Cationic/Anionic\nVacancies Constructed in WSe<sub>2</sub> toward Enhanced Performance\nof Rechargeable Magnesium Batteries

The development of appropriate cathodes has been deemed\nas the\nkey for the commercial utilization of rechargeable magnesium batteries\n(RMBs) with a high electrochemical performance. In this work, both\ncationic (W) vacancies and anionic (Se) vacancies are constructed\nin a V<sub>W/Se</sub>–WSe<sub>2</sub> structure by a simple\nchemical vapor deposition (CVD) method, where rich Se vacancies are\ngenerated under a H<sub>2</sub> atmosphere, and W vacancies are established\nunder an atmosphere of excess Se guided by absent solid solution formation\ntheory. A series of characterization results reveal that rich W and\nSe vacancies would not only expose more active sites for adsorbing\nMg<sup>2+</sup> to enhancing specific capacity but also enhance ionic\nconductivity for facilitating Mg<sup>2+</sup> diffusion to enhance\nrate capability. In addition, rich vacancies in the V<sub>W/Se</sub>–WSe<sub>2</sub> structure own enough space for alleviating\nthe structural change during the Mg<sup>2+</sup> insertion/extraction\nprocess, which is beneficial for enhancing the cycling stability.\nTherefore, V<sub>W/Se</sub>–WSe<sub>2</sub> delivers a higher\nspecific capacity of about 140 mAh g<sup>–1</sup> at 50 mA\ng<sup>–1</sup>, a superior rate capability of reversible specific\ncapacity at 500 mA g<sup>–1</sup>, and stable cycling performance\nwith a specific capacity retention ratio of 97.6% after 2700 cycles\nat 1000 mA g<sup>–1</sup>. This work provides new insights\nfor defect engineering of cathode modification for enhancing the electrochemical\nperformance of energy storage devices.