A series of titanium-substituted manganese oxides, Li x Ti y Mn1−y O2 (y=0.11,0.22,0.33,0.44, and 0.55) with the Na0.44MnO2 structure were prepared from Na x Ti y Mn1−y O2 (x≈0.44) precursors. The electrochemical characteristics of these compounds, which retain the unique double-tunnel structure during ion exchange, were examined in lithium/polymer electrolyte cells operating at 85°C. All of the substituted cathode materials intercalated lithium reversibly, with Li x Ti0.22Mn0.78O2 exhibiting the highest capacity in polymer cells, about 10–20% greater than that of unsubstituted Li x MnO2 made from Na0.44MnO2. In common with Li x MnO2, the Ti-substituted materials exhibited good capacity retention over one hundred or more cycles, with some compositions exhibiting a fade rate of less than 0.03% per cycle.