Implications of Aqueous Processing for High Energy Density Cathode Materials. Part I. Ni-Rich Layered Oxides
Combining the use of nickel-rich layered oxide cathode materials with the implementation of aqueous electrode processing can pave the way to cost-reduced and environmentally friendly electrodes and simultaneously increase the energy density of cells. Herein, LiNi0.33Co0.33Mn0.33O2 (NCM111), LiNi0.6Co0.2Mn0.2O2 (NCM622), LiNi0.8Co0.1Mn0.1O2 (NCM811) and LiNi0.8Co0.15Al0.05O2 (NCA) were evaluated in terms of their response to aqueous processing under the same conditions to facilitate a direct comparison. The results illustrate that mainly nickel driven processes lead to lithium leaching which is combined with the increase of the pH value in the alkaline region. For NCA an additional aluminum-involving lithium leaching mechanism is assumed, which could explain the highest amount of leached lithium and the additional detection of aluminum. Electrochemical tests show a reduced capacity for cells containing water-based electrodes compared to reference cells for the NCM-type materials which increases during the first cycles indicating a reversible Li+/H+-exchange mechanism. In contrast, the NCA cells were completely electrochemically inactive making NCA the most water sensitive material tested in this report. By comparing the cycling performance of cells containing aqueous processed electrodes, a more pronounced capacity fade for nickel-rich cathode materials as compared to their reference cells can be observed.