Synergistic Bimetallic Effects of BiSb Anodes Enable Long-Stable Sodium Storage

Alloy-type anodes are of interest for their resource-rich and high theoretical capacity performance in sodium-ion batteries (SIBs). However, severe volume expansion may lead to rapid capacity decay and electrode pulverization. In this work, metallic Bi with better structure stability is rationally selected as a skeleton to form a 2D BiSb alloy to alleviate the volume expansion. Interestingly, by combining in-situ XRD and ex-situ TEM characterizations, a reversible multi-step alloying sodium storage mechanism of BiSb ↔ Na(Bi, Sb) ↔ Na₃(Bi, Sb) in Bi_0.4Sb_0.6 anode is elucidated, and the partial amorphization and expanded interlayer spacing of BiSb alloy is also revealed, which greatly alleviate volume expansion thereby enhancing electrochemical stability. Furthermore, density functional theory and kinetic calculations demonstrate that Bi_0.4Sb_0.6 demonstrates lower Na⁺ adsorption energy and Na⁺ diffusion energy barriers, ensuring fast electron and ion transportation during sodium storage. Benefiting from the synergistic effects of binary alloy, Bi_0.4Sb_0.6 exhibits a high reversible capacity and cycling stability of 446 mAh g⁻¹ at 0.1 A g⁻¹, and 70% high capacity after 1100 cycles at 0.5 A g⁻¹. This work provides new insights and opportunities to develop advanced precise alloy-type anode materials for SIBs.