Preparation method of lithium battery positive electrode material

Abstract

The invention discloses a preparation method of a lithium battery positive electrode material in the technical field of lithium battery processing. The preparation method comprises the following steps: mixing a binder and a liquid solvent to form a glue solution; mixing a lithium source material, a metal oxide precursor and a conductive agent to form a premixed material; extracting carbon dioxide for compression and condensation to form supercritical carbon dioxide; mixing the glue solution and the premixed material, introducing the supercritical carbon dioxide, and fully mixing to obtain mixed slurry; and after the mixed slurry is mixed, releasing the carbon dioxide in the mixing container until the pressure in the mixing container is recovered to atmospheric pressure, thereby obtaining the product. According to the invention, the metal oxide precursor can react with the positive electrode raw material in supercritical carbon dioxide to form a stable lithium metal oxide with a layered structure, and a stable lithium ion intercalation / deintercalation channel can be provided, so that the cycling stability and structural integrity of the material are improved; and the structural stability of the prepared positive electrode material is further improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium battery processing, and more specifically, relates to a method for preparing a lithium battery positive electrode material. Background Art

[0002] The positive electrode slurry of lithium batteries is to dissolve the binder in the solvent to form a glue, and then mechanically mix the glue with the positive electrode raw materials and the conductive agent in the slurry tank. In order for the slurry to achieve good viscosity, the amount of glue needs to be controlled; in order for the slurry to achieve good dispersion, it needs to be fully stirred in the slurry tank. To improve the dispersion of the slurry, it can be achieved by adding excess glue or extending the stirring time in the tank. However, adding excess glue will affect the viscosity of the slurry on the one hand, and on the other hand, it will also increase the baking pressure of the back-end coating oven; extending the stirring time in the tank will affect the production efficiency of the production line.

[0003] Supercritical carbon dioxide is a supercritical fluid that is converted when gaseous carbon dioxide is at a critical temperature of 31.26°C or above and a critical pressure of 7.29MPa. Supercritical carbon dioxide has a density close to that of liquid, a viscosity close to that of gas, and a diffusion coefficient 100 times that of liquid, and therefore has an amazing solubility.

[0004] However, the structural stability of traditional electrode materials after preparation is poor and it is difficult to meet higher usage requirements. Summary of the invention

[0005] The purpose of the present invention is to address the above shortcomings and provide a method for preparing a positive electrode material for a lithium battery, which solves the problem of poor structural stability of existing positive electrode materials by forming stable lithium metal oxides, improves the cycle stability and structural integrity of the material, and thereby improves the structural stability of the positive electrode material after preparation.

[0006] To achieve the above object, the present invention is implemented by the following technical solutions: The present invention discloses a method for preparing a positive electrode material for a lithium battery, comprising: Mixing the binder with the liquid solvent to form a glue solution; Mixing a lithium source material, a metal oxide precursor and a conductive agent to form a premixed material; Extracting carbon dioxide, compressing and condensing it to form supercritical carbon dioxide; The glue solution and the premixed material are mixed, and then the supercritical carbon dioxide is introduced to mix them thoroughly to obtain a mixed slurry; After the above mixed slurries are mixed, the carbon dioxide in the mixing container is released until the pressure in the mixing container returns to atmospheric pressure, thereby obtaining the desired positive electrode material.

[0007] In the above scheme, by adding a metal oxide precursor and mixing it with the positive electrode raw material (lithium source) during the slurrying process, the metal oxide precursor can react with the positive electrode raw material (lithium source) in supercritical carbon dioxide to form stable lithium metal oxides. These lithium metal oxides have a layered structure and can provide stable lithium ion insertion / deinsertion channels, thereby improving the cycle stability and structural integrity of the material, thereby improving the structural stability of the positive electrode material after preparation.

[0008] Furthermore, the mass ratio of the binder to the liquid solvent is 1:(1-5), the mixing temperature is 20°C-60°C, and the mixing time is 30min-120min.

