LITHIUM INSERTION INTO VANADIUM PENTOXIDE BRONZES

Lithium insertion has been studied in the alpha-, beta- and gamma-LixV2O5 bronzes at 100 degrees C. At this temperature the reversible lithium composition ranges can be expanded far beyond the thermodynamic stability interval. By electrochemical intercalation the composition parameter x can be varied between zero and nearly three in all three bronzes. The insertion reactions are, however, not reversible in the entire interval for the layerlike alpha- and gamma-phases. They are converted into a weakly crystalline omega-phase when more than approximate to 1.8 Li per formula unit is inserted. As long as the discharge is limited to 2.25 V, lithium insertion is fully reversible in these materials. In contrast to the behaviour observed on cycling at room temperature we see no evidence for a structural rearrangement from alpha- to gamma-phase upon cycling past x = 1. The S-dimensional beta-structure can be cycled reversibly throughout the entire interval 0 < x < 3.