Li Plating Detection during Extreme Fast Charging of Li-Ion Batteries Using Operando Impedance Spectroscopy

Abstract

To promote the continued growth of the electric vehicle (EV) market—as well as to improve the performance of other battery-powered technologies such as phones, laptops, and drones—Li-ion battery charging times need to be significantly reduced. At higher charging rates, Li metal may plate on the graphite anode, which is a possible safety concern and leads to decreased cycle life of the battery.1 To date, no work has demonstrated a consistently reliable technique to detect the onset of Li plating in operando.2 Previous work has included dV/dQ analysis of discharge profiles after fast charging,3,4 impedance analysis after fast charging5 and during pseudo-operando measurements,6 dV/dt analysis of voltage relaxation profiles after fast charging,5,6 three electrode graphite potential monitoring,4 and simple optical inspection after many fast charging cycles, among other techniques.2 Our group has also developed ex situ mass spectrometry titrations to detect and quantify electrically isolated Li deposits,7 as well as an improved dV/dt technique to detect the onset of Li plating after fast charging.8 In this work, we use impedance spectroscopy—and specifically the Distribution of Relaxation Times (DRT) analysis method9—to detect in operando the onset of Li plating. There is a change in the graphite interfacial impedance upon Li plating on the graphite surface. Coupled with differential voltage relaxation for cross-validation, we can reliably detect the Li plating onset graphite state of charge (SOC) for rates as high as 6C at room temperature and for different graphite loadings with ~1% graphite capacity sensitivity. Three electrode cell measurements will be shown here, as well as some promising data from more applicable two electrode cells. We also see variation in the impedance for fast versus slow plating, and we discuss possible physical explanations for this behavior. This capability to detect the onset of Li plating allows for the safe implementation of fast charging protocols. References Y. Liu, Y. Zhu, and Y. Cui, Nat Energy, 4, 540–550 (2019). T. Waldmann, B.-I. Hogg, and M. Wohlfahrt-Mehrens, Journal of Power Sources, 384, 107–124 (2018). K. G. Gallagher, D. W. Dees, A. N. Jansen, D. P. Abraham, and S.-H. Kang, J. Electrochem. Soc., 159, A2029–A2037 (2012). C. Uhlmann, J. Illig, M. Ender, R. Schuster, and E. Ivers-Tiffée, Journal of Power Sources, 279, 428–438 (2015). S. Schindler, M. Bauer, M. Petzl, and M. A. Danzer, Journal of Power Sources, 304, 170–180 (2016). U. R. Koleti, T. Q. Dinh, and J. Marco, Journal of Power Sources, 451, 227798 (2020). Eric J. McShane et al., ACS Energy Letters, submitted (2020). Zachary M. Konz, Eric J. McShane, and Bryan D. McCloskey, ACS Energy Letters, submitted (2020). E. Ivers-Tiffée and A. Weber, J. Ceram. Soc. Japan, 125, 193–201 (2017).