Carbon-coated BiOCl/Bi heterojunction flowerlike microspheres for collaboratively boosting storage magnesium performance

BiOCl is considered a promising anode material for magnesium ion batteries (MIBs), but its further development is limited by the inherent semiconductor properties and the sluggish Mg2+ diffusion kinetics. Herein, carbon-coated BiOCl/Bi heterojunction flowerlike microspheres (BiOCl/Bi@C) were prepared via a simple solvothermal method followed by annealing and used as an anode for MIBs for the first time. In this intricately designed structure, the heterointerface not only provides additional active sites to increase capacity but also creates a built-in electric field to facilitate electron/ion transport, while the carbon-coated flowerlike microsphere not only shortens the ion diffusion path but also relieves volume variation during cycling. As expected, it exhibits impressive specific capacity (134.2 mAh g−1 after 130 cycles) and outstanding rate performance (156.7 mAh g−1 at 500 mA g−1). Importantly, the storage Mg mechanism of BiOCl/Bi@C was investigated, and the results suggest that BiOCl is first converted into Bi and then alloyed to Mg3Bi2 in the discharging process, while Mg3Bi2 is dealloyed to Bi and then turned back to BiOCl in the charging process. The current study provides an effective strategy for constructing heterostructure anodes to enhance the magnesium ion transfer and storage.