Impact of Fast-Charging Rates on Electrode Degradation in NMC/Gr Pouch Cells

With the rapid expansion of the electric vehicles market, fast charging lithium-ion batteries has become increasingly imperative and inevitable. However, as fast-charging technologies entering electric vehicle market, persistent challenges related to safety issue and cell degradation, such as lithium dendrite growth, thermal runaway etc. necessitate meticulous consideration. In this study, we investigated fast-charging rate effects on electrode degradation in 1.6 Ah pouch cells using LiNi0.5Mn 0.3Co 0.2O2 cathode and graphite anode provided by Nanoramic Laboratories. Our investigation involves a comparative analysis of the aging behavior of NMC/Gr cells subjected to various charging rates — 0.5C, 2C, 4C, and 6C. Notably, we observed that pouch cells charged at rates of 0.5C and 2C could persist 80% capacity retention over 1000 cycles while cells using 4C and 6C can survive no more than 400 cycles with 80% retention. Through a series of post-mortem characterizations, including electrochemical impedance spectroscopy (EIS), Raman, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) with energy dispersive X-ray spectroscopy (EDS), we scrutinized the harvested NMC and graphite electrodes. As expected, more dendrite formation was observed on graphite anodes with 4C and 6C fast charging rates. The deterioration of cell performance primarily resulted from the degradation of the graphite anode. This degradation could be attributed to distinct dendrite morphologies at the graphite anode under varying charging rates (see Fig. 1). In addition to dendrite formation on graphite electrodes, we observed more severe pulverization of NMC secondary particles under higher charging rates despite their lower cycle numbers. This investigation provides a comprehensive understanding of how NMC and graphite degrade under different charging rates, offering valuable insights into the practical impacts of charging rates on cell lifespan and highlighting potential challenges that need to be addressed. Acknowledgement This material is based upon work supported by the U. S. Department of Energy’s Office of Energy Efficiency and Renewable Energy (EERE) under the Advanced Manufacturing Office, award number DE-EE0009111. Argonne National Laboratory is operated for DOE Office of Science by UChicago Argonne, LLC under contract number DE-AC02-06CH11357 Figure 1