PVDF with low molecular weight, on the other hand, has the opposite effect. An increase in molecular weight within a certain range contributes to the improvement of adhesion and cohesion. The narrower the distribution of molecular weight, the more uniform the performance of the binder, and the better the overall performance of the material.
PVDF is a semi crystalline polymer with a crystallinity generally between 50% and 70%. The common crystal phases include a, b, and y phases, with a phase being the most stable. The crystallinity of PVDF directly affects its mechanical properties. The higher the crystallinity, the greater the polymer force, the stronger the adhesion, and the better the thermal stability. However, high crystallinity may lead to difficulties in molecular circulation in the electrolyte, increase the discharge load, and thus affect the overall comprehensive performance of the battery.
The melting point of PVDF is about 170 ° C, and the crystallization point is about 155 ° C. When the ambient temperature is above 300 ° C, it begins to gradually decompose, and below 155 ° C, it crystallizes into a solid. The specific melting point of PVDF depends on factors such as its molecular weight, crystallinity, and thermal history.
In terms of polymerization mode, the melting point of lotion polymerization is significantly lower than that of suspension polymerization.
The glass transition temperature of PVDF is approximately 40 degrees Celsius. Generally speaking, the lower the glass transition temperature, the greater the flexibility of the molecular weight. Therefore, the low glass transition temperature of PVDF gives it a certain degree of flexibility and strength.
The following is a description of template based PTFE (polytetrafluoroethylene) and PFA (perfluoroalkoxy resin), focusing on their main characteristic indicators and their impact on performance:
