An Aqueous Dual‐Ion Battery Cathode of Mn₃O₄ via Reversible Insertion of Nitrate

We report reversible electrochemical insertion of NO 3 − into manganese(II, III) oxide (Mn 3 O 4 ) as a cathode for aqueous dual‐ion batteries. Characterization by TGA, FTIR, EDX, XANES, EXAFS, and EQCM collectively provides unequivocal evidence that reversible oxidative NO 3 − insertion takes place inside Mn 3 O 4 . Ex situ HRTEM and corresponding EDX mapping results suggest that NO 3 − insertion de‐crystallizes the structure of Mn 3 O 4 . Kinetic studies reveal fast migration of NO 3 − in the Mn 3 O 4 structure. This finding may open a new direction for novel low‐cost aqueous dual‐ion batteries.