A dry-method electrode based on particle size grading mixing, a preparation method thereof and a sodium-ion battery

Abstract

This invention relates to a dry electrode based on particle size classification mixing, its preparation method, and a sodium-ion battery, belonging to the field of sodium-ion battery technology. The preparation method involves mixing large-particle positive electrode active material and a conductive agent to obtain a first mixture; mixing small-particle positive electrode active material and a conductive agent to obtain a second mixture; then mixing the first and second mixtures to obtain a final mixture; adding polytetrafluoroethylene (PTFE) twice to the final mixture for low-temperature mixing; then performing a fiberization treatment, followed by cooling and granulation; and finally forming and coating the granulated material to obtain the dry electrode. This invention uses a method of premixing large-particle (21~30μm) and small-particle (1.1~3μm) positive electrode active materials with a conductive agent separately before graded mixing, avoiding the segregation and small-particle agglomeration problems that easily occur when directly mixing particles of different sizes in traditional dry processes.

Description

Technical Field

[0001] This invention relates to the field of sodium-ion battery technology, and in particular to a dry electrode based on particle size classification mixing, its preparation method, and a sodium-ion battery. Background Technology

[0002] Sodium-ion battery electrode preparation is mainly divided into two categories: wet process and dry process. The wet process mainly uses solvent dispersion coating. Its advantages are good electrode uniformity, mature technology, and compatibility with most electrode material systems. However, it has obvious drawbacks. It requires the use of organic solvents such as NMP, which not only puts great pressure on the environment and causes high VOC emissions, but also has problems such as high solvent recovery costs, high energy consumption, and long production cycles. It does not conform to the trend of green and low-cost manufacturing. Moreover, solvent residue can easily affect the stability of the electrode interface and the cycle life of the battery.

[0003] Traditional dry electrode processes, which require no solvents, are green, efficient, and lower in cost, represent an important direction for sodium electrode manufacturing. However, existing technologies face several bottlenecks. First, the active materials often use a single particle size, which can easily lead to uneven electrode pore structure and excessively long ion diffusion paths, making it difficult to balance processability and electrochemical performance. Second, during the mixing process, particles are prone to segregation and small particles tend to agglomerate, resulting in poor electrode structure consistency, discontinuous conductive network construction, and high interfacial impedance. Third, the processing performance requirements for raw materials are stringent, making large-scale production difficult.

[0004] While existing patents attempt to improve performance by blending particles of different sizes, they still have significant limitations: for example, the blending particle size range is too broad and not precisely matched to the sodium electrochemical dry process system; the problems of small particle agglomeration and particle segregation have not been solved, and the contact between the conductive agent and the active material is insufficient; the adhesives are mostly non-fibrous systems that need to be pulverized to the micron level before use, and the synergistic adaptation between particles and adhesives has not been achieved, making it impossible to simultaneously meet the industrial requirements of dry processability and high rate and high density. Summary of the Invention

[0005] Based on the above analysis, the present invention aims to provide a dry electrode based on particle size classification mixing, its preparation method, and a sodium-ion battery, in order to solve existing problems such as particle segregation and discontinuous conductive network, and improve the high energy density and high rate capability of sodium-ion batteries.

[0006] On one hand, the present invention provides a method for preparing a dry electrode based on particle size classification mixing, comprising the following steps: S1: Mix large-particle positive electrode active material and conductive agent to obtain the first mixture; The particle size of the large-particle positive electrode active material is 21~30μm; S2: Mix small-particle positive electrode active material and conductive agent to obtain a second mixture; The particle size of the small-particle positive electrode active material is 1.1~3μm; S3: Then mix the first mixture and the second mixture to obtain a mixture. S4: Polytetrafluoroethylene is added to the mixture twice for low-temperature mixing; then fiberization is performed, followed by cooling and granulation; S5: The granulated material is film-formed and coated to obtain a dry electrode.

[0007] Furthermore, the mass ratio of the large-particle positive electrode active material to the conductive agent is (94-98):(4-1); the mass ratio of the small-particle positive electrode active material to the conductive agent is (94-98):(4-1).

[0008] Furthermore, in steps S1 and S2, the mixture is stirred at 200 rpm to 2000 rpm.

[0009] Further, in step S3, the first mixture and the second mixture are first stirred and mixed at 200 rpm to 1200 rpm, and then stirred and mixed at 1500 rpm to 2500 rpm.

