An Aqueous Symmetric Sodium‐Ion Battery with NASICON‐Structured Na3MnTi(PO4)3

A symmetric sodium-ion battery with an aqueous electrolyte is demonstrated; it utilizes the NASICON-structured Na3 MnTi(PO4 )3 as both the anode and the cathode. The NASICON-structured Na3 MnTi(PO4 )3 possesses two electrochemically active transition metals with the redox couples of Ti(4+) /Ti(3+) and Mn(3+) /Mn(2+) working on the anode and cathode sides, respectively. The symmetric cell based on this bipolar electrode material exhibits a well-defined voltage plateau centered at about 1.4 V in an aqueous electrolyte with a stable cycle performance and superior rate capability. The advent of aqueous symmetric sodium-ion battery with high safety and low cost may provide a solution for large-scale stationary energy storage.