Improving the Initial Coulombic Efficiency of Sodium-Storage Antimony Anodes via Electrochemically Alloying Bismuth

Improving cycling stability while maintaining a high initial Coulombic efficiency (ICE) of the antimony (Sb) anode is always a trade-off for the design of electrodes of sodium-ion batteries (SIBs). Herein, we prepare a carbon-free Sb₈Bi₁ anode with an ICE of 87.1% at 0.1 A g^-1 by a one-step electrochemical reduction of Sb₂O₃ and Bi₂O₃ in alkaline solutions. The improved ICE of the Sb₈Bi₁ anode is due to the alloying of bismuth (Bi) that prevents irreversible interfacial reactions during the sodiation process. Unlike carbon buffers, the use of Bi will reduce the number of side reactions between the carbon buffer and sodium. Moreover, Bi₂O₃ can promote the reduction of Sb₂O₃ and reduce the particle size of Sb from ∼20 μm to below 300 nm. The electrolytic products can be modulated by controlling the cell voltages and electrolysis time. The electrolytic Sb₈Bi₁ anode delivered a capacity of 625 mAh g^-1 after 200 cycles with an ICE of 87.1% at 0.1 A g^-1 and even 625 mAh g^-1 at 1 A g^-1 over 100 cycles. Hence, alloying Bi into Sb is an effective way to make a long-lasting Sb anode while maintaining a high Coulombic efficiency.