Abstract: To investigate the thermal runaway characteristics of lithium-ion batteries under different immersion conditions, this study takes the 18650 ternary lithium-ion battery as the research object and analyzes its performance changes after immersion in different types of salt solutions, as well as its surface temperature characteristics during thermal runaway. The results show that the corrosive and discharge effects of different salt solutions on lithium-ion batteries vary. Among the three salt solutions tested, NaCl solution exhibits the strongest effect on the discharge and corrosion of the batteries. Lithium-ion batteries soaked in all three salt solutions can undergo thermal runaway. As the immersion time increases, both the time required and the onset temperature for triggering thermal runaway increase. When the immersion time is 2 h, the initial thermal runaway temperature of batteries soaked in NaCl and Na2SO4 solutions is higher than that of dry batteries, while that of batteries soaked in Na2CO3 solution is lower. Moreover, the maximum surface temperature of lithium-ion batteries during thermal runaway after immersion is higher than that of dry batteries, with the peak temperature decreasing in the order of NaCl, Na₂SO₄, and Na₂CO₃ solutions. Although salt solution immersion raises the thermal runaway onset temperature of lithium-ion batteries to a certain extent, the corrosion caused by the solution increases the risk of thermal runaway. Therefore, the safe disposal of water-exposed lithium-ion batteries requires simultaneous consideration of the degree of damage and the state of charge to comprehensively assess the risk of thermal runaway.

Key words: lithium-ion batteries, thermal runaway, salt solution, immersion, temperature