Kinetically optimized copper sulfide cathodes for rechargeable magnesium batteries

Copper sulfides have been recognized as one of the most promising cathode materials for rechargeable magnesium batteries due to their large theoretical capacity and unique conversion-type mechanism. However, the solid-state diffusion of bivalent Mg²⁺ ions in CuS host lattice is subjected to huge electrostatic interaction and thus sluggish kinetics. Herein, anion substitution strategy and crystal engineering are reported to regulate electrochemical reaction kinetics and reinforce magnesium storage performances of tubular CuS cathodes. Benefitting from anion substitution and crystal facet regulation, the lattice well-exposed Se-substituted CuS nanotube cathodes demonstrate excellent magnesium storage capacity (372.9 mAh g⁻¹ at 100 mA g⁻¹), remarkable cycling stability (1600 cycles at 2.0 A g⁻¹), and a good rate capability (112.4 mAh g⁻¹ at 2.0 A g⁻¹). Electrochemical kinetics investigation further suggests that anionic Se-substitution and crystal facet regulation can significantly optimize electrochemical reaction kinetics and accelerate diffusion rate of Mg²⁺ ions. Ex-situ X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD) characterizations reveal the conversion reaction mechanism of Se-substituted CuS cathodes. These novel findings provide an effective approach to construct high-performance cathode materials for rechargeable magnesium batteries and hold great promise for development of other new battery systems.