The Formation of Residual Li Compounds on Ni-Rich NCM Cathodes and Their Effect on the Electrochemical Performance in LPSCl-Based ASSBs

LiNi_xCo_yMn_(1-x-y)O₂ (NCM) type lithium transition metal oxides with high nickel concentrations have attracted a significant interest as a cathode material in lithium ion batteries due to their high energy density and low cobalt content, however, their reactivity with air during storage/handling and how this affects the electrochemical performance had been overlooked until the recent years. Exposure to H₂O and CO₂ during air storage/handling can lead to formation of LiOH, Li₂CO₃ and also transition metal hydroxides/carbonates.^1,2 The formation of such Li-compounds can also cause structural changes near the surface of cathode particles.³ Therefore, it is very important to understand how these residual Li compounds are formed and how they affect the electrochemical performance. In all-solid-state batteries (ASSBs), the presence of Li₂CO₃ may improve the electrochemical performance in sulfide-based solid electrolytes,^4,5 however, there has been no dedicated study aiming to understand relationship between the cell performance and the presence of specific residual Li compounds. In this study, we prepare single crystal LiNi_0.83Mn_0.06Co_0.11O₂ powders with different residual Li amounts and compositions by either carefully controlling the washing, post-annealing, the ambient air exposure (e.g. humidity and CO₂ concentrations) conditions, or applying coatings with an external Li source. Characterization of these powders will be presented with valuable insights gained from a number of analytical techniques such as XPS, TOF-SIMS, TGA-MS, FIB-SEM, acid titration and XRD. In the next step, the relationship between the residual Li type/amount and the electrochemical performance will be evaluated in ASSB cells with Li₆PS₅Cl solid electrolyte and In-Li alloy counter electrode.<br/><br/>(1) Sicklinger, J.; Metzger, M.; Beyer, H.; Pritzl, D.; Gasteiger, H. A. Ambient Storage Derived Surface Contamination of NCM811 and NCM111: Performance Implications and Mitigation Strategies. <i>J. Electrochem. Soc.</i> <b>2019</b>, <i>166</i>, A2322–A2335.<br/>(2) Kim, Y.; Park, H.; Warner, J. H.; Manthiram, A. Unraveling the Intricacies of Residual Lithium in High-Ni Cathodes for Lithium-Ion Batteries. <i>ACS Energy Lett.</i> <b>2021</b>, 941–948.<br/>(3) Zhang, L.; Gubler, E. A. M.; Tai, C.-W.; Kondracki; Sommer, H.; Novák, P.; Kazzi, M. El; Trabesinger, S. Elucidating the Humidity-Induced Degradation of Ni-Rich Layered Cathodes for Li-Ion Batteries. <i>ACS Appl. Mater. Interfaces</i> <b>2022</b>, acsami.1c23128.<br/>(4) Jung, S. H.; Oh, K.; Nam, Y. J.; Oh, D. Y.; Brüner, P.; Kang, K.; Jung, Y. S. Li3BO3-Li2CO3: Rationally Designed Buffering Phase for Sulfide All-Solid-State Li-Ion Batteries. <i>Chem. Mater.</i> <b>2018</b>, 30, 22, 8190–8200<i> </i><br/>(5) Kim, A. Y.; Strauss, F.; Bartsch, T.; Teo, J. H.; Hatsukade, T.; Mazilkin, A.; Janek, J.; Hartmann, P.; Brezesinski, T. Stabilizing Effect of a Hybrid Surface Coating on a Ni-Rich NCM Cathode Material in All-Solid-State Batteries. <i>Chem. Mater.</i> <b>2019</b>, <i>31</i>, 9664–9672.