Lithiation/delithiation performance of Sn-Co alloy anode using rough Cu foil as current collector

Sn-Co alloys were electrodeposited on the rough Cu foil and smooth Cu sheet, respectively. The capacity retention of the Sn-Co alloy electrode electrodeposited on the rough Cu foil in the 70th cycle was found to be 80.0% compared with the maximal capacity, which was much better than that of the Sn-Co alloy electrode on the smooth Cu sheet. The revolution of the surface morphology of the Sn-Co alloy electrode during cycling was investigated by scanning electron microscopy. The result indicated that the reversibility of the expansion and contraction of the Sn-Co alloy electrode on the rough Cu foil during charging/discharging assisted by the unique rough surface was one main reason of improving the cycleability. Solid electrolyte interphase (SEI) film was detected on the Sn-Co alloy electrode surface by electrochemical impedance spectroscopy (EIS) during lithiation/delithiation, and the result demonstrated that the SEI film suffered breaking and repairing at different lithiation status. In addition, the unique phase transformation process for the Sn-Co alloy electrode during first lithiation was also investigated by EIS.