Thermal runaway characteristics of NaCl salt solution-immersed 18650 batteries: Impacts of concentration and state of charge

Abstract

Lithium-ion batteries are at risk of immersion in seawater during practical applications, presenting a substantial safety challenge. In this work, the thermal runaway characteristics and degree of corrosion of 18,650 lithium-ion batteries were examined at various NaCl concentrations and states of charge (SOCs). Results indicate that corrosion increases with both NaCl concentration and SOC. The onset time (tTR) and onset temperature (TTR) of thermal runaway decrease with increasing SOC. The TTR is considerably higher for batteries immersed in 5 % NaCl solution compared to batteries without immersion and immersed in 2.5 % NaCl solution, while the tTR demonstrates the opposite trend. The maximum temperature (Tmax) of thermal runaway initially increases and then decreases with increasing salt concentration for batteries with SOC >100 %, while it decreases as salt concentration increases for batteries with SOC <100 %. The mass loss of immersion increases with the increase in salt concentration and SOC. The mass loss and peak heat flux during thermal runaway of batteries immersed in salt solution are significantly lower than those of fresh batteries. These results will contribute to a better understanding of the thermal runaway risk of lithium-ion batteries with different SOCs following immersion in salt solution.