Carbon encapsulated Sn-Co alloy: A stabilized tin-based material for sodium storage

[Display omitted] •Carbon encapsulated Sn-Co alloy was designed and synthesized.•Sn-Co alloy core showed improved reversibility than pure Sn core.•Sn-Co alloy exhibited enhanced cycling stability and rate capability.•Cobalt acted as a stable and conductive matrix. A novel yolk-shell structure consisting of an intermetallic Sn-Co core, a carbon shell and void space between the core and shell has been designed and successfully synthesized. X-ray diffraction (XRD) measurements indicate that the core is SnCo alloy and the shell is amorphous. The yolk-shell structure is observed by scanning electron microscope (SEM). For comparison, carbon encapsulated pure Sn, which also possesses a yolk-shell structure, has been synthesized as well. Electrochemical characterizations reveal that the SnCo@C sample has significantly improved electrochemical reversibility, cycling stability and rate capability than Sn@C. The cobalt in the SnCo alloy is proved to play a critical role of conductive stable matrix to stabilize Sn during sodiation/desodiation process and facilitate the diffusion kinetics of sodium.