First-principles study of the distribution of excess intercalated lithium in Li3V2O5 with a disordered rock-salt structure

Abstract

Lithium (Li) incorporation in many metal oxides can form a disordered rock-salt (DRS) structure. Such Li-containing oxides are widely employed as high energy density electrode materials in Li-ion batteries. Here, we show that the atomic structures of these DRS oxides can only be correctly understood by using dynamical statistics. Taking Li_xV₂O₅ (3 ≤ x ≤ 5) as an example of Li-excess DRS materials, using first-principles molecular dynamics simulations assisted with machine-learning potentials, we show that the Li ions mostly occupy the octahedral sites and only the excess Li ions occupy the tetrahedral sites, which is different from the Li ion redistribution mechanism proposed previously based on the static statistics. Our study shows that when x > 3 the Li ions at the octahedral sites tend to be off center, benefiting their diffusion. Moreover, when x = 5 the volume expansion is found to be as high as 20%, significantly higher than the previously reported value of 5.9%, suggesting that the actual capacity of Li₃V₂O₅ as an anode material might be significantly overestimated.