Lithium-oxygen (Li-O2) batteries have attracted attention in the last decade for their remarkable theoretical energy density of 3,500 Wh kg-1 when mass of lithium and oxygen are counted which is over 10 times higher than that of conventional lithium-ion (Li-ion) batteries. However, cells have not yet demonstrated to be rechargeable as the internal reactions are highly unstable. The oxygen-rich environment in combination with a wide potential window and the presence of lithium promote uncontrolled and irreversible reactions in the cell. A fundamental understanding of the mechanisms behind the various complex reactions was the approach taken in this thesis. The targeted reaction should result in the reversible formation of lithium peroxide (Li2O2). Here, the characterization of Li2O2 formation in air electrode via titration techniques and electrochemical impedance spectroscopy (EIS) was proposed as a Master of Science thesis study. This research evaluated various carbon materials with different surface area and pore volumes and correlated it to the discharge capacity, yield of the desired discharge product (Li2O2), discharge-charge voltage profiles and the impedance spectra of the cell. Three testing techniques, life cycle testing, Li2O2 titration and EIS, provided the different perspectives on the complex chemical mechanisms in Li-O2 batteries. The results of this study showed slight variation in Li2O2 yield across the different carbon cathodes. Furthermore, the electrolyte decomposition was confirmed to be the main factor to the overall yield. As expected, the specific capacity significantly varied from carbon to carbon and the voltage profiles were demonstrated to be dependent on the carbon cathode. Lastly, the impedance spectrum showed to correlate to the discharge capacity of the battery but not directly to the Li2O2 yield
