The development of solid electrolytes (SEs) for high-performance solid-state batteries (SSBs) requires not only favorable electrochemical stability but also interfacial compatibility with diverse cathode chemistries. In this study, we systematically benchmark recently discovered Li₇Si₂S₇I against the well-established argyrodite Li₅. ₅PS₄. ₅Cl₁. ₅ as an SE in composite cathodes. Despite exhibiting comparable oxidative stability, Li₇Si₂S₇I demonstrates markedly different behaviors depending on the cathode chemistry. In composite cathodes with uncoated LiNi₀. ₈₃Co₀. ₁₁Mn₀. ₀₆O₂ as the cathode active material and Li₇Si₂S₇I as the electrolyte, rapid degradation occurs, with capacity retention dropping to 5% after 30 cycles, driven by fast degradation kinetics and interfacial instability toward the formation of SiOₓ species as a thermodynamic sink. In contrast, sulfur–carbon–Li₇Si₂S₇I composite cathodes show good performance in half-cells, comparable to that of the argyrodite benchmark. The reversible oxidative redox processes of Li₇Si₂S₇I in sulfur-based systems highlight its promise for Li–S and other oxygen-free battery chemistries. Overall, this work emphasizes the importance of a holistic approach to SE evaluation, integrating chemical and electrochemical stability with degradation kinetics, to inform the rational design of next-generation SSB materials.
Härtel et al. (Wed,) studied this question.