A method of manufacturing an electrode sheet

Abstract

The application provides a preparation method of an electrode sheet, and a nitrogen-doped carbon nanofiber membrane with high conductivity and rich active sites is prepared as a self-supporting conductive framework by taking a bacterial cellulose three-dimensional network as a template and melamine as a nitrogen source, and a binder system is composed of sodium alginate, functionalized guar gum and citric acid-based polyamide, the system realizes the unity of high bonding strength, excellent self-repairing ability and good ionic conductivity of the electrode sheet through the synergistic effect with a dynamic borate ester bond, and finally a green and environmentally-friendly electrode sheet with high energy density, long cycle life and excellent structural stability is successfully prepared.

Description

Technical Field

[0001] This invention belongs to the field of lithium-ion battery technology, specifically relating to a method for preparing an electrode sheet. Background Technology

[0002] As the core power source for modern portable electronic devices, electric vehicles, and large-scale energy storage systems, the continuous improvement of lithium-ion battery performance is crucial. Electrodes, as the sites of electrochemical reactions within the battery, directly determine the battery's energy density, power characteristics, cycle life, and safety through their microstructure design and material system. Traditional electrode fabrication processes typically involve mixing and coating active materials, conductive agents (such as carbon black and carbon nanotubes), and insulating polymer binders (such as polyvinylidene fluoride, PVDF) in an organic solvent (such as N-methylpyrrolidone, NMP). While this classic paradigm has been industrialized, its inherent material and structural limitations are becoming increasingly prominent, posing a bottleneck to the development of next-generation high-performance batteries, primarily in the areas of the conductive network and binder system.

[0003] In terms of conductive network construction, existing technologies heavily rely on the physical blending of zero-dimensional (carbon black) or one-dimensional (carbon nanotube) conductive fillers. These conductive agents are prone to agglomeration in the slurry due to van der Waals forces, making it difficult to achieve uniform and continuous dispersion among active material particles. The resulting conductive network is random, with point-to-line contact, low mechanical strength, and tortuous and unstable electron transport paths. During long-term charge-discharge cycles, the active material particles inevitably undergo volume expansion and contraction, easily damaging this fragile conductive network. This leads to some active materials becoming "dead zones" due to "electrical contact failure," resulting in a sharp increase in battery internal resistance and rapid capacity decay. Furthermore, to ensure sufficient electronic conductivity, a high proportion (typically >3%) of conductive agent is often added, directly sacrificing the proportion of active material in the electrode and limiting further improvements in battery energy density. Meanwhile, traditional methods for preparing highly conductive carbon materials (such as graphene and carbon nanofibers) often involve high temperatures, high pressures, and toxic precursors, which are environmentally unfriendly and costly. Therefore, developing a robust, continuous, three-dimensionally interconnected, and intrinsically highly active green conductive framework capable of in-situ construction is key to overcoming current limitations in electrode electron conduction. This not only ensures rapid electron transport at high rates but also endows the electrode with superior structural stability, which is crucial for improving battery power performance and extending cycle life.

[0004] Regarding binder systems, widely used traditional binders such as PVDF have significant drawbacks. First, they are pure insulators with extremely low ionic conductivity and generally poor electrolyte wettability, potentially increasing the resistance to lithium-ion transport within the electrode. Second, and most critically, these binders provide adhesion through relatively rigid molecular chain entanglement and weak van der Waals forces, resulting in limited bonding strength and a lack of dynamic adaptability. In electrodes with significant volume changes (>10%), such as silicon-based or high-nickel ternary materials, this rigid bonding network cannot effectively buffer repeated volumetric stresses, easily leading to bond failure, active material peeling from the current collector, and the pulverization and collapse of the overall electrode structure. Although some water-based binders (such as sodium carboxymethyl cellulose and styrene-butadiene rubber) have improved in terms of environmental friendliness and cost, their mechanical properties (especially toughness) and adaptability remain insufficient. Furthermore, the singular function of the binder itself (providing only adhesion) also limits further improvements in the overall electrode performance. Therefore, developing a novel smart binder system that combines excellent bonding strength, high ionic conductivity, and especially dynamic reversible bonding capability (i.e., self-healing function) is crucial for adapting to volume changes in high-capacity electrode materials, maintaining the integrity of the electrode structure, and thus greatly extending the cycle life of the battery.

[0005] In summary, the discrete and fragile conductive network and passive, rigid binder system in existing electrode technologies jointly lead to the irreversible degradation of the electrode microstructure during cycling, which is one of the core internal factors causing battery performance degradation. Addressing this issue is not only about improving individual performance indicators, but also about fundamentally reshaping the stable and vital "mechanical-electrical" dual network within the electrode. By combining a continuous, highly active three-dimensional conductive framework with a dynamically adaptive smart gel binder, it is hoped that multiple challenges, such as electron / ion transport, structural stress release, and interface stability, can be synergistically resolved. This transformative material and structural design will lead electrode fabrication from simple "physical mixing" to precise "integrated structural and functional construction," laying a solid foundation for the fabrication of next-generation lithium-ion batteries with ultra-high energy density, ultra-long cycle life, and excellent safety. Summary of the Invention

[0006] This invention discloses a method for preparing an electrode sheet to solve any of the above-mentioned or potential problems in the prior art. To solve the above-mentioned technical problems, the technical solution adopted by this invention is as follows.