[0009] In the above scheme, the mixing ratio of the binder and the liquid solvent directly affects the rheological properties and coating properties of the glue. A too low mixing ratio will result in insufficient binder content, affecting the mechanical strength and bonding properties of the electrode material; while a too high mixing ratio will result in excessive viscosity of the glue, making it difficult to coat evenly. The optimization of the mixing temperature and time can ensure that the binder is fully dissolved and evenly mixed with other electrode materials to form a stable glue. By precisely controlling the mixing ratio, temperature and time, the uniformity and stability of the glue can be further improved, ensuring the uniformity and consistency of the electrode material.

[0010] Furthermore, the binder is a PVDF (polyvinylidene fluoride) solution with a concentration of 5% to 15%; and the liquid solvent is a NMP solution with a concentration of 85% to 95%.

[0011] In the above scheme, the binder uses PVDF solution and the liquid solvent uses NMP solution. These two materials have good adhesion and solubility, and can effectively improve the uniformity and stability of the slurry. PVDF (polyvinylidene fluoride) is a commonly used lithium battery positive electrode binder with excellent chemical stability, mechanical strength and adhesion performance. It can form a uniform network structure in the electrode material, thereby improving the mechanical strength and electrochemical properties of the electrode. NMP (N-methylpyrrolidone) is an efficient organic solvent that can effectively dissolve PVDF and evenly mix with other electrode materials (such as active substances and conductive agents) to form a stable slurry. By optimizing the ratio of PVDF and NMP, the rheological properties and coating properties of the slurry can be further improved to ensure the uniformity and consistency of the electrode material. The concentration range of PVDF and NMP can ensure good solubility and dispersibility of the binder and solvent, while avoiding excessive slurry viscosity caused by too high concentration; specifically, too low PVDF concentration will lead to insufficient binder content, affecting the mechanical strength and bonding properties of the electrode material; while too high PVDF concentration will lead to excessive slurry viscosity, making it difficult to coat evenly. Optimization of NMP concentration can ensure full dissolution of PVDF and uniform mixing with other electrode materials to form a stable slurry. By precisely controlling the concentrations of PVDF and NMP, the rheological properties and coating properties of the slurry can be further improved to ensure the uniformity and consistency of the electrode material.

[0012] Furthermore, the adhesive is mixed with the liquid solvent to form the glue solution, specifically, the adhesive is added into the adhesive tank, the liquid solvent is added into the solvent tank, and the adhesive and the liquid solvent are respectively sent into the glue making tank for preliminary mixing to form the glue solution.

[0013] Using different tanks to store different raw materials makes it easier to observe the state of the raw materials and accurately measure them, control the reaction to proceed smoothly, reduce work errors, and improve the yield rate.

[0014] Furthermore, the mass ratio of the lithium source material, the metal oxide precursor and the conductive agent is 1: (0.1-0.5): (0.05-0.2), the mixing temperature is 20°C-60°C, and the mixing time is 30 min-120 min.

[0015] This condition can ensure the uniformity and electrochemical properties of the premixed materials. Specifically, the mixing ratio of lithium source materials, metal oxide precursors and conductive agents directly affects the electrochemical properties and process performance of electrode materials. Too low a mixing ratio will lead to insufficient conductive agent content, affecting the conductive properties of the electrode material; while too high a mixing ratio will lead to excessive conductive agent content, affecting the specific capacity of the electrode material. Optimization of mixing temperature and time can ensure uniform mixing of materials and form a stable mixed material.

[0016] Furthermore, the lithium source material includes LiOH or Li2CO3; the metal oxide precursor is CoO, NiO or MnO; and the conductive agent is a carbon black conductive agent, a graphite conductive agent or a carbon nanotube.

[0017] The above-mentioned lithium source materials and metal oxide precursors can form lithium metal oxides with high specific capacity and good conductivity during the reaction process, such as: LiCoO2 has a high specific capacity (about 140mAh / g) and excellent cycle performance, LiNiO2 has a higher specific capacity (about 180-200mAh / g), but needs to be doped with other elements (such as Co, Mn) to improve stability, LiMnO2 is low-cost and environmentally friendly, but has a low specific capacity (about 100-120mAh / g). These lithium metal oxides have a layered structure and can provide stable lithium ion insertion / deinsertion channels, thereby improving the cycle stability and structural integrity of the material. In addition, CoO, NiO and MnO have high specific capacity and good conductivity, which can significantly improve the energy density and power density of lithium batteries. Carbon black conductive agents can choose acetylene black or conductive carbon black, and their advantages are: good conductivity, can effectively improve the overall electronic conductivity of the positive electrode material, small particle size, large specific surface area, good dispersibility, and can be evenly distributed in the positive electrode material; graphite conductive agents can choose natural graphite or expanded graphite, and their advantages are: good conductivity, moderate price, easy processing, and suitable for large-scale industrialization; the advantages of carbon nanotubes are: excellent conductivity and mechanical properties, can form a three-dimensional conductive network, and a low addition amount (usually <1%) can significantly improve the conductive properties of the material.

