Method for improving stability of sodium ion battery polyanion positive electrode slurry

Abstract

The invention discloses a method for improving the stability of sodium-ion battery polyanion positive electrode slurry, and belongs to the technical field of sodium-ion battery positive electrode slurry preparation. In a wet stirring stage, the solid content of slurry added with main powder is controlled to be 60%-70%, the high-viscosity stirring time is controlled to be 1.5-2.5 hours, and the high-viscosity stirring time is controlled to be 1.5-2.5 hours; the dispersion rotating speed is cooperatively adjusted to be 2500-3500 rpm, the revolution rotating speed is adjusted to be 20-40 rpm, and a high-shear dispersion-mild convection homogenization process system is formed; by optimizing the high-viscosity stirring solid content of the polyanion material and the synergistic effect of the dispersion process, the standing viscosity fluctuation ratio of the slurry is remarkably reduced, and the stability standard that the viscosity of the slurry is increased by less than or equal to 20% within 6 hours and is increased by less than or equal to 50% within 12 hours is met; the slurry stability is improved by adjusting the high-viscosity stirring solid content and the dispersion rotating speed, and the production efficiency can be improved; meanwhile, a dispersing agent does not need to be added into a system, battery performance fluctuation is effectively avoided, and the method is suitable for large-scale production.

Description

Technical Field

[0001] The present invention belongs to the technical field of sodium ion battery positive electrode slurry preparation, and in particular relates to a method for improving the stability of sodium ion battery polyanion positive electrode slurry. Background Art

[0002] Sodium-ion batteries have become an important supplementary technology in the field of new energy due to their abundant resources and low cost. Polyanionic positive electrode materials (such as Na4Fe3(PO4)2(P2O7), Na3V2(PO4)3, Na2FePO4F, etc.) have become a research hotspot due to their stable structure and high voltage platform. However, their positive electrode slurries generally have poor stability during the wet stirring process, which directly affects the quality of electrode coating and battery performance. In order to avoid the risk of gelation of high-solid content slurries, traditional processes usually control the solid content below 55%. However, low solid content leads to a fast sedimentation rate of active materials, and frequent stirring is required to maintain uniformity, which increases production costs. In addition, the surface density of the electrode fluctuates greatly after the low-solid content slurry is coated, which directly affects the consistency of the battery capacity; existing stirring technologies mostly use a single speed or an unbalanced ratio of dispersion / revolution speed. When the dispersion speed is too low, particles can easily agglomerate, affecting the dispersion effect. However, when the revolution speed is too high, excessive shear degradation of the binder can occur, resulting in low viscosity. Long-term storage performance is also impaired: in existing technologies, the viscosity of polyanion slurries typically fluctuates by more than 80% after 12 hours of standing, and the active substance concentration stratifies significantly. These issues require the slurry to be prepared immediately, which cannot meet the material preparation requirements of large-scale production.

[0003] In order to solve the above problems, many practitioners and researchers have conducted many studies on improving the stability of polyanion slurry. CN119170767A discloses a Ca / Sr doped material designed to improve air stability, but the slurry process is not optimized, resulting in fluctuations in the surface density of the electrode after long-term storage. Patent CN119119378A discloses a comb-structured polymer dispersant containing benzene rings and carboxyl groups, which reduces viscosity and reduces the amount of NMP solvent used to improve dispersion stability. However, this method still requires the additional addition of a dispersant during the slurrying process, which increases process costs and reduces the proportion of active substances. CN119381407A discloses a method for improving the stability of lithium-ion battery positive electrode slurry by combining polyacrylic acid and a sodium source through an in-situ dispersion process, but the preparation process is complicated and not conducive to large-scale production. Therefore, there is an urgent need for a process optimization solution that does not require the addition of complex ingredients and is compatible with existing production line equipment to achieve stable dispersion of high solid content (≥60%) slurry, and the viscosity fluctuation rate of the static slurry is significantly reduced (≤50% for 12 hours). Summary of the Invention

[0004] In order to overcome the above problems, the present invention provides a method for improving the stability of polyanion positive electrode slurry for sodium ion batteries. By adjusting the high-viscosity stirring solid content and the dispersion speed to improve the slurry stability, the production efficiency can be improved. At the same time, there is no need to add a dispersant to the system, which effectively avoids fluctuations in battery performance and is suitable for large-scale production.

[0005] The technical solution adopted in the present invention is:

[0006] A method for improving the stability of polyanion cathode slurry for sodium ion batteries comprises: during the wet mixing stage, controlling the solid content of the slurry after the main powder is added to 60%-70%, controlling the high-viscosity stirring time to 1.5 hours-2.5 hours, and collaboratively adjusting the dispersion speed to 2500rpm-3500rpm and the revolution speed to 20rpm-40rpm to form a high-shear dispersion-mild convection homogenization process system.

