Rational Design of Sb@C@TiO₂ Triple-Shell Nanoboxes for High-Performance Sodium-Ion Batteries

Antimony is an attractive anode material for sodium-ion batteries (SIBs) owing to its high theoretical capacity and appropriate sodiation potential. However, its practical application is severely impeded by its poor cycling stability caused by dramatic volumetric variations during sodium uptake and release processes. Here, to circumvent this obstacle, Sb@C@TiO₂ triple-shell nanoboxes (TSNBs) are synthesized through a template-engaged galvanic replacement approach. The TSNB structure consists of an inner Sb hollow nanobox protected by a conductive carbon middle shell and a TiO₂ -nanosheet-constructed outer shell. This structure offers dual protection to the inner Sb and enough room to accommodate volume expansion, thus promoting the structural integrity of the electrode and the formation of a stable solid-electrolyte interface film. Benefiting from the rational structural design and synergistic effects of Sb, carbon, and TiO₂ , the Sb@C@TiO₂ electrode exhibits superior rate performance (212 mAh g^-1 at 10 A g^-1 ) and outstanding long-term cycling stability (193 mAh g^-1 at 1 A g^-1 after 4000 cycles). Moreover, a full cell assembled with a configuration of Sb@C@TiO₂ //Na₃ (VOPO₄ )₂ F displays a high output voltage of 2.8 V and a high energy density of 179 Wh kg^-1 , revealing the great promise of Sb@C@TiO₂ TSNBs as the electrode in SIBs.