[0007] A method for preparing an electrode sheet, the specific process being:

[0008] 1) Electrode slurry preparation: Dry mix 88-92% of active material, 4-6% of nitrogen-doped carbon nanofiber conductive framework and 4-6% of conductive carbon black for 5-10 min; then add 3-5% of binder precursor by the total solid mass of the slurry, add deionized water as dispersion liquid to adjust viscosity, first stir at low speed of 500-800 rpm for 20-30 min to fully wet all powders with liquid and form preliminary dispersion, then stir at high speed of 1500-2500 rpm for 30-60 min to completely break agglomerates with high shear force, so that conductive framework fibers, carbon black and active material are uniformly dispersed in binder network to form uniform and stable electrode slurry;

[0009] 2) Coating and Pre-curing: The electrode paste is coated onto the aluminum foil current collector, with the wet film thickness controlled at 200±5μm; then the coated wet electrode sheet is placed in a sealed cavity and exposed to calcium ion mist generated by ultrasonic atomization of a 5% (w / w) calcium chloride solution for 5-10 minutes, utilizing Ca... 2+ It undergoes rapid ionic cross-linking with the binder components, achieving initial fixation of the slurry surface and preventing flow and cracking;

[0010] 3) Drying and compaction: The coated and pre-cured electrode sheet is dried by blowing at 80°C for 2 hours, then vacuum dried at 120°C for 12 hours; finally, it is cold-pressed at 25°C and 10 MPa to obtain the electrode sheet.

[0011] Preferably, the method for preparing a nitrogen-doped carbon nanofiber conductive framework includes the following steps:

[0012] S1. Bacterial cellulose composite: Melamine powder is added to a bacterial cellulose dispersion with a solid content of 0.5%-1.0% at a ratio of bacterial cellulose dry weight to melamine weight of 1:(0.5~2.0). The mixture is stirred at 100-200 rpm for 10-15 min. The mixture is then heated to 50-60℃ and stirred continuously at this temperature for 2-4 h to allow melamine molecules to be fully adsorbed and uniformly dispersed in the bacterial cellulose fiber network through interactions such as hydrogen bonding. The mixture is then cooled and stirring is stopped. The mixture is allowed to stand at room temperature for 12-24 h to form a bacterial cellulose / melamine composite hydrogel with a uniform structure.

[0013] S2. Freeze-drying: The composite hydrogel is rapidly frozen to -80°C with liquid nitrogen, and then placed in a freeze dryer. Under the conditions of cold trap temperature below -50°C and vacuum degree below 10 Pa, it is freeze-dried for 24-48 hours to completely remove moisture and obtain bacterial cellulose / melamine aerogel film.

[0014] S3. Pre-oxidation and carbonization: The aerogel film is placed in a muffle furnace and heated from room temperature to 220-250℃ at a rate of 2-3℃ / min under air atmosphere, and held for 2 hours to allow partial cross-linking and stabilization of bacterial cellulose and melamine, preventing melting during subsequent carbonization. Then, the aerogel film is transferred to a tube furnace filled with argon gas at a flow rate of 200 sccm. The temperature is first increased to 400-500℃ at a rate of 2℃ / min and held for 60 minutes to allow melamine to fully decompose and begin doping. Then, the temperature is increased to 800-1000℃ at a rate of 5-8℃ / min and held for 90 minutes to ensure complete decomposition of melamine and complete nitrogen stabilization doping. After natural cooling, nitrogen-doped carbon nanofiber membrane is obtained.

[0015] S4. Pulverization: Nitrogen-doped carbon nanofiber membranes are ball-milled to 10-40 μm.

[0016] Preferably, the method for preparing the binder precursor includes the following steps:

[0017] A1. Synthesis of functionalized guar gum: 10 parts of natural guar gum powder were dispersed in 200 parts of deionized water and stirred at 40°C until completely dissolved; 2-5 parts of 3-aminophenylboronic acid were added, and the pH was adjusted to 9-10 with 1 mol / L sodium hydroxide solution; under nitrogen protection, the reaction system was heated to 70°C and reacted for 6 hours; after the reaction was completed, the mixture was cooled to room temperature, precipitated with anhydrous ethanol and washed three times, and the obtained product was vacuum dried at 50°C for 24 hours and ground to obtain functionalized guar gum powder;

[0018] A2. Synthesis of citric acid-based waterborne polyamide: Add 19-20 parts of citric acid and 12-15 parts of hexamethylenediamine to 150 parts of deionized water; under a nitrogen atmosphere, first heat the reaction system to 80°C and keep it at that temperature for 2 hours, then raise the temperature to 105°C and continue to reflux for 4 hours; after cooling, obtain an aqueous solution of citric acid-based waterborne polyamide.

[0019] A3. Compound preparation: Add 1-2 parts of sodium alginate powder to 100 parts of deionized water and dissolve it at 50℃ and 400 rpm to obtain a sodium alginate solution; under continuous stirring, add 0.3-0.6 parts of functionalized guar gum powder and 20-30 parts by weight of citric acid-based aqueous polyamide aqueous solution to the sodium alginate solution in sequence, and maintain stirring at 50℃ for 4 hours to obtain the binder precursor.

