Chemomechanical Stability Determines the Performance of Dry-Processed Cathode and Separator Sheets in Thiophosphate-Based Solid-State Batteries

Dry processing has recently emerged as a promising solvent-free manufacturing strategy for solid-state batteries (SSBs). In this work, we systematically investigate how dry-processed LiNi 0.85 Co 0.1 Mn 0.05 O 2 cathode and Li 6 PS 5 Cl solid electrolyte (SE) separator sheets influence performance and degradation in different SSB architectures. They were produced using a fibrillating polytetrafluoroethylene (PTFE) binder and compared to conventional powder-based (pelletized) configurations. In addition, various cathode formulations were investigated to elucidate the effect that both carbon black and protective surface coating of the cathode active material (CAM) have on cycling performance. It is demonstrated that introducing a fibrillar network improves particle-particle contact and mechanical integrity, resulting in higher initial capacities, better rate capability, and increased Coulomb efficiency compared to pelletized cells. However, the experimental data indicate that while carbon black improves electronic percolation, it simultaneously accelerates interfacial degradation in PTFE-containing SSB architectures. Post mortem characterization and in situ gas analysis further show that the sheet-type cathodes are subject to greater electrochemical degradation, but still perform better than their pelletized counterparts. Therefore, long-term cycling performance is determined more by chemomechanical stability than by the extent of SE degradation at the CAM|SE interface alone. Overall, this study provides mechanistic insights into the role of dry processing in thiophosphate-based cells, highlights both the advantages and limitations of PTFE as a binder, and offers design guidelines for future SSB manufacturing.