The role of allyl ethyl carbonate (AEC) as an additive in electrolytes used in lithium-ion batteries is investigated. The 1.0 M LiPF6 in propylene carbonate (PC): diethyl carbonate (DEC) (3:2 in volume) electrolyte containing AEC can suppress the co-intercalation of PC and inhibit the decomposition of electrolytes during the first lithium intercalation. A graphitic anode (MCMB-2528, mesocarbon microbeads) in a PC-based electrolyte exhibits a high reversible capacity of 320 mAh g(-1). The reduction potential of AEC is 1.5 V versus Li\Li+ as determined by cyclic voltammetry (CV). The morphology and structure of graphite electrodes after the first charge-discharge cycle are investigated by scanning electron microscopy (SEM) and X-ray powder diffraction (XRD). AEC decomposes and forms a proper solid electrolyte interphase (SEI) film on the MCMB surface. The SEI film not only prevents exfoliation of the graphite electrode but also stabilizes the electrolyte. AEC helps to improve the cycleability of lithium-ion batteries to a considerable extent. (C) 2004 Elsevier B.V. All rights reserved.