(Invited) Characterization of Commercial Lithium-Ion Battery Aging Mechanism

Lithium-ion batteries are crucial energy storage systems in various naval applications. Understanding of the lithium-ion battery aging mechanism and impacting factors provide guidance for energy design requirements, battery life optimization and effective battery maintenance. In this work, commercial 18650 lithium-ion cells were tested under accelerated aging conditions to end of life (80% capacity remaining) including both calendar aging and cycle aging at different conditions to include the effects of temperature, storage state of charge (SOC), cycling rate, and depth of discharge (DOD), etc. The aging mechanisms of the commercial 18650 lithium-ion cells were systematically characterized and summarized. The cells show strong dependence on temperature and SOC during storage, but weak dependence on temperature and rates during cycling. The distribution of relaxation times (DRT) analyses of full cell impedance showed significant difference between calendar life and cycle life cells on the solid electrolyte interphase (SEI) and the charge transfer resistance increases over degradation. A separate impedance analysis on electrodes harvested from degraded cells in coin cell half-cell showed that the cathode contributed more than the anode during the charge transfer process for calendar life storage. Thermal properties characterization of pristine and aged electrodes in differential scanning calorimetry (DSC) showed that the degradation hardly decreases the thermal stability. The X-ray photoelectron spectroscopy (XPS) showed that the ratio of Ni 2+ /Ni 3+ on the surface of the cathode increases over cycling.