Quantifying self-generated heat and thermal runaway characteristics of high-energy NCM pouch cells under different heating powers

This study experimentally investigates the influence of external heating power on the incubation characteristics and behavioral patterns of thermal runaway (TR) in 71 Ah nickel‑cobalt‑manganese (NCM) pouch cells. Three heating powers (300 W, 500 W, and 700 W) were used to trigger TR in cells at 100% state of charge (SOC). To analyze the characteristics of the entire TR process, a one-dimensional transient heat conduction model was established for the incubation phase, and key parameters — including temperature, voltage, heat release rate (HRR), and mass loss — were systematically examined. The model was based on the laws of energy conservation and Fourier's heat conduction, and an inverse algorithm was then developed to calculate the internal volumetric self-heat generation rate. Unlike previous accelerating rate calorimeter (ARC)-based adiabatic studies, this work decouples external heat input from internal self-generated heat via transient inverse modeling, thereby enabling real-time quantification of the energy flow that has not been previously achieved under external heating conditions. The results show that the temperature rise during the incubation phase is predominantly driven by external energy input. The external heat input at 300 W, 500 W, and 700 W was 304.2 kJ, 142 kJ, and 156.1 kJ, respectively, all substantially exceeding the battery's self-generated heat. Conversely, the peak self-generated heat flow rate decreased with increasing heating power, reaching 17.52 W, 16.66 W, and 14.02 W, respectively. Higher heating powers resulted in a larger temperature difference between the front and back surfaces of the battery. This increased the average internal TR propagation time from 6.67 s to 9 s and decreased the average propagation velocity from 1.8 mm/s to 1.33 mm/s. Concurrently, higher heating power shortened the TR initiation time from 1011 s to 226 s and intensified its severity, as evidenced by a marked increase in peak HRR from 147.89 kW to 283.98 kW. This study elucidates how heating power affects the energy flow during TR incubation and the subsequent internal propagation behavior in NCM batteries. The methodological framework established herein — decoupling external heat from internal self-generation — offers a new paradigm for analyzing energy flow during TR incubation that extends beyond the capabilities of conventional adiabatic calorimetry.