The structural stability of LiMn2O4, which is of interest as an insertion electrode for rechargeable lithium batteries, is discussed with respect to processing techniques, composition, Li-Mn-O phase diagram, and electrochemical behavior. Particular attention is paid to processing conditions that result in the formation of lithium-manganese-oxide spinel products in which Mn2+ ions partially occupy the tetrahedral sites of the spinel structure. The electrochemical behavior of electron-beam and r.f. magnetron sputtered thin-film electrodes suggests the existence of partially inverse Li1-xMn2O4 spinel structures during an initial charge to 5.3 V.