Preparation method suitable for large-specific-surface-area sodium vanadium phosphate pole piece

Abstract

The invention discloses a preparation method suitable for a large-specific-surface-area sodium vanadium phosphate pole piece, which comprises the following steps: weighing sodium polyacrylate, polyvinylidene fluoride and N-methyl pyrrolidone with the molecular weight of 80000-250000 according to the mass ratio of 1: (0.8-2): (40-60), putting into a container, and stirring to obtain an initial glue solution with the viscosity of 8000-15000mPa. S; adding a conductive agent and sodium vanadium phosphate, dispersing and stirring to obtain primary slurry with the viscosity of 5000-12000 mPa.s; adding N-methyl pyrrolidone, vacuumizing, dispersing and stirring, and controlling the viscosity of the slurry to be 5500 + / -1000 mPa.s to obtain positive electrode slurry; coating the surface of a foil and drying to obtain a pole roll; and carrying out rolling die cutting on the pole roll to obtain the pole piece. The problems of poor battery rate capability and poor cycle stability caused by poor processability during preparation of a large-specific-surface-area sodium vanadium phosphate pole piece are solved.

Description

Technical Field

[0001] This invention relates to the field of positive electrode sheets for sodium-ion batteries, and specifically to a process for preparing sodium vanadium phosphate electrode sheets with large specific surface area. Background Technology

[0002] With increasingly prominent environmental problems and growing societal emphasis on environmental protection, traditional energy sources can no longer meet people's energy demands. Therefore, there is an urgent need to develop renewable and clean energy sources. However, renewable resources such as wind, solar, and tidal energy are intermittent energy sources, unable to provide stable energy output for extended periods, thus requiring stable energy storage devices. Rechargeable lithium-ion batteries, with their stable performance, high energy density, and environmental friendliness, have become the preferred choice for new energy storage devices. However, lithium ions are scarce in the Earth's crust, leading to high costs for lithium-ion batteries. Developing alternatives to lithium-ion batteries has become an important research task in the energy storage industry. Sodium and lithium belong to the same group and have similar chemical properties. Furthermore, sodium is abundant in the Earth's crust, making sodium-ion batteries increasingly attractive to researchers.

[0003] Sodium vanadium phosphate (PVP) cathode materials belong to the polyanionic cathode material category. Its unique sodium superionic conductor structure provides three-dimensional sodium ion transport channels, resulting in excellent rate performance and superior low-temperature performance. Researchers often select porous PNP with a large specific surface area and employ carbon coating to further increase the specific surface area of ​​the cathode active material, thereby improving its cycle performance and rate performance. However, due to the unfilled d orbitals of vanadium ions in PNP, Jahn-Teller distortion easily occurs, causing twisting of the bond lengths or bond angles of the VO6 octahedrons. This leads to a locally metastable structure. While carbon coating of PNP increases the specific surface area, it further amplifies structural instability. The high surface atomic ratio and numerous unsaturated chemical bonds result in a sharp increase in surface energy and easy particle agglomeration, leading to poor processing performance during cell electrode fabrication. Because a high specific surface area means a large number of active adsorption sites, carbon-coated sodium vanadium phosphate materials are prone to forming surface hydroxyl groups (-OH) or adsorbing a large amount of solvent, making their surface highly hydrophilic. The carbon layer competes with the binder for solvent molecules, weakening the solubility and dispersion stability of the binder. This manifests as poor dispersion during the homogenization process, requiring dispersion treatment to achieve uniform slurry. Poor dispersion leads to uneven distribution of active materials in the positive electrode sheet, which can easily cause problems such as excessively high local current density and intensified polarization. This limits the ability of large specific surface area carbon-coated sodium vanadium phosphate positive electrodes to improve rate performance and cycle stability. It may also cause active material to fall off during long-term charge and discharge, leading to rapid capacity decay of the battery.

[0004] Therefore, it is necessary to develop a process for preparing sodium vanadium phosphate electrodes with good dispersion and bonding properties, suitable for large specific surface area, so as to improve the rate performance and cycle stability of the battery. Summary of the Invention

[0005] This invention addresses the existing technology's need for sodium vanadium phosphate (PVP) with a large specific surface area as the positive electrode active material in sodium-ion batteries, and the requirement for further carbon coating to improve the rate performance and cycle stability of the positive electrode material. However, due to the instability of the VO6 octahedral structure in PNP, the large specific surface area after carbon coating leads to poor processing performance during homogenization, and even active material detachment, thus limiting the improvement of the rate performance and cycle stability of the positive electrode active material. This invention innovatively uses sodium polyacrylate as a binder and proposes a new preparation process for PNP electrode sheets. It employs a strategy of first applying a binder, then gradually adding a conductive agent and PNP, and thoroughly stirring. By controlling the viscosity of the binder solution in multiple steps, this improves the processing performance during the preparation of large specific surface area PNP positive electrode sheets, increases the dispersion and bonding performance of the large specific surface area PNP positive electrode material during homogenization, and prevents active material detachment during long-term charge-discharge processes, resulting in better battery rate performance and cycle stability.

[0006] This invention is achieved through the following technical solution:

[0007] This invention provides a method for preparing sodium vanadium phosphate electrodes with large specific surface area, comprising the following steps:

[0008] S1: Applying adhesive: Weigh sodium polyacrylate, polyvinylidene fluoride and N-methylpyrrolidone (NMP) with a molecular weight of 800,000 to 2,500,000 in a mass ratio of 1:(0.8~2):(40~60) into a container and stir.

[0009] S2: Dispersion of adhesive solution: The adhesive solution obtained in S1 is vacuumed and dispersed and stirred to obtain the initial adhesive solution. The viscosity of the initial adhesive solution is controlled at 8000~15000mPa·s.

[0010] S3: Adding conductive agent and sodium vanadium phosphate: Add conductive agent and sodium vanadium phosphate to the initial colloid obtained in S2. After adding each component, disperse, stir, and scrape the mixture to obtain a primary slurry. The viscosity of the primary slurry is controlled between 5000 and 12000 mPa·s. The specific surface area of ​​the sodium vanadium phosphate cathode material is 18–20 m². 2 / g;

[0011] S4: Adjust viscosity: Add N-methylpyrrolidone (NMP), vacuum, disperse and stir, and adjust the viscosity of the slurry to 5500±1000mPa·s to obtain the positive electrode slurry;

[0012] S5: The positive electrode slurry obtained in S4 is coated onto the surface of the foil and dried to obtain an electrode roll; the electrode roll is rolled and die-cut to obtain an electrode sheet.

