Effect of parallel connection on 18650-type lithium ion battery thermal runaway propagation and active cooling prevention with water mist

Abstract

Water mist (WM) is an efficient cooling control strategy for thermal runaway (TR) propagation in lithium ion battery (LIB) modules, presenting potential for application in real systems. To comprehensively understand the cooling effect, WM is experimentally tested under significantly severe conditions, where LIB modules are connected in parallel and experience intensified TR propagation. Results show that 18650-type LIBs in the parallel connected module experience intensified TR hazard with higher propagation speeds. An extremely small voltage variation is detected during TR propagation, which leads to the negligible charge capacity. The enhanced heat transfer through pole connectors is demonstrated to be the major cause of the intensified TR propagation hazard. Batteries in the parallel connected module present much lower TR onset temperature, leading to a decreased critical control temperature. Once the critical control temperature reaches below 100 °C, the cooling process mainly depends on the sensible heat of water, and thus, the cooling efficiency of the WM is significantly weakened. The control mechanism is interpreted by qualitatively comparing the relationship between the battery heating rate and the WM cooling rate. The decreased critical control temperature and the enhanced heat transfer are identified as the main causes of the poor control effect.