Revealing and suppressing hot spot driven interface thermal runaway for all-solid-state lithium metal batteries

All-solid-state lithium metal batteries based on non-flammable inorganic ceramic electrolytes hold promise for achieving both high energy density and safety. However, inadequate physical contact and chemical incompatibility at the Li/electrolyte interface can provoke interfacial thermal runaway far exceeding those in liquid-electrolyte batteries. Here, we employ in situ high-resolution thermal imaging to monitor thermal runaway at the Li|LATP interface in real time. Results show that after the initial contact reaction at 320 °C, the interface enters a stochastic stress-release stage, during which LATP cracks nucleate and localized hot spots form at the cracks, with the representative hot-spot region showing a temperature-rise rate of ~9.5 °C s^-1 before violent ignition. Transitioning to violent ignition and combustion, the heating rate surges beyond 1943.8 °C s^-1 and interfacial temperature exceeds 1500 °C, causing catastrophic thermal breakdown. In situ imaging coupled with ex situ characterization delineates a safety failure pathway wherein interfacial failure generates hot spots that drive localized thermal runaway. Guided by this, we design a dual-passivation LiI|a-Si heterogeneous interlayer that substantially suppresses interfacial heat and oxygen- containing species releasing reactions, eliminating hot spots initiation and thermal runaway at their source. The all-solid-state lithium metal symmetric batteries with this interlayer demonstrate stable cycling at 150 °C. This work paves the way for developing safe and high-energy all-solid-state batteries.