[0010] Furthermore, in step S4, the mixture is stirred at 200 rpm to 2000 rpm and the temperature is below 19°C.

[0011] Furthermore, in the fiberization process of step S4, hot water heating at 50℃~100℃ is used, and stirring is performed at 2000rpm~3000rpm; in the cooling and granulation process, the following is adopted: Cool to below 30℃ with cold water at 10℃~10℃.

[0012] Furthermore, during the film formation and lamination process in step S5, the temperature is 80℃~120℃ and the pressure is 1~10T.

[0013] Furthermore, the resulting dry-process electrode exhibits an electrode resistance below 3Ω, a peel strength above 4.5N / m, and a compaction density of 2.20g / cm³. 3 above.

[0014] On the other hand, this invention provides a dry electrode based on particle size classification mixing, obtained by the preparation method described in this invention. The dry electrode obtained by this invention can be used in sodium-ion batteries, where the rate performance (2C / 1C ratio) is above 92%.

[0015] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects: 1. This invention employs a method of premixing large-particle (21~30μm) and small-particle (1.1~3μm) positive electrode active materials with conductive agents separately, followed by graded mixing. This avoids the segregation and small-particle agglomeration problems that easily occur when directly mixing particles of different sizes in traditional dry processes. This ensures that the conductive agent is evenly distributed in each particle size component, guaranteeing the continuity and structural uniformity of the conductive network inside the electrode. This effectively improves the compaction density and peeling force of the electrode, reduces interfacial impedance, and consequently improves the energy density and rate capability of sodium-ion batteries. 2. By adding polytetrafluoroethylene (PTFE) to the mixture in two stages and mixing at a low temperature below 19°C, combined with hot water heating for fiberization and cold water cooling for granulation, the degree of fiberization of the binder can be precisely controlled, avoiding material agglomeration or fiber breakage caused by excessive fiberization. This process enables the binder, active materials, and conductive agents to form a synergistic and compatible structure, resulting in a final dry electrode with a peel force of over 4 N / m, an electrode resistance below 3 Ω, and a compaction density of 2.20 g / cm³. 3 The battery assembled using this dry-process electrode achieves a rate performance (2C / 1C) of over 92%, demonstrating excellent rate characteristics.

[0016] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0017] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0018] Figure 1 Microscopic images of the mixture obtained after mixing the first and second mixtures in Example 9; Figure 2 Microscopic images of the mixture obtained after mixing the first and second mixtures in Comparative Example 7; Figure 3 Microscopic image of the mixture obtained after mixing the first and second mixtures in Comparative Example 8. Detailed Implementation

[0019] The preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0020] In the preparation of sodium-ion battery electrodes, although the wet process is mature and has good uniformity, it has environmental protection and VOC emission problems caused by NMP solvents. While the dry process, which is an important development direction, has advantages such as solvent-free, green and efficient, and low cost, it still faces bottlenecks such as structural inhomogeneity caused by the single particle size of active material, poor consistency caused by particle segregation and agglomeration, high interfacial impedance, and stringent requirements for raw material processing.

[0021] Existing improvement solutions, such as mixing of large and small particles, cannot simultaneously meet the industrial requirements of dry processability, high rate of application, and high density because the particle size matching is not precisely designed for the sodium electrochemical dry process system, the problems of small particle agglomeration and segregation are not solved, and the non-fibrous binder needs to be crushed and lacks synergistic adaptation with the particles. Overall, there is still a significant gap before large-scale application.

[0022] Therefore, the present invention provides a method for preparing a dry electrode based on particle size classification mixing, comprising the following steps: S1: Mix large-particle positive electrode active material and conductive agent to obtain the first mixture; The particle size of the large-particle positive electrode active material is 21~30μm; S2: Mix small-particle positive electrode active material and conductive agent to obtain a second mixture; The particle size of the small-particle positive electrode active material is 1.1~3μm; S3: Then mix the first mixture and the second mixture to obtain a mixture. S4: Polytetrafluoroethylene is added to the mixture twice for low-temperature mixing; then fiberization is performed, followed by cooling and granulation; S5: The granulated material is film-formed and coated to obtain a dry electrode.