[0013] This invention employs a strategy of first gelling sodium polyacrylate and polyvinylidene fluoride in a solution, followed by the step-by-step addition of a conductive agent and sodium vanadium phosphate. This strategy controls the viscosity of the adhesive or slurry at several key steps. Utilizing the dispersing and adhesive properties of sodium polyacrylate, it is selected as the key component for bonding and dispersion during the preparation of sodium vanadium phosphate electrodes. The mass ratio of sodium polyacrylate, polyvinylidene fluoride, and N-methylpyrrolidone (NMP) is also limited. This approach achieves good initial adhesive viscosity and dispersion performance, laying a solid foundation for obtaining large specific surface area sodium vanadium phosphate electrodes with further enhanced electrochemical performance. It avoids the problem of ineffective dispersion and agglomeration that can occur when directly adding large specific surface area sodium vanadium phosphate in the initial stage. Simultaneously, it controls the initial adhesive viscosity within a certain range to prevent… Because excessively low adhesive viscosity affects the bonding between materials, and also avoids the problem of excessively high initial adhesive viscosity affecting the subsequent dispersion of sodium vanadium phosphate and conductive agent, a strategy of adding conductive agent and sodium vanadium phosphate in stages is adopted. The viscosity of the initial slurry is controlled within a certain range. At this point, the final target slurry viscosity can be achieved with little or no NMP. The strategy of stirring at each step after adding materials in stages further improves the uniformity of the slurry. The above strategy overcomes the problem that sodium vanadium phosphate has an unstable vanadium-oxygen polyhedron (VO6) structure. After carbon coating of sodium vanadium phosphate, due to the instability of vanadium, the specific surface area further increases, and the particle surface energy increases. The particle surface groups are unstable and easy to agglomerate, resulting in poor solubility and dispersion stability of the binder, poor processing performance during homogenization, and limited improvement of the rate performance and cycle performance of the positive electrode active material.

[0014] As a further preferred embodiment, the viscosity of the initial adhesive in S2 is 8000-9000 mPa·s, and the viscosity of the initial slurry in S3 is 5000-7000 mPa·s.

[0015] As a further embodiment, the solid content of the adhesive in S1 is 4.3% to 5.3%.

[0016] As a further embodiment, the mass ratio of sodium polyacrylate to polyvinylidene fluoride in S1 is 1:(1-2).

[0017] As a further option, the molecular weight of sodium polyacrylate in S1 is 1 million to 2 million.

[0018] As a further preferred embodiment, the solid content of the adhesive in S1 is 4.5% to 5%.

[0019] As a further preferred embodiment, the mass ratio of sodium polyacrylate to polyvinylidene fluoride in S1 is 3:4.

[0020] As a further preferred embodiment, the molecular weight of sodium polyacrylate in S1 is 1.4 million to 1.6 million.

[0021] As a further embodiment, the total mass of the sodium polyacrylate accounts for 1.5 to 2.3% of the total mass of the material.

[0022] The total mass of the materials refers to the total mass of the powders of sodium polyacrylate, polyvinylidene fluoride, conductive agent Super P, sodium vanadium phosphate, and carbon nanotubes during the preparation of the large specific surface area sodium vanadium phosphate electrode.

[0023] As a further preferred embodiment, S1 specifically comprises:

[0024] Weigh out sodium polyacrylate, polyvinylidene fluoride and N-methylpyrrolidone in the target stoichiometric ratio, heat to 50-75°C, and after heating to the target temperature, set the dispersion disc speed to 400-600 rpm and the stirring paddle speed to 15-25 rpm, stir for 7-13 minutes, and scrape off the material adhering to the stirring paddle.

[0025] As a further preferred embodiment, step S2 is as follows: The adhesive solution obtained in step S1 is evacuated to -85 to -95 kPa, the dispersing disc speed is set to 3000 to 3500 rpm, the stirring paddle speed is set to 25 to 35 rpm, and the mixture is stirred for 25 to 35 minutes. After this is completed, scraping is performed. Alternatively, the adhesive solution is evacuated to -85 to -95 kPa, the dispersing disc speed is set to 3000 to 3500 rpm, the stirring paddle speed is set to 30 to 40 rpm, and the mixture is stirred for 120 to 180 minutes. After scraping, the viscosity of the initial adhesive solution is measured.

[0026] As a further embodiment, S3 involves weighing 2.4% to 3.5% of the total material mass of conductive agent Super P into a homogenizing tank, dispersing, stirring, and scraping the material; weighing 91% to 94% of the total material mass of sodium vanadium phosphate into a homogenizing tank, dispersing, stirring, and scraping the material; vacuuming the obtained material, dispersing, stirring, and scraping the material; weighing 0.45% to 0.6% of the total material mass of carbon nanotubes (CNTs), vacuuming, dispersing, stirring, and cooling the temperature to 25±2℃ before measuring the initial slurry viscosity.

[0027] As a further preferred embodiment, the dispersion disc used in S3 has a rotation speed of 100-3500 rpm, a stirring speed of 5-40 rpm, a vacuum degree of -85--95 kPa, and a stirring time of 5-180 min.

[0028] As a further preferred embodiment, step S3 involves weighing 2.4%–3.5% of the total material mass of conductive agent Super P into a homogenizing tank, setting the dispersion disc speed to 400–600 rpm and the stirring paddle speed to 15–25 rpm, stirring for 7–13 minutes, and then scraping the material. The tank is then evacuated to -85–-95 kPa, the dispersion disc speed is set to 3000–3500 rpm, and the stirring paddle speed to 30–40 rpm, stirring for 110–130 minutes, and then scraping the material. In two separate batches, 91%–94% of the total material mass of sodium vanadium phosphate is weighed into the homogenizing tank, and the dispersion disc speed is set to 100–300 rpm and the stirring paddle speed to 7–13 rpm, stirring for 5–15 minutes, and then scraping the material. The tank is then evacuated to -80–-100 kPa, the dispersion disc speed is set to 3000–3500 rpm, and the stirring paddle speed to 30–40 rpm, stirring for 50–70 minutes, and then scraping the material. Vacuum was applied to -85 to -95 kPa, the dispersion disc was rotated at 3000 to 3500 rpm, and the stirring paddle at 30 to 40 rpm. After stirring for 110 to 130 minutes, 0.45% to 0.6% of the total material mass of carbon nanotubes (CNTs) were weighed. Vacuum was applied to -85 to -95 kPa, the dispersion disc was rotated at 1500 to 2500 rpm, and the stirring paddle at 25 to 35 rpm. After stirring for 50 to 70 minutes, cooling water was circulated to lower the slurry temperature to 25 ± 2℃. During the cooling process, the dispersion disc was rotated at 0 rpm and the stirring paddle at 5 to 15 rpm. After the temperature stabilized, the initial slurry viscosity was measured.

[0029] As a further step, step S4 involves adding NMP, evacuating to -85 to -95 kPa, setting the dispersion disc speed to 1500 to 2500 rpm, the stirring paddle speed to 25 to 35 rpm, and stirring for 25 to 35 minutes. The viscosity is measured using a No. 4 rotor at 50 to 70 rpm, and adjusted to 5500 ± 1000 mPa·s. If the viscosity is too high, NMP is added for adjustment; if the viscosity is too low, the slurry needs to be homogenized again. The fineness of the slurry is ≤20.