[0018] Furthermore, the particle size of the metal oxide precursor is 0.1 μm to 10 μm, and the specific surface area is 10 m² / g to 100 m² / g.

[0019] The particle size and specific surface area range of the metal oxide precursor can ensure the high specific capacity and good electrochemical performance of the material. Specifically, a smaller particle size and a higher specific surface area can increase the active sites of the material and increase the insertion / deinsertion rate of lithium ions, thereby improving the rate performance of the material. In addition, a smaller particle size can shorten the diffusion path of lithium ions and improve the electrochemical performance of the material. However, a particle size that is too small may cause agglomeration of the material, affecting the uniformity and coating performance of the slurry. Therefore, by optimizing the particle size and specific surface area of ​​the metal oxide precursor, the electrochemical performance and process performance of the positive electrode material can be further improved.

[0020] Furthermore, the mixing of the lithium source material, the metal oxide precursor and the conductive agent to form a premixed material comprises: adding the lithium source material and the metal oxide precursor to the positive electrode raw material tank, adding the conductive agent to the conductive agent material tank, and respectively sending the lithium source material, the metal oxide precursor and the conductive agent into the material premixing tank for mixing to form the premixed material.

[0021] The lithium source material is first mixed with the metal oxide precursor and then with the conductive agent, which is beneficial to first forming a layered lithium metal oxide and avoiding other adverse reactions caused by direct mixing.

[0022] Furthermore, the extracting of carbon dioxide for compression and condensation to form supercritical carbon dioxide includes: extracting carbon dioxide from a carbon dioxide storage tank through a compressor for compression, the gas in the compression process passes through a condenser to form supercritical carbon dioxide, and is stored in a carbon dioxide tank.

[0023] In the above scheme, the carbon dioxide storage tank is used to store low-pressure carbon dioxide fresh gas. The tank body should be able to meet the relevant requirements of gas pressure vessels and observe the changes in the gas volume in the tank; the compressor is used to increase the gas pressure, at least pressurize the gaseous carbon dioxide to the pressure required for the supercritical state; the condenser is set at the rear end of the compressor, which is used to control the temperature above the critical temperature of supercritical carbon dioxide, while also considering the temperature required for the slurry process production; the supercritical carbon dioxide tank always maintains the conditions required for supercritical carbon dioxide, and is used to cache supercritical carbon dioxide to ensure that the carbon dioxide is always in a supercritical state.

[0024] Furthermore, the pressure of the supercritical carbon dioxide is controlled at 7 MPa to 40 MPa, and the gas temperature is controlled at 30° C. to 80° C.

[0025] This condition can ensure that the carbon dioxide is in a supercritical state, with high diffusivity and low surface tension, which is conducive to the uniform dispersion of materials. Specifically, the high diffusivity of supercritical carbon dioxide can promote the uniform mixing of metal oxide precursors and lithium sources at the molecular level, thereby avoiding the agglomeration phenomenon common in traditional wet processes. In addition, the low surface tension of supercritical carbon dioxide can reduce the interfacial energy of the material, promote the self-assembly of nanostructures, and form lithium metal oxides with high specific surface area and abundant active sites. By precisely controlling the pressure and temperature of carbon dioxide, the morphology and structure of the material can be further optimized, thereby improving its electrochemical performance.

[0026] Furthermore, the mass ratio of the glue solution to the premixed material is 1:(1-3), and the amount of supercritical carbon dioxide added is 5%-20% of the total weight of the mixed slurry; wherein the total weight of the mixed slurry includes the weight of the supercritical carbon dioxide.

