Five commercial Lithium manganese oxide powders have been studied. The XRD spectra showed all samples to exhibit the spinel structure. The composition and morphology were analyzed by Jaeger-Vetter titration and scanning electron microscopy. The Lithium intercalation/de-intercalation characteristics and the cycleability have been studied using state-of-the-art cells. The morphology of the particles and crystallites, as well as the defect structure of the spinel, were found to play an important role in the capacity retention during electrochemical cycling. The capacity corresponding to the 4.1 V phase transformation process faded faster than that of the 4.0 V single-phase transition during cycling, which enhanced lower plateau capacity fading and higher voltage polarization. The cycleability at the 3.0 V region has also been studied and indicated that the typical spinel lithium manganese oxide is not suitable to be cycled in the 3.0 V region. Therefore, it will be deleterious to overdischarge the spinel materials. (C) 2000 Elsevier Science B.V. All rights reserved.