CeO₂-Doping Induced High-Moisture Stability and Fast Lithium-Ion Transport with Li_5.5PS_4.5Cl_1.5 Solid-State Electrolyte for All-Solid-State Batteries

Sulfide solid electrolytes (SSEs) are particularly attractive in fabricating all-solid-state lithium metal batteries (ASSLMBs) due to their ultrahigh ionic conductivity and excellent process ability. However, SSEs face significant challenges, including poor air stability and interfacial compatibility with lithium metal anodes. To address these issues, this work devises a series of Li5.5+2xP1–xCexS4.5–2xO2xCl1.5 (0 ≤ x ≤ 0.3) SSEs using a cerium and oxygen codoping strategy. The Li5.8P0.85Ce0.15S4.2O0.3Cl1.5 variant exhibited good ionic conductivity (2.70 × 10–3 S cm–1 at room temperature) and enhanced air stability compared to the baseline Li5.5PS4.5Cl1.5. This composition effectively reduced the diffusion barrier for Li+, mitigating lithium dendrite growth. As a result, cells using this electrolyte showed optimal critical current density (1.5 mA cm–2) and good long-term cycle stability (800 h at 0.1 mA cm–2). A prototype battery with an NCM811 cathode and the Li5.8P0.85Ce0.15S4.2O0.3Cl1.5 SSE demonstrated promising electrochemical performance, highlighting the potential of cerium and oxygen codoping for the commercialization of ASSLMBs.