Highly defective and conductive Cu-doped 1T/2H-MoS2 nanosheets as high-capacity cathode materials toward enhanced magnesium ion storage

Limited by the poor electronic conductivity and strong interaction between Mg2+ and MoS2, the 2H phase of MoS2 as the cathode materials exhibits a low capacity along with poor rate capability. How to adopt the structure engineering to largely boost the Mg2+ diffusion kinetics and enhance the reaction activity are the current tasks that need to be addressed. Herein, the cation doping strategy is adopted to elaborately design the defective Cu-doped metallic MoS2 nanosheets (Cu-MoS2) via a hydrothermal process. The Cu2+ doping widens the layer distance, induces the formation of metallic 1T phase of MoS2, and ameliorates the structural stability. Thus, the Mg2+ ions diffusion kinetics and the electronic conductivity of Cu-MoS2 are largely boosted. Meanwhile, the MgCl+ in the electrolyte can decrease the reaction energy barrier, and therefore fasten the electrochemical reaction. Therefore, the optimized Cu-MoS2 as the cathode materials toward magnesium ion batteries exerts remarkable magnesium storage properties, evidently superior to the pure MoS2. When cycled at 0.1 A g-1 over 100 cycles, the discharge capacity can reach as high as 369.5 mAh g-1. Even cycled at a high rate of 1 A g-1, the Cu-MoS2 maintains a specific capacity of 267.3 mAh g-1 over 200 long cycles. The related kinetics tests confirm its rapid reaction kinetics and pseudocapacitance dominated charge storage process. The ex-situ XPS and HRTEM data largely verify the conversion reaction mechanism of Cu-MoS2 during cycling. This work provides guidelines for the long-term development of MoS2 in the field of magnesium ion batteries.