A hollow CuS nanocube cathode for rechargeable Mg batteries: effect of the structure on the performance

Abstract

Rechargeable Mg batteries are potential candidates for large-scale energy storage systems due to highly abundant and dendrite-free Mg anodes. However, their performance is hindered by the bivalent Mg²⁺ cation. A hollow structure is advantageous for Mg-storage cathodes because cavities could provide extra electrochemically active sites and a large electrolyte–electrode interface for fast Mg²⁺ ion diffusion. In this work, three hollow CuS nanocubes are prepared by a facile method and comparatively investigated as Mg battery cathodes to obtain a comprehensive structure–performance relationship. It is observed that a dilute solution would result in small hollow CuS nanocubes with a thin wall and large specific surface area, which are favorable for solid-state Mg²⁺ ion diffusion, and thus result in a high reversible Mg-storage capacity. The hollow structure is also favorable for a good cycling stability. The hollow CuS nanocube cathode could deliver a high reversible capacity of 200 mA h g⁻¹ at 100 mA g⁻¹, a remarkable rate capability of 50 mA h g⁻¹ at 1000 mA g⁻¹, and an excellent long-term cycling stability. Mechanism investigation demonstrates a conversion reaction during charge/discharge cycling. This work provides a promising cathode design strategy for rechargeable Mg batteries to overcome the sluggish solid-state Mg²⁺ diffusion.