Recently, investigations are focusing on Nickel-rich layered cathode active materials like LiNi0.8Co0.1Mn0.1O2 (NCM811) to improve the energy density of Lithium-ion batteries, providing reversible capacities of approximately 200 mAh g-1. Unfortunately, the increase in nickel-content comes along with a high sensitivity of the active material to moisture and carbon dioxide, which is why it is generally recommended to conduct production and processing at low dew points. [1] This leads to several challenges, as already existing production lines often do not provide the possibility of executing every process step at low dew point atmosphere. In addition, conducting the whole production route at low dew points would lead to a massive increase in costs, which also would have an impact on the consumer. Manufacturers aim at meeting these challenges by either doping or coating the bulk phase, among other things, but do not provide further detail about the bulk treatment or special requirements during electrode and cell production.
This is why three different NCM811 active materials (one doped monocrystalline, two coated polycrystalline materials) were used to produce and process LIB cathodes at normal ambient atmosphere in this study. For the necessary reduction of moisture before cell assembly [2, 3], two different intense post-drying procedures were investigated. From coating and drying up to cell assembly, the moisture content as well as microstructural properties (pore size distribution, adhesion strength, electrical resistance, SEM) were analyzed and compared to a NCM622 cathode. A recently developed model was applied to calculate the porosity of the conductive networks of the different cathodes. The electrochemical performance was finally tested in half coin cells.
Despite the production and processing at normal atmosphere, both polycrystalline NCM811 based cathodes obtained good physical and electrochemical properties with discharge capacities up to 199.6 mAh g-1 (after formation) after applying the more intense post-drying procedure. In contrast, the monocrystalline material showed superior performance. Due to their high nickel-content, all NCM811 cathodes contained high moisture levels in general, whereby a correlation between the porosity of the conductive network and the moisture content was detected. Overall, it was shown that Ni-rich active materials produced and processed at normal atmosphere can provide good cell properties and performance, when treated with a suitable post-drying procedure before cell assembly. The best properties were achieved by a polycrystalline NCM811. Future research is necessary to show whether the current results also apply to electrochemical long-term stability. Comparative investigations in dry room atmosphere will also be carried out.
[2] F. Huttner, W. Haselrieder, and A. Kwade, “The influence of different post‐drying procedures on remaining water content and physical and electrochemical properties of lithium‐ion batteries.” Energy Technology, 8, 1900245 (2019).
[3] F. Huttner, A. Marth, J. C. Eser, T. Heckmann, J. Mohacsi, J. K. Mayer, P. Scharfer, W. Schabel, and A. Kwade, “Design of vacuum post-drying procedures for electrodes of lithium-ion batteries.” Batteries & Supercaps, 4, 1499 (2021).