Fragility–structure–conductivity relations in vanadium tellurite glass

The electrodes of secondary batteries degrade during consecutive intercalation cycles, thus reducing their capacity. The amorphous nature of an electrode theoretically lowers the degree of such degradation. Since a vanadium tellurite system exhibits high electronic conductivity and possesses the ability to intercalate lithium-ions, it is a candidate as cathode material. Here, we investigate the correlation between liquid fragility, structure and electronic conductivity in a series of vanadium-tellurite glasses with varying vanadium concentration. We measure dynamic and thermodynamic fragility and observe a plateau in fragility up to 50% V2O5 after which a steep increase is observed. As Vickers hardness and the valence state of vanadium both exhibit an inverse relation with fragility, we propose a direct correlation between these properties. Based on 125Te and 51V NMR measurements, we calculate the number of bonding and non-bonding oxygen atoms per network former, while we use IS and ESR to determine the electronic conductivity and the valence states of the system. We correlate the changes in local atomic structures as determined by NMR to the observed changes in macroscopic properties. Since fragility and electronic conductivity are largely controlled by the valence state of vanadium (i.e., the concentration of V4+), optimization of these properties can be achieved by controlling the conditions of post heat-treatments.