Mitigating the cascading effects of thermal runaway and fire propagation in enclosed clusters of 18,650-type lithium-ion batteries

• The HRR of LIB cluster in confined space increased exponentially in the late stage. • The heating effect of cell ejections is the dominant reason for TRP. • The rupture of aluminum top delayed the TRP of LIB cluster in confined space. • Different mitigation measures were tested to guide safety design of LIB cluster. Thermal runaway (TR) propagation is one of the most crucial failure modes for lithium-ion batteries (LIB). However, previous studies mainly focused on TR propagation (TRP) in open space while the transportation and utilization of LIBs are mostly in confined spaces, for which significant knowledge gaps exist concerning TRP and related safety issues. In this study, a series of TRP tests were conducted in an enclosed LIB cluster. For comparison, tests were also conducted with an open cluster. The acceleration of the TRP and the exponential growth of the peak heat release rate were observed in the enclosed cluster. TRP in the open space was found to be not self-sustainable with some cells escaped TR. Different safety measures were applied to mitigate TRP including various spaces between the cells, barriers, cover plate, aluminum (Al) top and lower ambient temperature. The gaps between the cells were found to delay TRP occurrence from row 1 to row 2, but ineffective for the remaining 4 rows due to the preheating effects of the particles and flame. Jumping propagation of TR over rows was observed. For the Al top design, the hole created due to Al melting by fire was found to effectively slow down the propagation speed as the hot ejections were relieved from the hole. The cover plate was found to be most effective in delaying TRP from row 1 to row 2 as it blocked hot gases reaching the cell tops. However, it accelerated TRP in the remaining 4 rows. This was thought to be due to the thermal insulation effect. When the ambient temperature was lower than 17.4 °C, TR could only propagate in the first row even if there were no gaps between the cells in the confined cluster. Based on these results, recommendations are made on mitigation measures to help ensure safety during LIB transportation and utilization.