[0030] As an example, step S5 involves sieving the uniformly stirred slurry from step S4 through a sieve and setting a single-sided surface density of 15–20 mg / cm³. 2 The conveyor belt speed is 0.5–1.5 m / min. The coating width, coating length, and coating gap can be determined according to the electrode design and are not specifically limited. The slurry is applied to the aluminum foil surface using an intermittent coating method to obtain the electrode roll. The coated electrode roll is then rolled using a roller press to achieve a compaction density of 1.5–2.5 g / cm³. 3 The electrode roll is cut into electrode sheets using a die-cutting machine.

[0031] Preferably, the mesh size of the sieve is 100 to 300.

[0032] For example, the coating width is 95% to 99.5% of the foil width, the coating length is 50 to 90 mm, and the coating gap is 4 to 20 mm.

[0033] As a further preferred embodiment, the polyvinylidene fluoride is polyvinylidene fluoride with a molecular weight of 5130 and / or polyvinylidene fluoride with a molecular weight of 900.

[0034] As a further preferred embodiment, the polyvinylidene fluoride is polyvinylidene fluoride with a molecular weight of 5130.

[0035] As a further embodiment, the carbon nanotubes are a carbon nanotube dispersion, wherein the mass percentage of carbon nanotubes in the carbon nanotube dispersion is 4.5% to 5.5%.

[0036] As a further option, the foil material includes aluminum foil and / or carbon-coated aluminum foil.

[0037] The features and beneficial effects of this invention are as follows:

[0038] This invention provides a process for preparing sodium vanadium phosphate positive electrode sheets. This technical solution significantly improves the stability of sodium-ion batteries under high voltage, helps to construct a stable interfacial film, and enhances the interaction between the overall active particles and the binder. This invention is particularly suitable for sodium vanadium phosphate with a large specific surface area (18-20 μm²). 2 To address the issues of poor slurry processability and easy detachment of active materials, this method innovatively employs a composite bonding system of sodium polyacrylate and polyvinylidene fluoride. This involves first constructing a basic network through adhesive application, followed by a stepwise viscosity control process that adds two conductive agents (Super P and carbon nanotubes) and sodium vanadium phosphate. Combined with the electrostatic dispersion and flexible bridging effects of sodium polyacrylate, this significantly improves slurry uniformity and electrode bonding strength, effectively inhibiting active material agglomeration and detachment while reducing solvent usage. The resulting slurry has a moderate viscosity, requiring no additional or minimal NMP for viscosity adjustment. It exhibits fine slurry texture, uniform areal density, high electrode compaction density, and excellent electrode performance. This collaborative process effectively prevents structural collapse, active particle breakage, transition metal dissolution, and excessive side reactions in the cathode material under high voltage and high temperature, thereby significantly improving battery rate performance and cycle stability. Attached Figure Description

[0039] Figure 1 This is a schematic diagram showing the size of the electrode in Example 1;

[0040] Figure 2 A photograph of the positive electrode slurry prepared in Example 1;

[0041] Figure 3 A photograph of the positive electrode sheet prepared in Example 1;

[0042] Figure 4 A photograph of the positive electrode slurry prepared in Example 2;

[0043] Figure 5 A photograph of the positive electrode sheet prepared in Example 2;

[0044] Figure 6 A photograph of the positive electrode slurry prepared in Example 3;

[0045] Figure 7 A photograph of the positive electrode sheet prepared in Example 3. Detailed Implementation

[0046] To facilitate understanding of the present invention, the following will provide a more comprehensive description of the preparation process of the positive electrode sheet of the sodium vanadium phosphate soft-pack battery cell, in conjunction with the specific details and embodiments of the present invention, but this does not limit the scope of the present invention.

[0047] This invention addresses the need in existing technologies to use sodium vanadium phosphate (CNP) with a large specific surface area as the positive electrode active material for sodium-ion batteries, and the further requirement of carbon coating to improve the rate performance and cycle stability of the positive electrode material. However, due to the instability of the VO6 octahedral structure in CNP, the large specific surface area after carbon coating leads to poor processing performance during homogenization, and even active material detachment, thus limiting the improvement of the rate performance and cycle stability of the positive electrode active material. This invention innovatively uses sodium polyacrylate as a binder and optimizes the preparation process of CNP electrode sheets. It employs a strategy of first applying the adhesive, then gradually adding the conductive agent and CNP while thoroughly stirring, controlling the viscosity of the adhesive solution in multiple steps. This improves the processing performance of the large specific surface area CNP positive electrode sheet preparation, increases the dispersion and bonding performance of the large specific surface area CNP positive electrode material during homogenization, and makes the active material less prone to detachment during long-term charge and discharge, resulting in better battery rate performance and cycle stability.

[0048] This invention is achieved through the following technical solution:

[0049] This invention provides a process for preparing sodium vanadium phosphate electrodes with large specific surface area, comprising the following steps:

[0050] S1: Applying adhesive: Weigh sodium polyacrylate, polyvinylidene fluoride and N-methylpyrrolidone (NMP) with a molecular weight of 800,000 to 2,500,000 in a mass ratio of 1:(0.8~2):(40~60) into a container and stir.

[0051] S2: Dispersion of adhesive solution: The adhesive solution obtained in S1 is vacuumed and dispersed and stirred to obtain the initial adhesive solution. The viscosity of the initial adhesive solution is controlled at 8000~15000mPa·s.

[0052] S3: Adding conductive agent and sodium vanadium phosphate: Add conductive agent and sodium vanadium phosphate to the initial colloid obtained in S2. After adding each component, disperse, stir, and scrape the mixture to obtain a primary slurry. The viscosity of the primary slurry is controlled between 5000 and 12000 mPa·s. The specific surface area of ​​the sodium vanadium phosphate cathode material is 18–20 m². 2 / g;

[0053] S4: Adjust viscosity: Add N-methylpyrrolidone (NMP), vacuum, disperse and stir, and adjust the viscosity of the slurry to 5500±1000mPa·s to obtain the positive electrode slurry;

[0054] S5: The positive electrode slurry obtained in S4 is coated onto the surface of the foil and dried to obtain an electrode roll; the electrode roll is rolled and die-cut to obtain an electrode sheet.

