Preparation process of cathode material
By performing programmed solvothermal reactions and heat treatments on a three-dimensional porous conductive substrate, the problems of poor bonding and low transport efficiency in the preparation of traditional cathode materials were solved, realizing the integration of active materials and conductive framework and improving the electrochemical performance of the battery.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHENGDU ZHIWEI TANZHI MEDICAL TECHNOLOGY CO LTD
- Filing Date
- 2026-02-27
- Publication Date
- 2026-05-19
AI Technical Summary
Traditional cathode material preparation processes often result in weak bonding between the active material and the current collector, limiting electron and ion transport efficiency. Existing improved methods have failed to achieve integrated processing of the active material and the conductive carrier.
A three-dimensional porous conductive substrate is used for pretreatment to prepare a homogeneous precursor solution. Through programmed solvothermal reaction and heat treatment, the nucleation and growth of active materials are controlled to form a tightly bound composite, eliminating the need for powder preparation, mixing and binder steps, and directly obtaining an integrated electrode structure.
This achieves uniform coverage of active materials on the conductive framework, shortens the ion diffusion distance, provides a three-dimensional continuous conductive network, improves charge transport inside the electrode, and enhances battery performance.
Smart Images
Figure CN122067967A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of electrochemical energy storage materials technology, and more specifically, to a process for preparing a cathode material. Background Technology
[0002] In electrochemical energy storage devices such as lithium-ion and sodium-ion batteries, the microstructure, conductivity, and interfacial bonding strength between the cathode material and the current collector are crucial factors affecting its rate performance and cycle stability. Traditional cathode materials are often prepared by coating a mixture of micron-sized active material powder, conductive agent, and binder onto a metal foil current collector. This process suffers from problems such as insufficient contact between the active material and the conductive agent, the binder potentially hindering ion transport, and easy peeling of the coating from the current collector interface, limiting further improvements in battery performance.
[0003] To address these issues, existing technologies have proposed various improvement schemes. For example, Chinese patent CN116864703A discloses a method for preparing fuel cell cathode materials using the molten salt method, aiming to improve powder dispersion and conductivity. However, this method still focuses on preparing powder materials, and subsequent molding still requires processes such as binders, failing to achieve integrated integration of active materials and conductive carriers. Another example is Chinese patent CN116706028A, which discloses a method for improving the performance of lithium iron phosphate cathode materials by introducing CuO to repair the carbon coating network. This method focuses on surface modification but does not change the basic electrode structure of the powder coating, and its electron transport path still suffers from interfacial impedance problems. Therefore, developing a novel cathode preparation process that can achieve in-situ integration of active materials and conductive frameworks and construct an efficient synergistic transport network is an urgent problem to be solved. Therefore, a cathode material preparation process is proposed to address the above problems. Summary of the Invention
[0004] In order to overcome the above-mentioned defects of the prior art, the embodiments of the present invention provide a cathode material preparation process to solve the technical problems of insufficient dispersion of active material, poor bonding with current collector, and the resulting limited electron and ion transport efficiency in traditional powder coating processes.
[0005] To achieve the above objectives, the present invention provides the following technical solution: a cathode material preparation process, comprising steps S1 to S4: S1: The three-dimensional porous conductive substrate is pretreated to remove surface impurities, organic matter and oxides, and to improve its surface activity and wettability. The pretreatment includes sequential acid washing, alkali washing, ultrasonic cleaning with deionized water, and a first heat treatment in a protective atmosphere. S2: Prepare a homogeneous precursor solution to provide a stoichiometric source of metal ions and prevent premature precipitation of metal ions and stabilize the solution system through the complexation of organic ligands. The solution contains a lithium source compound, at least two transition metal source compounds and a bifunctional organic ligand. S3: The matrix treated by S1 is completely immersed in the precursor solution prepared in S2, and a programmed solvothermal reaction is performed in a closed reaction vessel. The solvothermal conditions are used to promote the decomposition and reaction of the precursor, and the uniform nucleation of the active material precursor on the surface of the matrix and the subsequent crystal directional growth kinetics are controlled by the staged temperature conditions. The reaction includes at least two stages with different heating rates and isothermal temperatures. S4: The matrix after the S3 reaction is cleaned and dried to remove soluble byproducts and residual reactants. Then, a programmed heat treatment is performed. Through staged heating under different atmospheres, the organic components and nitrates are completely decomposed, the amorphous precursor is transformed into a crystalline intermediate phase, and the final target active material crystals are grown, the crystallinity is improved, and the interfacial chemical bonding between the active material and the conductive matrix is strengthened under a controlled reducing atmosphere. This heat treatment includes a first heating and isothermal stage in an oxidizing atmosphere and a second heating and isothermal stage in a reducing or inert atmosphere.