[0027] This condition can ensure the uniformity of the slurry and the effective use of supercritical carbon dioxide. Specifically, the mixing ratio of the glue and the premixed material directly affects the rheological properties and coating properties of the slurry. A too low mixing ratio will result in excessive slurry viscosity, making it difficult to coat evenly; while a too high mixing ratio will result in too low slurry viscosity, affecting the mechanical strength of the electrode material. The addition of supercritical carbon dioxide can further optimize the dispersion and uniformity of the slurry and ensure uniform mixing of the materials.

[0028] Furthermore, the glue, premixed materials and supercritical carbon dioxide are placed in a slurry mixing tank for mixing, and after the mixing is completed, the slurry mixing exhaust valve is opened to exhaust.

[0029] In the above scheme, the gaseous high-pressure carbon dioxide in the mixing tank is depressurized and discharged. During this process, the supercritical carbon dioxide in the slurry precipitates out of the slurry in the form of cavitations, and the cavitations burst to generate mechanical energy, which further mixes the slurry and improves the dispersion and uniformity of the slurry.

[0030] Furthermore, the exhaust time is 10 to 30 minutes, and the temperature in the mixing tank is controlled at 20° C. to 40° C. during the exhaust process.

[0031] This condition can ensure the complete removal of carbon dioxide while avoiding the impact of excessive temperature on material properties. Specifically, the optimization of exhaust time can ensure the complete removal of carbon dioxide and avoid the impact of residual carbon dioxide on material properties. The control of exhaust temperature can avoid material decomposition or performance degradation caused by excessive temperature. The supercritical state is destroyed during exhaust, and the control of 20℃~40℃ is to stabilize the slurry properties.

[0032] Compared with the prior art, the present invention has the following beneficial effects: The present invention adds a metal oxide precursor to the positive electrode material during the slurrying process for mixing. The metal oxide precursor can react with the positive electrode raw material (lithium source) in supercritical carbon dioxide to form a stable lithium metal oxide. The lithium metal oxide has a layered structure and can provide a stable lithium ion embedding / de-embedding channel, thereby improving the cycle stability and structural integrity of the material, and further improving the structural stability of the positive electrode material after preparation. The superior solubility and diffusivity of supercritical carbon dioxide can promote the uniform mixing of metal oxide precursors and lithium sources at the molecular level. By adjusting the reaction conditions (such as temperature, pressure, concentration and reaction time), lithium metal oxides can be induced to form specific nanostructures (such as nanoparticles, nanowires or nanosheets). These nanostructures have high specific surface areas and abundant active sites, which can significantly improve the electrochemical properties of the materials. Supercritical carbon dioxide as a reaction medium can achieve uniform dispersion and reaction of metal oxide precursors and lithium sources, thereby avoiding the agglomeration and unevenness common in traditional wet processes. This uniformity can improve the consistency of the material and ensure the stability and reliability of battery performance. The inert environment of supercritical carbon dioxide can reduce the occurrence of side reactions and avoid the generation of impurities. For example, in traditional wet processes, organic solvents (such as NMP) may react with metal oxide precursors, resulting in a decrease in material performance. Supercritical carbon dioxide, as an inert medium, can effectively avoid this problem. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 A process flow chart of a method for preparing a positive electrode material for a lithium battery provided in an embodiment of the present invention; Figure 2 It is a schematic diagram of the overall structure of the lithium battery positive electrode material preparation system described in the embodiment; Figure 3 It is a structural schematic diagram of the liquid slurry premixing system described in the embodiment; Figure 4 It is a structural schematic diagram of the solid slurry premixing system described in the embodiment; Figure 5 It is a structural schematic diagram of the supercritical carbon dioxide supply and recycling system described in the embodiment; Figure 6 It is a schematic diagram of the structure of the slurry mixing system described in the embodiment.

[0034] In the figure: 1. adhesive tank; 101. adhesive valve; 2. solvent tank; 201. solvent valve; 3. glue tank; 301. glue valve; 4. glue liquid tank; 401. glue liquid valve; 5. slurry tank; 501. slurry exhaust valve 1; 502. slurry exhaust valve 2; 6. conductive agent material tank; 601. conductive agent material valve; 7. positive electrode raw material tank; 701. positive electrode material valve; 8. supercritical carbon dioxide tank; 801. supercritical carbon dioxide valve; 9. material premix tank; 9. material premix valve; 10. expansion valve; 11. evaporator; 12. slurry recovery pipe; 13. carbon dioxide recovery tank; 1301. carbon dioxide recovery outlet valve; 1302. carbon dioxide recovery inlet check valve; 14. carbon dioxide storage tank; 1401. carbon dioxide storage valve; 15. compressor; 16. condenser; 17. vacuum pump. DETAILED DESCRIPTION

[0035] The preferred embodiments of the present invention will be described in more detail below in conjunction with the accompanying drawings and specific examples.

