The study of thermal runaway characteristics of multiple lithium batteries under different immersion times

The lithium-ion battery (LIB) pack for an electric vehicle immersed in seawater is easy to induce short circuit and other thermal runaway (TR) safety accidents. In order to better understand the TR characteristics of LIB pack after immersion, and to effectively prevent safety accidents, a series of experiments on LIBs immersed in seawater have been conducted. In this study, LIB packs under 100% charging state were immersed in 3.5 mass% NaCl solution (used as seawater) for different immersion times (0–12 h). The maximum temperature, surface electric fire temperature, total mass loss, heat release rate (HRR) and total heat release (THR) were measured to evaluate the fire hazard of LIBs. The experimental results showed that the ignition temperature decreased with the increase of immersion times. However, the maximum temperature increased with increase in immersion times. The total mass loss firstly decreased and then stabilized with the increase of immersion times. The loss of electrolyte and combustible materials was the largest when immersion times reaches 3 h. Both HRR peak value and THR reached the maximum value when immersion times reaches 3 h. The spread rate of thermal runaway remains a stable value when the immersion time is larger than 3 h.