Highly Safe All‐Solid‐State Lithium Metal Battery Enabled by Interface Thermal Runaway Regulation Between Lithium Metal and Solid‐State Electrolyte

Abstract All‐solid‐state (ASS) Li‐metal batteries are regarded as promising energy‐storage devices due to their high energy density and improved safety. Recently, the interface thermal runaway issues between reactive Li‐metal and solid‐state electrolytes (SSEs) have attracted increasing attention, but it has been less studied. Here, using in situ high‐resolution thermal imaging, a significant stress‐release period before the interface catches fire and burns between Li metal and Li_1.5Al_0.5Ge_1.5(PO₄)₃ (LAGP) SSE is found that can provide opportunities for early thermal runaway warning for the batteries. Further, a highly safe ASS Li‐metal battery without external pressure package is reported by constructing a stable heterogeneous interface layer (HIL) consisting of ALD‐coated aluminum oxide and PECVD‐deposited amorphous silicon (a‐Si), which significantly reduces the interface exothermic reaction and suppresses the interface thermal runaway both theoretically and experimentally. The ASS Li‐metal symmetric battery shows a long cycling stability both at RT and high temperature over 150 °C being at least 8‐times higher than that of the one without HIL. The assembled Li‐CO₂ battery is capable of 100 stable cycles with <3.2 V low charge potential at 500 mAg⁻¹ at 150 °C. This work paves a way for the development of the next‐generation safe and high‐energy lithium batteries.