A high-safety and low-cost route is important in the development of sodium-ion batteries, especially for large-scale stationary battery systems. An aqueous sodium-ion battery is demonstrated using a single NASICON-structured Na₂VTi(PO₄)₃ material with the redox couples of V⁴⁺/V³⁺ and Ti⁴⁺/Ti³⁺ working on the cathode and anode, respectively. The symmetric full cell fabricated based on the bi-functional electrode material exhibits a well-defined voltage plateau at ~1.2 V and an impressive cycling stability with capacity retention of 70% exceeding 1, 000 cycles at 10C (1C = 62 mA·g^-1). This study provides a feasible strategy for obtaining high-safety and low-cost rechargeable batteries using a single active material in aqueous media.