Reversible\nDisorder-to-Order Transition Induced by\nAqueous Lithiation in Vanadate Electrode Materials

Vanadium-based oxides are intriguing electrode materials\nin aqueous\nelectrochemical systems owing to their low cost and high theoretical\ncapacity for alkali storage, especially lithium (Li) ions. However,\na sequence of phase transformations and irreversible structure distortion\nupon Li-ion intercalation causes structural instability and has been\na lingering problem for vanadium oxide electrodes. Here, we investigate\nlithium vanadate (Li–V<sub>3</sub>O<sub>8</sub>) for aqueous\nLi-ion intercalation and deintercalation processes. Unlike its crystalline\nV<sub>2</sub>O<sub>5</sub> polymorph, Li–V<sub>3</sub>O<sub>8</sub> retains monophasic lithiation, which is attributed to its\ndisordered crystalline nature and large interplanar distance. Importantly,\nwe show a unique and reversible sequence of disorder-to-order structural\ntransition induced by the extent of lithiation, which indicates sequential\ninterlayer and intralayer lithiation process, and <i>vice versa</i> in delithiation process, supported by electrokinetic analysis, <i>in situ</i> X-ray diffraction (XRD), and Debye scattering simulations.\nThe absence of distortive phase transitions and multilithiation pathways\nfacilitates Li-ion diffusion across the vanadate electrode materials\nto improve storage capacity. This work opens a new dimension for vanadium-based\ndisordered oxides, accelerating the development of low-cost, aqueous\nelectrochemical systems.