For the layered oxide cathode, Li-ions intercalate into the host structure, creating a gradient in the lattice parameter and a concurrent non-uniform elastic strain and large volume change (7.8% volume change for LiNi 0.8 Mn 0.1 Co 0.1 O 2 (NMC811) ). The high stress buildup resulting from Li transport and crystalline anisotropy inevitably leads to contact loss and the formation of crystal defects in cathodes, in particular dislocations and stacking faults , as sketched in Fig. . The appearance of crystal defects in ion-insertion materials can generate heterogeneous nanoscale lattice strain and modify the local bonding environment, for example, the number of covalent bonding partners for oxygen, as revealed by coherent X-ray diffraction and atomic-scale characterisation . The metal-oxygen decoordination owing to defects leads to significant change in the local electronic structure, and can even change the relative ordering of electronic states . Although the exact nature of the defect-induced bonding environment change is debated and may vary among different materials, such as Ni-rich and Li-rich layered oxides, the large lattice strain associated with crystal defects can markedly reduce the energy barriers to remove lattice oxygen and trigger Li/TM ion mixing . Therefore, besides the electrochemical instability of the cathode/electrolyte interface, the continuous accumulation of crystal defects in cathode particles due to Li (de)intercalation over cycling acts as the primary driving force for aggravating oxygen loss and altering the structural stability.