Titration methods for the determination of hydroxides and carbonates in lithium metal oxide cathode materials

Summary:

With lithium-ion batteries (LIBs) being one of the most important energy storage technologies today, there is also an increasing need for LIB production to become more sustainable.1 For the anode, aqueous processing has already been realised, eliminating the use of harmful N-methyl-2-pyrrolidone (NMP) during electrode fabrication.2 Unfortunately, the main obstacle to the implementation of aqueous processing of cathode active materials is the fact that they are very sensitive towards water. Contact with water leads to reactions on the cathode active material surfaces, and most prominently to the formation of surface species, i.e. LiOH and Li2CO3. The detection and quantification of these surface species is of outermost interest as it can be used as a method for quality control by allowing conclusions about pre-treatment, e.g. washing procedures. Moreover, performance issues of the material can be predicted as they have been linked to surface contaminations like LiOH and Li2CO3.3 Warder titration is a well-known method for the quantification of carbonates and hydroxides that is frequently used in research and industry.4,5 However, the method is optimized for large volumes of sample and large amounts of cathode active materials. Here, we are investigating different approaches for the Warder titration to increase the accuracy of the measured carbonate and hydroxide amounts in small samples. To prevent overestimation of hydroxide, the stirring time and titration medium was optimized. The titration set-up was adjusted to lab-scale quantities and tailored to avoid any additional carbon uptake from the air. Additionally, different powder-to-liquid ratios are investigated in order to find the optimum conditions for the determination of LiOH and Li2CO3 in small, lab-scale amounts of cathode active material powders.

References
(1) Marinaro, M.; Bresser, D.; Beyer, E.; Faguy, P.; Hosoi, K.; Li, H.; Sakovica, J.; Amine, K.; Wohlfahrt-Mehrens, M.; Passerini, S. Bringing Forward the Development of Battery Cells for Automotive Applications: Perspective of R&D Activities in China, Japan, the EU and the USA. J. Power Sources 2020, 459 (March), 228073. https://doi.org/10.1016/j.jpowsour.2020.228073.
(2) Asenbauer, J.; Eisenmann, T.; Kuenzel, M.; Chen, Z.; Bresser, D. The Success Story of Graphite as a Lithium-Ion Anode Material – Fundamentals, Remaining Challenges, and Recent Developments Including Silicon (Oxide) Composites. Sustain. Energy Fuels 2020, 4 (11). https://doi.org/10.1039/d0se00175a.
(3) Kuenzel, M.; Bresser, D.; Diemant, T.; Carvalho, D. V.; Kim, G. T.; Behm, R. J.; Passerini, S. Complementary Strategies Toward the Aqueous Processing of High-Voltage LiNi0.5Mn1.5O4Lithium-Ion Cathodes. ChemSusChem 2018, 11 (3), 562–573. https://doi.org/10.1002/cssc.201702021.
(4) Bichon, M.; Sotta, D.; Dupré, N.; De Vito, E.; Boulineau, A.; Porcher, W.; Lestriez, B. Study of Immersion of LiNi0.5Mn0.3Co0.2O2 Material in Water for Aqueous Processing of Positive Electrode for Li-Ion Batteries. ACS Appl. Mater. Interfaces 2019, 11 (20), 18331–18341. https://doi.org/10.1021/acsami.9b00999.
(5) Winkler, C. Praktische Übungen in Der Maßanalyse, 5. Auflage.; Verlag von A.Felix: Leipzig, 1920.