[0007] The binder used is PVDF or an organic binder of the same type.

[0008] The prepared polyanion positive electrode slurry meets the stability standards of slurry viscosity increase of ≤20% within 6 hours and slurry viscosity increase of ≤50% within 12 hours.

[0009] Among them, the ratio of dispersion speed to revolution speed during high viscosity stirring is 75-175:1.

[0010] Among them, the positive electrode material is a sodium ion battery polyanion positive electrode material, including at least one of NFPP, NVP, and NFPF.

[0011] The slurry temperature is monitored in real time during the stirring process. If the temperature exceeds 28°C, the circulating water temperature is lowered to maintain the slurry temperature at 25°C±3°C.

[0012] The advantages of the present invention are as follows:

[0013] The present invention optimizes the synergistic effect of high viscosity and solid content of the polyanion material and the dispersion process, so as to significantly reduce the volatility of the static viscosity of the slurry and meet the stability standards of slurry viscosity increase of ≤20% within 6 hours and slurry viscosity increase of ≤50% within 12 hours.

[0014] By adjusting the high-viscosity solid content and dispersion speed to improve slurry stability, production efficiency can be improved; at the same time, there is no need to add dispersants to the system, which effectively avoids fluctuations in battery performance and is suitable for large-scale production. DETAILED DESCRIPTION

[0015] Obviously, the embodiments described are only some of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0016] A method for improving the stability of a polyanion cathode slurry for sodium ion batteries comprises the following steps: in a wet stirring stage, controlling the solid content of the slurry after adding a main powder to 60%-70%, which can effectively improve the stability of the cathode slurry; controlling the high-viscosity stirring time to 1.5 hours-2.5 hours, which can effectively improve the dispersibility of the slurry; and synergistically adjusting the dispersion speed to 2500rpm-3500rpm and the revolution speed to 20rpm-40rpm to form a high-shear dispersion-mild convection homogenization process system; the ratio of the dispersion speed to the revolution speed is 75-175:1, which can effectively reduce the energy consumption and equipment loss of the slurry mixing process; monitoring the slurry temperature in real time during the stirring process; and when the temperature exceeds 28°C, maintaining the slurry temperature above 25°C±3°C by lowering the circulating water temperature. The prepared polyanion cathode slurry meets the stability standards of a slurry viscosity increase of ≤20% within 6 hours and a slurry viscosity increase of ≤50% within 12 hours.

[0017] The binder used is PVDF or an organic binder of the same type.

[0018] Among them, the positive electrode material is a sodium ion battery polyanion positive electrode material, including at least one of NFPP, NVP, and NFPF.

[0019] The embodiments are only used to illustrate the technical solutions of the present application, rather than to limit them. Although the present application has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or make equivalent replacements for some of the technical features therein. These modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present application, and should all be included in the scope of protection of the present application.

Claims

1. A method for improving the stability of polyanion cathode slurry for sodium ion batteries, characterized by: During the wet mixing stage, the solid content of the slurry after the main powder is added is controlled at 60%-70%, the high viscosity stirring time is controlled at 1.5 hours-2.5 hours, and the dispersion speed is coordinated to 2500rpm-3500rpm and the revolution speed is 20rpm-40rpm to form a high shear dispersion-mild convection homogenization process system.

2. The method for improving the stability of a polyanion cathode slurry for sodium ion batteries according to claim 1, characterized in that: The binder used is PVDF or an organic binder of the same type.

3. The method for improving the stability of polyanion cathode slurry for sodium ion batteries according to claim 1, characterized in that: The prepared polyanion positive electrode slurry meets the stability standards of slurry viscosity increase of ≤20% within 6 hours and slurry viscosity increase of ≤50% within 12 hours.

4. The method for improving the stability of a polyanion cathode slurry for sodium ion batteries according to claim 1, wherein: During high viscosity stirring, the ratio of dispersion speed to revolution speed is 75-175:

1.

5. The method for improving the stability of polyanion cathode slurry for sodium ion batteries according to claim 1, characterized in that: The positive electrode material is a sodium ion battery polyanion positive electrode material, including at least one of NFPP, NVP, and NFPF.

6. The method for improving the stability of polyanion cathode slurry for sodium ion batteries according to claim 1, characterized in that: During the stirring process, the slurry temperature is monitored in real time. If the temperature exceeds 28°C, the circulating water temperature is lowered to maintain the slurry temperature at 25°C ± 3°C.