[0036] Example 1 This embodiment provides a method for preparing a positive electrode material for a lithium battery. Figure 1 As shown, including: Liquid slurry premixing process: mixing the binder with the liquid solvent to form a glue solution; Solid slurry premixing process: mixing lithium source material, metal oxide precursor and conductive agent to form a premixed material; Preparation of supercritical carbon dioxide: extract carbon dioxide, compress it, and condense it to form supercritical carbon dioxide; Slurry mixing process: mixing the above-mentioned glue solution and premixed materials, and then introducing the above-mentioned supercritical carbon dioxide to fully mix to obtain a mixed slurry; Exhaust process: After the above-mentioned mixed slurry is mixed, the carbon dioxide in the mixing container is released until the pressure in the mixing container returns to atmospheric pressure to obtain the desired positive electrode material.

[0037] Specifically, the preparation method comprises the following steps: Liquid slurry premixing process: add 1 kg of 5% PVDF solution into the binder tank 1, add 1 kg of 85% NMP solution into the solvent tank 2, and then send the PVDF solution and the NMP solution into the glue tank 3 for preliminary mixing to form glue solution; the mixing temperature is 20°C and the mixing time is 120 min; Solid slurry premixing process: add 1KG LiOH and 0.1kg CoO powder to the positive electrode raw material tank 7, add 0.05kg conductive carbon black to the conductive agent material tank 6, and send LiOH, CoO and the conductive agent to the material premixing tank 9 for mixing to form a premixed material; the mixing temperature is 20°C and the mixing time is 120min; the particle size of the CoO powder is 0.1μm~10μm, and the specific surface area is 10m² / g~100m² / g; Preparation of supercritical carbon dioxide: The compressor 15 extracts carbon dioxide from the carbon dioxide storage tank 14 for compression, and the gas in the compression process passes through the condenser 16 to form supercritical carbon dioxide, which is stored in the carbon dioxide tank; the pressure of the supercritical carbon dioxide is 7Mpa and the temperature is 30°C; Slurry mixing process: first, 1 kg of glue and 1 kg of premixed material are sent to the slurry mixing tank 5 for mixing, and then 0.12 kg of supercritical carbon dioxide is sent to the slurry mixing tank 5 for full mixing to obtain a mixed slurry; Exhaust process: After the mixing is completed, open the slurry exhaust valve 501 to release the carbon dioxide inside the slurry tank 5. The exhaust time is 10 minutes and the temperature is 20°C; until the pressure in the slurry tank 5 returns to atmospheric pressure, the required positive electrode material is obtained.

[0038] Example 2 This embodiment provides a method for preparing a positive electrode material for a lithium battery, which specifically includes the following steps: Liquid slurry premixing process: add 1kg of 10% PVDF solution into the binder tank 1, add 3kg of 90% NMP solution into the solvent tank 2, and then send the PVDF solution and the NMP solution into the glue tank 3 for preliminary mixing to form glue solution; the mixing temperature is 40°C and the mixing time is 60min; Solid slurry premixing process: add 2KG LiOH and 0.6kg MnO powder to the positive electrode raw material tank 7, add 0.2kg carbon nanotubes to the conductive agent material tank 6, and send LiOH, MnO and the conductive agent to the material premixing tank 9 for mixing to form a premixed material; the mixing temperature is 40°C and the mixing time is 60min; the particle size of the MnO powder is 0.1μm~10μm, and the specific surface area is 10m² / g~100m² / g; Preparation of supercritical carbon dioxide: The compressor 15 extracts carbon dioxide from the carbon dioxide storage tank 14 for compression, and the gas in the compression process passes through the condenser 16 to form supercritical carbon dioxide, which is stored in the carbon dioxide tank; the pressure of the supercritical carbon dioxide is 20MPa and the gas temperature is 50°C; Slurry mixing process: first, 1 kg of glue and 2 kg of premixed materials are sent to the slurry mixing tank 5 for mixing, and then 0.35 kg of supercritical carbon dioxide is sent to the slurry mixing tank 5 for full mixing to obtain a mixed slurry; Exhaust process: After mixing is completed, open the slurry exhaust valve 501 to release the carbon dioxide inside the slurry tank 5. The exhaust time is 20 minutes and the temperature is 30°C; until the pressure in the slurry tank 5 returns to atmospheric pressure, the required positive electrode material is obtained.