[0006] Furthermore, step S2 specifically includes sub-steps S21 to S23: S21: Dissolve the lithium source compound and part of the bifunctional organic ligand in a first solvent to form a first solution, and stir at a temperature L1 for a time T1 to promote the pre-complexation of lithium ions and ensure their full dissolution. The temperature L1 is 40°C to 60°C and the time T1 is 30 minutes to 90 minutes. S22: Dissolve the at least two transition metal source compounds and the remaining bifunctional organic ligands in a second solvent to form a second solution, ensuring that all transition metal ions are effectively complexed; S23: Under continuous stirring and temperature L1, the second solution is added dropwise to the first solution at a constant dropping rate V. Slow mixing is used to avoid local high concentrations that could lead to precipitation, ensuring that different metal ions are uniformly mixed and co-complexed at the molecular level. After the addition is complete, stirring is continued for time T2 to complete the aging of the precursor solution, promoting the complex structure to become more homogeneous and stable, forming the homogeneous precursor solution. V is 1 drop per second to 3 drops per second, and T2 is 2 hours to 6 hours.
[0007] Furthermore, the procedural heat treatment in step S4 specifically includes sub-steps S41 to S43: S41: In the first heating and isothermal stage, the dried matrix is placed in a tube furnace and heated from room temperature to temperature T3 at a rate of R1 under an oxygen-containing atmosphere with a flow rate of F1, and held at that temperature for a time of t3. Oxygen is used to promote the oxidative decomposition of residual organic ligands and nitrate ions, while simultaneously causing the amorphous precursor to initially transform into an oxide crystalline phase. The values of F1 are 100 mL / s to 300 mL / s, R1 is 3 °C / min to 8 °C / min, T3 is 350 °C to 480 °C, and t3 is 2 hours to 4 hours. S42: Intermediate transition stage, the atmosphere is switched to an inert atmosphere with a flow rate of F2, and the temperature is reduced from T3 to T4 at a rate of R2, wherein F2 is 50 mL / s to 150 mL / s, R2 is 5°C / min to 15°C / min, and T4 is 200°C to 280°C; this stage of cooling under inert gas protection can prevent the intermediate product from being over-oxidized during the cooling process and create a suitable starting temperature and atmosphere environment for the next stage; S43: In the second heating and isothermal stage, the atmosphere is switched to a reducing mixed atmosphere with a flow rate of F3, and the temperature is increased from T4 to T5 at a rate of R3, and held at a constant temperature for a time t4. In the presence of reducing components such as hydrogen, by controlling the heating rate and the high-temperature holding time, the oxide grains are further grown and the crystallinity is improved. The valence state of transition metal ions and the oxygen vacancy concentration in the material can be adjusted, ultimately forming a cathode material with a defined crystal structure and good electrochemical activity. The F3 is 80 mL / s to 200 mL / s, the R3 is 1 °C / min to 2 °C / min, the T5 is 700 °C to 780 °C, and the t4 is 6 hours to 12 hours.
[0008] Furthermore, in S3, the first stage of the programmed solvothermal reaction is: heating from room temperature to temperature T6 at a rate V1 and holding at that temperature for a time t5, where V1 is 1°C / min to 3°C / min, T6 is 130°C to 160°C, and t5 is 2 hours to 4 hours. The relatively mild heating and medium-temperature isobaric conditions in this stage are mainly conducive to the formation of a large number of small and uniformly distributed crystal nuclei, providing a basis for subsequent growth. The second stage is: heating from T6 to temperature T7 at a rate V2 and holding at that temperature for a time t6, where V2 is 0.3°C / min to 1°C / min, T7 is 180°C to 210°C, and t6 is 10 hours to 18 hours. In this stage, a slower heating and a higher isothermal temperature are used to provide sufficient energy and time for the crystal nuclei to preferentially grow along thermodynamically favorable crystal planes, thereby forming a firmly attached and regularly morphologically regular nanostructure array on the substrate surface.
