Operando Analysis of Li Plating on Graphite Anodes During Fast Charging of Li-Ion Batteries

The rapidly growing EV market is increasing the demand for fast-charging (&lt;15 min) of high-energy-density Lithium (Li)-ion batteries. However, state-of-art Li-ion batteries with thick graphite electrodes suffer from Li plating when charged at &gt;4C rates. Therefore, to inform mitigation strategies for Li plating under fast-charging conditions, there is a need to improve our fundamental understanding of the Li plating process.<br/><br/>In this work, I will present two recent studies on <i>operando</i> detection and characterization of Li plating on graphite anodes. In the first study, plan-view <i>operando</i> video microscopy was performed on &gt;3 mAh cm^- graphite electrodes during 6C charging [1]. During a 6C charging half-cycle, the cell was used to visualize the spatial heterogeneity of SoC across the electrode surface, and the nucleation and growth of the plated Li. During the subsequent open circuit voltage (OCV) rest and discharge steps, the re-interaction of the plated Li into graphite was also studied. Furthermore, a 3D understanding of the changes across the electrode volume was developed by performing <i>ex situ</i> cross-sectional microscopy. Finally, pouch cells were fabricated to confirm the voltage signature associated with dead Li formation in a commercially relevant cell format.<br/><br/>In the second study, we built upon this understanding to demonstrate a new method for <i>operando </i>detection of Li plating during fast charging, using incremental capacity (IC) analysis [2]. To identify the electrochemical signature of plating, 3-electrode pouch cells were assembled, allowing for a correlation of the IC curve with the onset of Li nucleation. This was validated using post mortem microscopy, to demonstrate the ability to uniquely identify the onset of Li plating with high resolution. This provides a pathway towards advanced control and mitigation strategies to enable fast charging while eliminating the most deleterious side reactions within the cell.<br/><br/>[1] Y. Chen, K.-H. Chen, A. J. Sanchez, E. Kazyak, V. Goel, Y. Gorlin, J. Christensen, K. Thornton, N. P. Dasgupta. <i>J. Mater Chem. A </i><b>9</b>, 23522 (2021).<br/>[2] Y. Chen, L. Torres-Castro, K.-H. Chen, D. Penley, J. Lamb, N. P. Dasgupta, <i>J. Power Sources </i><b>539</b>, 231601 (2022).