As a new class of lithium rich cathodes,disordered rock-salt cathodes have been of primary interest,because of their ability to deliver a promisingly high capacity up to 300 mA h/g.Nevertheless,some fundamental issues are yet to be fully understood and a comprehensive mastering of their solid-state chemistry,kinetics and thermal stability is required.Here,we select a high capacity cation-disordered positive electrode-Li1.2Ni0.4Nb0.4O2 as a model compound to study intrinsic reaction mechanism,including charge compensation mechanism,kinetics,thermal stability,and structural evolution.By combining soft and hard X-ray absorption spectroscopy (XAS),X-ray photoelectron spectroscopy (XPS) with operando and exsitu differential scanning calorimetry (DSC),galvanostatic intermittent titration technique (GITr),cyclic voltammetry (CV),and X-ray diffraction (XRD),we present holistic information on disordered rock-salt cathode.This work provides beneficial insights into designing and tailoring new positive electrodes with disordered rock-salt structure.