[0055] This invention employs a strategy of first gelling sodium polyacrylate and polyvinylidene fluoride in a solution, followed by the step-by-step addition of a conductive agent and sodium vanadium phosphate. This strategy controls the viscosity of the adhesive or slurry at several key steps. Utilizing the dispersing and adhesive properties of sodium polyacrylate, it is selected as the key component for bonding and dispersion during the preparation of sodium vanadium phosphate electrodes. The mass ratio of sodium polyacrylate, polyvinylidene fluoride, and N-methylpyrrolidone (NMP) is also limited. This approach achieves good initial adhesive viscosity and dispersion performance, laying a solid foundation for obtaining large specific surface area sodium vanadium phosphate electrodes with further enhanced electrochemical performance. It avoids the problem of ineffective dispersion and agglomeration that can occur when directly adding large specific surface area sodium vanadium phosphate in the initial stage. Simultaneously, it controls the initial adhesive viscosity within a certain range to prevent… Because excessively low adhesive viscosity affects the bonding between materials, and also avoids the problem of excessively high initial adhesive viscosity affecting the subsequent dispersion of sodium vanadium phosphate and conductive agent, a strategy of adding conductive agent and sodium vanadium phosphate in stages is adopted. The viscosity of the initial slurry is controlled within a certain range. At this point, the final target slurry viscosity can be achieved with little or no NMP. The strategy of stirring at each step after adding materials in stages further improves the uniformity of the slurry. The above strategy overcomes the problem that sodium vanadium phosphate has an unstable vanadium-oxygen polyhedron (VO6) structure. After carbon coating of sodium vanadium phosphate, due to the instability of vanadium, the specific surface area further increases, and the particle surface energy increases. The particle surface groups are unstable and easy to agglomerate, resulting in poor solubility and dispersion stability of the binder, poor processing performance during homogenization, and limited improvement of the rate performance and cycle performance of the positive electrode active material.

[0056] As a further preferred example, the viscosity of the initial adhesive in S2 is 8000-9000 mPa·s, and the viscosity of the initial slurry in S3 is 5000-7000 mPa·s.

[0057] This invention can further control the viscosity of the initial adhesive solution and the viscosity of the initial slurry during the preparation of sodium vanadium phosphate electrodes with large specific surface area, thereby obtaining a sodium vanadium phosphate electrode with a large specific surface area that can achieve the final target slurry viscosity without or with less NMP. At this time, the slurry has better bonding and dispersing properties, thus obtaining better electrochemical performance. The viscosity of the initial adhesive solution and the viscosity of the initial slurry can be further optimized individually or in combination with parameters such as the solid content of the adhesive solution, the mass ratio of sodium polyacrylate to polyvinylidene fluoride, the molecular weight of sodium polyacrylate, and the stirring parameters in the preparation method.

[0058] As a further example, the solid content of the adhesive in S1 is 4.3% to 5.3%.

[0059] As a further example, the mass ratio of sodium polyacrylate to polyvinylidene fluoride in S1 is 1:(1-2).

[0060] As a further example, the molecular weight of sodium polyacrylate in S1 is 1 million to 2 million.

[0061] The sodium polyacrylate used in this invention is a chain-like polymer with good adhesive properties, and its molecular chain contains carboxyl groups (-COO). - It can provide steric hindrance through electrostatic repulsion, significantly improving the dispersion uniformity of large specific surface area sodium vanadium phosphate particles in the slurry, reducing the aggregation of large specific surface area carbon-coated sodium vanadium phosphate, and counteracting the high surface energy of carbon-coated sodium vanadium phosphate; at the same time, its flexible long-chain structure can effectively bridge the active material, conductive agent (Super P / CNT) and current collector, enhance the interfacial bonding force, and inhibit the shedding of active material during charging and discharging. In addition, it contains only sodium element besides carbon, hydrogen and oxygen elements, so it will not introduce impurities during the charging and discharging of the cell and cause the cell performance to deteriorate. Furthermore, the sodium ions in sodium polyacrylate can optimize the ion diffusion kinetics of the electrode / electrolyte interface, reduce the interfacial impedance, and thus improve the rate performance and cycle stability of the battery; while controlling the solid content of the adhesive, by compounding sodium polyacrylate and PVDF and optimizing the mass ratio in the range of 1:1 to 1:2, the solubility limitation of a single polymer is overcome, and the strong film-forming properties of PVDF and the ion conduction advantages of sodium polyacrylate are synergistically utilized to form a complementary bonding network. This invention can also optimize the molecular weight of sodium polyacrylate within a certain range, avoiding excessive molecular chain entanglement, slurry viscosity increase and coating performance deterioration caused by excessively high molecular weight; it also avoids insufficient chain length, reduced bonding strength and reduced electrode flexibility when the molecular weight is too low. When the molecular weight of sodium polyacrylate is between 1 million and 2 million, the solubility, dispersibility and bonding strength of sodium polyacrylate are balanced.

[0062] As a further preferred example, the solid content of the adhesive in S1 is 4.5% to 5%.

[0063] As a further preferred example, the mass ratio of sodium polyacrylate to polyvinylidene fluoride in S1 is 3:4.

[0064] As a further preferred example, the molecular weight of sodium polyacrylate in S1 is 1.4 million to 1.6 million.

[0065] The present invention can further optimize the solid content of the adhesive solution, the mass ratio of sodium polyacrylate and polyvinylidene fluoride, and the molecular weight of sodium polyacrylate in S1, either individually or simultaneously, to obtain a more ideal initial adhesive solution viscosity and dispersibility.

[0066] As a further example, the total mass of the sodium polyacrylate accounts for 1.5 to 2.3% of the total mass of the material.

[0067] The total mass of the materials refers to the total mass of the powders of sodium polyacrylate, polyvinylidene fluoride, conductive agent Super P, sodium vanadium phosphate, and carbon nanotubes during the preparation of the large specific surface area sodium vanadium phosphate electrode.

[0068] As a further preferred example, S1 specifically refers to:

[0069] Weigh out sodium polyacrylate, polyvinylidene fluoride and N-methylpyrrolidone in the target stoichiometric ratio, heat to 50-75°C, and after heating to the target temperature, set the dispersion disc speed to 400-600 rpm and the stirring paddle speed to 15-25 rpm, stir for 7-13 minutes, and scrape off the material adhering to the stirring paddle.

[0070] As a further preferred example, step S2 is as follows: The adhesive solution obtained in step S1 is evacuated to -85 to -95 kPa, the dispersing disc speed is set to 3000 to 3500 rpm, the stirring paddle speed is set to 25 to 35 rpm, and the mixture is stirred for 25 to 35 minutes. After this is completed, the material is scraped off. Alternatively, the initial viscosity of the adhesive solution is measured after scraping off the material, with the dispersing disc speed set to -85 to -95 kPa, the stirring paddle speed set to 3000 to 3500 rpm, the stirring paddle speed set to 30 to 40 rpm, and the mixture stirred for 120 to 180 minutes.

[0071] As a further example, S3 involves weighing 2.4% to 3.5% of the total material mass of conductive agent Super P into a homogenizing tank, dispersing, stirring, and scraping the material; weighing 91% to 94% of the total material mass of sodium vanadium phosphate into a homogenizing tank, dispersing, stirring, and scraping the material; vacuuming the obtained material, dispersing, stirring, and scraping the material; weighing 0.45% to 0.6% of the total material mass of carbon nanotubes (CNTs), vacuuming, dispersing, stirring, and cooling the temperature to 25±2℃ before measuring the initial slurry viscosity.

