Analysis of the Electrochemical Stability of Sulfide Solid Electrolyte Dry Films for Improved Dry-Processed Solid-State Batteries

The solvent-free processing of cell components is attracting growing interest, as it avoids energy-intensive drying and solvent recovery procedures. In solid-state batteries, the dry processing of solid electrolyte (SE) films results in improved ionic conductivities compared to wet processing and eliminates degradation due to residual solvent traces. For dry processing, the binder polytetrafluoroethylene (PTFE) is widely used due to its excellent fibrillation, but it shows poor electrochemical stability at low anode potentials. Here, the influence of processing parameters on the binder structure is evaluated, and the electrochemical degradation of the dry film separators is systematically investigated (e.g., CTTA measurements) at different anode potentials (Si and Li anode). A combination of electrochemical and surface characterization at the SE dry film/anode interface is conducted. The results confirm that processing has a large influence on the stability at the dry film/anode interface. By adapting the SE dry film processing, long-term cycling in Si||NMC pouch cells is demonstrated over more than 1300 cycles. Additionally, a high initial coulombic efficiency of 92% and an average CE of 99.7% are obtained over 100 cycles, highlighting the potential of dry film separators for the application with Si anodes.