Structural Evolution of Disordered Li_<i>x</i>V₂O₅ Bronzes in V₂O₅ Cathodes for\nLi-Ion Batteries

Abstract

Vanadium pentaoxide,\nV₂O₅, is an attractive\ncathode material for Li-ion batteries, which can store up to three\nLi ion per formula unit. At deep discharge, an irreversible reconstructive\nphase transition occurs with formation of the disordered ω-Li_<i>x</i>V₂O₅ bronze, which,\ndespite the lack of long-range order, exhibits a high reversible capacity\n(∼310 mAh/g) without regaining the crystallinity upon recharge.\nHere, we utilize <i>operando</i> powder X-ray diffraction\nand total scattering (i.e., pair distribution function analysis) to\ninvestigate the atomic-scale structures of the deep-discharge phase\nω-Li_<i>x</i>V₂O₅ (<i>x</i> ∼ 3) and, for the first time, the highly disordered\nphase β-Li_<i>x</i>V₂O₅ (<i>x</i> ∼ 0.3) formed during subsequent Li-extraction.\nOur studies reveal that the deep discharge ω-Li₃V₂O₅ phase consists of ∼60 Å domains\nrock salt structure with a local cation ordering on an ∼15\nÅ length scale. The charged β-Li_<i>x</i>V₂O₅ phase only exhibits very short-range\nordering (∼10 Å). The phase transition between these phases\nis structurally reversible and appears unexpectedly to occur via a\ntwo-phase transition mechanism.