Enhanced Performance of Aqueous Sodium‐Ion Batteries Using Electrodes Based on the NaTi₂(PO₄)₃/MWNTs–Na0.44MnO₂ System

Sodium‐ion batteries with good electrochemical performance are of great significance for grid‐scale energy storage applications. Herein, an aqueous rechargeable Na‐ion battery has been fabricated with multiwalled carbon nanotube (MWNT)‐containing NaTi 2 (PO 4 ) 3 /MWNTs nanocomposites as the anode and Na 0.44 MnO 2 nanorods as the cathode in a 1 M aqueous Na 2 SO 4 electrolyte and the device was carefully studied. Owing to the open framework structures (containing large interstitial sites) that both NaTi 2 (PO 4 ) 3 and Na 0.44 MnO 2 possess, the fast Na‐ions will facilitate free transport. Benefiting from their unique structural features, the aqueous battery system exhibited an average charge and discharge voltage of approximately 1.1 V, a high energy density of 58.7 Wh kg −1 in terms of total electroactive materials, and could deliver a reversible capacity of approximately 50 mAh g −1 after 300 cycles at 2 C rate; the corresponding coulombic efficiency was nearly constant at approximately 95 %. These results, together with the safety and cost perspectives of aqueous electrolytes indicated that the aqueous Na‐ion battery may be a good candidate for safe, inexpensive, high‐power energy storage systems.