[0009] Furthermore, after the second stage of the programmed solvothermal reaction isothermally held for time t6, a third stage is included: injecting an auxiliary solvent of volume Vx into the sealed reaction vessel, wherein the auxiliary solvent is isopropanol or ethylene glycol, and maintaining the temperature T7 after injection, continuing the isothermal reaction for time t7, wherein t7 is 1 to 3 hours; the introduction of the auxiliary solvent can change the polarity, dielectric constant or viscosity of the reaction system, thereby affecting the surface energy of the formed nanostructure, and may play a role in passivating the surface, modifying the morphology or introducing trace carbon sources.
[0010] Furthermore, after the first heat treatment in S1, the method further includes step S1a: immersing the heat-treated substrate in an aqueous solution of chloroplatinic acid with a concentration of 0.01 mol / L to 0.1 mol / L at room temperature for a time T8, using ion adsorption or electrostatic interaction to load the platinum precursor onto the substrate surface, removing it and washing it to remove physically adsorbed ions, and then baking it in a protective atmosphere at a temperature L2 for a time T9 to decompose and reduce the adsorbed chloroplatinic acid, forming highly dispersed nanoscale noble metal particles on the substrate surface. T8 is 5 to 20 minutes, L2 is 150°C to 250°C, and T9 is 10 to 30 minutes. This step aims to provide additional catalytic sites or improve interfacial electron transport for the subsequent growth of active materials.
[0011] Furthermore, the organic ligand is a mixture of citric acid and ammonium tartrate, with a molar ratio M1 ranging from 2:1 to 4:1. Citric acid has a strong complexing ability, while ammonium tartrate may generate a reducing atmosphere and affect the carbon residue morphology during thermal decomposition. The specific ratio of the two can stabilize metal ions in the solution stage and affect the crystallization behavior and surface properties of the material in the heat treatment stage.
[0012] Furthermore, after the isothermal holding time t4 of the second heating and isothermal stage in sub-step S43, the in-situ carbon source introduction step is performed: a gaseous carbon source, which is methane or acetylene, is pulsed into the reducing mixed atmosphere. The duration of each pulse, P1, is 5 to 20 seconds, the interval time, P2, is 30 to 90 seconds, and the number of pulses, N, is 10 to 30. The entire process is carried out under the condition of maintaining a temperature of T5. The pulsed gas introduction method helps to control the rate and uniformity of carbon deposition, forming a thin and continuous amorphous carbon or nano-carbon layer on the surface of the active material. This carbon layer can act as a protective layer to reduce electrolyte side reactions and enhance the overall electronic conductivity of the material.
[0013] Furthermore, the three-dimensional porous conductive matrix is a three-dimensional graphene foam or carbon nanotube sponge with a porosity of 92% to 95% and an average pore size of 200 to 350 micrometers. The high porosity provides space for the large loading of active materials, the continuous pore structure is conducive to the wetting of electrolyte and the rapid transport of ions, and the intrinsic conductive network ensures the efficient collection and transport of electrons, realizing the integration of current collector, conductive agent and active material carrier.
[0014] Furthermore, the injection volume Vx of the auxiliary solvent is 5% to 20% of the total volume Vy of the precursor solution; this range is set based on the following considerations: too little addition may not be sufficient to effectively change the reaction microenvironment, while too much addition may lead to a sudden increase in the pressure of the reaction system or an excessively strong dilution effect, affecting the stability of the generated structure and the reaction equilibrium.
