Mechanisms of Degradation in Li‐Ion Batteries Under Low Temperature Exposures

This study demonstrates that subjecting Nickel Manganese Cobalt Oxide (NMC) graphite single‐layer pouch cells to temperatures down to −60°C during rest periods leads to performance reduction over 4× greater than control cells tested without low‐temperature exposure. A combination of the observed irreversible electrolyte phase separation effects along with mechanochemical stress build‐up during cathode delithiation results in a combined series of short‐ and long‐term degradation effects associated with low‐temperature exposures. In particular, these findings show that low‐temperature exposures lead to more brittle behavior of primary NMC particles that restrict c ‐axis expansion during delithiation and accelerate localized primary and secondary particle cracking as a long‐term sustained low‐temperature degradation mode. These findings provide mechanistic atomic‐ and molecular‐scale insight into an ongoing and controversial topic of low‐temperature effects in batteries that are central for emerging applications in military, commercial, and space systems.