Mg-storage properties of hollow copper selenide nanocubes

Rechargeable Mg batteries are thought to be suitable for scaleable energy-storage applications because of their high safety and low cost. However, the bivalent Mg2+ cation suffers from sluggish solid-state diffusion kinetics. Herein, a hollow morphology approach is introduced to design copper selenide cathodes for rechargeable Mg batteries. Hollow Cu2‒xSe nanocubes are fabricated via a solution reaction, and the Mg-storage properties are investigated in comparison with simple nanoparticles. The hollow structures accommodate the volume change during magnesiation/demagnesiation and maintain the material integrity, and thus a remarkable cycling stability over 200 cycles is achieved. Kinetic study demonstrates the hollow structure favors solid-phase Mg2+ diffusion, and therefore the hollow Cu2‒xSe nanocubes exhibit a high capacity of 250 mAh g‒1 at 100 mA g‒1 as well as a superior rate capability. Mechanism investigation indicates Cu2‒xSe experiences a structure conversion during which a phase transformation occurs. This work develops a facile method for preparation of hollow copper selenides, and highlights the privileges of hollow structures for the design of high-performance Mg-storage materials.