Role of External Pressure in Thermal Stability of Solid-State Batteries

Despite the significant promise of solid-state batteries (SSBs) for delivering higher energy and power densities, their thermal stability and safety still require rigorous investigation. While stack pressure is widely recognized for enhancing electrochemical performance, its mechanistic role in governing the thermal stability has not been established. In this work, we investigate the relationship between stack pressure and thermal stability in sulfide-based SSBs, focusing on electrochemical interactions at the Li metal anode and oxide cathode interfaces as an exemplar system. Accelerating rate calorimetry reveals that the absence of external stack pressure triggers rapid thermal runaway at the Li/solid-electrolyte interface, whereas applied pressure delays the onset of self-heating and reduces the severity of thermal cascades. A mechanistic cell-level safety map is developed for SSB cell architectures, capturing the interplay between interphase behavior and cathode-Li crosstalk under abuse conditions. These results identify stack pressure as a critical design parameter for improving the thermo-electrochemical stability of SSBs.