Addition of Na₃PO₄ for Enhanced Positive Electrode Performance in All-Solid-State Sodium Batteries (Supporting Information)

All-solid-state sodium secondary batteries have attracted attention as next-generation batteries owing to their balanced performances in terms of energy density, battery life, abundant availability of sodium resources, and resulting cost reduction. For the positive electrode materials, NaFe_0.5Mn_0.5O₂ is promising because it consists of abundant elements. However, its application in all-solid-state batteries with sulfide solid electrolytes are hindered by side reactions with the solid electrolytes, which lower the operating voltage. In this study, the electrode performances of all-solid-state sodium batteries were enhanced by mixing Na₃PO₄ with NaFe_0.5Mn_0.5O₂ particles. Subsequent heat treatment further improved the electrode performance, resulting in an increased discharge voltage and a reversible capacity of 140 mAh g⁻¹.