[0015] The technical effects and advantages of this invention are as follows: This invention utilizes a three-dimensional porous conductive substrate as a self-supporting framework, on which a programmed solvothermal reaction and subsequent heat treatment of the active material precursor are performed to achieve in-situ growth and crystallization of the active material. This process allows the active material to uniformly cover the surface and channels of the conductive framework in the form of a nanostructure array, forming a tightly bound composite. This structural design helps to shorten the ion diffusion distance and provides a three-dimensional continuous conductive network for electron transport, thereby improving charge transport within the electrode.
[0016] Specifically, programmed solvothermal reactions, by controlling temperature and time in stages, can regulate the nucleation and growth process of the active material precursor, contributing to the acquisition of primary structures with regular morphology and uniform distribution. Subsequent programmed heat treatment, under a controlled atmosphere, completes the decomposition of organic components and material crystallization, while simultaneously strengthening the interfacial bonding between the active material and the conductive matrix. The entire process eliminates the steps of powder preparation, mixing, coating, and the use of binders in traditional methods, directly obtaining an integrated electrode structure and simplifying the preparation process.
[0017] By implementing different optimization steps in the embodiments, such as introducing auxiliary solvents to adjust the growth environment, modifying the matrix with noble metals to provide more active sites, or introducing carbon sources for surface coating during heat treatment, the surface properties and interface characteristics of the final composite cathode material can be further controlled. These optimization measures can specifically improve the electrochemical activity, structural stability, or interfacial impedance of the material, making the preparation process highly controllable and adaptable. Attached Figure Description
[0018] Figure 1 This is a linear flow chart of the overall process for preparing the cathode material of the present invention.
[0019] Figure 2 This is a linear flow chart for the programmed solvothermal reaction stage control of the present invention.
[0020] Figure 3 This is a branch structure diagram of the programmed heat treatment atmosphere and temperature control of the present invention. Detailed Implementation
[0021] The following detailed description of the cathode material preparation process claimed in this invention, using several specific embodiments, illustrates this point. The described embodiments are only a portion, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without inventive effort are within the scope of protection of this invention. Experimental methods not specifying specific conditions in the embodiments are generally performed under conventional conditions in the art or as recommended by the manufacturer. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.
[0022] like Figures 1-3 As shown in the figure, this embodiment demonstrates a basic preparation process for a cathode material.
[0023] S1: Pretreatment of three-dimensional porous conductive substrate.
[0024] 1. Matrix Selection: A commercially available three-dimensional graphene foam with dimensions of approximately 20mm × 20mm × 1.5mm was selected as the matrix. Its macroscopic porosity P is approximately 94%, and the average pore size Φ is approximately 300 micrometers.
[0025] 2. Chemical cleaning: Immerse the substrate sequentially in beakers containing 1.0 mol / L hydrochloric acid solution and stir magnetically for 20 minutes at room temperature; then transfer it to a beaker containing 1.0 mol / L sodium hydroxide solution and soak for 20 minutes under the same conditions.
[0026] 3. Physical cleaning: Place the substrate, after acid and alkali cleaning, into a beaker containing 200 ml of deionized water and place it in an ultrasonic cleaner. Clean the substrate for 30 minutes at 40 kHz and 300 W power.
[0027] 4. First heat treatment: Transfer the cleaned substrate to an alumina boat and place it in the isothermal zone of a tube furnace. Introduce high-purity argon gas into the furnace tubes as a protective atmosphere, setting the gas flow rate F0 to 200 ml / min. Proceed to a programmed temperature of 5°C / min from room temperature to 500°C and maintain this temperature for 120 minutes. After heat treatment, allow the furnace to cool naturally to below 80°C under continuous argon gas flow protection before removing the substrate for later use.
[0028] S2: Prepare a homogeneous precursor solution.
[0029] 1. Raw Material Weighing: The goal is to prepare an active material with an approximate stoichiometric ratio of LiNi0.8Co0.1Mn0.1O2. Accurately weigh the following: lithium nitrate as the lithium source, 1.05 mol; nickel nitrate, 0.8 mol; cobalt nitrate, 0.1 mol; and manganese nitrate, 0.1 mol. Weigh citric acid as the bifunctional organic ligand; its total molar amount is 1.8 times the total molar amount of all transition metal ions (1.0 mol), i.e., 1.8 mol.
