Superior electrochemical performance of Sb–Bi alloy for sodium storage: Understanding from alloying element effects and new cause of capacity attenuation

Sb–Bi alloy has attracted increased attention as anode material for sodium-ion batteries (SIBs) owing to its particular crystal structure relevance and synergy effect. However, the cycle performance and actual capacity of Sb–Bi alloy are still not satisfactory, and the mysteries about partial role of elemental compositions and causes of capacity attenuation remain unsolved either. Herein, 3D Sb–Bi alloy/N-doped porous carbons (N–PCs) with different Sb/Bi mole ratios have been synthesized successfully. As for SIB anodes, 3D Bi3Sb1/N-PC presents a superior rate capability up to 30 A g−1 (specific capacity: 318.3 mAh g−1) and cyclic stability (capacity decays: 0.0054% per cycle at 10 A g−1 after 6000 cycles). Furthermore, the dissolution behavior of metallic Sb can be found after long-term cycles with DME-based electrolyte, and the dissolved Sb can shuttle to the other side of the separators, leading to "dead antimony" with low specific capacity and unsatisfactory cycle performance. Notably, Bi crystal shows strong fixing effect on Sb atoms with low loss of "active antimony". Our work presents a great potential of alloy-type anode materials for practical applications of high-energy SIBs, and also provide a new direction to analyze element roles and attenuation causes of Sb–Bi alloys for sodium storage.