Co0.85Se hollow polyhedrons entangled by carbon nanotubes as a high-performance cathode for magnesium secondary batteries

Magnesium secondary batteries are suitable for large-scale applications owing to the low cost and dendrite-free features of the magnesium metal anode. Currently, exploration of high-performance cathodes is the main challenge of magnesium batteries, and rational structure design strategies are the cores of cathode material development. In the present study, a new approach is introduced combining hollow structure and conductive framework. ZIF-67 derived Co0.85Se hollow polyhedrons entangled by carbon nanotubes (Co0.85Se/CNTs) are fabricated and investigated as rechargeable magnesium battery cathodes. The hollow structure facilitates Mg2+ transportation and the CNT framework favors electron conduction, constructing active nanodomains for highly reversible magnesium storage reactions. Co0.85Se/CNTs shows a high capacity of 194 mAh g−1 and a superior rate capability providing 95 mAh g−1 at 1000 mA g−1. Prominently, the rigid CNTs enhance the stability of the Co0.85Se/CNTs composite and improve the cyclability. A 76% capacity retention is maintained after 500 cycles at 200 mA g−1, corresponding to a decay of 0.048% per cycle. This work highlights a micro-nanostructure favoring magnesium storage reaction reversibility and cyclability, which would enlighten rational electrode design for the storage of magnesium cations.