[0030] 2. Preparation of the first solution (S21): Weigh the lithium nitrate and add 60% of the total amount of citric acid (i.e., 1.08 mol) to a 250 mL three-necked flask containing 80 mL of deionized water. Place the flask in a thermostatic magnetic stirrer, setting the water bath temperature to L1 = 50 °C. Start stirring at 300 rpm and continue stirring at this temperature (L1) for T1 = 60 minutes to obtain a clear first solution.
[0031] 3. Preparation of the second solution (S22): Weigh out nickel nitrate, cobalt nitrate, manganese nitrate and the remaining 40% of citric acid (i.e. 0.72 mol) and add them together to a 100 mL beaker containing 50 mL of deionized water. Stir at room temperature until completely dissolved to obtain the second solution.
[0032] 4. Solution Mixing and Aging (S23): Maintain continuous stirring of the first solution at L1 = 50°C. Using a constant flow syringe pump, slowly add the second solution dropwise to the first solution at a constant dropping rate of V = 2 drops / second. The dropping process takes approximately 500 seconds. After the addition is complete, continue stirring at L1 = 50°C and 300 rpm for T2 = 4 hours, finally obtaining a homogeneous precursor solution with a total volume Vy of approximately 130 mL.
[0033] S3: Programmed solvothermal reaction.
[0034] 1. Loading: Completely immerse the pretreated three-dimensional graphene foam matrix from S1 into approximately 130 ml of the precursor solution prepared in S2. Gently shake the reaction vessel to remove internal air bubbles, ensuring that the precursor solution completely and uniformly wets all pores of the matrix. The volume of the precursor solution should be approximately 65% of the 200 ml PTFE liner volume.
[0035] 2. Reaction apparatus: Transfer the above mixture into a 200 ml volume polytetrafluoroethylene liner, and then seal the liner inside a stainless steel high-pressure reactor.
[0036] 3. Two-stage reaction procedure execution: First stage: Place the sealed reactor into a programmable temperature-controlled drying oven. Set the program to heat from room temperature to T6 = 150℃ at a rate of V1 = 2℃ / min. After reaching T6, maintain the temperature for t5 = 3 hours.
[0037] Second stage: After the first stage of temperature control is completed, the drying oven continues to raise the temperature from T6=150℃ to T7=200℃ at a rate of V2=0.5℃ / min. After reaching T7, the temperature is maintained at t6=15 hours.
[0038] 4. Reaction Termination and Sampling: After the reaction is complete, turn off the drying oven heating and allow the reactor to cool naturally to room temperature (the cooling process takes about 10 hours). Open the reactor, remove the substrate, and proceed with post-processing.
[0039] S4: Programmed heat treatment.
[0040] 1. Post-cleaning and drying: The substrate removed from S3 was ultrasonically cleaned three times each in large amounts of deionized water and anhydrous ethanol, for 5 minutes each time. After cleaning, the substrate was placed in a vacuum drying oven at 80°C and dried for 12 hours.
[0041] 2. Procedure for heat treatment execution: S41 First Heating and Isotherm Stage: Place the dried sample into a tube furnace. Pour in dry air at a flow rate F1 of 200 mL / min. Increase the temperature from room temperature to T3 = 400 °C at a rate R1 = 5 °C / min. After reaching T3, maintain the temperature for t3 = 3 hours.
[0042] S42 Intermediate Transition Stage: After t3 ends, the gas inlet is switched to high-purity argon gas with a flow rate F2 of 100 ml / min. At the same time, the furnace temperature is reduced from T3=400℃ to T4=250℃ at a rate R2=10℃ / min.
[0043] S43 Second Heating and Isothermation Stage: After the temperature stabilizes at T4=250℃, the atmosphere is switched to an argon-hydrogen mixture (with hydrogen comprising 5%) at a flow rate F3 of 150 mL / min. Then, the temperature is programmed to increase from T4=250℃ to T5=750℃ at a rate R3=1.5℃ / min. After reaching T5, the isotherm is maintained for t4=8 hours.
[0044] 3. Cooling and Finished Product: After the isothermal period, heating is stopped, and the material is allowed to cool naturally to room temperature while continuously purging with an argon-hydrogen mixture. Once removed, the final self-supporting integrated composite cathode material is obtained, denoted as sample C1.
