Lithium-ion battery cells exhibit a complex and nonlinear coupling of thermal, electrochemical, and mechanical behavior. In order to increase insight into these processes, we report the development of a pseudo-three-dimensional (P3D) thermo-electro-mechanical model of a commercial lithium-ion pouch cell with graphite negative electrode and lithium nickel cobalt aluminum oxide/lithium cobalt oxide blend positive electrode. Nonlinear molar volumes of the active materials as function of lithium stoichiometry are taken from literature and implemented into the open-source software Cantera for convenient coupling to battery simulation codes. The model is parameterized and validated using electrical, thermal and thickness measurements over a wide range of C-rates from 0.05 C to 10 C. The combined experimental and simulated analyses show that thickness change during cycling is dominated by intercalation-induced swelling of graphite, while swelling of the two blend components partially cancel each other. At C-rates above 2 C, electrochemistry-induced temperature increase significantly contributes to cell swelling due to thermal expansion. The thickness changes are nonlinearly distributed over the thickness of the electrode pair due to gradients in the local lithiation, which may accelerate local degradation. Remaining discrepancies between simulation and experiment at high C-rates might be attributed to lithium plating, which is not considered in the model at present.

Lithium plating is a critical factor that limits the fast-charging capabilities of lithium-ion batteries. Here we investigate the contributions of lithium plating and intra-particle lithium concentration gradients to the rate-dependent thickness change observed experimentally in a commercial high-power lithium-ion pouch cell with graphite negative electrode and a blend of lithium nickel cobalt aluminum oxide and lithium cobalt oxide positive electrode. This cell exhibits a thickness “overshoot” during charging at high C-rates, which partially recovers during the constant-voltage (CV) phase. We utilize a previously-developed pseudo-three-dimensional (P3D) thermo-electro-mechanical model to simulate these effects and validate the model against experimental data. Our findings show that intra-particle lithium concentration gradients significantly contribute to the thickness change at moderate C-rates due to the nonlinear volume expansion of graphite. At higher C-rates, lithium plating becomes a major factor, contributing both reversibly and irreversibly to the thickness change. A model including these effects accurately captures experimentally-observed behavior, providing insights into the complex thermo-electro-mechanical interactions inside the electrodes. This understanding is crucial for optimizing in operando lithium plating detection methods relying on thickness or mechanical stress measurements.

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.