Vanadium phosphate glasses. Effect of composition on their structure and performance as cathodes in high-temperature lithium polymer-electrolyte cells

Abstract

Five vanadium phosphate (V₂O₅–P₂O₅) glasses, containing between 58 and 88 mol% V₂O₅, have been prepared using the melt-quenching technique. IR spectroscopy, in conjunction with powder X-ray diffraction (XRD) of the devitrified materials, has been used to show that the glasses containing ⩽ 70 mol% V₂O₅ have a microstructure which is similar to that of β-VPO₅ whereas the remainder show both orthorhombic-V₂O₅ and β-VPO₅ structural features. Molar-volume data suggest that there is a fairly abrupt change in microstructure atca. 75 mol% V₂O₅.

The glasses have been employed as the active component of the cathode in lithium polymer-electrolyte cells operating at 120 °C and the cycling performance has been investigated as a function of glass composition. After an initial capacity decline the cells showed good reversibility, although this was not achieved at capacities as high as that of V₆O₁₃ in a similar cell. Glasses containing less than 78 mol% V₂O₅ cycled at considerably lower capacities than those with higher vanadium content and this has been related to the above change in microstructure from a layered V₂O₅-type to a network β-VPO₅ type.