The rechargeable capacity of 4 V LixMn2O4 spinel cathodes (0 < x less-than-or-equal-to 1) has been improved by modifying the composition of the spinel electrode. Stable rechargeable capacities in excess of 100 mAh/g in flooded-electrolyte lithium cells can be achieved if LiMn2O4 is doped with mono- or multivalent cations (e.g. Li+, Mg2+, Zn2+) or, alternatively, with additional oxygen to increase the average manganese-ion oxidation state marginally above 3.5.