[0020] Preferably, the active material is one of lithium iron phosphate, ternary materials, or silicon-carbon composite materials.

[0021] The advantages and beneficial effects of this invention are as follows:

[0022] 1. The electrode sheet preparation method provided by the present invention, through the synergistic effect of constructing a three-dimensional self-supporting conductive framework and a binder system, ultimately produces an electrode sheet with ultra-high electrochemical performance, excellent structural stability and excellent environmental friendliness.

[0023] 2. Regarding the conductive framework, this invention uses bacterial cellulose, a natural three-dimensional nanofiber network, as a biological template and melamine as a nitrogen source for doping. The conductive framework prepared by this method not only possesses the inherent three-dimensional interconnected nanofiber network structure of bacterial cellulose, constructing a natural highway for electron transport and significantly reducing the internal resistance of the electrode, but also utilizes the high nitrogen content of melamine to introduce a large number of electrochemical active sites. The good interaction between its molecular structure and cellulose fibers can achieve uniform composite at the molecular level, ensuring the uniformity of nitrogen doping after pyrolysis. Furthermore, the carbonization of melamine not only provides a nitrogen source, but its cyclic structure can also promote the degree of graphitization, further optimizing the electronic structure of carbon materials and greatly improving the intrinsic electrocatalytic activity and ion adsorption capacity of the electrode material. At the same time, the framework also has self-supporting properties, which can directly load active materials to form electrodes, eliminating the need for traditional metal current collectors and insulating polymer binders, thereby significantly improving the overall energy density of the battery.

[0024] 3. Regarding the binder, a triple gel system is composed of sodium alginate, functionalized guar gum, and citric acid-based waterborne polyamide. The stable eggshell structure formed by the cross-linking of sodium alginate with calcium ions provides a strong and rigid first network, ensuring excellent initial bonding strength and structural integrity of the electrode sheet. The borate ester groups introduced on the functionalized guar gum form reversible dynamic covalent bonds with the hydroxyl groups on the conductive framework or the surface of the active material, constituting the second network. This network can undergo reversible fracture and reconstruction under external stress, acting like a molecular-level shock absorber, effectively dissipating energy, thereby endowing the electrode sheet with excellent toughness and unprecedented self-healing ability, greatly mitigating the damage caused by the volume change of the active material during charging and discharging, and extending cycle life. The citric acid-based waterborne polyamide, as a flexible third network, acts as a flexible bridge between the first two networks through a large number of hydrogen bonds and molecular chain entanglements, not only further enhancing the bonding force but also significantly improving the flexibility of the electrode sheet. Furthermore, the all-aqueous nature of this binder system eliminates the need for traditional N-methylpyrrolidone solvents, making the production process greener, more environmentally friendly, and safer. Ultimately, this adaptive gel network forms in situ inside the electrode, achieving high bonding strength, high ionic conductivity, and self-healing capabilities.

[0025] 4. In summary, the electrode sheet preparation method of the present invention combines green and sustainable material design concepts with cutting-edge functional design. Through the synergistic effect of the above-mentioned conductive framework and binder system, the final electrode sheet exhibits significant advantages in terms of conductivity, structural stability, cycle life and energy density. At the same time, the entire preparation process is environmentally friendly and has significant practical application value. Detailed Implementation

[0026] The present invention will be further described in detail below with reference to the embodiments. The bacterial cellulose dispersion, model TL-008, was purchased from Nanjing Tianlu Nanotechnology Co., Ltd., with a solid content of 0.8%, a fiber length of 20 μm, and a diameter of 10-100 nm. It was obtained by dispersing bacterial cellulose purified with 1% sodium hydroxide.

[0027] Example 1

[0028] A method for preparing an electrode sheet, the specific process being:

[0029] 1) Preparation of nitrogen-doped carbon nanofiber conductive framework:

[0030] S1. Melamine powder was added to the bacterial cellulose dispersion at a ratio of 1:1 (dry weight of bacterial cellulose to mass of melamine). The mixture was stirred at 150 rpm for 10 min. The mixture was heated to 55°C and stirred continuously at this temperature for 3 h. The mixture was then cooled and stirring was stopped. The mixture was allowed to stand at room temperature for 18 h to obtain the composite hydrogel.

[0031] S2. Freeze-drying: The composite hydrogel was rapidly frozen to -80°C with liquid nitrogen, and then placed in a freeze dryer. Under the conditions of cold trap temperature below -50°C and vacuum degree below 10 Pa, it was freeze-dried for 36 hours to obtain bacterial cellulose / melamine aerogel film.

[0032] S3. Pre-oxidation and carbonization: The aerogel film was placed in a muffle furnace and heated from room temperature to 230°C at a heating rate of 2°C / min under air atmosphere, and held for 2 hours. Then the aerogel film was transferred to a tube furnace filled with argon gas at a flow rate of 200 sccm. The temperature was first raised to 450°C at a heating rate of 2°C / min and held for 60 minutes, and then raised to 900°C at a heating rate of 6°C / min and held for 90 minutes. After natural cooling, nitrogen-doped carbon nanofiber membrane was obtained.

[0033] S4. Pulverization: The nitrogen-doped carbon nanofiber membrane is ball-milled to 10-40μm and set aside.

