Unraveling soft breakdown in solid-state electrolytes

All-solid-state lithium metal batteries (ASSLMBs) with solid-state electrolytes (SSEs) are regarded as next-generation energy storage technology due to their superior safety and exceptional energy density. However, soft breakdown—a prevalent failure mechanism in ASSLMBs—has hindered their development. In this study, we introduce Li/SSE/current collector (CC) asymmetric cells as a novel evaluation method to assess the susceptibility of various SSEs to soft breakdown. Our findings reveal that metal-contained SSEs (e.g., LGPS) exhibit a stronger resistance to soft breakdown compared to metal-free SSEs (e.g., LPSC) through phase characterization including ToF-SIMS and XPS. This enhanced stability is attributed to the formation of a metal-containing solid electrolyte interphase (SEI) at the interface. Moreover, the impact of practical cell configuration including current density, stack pressure, cutoff voltage on the occurrence of soft breakdown was also discussed. The insights gained from this work deepen the understanding of the soft breakdown phenomenon in SSEs and provide valuable guidance for the design of advanced solid-state electrolytes.