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

Limited by the poor electronic conductivity and strong interaction between Mg²⁺ and MoS₂, the 2H phase of MoS₂ as a cathode material exhibits low capacity and poor rate capability. How to adopt structure engineering to significantly boost Mg²⁺-diffusion kinetics and enhance reaction activity are the current challenges that need to be addressed. Herein, a cation-doping strategy was adopted to elaborately design defective Cu-doped metallic MoS₂ nanosheets (Cu-MoS₂) via a hydrothermal process. Cu²⁺ doping widened the layer distance, induced the formation of the metallic 1T phase of MoS₂, and ameliorated structural stability. Thus, Mg²⁺-ion-diffusion kinetics and the electronic conductivity of Cu-MoS₂ were significantly boosted. Meanwhile, MgCl⁺ in the electrolyte could decrease the reaction energy barrier, thereby leading to rapid electrochemical reactions. Therefore, the optimized Cu-MoS₂ as a cathode material for magnesium-ion batteries demonstrated remarkable magnesium-storage properties, evidently superior to those of pure MoS₂. When cycled at 0.1 A g⁻¹ over 100 cycles, its discharge capacity could reach as high as 369.5 mA h g⁻¹. Even when cycled at a high rate of 1 A g⁻¹, Cu-MoS₂ maintained a specific capacity of 267.3 mA h g⁻¹ over 200 cycles. The related kinetics results confirmed its rapid reaction kinetics and pseudocapacitance dominated charge-storage process. Ex situ XPS, HRTEM and Raman data significantly verified 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.