Iodine-containing, cation-deficient, lithium manganese oxides (ICCD-LMO) are prepared by reaction of MnO2 with LiI. The MnO2 is completely transformed into spinel-structured compounds with a nominal composition of Li1−δ Mn2−2δ O4I x . A sample prepared at 800°C, viz. Li0.99Mn1.98O4I0.02, exhibits an initial discharge capacity of 113mAhg−1 with good cycleability and rate capability in the 4-V region. Iodine-containing, lithium-rich lithium manganese oxides (ICLR-LMO) are also prepared by reaction of LiMn2O4 with LiI, which results in a nominal composition of Li1+x Mn2−x O4I x . Li1.01Mn1.99O4I0.02 shows a discharge capacity of 124mAhg−1 on the first cycle and 119mAhg−1 a on the 20th cycle. Both results indicate that a small amount of iodine species helps to maintain cycle performance.