Multi-Physics Coupled Modeling and Failure Deduction of Large-Capacity LFP Batteries During Overcharge-Induced Thermal Runaway

As energy storage scales up, overcharge-induced thermal runaway (TR) in large-capacity batteries poses critical risks. This study develops a 3D multiphysics model for 280 Ah prismatic lithium iron phosphate (LFP) batteries, coupling electrochemistry, heat conduction, and side reactions while incorporating gas-pressure-structural response dynamics. To resolve high-dimensional parameter identification challenges, a staged strategy using Bayesian optimization and cross-dimensional mapping is proposed, ensuring consistency between 1D and 3D models while minimizing computational costs. Validated against 0.5C and 1C overcharge tests, the model accurately predicts voltage and temperature evolution, with TR onset and peak temperature errors under 5% and 3%, respectively. Mechanistic analysis reveals a transition from electrochemical to side-reaction-dominated heat generation, with electrolyte oxidation being the primary driver of heat and gas evolution during deep overcharge. Furthermore, results indicate that battery expansion is primarily driven by internal pressure accumulation, characterizing overcharge TR as a coupled thermal-gas-mechanical failure process. This framework provides a robust tool for safety characterization and early warning in large-scale energy storage systems.