Characterization of Venting Rate During Thermal Runaway in Pouch-Type Lithium-Ion Batteries

Abstract

Thermal runaway of lithium-ion batteries has emerged as a critical safety concern due to the rapid release of heat and flammable gases. Accurate estimation of gas generation during lithium-ion battery thermal runaway is important for evaluating venting behavior and safety. Conventional gas calculation methods based on the ideal gas law often exhibit errors due to strong eruption and temporal temperature nonuniformity inside the chamber during thermal runaway. In this study, a pressure-based weighted temperature correction method is proposed to improve the accuracy of gas generation estimation. The chamber-averaged temperature was calculated using a dynamically adjusted weighted-average approach, in which the relative contributions of high-temperature and low-temperature regions were determined from the temporal evolution of chamber pressure. In addition, the gas generation behavior was formulated by explicitly reflecting the thermal runaway process. The venting behavior was divided into three stages: an initial state, a main venting stage characterized by increasing and decreasing gas release rates, and a minor venting stage dominated by cooling effects. These stages were modeled using a linear function, a logistic function, and a saturation function, respectively, and combined into a composite formulation. The proposed method effectively reduced gas estimation undershoot in the early stage and overshoot in the late stage. The composite model showed agreement with experimental results, achieving a correlation coefficient exceeding 0.97 and NRMSE 4.63%.