Thermal Runaway Characteristics and Fire Behaviors of Lithium-Ion Batteries Corroded by Salt Solution Immersion

Salt solution immersion experiments are crucial for ensuring the safety of lithium-ion batteries during their usage and recycling. This study focused on investigating the impact of immersion time, salt concentration, and state of charge (SOC) on the thermal runaway (TR) fire hazard of 18,650 lithium-ion batteries. The results indicate that corrosion becomes more severe with an increase in immersion time, salt concentration, and SOC. Shorter immersion durations or lower salt concentrations may lead to an increase in the maximum surface temperature of the battery during TR. Within a specific range of immersion time and salt concentration, the immersion can cause TR to happen earlier than usual. Among batteries immersed in a 3.5% NaCl solution for different durations (immersion 2 h in various NaCl concentrations), the earliest instance of TR was observed at a 4 h immersion time (5% immersion concentration). The onset temperature (T_TR) of TR increases with longer immersion times, a higher salt concentration, and a lower SOC, while the total mass loss during TR, as well as the rebound force, decreases. Furthermore, the maximum flame temperature and flame radiant heat flux saw significant reductions after immersion. The rapid decrease in the maximum heat release rate during stable combustion is attributed to the hydrolysis of the electrolyte and the depletion of the electrode active material following the corrosion failure of the safety valve. These findings provide valuable insights into the TR risks to batteries after salt solution immersion.