[0039] Example 3 This embodiment provides a method for preparing a positive electrode material for a lithium battery, which specifically includes the following steps: Liquid slurry premixing process: add 1kg of 15% PVDF solution into the binder tank 1, add 5kg of 95% NMP solution into the solvent tank 2, and then send the PVDF solution and the NMP solution into the glue tank 3 for preliminary mixing to form glue solution; the mixing temperature is 60°C and the mixing time is 30min; Solid slurry premixing process: add 3KG Li2CO3 and 1.5kg NiO powder to the positive electrode raw material tank 7, add 0.6kg natural graphite to the conductive agent material tank 6, and send Li2CO3, NiO and the conductive agent to the material premixing tank 9 for mixing to form a premixed material; the mixing temperature is 60°C and the mixing time is 30min; the particle size of the NiO powder is 0.1μm~10μm, and the specific surface area is 10m² / g~100m² / g; Preparation of supercritical carbon dioxide: The compressor 15 extracts carbon dioxide from the carbon dioxide storage tank 14 for compression, and the gas in the compression process passes through the condenser 16 to form supercritical carbon dioxide, which is stored in the carbon dioxide tank; the pressure of the supercritical carbon dioxide is 40MPa and the gas temperature is 80°C; Slurry mixing process: first, 1 kg of glue and 3 kg of premixed materials are sent to the slurry mixing tank 5 for mixing, and then 1 kg of supercritical carbon dioxide is sent to the slurry mixing tank 5 for full mixing to obtain a mixed slurry; Exhaust process: After the mixing is completed, open the slurry exhaust valve 501 to release the carbon dioxide inside the slurry tank 5. The exhaust time is 30 minutes and the temperature is 40°C; until the pressure in the slurry tank 5 returns to atmospheric pressure, the required positive electrode material is obtained.

[0040] Example 4 This embodiment provides a lithium battery positive electrode material preparation system for implementing the preparation method described in Example 1, Example 2 or Example 3, such as Figure 2 As shown, it includes a binder tank 1, a solvent tank 2, a glue making tank 3, a glue liquid tank 4, a slurry mixing tank 5, a conductive agent material tank 6, a positive electrode raw material tank 7, a supercritical carbon dioxide tank 8, a material premixing tank 9, an expansion valve 10, an evaporator 11, a slurry recovery pipe 12, a carbon dioxide recovery tank 13, a carbon dioxide storage tank 14, a compressor 15, a condenser 16, a vacuum pump 17 and connecting pipes and control valves between various components.

[0041] like Figures 2 to 6 As shown, during the preparation process, the operation process of the preparation system is as follows: like Figure 3 As shown, in the liquid slurry premixing system, the binder tank 1 stores the binder PVDF, and the solvent tank 2 stores the liquid solvent NMP. When mixing the slurry, the binder valve 101 and the solvent valve 201 are opened, and the PVDF and NMP enter the glue tank 3 in proportion, and are preliminarily mixed in the glue tank 3 to form a glue solution; after the mixing is completed, the glue valve 301 is opened, and the glue solution enters the glue liquid tank 4 for temporary storage, and the glue liquid tank 4 is stirred at a low speed to prevent sedimentation.

[0042] like Figure 4 As shown, in the solid slurry premixing system, the conductive agent material tank 6 stores solid powder conductive agent, and the positive electrode raw material tank 7 stores lithium source solid powder and metal oxide precursor powder. When the solid slurry is premixed, the conductive agent material valve 601 and the positive electrode material valve 701 are opened, and the conductive agent and lithium iron phosphate powder enter the material premixing tank 9 in proportion, and then the conductive agent material valve 601 and the positive electrode material valve 701 are closed.

