1. Kneading
Function: By using mechanical shearing force to initially mix active materials, conductive agents and binders, a high-solids-content slurry is formed, which promotes particle wetting and initial dispersion and reduces agglomeration.
Control points:
Solid content: usually controlled at around 68%.
Rotation speed and time: Low-speed mixing avoids damaging the material structure, such as a rotation speed ≤ 500 rpm (example, subject to actual conditions).
Temperature: Avoid excessively high temperatures that could degrade the adhesive (e.g., PVDF needs to be dissolved at 50-60℃).
Adding sequence: Add the adhesive or solvent in stages to ensure that the powder is fully wetted.
2. Wetting
Function: The solvent penetrates the surface of powder particles, replacing air and forming a uniformly wetted slurry system.
Control points:
Solvent addition amount: Add in steps, with the first addition being 40%~90% of the adhesive solution.
Wetting time: Ensure the powder is fully wetted to avoid dry powder residue.
Ambient humidity: negative electrode homogenate humidity ≤65%, positive electrode: lithium iron phosphate system humidity ≤20%, ternary system dew point ⇐25℃.
3. Dispersion
Function: By using high-speed shearing force to break up particle agglomeration, it achieves uniform dispersion at the nanoscale and forms a stable slurry.
Control points:
Shear rate: High-speed dispersion linear velocity 18~20 m/s.
Dispersion time: Avoid too long, which may cause material breakage, or too short, which may result in insufficient dispersion.
Equipment selection: dual planetary mixer or twin screw continuous disperser.
4. Viscosity Adjustment
Function: To adjust the fluidity of the slurry to suit the coating process and ensure the consistency of electrode thickness and areal density.
Control points:
Target viscosity: typically 4000~6000 mPa·s for negative electrode slurry.
Solvent addition method: adjust in small amounts multiple times to avoid over-dilution (for example, you can reduce the amount by 1%~2% each time according to the solid content).
Stability monitoring: The viscosity change is tested every hour to assess the stability of the slurry.
In addition to the four core homogenization steps of kneading, wetting, dispersing, and viscosity adjustment, a complete homogenization process also includes:
Vacuum degassing: Removes air bubbles from the slurry.
Filtering and demagnetizing: Removes metallic foreign objects.
Slurry delivery and storage: Ensure slurry uniformity.
Summarize
The homogenization process achieves slurry uniformity through four core steps: kneading, wetting, dispersing, and viscosity adjustment. Control points include parameters such as solid content, rotation speed, temperature, and humidity. The complete process also requires auxiliary steps such as degassing and filtration to ensure that the slurry quality meets the requirements of subsequent coating and battery performance.