[0072] This invention can also be improved by adding two conductive agents. Super P, a conductive agent with high specific surface area and excellent dispersibility, is preferentially adsorbed on the surface of sodium vanadium phosphate particles with large specific surface area, thereby reducing the interfacial contact resistance. Meanwhile, carbon nanotubes (CNTs) are introduced into a one-dimensional tubular structure to construct a three-dimensional through-conductive framework in the electrode, which enhances long-range electron transport. The synergistic effect of the two agents results in both good dispersion performance and electron transport performance.

[0073] As a further preferred example, the dispersion disc used in S3 has a rotation speed of 100-3500 rpm, a stirring speed of 5-40 rpm, a vacuum degree of -85--95 kPa, and a stirring time of 5-180 min.

[0074] As a further preferred example, step S3 involves weighing 2.4%–3.5% of the total material mass of conductive agent Super P into a homogenizing tank, setting the dispersion disc speed to 400–600 rpm and the stirring paddle speed to 15–25 rpm, stirring for 7–13 minutes, and then scraping the material. The tank is then evacuated to -85–-95 kPa, the dispersion disc speed to 3000–3500 rpm, and the stirring paddle speed to 30–40 rpm, stirring for 110–130 minutes, and then scraping the material. In two separate batches, 91%–94% of the total material mass of sodium vanadium phosphate is weighed into the homogenizing tank, and the dispersion disc speed is set to 100–300 rpm and the stirring paddle speed to 7–13 rpm, stirring for 5–15 minutes, and then scraping the material. The tank is then evacuated to -80–-100 kPa, the dispersion disc speed to 3000–3500 rpm, and the stirring paddle speed to 30–40 rpm, stirring for 50–70 minutes, and then scraping the material. Vacuum was applied to -85 to -95 kPa, the dispersion disc was rotated at 3000 to 3500 rpm, and the stirring paddle at 30 to 40 rpm. After stirring for 110 to 130 minutes, 0.45% to 0.6% of the total material mass of carbon nanotubes (CNTs) were weighed. Vacuum was applied to -85 to -95 kPa, the dispersion disc was rotated at 1500 to 2500 rpm, and the stirring paddle at 25 to 35 rpm. After stirring for 50 to 70 minutes, cooling water was circulated to lower the slurry temperature to 25 ± 2℃. During the cooling process, the dispersion disc was rotated at 0 rpm and the stirring paddle at 5 to 15 rpm. After the temperature stabilized, the initial slurry viscosity was measured.

[0075] As a further example, S4 involves adding NMP, evacuating to -85 to -95 kPa, setting the dispersion disc speed to 1500 to 2500 rpm, the stirring paddle speed to 25 to 35 rpm, and stirring for 25 to 35 minutes. The viscosity is measured using a No. 4 rotor at 50 to 70 rpm, and adjusted to 5500 ± 1000 mPa·s. If the viscosity is too high, NMP is added for adjustment; if the viscosity is too low, homogenization is required again. The fineness of the slurry is ≤20.

[0076] As an example, step S5 involves sieving the uniformly stirred slurry from step S4 through a sieve and setting a single-sided surface density of 15–20 mg / cm³. 2 The conveyor belt speed is 0.5–1.5 m / min. The coating width, coating length, and coating gap can be determined according to the electrode design and are not specifically limited. The slurry is applied to the aluminum foil surface using an intermittent coating method to obtain the electrode roll. The coated electrode roll is then rolled using a roller press to achieve a compaction density of 1.5–2.5 g / cm³. 3 The electrode roll is cut into electrode sheets using a die-cutting machine.

[0077] Preferably, the mesh size of the sieve is 100 to 300.

[0078] For example, the coating width is 95% to 99.5% of the foil width, the coating length is 50 to 90 mm, and the coating gap is 4 to 20 mm.

[0079] As a further preferred example, the polyvinylidene fluoride is polyvinylidene fluoride with a molecular weight of 5130 and / or polyvinylidene fluoride with a molecular weight of 900.

[0080] As a further preferred example, the polyvinylidene fluoride is polyvinylidene fluoride with a molecular weight of 5130.

[0081] As a further example, the carbon nanotubes are a carbon nanotube dispersion, and the mass percentage of carbon nanotubes in the carbon nanotube dispersion is 4.5% to 5.5%.

[0082] As a further example, the foil includes aluminum foil and / or carbon-coated aluminum foil.

[0083] As a specific example of the implementation of this invention, detailed cases are provided below:

[0084] Example 1

[0085] This embodiment provides the preparation process of the sodium vanadium phosphate positive electrode sheet, including the following steps:

[0086] When the ambient dew point is -30 to -40°C and the ambient temperature is 20 to 25°C...

[0087] (1) Homogenization

[0088] Step 1: Applying the adhesive. Set the solid content of the adhesive solution to 4.6%, and the mass ratio of sodium polyacrylate to polyvinylidene fluoride (PVDF) to 3:4. Under the condition of ensuring the ambient dew point and ambient temperature, weigh out 2016.4g of NMP, 55.56g of PVDF5130, and 41.67g of 1.5 million molecular weight sodium polyacrylate and add them to the homogenizing tank. Heat to 60℃±2℃. After reaching the temperature, set the dispersion disc speed to 500rpm and the stirring paddle speed to 20rpm, and stir for 10min. Scrape off the material adhering to the stirring paddle.

[0089] Step 2: Dispersion of the adhesive. Vacuum to -90 kPa, disperse disc speed 3200 rpm, agitator speed 30 rpm, stir for 30 minutes, then scrape the material. Vacuum to -90 kPa, disperse disc speed 3200 rpm, agitator speed 35 rpm, stir for 150 minutes, then scrape the material.

[0090] Step 3: Add conductive agent Super P. Weigh 58.33g of conductive agent Super P and add it to the homogenizing tank. Set the dispersion disc speed to 500rpm and the stirring paddle speed to 20rpm, stir for 10min, and then scrape the material. Vacuum to -90Kpa, set the dispersion disc speed to 3200rpm and the stirring paddle speed to 35rpm, stir for 120min, and then scrape the material.

[0091] Step 4: Add sodium vanadium phosphate. Weigh out 1000g in two batches, for a total of 2000g, with a specific surface area of ​​18-20m². 2 / g of sodium vanadium phosphate was added to a homogenizing tank, and the dispersion disc was set to 200 rpm and the stirring paddle to 10 rpm. The mixture was stirred for 10 minutes and then scraped off.

[0092] Step 5: Dispersion of main materials. Vacuum to -90 kPa, disperse disc speed 3200 rpm, agitator speed 35 rpm, stir for 60 minutes, then scrape the material. Vacuum to -90 kPa, disperse disc speed 3200 rpm, agitator speed 35 rpm, stir for 120 minutes.

