Structural Connectivities and Li (De)intercalation in Vanadium Molybdates

Intercalation battery cathode material a-V2O5 has a high theoretical capacity, but in practice has multiple phase transformations during Li intercalation, poor electronic conductivity, and lack of structural stability. Mitigation of irreversible phase transformations may improve the performance in V2O5, similar to what has been seen for Wadsley-Roth phases. Structurally related to ReO3, Wadsley-Roth materials stabilize against octahedral rotations during cycling due to crystallographic shear planes. According to our previous findings, Wadsley-Roth and V2O5 structures are ‘bridged’ structurally through metastable R-Nb2O5. The ‘idealized’ V2O5 structure of R-Nb2O5, with perpendicular shear planes, resulted in minimal structural evolution, reduced polyhedral distortions, symmetric cycling profiles, and enhanced structural stability during (de)lithiation.<br/>With an interest in mitigating phase transformation in V2O5, we investigated a series of Mo-doped V2O5, V2-xMoxO5, (0.05 = x = 0.8). Using synchrotron X-ray diffraction and battery cycling we probed the degree to which this ‘idealization’ of V2O5 is possible with a transition metal ion substitution. With increasing Mo-content, we find an overall improvement in capacity retention and Coulombic efficiency. Although significant changes in electrochemical behavior are observed, the consistent presence of specific impurities indicate that idealization of the structure is not feasible, which reflects on the metastability of these compounds. With an interest in more general relationships between structural connectivity and battery cycling behavior, we are using data science to establish structure-property-performance relationships in Wadsley-Roth and related materials. Using reported structure and cycling data for a subset of transition metal oxide electrodes and machine learning algorithms, we correlate inter- and intra-polyhedral connectivities and electrochemical behavior. These data and approaches can be used to identify structure-property relationships and inform future synthetic targets and next-generation battery materials.