[0023] Compared with existing technologies, this invention uses a method of premixing large-particle (21~30μm) and small-particle (1.1~3μm) positive electrode active materials with conductive agents separately, and then mixing them in stages. This avoids the segregation and small particle agglomeration problems that are easy to occur when directly mixing particles of different sizes in traditional dry processes. This ensures that the conductive agent is evenly distributed in each particle size component, guaranteeing the continuity and structural uniformity of the conductive network inside the electrode. This effectively reduces interfacial impedance, improves the compaction density and peeling force of the electrode, and thus improves the energy density (the higher the compaction density of the electrode, the higher the energy density of the battery) and rate capability of the sodium-ion battery.

[0024] It should be noted that this invention controls the particle size of the large-particle positive electrode active material to 21-30 μm and the particle size of the small-particle positive electrode active material to 1.1-3 μm. This significant difference in particle size allows each material to perform an independent electrochemical function within the electrode structure. The large particles, with their moderate size, maintain a high single-particle capacity while providing a relatively stable buffer against volume changes; the small particles, with their fine size, significantly shorten the solid-phase diffusion path of sodium ions, ultimately improving the battery's rate performance. The two particle sizes of active materials complement each other during the electrochemical reaction, enabling the battery to possess both high capacity and high rate performance.

[0025] In addition, small-particle positive electrode active materials have good affinity with polytetrafluoroethylene fibrous networks and can be uniformly embedded in the fiber network during low-temperature mixing; large-particle positive electrode active materials, due to their suitable particle size and morphology, are not prone to segregation during mixing and do not damage the mechanical stability of the fiber network.

[0026] When the particle size of large-particle positive electrode active material exceeds 30 μm, the sodium ion solid-phase diffusion distance increases, the rate performance decreases significantly, and large particles are prone to sedimentation, resulting in poor uniformity of contact with the conductive agent, leading to discontinuity of the conductive network, increased electrode resistance, decreased surface smoothness during calendering, and local defects at the bonding interface, affecting consistency. If the particle size of large-particle positive electrode active material is less than 21 μm, the overall particle size is too fine, the particles are prone to agglomeration, the conductive agent and binder (polytetrafluoroethylene) are difficult to disperse uniformly, and the increased specific surface area exacerbates the risk of side reactions, which may affect cycle life.

[0027] For example, the particle size of the large-particle positive electrode active material in this invention can be 21μm, 22μm, 23μm, 24μm, 25μm, 26μm, 27μm, 28μm, 29μm or 30μm.

[0028] Preferably, the particle size of the large-particle positive electrode active material is 21~25μm.

[0029] When the particle size of small-particle positive electrode active material exceeds 3μm, its particle size advantage weakens, the sodium ion diffusion path is shortened only slightly, the rate performance is not improved sufficiently, the specific surface area of ​​fine particles is insufficient, and the conductive agent is easily unevenly distributed. If the particle size is less than 1.1μm, the surface energy of ultrafine particles is extremely high, and hard agglomerates are easily formed in the dry system, which are difficult to disperse, resulting in uneven distribution of active materials and incomplete fibrous network coating. At the same time, ultrafine powder is easy to fly and adhere to the inner wall of equipment, increasing material loss and significantly increasing the difficulty of large-scale production.

[0030] For example, the particle size of the small-particle positive electrode active material can be 1.1μm, 1.2μm, 1.3μm, 1.4μm, 1.5μm, 1.6μm, 1.7μm, 1.8μm, 1.9μm, 2.0μm, 2.1μm, 2.2μm, 2.3μm, 2.4μm, 2.5μm, 2.6μm, 2.7μm, 2.8μm, 2.9μm or 3.0μm.

[0031] Preferably, the particle size of the small-particle positive electrode active material is 1.1~2μm.

[0032] Specifically, the mass ratio of the large-particle positive electrode active material to the conductive agent is (94-98):(4-1). The mass ratio of the small particle positive electrode active material to the conductive agent is (94-98):(4-1).

[0033] It should be noted that when the content of conductive agent is too low, the electrode resistance increases, the electron conduction path is obstructed, polarization increases, and the battery rate performance decreases, limiting the ability to charge and discharge at high rates. When the content of conductive agent is too high, although the resistance can be reduced, it will reduce the mass ratio of active material, thus reducing the battery energy density. At the same time, conductive agents are expensive auxiliary materials, and excessive addition will significantly increase the battery manufacturing cost, which does not conform to the principle of low cost design.