[0093] Step 6: Add carbon nanotubes. Weigh 11.4g of carbon nanotubes (CNTs). Evacuate to -90Kpa, set the dispersion disk speed to 2000rpm and the stirring paddle speed to 30rpm, stir for 60min, then circulate cooling water to cool the slurry temperature to 25±2℃. During the cooling process, the dispersion disk speed is 0rpm and the stirring paddle speed is 10rpm. After the temperature stabilizes, measure the initial slurry viscosity.

[0094] Step 7: Adjust viscosity. Add an appropriate amount of NMP, evacuate to -90 kPa, set the dispersion disc speed to 2000 rpm and the stirring paddle speed to 30 rpm, and stir for 30 minutes. Use a No. 4 rotor at 60 rpm to measure the viscosity, and adjust the viscosity to 5500 ± 1000 mPa·s.

[0095] Step 8: Discharge. After the well-mixed slurry is passed through a sieve, it is transferred to the feeding bucket of the coating machine.

[0096] (2) Coating

[0097] Under the condition of ensuring the ambient dew point and temperature, the surface density of a single surface is set to 18 mg / cm³. 2 The coating width is 268 mm, the coating length is 70 mm, the coating gap is 8 mm, and the belt speed is 1 m / min. The slurry is applied to the surface of the carbon-coated aluminum foil using an intermittent coating method to obtain the electrode roll.

[0098] (3) Roller pressing

[0099] Under conditions that ensure the ambient dew point and temperature, the coated electrode rolls are rolled using a roll press to achieve a compaction density of 2.0 g / cm³. 3 .

[0100] (4) Die-cutting

[0101] Under conditions that ensure the ambient dew point and temperature, the electrode roll is cut into the designed size using a die-cutting machine to obtain the electrode sheet.

[0102] like Figure 1 The electrode size shown is that of Example 1.

[0103] Example 2

[0104] The difference between this embodiment and Example 1 is that the solid content of the adhesive is 5.6%, the mass ratio of sodium polyacrylate to polyvinylidene fluoride (PVDF) is 3:4, and under the condition of ensuring the ambient dew point and ambient temperature, 2016.4g of NMP, 68.35g of PVDF 5130 and 51.26g of 1.5 million molecular weight sodium polyacrylate are weighed and added to the homogenizing tank.

[0105] Example 3

[0106] The difference between this embodiment and Example 1 is that the ratio of sodium polyacrylate to polyvinylidene fluoride is 1:1, PVDF5130 is 48.62g, and sodium polyacrylate with a molecular weight of 1.5 million is 48.62g. Everything else is the same as in Example 1.

[0107] Comparative Example 1

[0108] The difference between this comparative example and Example 1 is that the preparation process of the sodium vanadium phosphate electrode is the same as that of Example 1, except that only sodium polyacrylate with a molecular weight of 1.5 million is used as a binder.

[0109] Comparative Example 2

[0110] The difference between this comparative example and Example 1 is that the preparation process of the sodium vanadium phosphate electrode is the same as that of Example 1, except that only polyvinylidene fluoride 5130 is used as a binder.

[0111] Comparative Example 3

[0112] The difference between this comparative example and Example 1 is that the preparation process of the sodium vanadium phosphate electrode is different from that of Example 1 in that sodium polyacrylate with a molecular weight of 3 million and polyvinylidene fluoride 5130 are used as binders. Otherwise, it is the same as Example 1.

[0113] Comparative Example 4

[0114] The difference between this comparative example and Example 1 is that the preparation process of the sodium vanadium phosphate electrode is different from that of Example 1 in that sodium polyacrylate with a molecular weight of 2100 and polyvinylidene fluoride 5130 are used as binders. Otherwise, it is the same as Example 1.

[0115] Comparative Example 5

[0116] The difference between this comparative example and Example 1 is that the preparation process of the sodium vanadium phosphate electrode is different from that of Example 1 in that sodium carboxymethyl cellulose (CMC) with a molecular weight of 230,000 and polyvinylidene fluoride 5130 are used as binders. Otherwise, it is the same as Example 1.

[0117] Comparative Example 6

[0118] The difference between this comparative example and Example 1 is that the preparation process of the sodium vanadium phosphate electrode is different from that of Example 1 in that the mass ratio of sodium polyacrylate and polyvinylidene fluoride is 4:3, the amount of PVDF 5130 is 41.67g, and the amount of 1.5 million molecular weight sodium polyacrylate is 55.56g. Everything else is the same as in Example 1.

[0119] Comparative Example 7:

[0120] The difference between this comparative example and Example 1 is that:

[0121] (1) Homogenization

[0122] Step 1: Applying the adhesive. Set the solid content of the adhesive solution to 4.6%, and the mass ratio of sodium polyacrylate to polyvinylidene fluoride to 3:4. Under the condition of ensuring the ambient dew point and ambient temperature, weigh out 2016.4g of NMP, 55.56g of PVDF 5130, and 41.67g of 1.5 million molecular weight sodium polyacrylate and add them to the homogenizing tank. Heat to 60℃±2℃. After reaching the temperature, set the dispersion disc speed to 500rpm and the stirring paddle speed to 13rpm, and stir for 6 minutes. Scrape off the material adhering to the stirring paddle.

[0123] Step 2: Dispersion of the adhesive. Vacuum to -90 kPa, disperse disc speed 2800 rpm, agitator speed 23 rpm, stir for 30 minutes, then scrape the material. Vacuum to -90 kPa, disperse disc speed 3200 rpm, agitator speed 35 rpm, stir for 150 minutes, then scrape the material.

[0124] The other steps are the same as in Example 1.

[0125] The following tests were performed on some or all of the examples in Examples 1-3 and Comparative Examples 1-7:

[0126] Slurry viscosity test method: Use rotational viscometer method to test. Place the slurry at a constant temperature of 25±0.5℃, let it stand or centrifuge to avoid increasing the apparent viscosity due to air bubbles. Select a rotor with a range of 50-110% according to the estimated viscosity, and use rotational viscometer to measure the viscosity of the adhesive or slurry.

[0127] Slurry fineness test method: Fineness scraper test is adopted. A precision double-edged stainless steel scraper (wedge-shaped groove with depth continuously varying from 0 to a specified maximum value) is used to scrape the slurry. The deepest part of the groove can accommodate large particles, while the shallower part only allows small particles to pass through. After scraping, observe the position where obvious particle streaks or scratches appear on the slurry surface. The groove depth corresponding to this position is the size of the largest particle in the slurry (usually in μm).

[0128] Method for measuring the resistivity of the electrode after rolling: The resistivity of the electrode is measured using the four-probe test method.

[0129] Method for determining the peel strength of the electrode after roll forming: The 90° peel test method is used. Strong adhesive tape is used to bond and fix the coating to the current collector interface. Then, the coating (along with the tape) is peeled off the current collector at a 90° angle and a constant speed. The peel force is continuously recorded during the process, and the average peel force is calculated and converted into peel strength.

