Phase transformation mechanism of MnCO₃ as cathode materials for aqueous zinc-ion batteries

Aqueous rechargeable zinc-ion batteries (ZIBs) have been given more and more attention because of their high specific capacity, high safety, and low cost. The reasonable design of Mn-based cathode materials is an effective way to improve the performance of ZIBs. Herein, a square block MnCO₃ electrode material is synthesized on the surface of carbon cloth by a one-step hydrothermal method. The phase transition of MnCO₃ was accompanied by the continuous increase of specific capacity, and finally maintained good cycle stability in the charge-discharge process. The maximum specific capacity of MnCO₃ electrode material can reach 83.62 mAh g^-1 at 1 A g^-1. The retention rate of the capacity can reach 85.24% after 1,500 cycles compared with the stable capacity (the capacity is 61.44 mAh g^-1 under the 270th cycle). Ex situ characterization indicates that the initial MnCO₃ gradually transformed into MnO₂ accompanied by the embedding and stripping of H⁺ and Zn²⁺ in charge and discharge. When MnCO₃ is no longer transformed into MnO₂, the cycle tends to be stable. The phase transformation of MnCO₃ could provide a new research idea for improving the performance of electrode materials for energy devices.