[0034] Therefore, by controlling the mass ratio of large / small particle positive electrode active material to conductive agent within the range of (94-98):(4-1), it is possible to achieve an optimized balance of comprehensive performance while ensuring good conductivity and taking into account energy density and cost-effectiveness.

[0035] Preferably, the positive electrode active material includes polyanionic and layered oxide sodium ion positive electrode materials.

[0036] Preferably, the conductive agent includes conductive carbon black, graphene, carbon nanotubes, and VGCF.

[0037] Specifically, the mass ratio of the first mixture to the second mixture is 9:1-7:3.

[0038] It should be noted that controlling the mass ratio of the first mixture to the second mixture within the range of 9:1 to 7:3 is crucial for achieving a balance between good processing performance and excellent electrochemical performance of the dry electrode. When the proportion of small particles is too high, i.e., the proportion of the second mixture exceeds the above range, on the one hand, small particles have a large specific surface area and high surface energy, making them prone to agglomeration during the dry mixing process. This leads to poor material flowability, reduced mixing uniformity with the binder fibrous network, and quality problems such as uneven film thickness, rough surface, and edge cracking during calendering. On the other hand, an excessively high proportion of small particles weakens the supporting role of large particles in the electrode structure, reduces the overall mechanical strength of the electrode, and results in insufficient bonding force at the interface with the current collector, leading to a decrease in peel strength.

[0039] Furthermore, an excessively high proportion of fine particles can make the electrode pore structure too dense, hindering electrolyte wetting, obstructing ion transport, and ultimately affecting the battery's rate performance. Therefore, controlling the mass ratio of the first mixture to the second mixture within a reasonable range can ensure the processability and shapeability of the dry electrode while maintaining excellent electrochemical performance of the battery.

[0040] Therefore, the mass ratio of the first mixture to the second mixture can be 9:1, 9:2, 9:3, 8:1, 8:2, 8:3, 7:1, 7:2, or 7:3.

[0041] Specifically, the mass ratio of the mixture to polytetrafluoroethylene is 98:1-90:5.

[0042] It should be noted that a low PTFE content will not provide sufficient adhesion, which will lead to a decrease in the cohesion of the electrode and affect the quality of the electrode. Since PTFE can react with the hard carbon of the negative electrode, it will affect the quality of the battery. If the PTFE content is too high, it will affect the battery capacity.

[0043] Therefore, the mass ratio of the mixture to polytetrafluoroethylene can be 98:1, 97:1, 96:1, 95:1, 94:1, 93:1, 92:1, 91:1, 90:1, 98:2, 97:2, 96:2, 95:2, 94:2, 93:2, 92:2, 91:2, 90:2, 98:3, 97:3, 96:3, 95:3, 94:3, 93:3, 92:3, 91:3, 90:3, 98:4, 97:4, 96:4, 95:4, 94:4, 93:4, 92:4, 91:4, 90:4, 98:5, 97:5, 96:5, 95:5, 94:5, 93:5, 92:5, 91:5, or 90:5.

[0044] Preferably, the weight-average molecular weight of polytetrafluoroethylene is above 8 million.

[0045] Specifically, in steps S1 and S2, the mixture is stirred at 200 rpm to 2000 rpm.

[0046] It should be noted that controlling the stirring speed within the range of 200 rpm to 2000 rpm is crucial for achieving a balance between uniform mixing of materials and the integrity of the material structure. If the speed is too low, the shear force is insufficient, making it difficult for the conductive agent to disperse uniformly on the surface of the active material, easily leading to localized agglomeration. This results in discontinuous construction of the subsequent conductive network and increased electrode resistance. If the speed is too high, the strong mechanical shear force may break the active material particles, damaging their crystal structure, introducing surface defects, and causing irreversible capacity loss. Simultaneously, the particle size distribution changes after particle breakage, affecting the consistency of the electrode structure and ultimately leading to a decline in the battery's electrochemical performance.

[0047] Therefore, controlling the stirring speed between 200 rpm and 2000 rpm can ensure uniform mixing while avoiding damage to the material structure and ensuring stable electrode performance.

[0048] For example, in steps S1 and S2, the stirring speed can be 200 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, 1000 rpm, 1100 rpm, 1200 rpm, 1300 rpm, 1400 rpm, 1500 rpm, 1600 rpm, 1700 rpm, 1800 rpm, 1900 rpm, or 2000 rpm.

