheet was cut into small pieces of the desired size by a slitting machine for subsequent battery assembly.

[0045] Comparative Example 1

[0046] Polymer conductive agent preparation: 30 parts of MWCNTs were ultrasonically treated in 200 parts of anhydrous DMF with anthraquinone-2-carboxylic acid in a mass ratio of 1:2 for 20 min to form a uniform dispersion. Then, 50 parts of triethylamine were added as a catalyst, and the mixture was stirred at 80°C for 4h to obtain the product. The product was washed with ethanol, dialyzed, and dried. Then, 40% polyethylene glycol by mass was added to the product, and the mixture was stirred at 500 rpm for 10 min for use.

[0047] Se-CeO2 preparation method: Ce(NO3)3·6H2O and Na2SeO3 were mixed in a mass ratio of 1:9, and ammonia water with pH=10 was slowly injected into the mixture at a solid-liquid ratio of 1:3, and then placed in a hydrothermal reactor at 160°C for 12 hours. The product was centrifuged, washed, calcined at 600°C for 2 hours, and then ball milled to obtain Se-CeO2 powder with a particle size of 60-80 nm.

[0048] Positive electrode material: 1.0wt% Se-CeO2 nano powder, 0.5wt% stearic acid, ball milling speed 300 rpm, time 2h, in O2 atmosphere, heating rate 5℃ / min, 700℃ heat treatment for 4 hours to obtain the positive electrode material.

[0049] PVDF was dissolved in NMP to prepare a binder with a mass concentration of 10%; 16 parts of a polymer conductive agent was added to 8 parts of the binder solution, stirred at 1650 rpm for 25 min, and the positive electrode material was added in batches, first 44 parts of the positive electrode material was added, stirred and dispersed at a speed of 2650 rpm for 10 min, supplemented with 4% of the binder, then 50 parts of the positive electrode material was added, and the stirring and dispersion was continued for 10 min, then the speed was reduced to 200 rpm, and the uniform positive electrode slurry was formed after stirring for 15 min to defoam, the viscosity of the slurry was controlled at 7500 mPa·s, then the mixed slurry was coated on the carbon-coated aluminum foil current collector, dried at 120℃ for 6h, and the dried positive electrode sheet was compacted by a rolling machine to a compacted density of 2.8g / cm³, and the obtained positive electrode sheet had an active material loading of 7mg / cm 2 The rolled positive electrode sheet was cut into small pieces of the required size by a slitting machine for subsequent battery assembly.

[0050] Comparative Example 2

[0051] Preparation of polymer conductive agent: 18 parts of MWCNTs were placed in 65 parts of 70% concentrated HNO3 and ultrasonically treated at 70℃ for 3 hours, then cooled to room temperature, vacuum filtered, washed with deionized water until the pH of the filtrate was 7.0, and dried to obtain carboxylated MWCNTs. The carboxylated MWCNTs were dissolved in SOCl2 solution according to the solid-liquid ratio of 1:20, and refluxed at 70℃ for 6 hours to further acyl chloride to obtain the polymer conductive agent, and 40% polyethylene glycol by mass was added, and stirred and dispersed at 500 rpm for 10 min for standby use;

[0052] Preparation method of Se-CeO2: Ce(NO3)3·6H2O and Na2SeO3 were mixed according to a mass ratio of 1:9, and 1:3 of solid-liquid ratio of the mixture was slowly injected into ammonia water with pH=10, and placed in a hydrothermal reactor at 160℃ for 12 hours. The product was centrifuged and washed, calcined at 600℃ for 2 hours, and ball milled to obtain Se-CeO2 powder with a particle size of 50-80nm.

[0053] Positive electrode material: 1.0wt% Se-CeO2 nano powder, 0.5wt% stearic acid, ball milling speed 300 rpm, time 2h, in O2 atmosphere, heating rate 5℃ / min, 700℃ heat treatment for 4 hours to obtain the positive electrode material.

