A cation-disordered Li-excess cathode material on the binary system xLi3NbO4-(1 - x)LiCrO2 (x = 0.43) has been successfully prepared by mechanical milling, and delivers a high reversible capacity of ∼362 mA h g-1, which originates from a highly reversible Cr3+/Cr6+ three-electron redox reaction with electrochemically inactive niobium ions.