Binary solvent mixtures containing NaClO4 salt were investigated as electrolytes for sodium-ion batteries. The electrochemical performance of Na4Fe3(PO4)2(P2O 7) cathodes was substantially improved when paired with an ethylene carbonate (EC)/propylene carbonate (PC)-based electrolyte. Our investigation revealed that EC/PC/1 M NaClO4 exhibits superior oxidation durability at the cathode and is highly stable toward a Na-metal electrode.