[0034] 2) Preparation of binder precursor:

[0035] A1. Synthesis of functionalized guar gum: 10 parts of natural guar gum powder were dispersed in 200 parts of deionized water and stirred at 40°C until completely dissolved; 3 parts of 3-aminophenylboronic acid were added, and the pH was adjusted to 9-10 with 1 mol / L sodium hydroxide solution; under nitrogen protection, the reaction system was heated to 70°C and reacted for 6 hours; after the reaction was completed, the mixture was cooled to room temperature, precipitated with anhydrous ethanol and washed three times, and the obtained product was vacuum dried at 50°C for 24 hours and ground to obtain functionalized guar gum powder;

[0036] A2. Synthesis of citric acid-based waterborne polyamide: 19 parts of citric acid and 13 parts of hexamethylenediamine were added to 150 parts of deionized water; under a nitrogen atmosphere, the reaction system was first heated to 80°C and kept at that temperature for 2 hours, and then the temperature was raised to 105°C and refluxed for 4 hours; after cooling, an aqueous solution of citric acid-based waterborne polyamide was obtained.

[0037] A3. Compound preparation: Add 1 part of sodium alginate powder to 100 parts of deionized water and dissolve it at 50℃ and 400 rpm to obtain a sodium alginate solution; under continuous stirring, add 0.5 parts of functionalized guar gum powder and 25 parts by weight of citric acid-based aqueous polyamide solution to the sodium alginate solution in sequence, and maintain stirring at 50℃ for 4 hours to obtain the binder precursor for later use;

[0038] 3) Electrode slurry preparation: 90% lithium iron phosphate, 5% nitrogen-doped carbon nanofiber conductive framework and 5% conductive carbon black (Super P) were dry mixed for 8 min; then 4% of the total solid mass of the slurry was added as a binder precursor, and deionized water was added to adjust the viscosity of the dispersion. The mixture was first stirred at a low speed of 700 rpm for 25 min, and then stirred at a high speed of 2000 rpm for 45 min to form the electrode slurry.

[0039] 4) Coating and pre-curing: The electrode paste is coated on the aluminum foil current collector, and the wet film thickness is controlled at 200±5μm; then the coated wet electrode sheet is placed in a sealed cavity and exposed to calcium ion mist generated by ultrasonic atomization of 5% calcium chloride solution for 8 min.

[0040] 5) Drying and compaction: The coated and pre-cured electrode sheet is dried by blowing at 80°C for 2 hours, then vacuum dried at 120°C for 12 hours; finally, it is cold-pressed at 25°C and 10 MPa to obtain the electrode sheet.

[0041] Example 2

[0042] A method for preparing an electrode sheet, the specific process being:

[0043] 1) Preparation of nitrogen-doped carbon nanofiber conductive framework:

[0044] S1. Melamine powder was added to the bacterial cellulose dispersion at a ratio of 1:0.5 between the dry weight of bacterial cellulose and the mass of melamine. The mixture was stirred at 200 rpm for 10 min. The mixture was heated to 60°C and stirred continuously at this temperature for 2 h. The mixture was then cooled and stirred. The mixture was allowed to stand at room temperature for 24 h to obtain the composite hydrogel.

[0045] S2. Freeze-drying: The composite hydrogel was rapidly frozen to -80°C with liquid nitrogen, and then placed in a freeze dryer. Under the conditions of cold trap temperature below -50°C and vacuum degree below 10 Pa, it was freeze-dried for 48 hours to obtain bacterial cellulose / melamine aerogel film.

[0046] S3. Pre-oxidation and carbonization: The aerogel film was placed in a muffle furnace and heated from room temperature to 250°C at a heating rate of 3°C / min under air atmosphere, and held for 2 hours. Then the aerogel film was transferred to a tube furnace filled with argon gas at a flow rate of 200 sccm. The temperature was first raised to 500°C at a heating rate of 2°C / min and held for 60 minutes, and then raised to 800°C at a heating rate of 5°C / min and held for 90 minutes. After natural cooling, nitrogen-doped carbon nanofiber membrane was obtained.

[0047] S4. Pulverization: The nitrogen-doped carbon nanofiber membrane is ball-milled to 10-40μm and set aside.

[0048] 2) Preparation of binder precursor:

[0049] A1. Synthesis of functionalized guar gum: 10 parts of natural guar gum powder were dispersed in 200 parts of deionized water and stirred at 40°C until completely dissolved; 2 parts of 3-aminophenylboronic acid were added, and the pH was adjusted to 9-10 with 1 mol / L sodium hydroxide solution; under nitrogen protection, the reaction system was heated to 70°C and reacted for 6 hours; after the reaction was completed, the mixture was cooled to room temperature, precipitated with anhydrous ethanol and washed three times, and the obtained product was vacuum dried at 50°C for 24 hours and ground to obtain functionalized guar gum powder;

[0050] A2. Synthesis of citric acid-based waterborne polyamide: 20 parts of citric acid and 12 parts of hexamethylenediamine were added to 150 parts of deionized water; under a nitrogen atmosphere, the reaction system was first heated to 80°C and kept at that temperature for 2 hours, and then the temperature was raised to 105°C and refluxed for 4 hours; after cooling, an aqueous solution of citric acid-based waterborne polyamide was obtained.