[0043] like Figure 5 As shown, in the supercritical carbon dioxide supply and reuse system, the carbon dioxide recovery outlet valve 1301 is closed, the carbon dioxide storage valve 1401 is opened, and the compressor 15 starts to work, extracting the low-pressure carbon dioxide in the carbon dioxide storage tank 14 for compression, and the gas heat generated during the compression process controls the gas temperature through the condenser 16 to form supercritical carbon dioxide, which is temporarily stored in the supercritical carbon dioxide tank 8. The tank body material of the supercritical carbon dioxide tank 8 is selected from materials that do not participate in the reaction, and the tank body adopts a double-layer insulation tank body. The tank body should be able to withstand a pressure of at least 7.29MPa, and the tank body is equipped with a temperature control system to control the temperature inside the tank at a constant temperature.

[0044] like Figure 6 As shown, in the slurry mixing system, when slurry mixing starts, the slurry mixing exhaust valve 1 501 and the slurry mixing exhaust valve 2 502 are closed, and the glue valve 401 and the material premixing valve 9 are opened to make the materials preliminarily mixed in the slurry mixing tank 5, and the corresponding valves are closed after the materials are added; Open the supercritical carbon dioxide valve 801 to allow the supercritical carbon dioxide to enter the slurry tank 5. The compressor 15 continuously replenishes carbon dioxide to maintain the tank pressure. The slurry tank 5 starts the temperature control system to maintain the temperature in the slurry tank 5, so that the carbon dioxide in the tank is always kept in a supercritical state, and the supercritical carbon dioxide and the slurry are fully mixed in the entire slurry tank 5. The tank material of the slurry tank 5 is selected from wear-resistant materials that do not participate in the reaction. The tank body should be able to withstand at least 7.29MPa positive pressure and 0.05MPa negative pressure; the tank body adopts a double-layer insulation tank body, and the tank body is equipped with a temperature control system to control the increase and decrease of the temperature in the slurry tank 5; the tank body should include a pressure detection and temperature detection system for monitoring the pressure and temperature in the tank; the tank body stirring system adopts magnetic coupling connection to ensure the air tightness of the tank body; all inlets and outlets of the tank body are connected by sealing flanges to ensure the air tightness of the tank body; the pipes and valves directly connected to the tank body should all use high-pressure pipes and high-pressure valves.

[0045] After a certain period of stirring, the compressor 15 is turned off to reduce the temperature in the slurry mixing tank 5, destroying the critical condition, and the carbon dioxide is converted from the supercritical state to the gaseous state. The mixed slurry falls back to the bottom, and the carbon dioxide is precipitated from the slurry in the form of gas cavitations and bursts during the precipitation process. The mechanical energy of the cavitation rupture further stirs the slurry to make the mixing more uniform.

[0046] Open the slurry mixing exhaust valve 1 501 to release the carbon dioxide in the tank, and the pressure in the slurry mixing tank 5 is restored to atmospheric pressure. Then close the slurry mixing exhaust valve 1 501, open the slurry mixing exhaust valve 2 502, and start the vacuum pump 17 to fully release the gas in the slurry until the slurry mixing step is completed.

[0047] It should be noted that during the entire slurry mixing process, the stirring paddle in the slurry mixing tank 5 is always rotating to prevent the slurry from being separated into layers. The stirring paddle in the slurry mixing tank 5 is driven by a motor using magnetic coupling to ensure the air tightness of the slurry mixing tank 5. The carbon dioxide entering the evaporator 11 will carry a portion of the slurry, and will be discharged from the slurry recovery pipe 12 when it is cooled at the bottom of the evaporator 11. An expansion valve 10 is also provided between the evaporator 11 and the slurry mixing tank 5, and a carbon dioxide recovery inlet check valve 1302 is provided between the evaporator 11 and the carbon dioxide recovery tank 13; The air inlet of the carbon dioxide recovery tank 13 is provided with a gas one-way valve to prevent the gas in the tank from flowing back. The collected atmospheric pressure carbon dioxide first enters the compressor 15 for compression, and the insufficient amount is supplemented by the low-pressure carbon dioxide.

