Electrochemical Lithium Storage Performance of Molten Salt Derived VSnC MAX Phase.

MAX phases are gaining attention as precursors of two-dimensional MXenes that are intensively pursued in applications for electrochemical energy storage. Here, we report the preparation of VSnC MAX phase by the molten salt method. VSnC is investigated as a lithium storage anode, showing a high gravimetric capacity of 490 mAh g and volumetric capacity of 570 mAh cm as well as superior rate performance of 95 mAh g (110 mAh cm) at 50 C, surpassing the ever-reported performance of MAX phase anodes. Supported by operando X-ray diffraction and density functional theory, a charge storage mechanism with dual redox reaction is proposed with a Sn-Li (de)alloying reaction that occurs at the edge sites of VSnC particles where Sn atoms are exposed to the electrolyte followed by a redox reaction that occurs at VC layers with Li. This study offers promise of using MAX phases with M-site and A-site elements that are redox active as high-rate lithium storage materials.