[0045] Example 2 This embodiment demonstrates a process in which an auxiliary solvent is added as a third stage in step S3 of Example 1.
[0046] Steps S1 and S2 are exactly the same as in Example 1.
[0047] Modification and specific implementation of step S3: 1. First and second stages: Perform in full accordance with step S3 of Example 1.
[0048] 2. Third stage: After the second stage of constant temperature maintenance (t6 = 15 hours) is completed, no cooling is performed. Isopropanol is injected into the reactor as an auxiliary solvent using a high-temperature, high-pressure injector through the reactor's filling valve.
[0049] The initial total volume of the precursor solution, Vy, is 130 ml. The auxiliary solvent injection volume, Vx, is set to 12% of Vy, i.e., Vx = 130 ml * 12% = 15.6 ml (16 ml is injected in actual operation).
[0050] 3. Third stage isothermal reaction: After the auxiliary solvent is injected, the reactor is immediately placed back into the drying oven that has been preheated to T7=200℃, and the reaction is continued at this temperature for t7=2 hours.
[0051] 4. After the third stage is completed, allow it to cool naturally to room temperature.
[0052] Step S4 is exactly the same as in Example 1. The final cathode material is denoted as sample C2.
[0053] Example 3 This embodiment demonstrates a process of adding a noble metal modification step to the substrate surface after step S1 in Example 1.
[0054] Modification and specific implementation of step S1: 1. S1 Basic Pretreatment: First, the three-dimensional graphene foam matrix is treated exactly according to the S1 step of Example 1.
[0055] 2. Precious metal finishing steps: Preparation of the modification solution: Prepare an aqueous solution of chloroplatinic acid with a concentration of 0.05 mol / L.
[0056] Impregnation: The substrate treated with S1 and cooled is completely immersed in the above chloroplatinic acid solution. The substrate is left to stand at room temperature for 10 minutes (T8 = 10 minutes).
[0057] Cleaning: Remove the substrate, rinse with plenty of deionized water and ultrasonically clean it to remove physically adsorbed platinum ions.
[0058] Baking and reduction: The cleaned substrate is placed in a tube furnace and heated to L2=200℃ under argon protection, and then baked at this temperature for T9=20 minutes. After baking, it is cooled to room temperature under argon protection.
[0059] Steps S2, S3, and S4 are exactly the same as in Example 1. The final cathode material is denoted as sample C3.
[0060] Example 4 This embodiment demonstrates a process that adds an in-situ carbon source introduction step to step S4 of embodiment 1.
[0061] Steps S1, S2, and S3 are exactly the same as in Example 1.
[0062] Modification and specific implementation of step S4: 1. S41 and S42 stages: Perform exactly as described in step S4 of Example 1.
[0063] 2. S43 High-temperature crystallization stage: Performed according to Example 1.
[0064] 3. In-situ carbon source introduction steps: At the end of the isothermal period of t4=8 hours, the temperature of the tubular furnace is kept stable at T5=750℃, and the argon-hydrogen mixture is kept as the base gas flow.
[0065] High-purity acetylene gas is pulsed into the gas stream as a gaseous carbon source. The specific pulse program is set as follows: within each pulse cycle, the ventilation time P1 = 10 seconds, followed by a purging time P2 = 60 seconds.
[0066] Execute the above pulse N=20 times consecutively.
[0067] 4. Cooling: After the pulse program ends, the acetylene supply is stopped, and the material is cooled to room temperature under a protective atmosphere. The final carbon-coated cathode material is designated as sample C4.
[0068] Example 5 This embodiment demonstrates an implementation using a specific molar ratio of mixed organic ligands.
[0069] Step S1 is exactly the same as in Example 1.
[0070] Modification and specific implementation of step S2: 1. Raw material weighing: The weighing of the target active material and the metal source is the same as in Example 1. Change of organic ligands: A mixture of citric acid and ammonium tartrate is used. The molar ratio M1 (citric acid:ammonium tartrate) is set to 3:1. The total molar amount of the mixed ligands is controlled to remain 1.8 times the total molar amount of all transition metal ions.
