Compatibility Integrated Sulfide‐Based Cathode and Electrolyte for High‐Energy Solid‐State Sodium Batteries ^†

Comprehensive Summary The scarcity of critical raw materials in lithium‐ion batteries has driven increasing interest in alternative chemistries, such as sodium‐ based all‐solid‐state batteries. Among various solid electrolytes, sulfide‐based Na 3 PS 4 stands out for its high ionic conductivity and excellent formability. However, its poor interfacial compatibility with conventional high‐voltage oxide cathodes remains a major limitation. In this study, we report the successful integration of amorphous Na 2 MoS 4 —a high‐capacity, sulfide‐compatible cathode—into Na 3 PS 4 ‐based all‐solid‐state sodium batteries. Benefiting from a moderate redox potential window (1.1–2.7 V vs. Na + /Na), Na 2 MoS 4 exhibits excellent chemical and electrochemical compatibility with Na 3 PS 4 , as confirmed by structural and spectroscopic analyses. Further investigation reveals that intimate interfacial contact between both electrodes and the solid‐state electrolyte is critical for achieving long‐term cycling stability. Based on these insights, the optimized Na 15 Sn 4 | Na 3 PS 4 | Na 2 MoS 4 ‐Na 3 PS 4 ‐carbon nanofiber cell delivers a reversible capacity of ~372 mAh·g –1 at 0.1 C and retains nearly 100% capacity over 450 cycles at 0.3 C. In situ impedance spectroscopy further confirms the stability of interfacial resistance throughout cycling. This work identifies Na 2 MoS 4 as a highly promising sulfide cathode for high‐energy, long‐life sodium solid‐state batteries and provides valuable design principles for future development of sulfide‐based electrode‐electrolyte interfaces in next‐generation energy storage systems.