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.

Constructing an interspace in MnO@NC microspheres for superior lithium ion battery anodes

In this work, silica nanospheres were introduced into nitrogen-carbon (NC) coated MnO microspheres and filled the gap between NC and MnO. After etching, an interspace was formed between the coating layer and the MnO microspheres. The structure not only provides a conductive NC layer, but also constructs a space to mitigate the volume effect of MnO. As expected, the specific capacity remained at 1143.93 mA h g^-1 after 200 cycles at a current density of 0.2 A g^-1, and 726.96 mA h g^-1 after 450 cycles at a high current density of 1 A g^-1. The superior performance can be attributed to the unique structure with an internal void space and the excellent protection of MnO microspheres by the surface NC layer.