[0071] 2. Solution preparation: The operation procedure is the same as step S2 in Example 1. The mixing, dropping, and aging conditions (L1=50℃, V=2 drops / second, T2=4 hours) remain unchanged.
[0072] Steps S3 and S4 are exactly the same as in Example 1. The final cathode material is denoted as sample C5.
[0073] Comparative Example 1: Traditional Slurry Coating Process For comparison, electrodes were prepared using a traditional slurry coating process.
[0074] 1. Preparation of active materials: LiNi0.8Co0.1Mn0.1O2 micron-sized powder with the same target composition as in Example 1 was synthesized by co-precipitation-high temperature solid-state method.
[0075] 2. Electrode preparation: The above-mentioned active material powder, conductive agent acetylene black, and binder polyvinylidene fluoride are mixed at a mass ratio of 90:5:5. N-methylpyrrolidone solvent is added to the mixture, and the mixture is stirred to form a uniform slurry. The slurry is then uniformly coated onto the aluminum foil current collector using a coater.
[0076] 3. Drying and processing: After the coated electrode is dried, it is rolled and cut into round pieces as a control electrode, denoted as sample D1.
[0077] To test the cathode material obtained by this preparation process, the samples obtained in Examples 1-5 and Comparative Example 1 were subjected to structural characterization and electrochemical performance testing.
[0078] 1. Structural Characterization: The surface morphology of the samples was observed using field emission scanning electron microscopy, and the crystal structure was analyzed using X-ray diffraction. The characterization results are summarized in Table 1.
[0079] 2. Electrochemical Performance Testing: CR2032 coin cells were assembled in an argon-atmospheric glove box using the sample as the working electrode, a lithium metal sheet as the counter electrode, a Celgard 2400 membrane as the separator, and a 1 mol / L LiPF6 EC / DMC (volume ratio 1:1) solution as the electrolyte. After a 12-hour resting period, the cells were tested using a LAND battery testing system. Test conditions: voltage window 2.8-4.3V, initial charge / discharge rate 0.1C (C-rate calculated based on the initial discharge specific capacity of sample C1), and cycle performance test rate 1C. Key performance data are summarized in Table 2.
[0080] Table 1 Sample structure characterization results Table 2 Electrochemical performance data of samples The results in Tables 1 and 2 show that the active material layer of samples C1-C5 obtained using this preparation process forms a uniform in-situ grown structure on the three-dimensional conductive framework. Under the same electrochemical testing conditions, the initial discharge specific capacity, initial coulombic efficiency, and cycle capacity retention of samples C1-C5 are all higher than those of sample D1 prepared using the traditional coating process. Samples C2-C5 also show corresponding changes in relevant performance data compared to sample C1.
[0081] In conclusion, the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.
Claims
1. A process for preparing a cathode material, characterized in that, Including steps S1 to S4: S1: Pre-treatment of the three-dimensional porous conductive substrate, the pre-treatment including sequential acid washing, alkali washing, ultrasonic cleaning with deionized water, and a first heat treatment in a protective atmosphere. S2: Prepare a homogeneous precursor solution, wherein the solution contains a lithium source compound, at least two transition metal source compounds, and a bifunctional organic ligand; S3: The matrix treated by S1 is completely immersed in the precursor solution prepared in S2, and a programmed solvothermal reaction is performed in a closed reaction vessel. The reaction includes at least two stages with different heating rates and isothermal temperatures. S4: The matrix after the S3 reaction is cleaned and dried, and then subjected to a programmed heat treatment, which includes a first heating and holding stage in an oxidizing atmosphere and a second heating and holding stage in a reducing or inert atmosphere.
2. The cathode material preparation process according to claim 1, characterized in that, Step S2 specifically includes sub-steps S21 to S23: S21: Dissolve the lithium source compound and a portion of the bifunctional organic ligand in a first solvent to form a first solution, and stir at a temperature L1 for a time T1, wherein L1 is 40°C to 60°C and T1 is 30 minutes to 90 minutes. S22: Dissolve the at least two transition metal source compounds and the remaining bifunctional organic ligands in a second solvent to form a second solution; S23: Under continuous stirring and temperature L1, the second solution is added to the first solution at a constant dropping rate V. After the addition is complete, stirring is continued for time T2 to form the homogeneous precursor solution. V is 1 drop per second to 3 drops per second, and T2 is 2 hours to 6 hours.
