The influences of Mg intercalation on the structure and supercapacitive behaviors of MoS₂

Metallic 1T MoS₂ greatly benefits the supercapacitance of MoS₂ due to its considerably higher conductivity as compared to semiconducting 2H MoS₂. Alkali metals, such as Li, Na and K, are always used to prepare 1T MoS₂ through intercalation of alkali metal ions into the interlayer of 2H MoS₂. Nevertheless, the influences of the alkali-earth metals as the guest in the interlayer of MoS₂ on its structure and electrochemical capacitor performance are rarely investigated. Herein, we introduced hydrated Mg ions as the guest into MoS₂ nanosheets. The interlayer spacing was increased to 1.144 nm after the introduction of hydrated Mg ions, larger than that of the pristine MoS₂ (0.620 nm) and restacking MoS₂ (0.626 nm). The enlarged interlayer spacing can accommodate more ions during intercalation process. Moreover, the 1T phase concentration after the introduction of hydrated Mg ions was as high as ~ 90%, which benefits the charge transfer during the charging/discharging processes. Consequently, the specific capacitance of the MoS₂ with Mg guest ions as well as the energy densities and power densities was greatly improved as compared to those of the restacking MoS₂ or pristine MoS₂ counterparts. The present work not only demonstrated a new strategy for engineering the physical properties and improving the electrochemical performance of MoS₂ supercapacitor electrode through pre-intercalation of alkali-earth metal ions in the interlayer of MoS₂, but also has directive significance for the design of other layered electrode materials for energy storage systems.