Pursuit of a high-capacity and long-life Mg-storage cathode by tailoring sandwich-structured MXene@carbon nanosphere composites

In this paper, we report on the fabrication of MXenes sandwiched by carbon nanospheres (MXenes@C) and their application as an electrode for magnesium-ion storage. The heterostructure synthesis is realized via electrostatic interactions between negatively charged 2D MXene nanosheets and positively charged 3D carbon nanospheres. This approach effectively opens up the interlayer and prevents the restacking of MXene nanosheets, thus promoting the electrolyte transport and shortening the ion diffusion path. Through ex situ X-ray diffraction characterization and density functional theory computations, the magnesiation/demagnesiation mechanism and Mg-migration kinetics of the tailored Ti3C2Tx@C nanospheres are elucidated. Using Ti3C2Tx@C as a cathode for magnesium-ion batteries, a remarkable reversible specific capacity (198.7 mA h g−1 at 10 mA g−1), outstanding rate capability (123.3 mA h g−1 at 200 mA g−1), and impressive cycling stability (∼85% capacity retention after 400 cycles) are achieved. This method can also be applied to other MXenes, such as V2CTx, to prepare a sandwich-structure with nice rate performance and cycle life. The synthesis of MXene@C nanospheres using a simple self-assembly method offers new and feasible avenues to develop promising Mg-storage materials with excellent capacity and long cycle life.