Non-stoichiometric Cu2-xSe hollow nanocubes cathodes enabling high-rate capability and ultra-long cyclic stability rechargeable Mg batteries

Rechargeable Mg batteries with the merits of low cost, high safety and environmental compatibility are deemed as promising energy storage techniques for large-scale applications. However, the actual development of rechargeable Mg batteries is constantly hindered by the difficulty of finding suitable electrode materials to accommodate Mg2+. Cu2-xSe has exceptionally high electrical conductivity and its unique crystal structure could be better compatible with Mg2+ cations. Herein, a novel Cu2-xSe hollow nanocube with extraordinarily high conductivity and unique structure was designed and synthesized by facile one-step template-directed selenation reaction methods. The excellent Mg electrochemical performance of Cu2-xSe hollow nanocube cathodes was demonstrated based on rechargeable Mg batteries. The Cu2-xSe NCs provide a high specific capacity of 232.5 mAh g-1 at 100 mA g-1, superior cycling stability over 3700 cycles, and an excellent rate capacity of 163.1 mAh g-1 at 3000 mA g-1. Furthermore, the two-step magnesiation/demagnesiation processes of the Cu2-xSe NC cathodes were revealed, and the accelerating effects of the fast Mg2+ diffusion in the unique hierarchical structure on magnesium storage performance were analyzed. The outcomes of this study not only provide simple methods for fabricating high-performance Cu2-xSe cathodes but also propose valuable insights for exploring conversion-type Mg-storage materials.