[0130] Method for determining the 1C / 3C / 5C cycle capacity retention rate: At 25℃, record the cycle capacity retention rate after 10 cycles at 1C, 3C, and 5C respectively.

[0131] This invention conducted comparative tests on different adhesive combinations, and the specific indicators are shown in the table below:

[0132]

[0133]

[0134] As can be seen from the comparison of Example 1 and Comparative Examples 1-6, the composite bonding system designed by the present invention, which involves first applying adhesive and then adding adhesive with a solid content of 4.6% and a ratio of sodium polyacrylate to polyvinylidene fluoride of 3:4, can obtain a slurry with moderate viscosity, good dispersion performance, and lower slurry fineness. This significantly improves the dispersion uniformity of sodium vanadium phosphate particles with large specific surface area in the slurry, thereby improving the battery rate performance and cycle stability.

[0135] like Figures 2-6 As shown, Examples 1 to 3 all yielded relatively uniform slurries with uniform dispersion and moderate viscosity, and the positive electrode sheets were uniformly coated without agglomeration.

[0136] In Example 1, using sodium polyacrylate with a molecular weight of 1.5 million, the initial adhesive solution exhibited good viscosity and thixotropy, with an initial viscosity in the range of 8000–9000 mPa·s. Furthermore, it demonstrated good slurry properties during the homogenization stage, with a suitable viscosity; the initial slurry viscosity was in the range of 5000–7000 mPa·s. Moreover, a slurry with good flowability, good adhesion, and uniform dispersion could be obtained without adjusting the viscosity using NMP.

[0137] Comparative Example 1: Sodium polyacrylate alone could not be applied smoothly, and the adhesive solution was cloudy with white flocculent suspension.

[0138] Comparative Example 2 used only polyvinylidene fluoride 5130. In this case, the initial adhesive viscosity was slightly lower, but the initial slurry viscosity was higher, resulting in poor slurry flowability. NMP was needed to adjust the viscosity. In addition, the resistivity of the electrode after rolling in Comparative Example 2 was higher than 50 Ω·cm, and the peel strength of the electrode was lower. At this time, the capacity retention rate was also lower. This may be due to the lack of good dispersibility and bonding properties of sodium polyacrylate, as well as the lack of the effect of sodium ions in sodium polyacrylate to optimize the ion diffusion kinetics of the electrode / electrolyte interface.

[0139] The slurry used in Comparative Example 3, containing sodium polyacrylate with a molecular weight of 3 million, had excessive viscosity, contained white particles, and had poor flowability, which affected subsequent coating and prevented the preparation of electrode sheets.

[0140] Comparative Example 4 uses sodium polyacrylate with a small molecular weight as an adhesive, resulting in poor slurry adhesion. The initial adhesive viscosity is too low, falling outside the initial adhesive viscosity range defined in this invention. In subsequent preparation processes, the initial slurry viscosity is too low. Although good dispersion performance is obtained, good bonding performance is lacking, which may lead to material and current collector separation during subsequent rolling processes. At this time, there is a lack of good interfacial contact, and the capacity retention rate is also low.

[0141] The sodium carboxymethyl cellulose solution used in Comparative Example 5 was of poor quality, containing white particulate matter, and could not achieve good dispersion, thus failing to prepare electrode sheets.

[0142] In Comparative Example 6, the ratio of sodium polyacrylate to polyvinylidene fluoride was 4:3. Although a certain initial viscosity of the adhesive was obtained, the thixotropy was poor and the fineness of the slurry was too high. The initial slurry viscosity was high, and a large amount of NMP was required to adjust the viscosity. This was not conducive to the dispersion of sodium vanadium phosphate with a large specific surface area and was not conducive to obtaining good electrochemical performance.

[0143] In Comparative Example 7, we changed the stirring speed and stirring time, which altered the degree of gelation and dispersion of the raw materials during the mixing and dispersing processes. This resulted in a change in viscosity control; the solution became a turbid gel, and the initial gel concentration was not controlled within the range of 8000–15000 mPa·s. The initial gel viscosity was too high, and even with the addition of a large amount of NMP, the positive electrode slurry of this comparative example could not be controlled within the range of 5500 ± 1000 mPa·s. This demonstrates that controlling the viscosity at each stage of slurry preparation can achieve good dispersion of the binder, conductive agent, and sodium vanadium phosphate in the gel, thereby reducing the electrode resistivity and improving the cycle capacity retention rate.

[0144] When neither sodium polyacrylate nor polyvinylidene fluoride 5130 binder is used, or when the molecular weight of sodium polyacrylate is not within the specified range, or when the mass ratio of sodium polyacrylate to polyvinylidene fluoride 5130 is not within the specified range, the slurry viscosity is too high, resulting in poor fluidity and affecting subsequent coating, leading to poor electrode quality. Furthermore, poor slurry quality results in lower compaction density of the subsequently rolled electrode, in which case the resistivity is significantly higher than in the example, and the peel strength is lower than in the example. The indicators are shown in the table below:

[0145]

[0146] As can be seen from Examples 1-3 and Comparative Examples 2-4 and 6-7, when this scheme is used with both sodium polyacrylate and polyvinylidene fluoride as binders, and the mass ratio of sodium polyacrylate and polyvinylidene fluoride is limited to a certain range, the strategy of first applying the adhesive and then gradually adding the conductive agent and sodium vanadium phosphate achieves better bonding performance, dispersion performance, and ion transport performance. This results in a stable interfacial film, enhancing the interaction between the overall active particles and the binder, and significantly improving the battery's cycle performance and rate performance. Under 3C cycling, the capacity retention rate is ≥98% after 10 cycles. Under 5C cycling, the capacity retention rate is ≥95% after 10 cycles.

[0147] Capacity retention 1C discharge 3C discharge 5C discharge Example 1 99.99％ 98.62％ 97.4％ Example 2 99.81％ 98.21％ 95.1％ Example 3 99.89％ 98.33％ 96.4％ Comparative Example 2 98.95％ 96.77％ 94.5％ Comparative Example 4 98.52％ 93.10％ 91.2％ Comparative Example 6 98.74％ 95.73％ 92.2％ Comparative Example 7 95.32％ 90.73％ 75.98％

[0148] In summary, the present invention provides a process for preparing sodium vanadium phosphate positive electrode sheets. This technical solution significantly improves the stability of sodium-ion batteries under high voltage, helps to construct a stable interfacial film, and enhances the interaction between the overall active particles and the binder. This invention is particularly suitable for sodium vanadium phosphate with a large specific surface area (18-20 μm²). 2 To address the issues of poor slurry processability and easy detachment of active materials, this method innovatively employs a composite bonding system of sodium polyacrylate and polyvinylidene fluoride. This involves first constructing a basic network through adhesive application, followed by a stepwise viscosity control process that adds two conductive agents (Super P and carbon nanotubes) and sodium vanadium phosphate. Combined with the electrostatic dispersion and flexible bridging effects of sodium polyacrylate, this significantly improves slurry uniformity and electrode bonding strength, effectively inhibiting active material agglomeration and detachment while reducing solvent usage. The resulting slurry has a moderate viscosity, requiring no additional or minimal NMP for viscosity adjustment. It exhibits fine slurry texture, uniform areal density, high electrode compaction density, and excellent electrode performance. This collaborative process effectively prevents structural collapse, active particle breakage, transition metal dissolution, and excessive side reactions in the cathode material under high voltage and temperature conditions, resulting in superior electrode performance and significantly improved battery rate performance and cycle stability.

