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 Li 1.3 Al 0.3 Ti 1.7 P 3 O 12 (LATP). Li reacts with LATP to form an amorphous phase at elevated temperatures, which then crystallizes into Li 3 PO 4 and LiP with additional Li 3 P and Li 0.5 TiO 2 at even higher temperatures. The instability of the corner-sharing PO 4 tetrahedra and TiO 6 octahedra against Li at high temperature is the root cause of thermal runaway for LATP. Li diffusion into LATP causes the collapse of the PO 4 tetrahedra and TiO 6 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.