Air‐stable Li3.12P0.94Bi0.06S3.91I0.18 solid‐state electrolyte with high ionic conductivity and lithium anode compatibility toward high‐performance all‐solid‐state lithium metal batteries

Sulfide solid‐state electrolytes (SSEs) with superior ionic conductivity and processability are highly promising candidates for constructing all‐solid‐state lithium metal batteries (ASSLMBs). However, their practical applications are limited by their intrinsic air instability and serious interfacial incompatibility. Herein, a novel glass‐ceramic electrolyte Li3.12P0.94Bi0.06S3.91I0.18 was synthesized by co‐doping Li3PS4 with Bi and I for high‐performance ASSLMBs. Owing to the strong Bi‒S bonds that are thermodynamically stable to water, increased unit cell volume and Li+ concentration caused by P5+ substitution with Bi3+, and the in situ formed robust solid electrolyte interphase layer LiI at lithium surface, the as‐prepared Li3.12P0.94Bi0.06S3.91I0.18 SSE achieved excellent air stability with a H2S concentration of only 0.205 cm3 g−1 (after 300 min of air exposure), outperforming Li3PS4 (0.632 cm3 g−1) and the most reported sulfide SSEs, together with high ionic conductivity of 4.05 mS cm−1. Furthermore, the Li3.12P0.94Bi0.06S3.91I0.18 effectively improved lithium metal stability. With this SSE, an ultralong cyclability of 700 h at 0.1 mA cm−2 was realized in a lithium symmetrical cell. Moreover, the Li3.12P0.94Bi0.06S3.91I0.18‐based ASSLMBs with LiNi0.8Mn0.1Co0.1O2 cathode achieved ultrastable capacity retention rate of 95.8% after 300 cycles at 0.1 C. This work provides reliable strategy for designing advanced sulfide SSEs for commercial applications in ASSLMBs.