Electrochemical conversion reaction of Cu-MnO for aqueous rechargeable zinc-ion batteries with high performance and long cycle life
Rechargeable aqueous zinc-ion batteries (ZIBs) are emerging as alternative lithium-ion batteries for large-scale energy storage applications due to their safety and environmental friendliness. However, their applications are hindered by the lack of suitable cathode materials that provide high capacity and long cyclic stability. In this work, we design Cu-MnO nanospheres cathode material having abundant manganese/oxygen defects via calcination and reduction of manganese dioxide (MnO2) in Ar/H2 atmosphere. Electrochemical mechanism investigation shows that the spinel-type Cu-MnO electrode starts to transform into layered-type Cu-MnO2.nH2O nanoflowers upon initial charging, and thus the subsequent Zn2+ intercalation and H+ conversion reactions take place in Cu-MnO2.nH2O material. The underlying phase transformation of Cu-MnO nanospheres and energy storage mechanism of Cu-MnO2.nH2O nanoflowers are systematically investigated with a broad range of characterizations. The manganese vacancy is also observed in Cu-MnO2.nH2O, which interestingly triggers lattice oxygen redox reaction. As a result, when demonstrated as cathode material for zinc ion batteries, the Cu-MnO2.nH2O delivers a high specific capacity of 320 mAh g-1 and long-term cyclic stability with a capacity retention of over 70% after 1000 cycles. This work not only opens an insight into the design of transition metal modified manganese monoxide cathodes but also broadens the horizons of understanding the electrochemical properties and energy storage mechanism of low valance manganese-based cathode materials for rechargeable zinc-ion batteries.