Effect of Molecular Weight of PTFE on the Cycling Performance of Dry-Processed Composite Cathode for Sulfide-Based All-Solid-State Batteries

All-solid-state batteries (ASSBs) with sulfide solid electrolytes have attracted considerable attention owing to enhanced safety and high energy density. The composite cathode fabricated by solvent-free dry process can maintain high ionic conductivity of solid electrolytes. Moreover, the active mass loading can be increased without increasing the resistance in the electrode owing to the inhibited migration of conductive carbon and binder, thereby increasing the energy density of ASSBs. The dry process relies on the fibrillation of polytetrafluoroethylene (PTFE) induced by shear force, facilitating the binding of active material, solid electrolyte, and conductive agent. However, insufficient fibrillation and aggregation of PTFE may deteriorate the mechanical properties and ionic conductivities of the composite cathode. In this work, we employed three PTFE binders with different molecular weights and investigated the effect of the molecular weight of PTFE on fibrillation and distribution in the composite cathode. Then, we compared the mechanical and electrochemical properties of the composite cathode using three different PTFE. In addition, the cycling performance and interfacial properties of the composite cathode, depending on the molecular weight of PTFE, will be presented and discussed.