Performance degradation of high-power lithium-ion cells—Electrochemistry of harvested electrodes

The performance of 18650-type high-power lithium-ion cells is being evaluated as part of the U.S. Department of Energy's (DOEs) Advanced Technology Development (ATD) program. In this article, we present accelerated aging data acquired on 18650-cells containing LiNi0.8Co0.15Al0.05O2- or LiNi0.8Co0.1Al0.1O2-based positive electrodes, MAG-10 graphite-based negative electrodes, and 1.2-M LiPF6 in EC:EMC (3:7 by wt.) electrolyte. Capacity and impedance data acquired on electrodes harvested from these cells highlight the contributions of the positive and negative electrodes to the degradation of cell performance. We also describe test methodologies used to examine the electrochemical characteristics of the harvested electrodes. Identifying and optimizing cell components responsible for performance degradation should enable the development of new lithium-ion cell chemistries that will meet the 15-year cell calendar life goal established by DOEs FreedomCar initiative.