Here, we report an
aqueous/nonaqueous hybrid electrolyte based
on sodium trifluoromethanesulfonate with an expanded electrochemical
window up to 2.8 V and high conductivity (∼25 mS cm<sup>–1</sup> at 20 °C). The hybrid electrolyte inherits the safety characteristic
of aqueous electrolytes and the electrochemical stability of nonaqueous
systems, enabling stable and reversible operation of the Na<sub>3</sub>V<sub>2</sub>(PO<sub>4</sub>)<sub>3</sub>/NaTi<sub>2</sub>(PO<sub>4</sub>)<sub>3</sub> sodium-ion battery
