Thin-film LiMn2O4 electrodes that are deposited either by electron-beam evaporation or radio-frequency sputtering show electrochemical activity between 4 and 5 V vs. metallic lithium. This behavior is significantly different to that expected from a standard Li[Mn-2]O-4 spinel electrode. The unusual electrochemical behavior of thin-film LiMn2O4 electrodes can be accounted for in terms of a structural model that may be considered as an intergrowth of two spinels, Li-8a[Mn-2](16d)O-4 and Li-8b[Mn-2](16c)O-4, where 8a and 8b refer to tetrahedral sites, and 16c and 16d refer to octahedral sites of the space group Fd3m.