How does saltwater immersion affect the topographic, electrochemical and thermal characteristics of lithium-ion cells?

Given that many safety standards for lithium-ion cells include a saltwater immersion test and the possibility of cell immersion by water by accident, this work prepares five kinds of cells by varying immersion time and saltwater concentration to explore the influence of saltwater immersion on the topographic, electrochemical and thermal characteristics of cells. The exterior morphology of cells varies after immersion due to the corrosion of saltwater, and the severity worsens with the increase of immersion time and saltwater concentration. Besides that, saltwater immersion accelerates the degradation behavior of cells over cycling. Both electrode materials after immersion release less heat at elevated temperatures. The thermal runaway behavior is intensified if a cell is immersed in the 3.5% (wt.) saltwater for 2 h, while a more gentle thermal runaway behavior is illustrated if the immersion time lasts longer than 2 h or a saltwater with a higher concentration is used. Moreover, the thermal runaway propagation risk within modules after immersion is also significantly suppressed due to the decline of heat release. It is hoped that this research would aid in a better understanding of saltwater-immersed cells. • The cell after saltwater immersion shows larger internal resistance. • The degradation mechanism of cells after saltwater immersion is provided. • Saltwater immersion inhibits the thermal runaway propagation of cells. • Immersion in 3.5% (wt.) saltwater for 2 h is a judicious safety test for cells.