Structural evolution dependency on depth-of-discharge in VO2(B) Li-ion battery electrodes

Abstract

Bronze vanadium oxide, VO2(B), has gained significant interest as electrode for Li-ion mainly due to the ease of preparation and the experimentally obtainable capacities of >325 mAh g−1 with intercalation of >1Li. In this work, we investigate for the first time the effects of intercalating >0.5Li on the structural phase evolution. Using operando X-ray diffraction, we find that deep discharge (i.e. inserting >0.7Li), has a dramatic effect on the subsequent charge process by introducing significant solid-solution behavior in the two-phase transition between the Li-rich and Li-poor phases. Rietveld refinement shows that the discharge-charge asymmetry is caused by severe structural deformations in the Li-rich state. Furthermore, we find that deep discharge causes capacity fade. This appears to be linked to the structural deformation causing an irreversible decrease in the Li-ion diffusion coefficients, determined herein by galvanostatic intermittent titrations.