The present invention provides a manganese bismuth mixed metal oxide cathode material through a solid-state reaction between manganese dioxide, and either bismuth or a bismuth compound in a compound having the general formula MnO_y(Bi₂O₃)_x, which affords charge transfer catalytic behavior that allows the cathode to be fully reversible at suppressed charge potentials and increased discharge potentials. The MnO_y(Bi₂O₃)_x cathode material may be incorporated into an electrochemical cell with either a lithium metal or lithium ion anode and an organic electrolyte. The present invention provides a compound with the general formula MnO_y(Bi₂O₃)_x, where subscript x is between 0.05 and 0.25, subscript y is about 2 and the overcharge protection is not needed as the subscript z approaches 0.0. In the preferred embodiment, a cathode material where subscript x is between 0.05 and 0.135 with the formula MnO₂(Bi₂O₃)_0.12 provides the much-needed full reversibility, high voltage stability and reduced charge transfer impedance. A manganese bismuth mixed metal oxide cathode for an lithium electrochemical system, a lithium electrochemical system and a rechargeable lithium battery employing the same compound with the general formula MnO_y(Bi₂O₃)_x and methods for making manganese bismuth mixed metal oxide cathode material for lithium electrochemical devices having the general formula MnO_y(Bi₂O₃)_x are also provided.