[0054] PVDF was dissolved in NMP to prepare a binder with a mass concentration of 10%; 16 parts of a polymer conductive agent was added to 8 parts of the binder solution, stirred at 1650 rpm for 25 min, and the cathode material was added in batches, 44 parts of the cathode material was first added, stirred and dispersed at a speed of 2650 rpm for 10 min, 4% of the binder was supplemented, and then 50 parts of the cathode material was added, and the stirring and dispersion was continued for 10 min, and then the speed was reduced to 200 rpm, and the stirring was continued for 15 min to defoam and form a uniform cathode slurry, the viscosity of the slurry was controlled at 7500 mPa·s, and then the mixed slurry was coated on a carbon-coated aluminum foil current collector, dried at 120℃ for 6h, and the dried cathode sheet was compacted by a rolling machine to a compacted density of 2.8g / cm³, and the active material loading of the obtained cathode sheet was 7mg / cm 2 The rolled cathode sheet was cut into small pieces of the required size by a slitting machine for subsequent battery assembly.

[0055] Comparative Example 3

[0056] 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.

[0057] Comparative Example 4

[0058] The difference between this comparative example and Example 1 is that 1.0wt% Se nanopowder and 0.5wt% stearic acid are added to the NCM523 cathode active material, the ball milling speed is 300 rpm, the time is 2h, the heat treatment is carried out in O2 atmosphere at a heating rate of 5℃ / min at 700℃ for 4 hours to obtain the cathode material; the rest is the same as Example 1.

[0059] Comparative Example 5

[0060] The difference between this comparative example and Example 1 is that 1.0wt% CeO2 nanopowder and 0.5wt% stearic acid are added to the NCM52 cathode active material, the ball milling speed is 300 rpm, the time is 2h, the heat treatment is carried out in O2 atmosphere at a heating rate of 5℃ / min at 700℃ for 4 hours to obtain the cathode material; the rest is the same as Example 1.

[0061] Comparative Example 6

[0062] The difference between this comparative example and Example 1 is that the Se-CeO2 preparation method: Ce(NO3)3·6H2O and Na2SeO3 are mixed according to a mass ratio of 3:7, and pH=10 ammonia water is slowly injected into the mixture according to a solid-liquid ratio of 1:3, and then the mixture is placed in a water bath at 160℃ for 12 hours of hydrothermal reaction, and then the product is centrifuged and washed, and then calcined at 600℃ for 2 hours, and then ball milled to obtain Se-CeO2 nanopowder with a particle size of 50-80nm; the rest is the same as Example 1.

[0063] Comparative Example 7

[0064] The difference between the present comparative example and Example 1 is the preparation method of Se-CeO2 in the present comparative example: Ce(NO3)3·6H2O and Na2SeO3 were mixed in a mass ratio of 1:1, and ammonia water with pH = 10 was slowly injected into the mixture at a solid-liquid ratio of 1:3, and then the mixture was placed in a hydrothermal reactor at 160°C for 12 hours. The product was centrifuged, washed, calcined at 600°C for 2 hours, and then ball-milled to obtain Se-CeO2 nanopowder with a particle size of 60-90 nm. The rest was the same as in Example 1.

[0065] Comparative Example 8

[0066] MWCNTs pretreatment: 18 parts of MWCNTs were placed in 65 parts of 70% concentrated 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 dried, and then dissolved in an SOCl2 solution at a solid-liquid ratio of 1:20 and refluxed at 70°C for 6 hours for further acyl chloride treatment.

[0067] Polymer conductive agent preparation: 30 parts of pretreated MWCNTs were ultrasonically treated in 200 parts of anhydrous DMF at a mass ratio of anthraquinone-2-carboxylic acid to MWCNTs of 1:2 to form a uniform dispersion. 50 parts of triethylamine was added as a catalyst, and the mixture was stirred at 80°C for 4 hours to obtain the product. The product was washed with ethanol, dialyzed, dried, and then 40% polyethylene glycol by mass was added. The mixture was stirred at 500 rpm for 10 minutes for dispersion and standby.

[0068] Se-CeO2 preparation method: Ce(NO3)3·6H2O and Na2SeO3 were mixed in a mass ratio of 1:9, and ammonia water with pH = 10 was slowly injected into the mixture at a solid-liquid ratio of 1:3. The mixture was placed in a hydrothermal reactor at 160°C for 12 hours. The product was centrifuged, washed, calcined at 600°C for 2 hours, and then ball-milled to obtain Se-CeO2 powder with a particle size of 90-100 nm.

[0069] Positive electrode material: 1.0 wt% of Se-CeO2 nanopowder and 0.5 wt% of stearic acid were added to NCM523 positive electrode active material, and the mixture was ball-milled at a speed of 300 rpm for 2 hours. The positive electrode material was obtained by heat treatment at 700°C for 4 hours in an O2 atmosphere at a heating rate of 5°C / min.

