Modelling of electrode swelling in lithium-ion batteries

Abstract

As the global adoption of electric vehicle (EV) technology accelerates, the demand for safe, sustainable, and reliable battery technologies has increased. Currently, lithium-ion batteries offer the most promising option due to their high energy density and long cycle life. However, a significant concern with lithium-ion batteries is their tendency to swell during operation. This swelling is not just a cosmetic issue; it can seriously impact the battery’s efficiency and safety. When battery cells swell, they may experience a reduction in energy storage capacity, which affects the overall performance of the vehicle. Additionally, this expansion can lead to mechanical failures or even pose fire hazards if not properly managed. Since the effects of swelling are long term in nature, physically testing the batteries can be both expensive and time consuming. Therefore, there is a need to develop virtual testing models to analyze the mechanical response of battery cells while considering the effects of swelling. This study builds on the previous work and research done in the Battery Structural & Thermal Simulation department at Volvo Cars and aims to develop a methodology for predicting the mechanical response of battery cells by integrating the effects of state of charge induced swelling using a coupled electrochemical-mechanical simulation. A multiscale modeling approach is utilized to analyze the battery at micro, meso, and macro scale levels. At the microscale, the mechanical response to particle-level expansion is examined, and an effective swelling coefficient is determined through virtual tests. This effective swelling coefficient is then scaled up to the mesoscale, where coupled electrochemical and mechanical simulations are conducted to assess the impact of lithium insertion on the expansion at the electrode level. Finally, this effective expansion is further upscaled to capture the volume changes occurring at the cell level. The developed methodology in this work can be further utilized to analyze the pack or module level swelling. A key limitation of the developed framework is that it only accounts for swelling induced by change in the state of charge. Consequently, additional work is needed to enhance the model by incorporating swelling caused by lithium plating, degradation of the solid electrolyte interphase (SEI) layer, and gas generation. These factors have a significant impact on the cell’s long-term response and require further investigation.