Co1-xS@CNT composite with a three-dimensional skeleton for high-performance magnesium-lithium hybrid batteries

Magnesium-lithium hybrid batteries (MLHB) combine the advantages of magnesium and lithium ions for recharging, thus becoming a very attractive energy storage system. Transitional metal sulfides (TMSs) have attracted attention owing to their large theoretical capacity. However, these materials are accompanied by a huge volume change during charging and discharging processes. This leads to a serious decline in the capacity of their electrode material. In this study, we used low-cost materials to prepare a Co1-xS@CNT composite material and used it as the positive electrode for Mg2+/Li+ hybrid batteries. X-ray diffraction, scanning electron microscopy, and transmitting electron microscopy analyses were employed for the structural and morphological characterisation of the prepared Co1-xS@CNT. Cyclic voltammetry, electrochemical impedance spectroscopy, and X-ray photoelectronic spectroscopy methods were used to determine the mechanism and material reversibility of magnesium ions inserted into the substrate material. The Co1-xS@CNT was assembled as a positive material in a magnesium-lithium hybrid battery and it showed good circulation stability (a capacity retention of 68% after 200 cycles at a current density of 200 mA g(-1)). This study provides a new idea for the design and synthesis of metal sulfide nanocomposites.