A distributed thermal-pressure coupling model of large-format lithium iron phosphate battery thermal runaway

Abstract

The inner pressure that increases due to the complex physical and chemical reactions of batteries plays an important role in thermal runaway early warning and gas injection. However, most of the current thermal-pressure coupling models for batteries cannot accurately describe the gas generation sources and predict the inner pressure increases of multiple jelly rolls. In this work, we propose a thermal-pressure coupling model by combining the gas composition data and the fitting data from the accelerating rate calorimeter experiment. The electrolyte vapor pressure and internal gas composition are obtained under uniform heating conditions. The internal pressure growth source relies on the variation in the gas composition at different temperature ranges to infer. The reaction kinetics equations are then combined with gas generation sources, energy conservation equations and venting process to form a thermal-pressure model, which adopts a distributed structure to adapt to the temperature gradient between jelly rolls. The simulation results indicate that the model can accurately match the reaction gas accumulation phase before the valve venting, as well as the thermal runaway and cooling process temperature after the ejection. The simulation results indicate that when the pressure threshold increases from 0.5 MPa to 0.75 MPa, both the time-to-venting and time-to-peak temperature increase, but the interval between them decreases. Additionally, the explosion concentration range of the mixture gas also increases accordingly. This model revealed the inner pressure increase and thermal runaway process in large-format lithium iron phosphate batteries, offering guidance for early warning and safety design.