An Air‐Stable and Electrode‐Compatible Lithium Superionic Conductor

ABSTRACT The development of high‐performance sulfide solid electrolytes necessitates materials that simultaneously exhibit superior ionic conductivity, excellent electrochemical stability, and enhanced environmental tolerance. This work reports a novel lithium solid electrolyte, Li 5.3 P 0.98 Nb 0.02 S 4.25 O 0.05 Cl 1.7 (LPNbSOCl), which demonstrates remarkable improvements in these critical properties. The optimized composition achieves an ionic conductivity of 10.6 mS cm −1 at room temperature with an activation energy of 0.249 eV. Electrochemical characterization reveals exceptional stability against lithium metal, with a critical current density （CCD) reaching 3.82 mA cm −2 and stable cycling performance for 1000 h in symmetric cell configurations. The material exhibits significantly improved air stability, maintaining 78.4% of its initial conductivity after air exposure while substantially reducing H 2 S evolution compared to conventional sulfide electrolytes. Interfacial analysis indicates the formation of a stable solid electrolyte interphase containing Li─Nb alloy and Li 2 O at the anode. In all‐solid‐state battery configurations with LiCoO 2 (LCO) cathodes, this electrolyte enables outstanding cycling stability over 90% capacity retention after 1000 cycles at a 1C rate and delivers 115.4 mAh g −1 at high current densities of 5C. These results demonstrate the potential of compositionally optimized lithium argyrodite materials to address the key challenges in solid‐state battery technology.