The reversible lithiation/delithiation mechanism of the cation-disordered Li VO material was elucidated, including the understanding of structural and electrochemical signature changes during cycling. The initial exchange of two Li induces a progressive and irreversible 7migration of Li and V ions from tetrahedral to octahedral sites, confirmed by the combination of in situ/operando X-ray diffraction and X-ray absorption fine structure analyses. The resulting cation-disordered Li VO can smoothly and reversibly accommodate two Li and shows a Li diffusion coefficient larger by 2 orders of magnitude than the one of pristine Li VO , leading to improved electrochemical performance. This cation-disordered Li VO negative electrode offers new opportunities for designing high-energy and high-power supercapacitors. Furthermore, it opens new paths for preparing disordered compounds with the general hexagonal close-packing structure, including most polyanionic compounds, whose electrochemical performance can be easily improved by simple cation mixing. 3 4 3 4 3 4 3 4 +