Structure and Electrochemistry of Li2Cr x Mn2 − x  O 4 for 1.0 ⩽ x ⩽ 1.5

Li 2 Cr x Mn 2 − x O 4 samples with x = 1.0, 1.25, and 1.5 were prepared by heating sol‐gel precursors to elevated temperatures in argon. Three crystalline phases were observed as a function of the final heating temperature and x , and these were plotted on a structure‐composition‐temperature diagram. The samples lose some oxygen as they are heated, and this is probably part of the cause for the structural changes observed. The structure of Li 2 CrMnO 4 heated to 1000 °C has been determined to be a distorted‐hexagonal layered structure, much like that of the layered LiMnO 2 phase recently reported by Armstrong and Bruce. This does not agree with previous work by Davidson et al., who claimed this phase was a tetragonal or orthorhombic distortion of the spinel structure. We show that Davidson's data are better explained by our model. At lower temperatures (e.g., 700 °C), the compounds are isostructural with LiCoO 2 , with the R‐3m space group. Li / Li 2 Cr x Mn 2 − x O 4 electrochemical cells were made for all the samples and voltage‐composition profiles measured. Li 2 Cr 1.25 Mn 0.75 O 4 heated at 700 °C has an attractive voltage profile and a reversible capacity near 150 mAh/g when measured at a low rate of discharge.