The effect of an electrolyte additive, succinic anhydride (SA), on the electrochemical performances of a silicon thin-film electrode, which is prepared by radio-frequency magnetron sputtering, is investigated. The introduction of SA into a liquid electrolyte consisting of ethylene carbonate/diethyl carbonate/1 M LiPF6 significantly enhances the capacity retention and coulombic efficiency of the electrode. This improvement in the electrochemical performance of the electrode is attributed to modification of the solid/electrolyte interphase (SEI) layer by the introduction of SA. The differences in the characteristic properties of SEI layers, with or without SA, are explained by analysis with scanning electron microscopy, electrochemical impedance spectroscopy, and X-ray photoelectron spectroscopy.