Inhomogeneous aging of cathode materials in commercial 18650 lithium ion battery cells
Han Wang, Jay Whitacre
Abstract
To understand the relationships among first life use case, battery state of health, and end-of-life condition, the materials in commercial 18650 Li-ion cells were aged using prolonged cycling under different conditions and subsequently harvested and analyzed. In particular, different charge termination protocols and temperatures were applied to potential-limited galvanostatic cycling over 1000 cycles. Relationships between observed aging phenomenon and cycling conditions were explored at the cell and cathode materials level. We noted area-specific inhomogeneities in cathode cycled under constant current charge protocol at 25 °C while such inhomogeneity was not observed in three other conditions. The mechanism behind the cathode inhomogeneity was discussed in the context of uneven growth of a secondary solid electrolyte interphase (SEI) on the anode surface occuring during constant-current charge protocol at 25 °C.