Crystallisation behavior and electronic conductivity of vanadium tellurite glass-ceramics

The electrodes of secondary batteries degrade during consecutive intercalation cycles, thus reducing the units’ capacity. The amorphous nature of an electrode could theoretically lower the degree of such degradation. Since a vanadium tellurite system exhibit high electronic conductivity and the ability to intercalate lithium-ions, it is a candidate for usage as cathode material. In the present work, we optimize the electronic conductivity of the congruent 2TeO2-V2O5 composition by tuning both the redox state of the vanadium and the overall degree of crystallinity. Amorphous 2TeO2-V2O5 is synthesized via the melt quenching technique, and crystalline 2TeO2-V2O5 is obtained by further heat-treatment of the quenched glass. Both states are confirmed by x-ray diffraction, scanning electron microscopy and differential scanning calorimetry. The redox state of vanadium is controlled via the melting temperature of synthesis, and it is measured by electron paramagnetic resonance spectroscopy. The electronic conductivity is measured by impedance spectroscopy in the temperature range from 298 to 523 K. The results indicate that the electronic conductivity is independent of the degree of crystallinity, but that it strongly depends on the valence of vanadium. The exact correlation between redox state and electronic conductivity remains an unsolved issue.