The tested lithium-ion cells were exposed to liquid nitrogen (LN2). Electrochemical characterization before and after the exposure did not indicate immediate changes in the cell
Source: BAM
The transportation and storage of lithium-ion batteries (especially in a damaged or undefined state) is a major safety challenge for transport companies, manufacturers, and, ultimately, BAM as the competent authority for the transport of critically defective batteries. As the (electro)chemical reactivity depends exponentially on the temperature, cooling such batteries is an obvious measure to improve their safety. This can, in turn, lead to mechanical damage to the cell. Consequently, a more appropriate cooling solution — less extreme than direct LN2 exposure — needs to be found.
This study investigates the effects of cryogenic freezing on the electrochemical and physical stability of Li-ion cells. For this purpose, three different cell types were repeatedly cooled with liquid nitrogen (LN2). Electrical and electrochemical measurements were performed before and after each cooling cycle to evaluate the effects of each freezing process. While the electrochemical behavior of the cells did not change significantly upon freezing in LN2, it was found that a significant number of cells showed physical changes (swelling) and functional failures after a cooling period. The latter defect was identified to be caused by an internal safety mechanism in round cells of the cylindrical cells. This safety mechanism is triggered by the overpressure of the expanding nitrogen that enters the cells at cryogenic temperatures.
This study emphasizes that the widely accepted assumption that LN2 cooling does not cause changes at the material level does not allow direct extrapolation to the physical integrity of the complete cell. As nitrogen penetrates the cell at cryogenic temperatures and expands during thawing, it can cause internal overpressure. This, in turn, can lead to mechanical damage to the cell. Therefore, a more suitable cooling condition for deep-frozen transport must be found that is less extreme than direct LN2 exposure.
Exploring the electrochemical and physical stability of lithium-ion cells exposed to liquid nitrogen
Robert Leonhardt, Nils Böttcher, Shahab Dayani, Arielle Rieck, Henning Markötter, Anita Schmidt, Julia Kowal, Tim Tichter, Jonas Krug von Nidda
Journal of Energy Storage, 2024