Kinetics of Lithium Insertion and Plating on Basal and Edge Planes of Graphite

Abstract

Lithium-ion batteries (LIBs) with graphitic anodes dominate the energy storage market1, 2, and it is of interest to accelerate charging of LIBs for a number of applications, especially electric vehicles. A common issue upon fast charging is that parts of a graphitic anode are polarized to negative voltages vs Li/Li+, leading to lithium plating3. The reversibility of Li plating on graphitic anodes is poor, and Li plating leads to exothermic reactions with standard electrolytes, and can lead to dendrite growth and shorts in the cell3. It is therefore of interest to understand the onset of Li plating, and the maximum current that can be sustained without plating.In commercially relevant cells such measurements are complicated by the three-dimensional porous composite nature of the anode and its interaction with an electrolyte whose lithium concentration at the interface with the graphite varies as a function of depth within the electrode during fast charging4, 5. The goal of our work is to determine the fundamental kinetics of Li intercalation and plating at edge and basal plane graphite surfaces by performing fast charging experiments using highly oriented pyrolytic graphite (HOPG) samples.HOPG consists of a stack of graphite planes, with in-plane grain sizes on the order of 0.1 mm, enabling such measurements at a well-controlled current density. We confirm that Li intercalation occurs almost exclusively at edge planes, and show that current densities above 1 mA/cm2 can be sustained at pristine edge surfaces (see figure, which shows potential as a function of linearly increasing current density). We also show that Li plating can nucleate on both edge and basal planes with an overpotential below 0.1 V, and explore the differences in Li insertion rate and plating overpotential for different stages of graphite.Funding was provided by the U.S. DOE Office of Vehicle Technology Applied Battery Research and Extreme Fast Charge Program (XCEL). T. Placke, R. Kloepsch, S. Dühnen and M. Winter, Journal of Solid State Electrochemistry, 2017, 21, 1939-1964.N. Nitta, F. Wu, J. T. Lee and G. Yushin, Materials Today, 2015, 18, 252-264.Q. Liu, C. Du, B. Shen, P. Zuo, X. Cheng, Y. Ma, G. Yin and Y. Gao, RSC Advances, 2016, 6, 88683-88700.A. M. Colclasure, A. R. Dunlop, S. E. Trask, B. J. Polzin, A. N. Jansen and K. Smith, Journal of The Electrochemical Society, 2019, 166, A1412-A1424.A. M. Colclasure, T. R. Tanim, A. N. Jansen, S. E. Trask, A. R. Dunlop, B. J. Polzin, I. Bloom, D. Robertson, L. Flores, M. Evans, E. J. Dufek and K. Smith, Electrochimica Acta, 2020, 337, 135854. Figure 1