[0049] Preferably, in steps S1 and S2, the mixing is carried out at 1000 rpm to 1500 rpm.

[0050] Specifically, in step S3, the first mixture and the second mixture are first stirred and mixed at 200 rpm to 1200 rpm, and then stirred and mixed at 1500 rpm to 2500 rpm.

[0051] It should be noted that the first stage is a low-speed stirring and premixing stage to avoid the separation and agglomeration of particles of different sizes under high centrifugal force. The second stage is a high-speed stirring and thorough mixing stage to provide sufficient shear force to ensure that particles of different sizes are mixed evenly.

[0052] For example, in step S3, the first mixture and the second mixture are first stirred and mixed at 200 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, 1000 rpm, 1100 rpm or 1200 rpm; and then stirred and mixed at 2000 rpm, 2050 rpm, 2100 rpm, 2150 rpm or 2200 rpm.

[0053] Preferably, in step S3, the first mixture and the second mixture are first stirred and mixed at 400 rpm to 800 rpm, and then stirred and mixed at 2000 rpm to 2200 rpm.

[0054] Specifically, in step S4, the mixture is stirred at 200 rpm to 1200 rpm and the temperature is below 19°C.

[0055] It should be noted that controlling the stirring speed between 200 rpm and 1200 rpm and the temperature below 19°C is crucial for ensuring uniform mixing of polytetrafluoroethylene (PTFE) and preventing premature fiberization. If the speed is too low, the shear force is insufficient, making it difficult for PTFE to disperse evenly in the material, affecting subsequent fiberization. If the speed is too high, the heat generated by mechanical friction can easily cause localized temperature increases, leading to premature PTFE fiberization, a sharp increase in material viscosity, decreased flowability, increased stirring resistance, and reduced mixing uniformity, ultimately affecting the performance of the electrodes and the final battery.

[0056] For example, in step S4, the stirring speed can be 200 rpm, 300 rpm, 400 rpm, 500 rpm, 600 rpm, 700 rpm, 800 rpm, 900 rpm, 1000 rpm, 1100 rpm, or 1200 rpm.

[0057] Preferably, in step S4, the mixture is stirred at 600 rpm to 1000 rpm.

[0058] Specifically, in the fiberization process of step S4, hot water at 50℃~100℃ is used for heating, and stirring is carried out at 2000rpm~3000rpm; in the cooling and granulation process, the following is adopted: Cool to below 30℃ with cold water at 10℃~10℃.

[0059] It should be noted that controlling the stirring speed during the fiberization process within the range of 2000 rpm to 3000 rpm is crucial for achieving a balance between sufficient PTFE fiberization and material structural integrity. If the speed is too low, the shear force is insufficient to fully stretch the PTFE into a three-dimensional fiber network, resulting in insufficient fiberization. This leads to low film strength, easy cracking, poor continuity of the conductive network, and increased electrode resistance during film formation. Conversely, if the speed is too high, the strong mechanical shear force may break the active material particles, damaging their crystal structure, introducing surface defects, and causing irreversible capacity loss. Furthermore, excessive fiberization can result in excessively high material viscosity, making subsequent granulation difficult.

[0060] Heating with hot water at 50~100℃ can promote the fiberization process. With an appropriate rotation speed of 2000rpm~3000rpm, the fiberization effect can be guaranteed while avoiding material damage. Then, the material is rapidly cooled to below 30℃ with cold water at -10℃~10℃ to terminate the fiberization reaction in time, ensure the stability of the material state, and guarantee the performance of the dry electrode and the battery.

[0061] For example, during the fiberization process in step S4, the stirring speed can be 2000 rpm, 2100 rpm, 2200 rpm, 2300 rpm, 2400 rpm, 2500 rpm, 2600 rpm, 2700 rpm, 2800 rpm, 2900 rpm or 3000 rpm.

[0062] Specifically, in the film formation and coating process of step S5, the temperature is 80℃~120℃ and the pressure is 1~10T.

[0063] It should be noted that during the film formation and lamination process in step S5, the temperature is 80℃~120℃ and the pressure is 1~10T. If the temperature is too low, it is difficult to reach the glass transition temperature of the binder, and the active material cannot be effectively laminated onto the current collector; if the temperature is too high, the binder will soften excessively or even melt completely, and the fluidity will increase significantly, which will easily cause the binder to migrate, leading to the failure of the internal bonding of the electrode and affecting the battery performance and safety.

