The chemomechanical behaviors of composite electrodes are largely different from that of single particles or mono-phase materials. The stress field, state of charge, and mechanical failure are strongly affected by the local details of the microstructure. We study the structural disintegration of NMC cathode materials of a hierarchical structure by tracking the microstructural evolution of different marked regimes. Decohesion of primary particles constitutes the major mechanical degradation. We employ operando nanoindentation to measure the evolution of elastic modulus, hardness, and interfacial strength of NMC cathodes at different states of charge and different cycles. We further use home-developed computational program to investigate the chemomechanical behaviors of NMC composites in reconstructed 3D models. An ample space of design is open for the optimization of the capacity and mechanical performance of electrodes by tuning the size, shape, and pattern of active particles, as well as the properties of the inactive matrix.