The presented model captures fundamental phenomena regarding the complex interplay between the active material components in graphite/Si composite electrodes that have been experimentally observed. For instance, the model captures different stages of discharge, where graphite and Si contribute in varying percentages to the total electrode current, with a dependence on the applied C rate. Particularly, it is shown that Si dominates the first stages of the discharge process, where its SOC increases sharply, while graphite takes over at higher depths of discharge. Moreover, lithium crosstalk between graphite and Si phases was observed, where, due to differences in the electrode potentials of each materials, Si suffers local delithiation. Additionally, mass transport limitations were analyzed, where lithium concentration gradients in the electrolyte lead to a heterogeneous SOC of the active materials. Regarding the mechanics of the composite electrode, we show that the model captures some of the basic observables for microstructural evolution upon Si and graphite volume expansion, such as the evolution of the electrode thickness. We also assessed the effects of stress and pressure on the electrode's CBD phase. The model captures potential failure points for the CBD phase, by looking at regions where Von Mises stresses are high. This high stress zones are correlated with negative pressure zones, indicating the stretching of the CBD phase. We argue that this potential failure points may cause detachment of the CBD phase from the active material particles, thus damaging the conductive percolation network. We also observe potential failure points at the CBD and CC (Separator) interfaces.