Evolution of Interfacial Cathode Kinetics in Sulfide All-Solid-State Li Batteries Measured with Electrochemical Impedance Spectroscopy (EIS)

Sulfide all-solid-state Li batteries (ASLBs) suffer from a large capacity loss on the first cycle jeopardizing their commercialization and energy density. This large initial coulombic mismatch is theorized to be due to formation of the cathode electrolyte interface (CEI) and volume changes in the cathode material resulting in increased internal resistance and a loss of electrochemically active surface area respectively.¹ We have previously reported an operando analysis of Li⁺ and e^- conduction across a composite cathode based on Li-Ni_1/3Mn_1/3Co_1/3O₂ (NMC111) and Li₆PS₅Cl (LPSC) during initial cycling.² This analysis indicated that conduction during initial cycling was subject to high tortuosity factors (t²) for both the LPSC and NMC phases. Additionally, the t² values evolved during the initial battery charge step. Because cathode performance was limited by conduction, we were unable to infer information about kinetic phenomena, e.g. the charge transfer rate between LPSC and NMC, from the experimental results. In particular, the first cycle capacity loss may be caused by a drop in interfacial kinetics.<br/><br/>To study this capacity loss as a function of state-of-charge, in situ EIS was performed during initial cycling of a full cell with a composite cathode based on NMC111 and LPSC (Li/In| Li₆PS₅Cl| NMC111/Li₆PS₅Cl). This piecewise EIS allows us to analyze both time dependent and state-of-charge dependent interfacial processes while the battery cycles with no modifications to cell design. A transmission line model allowed for quantification of the electrochemically active surface area and its effect on resulting capacity during the first charge of this ASLB system.<br/><br/><b>Acknowledgments </b><br/>We acknowledge financial support from the National Science Foundation under Award Number CBET-ES- 1924534.<br/><br/><b>References </b><br/>1. Koerver, R.; Aygün, I.; Leichtweiß, T.; Dietrich, C.; Zhang, W.; Binder, J. O.; Hartmann, P.; Zeier, W. G.; Janek, J., Capacity Fade in Solid-State Batteries: Interphase Formation and Chemomechanical Processes in Nickel-Rich Layered Oxide Cathodes and Lithium Thiophosphate Solid Electrolytes. <i>Chemistry of Materials </i><b>2017,</b> <i>29</i> (13), 5574-5582.<br/>2. Stavola, A.M.; Sun, X.; Guida, D.P.; Bruck, A.M.; Cao, D.; Okasinski, J.S.; Chuang, A.C.; Zhu, H.; and Gallaway, J.W. "Lithiation Gradients And Tortuosity Factors In Thick NMC111-Argyrodite Solid-State Cathodes," <i>ACS Energy Letters</i>, <b>2023</b>, 8, 1273−1280.