A family of potassium-doped manganese oxide materials were synthesized with the stoichiometric formula Li0.9−X K X Mn2O4, where X =0.0–0.25 and evaluated for their viability as a cathode material for a rechargeable lithium battery. A performance maximum was found at X =0.1 where the initial specific capacity for the lithium–potassium-doped manganese dioxide electrochemical couple was 130mAhg−1 of active cathode material. The discharge capacity of the system was maintained through 90 cycles (95% initial capacity). Additionally, the capacity was maintained at greater than 90% initial discharge through 200 cycles. Other variants demonstrated greater than 75% initial discharge through 200 cycles at comparable capacity.