Na-ion batteries (NIBs), as the analogy to Li-ion batteries, are regarded as one of the most promising technologies to satisfy the request on both performance and cost for grid energy storage. To further boost the specific energy and power of the state-of-the-art NIB, an anode material with comparable capacity and long-term stability to graphite anodes in lithium-ion batteries (LIBs) is highly desired. Antimony (Sb) has a theoretical capacity of 660 mAh g⁻¹ upon full sodiation and hence holds great promises as the good anode candidate for high energy Na-ion batteries.

A low cost and scalable approach of annealing poly-dopamine (PDA) coated Sb₂O₃ was used to prepare the yolk-shell structured Sb@C nanocomposite for high performance Na-ion battery anodes. Controlled reduction reaction and selective removal of Sb₂O₃ by acid etching generate the promised void space to accommodate the volume expansion of Sb while carbonization of the PDA forms highly conductive carbon shells. The by-product from the etching, SbCl₃, can be reused rendering the approach a scalable and economic one. The yolk-shell Sb@C anode exhibits excellent electrochemical performance in terms of specific capacity, rate capability and cycling stability. The reversible phase transformation of crystalline Sb during charge/discharge was observed by the in-situ XRD for the first time. The designed composite with Sb: C of 70: 30 delivers almost theoretical capacity of ~ 554 mAh g⁻¹. The specific capacity is still ~ 315 mhA g⁻¹ at the current density of 5 A g⁻¹ (10 C rate). The O3-Na_0.9[Cu_0.22Fe_0.30Mn_0.48]O₂ (cathode)-Sb@C-hard carbon (anode) full-cell shows high specific energy of ~ 130 Wh kg⁻¹ (based on the total weight of cathode and anode) in the voltage range of 2.0–4.0 V in NaClO₄ electrolyte with 10 wt% fluoroethylene carbonate (FEC) additive. It is ~ 1.5 times energy of the full-cells with similar design using hard carbon anodes (~ 84 Wh kg⁻¹).