Evaluation of a New Type of Vanadium Oxide from Peroxo‐polyvanadate as a Cathode Material for Rechargeable Lithium Batteries

A new type of vanadium oxide ( V 2 O 5 ‐ n H 2 O ) with a structure intermediate between the amorphous and the crystalline state is synthesized by a reaction of metallic vanadium with hydrogen peroxide. Its electrochemical properties in relation to lithium intercalation have been investigated in a 1 M LiClO 4 / propylene carbonate solution at room temperature. When carbon powder is added to the electrode, this material can accommodate lithium up to x = 2.55 ( x : Li / V 2 O 5 unit ) , which is equivalent to the theoretical capacity of 370 Ah / kg ‐ V 2 O 5 . The equilibrium potential ( E vs . Li ) changes from 3.6 to 1.8 V, as the x is increased from 0 to 2.55. The E − x relationship is, on the whole, smooth, but it consists of three straight lines with different slopes, suggesting that there are two kinds of intercalation sites. The specific discharge capacity for the cutoff voltage of 2.0 V amounts to 280 Ah/kg, when the Li / V 2 O 5 cell is discharged at a constant current density of 20 mA / g ‐ V 2 O 5 . The charge and discharge capacities between the working voltages of 4.3 and 2.0 V agree completely with each other, indicating an excellent reversibility. A special role of carbon for lithium insertion into the present V 2 O 5 is also discussed.