Electrolyte dependence of the performance of a Na₂FeP₂O₇//NaTi₂(PO₄)₃ rechargeable aqueous sodium-ion battery

Aqueous sodium-ion battery is attractive, because of the low cost and the high safety. However, since the electrochemical window of the aqueous electrolyte is narrow, there have been few reports concerning the optimum cathode materials for use in aqueous sodium-ion batteries up to now. This work focused on Na₂FeP₂O₇ as a cathode material for a novel aqueous sodium-ion battery, and investigated the electrolyte dependence of the performances of a Na₂FeP₂O₇//NaTi₂(PO₄)₃ full-cell. The battery performances such as the rate capability and cyclability of Na₂FeP₂O₇//NaTi₂(PO₄)₃ full-cell with 2 M Na₂SO₄ or 4 M NaClO₄ aqueous electrolyte were better than that with the non-aqueous electrolyte. However, a Na₂FeP₂O₇//NaTi₂(PO₄)₃ full-cell with 4 M NaNO₃ aqueous electrolyte exhibited a large irreversible capacity due to the corrosive side reaction.