Constructing defect-rich unconventional phase Cu_7.2S₄ nanotubes via microwave-induced selective etching for ultra-stable rechargeable magnesium batteries

Copper sulfide is promising great potential for capable cathode in rechargeable magnesium batteries. However, divalent Mg²⁺ diffusion in its host lattice is subject to high lattice strain and mechanical stress mainly due to strong Coulombic interaction. Herein, a microwave-induced selective etching strategy is reported to construct non-stoichiometric-phase robust Cu_7.2S₄ nanotubes with rich lattice defects, which can proceed with ultra-long-cycling stability over 1600 cycles with ultra-low capacity decay of 0.0109 % per cycle at 1.0 A g⁻¹. Furthermore, the Cu_7.2S₄ nanotube cathode can also exhibit a large specific capacity of 314 mAh g⁻¹ at 0.1 A g⁻¹ as well as an excellent rate capability of 91.7 mAh g⁻¹ at 1.0 A g⁻¹. The present electrochemical performances greatly surpass those of Cu_7.2S₄ nanowire, Cu_7.2S₄ nanoparticle, and conventional phase CuS nanotubes and at least are comparable to the conversion-type cathode materials reported so far. The generated lattice defect combined with the optimized robust nanotube structure can effectively buffer lattice strain and mechanical stress to provide a favorable diffusion kinetic. Our designed microwave-induced selective etching system demonstrates significant superiority in morphology, phase, and defect engineering of Cu_7.2S₄ nanotubes to accommodate reversible Mg²⁺ storage for high-performance rechargeable magnesium batteries.