Deformation and Degradation in 18650 Li-Ion Cells Under Freeze-Thaw Cycling

Cylindrical 18650 cells are widely used in electric vehicles and space applications, where exposure to extreme temperature fluctuations is common. Repeated exposure to freezing and thawing cycles may accelerate electrode-level degradation due to the associated temperature fluctuations. This study investigates the electrochemical and structural degradation of 18650 lithium-ion batteries (LIB) subjected to more than 1000 cycles at 1C and 4C rates with periodic freeze-thaw cycles. Using synchrotron-based X-ray computed tomography (XCT) and virtual unrolling techniques, it is found that freeze-thaw cells cycled at 4C exhibited greater structural damage, including jelly roll buckling and electrode delamination, than regular cells cycled at 4C, while 1C cycled cells showed good freeze-thaw resistance. This diagnostic framework offers a powerful approach to uncovering these hidden degradation pathways and informing more resilient battery designs for extreme use scenarios such as rovers or devices in space, where a high C-rate is often required with extreme temperature swings between night and day.