A Multi-Physics Coupled Model for Elucidating Expansion in Si–C Composite Anode Lithium-Ion Batteries

Silicon–carbon (Si–C) composite anodes are a promising pathway to enhance the energy density of lithium-ion batteries (LIBs), yet the substantial volume changes of silicon during (de)lithiation cause mechanical degradation, capacity fading, and safety risks that hinder practical use. To address these challenges, we develop an electrochemical–thermal–mechanical coupled model tailored for LIBs with Si–C anodes. Built upon the Newman pseudo-two-dimensional framework, the multi-scale model integrates particle-, electrode-, and cell-level submodels. Electrochemical–mechanical coupling is captured through intercalation-induced particle expansion and cell-level thermal expansion, while bidirectional electrochemical–thermal coupling is introduced via a lumped thermal model with temperature-dependent electrochemical kinetics. The model is validated against experimental data, accurately reproducing current–voltage profiles, temperature rise, and displacement under various operating conditions. Simulations further reveal the distinct contributions of silicon and graphite: although silicon accounts for only a small fraction of anode mass, it can contribute 30% to the capacity of the cell owing to the high specific capacity of Si. At the same time, while silicon particles undergo volume changes exceeding 300%, the overall cell expansion remains below 7.5% due to structural dilution effects from other components. These findings establish a quantitative link between silicon content, electrochemical behavior, and cell expansion, providing theoretical guidance for the rational design of high-energy-density LIBs.