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 -V 2 O 5 ), and its electrode performances are compared to those for its crystalline counterpart ( c- V 2 O 5 ). The a -V 2 O 5 electrode outperforms c- V 2 O 5 in several ways. First, it is free from irreversible phase transitions and Li trapping, which evolve in c -V 2 O 5, probably due to the lack of interactions between the inserted Li + ions/electrons and V 2 O 5 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- V 2 O 5 . 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 -V 2 O 5, which Li + ions can easily access. However, irreversible capacity of a -V 2 O 5 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.