[0064] If the pressure is too low, the material will be difficult to form a film and the compaction will be low. If the pressure is too high, the film will be pressed onto the roller surface and it will be difficult to transfer and coat onto the current collector. There is also a risk of material particles breaking.

[0065] For example, the temperature during the film formation and lamination process in step S5 can be 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, or 120°C.

[0066] For example, the pressure during the film formation and lamination process in step S5 can be 1T, 2T, 3T, 4T, 5T, 6T, 7T, 8T, 9T or 10T.

[0067] This invention provides a dry electrode, which is obtained based on a particle size classification mixing method. The resulting dry electrode has an electrode resistance of less than 3Ω, a peeling force of more than 4.5N / m, and a compaction density of more than 2.20g / cm3.

[0068] This invention also provides a sodium-ion battery, comprising the dry electrode described herein. The rate performance of the sodium-ion battery is above 92% at 2C / 1C.

[0069] To more clearly describe the present invention, the following embodiments and comparative examples are provided for further illustration.

[0070] Example 1 A method for preparing a dry electrode based on particle size classification mixing includes the following steps: S1: Mix large-particle positive electrode active material and conductive agent to obtain a first mixture; wherein the particle size of the large-particle positive electrode active material is 25μm, the mass ratio of the large-particle positive electrode active material to the conductive agent is 96:4, and the mixture is stirred at 1000rpm.

[0071] S2: Mix the small-particle positive electrode active material and the conductive agent to obtain a second mixture; wherein the particle size of the small-particle positive electrode active material is 2μm, the mass ratio of the small-particle positive electrode active material to the conductive agent is 96:4, and the mixture is stirred at 1000rpm.

[0072] The large-particle positive electrode active material is a composite sodium iron phosphate NFPP; The small-particle positive electrode active material is a composite sodium iron phosphate NFPP; The conductive agent is conductive carbon black SP; S3: Then mix the first mixture and the second mixture at a mass ratio of 8:2. First, stir and mix at a speed of 800 rpm, and then stir and mix at a speed of 2000 rpm to obtain the mixture.

[0073] S4: Polytetrafluoroethylene (PTFE) with a weight-average molecular weight of 10 million is added to the mixture in two batches, with a mass ratio of 96:4 between the mixture and PTFE. The mixture is then mixed at a low temperature of 1000 rpm and 15°C. The mixture is then heated with 75°C hot water and subjected to fiberization at 2500 rpm. Finally, the mixture is cooled to 25°C with 0°C cold water for granulation.

[0074] S5: The granulated material is subjected to film formation and coating at 100℃ and 5T to obtain a dry J-type electrode.

[0075] The preparation processes of Examples 2-9 and Comparative Examples 1-17 are largely the same as those of Example 1, with the differences shown in Table 1.

[0076] Table 1. Parameters that differentiate Examples 1-9 and Comparative Examples 1-17

[0077] Comparative Example 18 The preparation process of Comparative Example 18 is largely the same as that of Example 1, except that Comparative Example 18 includes the following steps: S1: Mix large-particle positive electrode active material and small-particle positive electrode active material uniformly at a mass ratio of 8:2 to obtain mixed raw material; S2: Add a conductive agent to the mixed raw materials, with the ratio of positive electrode material to conductive agent being 96:4; S3: Polytetrafluoroethylene with a weight-average molecular weight of 10 million is added to the mixture in two batches and mixed at a low temperature of 1000 rpm and 15°C. Then, it is heated with hot water at 75°C and subjected to fiberization treatment at 2500 rpm. Subsequently, it is cooled to 25°C with cold water at 0°C for cooling and granulation.

[0078] S4: The granulated material is subjected to film formation and coating at 100℃ and 5T to obtain the dry J method electrode.

[0079] Performance testing The above embodiments and comparative examples were subjected to performance tests, mainly including the compaction density, electrode resistance and peeling force of the obtained electrode sheets. The obtained electrode sheets were then used to prepare sodium-ion batteries, and the rate performance (2C / 1C) was tested. The specific test results are shown in Table 2.

