Towards Fire Forensic Characteristics of Failed Cylindrical Format Lithium–Ion Cells and Batteries

Fire forensic investigators are challenged to determine in what scenarios can lithium ion batteries initiate a fire, and what post-fire signatures exist to determine if the battery was more likely the cause of the fire or a victim of the fire. Towards this goal, this study experimentally characterizes the ignition characteristics of cylindrical format 18650 cells and the post-failure properties of the cells. First, failure tests of individual 18650 cell were used to quantify the temperature of vented gases and heat fluxes from these gases to cold objects for battery thermal failure at various states-of-charge (SOC) in either inert or normal oxygen environments. Experiments were then conducted with 18650 cells failed on composite cushion materials to evaluate how failures from different SOC cells ignite common fabric materials. Finally, laptop tests were conducted to investigate the effect of a common appliance package on the propagation of individual cell thermal runaway within the power bank of a common laptop configuration. The experimental results show that in the event of a thermal runaway, batteries can either explode or release a jet flame. The ignition behavior of fabric materials varies with varying SOCs with more vigorous ignition occurring at larger SOC. It was observed that the final mass of failed batteries is lower for higher SOC cells. Finally, propagation of thermal runaway inside a laptop power bank can be facilitated by having the failure take place at the center location of the power bank and can be hindered if the SOC is sufficiently low.