Self-sacrifice of sulfide electrolytes facilitating stable solid-state sodium–sulfur batteries†

Sulfide electrolytes have emerged as the preferred choice for solid-state sodium–sulfur (Na–S) batteries due to their excellent compatibility with sulfur cathodes. Despite their advantages, such as high ionic conductivity, mechanical flexibility, and enhanced safety, challenges like narrow electrochemical stability windows and inadequate interfacial contact persist and require urgent resolution. Contrary to the conventional approach of minimizing electrolyte degradation, this study leverages the decomposition of a typically unstable sulfide electrolyte, Na₃SbS₄ (NAS), to enhance both cathode and anode interfaces. By elucidating the reversible self-redox mechanism of NAS, we demonstrate that a cathode composite containing NAS-S as a co-active material achieves an exceptional discharge capacity at room temperature, surpassing the theoretical specific capacity of sulfur alone. Furthermore, the strong interaction between NAS and a Na-based alloy anode leads to the in situ formation of a homogeneous interlayer. This passivation layer, acting as both an electron regulator and protective barrier, prevents further electrolyte corrosion and dendrite penetration, resulting in remarkable cycling stability. This novel approach of utilizing electrolyte decomposition offers a fresh perspective on interface engineering, advancing solid-state Na–S batteries towards practical, next-generation energy storage solutions with improved capacity output and cycle life.