[0080] Table 2 Performance Test Results

[0081] As can be seen from Examples 1-9 and Comparative Examples 1-18 and Table 2, the preparation method of this invention, which uses large-particle (21~30μm) and small-particle (1.1~3μm) positive electrode active materials premixed with conductive agents and then mixed in stages, avoids the segregation and small-particle agglomeration problems that easily occur when directly mixing particles of different sizes in traditional dry processes. This ensures that the conductive agent is evenly distributed in each particle size component, guaranteeing the continuity and structural uniformity of the conductive network inside the electrode, thereby effectively improving the compaction density and peeling force of the electrode and reducing the interfacial impedance; thus improving the energy density and rate capability of the sodium-ion battery; ultimately, the peeling force of the dry electrode can reach above 4 N / m, the electrode resistance is below 3Ω, and the compaction density is 2.20 g / cm³. 3 The above describes the battery assembled using this dry-process electrode, which achieves a rate performance (2C / 1C) of over 92%, demonstrating excellent rate characteristics.

[0082] Combining Examples 1-9 and Comparative Example 18, in the mixing process of these examples, large / small particle positive electrode active materials are first mixed with conductive agents separately. The nanoparticles of the conductive agent can effectively embed between the small particles or adsorb onto their surface, playing a dual role of physical isolation and conductive bridging, breaking down and preventing the agglomeration of small particles from the source. The small particles "modified" by the conductive agent have fundamentally improved dispersibility and conductivity.

[0083] In Comparative Example 18, the conductive agent was added to a pre-mixed mixture of particles of varying sizes. At this point, the small particles had already agglomerated to varying degrees. After the conductive agent was added, it tended to distribute between the large particles or on the surface of the small particle agglomerates, making it difficult to effectively penetrate into the interior of the small particle agglomerates. This resulted in the interior of the agglomerates becoming conductive islands, with long and tortuous electron conduction paths.

[0084] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a dry electrode based on a size fractionated mixture, characterized in that, Includes the following steps: S1: Mix large-particle positive electrode active material and conductive agent to obtain the first mixture; The particle size of the large-particle positive electrode active material is 21~30μm; S2: Mix small-particle positive electrode active material and conductive agent to obtain a second mixture; The particle size of the small-particle positive electrode active material is 1.1~3μm; S3: Then mix the first mixture and the second mixture to obtain a mixture. S4: Polytetrafluoroethylene is added to the mixture twice for low-temperature mixing; then fiberization is performed, followed by cooling and granulation; S5: The granulated material is film-formed and coated to obtain a dry electrode.

2. The method of claim 1, wherein the dry electrode is prepared based on a size fraction mixing. The mass ratio of the large-particle positive electrode active material to the conductive agent is (94-98):(4-1). The mass ratio of the small particle positive electrode active material to the conductive agent is (94-98):(4-1).

3. The method of claim 1, wherein the dry electrode is prepared by a particle size classification mixing method. In steps S1 and S2, the mixture is stirred at 200 rpm to 2000 rpm.

4. The method of claim 1, wherein the dry electrode is prepared based on a size fraction mixing. In step S3, the first mixture and the second mixture are first stirred and mixed at 200 rpm to 1200 rpm, and then stirred and mixed at 1500 rpm to 2500 rpm.

5. The method of claim 1, wherein the dry electrode is prepared based on a size fraction mixing. In step S4, the mixture is stirred at 200 rpm to 2000 rpm and the temperature is below 19°C.

6. The method for preparing a dry electrode based on particle size classification mixing according to claim 1, characterized in that, In the fiberization process of step S4, hot water at 50℃~100℃ is used for heating, and stirring is performed at 2000rpm~3000rpm; in the cooling and granulation process, the following is adopted: Cool to below 30℃ with cold water at 10℃~10℃.

7. The method for preparing a dry electrode based on particle size classification mixing according to claim 1, characterized in that, During the film formation and lamination process in step S5, the temperature is 80℃~120℃ and the pressure is 1~10T.

8. The method for preparing a dry electrode based on particle size classification mixing according to claim 1, characterized in that, The sheet resistance of the dry electrode obtained is 3 Ω or less, the peeling force is 4.5 N / m or more, and the compact density is 2.20 g / cm 3 The above.

9. A dry electrode based on particle size classification mixing, characterized in that, Obtained by the preparation method according to any one of claims 1-8.

10. A sodium-ion battery, characterized in that, The sodium-ion battery includes a dry electrode obtained by the preparation method according to any one of claims 1-8, wherein the rate performance of the sodium-ion battery is above 92% at 2C / 1C.

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