3. The cathode material preparation process according to claim 1, characterized in that, The programmed heat treatment in step S4 specifically includes sub-steps S41 to S43: S41: In the first heating and holding stage, the dried substrate is placed in a tube furnace and heated from room temperature to temperature T3 at a rate R1 under an oxygen-containing atmosphere with a flow rate F1, and held at that temperature for a time t3; where F1 is 100 ml / s to 300 ml / s, R1 is 3°C / min to 8°C / min, T3 is 350°C to 480°C, and t3 is 2 hours to 4 hours. S42: Intermediate transition phase, switch the atmosphere to an inert atmosphere with a flow rate of F2, and reduce the temperature from T3 to T4 at a rate of R2, wherein F2 is 50 mL / s to 150 mL / s, R2 is 5°C / min to 15°C / min, and T4 is 200°C to 280°C. S43: In the second heating and holding stage, the atmosphere is switched to a reducing mixed atmosphere with a flow rate of F3, and the temperature is increased from T4 to T5 at a rate of R3, and held at a constant temperature for a time t4. The F3 is 80 ml / s to 200 ml / s, the R3 is 1°C / min to 2°C / min, the T5 is 700°C to 780°C, and the t4 is 6 hours to 12 hours.
4. The cathode material preparation process according to claim 1, characterized in that, In S3, the first stage of the programmed solvothermal reaction is: heating from room temperature to temperature T6 at a rate V1 and holding at that temperature for a time t5, where V1 is 1°C / min to 3°C / min, T6 is 130°C to 160°C, and t5 is 2 hours to 4 hours; the second stage is: heating from T6 to temperature T7 at a rate V2 and holding at that temperature for a time t6, where V2 is 0.3°C / min to 1°C / min, T7 is 180°C to 210°C, and t6 is 10 hours to 18 hours.
5. The cathode material preparation process according to claim 4, characterized in that, After the second stage of the programmed solvothermal reaction is held at a constant temperature for time t6, a third stage is included: an auxiliary solvent of volume Vx, which is isopropanol or ethylene glycol, is injected into the sealed reaction vessel. After injection, the temperature is kept constant at T7, and the isothermal reaction continues for time t7, which is 1 to 3 hours.
6. The cathode material preparation process according to claim 1, characterized in that, After the first heat treatment in S1, the method further includes step S1a: immersing the heat-treated substrate in an aqueous solution of chloroplatinic acid with a concentration of 0.01 mol / L to 0.1 mol / L at room temperature for a soaking time T8, removing it, cleaning it, and baking it in a protective atmosphere at a temperature L2 for a baking time T9, wherein T8 is 5 to 20 minutes, L2 is 150°C to 250°C, and T9 is 10 to 30 minutes.
7. The cathode material preparation process according to claim 2 or 6, characterized in that, The organic ligand is a mixture of citric acid and ammonium tartrate, with a molar ratio M1 ranging from 2:1 to 4:
1.
8. The cathode material preparation process according to claim 3, characterized in that, After the second heating and isothermal stage of sub-step S43 has ended and the isothermal holding time t4 has ended, the in-situ carbon source introduction step is performed: a gaseous carbon source, which is methane or acetylene, is pulsed into the reducing mixed atmosphere. The duration of each pulse, P1, is 5 to 20 seconds, the interval time, P2, is 30 to 90 seconds, and the number of pulses, N, is 10 to 30. The entire process is carried out under the condition of maintaining a temperature, T5.
9. The cathode material preparation process according to claim 1, characterized in that, The three-dimensional porous conductive substrate is a three-dimensional graphene foam or carbon nanotube sponge with a porosity of 92% to 95% and an average pore size of 200 to 350 micrometers.
10. The cathode material preparation process according to claim 5, characterized in that, The injection volume Vx of the auxiliary solvent is 5% to 20% of the total volume Vy of the precursor solution.