Effect of Magnesium Site Doping on Electrochemical Properties of Mg-Mn Composite Materials and Application of Carpet-Like Sheets Composite Formed by Cr Doping in Aqueous Zinc-Ion Batteries

Abstract

Manganese based compounds have very stable electrochemical properties, thus they are widely applied in aqueous zinc-ion battery. However, it is easy to dissolve manganese in the process of charge and discharge, which leads to the collapse of the cathode material structure. In this paper, the composite materials of manganese carbonate and magnesium carbonate were synthesized by hydrothermal method, and its properties were optimized by doping modification. According to the electrochemical tests, the electrochemical performance of the material synthesized with 5% Cr doping is relatively stable. Moreover, with the increase of Cr content, the charge transfer impedance of the material can be significantly reduced. In the cyclic tests, after 60 cycles of charge and discharge under different current densities, and another several cycles at the current density of 50 mA g−1, the capacity rises to 212.01 mAh g−1, higher than the first discharge capacity. SEM tests are also conducted to survey the micro-structure of the material, besides the cube unit, there are also carpet-like sheets made of nano-sized joined petal-like unit, which greatly increases the specific surface area of the material. According to the data of EDS and XPS, the fact that that the types and valence states of elements in the composites were consistent with those in manganese carbonate and magnesium carbonate are confirmed. Through the infrared and Raman tests, the functional groups in the synthesized material are proven to correspond to the molecular formula. From the XRD pattern, no obvious impurity peaks can be observed. With all the data obtained from physical characterization, it can be concluded that the material is mainly composed of manganese carbonate and magnesium carbonate.