[0149] It should be noted that 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 method for preparing sodium vanadium phosphate electrodes with large specific surface area, comprising the following steps: S1: Applying adhesive: Weigh sodium polyacrylate, polyvinylidene fluoride and N-methylpyrrolidone (NMP) with a molecular weight of 800,000 to 2,500,000 in a mass ratio of 1:(0.8~2):(40~60) into a container and stir. S2: Dispersion of adhesive solution: The adhesive solution obtained in S1 is vacuumed and dispersed and stirred to obtain the initial adhesive solution. The viscosity of the initial adhesive solution is controlled at 8000~15000mPa·s. S3: Adding conductive agent and sodium vanadium phosphate: Add conductive agent and sodium vanadium phosphate to the initial colloid obtained in S2. After adding each component, disperse, stir, and scrape the mixture to obtain a primary slurry. The viscosity of the primary slurry is controlled between 5000 and 12000 mPa·s. The specific surface area of ​​the sodium vanadium phosphate cathode material is 18–20 m². 2 / g; S4: Adjust viscosity: Add N-methylpyrrolidone (NMP), vacuum, disperse and stir, and adjust the viscosity of the slurry to 5500±1000mPa·s to obtain the positive electrode slurry; S5: The positive electrode slurry obtained in S4 is coated on the surface of the foil and dried to obtain an electrode roll; the electrode roll is rolled and die-cut to obtain an electrode sheet.

2. The method for preparing sodium vanadium phosphate electrodes with large specific surface area according to claim 1, characterized in that, The viscosity of the initial adhesive solution in S2 is 8000-9000 mPa·s, and the viscosity of the initial slurry in S3 is 5000-7000 mPa·s.

3. The method for preparing sodium vanadium phosphate electrodes with large specific surface area according to claim 1, characterized in that, The solid content of the adhesive solution in S1 is 4.3% to 5.3%. Preferably, the mass ratio of sodium polyacrylate to polyvinylidene fluoride in S1 is 1:(1-2); Preferably, the molecular weight of sodium polyacrylate in S1 is 1 million to 2 million.

4. The method for preparing sodium vanadium phosphate electrodes with large specific surface area according to claim 1, characterized in that, The solid content of the adhesive solution in S1 is 4.5% to 5%; The mass ratio of sodium polyacrylate to polyvinylidene fluoride in S1 is 3:4; The molecular weight of sodium polyacrylate in S1 is 1.4 million to 1.6 million. Preferably, the total mass of the sodium polyacrylate accounts for 1.5 to 2.3% of the total mass of the material.

5. The method for preparing sodium vanadium phosphate electrodes with large specific surface area according to claim 1, characterized in that, The specific steps for S1 are as follows: Weigh out sodium polyacrylate, polyvinylidene fluoride and N-methylpyrrolidone in the target stoichiometric ratio, heat to 50-75°C, and after heating to the target temperature, set the dispersion disc speed to 400-600 rpm and the stirring paddle speed to 15-25 rpm, stir for 7-13 minutes, and scrape off the material adhering to the stirring paddle.

6. The method for preparing sodium vanadium phosphate electrodes with large specific surface area according to claim 1, characterized in that, The specific steps for S2 are as follows: Vacuum the adhesive obtained in S1 to -85 to -95 kPa, set the dispersion disc speed to 3000 to 3500 rpm, the stirring paddle speed to 25 to 35 rpm, stir for 25 to 35 minutes, and then scrape the material; Vacuum the adhesive to -85 to -95 kPa, set the dispersion disc speed to 3000 to 3500 rpm, the stirring paddle speed to 30 to 40 rpm, stir for 120 to 180 minutes, scrape the material, and then measure the viscosity of the initial adhesive.

7. The method for preparing sodium vanadium phosphate electrodes with large specific surface area according to claim 1, characterized in that, S3 involves weighing 2.4%–3.5% of the total material mass of conductive agent Super P into a homogenizing tank, dispersing, stirring, and scraping the material; weighing 91%–94% of the total material mass of sodium vanadium phosphate into a homogenizing tank, dispersing, stirring, and scraping the material; vacuuming the obtained material, dispersing, stirring, and scraping the material; weighing 0.45%–0.6% of the total material mass of carbon nanotubes (CNTs), vacuuming, dispersing, stirring, and cooling the temperature to 25±2℃ before measuring the initial slurry viscosity. Preferably, in step S3, the dispersion disc rotation speed is 100–3500 rpm, the stirring speed is 5–40 rpm, the vacuum degree is -85–-95 kPa, and the stirring time is 5–180 min.

8. The method for preparing sodium vanadium phosphate electrodes with large specific surface area according to claim 1, characterized in that, S4 involves adding NMP, evacuating to -85 to -95 kPa, setting the dispersion disc speed to 1500 to 2500 rpm, the stirring paddle speed to 25 to 35 rpm, and stirring for 25 to 35 minutes. The viscosity is measured using a No. 4 rotor at 50 to 70 rpm, and adjusted to 5500 ± 1000 mPa·s. If the viscosity is too high, NMP is added for adjustment; if the viscosity is too low, homogenization is required again. The fineness of the slurry is ≤20.

9. The method for preparing sodium vanadium phosphate electrodes with large specific surface area according to claim 1, characterized in that, S5 involves passing the slurry, which has been thoroughly stirred in S4, through a sieve and setting a single-sided surface density of 15–20 mg / cm³. 2 The conveyor belt speed is 0.5–1.5 m / min. The slurry is applied to the aluminum foil surface using an intermittent coating method to obtain the electrode roll. The coated electrode roll is then rolled using a roller press to achieve a compaction density of 1.5–2.5 g / cm³. 3 The electrode rolls are cut using a die-cutting machine to obtain electrode sheets; Preferably, the mesh size of the sieve is 100 to 300.

10. The method for preparing sodium vanadium phosphate electrodes with large specific surface area according to claim 7, characterized in that, The carbon nanotubes are a carbon nanotube dispersion, and the mass percentage of carbon nanotubes in the carbon nanotube dispersion is 4.5% to 5.5%. Preferably, the foil material includes aluminum foil and / or carbon-coated aluminum foil.

Images