[0051] A3. Compound preparation: Add 2 parts of sodium alginate powder to 100 parts of deionized water and dissolve it at 50℃ and 400 rpm to obtain a sodium alginate solution; under continuous stirring, add 0.3 parts of functionalized guar gum powder and 30 parts by weight of citric acid-based aqueous polyamide solution to the sodium alginate solution in sequence, and maintain stirring at 50℃ for 4 hours to obtain the binder precursor for later use;

[0052] 3) Electrode slurry preparation: 88% lithium iron phosphate, 6% nitrogen-doped carbon nanofiber conductive framework and 6% conductive carbon black (Super P) were dry mixed for 10 min; then 5% binder precursor of total solid mass of slurry was added, and deionized water was added to adjust the viscosity of the dispersion. The mixture was first stirred at a low speed of 500 rpm for 30 min, and then stirred at a high speed of 2500 rpm for 60 min to form electrode slurry.

[0053] 4) Coating and pre-curing: The electrode paste is coated on the aluminum foil current collector, and the wet film thickness is controlled at 200±5μm; then the coated wet electrode sheet is placed in a sealed cavity and exposed to calcium ion mist generated by ultrasonic atomization of 5% calcium chloride solution for 5 min.

[0054] 5) Drying and compaction: The coated and pre-cured electrode sheet is dried by blowing at 80°C for 2 hours, then vacuum dried at 120°C for 12 hours; finally, it is cold-pressed at 25°C and 10 MPa to obtain the electrode sheet.

[0055] Example 3

[0056] A method for preparing an electrode sheet, the specific process being:

[0057] 1) Preparation of nitrogen-doped carbon nanofiber conductive framework:

[0058] S1. Melamine powder was added to the bacterial cellulose dispersion at a ratio of 1:2 (dry weight of bacterial cellulose to melamine). The mixture was stirred at 100 rpm for 15 min. The mixture was heated to 50°C and stirred continuously at this temperature for 4 h. The mixture was then cooled and stirring was stopped. The mixture was allowed to stand at room temperature for 12 h to obtain the composite hydrogel.

[0059] S2. Freeze-drying: The composite hydrogel is rapidly frozen to -80°C with liquid nitrogen, and then placed in a freeze dryer. Under the conditions of cold trap temperature below -50°C and vacuum degree below 10 Pa, it is freeze-dried for 24-48 hours to obtain bacterial cellulose / melamine aerogel film.

[0060] S3. Pre-oxidation and carbonization: The aerogel film was placed in a muffle furnace and heated from room temperature to 220°C at a heating rate of 2°C / min under air atmosphere, and held at that temperature for 2 hours. Then, the aerogel film was transferred to a tube furnace filled with argon gas at a flow rate of 200 sccm. The temperature was first raised to 400°C at a heating rate of 2°C / min and held for 60 minutes, and then raised to 1000°C at a heating rate of 8°C / min and held for 90 minutes. After natural cooling, nitrogen-doped carbon nanofiber membrane was obtained.

[0061] S4. Pulverization: The nitrogen-doped carbon nanofiber membrane is ball-milled to 10-40μm and set aside.

[0062] 2) Preparation of binder precursor:

[0063] A1. Synthesis of functionalized guar gum: 10 parts of natural guar gum powder were dispersed in 200 parts of deionized water and stirred at 40°C until completely dissolved; 5 parts of 3-aminophenylboronic acid were added, and the pH was adjusted to 9-10 with 1 mol / L sodium hydroxide solution; under nitrogen protection, the reaction system was heated to 70°C and reacted for 6 hours; after the reaction was completed, the mixture was cooled to room temperature, precipitated with anhydrous ethanol and washed three times, and the obtained product was vacuum dried at 50°C for 24 hours and ground to obtain functionalized guar gum powder;

[0064] A2. Synthesis of citric acid-based waterborne polyamide: 20 parts of citric acid and 15 parts of hexamethylenediamine were added to 150 parts of deionized water; under a nitrogen atmosphere, the reaction system was first heated to 80°C and kept at that temperature for 2 hours, and then the temperature was raised to 105°C and refluxed for 4 hours; after cooling, an aqueous solution of citric acid-based waterborne polyamide was obtained.

[0065] A3. Compound preparation: Add 1 part of sodium alginate powder to 100 parts of deionized water and dissolve it at 50℃ and 400 rpm to obtain a sodium alginate solution; under continuous stirring, add 0.6 parts of functionalized guar gum powder and 20 parts by weight of citric acid-based aqueous polyamide solution to the sodium alginate solution in sequence, and maintain stirring at 50℃ for 4 hours to obtain the binder precursor for later use;

[0066] 3) Electrode slurry preparation: 92% lithium iron phosphate, 4% nitrogen-doped carbon nanofiber conductive framework and 4% conductive carbon black (Super P) were dry mixed for 10 min; then 3% of the total solid mass of the slurry was added as a binder precursor, and deionized water was added to adjust the viscosity of the dispersion. The mixture was first stirred at a low speed of 800 rpm for 20 min, and then stirred at a high speed of 1500 rpm for 30 min to form the electrode slurry.

