Thermal-Induced Cathodic Interface Change on Na₃PS₄-Based All-Solid-State Sodium Batteries

FeS2 conversion electrode materials demonstrate excellent (electro)chemical stability with sulfide electrolytes and can provide a high capacity at room temperature. However, the effect of operating temperature on their conversion kinetics and capacity has not yet been reported. In this study, we incorporated ionic conductors of Na3PS4 as ionic additives in the composite cathode and separator layer. The additives exhibit high ionic conductivity and good anode stability. The increased operating temperature accelerates the Na+ ion diffusion rate in both Na3PS4 solid electrolyte and cathode composite mixture, resulting in reduced resistance and excellent electrochemical performance for the corresponding all-solid-state sodium battery. XPS results indicate that the FeS2 active material maintains its original activity over extended cycles at varying operating temperatures. Moreover, the Na3PS4 solid electrolyte undergoes slight decomposition when induced by conductive carbon at room temperature, and this phenomenon worsens with increasing working temperatures. Na2Sn/Na3PS4/FeS2 shows high discharge capacities and superior cyclability at various operating temperatures. It delivers discharge capacities of 264.4 and 585.3 mA h g–1 at 30 and 60 °C, respectively, when cycled at 0.5 A g–1 and retains a discharge capacity of 210.3 mA h g–1 after 260 cycles and 425.8 mA h g–1 after 700 cycles. These results provide guidance for designing high-energy-density, all-solid-state sodium batteries with conversion electrode materials.