An experimental study on thermal runaway propagation over cyclic aging lithium-ion battery modules with different electrical connections

Abstract

This paper investigates the thermal runaway propagation characteristics of cyclic aging battery modules connected in series, parallel, and series-parallel configurations. Additionally, a comparative analysis of the thermal runaway characteristics among the three battery module configurations is performed. In this experiment, voltage, mass, and other parameters of cells are measured. The temperature response reveals that: when comparing the three battery module configurations, the parallel module has the highest maximum temperature of thermal runaway at 720 °C, followed by the series and series-parallel combined configurations at 683 °C and 669 °C, respectively. The parallel module also exhibits the fastest propagation rate of thermal runaway, which is further intensified by cyclic aging. Regarding the voltage response: the series configuration has five stages of voltage variation during thermal runaway, while the parallel configuration has two stages, and the series-parallel combined configuration has three stages. Cyclic aging accelerates the voltage decline during thermal runaway for all three battery module types. In terms of mass response: the 2P2S configuration experiences the highest mass loss of 55.7 g, followed by the parallel (40.8 g) and series (34.7 g) configurations. Preliminary heat transfer analysis shows that: the average heat transfer during thermal runaway is highest for the 2P2S configuration (20,161 J), followed by the 4S (18,913 J) and 4P (18,773 J) configurations. Cyclic aging reduces the overall heat transfer. Electrical connections have minimal impact on heat transfer within the battery modules. Specifically, in the 4S, 4P, and 2P2S configurations, the heat transfer attributed to electrical connections accounts for only 1.2 %, 0.4 %, and 7.3 % respectively, of the overall heat conduction through the battery shell.