Copper-doped amorphous manganese oxides were synthesized via a room-temperature aqueous solution route involving oxidation of Mn(II) precursors. Doping of copper ions did not significantly affect the low rate specific capacity or the intrinsic lithium intercalation capacity of the amorphous materials. However, even a small amount of copper doping dramatically increased the specific capacity at high rates. Larger amounts of copper doping also significantly enhanced capacity retention upon cycling. For an amorphous manganese dioxide doped with 0.18 Cu per Mn, a specific capacity of 275 mAh/g was attained between 4.0 and 1.5 V vs. Li+/Li at a high discharge/charge rate of C/5 (0.78 mA/cm(2)), with capacity fading of less than 0.5% per cycle upon cycling. It is believed that copper doping has the dual effect of both improving the lithium intercalation kinetics and stabilizing the local structure of the amorphous materials during lithium intercalation and cycling. (C) 2002 The Electrochemical Society.