Aqueous zinc-ion batteries (ZIBs) are considered as one of the ideal devices for large-scale energy storage because of their safety, low cost, and nontoxicity. Unfortunately, the choice of cathode materials for ZIBs is still limited. Herein, a novel oxygen vacancy-rich nitrogen-doped MnCO3 (MnCO3@N) microsphere is reported as a cathode material for rechargeable ZIBs, which displays a relatively high reversible capacity of 171.6 mAh g-1 at 100 mA g-1, outstanding rate performance, and long-term cyclic stability up to 1000 cycles at 1000 mA g-1. The better electrochemical performances of MnCO3@N should be attributed to the introduction of oxygen vacancies in the MnCO3 microcrystal by nitrogen doping, which not only improves the conductivity of MnCO3 microspheres but also creates more active sites for zinc-ion diffusion. In addition, the energy storage mechanism of the MnCO3@N microspheres is systematically investigated. During the initial charge process, the MnCO3@N microspheres are activated to form MnO@N due to the insertion of Zn2+, and partial MnO@N is further oxidized into layered-type MnO2@N, which becomes a part of the active material for subsequent energy storage. This work not only provides a new insight for the ZIB cathode but also deepens the understanding of the energy storage mechanism of carbonate materials.
Keywords: charge storage mechanism; defect structure; high-capacity cathode; manganese carbonate; zinc-ion batteries.