Atomic-Scale Cryo-TEM Studies of the Thermal Runaway Mechanism of Li1.3Al0.3Ti1.7P3O12 Solid Electrolyte

Understanding the thermal runaway mechanism of solid-state electrolytes is critical for the development of all-solid-state Li-metal batteries (ASLMBs). Herein we employ multiscale methods including in situ optical microscopy and cryo-transmission electron microscopy combining with density functional theory to reveal the failure mechanism of Li1.3Al0.3Ti1.7P3O12 (LATP). Li reacts with LATP to form an amorphous phase at elevated temperatures, which then crystallizes into Li3PO4 and LiP with additional Li3P and Li0.5TiO2 at even higher temperatures. The instability of the corner-sharing PO4 tetrahedra and TiO6 octahedra against Li at high temperature is the root cause of thermal runaway for LATP. Li diffusion into LATP causes the collapse of the PO4 tetrahedra and TiO6 octahedra, forming Li–O, Li–P–O, and Li–Ti–O species which release a large amount of heat, triggering thermal runaway of LATP. This work provides atomic-scale understanding of the thermal runaway of LATP, which offers an important clue to mitigate failure of ASLMBs.