Simple synthesis of a porous Sb/Sb₂O₃ nanocomposite for a high-capacity anode material in Na-ion batteries

High-capacity anode materials are highly desirable for sodium ion batteries. Here, a porous Sb/Sb₂O₃ nanocomposite is successfully synthesized by the mild oxidization of Sb nanocrystals in air. In the composite, Sb contributes good conductivity and Sb₂O₃ improves cycling stability, particularly within the voltage window of 0.02–1.5 V. It remains at a reversible capacity of 540 mAh·g^–1 after 180 cycles at 0.66 A·g^–1. Even at 10 A·g^–1, the reversible capacity is still preserved at 412 mAh·g^–1, equivalent to 71.6% of that at 0.066 A·g^–1. These results are much better than Sb nanocrystals with a similar size and structure. Expanding the voltage window to 0.02–2.5 V includes the conversion reaction between Sb₂O₃ and Sb into the discharge/charge profiles. This would induce a large volume change and high structure strain/stress, deteriorating the cycling stability. The identification of a proper voltage window for Sb/Sb₂O₃ paves the way for its development in sodium ion batteries.