Processing is a key factor for the lithium battery industry. Some evaluations have been performed for a better understanding of the parameters to be controlled in order to optimize processing and performance of PVDF.
The first step of electrodes manufacturing is the dissolution of PVDF in an organic solvent such as NMP. Some guidelines may be taken into consideration for improving the efficiency of this process.
- The method for adding the powder to the solution plays a major role in dissolution ease and duration: in particular it is advised to slowly add the powder to the solution while stirring.
- Mixing speed, geometry of the stirrer and temperature of the solution play key roles in the kinetics of dissolution. It is advised to give enough time to the polymer to completely dissolve in the solvent; a slight heating of the solution can improve the dissolution time.
- It is important to use dry materials and solvents and to operate in a dry environment in order to improve the dissolution process.
Solef® PVDF grades in NMP
Flow curves measured by rheometer RFS III; T = 25 °C, concentration 8 % w/w
Slurry viscosity – LiCoO2
PVDF grade, concentration of the solution and temperature are key factors in determining the solution viscosity. Slurry viscosity is furthermore affected by the chemical nature and the concentration of active materials, as well as slurry viscosity. It is therefore recommended to optimize PVDF concentration and slurry formulation in order to reach suitable processing conditions. For example, some results of slurry viscosity are reported, where slurries have been prepared with the same active material (LiCoO2) but with different polymer content. It may be also necessary to optimize the total solid content of the slurry in order to obtain the targeted slurry viscosity for the coating process. Besides, the nature of active materials and its particle size also play an important role in the determination of slurry viscosity.
Slurry for electrodes coating