Insight on air-induced degradation mechanism of Li₇P₃S₁₁ to design a chemical-stable solid electrolyte with high Li₂S utilization in all-solid-state Li/S batteries

The ideal solid-state electrolyte must have exceptional chemical and electrochemical stability, high ionic conductivity, lower interfacial resistance and high active material utilization. Inspired by discovering new lithium thiophosphate superionic conductors for all-solid-state Li/S batteries (ASSLSBs), we designed and explored the local structure of Li_6.95Zr_0.05P_2.9S_10.8O_0.1I_0.4 (LZPSOI) solid-state electrolyte, which owns a high ionic conductivity of 3.01 mS cm⁻¹ with improved air-stability at RT. The structure–property correlation behavior of the chemical stability of LZPSOI electrolyte was sequentially premeditated by a combination of ex-situ XRD, MAS-NMR, XPS and SEM. A mechanistically driven approach has been extensively evaluated that the chemical stability of Li₇P₃S₁₁ could be enhanced via oxide doping, in which S^2- was partly replaced by O^2– in conductive structural units to yield POS₃^3- and P₂OS₆^4- which was confirmed by XPS and ³¹P MAS-NMR. The ASSLSBs assembled with LZPSOI electrolyte exhibited a remarkable initial discharge capacity of 932 mAh g⁻¹ and a coulombic efficiency of 99.2% under 0.064 mA cm⁻² at RT, compared to Li₇P₃S₁₁ counterpart. The exceptional cyclic performance was benefitted from higher electronic and ionic conductivities with LiI additive and additional reaction sites, which collectively enhanced the utilization of Li₂S active material. This exploration gives birth to a potential contender as a solid-state electrolyte with high ionic conductivity and chemical stability to apply for next-generation ASSLSBs.