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

: We report reversible electrochemical insertion of NO3- into manganese(II, III) oxide (Mn3 O4 ) as a cathode for aqueous dual-ion batteries. Characterization by TGA, FTIR, EDX, XANES, EXAFS, and EQCM collectively provides unequivocal evidence that reversible oxidative NO3- insertion takes place inside Mn3 O4 . Ex situ HRTEM and corresponding EDX mapping results suggest that NO3- insertion de-crystallizes the structure of Mn3 O4 . Kinetic studies reveal fast migration of NO3- in the Mn3 O4 structure. This finding may open a new direction for novel low-cost aqueous dual-ion batteries.