[0067] 4) Coating and pre-curing: The electrode paste is coated on the aluminum foil current collector, and the wet film thickness is controlled at 200±5μm; then the coated wet electrode sheet is placed in a sealed cavity and exposed to calcium ion mist generated by ultrasonic atomization of 5% calcium chloride solution for 10min.

[0068] 5) Drying and compaction: The coated and pre-cured electrode sheet is dried by blowing at 80°C for 2 hours, then vacuum dried at 120°C for 12 hours; finally, it is cold-pressed at 25°C and 10 MPa to obtain the electrode sheet.

[0069] Comparative Example 1

[0070] A method for preparing an electrode sheet, the specific process being:

[0071] 1) Conductive framework: The bacterial cellulose gel membrane purchased from Nanjing Tianlu Nanotechnology Co., Ltd. was ground to 10-40μm and set aside.

[0072] 2) Preparation of binder precursor:

[0073] A1. Synthesis of functionalized guar gum: 10 parts of natural guar gum powder were dispersed in 200 parts of deionized water and stirred at 40°C until completely dissolved; 3 parts of 3-aminophenylboronic acid were added, and the pH was adjusted to 9-10 with 1 mol / L sodium hydroxide solution; under nitrogen protection, the reaction system was heated to 70°C and reacted for 6 hours; after the reaction was completed, the mixture was cooled to room temperature, precipitated with anhydrous ethanol and washed three times, and the obtained product was vacuum dried at 50°C for 24 hours and ground to obtain functionalized guar gum powder;

[0074] A2. Synthesis of citric acid-based waterborne polyamide: 19 parts of citric acid and 13 parts of hexamethylenediamine were added to 150 parts of deionized water; under a nitrogen atmosphere, the reaction system was first heated to 80°C and kept at that temperature for 2 hours, and then the temperature was raised to 105°C and refluxed for 4 hours; after cooling, an aqueous solution of citric acid-based waterborne polyamide was obtained.

[0075] A3. Compound preparation: Add 1 part of sodium alginate powder to 100 parts of deionized water and dissolve it at 50℃ and 400 rpm to obtain a sodium alginate solution; under continuous stirring, add 0.5 parts of functionalized guar gum powder and 25 parts by weight of citric acid-based aqueous polyamide solution to the sodium alginate solution in sequence, and maintain stirring at 50℃ for 4 hours to obtain the binder precursor for later use;

[0076] 3) Electrode slurry preparation: 90% lithium iron phosphate, 5% conductive skeleton and 5% conductive carbon black were dry mixed for 8 min; then 4% of the total solid mass of the slurry was added as binder precursor, and deionized water was added to adjust the viscosity of the dispersion. The mixture was first stirred at a low speed of 700 rpm for 25 min, and then stirred at a high speed of 2000 rpm for 45 min to form the electrode slurry.

[0077] 4) Coating and pre-curing: The electrode paste is coated on the aluminum foil current collector, and the wet film thickness is controlled at 200±5μm; then the coated wet electrode sheet is placed in a sealed cavity and exposed to calcium ion mist generated by ultrasonic atomization of 5% calcium chloride solution for 8 min.

[0078] 5) Drying and compaction: The coated and pre-cured electrode sheet is dried by blowing at 80°C for 2 hours, then vacuum dried at 120°C for 12 hours; finally, it is cold-pressed at 25°C and 10 MPa to obtain the electrode sheet.

[0079] Comparative Example 2

[0080] In this comparative example, melamine powder was replaced with urea, and the rest was the same as in Example 1.

[0081] Comparative Example 3

[0082] Preparation of nitrogen-doped carbon nanofiber conductive framework in this comparative example:

[0083] S1. Melamine powder was added to the bacterial cellulose dispersion at a ratio of 1:0.5 between the dry weight of bacterial cellulose and the mass of melamine. The mixture was stirred at 200 rpm for 10 min. The mixture was heated to 60°C and stirred continuously at this temperature for 2 h. The mixture was then cooled and stirred. The mixture was allowed to stand at room temperature for 24 h to obtain the composite hydrogel.

[0084] S2. Freeze-drying: The composite hydrogel was rapidly frozen to -80°C with liquid nitrogen, and then placed in a freeze dryer. Under the conditions of cold trap temperature below -50°C and vacuum degree below 10 Pa, it was freeze-dried for 48 hours to obtain bacterial cellulose / melamine aerogel film.

[0085] S3. Pre-oxidation and carbonization: The aerogel film was placed in a muffle furnace and heated from room temperature to 250°C at a heating rate of 3°C / min in air atmosphere, and held at that temperature for 2 hours. Then the aerogel film was transferred to a tube furnace filled with argon gas at a flow rate of 200 sccm. The temperature was first raised to 900°C at a heating rate of 5°C / min and held at that temperature for 150 minutes. After natural cooling, nitrogen-doped carbon nanofiber membrane was obtained.

[0086] S4. Pulverization: The nitrogen-doped carbon nanofiber membrane is ball-milled to 10-40μm and set aside.

[0087] The rest is the same as in Example 1.

