The electrolyte additive has significant impact on the electrochemical performance of the alloy anode material for sodium-ion batteries. In this work, the surface structure, component and electrochemical performance of the SiC-Sb-C electrode in FEC-free and -containing electrolyte have been investigated by XPS, FTIR, EIS and electrochemical characterizations. The experimental results suggest that FEC actually participates in the formation process of the SEI films on the surface of the electrode. Based on the analysis of the experimental data, a double-layer SEI film mechanism should be suggested and can well explain the mutation of the resistant and potential observed in the charge/discharge curves and EIS. Therefore, the presence of FEC in the electrolyte can minimize the reductive decomposition of the electrolyte and change the morphology, structure and chemical component of the electrode, resulting in the improvement of the electrochemical performance of the electrode.