[0070] PVDF was dissolved in NMP to prepare a binder with a mass concentration of 10%; 8 parts of the binder, 16 parts of a polymer conductive agent, and 94 parts of a positive electrode material were stirred and dispersed at a speed of 2650 rpm for 10 min, 4% of the binder was then added, and stirring was continued at the same speed for another 15 min to form a uniform positive electrode slurry, the viscosity of the slurry was controlled at 7000 mPa·s, and then the mixed slurry was coated on a carbon-coated aluminum foil current collector, dried at 120°C for 6 h, and the dried positive electrode sheet was compacted by a rolling machine to a compacted density of 2.8 g / cm³, and the active material loading of the obtained positive electrode sheet was 7 mg / cm 2 The rolled positive electrode sheet was cut into small pieces of the required size by a slitting machine for subsequent battery assembly.

[0071] Test 1: battery performance test

[0072] A button cell was assembled in an argon-filled glove box, and a tester was used to perform charge-discharge cycle tests, the voltage window was 2.75-4.3 V, the initial efficiency under a 2C current density was tested, and the cycle performance under a 2C current density at different temperatures was tested; the different temperatures included room temperature (25°C) and high temperature (60°C).

[0073] The results are shown in Table 1 below:

[0074] Table 1

[0075]

Claims

1. A method for preparing a polymer lithium battery positive electrode sheet, characterized in that, The specific process is as follows: (1) Preparation of adhesive solution: Dissolve PVDF in NMP to prepare an adhesive solution with a mass concentration of 8%-12%; (2) Dispersing the polymer conductive agent: Add 40% of the polymer conductive agent by mass to 15-18 parts by mass of polyethylene glycol, and stir and disperse at 500 rpm for 10 minutes. (3) Preparation of positive electrode slurry: Add the dispersed polymer conductive agent obtained in step (2) to 7-10 parts by weight of binder solution, and stir at 1500-1800 rpm for 20-30 minutes; Add the cathode material in batches: First, add 40-48 parts by weight of the cathode material and stir and disperse at 2500-2800 rpm for 10 minutes; add 2-5% binder solution; then add 48-52 parts by weight of the cathode material and continue stirring and dispersing for 10 minutes; switch to low speed of 200 rpm and stir for 15 minutes to defoam, to obtain a cathode slurry with a viscosity of 6500-8500 mPa·s; (4) Coating and drying: Coat the slurry onto the carbon-coated aluminum foil current collector and bake at 120°C for 6 hours; (5) Rolling: The dried positive electrode sheet is rolled to a compaction density of 2.4-3.4 g / cm³ and an active material loading of 4.0-10.0 mg / cm²; (6) Slitting: The rolled positive electrode sheet is slitted into the required size; 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. The mixture is ultrasonically treated for 10-30 min to form a uniform dispersion. Then, 45-55 parts of triethylamine are added for catalysis, and the mixture is stirred at 80°C for 4 h to obtain the product. The product is washed with ethanol, dialyzed, and dried. The 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℃ for 2-4 hours. After cooling to room temperature, the mixture is vacuum filtered and washed with deionized water until the pH of the filtrate is 6.8-7.

3. The filtrate is then dried to obtain carboxylated MWCNTs. The carboxylated MWCNTs are then dissolved in SOCl2 solution at a material-to-liquid ratio of 1:20 and refluxed at 70℃ for 6 hours for further acylation. The positive electrode material is prepared by the following steps: adding 0.5-1.5 wt% of Se-CeO2 nanoparticles and 0.5 wt% of stearic acid to the positive electrode active material, and ball milling at 300 rpm for 2 hours; then heat-treating in an O2 atmosphere at 5℃ / min to 700℃ for 4 hours.

2. The method for preparing a polymer lithium battery positive electrode sheet according to claim 1, characterized in that: The preparation method of the Se-CeO2 nanopowder is as follows: Ce(NO3)3·6H2O and Na2SeO3 are mixed at 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℃ for 12 hours. The product is centrifuged and washed, and calcined at 600℃ for 2 hours to obtain Se-CeO2 nanopowder. The nanopowder is then ball-milled to obtain a particle size of 50-100nm.

3. The method for preparing a polymer lithium battery positive electrode sheet according to claim 1, characterized in that: The positive electrode active material is one or more of LiCoO2, NCM523 and NCM333.

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