Titration Techniques for the Determination of Surface Species on Cathode Active Materials

Lithium ion batteries (LIBs) are the most important energy storage technology of our time. The number of LIBs has been constantly growing during the last years as well as the range of applications where LIBs are used, increasing the need for high energy density LIBs. One of the main cathode materials for high energy density LIBs is Ni-rich LiNi 0.8 Co 0.1 Mn 0.1 O 2 (NCM811). 1 Unfortunately, due to the high Ni content this material is extremely sensitive towards water which poses a particular challenge for more sustainable aqueous processing. Contact with even traces of moisture from the air causes immediate formation of surface species such as LiOH and Li 2 CO 3 . 2,3 The presence of these surface species not only leads to Li leaching from the structure and subsequent capacity loss but also facilitates side reactions with the electrolyte resulting in gas evolution and ultimately early failure of the battery. 4 Developing reliable methods for the quantification of these harmful surface species can provide a link between the amount of surface species and the detrimental impact on the cell performance. Here we employed different measurement techniques to quantify the amount of LiOH and Li 2 CO 3 on the NCM811 material surface. 5 Warder titration 6 and Winkler titration 7 are two methods that have been long known for the determination of hydroxides and carbonates. We optimized these techniques for the determination of very small quantities of surface carbonate or hydroxide by testing the sensitivity for small lab size quantities of material and removing the possibility of additional CO 2 uptake through the air. Titration as a way to quantify the amount of LiOH and Li 2 CO 3 is a valuable measurement technique that can help to predict performance issues of the battery and can serve as a tool for quality control of cathode active materials. References (1) Armand, M.; Axmann, P.; Bresser, D.; Copley, M.; Edström, K.; Ekberg, C.; Guyomard, D.; Lestriez, B.; Novák, P.; Petranikova, M.; Porcher, W.; Trabesinger, S.; Wohlfahrt-Mehrens, M.; Zhang, H. J. Power Sources 2020 , 479 , 228708. (2) Hofmann, M.; Kapuschinski, M.; Guntow, U.; Giffin, G. A. J. Electrochem. Soc. 2020 , (3) Jung, R.; Morasch, R.; Karayaylali, P.; Phillips, K.; Maglia, F.; Stinner, C.; Shao-Horn, Y.; Gasteiger, H. A. J. Electrochem. Soc. 2018 , 165 (2), A132–A141. (4) Kim, Y. J. Mater. Sci. 2013 , 48 (24), 8547–8551. (5) Schuer, A. R.; Kuenzel, M.; Yang, S.; Kosfeld, M.; Mueller, F.; Passerini, S.; Bresser, D. J. Power Sources 2022 , 525 (231111). (6) Benedetti-Pichler, A. A.; Cefola, M.; Waldman, B. Ind. Eng. Chem. - Anal. Ed. 1939 , 11 (6), 327–332. (7) Winkler, C. Praktische Übungen in Der Maßanalyse , 5. Auflage.; Verlag von A.Felix: Leipzig, 1920.