Enhancing Magnesium-Ion Storage in a Bi–Sn Anode through Dual-Phase Engineering

High Resolution Image Download MS PowerPoint Slide Magnesium-ion batteries (MIBs) are a “beyond Li-ion” technology that are hampered by Mg metal reactivity, which motivates the development of anode materials such as tin (Sn) with high theoretical capacity (903 mAh g –1 ). However, pure Sn is inactive for Mg 2+ storage. Herein, Mg alloying with Sn is enabled within dual-phase Bi–Sn anodes, where the optimal composition (Bi 66.5 Sn 33.5 ) outperformed single-phase Bi and Sn electrodes to deliver high specific capacity (462 mAh g –1 at 100 mA g –1 ), good cycle life (84% after 200 cycles), and significantly improved rate capability (403 mAh g –1 at 1000 mA g –1 ). Density functional theory (DFT) calculations revealed that Mg alloys first with Bi and the subsequent formation of the Mg 3 Bi 2 //Sn interfaces is energetically more favorable compared to the individual Mg 3 Bi 2 and Sn phases. Mg insertion into Sn is facilitated when Mg 3 Bi 2 is present. Moreover, dealloying Mg from Mg 3 Bi 2:Mg 2 Sn systems requires the creation of Mg vacancies and subsequent Mg diffusion. Mg vacancy creation is easier for Mg 2 Sn compared to Mg 3 Bi 2, while the latter has slightly lower activated Mg-diffusion pathways. The computational findings point toward easier magnesiation/demagnesiation for BiSn alloys over pure Bi or pure Sn, corroborating the superior Mg storage performance of Bi–Sn electrodes over the corresponding single-phase electrodes.