Comparative analysis of external heating and nail penetration to trigger thermal runaway of lithium ion battery

The thermal runaway (TR) characteristics of lithium iron phosphate (LFP) batteries and LiNi_xCo_yMn_zO₂ (NCM, x+y+z=1, x=0.6) batteries that triggered by external heating with heating powers ranging from 400 W to 1000 W, as well as nail penetration, are thoroughly compared in this work. The times that needed to trigger TR, the highest temperatures of the battery big face and morphology of the battery casing after experiment are recorded and utilized for TR severity comparison. The results indicate that both types of batteries exhibit more severe TR when triggered by external heating compared to nail penetration. Additionally, under the same test conditions, NCM batteries undergo more intense TR than LFP batteries. The outcomes of TR triggered by external heating are influenced by the heating power, higher heating power results in shorter time required for the initiation and lower severity of the TR. It is surprising that LFP battery exhibited explosion under low-power heating at 400 W, with the battery's top cover separating from the casing and the inner electrodes spilling out. This underscores the need for particular attention to the safety of LFP batteries when TR is triggered by low-power external heating. This study provides guidance for safety assessments during battery development and the selection of triggering methods for thermal propagation tests at the pack level. Low-power external heating is recommended to assess the battery safety during the early development stage. For the thermal propagation test at the pack level, the trigger method should be selected carefully based on the test objective.