Observing sodiation process and achieving high efficiency of yolk-shell antimony@carbon rods

As a promising anode material candidate for sodium-ion batteries, antimony (Sb) has attracted enormous research interest due to its high specific capacity and low sodiation voltage. However, its dramatic volume expansion upon sodiation adversely affects its cycle stability. We have developed an oxidation-coating-reduction strategy for fabricating yolk-shell Sb@C rods from commercially available Sb powder. In particular, the thermal reduction of vaporized Sb2O3 generates densely distributed Sb single atoms and clusters on the carbon shell. The sodiation process of the Sb@C sample was recorded through in situ transmission electron microscopy. Irregular expansion of Sb particles was observed, and it was also revealed that the carbon shell could deform with the expanded Sb particles. Beyond the intuitively understood advantage that internal voids can provide space for expansion of internal active materials, the deformability of carbon shells can add further ability to withstand the volume expansion. The two structural merits of the yolk-shell construction enable the Sb@C material to deliver an enhanced cycle performance. Its reversible capacity exceeds 620 mA h g(-1) at 0.1 C, with an initial coulombic efficiency of up to 84.9%, and about 95% of the capacity in the charging voltage profile is delivered below 1.0 V vs. Na+/Na. These performance metrics are very promising for potential practical applications.