[0048] The embodiments of the present invention have been described above, and the above description is exemplary, not exhaustive, and is not limited to the disclosed embodiments. Without departing from the scope and technical principles of the described embodiments, many modifications and changes are obvious to those of ordinary skill in the art, and these modifications and changes should also be regarded as the scope of protection of the present invention.

Claims

1. A method for preparing a positive electrode material for a lithium battery, characterized in that: include: Mixing the binder with the liquid solvent to form a glue solution; Mixing a lithium source material, a metal oxide precursor and a conductive agent to form a premixed material; Extracting carbon dioxide, compressing and condensing it to form supercritical carbon dioxide; The glue solution and the premixed material are mixed, and then the supercritical carbon dioxide is introduced to mix them thoroughly to obtain a mixed slurry; After the above mixed slurries are mixed, the carbon dioxide in the mixing container is released until the pressure in the mixing container returns to atmospheric pressure, thereby obtaining the desired positive electrode material.

2. The method for preparing a positive electrode material for a lithium battery according to claim 1, characterized in that: The mass ratio of the binder to the liquid solvent is 1:(1-5), the mixing temperature is 20°C-60°C, and the mixing time is 30min-120min.

3. The method for preparing a positive electrode material for a lithium battery according to claim 2, characterized in that: The binder is a PVDF solution with a concentration of 5% to 15%; the liquid solvent is a NMP solution with a concentration of 85% to 95%.

4. The method for preparing a positive electrode material for a lithium battery according to claim 1, characterized in that: The step of mixing the binder with the liquid solvent to form a glue solution is specifically as follows: Add adhesive into the adhesive tank, add liquid solvent into the solvent tank, and send the adhesive and liquid solvent into the glue making tank respectively to be preliminarily mixed to form glue solution.

5. The method for preparing a positive electrode material for a lithium battery according to claim 1, characterized in that: The mass ratio of the lithium source material, the metal oxide precursor and the conductive agent is 1: (0.1-0.5): (0.05-0.2), the mixing temperature is 20° C.-60° C., and the mixing time is 30 min-120 min.

6. The method for preparing a positive electrode material for a lithium battery according to claim 5, characterized in that: The lithium source material includes LiOH or Li2CO3; the metal oxide precursor is CoO, NiO or MnO; and the conductive agent is a carbon black conductive agent, a graphite conductive agent or a carbon nanotube.

7. The method for preparing a positive electrode material for a lithium battery according to claim 6, characterized in that: The metal oxide precursor has a particle size of 0.1 μm to 10 μm and a specific surface area of ​​10 m² / g to 100 m² / g.

8. The method for preparing a positive electrode material for a lithium battery according to claim 1, characterized in that: The method of mixing the lithium source material, the metal oxide precursor and the conductive agent to form a premixed material comprises: Lithium source material and metal oxide precursor are added to the positive electrode raw material tank, and conductive agent is added to the conductive agent material tank. The lithium source material, metal oxide precursor and conductive agent are respectively sent to the material premixing tank for mixing to form a premixed material.

9. The method for preparing a positive electrode material for a lithium battery according to claim 1, characterized in that: The extraction of carbon dioxide, compression and condensation to form supercritical carbon dioxide comprises: The carbon dioxide in the carbon dioxide storage tank is extracted by a compressor and compressed. The gas in the compression process passes through a condenser to form supercritical carbon dioxide, which is stored in a carbon dioxide tank.

10. The method for preparing a positive electrode material for a lithium battery according to claim 9, characterized in that: The pressure of the supercritical carbon dioxide is controlled at 7 MPa-40 MPa, and the gas temperature is controlled at 30° C.-80° C.

11. The method for preparing a positive electrode material for a lithium battery according to claim 1, characterized in that: The mass ratio of the glue solution to the premixed material is 1:(1-3), and the amount of supercritical carbon dioxide added is 5%-20% of the total weight of the mixed slurry.

12. The method for preparing a positive electrode material for a lithium battery according to claim 1, characterized in that: The glue, premixed materials and supercritical carbon dioxide are placed in a slurry mixing tank for mixing, and after the mixing is completed, the slurry mixing exhaust valve is opened for exhaust.

13. The method for preparing a positive electrode material for a lithium battery according to claim 12, characterized in that: The exhaust time is 10 to 30 minutes, and the temperature in the mixing tank is controlled at 20° C. to 40° C. during the exhaust process.

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