Nanoscale Origin of the Soft-to-Hard Short-Circuit Transition in Inorganic Solid-State Electrolytes.

Understanding and overcoming the chemomechanical failures of polycrystalline inorganic solid-state electrolytes (SSEs) are critical for next-generation all-solid-state batteries. Yet, so far, the nanoscale origin of SSEs' chemomechanical failure under operation conditions remains a mystery. Here, by using in situ electron microscopy, we decipher the nanoscale origin of the soft-to-hard short-circuit transition─a conventionally underestimated failure mechanism─caused by electronic leakage-induced Li precipitation in SSEs. For the first time, we directly visualize stochastic Li interconnection-induced soft short circuits, during which the SSEs undergo the transition from a nominal electronic insulator to a state exhibiting memristor-like nonlinear conduction (electronic leakages), ultimately evolving into hard short circuits. Furthermore, we first capture intragranular cracking caused by Li penetration, demonstrating that fully wetted Li can fracture polycrystalline oxide SSEs via a liquid-metal embrittlement-like mechanism. Guided by these insights, we show that incorporating an electronically insulating and mechanically resilient 3D polymer network into an inorganic/polymer composite SSE effectively suppresses Li precipitation, interconnection, and short circuits, significantly enhancing its electrochemical stability. Our work, by elucidating the soft-to-hard short-circuit transition kinetics of SSEs, offers new insights into their nanoscale failure mechanisms.