Microstructural features such as porosity, tortuosity, and coordination number play a crucial role in determining energy density and efficiency. Although calendaring is a key step in electrode manufacturing, its impact on granular-scale structural evolution is still deserves deeper investigation. This situation arises primarily from the microscale interactions between active materials (AM) and the carbon binder domain (CBD), which are difficult to observe experimentally. To address this challenge, advanced computational modelling is essentially needed. In this work, a high-fidelity numerical framework based on the material point - discrete-element method (MP-DEM) is presented to investigate the deformation and structural evolution of positive electrode under mechanical compression. AMs are modelled as individual discrete particles, while the CBD is represented as a viscoelastic continuum using the MP. By leveraging the advantages of both MP and DEM, our approach enables accurate numerical analysis of highly heterogeneous granular systems through interactive force exchanges between components. The results reveal critical points between processing conditions and microstructural changes, providing quantitative insights that can guide the optimization of electrode manufacturing processes.