Hierarchical Bi@Ni Foam as a Self-Supporting Anode for Superior Magnesium Storage

Rechargeable magnesium-ion batteries (MIBs) are regarded as promising electrochemical energy storage systems due to their inherent safety and cost-effectiveness. However, the incompatibility between Mg metal anodes and conventional electrolytes remains a bottleneck. Bismuth (Bi) has drawn considerable interest as an alternative anode owing to its exceptional theoretical volumetric capacity (3783 mAh cm^-3) and low working potential, yet its practical application is hindered by severe volume variation during (de)magnesiation. Here, we report a binder-free, self-supporting Bi@Ni foam anode fabricated via a facile spontaneous displacement reaction. The three-dimensional (3D) interconnected architecture effectively accommodates the mechanical strain induced by volume expansion, preventing material pulverization. Density functional theory (DFT) calculations further reveal that the Ni substrate significantly strengthens the adsorption energy of Mg²⁺ on the anode surface, thereby accelerating the reaction kinetics. Consequently, the Bi@Ni foam exhibits superior rate performance and cycling stability, maintaining a reversible capacity of 202.4 mAh g^-1 after 200 cycles at 0.25C (1C = 385 mA g^-1). Moreover, a Bi₂Mg₃||Mo₆S₈ full cell was successfully assembled, delivering a discharge capacity of 61.2 mAh g^-1 after 23 cycles at 0.2C. This study offers a scalable strategy for developing high-performance alloy-based anodes for next-generation multivalent-ion batteries.