Model-Based Investigation of the Electrochemical and Mechanical Behavior in Lithium-Ion Cells with Silicon-Graphite Negative Electrodes

Abstract

This study investigates the electrochemical and mechanical behavior of lithium-ion cells with silicon–graphite blend negative electrodes using a physics-based pseudo-three-dimensional (P3D) model extended to include thermal and mechanical effects. Silicon particles were fictitiously introduced into a 350 mAh pouch cell model with an LCO/NCA positive electrode and graphite negative electrode. A thermodynamic hysteresis model was implemented to account for silicon’s open-circuit voltage hysteresis. Simulations examined the effects of negative electrode thickness, silicon content, and particle size on capacity, energy density, and expansion. The results indicate that both electrode thickness and silicon content exert strong, nonlinear effects on voltage behavior, capacity, and expansion. Specific energy exhibits a maximum near an N/P ratio of 1, where both electrodes co-limit performance. At 10 vol.-% silicon, both graphite and silicon are electrochemically active; at 50 vol.-%, silicon dominates, while graphite becomes largely inactive. Cell expansion increases superlinearly with capacity, rising by a factor of 11 from 6.25 µm to 100 µm thickness, whereas the available capacity increases by only about a factor of two over the same range. These results emphasize the need to co-optimize material composition, electrode architecture, and particle size to balance energy density and mechanical stability in next-generation lithium-ion cells.