Investigating the effect of packing format on LiNi x Co y Mn z O 2 lithium-ion battery failure behavior based on multidimensional signals

Prismatic and pouch packaging formats are commonly used in LiNi x Co y Mn z O 2 (NCM) batteries for electric vehicles, each showing distinct failure dynamics. However, a comprehensive study is lacking on how these packaging types affect thermal runaway (TR) at the cell level and its propagation at the module level, with a particular gap in understanding the dynamics of multidimensional signals. In this study, we experimentally explore the effect of cell format on 40 Ah NCM523 prismatic and pouch battery failure behaviors under overcharging and overheating conditions, by applying multidimensional signals, including the swelling force, gas, voltage, and temperature of the batteries. Results indicate that both types of batteries exhibit similar time scales for the failure modes when overcharged. In contrast, under overheating conditions, the pouch batteries fail significantly earlier than the prismatic batteries, including abnormal swelling, venting, gas emission, internal short circuit, and TR. Additionally, the prismatic batteries can withstand a swelling force of 5000 N at venting, while it is 2000 N for the pouch batteries. During TR, the prismatic batteries present a maximum temperature increase rate below 100 K/s, while the pouch batteries exhibit one over 200 K/s. Furthermore, the pouch batteries generally display more severe TR hazards and faster TR propagation than the prismatic cells. This study enhances the comprehension of TR and TR propagation mechanisms across different cell formats, providing crucial insights for the safety design and early warning strategies of battery modules.