Reversible Lithium Storage at Highly Populated Vacant Sites in an Amorphous Vanadium Pentoxide Electrode

A vanadium pentoxide electrode is prepared in the amorphous form (a-V2O5), and its electrode performances are compared to those for its crystalline counterpart (c-V2O5). The a-V2O5 electrode outperforms c-V2O5 in several ways. First, it is free from irreversible phase transitions and Li trapping, which evolve in c-V2O5, probably due to the lack of interactions between the inserted Li+ ions/electrons and V2O5 matrix. Second, the absence of Li trapping allows a reversible capacity amounting to >600 mA h g–1, which is larger than that given by c-V2O5. Third, it shows an excellent rate property. The notably high reversible capacity and rate capability seem to be due to Li storage at vacant sites that are ill-defined but numerous in a-V2O5, which Li+ ions can easily access. However, irreversible capacity of a-V2O5 is appreciable in the first cycle due to a parasitic Li reaction with surface hydroxyl groups. Treatment with n-butyllithium can suppress the irreversible capacity by removing the surface hydroxyl groups.