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.