Enhancing thermal safety in lithium-ion battery packs through parallel cell ‘current dumping’ mitigation

This paper presents the first comprehensive study of a propagation mechanism referred to as ‘current dumping’, which has been identified as a dominant cause for thermal runaway in Lithium-ion battery packs. Baseline nail penetration tests were performed on commercial, fully charged lithium-ion battery packs with 18650 nickel-manganese-cobalt cells and Phase Change Composite to study the propagation of thermal runaway in packs with both electrically connected and disconnected cells. This study showed that packs with electrically connected cells experience thermal runaway propagation due to neighboring cell current dumping. Packs with electrically disconnected cells did not propagate and maximum neighboring cell temperatures were less than 85 °C, below the cell thermal runaway threshold temperatures characterized by accelerating rate calorimetry tests. Cell-to-cell current dumping tests were performed on 18650 and 21700 cells at 60, 80 and 100% state-of-charge. These tests demonstrated that cell current interrupt device activation times vary over several minutes, and trigger cell short resistance vary between 17 and 62 mΩ. Along with neighboring cell internal resistance data obtained from hybrid pulse power characterization testing, the current dumping study allowed accurate prediction of the magnitude of current dumping for various battery designs. This enabled the first battery design with individual cell fusing integrated into battery current collectors. Nail penetration tests performed on commercial 18650 battery packs incorporating the engineered fuse did not propagate and current dumping was prevented. Practical insights from this study can play a critical role in solving the thermal runaway propagation problem plaguing lithium-ion battery manufacturers globally.