Constructing sheet-assembled hollow CuSe nanocubes to boost the rate capability of rechargeable magnesium batteries

Copper selenide has been considered as a much more promising conversion-type cathode material for rechargeable magnesium batteries than copper sulfide because of its better conductivity. However, the magnesium ion diffusion in the lattice of the CuSe host is subject to a great coulombic resistance due to the relatively high charge density and ion polarization of the divalent Mg²⁺, leading to undesired rate capability and low reversible capacity. Herein, a morphology engineering strategy is presented to construct sheet-assembled hollow CuSe nanocubes by a simple template-directed selenation reaction at room temperature. Electrochemical measurements suggest that the CuSe nanocubes could exhibit an ultra-high initial discharge capacity of 596 mA h g⁻¹and maximum specific capacity of 252 mA h g⁻¹and maintain a relatively high reversible capacity of 170 mA h g⁻¹after 100 cycles at 200 mA g⁻¹. Furthermore, a remarkable rate capability could be obtained with 77.6 mA h g⁻¹discharge capacity at 5 A g⁻¹. Additionally, the CuSe nanocubes exhibit excellent compatibility with Mg(BH₄)₂/(CF₃)₂CHOH/DME electrolyte and follow a two-step conversion mechanism. Such superior magnesium storage properties demonstrate that constructing a hierarchical hollow structure could be one of the effective methods to promote the magnesium storage kinetics of CuSe cathode materials.