New quarternary oxides (Li2O)(x).MnO2.yV(2)O(5) (x = 0.125 similar to 0.25, y = 0.125 similar to 0.25), formed by heating mixtures of MnO2, NH4VO3 and LiNO3 at various Li/Mn and V/Mn atomic ratios and at different temperatures (300 similar to 400 degrees C) in air, have been characterized by X-ray diffraction, X-ray photoelectron spectroscopy (ESCA) and infrared spectroscopy. The quarternary oxide with x = 0.25 and y = 0.25 showed a discharge capacity of 220 Ah (kg oxide)(-1) and an energy density of ca. 600 Wh (kg oxide)(-1) at a current density of 0.20 mA cm(-2) in 1 M LiClO4-propylene carbonate at 25 degrees C. When charge-discharge cycling with the (Li2O).MnO2.0.25V(2)O(5) electrode was performed at a constant capacity of 30 Ah (kg oxide)(-1) and at a constant current density of 0.10 0.20 mA cm(-2), the electrode sustained over 100 cycles at a high mean discharge potential of ca. 3V vs Li/Li+.