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, NaFe0.5Mn0.5O2 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 NaFe0.5Mn0.5O2 particles. Subsequent heat treatment further improved the electrode performance, resulting in an increased discharge voltage and a reversible capacity of 140 mAh g−1.