Lithium-ion batteries (LIBs) have been widely used in the field of energy storage due to their advantages such as high energy density, no memory effect, low self-discharge rate, and long cycle life. However, battery aging remains one of the main bottlenecks restricting further development. In particular, the formation and continuous growth of the solid electrolyte interphase (SEI) film on the anode is a key factor leading to capacity fade. This study focuses on the bidirectional mechano-chemical coupling effects during SEI growth. Using a silicon anode as the model system, we develop a coupling framework that accounts for active-particle volumetric expansion and stress-dependent interfacial side-reaction kinetics together with dynamic SEI thickening, to elucidate their interactions during charge/discharge. Simulations show that hydrostatic stress increases the side-reaction current density, accelerates SEI growth, and thereby exacerbates capacity degradation. Parametric analysis further indicates that, within a non-cracking particle-size window, increasing the silicon particle radius improves capacity retention, while lowering the depth of discharge (i.e., using a lower cutoff voltage) shortens the reactive time window, suppresses SEI growth, and likewise enhances cycling stability. This study provides theoretical guidance for the design of high performance lithium-ion batteries.