A Method to Measure the Swelling of Water-Soluble PVDF Binder System and Its Electrochemical Performance for Lithium Ion Batteries

Water-soluble CMC/PVDF binder systems were used to prepare graphite anodes and compared mechanically and electrochemically with CMC/SBR binder systems. The effect of crystallinity of PVDF binder on the mechanical and electrochemical performance of the anodes is studied. A contact free method easy to operate and equipped with high accuracy was developed by using capacitance measurement. The swelling of graphite electrodes was controlled and showed different results for different binder crystallinities (no swelling of binder with high crystallinity vs 12% for medium crystallinity and 17% for low crystallinity binder). The discharge capacity depends on the crystallinity of the binders and half-cells delivered a capacity in the range of 230-360 mAh g−1. The binder with medium crystallinity in particular exhibited the best mechanical and electrochemical performance and showed an excellent C-rate stability with specific capacities up to 10 C. Full cell tests showed good cycling stability over 180 cycles. The water-based PVDF binders seem to be a promising alternative to solvent-based binders.