An Air‐Stable and Li‐Metal‐Compatible Glass‐Ceramic Electrolyte enabling High‐Performance All‐Solid‐State Li Metal Batteries

The development of all-solid-state Li metal batteries (ASSLMBs) has attracted significant attention due to their potential to maximize energy density and improved safety compared to the conventional liquid-electrolyte-based Li-ion batteries. However, it is very challenging to fabricate an ideal solid-state electrolyte (SSE) that simultaneously possesses high ionic conductivity, excellent air-stability, and good Li metal compatibility. Herein, a new glass-ceramic Li_3.2 P_0.8 Sn_0.2 S₄ (gc-Li_3.2 P_0.8 Sn_0.2 S₄ ) SSE is synthesized to satisfy the aforementioned requirements, enabling high-performance ASSLMBs at room temperature (RT). Compared with the conventional Li₃ PS₄ glass-ceramics, the present gc-Li_3.2 P_0.8 Sn_0.2 S₄ SSE with 12% amorphous content has an enlarged unit cell and a high Li⁺ ion concentration, which leads to 6.2-times higher ionic conductivity (1.21 × 10^-3 S cm^-1 at RT) after a simple cold sintering process. The (P/Sn)S₄ tetrahedron inside the gc-Li_3.2 P_0.8 Sn_0.2 S₄ SSE is verified to show a strong resistance toward reaction with H₂ O in 5%-humidity air, demonstrating excellent air-stability. Moreover, the gc-Li_3.2 P_0.8 Sn_0.2 S₄ SSE triggers the formation of Li-Sn alloys at the Li/SSE interface, serving as an essential component to stabilize the interface and deliver good electrochemical performance in both symmetric and full cells. The discovery of this gc-Li_3.2 P_0.8 Sn_0.2 S₄ superionic conductor enriches the choice of advanced SSEs and accelerates the commercialization of ASSLMBs.