Spontaneously dissolved MnO: A better cathode material for rechargeable aqueous zinc-manganese batteries

Abstract

Manganese-based oxides (MnOx) cathodes, with profuse crystal structures and valence states, have raised extensive research interstate for aqueous zinc-manganese batteries. However, the lack of a clear reaction mechanism and source of capacity presents significant challenges for the design and development of advanced manganese-based oxide cathodes. Herein, by exploring the electrochemical activation processes and reaction mechanisms of MnOx (including MnO2, Mn2O3, Mn3O4 and MnO), MnO is proved to hold superior potential for zinc-ion batteries cathode application compared to other MnOx owing to its exceptional spontaneous dissolution activation activity and the largest proportion of Mn. Further, to ulteriorly enhance the dissolution activation and poor electronic conductivity of MnO, a porous carbon matrix-encapsulated MnO nanocomposite (MnO@PC) is successfully synthesized. Moreover, the porous carbon matrix could facilitate electrolyte infiltration and promote adsorption towards Mn2+ and Zn2+ cations, leading to more Zn4SO4·(OH)6·xH2O (ZSH) deposition and greater stability of the reversible ZSH-assisted deposition/dissolution reaction. Therefore, MnO@PC can display improved capacity of 269 mAh g-1 (0.1 A g-1) with an exceptional capacity retention of 93% after 120 cycles in pure ZnSO4 electrolyte. And at 2.0 A g-1, the capacity could reach 75 mAh g-1 and be well maintained in 2000 cycles.