LiNi0.33Co0.33Mn0.33O2 which was synthesized by co-precipitation method has been used to investigate the relationships between crystal/interfacial structures and electrochemical performance of the material in the voltage range of 2.5–4.6V. X-ray diffraction showed that the material maintained high structural stability with charge–discharge cycling. Formation of SEI film was observed by transmission electron microscopy. The chemical compositions of the SEI film were analyzed by X-ray photoelectron spectroscopy, which were mainly composed of some organic compounds such as lithium alkyl carbonate RCH2OCO2Li, as well as some inorganic compounds such as Li x PF y and Li x PO y F z . Transmission electron microscopy showed that the SEI film gradually grew to a thickness of about 40nm after 30 cycles. This caused larger and larger interfacial resistance with charge–discharge cycling, which has been attributed to the continuous capacity fading of LiNi0.33Co0.33Mn0.33O2 in the voltage window of 2.5–4.6V.