Bismuth-Antimony Alloy Embedded in Carbon Matrix for Ultra-Stable Sodium Storage

Alloy-type anodes are the most promising candidates for sodium-ion batteries (SIBs) due to their impressive Na storage capacity and suitable voltage platform. However, the implementation of alloy-type anodes is significantly hindered by their huge volume expansion during the alloying/dealloying processes, which leads to their pulverization and detachment from current collectors for active materials and the unsatisfactory cycling performance. In this work, bimetallic Bi-Sb solid solutions in a porous carbon matrix are synthesized by a pyrolysis method as anode material for SIBs. Adjustable alloy composition, the introduction of porous carbon matrix, and nanosized bimetallic particles effectively suppress the volume change during cycling and accelerate the electrons/ions transport kinetics. The optimized Bi₁Sb₁@C electrode exhibits an excellent electrochemical performance with an ultralong cycle life (167.2 mAh g^-1 at 1 A g^-1 over 8000 cycles). In situ X-ray diffraction investigation is conducted to reveal the reversible and synchronous sodium storage pathway of the Bi₁Sb₁@C electrode: (Bi,Sb) Na(Bi,Sb) Na₃(Bi,Sb). Furthermore, online electrochemical mass spectrometry unveils the evolution of gas products of the Bi₁Sb₁@C electrode during the cell operation.