[0088] Comparative Example 4

[0089] In this comparative example, the binder precursor was prepared as follows:

[0090] A1. Synthesis of citric acid-based waterborne polyamide: 19 parts of citric acid and 13 parts of hexamethylenediamine were added to 150 parts of deionized water; under a nitrogen atmosphere, the reaction system was first heated to 80°C and kept at that temperature for 2 hours, and then the temperature was raised to 105°C and refluxed for 4 hours; after cooling, an aqueous solution of citric acid-based waterborne polyamide was obtained.

[0091] A2. Composite preparation: Add 1 part of sodium alginate powder to 100 parts of deionized water and dissolve it at 50℃ and 400 rpm to obtain a sodium alginate solution; under continuous stirring, add 25.5 parts by weight of citric acid-based aqueous polyamide aqueous solution to the sodium alginate solution and maintain stirring at 50℃ for 4 hours to obtain the binder precursor for later use.

[0092] The rest is the same as in Example 1.

[0093] Comparative Example 5

[0094] In this comparative example, the binder precursor was prepared as follows:

[0095] A1. Synthesis of functionalized guar gum: 10 parts of natural guar gum powder were dispersed in 200 parts of deionized water and stirred at 40°C until completely dissolved; 3 parts of 3-aminophenylboronic acid were added, and the pH was adjusted to 9-10 with 1 mol / L sodium hydroxide solution; under nitrogen protection, the reaction system was heated to 70°C and reacted for 6 hours; after the reaction was completed, the mixture was cooled to room temperature, precipitated with anhydrous ethanol and washed three times, and the obtained product was vacuum dried at 50°C for 24 hours and ground to obtain functionalized guar gum powder;

[0096] A2. Compound preparation: Add 1 part of sodium alginate powder to 100 parts of deionized water and dissolve it at 50℃ and 400 rpm to obtain sodium alginate solution; under continuous stirring, add 0.5 parts of functionalized guar gum powder to the sodium alginate solution in sequence, and maintain stirring at 50℃ for 4 hours to obtain the binder precursor for later use.

[0097] The rest is the same as in Example 1.

[0098] Comparative Example 6

[0099] In this comparative example, the electrode slurry was prepared as follows: 90% lithium iron phosphate, 5% conductive skeleton and 5% conductive carbon black were dry mixed for 8 min; then 1% of the total solid mass of the slurry was added as a binder precursor, and deionized water was added to adjust the viscosity of the dispersion. The mixture was first stirred at a low speed of 700 rpm for 25 min, and then stirred at a high speed of 2000 rpm for 45 min to form the electrode slurry; the rest was the same as in Example 1.

[0100] Comparative Example 7

[0101] The electrode sheet in this comparative example is prepared by the following method:

[0102] 1) Electrode slurry preparation: 90% lithium iron phosphate, 5% conductive skeleton and 5% conductive carbon black were dry mixed for 8 min; then 4% of the total solid mass of the slurry was added as binder precursor, and deionized water was added as dispersion to adjust the viscosity. The mixture was first stirred at a low speed of 700 rpm for 25 min, and then stirred at a high speed of 2000 rpm for 45 min to form the electrode slurry.

[0103] 2) Coating: The electrode paste is coated onto the aluminum foil current collector, and the wet film thickness is controlled at 200±5μm;

[0104] 3) Drying and compaction: The coated electrode sheet is dried by blowing at 80°C for 2 hours, then vacuum dried at 120°C for 12 hours; finally, it is cold-pressed at 25°C and 10 MPa to obtain the electrode sheet.

[0105] The rest is the same as in Example 1.

[0106] Comparative Example 8

[0107] The electrode sheet in this comparative example is prepared by the following method:

[0108] 1) Preparation of electrode paste: 90% lithium iron phosphate, 5% flake graphite conductive agent (KS-6) and 5% conductive carbon black were dry mixed for 10 min;

[0109] 2) Slowly add an equal amount of conductive carbon black PVDF powder to NMP solvent, and stir at 800 rpm for 2 hours in a 60°C water bath to prepare a homogeneous adhesive solution;

[0110] 3) Slowly pour the PVDF adhesive into the dry-mixed powder, add NMP solvent to control the solid content of the slurry at 65±3%; stir at 300 rpm for 20 min, then disperse at 1500 rpm for 90 min, add NMP to adjust the viscosity, then vacuum to -0.09 MPa, degas and stir at 100 rpm for 20 min until the slurry is a uniform dark gray paste with a viscosity of 8000±1000 mPa·s, then coat it at 0.8 m / min with a thickness controlled at 200±5 μm; then dry at 85℃ for 5 min, then heat to 105℃ and dry for 10 min, then cool naturally, and finally cold press at 25℃ and 10 MPa pressure to obtain the electrode sheet.

[0111] Experiment 1: Performance Testing

[0112] (1) Adhesion strength test: According to ASTM D3359, the adhesion of the electrode surface is verified by applying pressure-sensitive tape to the surface of the current collector coated with N-CNF and peeling it quickly at a 180° angle. Peeling speed: 300 mm / min. Effective peeling section: ignore the first 25 mm and take the average force value of the subsequent 50 mm. Five samples are taken from each group for testing to obtain the required force value.

[0113] (2) The electrode sheets prepared in Examples 1-3 and Comparative Examples 1-8 were used as working electrodes, lithium metal sheets were used as counter / reference electrodes, polypropylene microporous membranes were used as separators, and conventional lithium battery electrolytes were used to assemble CR2025 coin cells. The discharge specific capacity of the cells was recorded at different current densities of 0.2C and 1C under normal temperature conditions.

