Li+ additive accelerated structural transformation of MoS2 cathodes for performance-enhancing rechargeable Mg2+ batteries

Abstract

Rechargeable magnesium ion batteries (MIBs) with intercalation materials as the cathode are found to offer better performance in Li+ based electrolytes. Herein, we compare the electrochemical performance of MIBs using all-phenyl complex (APC) electrolytes before and after adding Li+ additives with layered MoS2 cathodes. We coincidentally describe the lithiation mechanism that leads to a phase transition whereby Li+ additives accelerate a MoS2 structural transformation from 2H to 1T which accounts for the superior battery performance (150 mAh/g, around two times the capacity of that without Li+ additives). In this process, MoS2 is partly exfoliated into single-layer nanosheets during cycle as evidenced by operando electrochemical synchrotron X-ray diffraction, ex situ X-ray photoelectron spectroscopy and scanning electron microscopy analyses. Accordingly, electrochemical cells with pre-exfoliated MoS2 nanosheets (liquid phase exfoliation) require fewer activation cycles (50 cycles, a quart of the cycles that using pristine MoS2) in APC electrolyte and better rate performance. Our work thus provides new insight in designing high-performance rechargeable MIBs by optimizing the intercalation cathodes using Li+ additives.