Cu+ redox activation and polyselenide stabilization via strong Se-C interaction for superior magnesium storage

Copper selenides have been recognized as one of the most promising Mg2+ host materials due to their high electrical conductivity and unique ionic displacement mechanism, yet they suffer from low magnesium storage capacity and inferior cycling stability caused by insufficient Cu+ conversion and inevitable polyselenide dissolution. Herein, the graphene-supported CuSe (CuSe@G) with strong Se-C interaction is prepared as the high-performance cathode material for rechargeable magnesium batteries. The strong Se-C interaction between CuSe monomers and graphene substrate can not only immobilize the Se species but also boost the electrochemical replacement reaction between Cu2+ and Mg2+. The highly dispersed CuSe nanoparticles on graphene can also accelerate Mg2+ diffusion rate at the cathode-electrolyte interfaces and further regulate the electrochemical reaction kinetics. Such well-designed method can significantly improve the reversible capacity from 167 to 233.7 mAh g–1 at 0.1 A g–1 current density and cycling stability (63 mAh g–1 after 1000 cycles with 0.039% capacity decay per cycle) of copper selenide cathode materials. This work presents an in-depth insight into graphene bonding strategy for fabricating superior conversion-type selenide cathodes for rechargeable magnesium batteries.