[0114] (3) Cyclic performance test:

[0115] Test procedure: Under constant current charge / discharge of 0.1C, cycle 60 times and record the charge / discharge data for the first, 20, 40, and 60 cycles. Under constant current charge / discharge of 0.5C, cycle 300 times and record the charge amount, i.e., the charge / discharge capacity, for the first, 100, and 200 cycles.

[0116] The results are shown in Tables 1, 2, and 3 below:

[0117] Table 1

[0118]

[0119] Table 2

[0120]

[0121] Table 3

[0122]

Claims

1. A method for preparing an electrode sheet, comprising electrode slurry preparation, coating and pre-curing, drying and compaction; characterized in that: The electrode slurry is prepared by: dry mixing 88-92% of active material, 4-6% of nitrogen-doped carbon nanofiber conductive framework and 4-6% of conductive carbon black for 5-10 minutes; then adding 3-5% of binder precursor by the total solid mass of the slurry, adding deionized water as dispersion, stirring at low speed of 500-800 rpm for 20-30 minutes, and then stirring at high speed of 1500-2500 rpm for 30-60 minutes to prepare the electrode slurry; The method for preparing the nitrogen-doped carbon nanofiber conductive framework includes the following steps: S1. Bacterial cellulose composite: Melamine powder is added to a bacterial cellulose dispersion with a solid content of 0.5%-1.0% at a ratio of bacterial cellulose dry weight to melamine weight of 1:(0.5~2.0). The mixture is stirred at 100-200 rpm for 10-15 min. The mixture is then heated to 50-60℃ and stirred continuously at this temperature for 2-4 h. The mixture is then cooled and stirred, and allowed to stand at room temperature for 12-24 h to form a bacterial cellulose / melamine composite hydrogel with a uniform structure. S2. Freeze-drying: The composite hydrogel is rapidly frozen to -80°C with liquid nitrogen, and then placed in a freeze dryer. Under the conditions of cold trap temperature below -50°C and vacuum degree below 10 Pa, it is freeze-dried for 24-48 hours to obtain bacterial cellulose / melamine aerogel film. S3. Pre-oxidation and carbonization: The aerogel film is placed in a muffle furnace and heated from room temperature to 220-250℃ at a heating rate of 2-3℃ / min in air atmosphere, and held for 2 hours. Then the aerogel film is transferred to a tube furnace filled with argon gas at a flow rate of 200 sccm. The temperature is first raised to 400-500℃ at a heating rate of 2℃ / min and held for 60 minutes, and then raised to 800-1000℃ at a heating rate of 5-8℃ / min and held for 90 minutes. After natural cooling, nitrogen-doped carbon nanofiber membrane is obtained. S4. Pulverization: Nitrogen-doped carbon nanofiber membranes are pulverized to 10-40 μm to obtain the final product. The method for preparing the binder precursor includes the following steps: A1. Synthesis of functionalized guar gum: 10 parts of natural guar gum powder were dispersed in 200 parts of deionized water and stirred at 40°C until completely dissolved; 2-5 parts of 3-aminophenylboronic acid were added, and the pH was adjusted to 9-10 with 1 mol / L sodium hydroxide solution; under nitrogen protection, the reaction system was heated to 70°C and reacted for 6 hours; after the reaction was completed, the mixture was cooled to room temperature, precipitated with anhydrous ethanol and washed three times, and the obtained product was vacuum dried at 50°C for 24 hours and ground to obtain functionalized guar gum powder; A2. Synthesis of citric acid-based waterborne polyamide: Add 19-20 parts of citric acid and 12-15 parts of hexamethylenediamine to 150 parts of deionized water; under a nitrogen atmosphere, first heat the reaction system to 80°C and keep it at that temperature for 2 hours, then raise the temperature to 105°C and continue to reflux for 4 hours; after cooling, obtain an aqueous solution of citric acid-based waterborne polyamide. A3. Composite preparation: Add 1-2 parts of sodium alginate powder to 100 parts of deionized water and dissolve it at 50℃ and 400 rpm to obtain a sodium alginate solution; under continuous stirring, add 0.3-0.6 parts of functionalized guar gum powder and 20-30 parts of citric acid-based aqueous polyamide solution to the sodium alginate solution in sequence, and maintain stirring at 50℃ for 4 hours to obtain the binder precursor.

2. The preparation method according to claim 1, characterized in that: The active material is one of lithium iron phosphate, ternary materials, or silicon-carbon composite materials.

3. The preparation method according to claim 1, characterized in that: The coating and pre-curing process includes: coating the electrode slurry onto the current collector, with the wet film thickness controlled at 200±5μm; then placing the coated wet electrode sheet in a sealed cavity and exposing it to calcium ion mist generated by ultrasonic atomization of a 5% (w / w) calcium chloride solution for 5-10 minutes.

4. The preparation method according to claim 1, characterized in that: The drying and compaction process involves drying the coated and pre-cured electrode sheet in a forced-air dryer at 80°C for 2 hours, followed by vacuum drying at 120°C for 12 hours. Finally, the electrode sheet is cold-pressed at 25°C and 10MPa to obtain the electrode sheet.

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