A Mechanical Aging Mechanism in Lithium-Ion Batteries

Cycling at different C-rates, as well as storage aging is performed with five different types of commercial 18650-type Lithium-ion cells. X-ray computed tomography measurements show strong deformations of the inner part of the jelly rolls for three different cell types without center pin after cycling at rates in the range of 3.6-16.6C. For cells cycled at 1C, this deformation is less pronounced, whereas it is totally absent for stored cells. The consequence on capacity loss of the cells was investigated by Post-Mortem analysis with unrolled electrodes, as well as scanning electron microscopy imaging with cross-sections of 18650 cells. In order to investigate the reason for the jelly roll deformation, we conducted in-operando temperature measurements in the middle of the jelly roll and at the cell surface during discharge with 16C for one selected cell type. Finally, the effect of a center pin on jelly roll deformation is tested by X-ray computed tomography imaging for two different cell types after cycling.