Realizing high-stability anodes for rechargeable magnesium batteries via in situ-formed nanoporous Bi and nanosized Sn†

Rechargeable magnesium batteries (RMBs) are regarded as potential next-generation energy storage technologies, thanks to their high theoretical specific capacity and abundance of magnesium resources. However, magnesium anodes tend to form passivating surface films, which hinder the reversible transport of Mg²⁺ ions and narrow the selection of suitable electrolytes. Herein, the Bi–Sn alloy loaded with SnO₂ (Bi–Sn@SnO₂) is synthesized to be the anode for RMBs and improve diffusion kinetics of Mg²⁺ ions. The Bi–Sn@SnO₂ anode delivers a reversible capacity of 314 mA h g⁻¹ at 50 mA g⁻¹. In addition, the Bi–Sn@SnO₂ anode exhibits high rate performance (297 mA h g⁻¹ at 500 mA g⁻¹) and long cycle life (148 mA h g⁻¹ at 1 A g⁻¹ after 300 cycles) due to the in situ formation of nanoporous Bi and nanosized Sn by the synergistic effect of Bi–Sn phase separation, defects and the Mg²⁺ insertion/extraction reaction. The loading of SnO₂ on the Bi–Sn alloy surface can restrict the growth of alloy particles and reduce the decomposition of electrolytes. Noticeably, the Bi–Sn@SnO₂ anode shows good compatibility with the chloride-free Mg(TFSI)₂/G2 electrolyte.