Dual phase enhanced superior electrochemical performance of nanoporous bismuth-tin alloy anodes for magnesium-ion batteries

Magnesium-ion batteries (MIBs) have recently received great concerns, but are restrained by the challenge of exploring advanced anode materials with superior capacity and fast diffusion kinetics. Herein, for the first time we proposed a dual phase alloying strategy to address this issue, and developed novel high-performance bismuth (Bi)-tin (Sn) alloys with a unique nanoporous structure and high density of phase boundaries. As an anode for MIBs, the dual phase Bi-Sn alloys exhibit excellent Mg storage properties as compared to their single phase counterparts. Specially, the Bi6Sn4 electrode can deliver large discharge specific capacity (434 mA h g(-1) at 50 mA g(-1)), good cycling stability (280 mA h g(-1) after 200 cycles), greatly improved rate capability (362 mA h g(-1) at 1000 mA g(-1)) and high Coulombic efficiency (close to 99% after 30 cycles). Ex situ X-ray diffraction and transmission electron microscopy further clarify the phase and structural evolution during the first discharge/charge processes of the Bi6Sn4 anode. The superior electrochemical performance of the Bi-Sn alloys is attributed to the increased phase/grain boundaries which can provide more channels for fast Mg2+ transport as well as unique nanoporous structure which can accommodate large volume changes and shorten diffusion lengths. The present strategy provides useful information on design of high-performance anode materials for MIBs.