The first is to confirm and bake the battery material. Generally, the battery conductive agent needs to be baked at 120℃ for 8 hours. The PVDF powder should be baked at 80℃ for 8 hours. The cathode active material (LFP, NCM, etc.) depends on the state and process of incoming material whether it needs to be baked and dried.
After drying, (wet process) Mixing the PVDF powder and NMP solvent to make the binder (glue) for electrode. The quality of PVDF binder (glue) is very important to the internal resistance and electrical performance of the battery. The factors that affect the binder mixing include temperature and stirring speed. The higher the temperature of the binder out of yellowing, affecting the adhesion; The mixing speed is too high and the binder is easy to be broken. The specific speed depends on the size of the dispersion plate. In general, the linear speed of the dispersion plate is 10-15m/s (high dependence on equipment). At this time, it is required to open the circulating water in the mixing tank, and the temperature is ≤30℃.
Next is cathode active material preparation. At this point need to pay attention to the feeding sequence (add cathode active material and conductive agent slowly mix, then add binder), feeding time, feeding ratio, to strictly according to the process. Secondly, it is necessary to strictly control the rotation and rotation speed of equipment, vacuum degree and temperature of stirring. In this stage, it is necessary to regularly test the size and viscosity of the slurry, and the size and viscosity are closely related to the solid content, material performance, feeding sequence and process. At this time, the conventional process requirements: Temperature ≤30℃, Humidity ≤25%RH, Vacuum ≤-0.085mpa.
After the slurry mixing will be turned out to transfer tank or coating workshop, the slurry needs to be filtered when it is turned out, the purpose of filtration is to filter large particles, precipitation and removal of ferromagnetism and other substances. The influence of large particles coating to the final may lead to the battery from the risk of large or short circuit; The size of the ferromagnetic material too high will lead to the battery self-discharge too large and so on. At this time, the process requirements: Temperature ≤40℃, Humidity ≤25%RH, Screen ≤100 mesh, Particle size ≤15um (parameters are for reference only).