Crack propagation has been extensively spotlighted as a main reason for the degradation of secondary-particle-type active materials, including LiNixMnyCo1−x−yO2 (NMC). Numerous experimental analyses and 3D-modeling-based investigations have been conducted to unravel this complicated phenomenon, especially for nickel-rich NMCs, which experience substantial crack propagation during high-voltage, high-temperature, or high-depth-of-discharge operations. To fundamentally clarify this unavoidable degradation factor and permit its suppression, a digital-twin-guided electro–chemo–mechanical (ECM) model of a single few-micrometer-sized LiNi0.7Mn0.15Co0.15O2 (NMC711) particle is developed in this study using a 3D reconstruction technique. Because the digital twin technique replicates a real pore-containing NMC711 secondary particle, this digital-twin electrochemical model simulates voltage profiles even at 8C-rate within an error of 0.48% by fitting two key parameters: diffusion coefficient and exchange current density. The digital-twin-based ECM model is developed based on the verified electrochemical parameters and mechanical properties such as lithium-induced strain from axis lattice parameters and stress–strain curve measured by nanoindentation. Using this model, the electrochemical-reaction-induced mechanical properties including strain, stress, and strain energy density are also visualized in operando in a single NMC711 particle. Finally, the advanced operando ECM analysis allows for the diagnosis of crack formation, highlighting the effectiveness of this platform in elucidating crack formation in active materials.