Herstellung und Charakterisierung bifunktioneller Metalloxid-Sauerstoffelektroden für hochenergetische Lithium-Luft-Batterien

Kurzfassung

Current research at the German Aerospace Center is among others focused on metal-air-batteries. Lithium-air-batteries promise the highest energy density out of these battery types. Major problems of lithium-air-batteries are high overpotentials during charge and discharge processes and lacking long cycle stability. For economic reasons it is aspired to substitute expensive noble metal catalysts by more inexpensive metal oxide catalysts. Cathodes based on cobalt oxide are a relatively low-cost and promising option. This thesis includes the preparation, characterization and optimization of such cobalt oxide cathodes. Nickel was used as conductor for the carbon free electrode. The electrodes were optimized in structure and composition by variation of different parameters. To increase performance especially in oxygen reduction reaction (ORR), cobalt oxide was added step by step as catalyst until the optimum balance between catalyst and conductor was found. Based on an electrode with 20 wt.% cobalt oxide, the next step aimed at determining the optimum amount of the binder polytetrafluorethylen (PTFE) which was finally set at 6 wt.% PTFE. Research on electrode thickness and on influences of porosity can be found in chapter “structural optimizations”. Due to the pre-defined benchmarks of the standard electrode, a variation of those two parameters did not result in another performance improvement. For the electrochemical characterization of the electrodes, different in-situ and ex-situ methods were used. Methods like XRD, REM and Hg-porosimetry enabled research concerning structure and composition of the electrode. Electrochemical characterization of the different electrodes was conducted by electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV) and conductivity measurements.