Multiscale & Multiphysics Model of Damage in Lithium-Ion Batteries

The demand for safer and more reliable lithium-ion batteries (LIBs) in electric vehicles has increased significantly, especially in addressing mechanical failures like internal short circuits (ISCs), which can lead to thermal runaway. This research investigates the mechanical behavior and damage mechanisms in lithium-ion pouch cells through a multiscale and multiphysics approach, focusing on Lithium Nickel Manganese Cobalt Oxide (NMC) and Lithium Iron Phosphate (LFP) batteries.\nThe study involved quasi-static and dynamic mechanical tests, including indentation and high-speed penetration, to evaluate stress-strain responses and fracture behaviors. Anisotropic mechanical properties were measured for individual battery components (anode, cathode, separator, and shell) using tensile tests in different directions. A custom-designed fixture minimized bulging effects during indentation, allowing for more accurate force-displacement data collection. Additionally, a comparative analysis between fresh and aged cells revealed that aged cells exhibit increased ISC triggering strain, suggesting improved safety due to aging effects.\nA layered finite element (FE) model was developed to simulate the battery's mechanical response, incorporating material anisotropy and strain-rate sensitivity, with validation through experimental data. A novel framework was also created to extract stress-strain curves from indentation tests, overcoming the limitations of traditional methods. A viscoplastic constitutive model was implemented to predict failure initiation and ISC progression during mechanical abuse, providing a more accurate simulation of battery behavior under extreme conditions.\nThis combined experimental and computational approach advances the understanding of damage initiation and propagation in lithium-ion pouch cells, contributing to the design of safer and more reliable battery systems. The findings provide valuable insights for the development of LIBs, particularly in improving safety for electric vehicles and portable electronic devices by addressing key factors like strain-rate dependence, anisotropy, and thermal effects.