Department of Energy Engineering (Battery Science and Technology)Aprotic electrolyte based lithium-oxygen batteries are of considerable interest due to its ultrahigh theoretical specific energy density (1675 mAh per gram of oxygen) against the present lithium-ion battery. In spite of the attractiveness of its high theoretical capacity, there is a number of drawbacks such as instability of electrochemical reaction of electrode and electrolytes. In order to overcome these parasitic reactions, significant efforts have been devoted to developing the key materials such as carbon-free air cathodes and high concentrated electrolytes. However, the CO2 evolution during the charging process and low ionic conductivity limit the ideal electrochemical reaction in aprotic electrolytes.
In this thesis, we applied the molten electrolyte based on nitrate-based electrolyte (Li/Na/K/Cs/Ca-NO3). The molten electrolyte, which has a eutectic point of 65???, has the advantages of high stability and high-temperature operation, thereby preventing detrimental solvent byproducts in lithium-oxygen batteries. We examined the Oxygen Evolution Reaction (OER) and Oxygen Reduction Reaction (ORR) on operating temperature using in situ pressure drop and gas analyses, Differential Electrochemical Mass Spectrometry (DEMS). Our results demonstrated that the Li2O2, a discharge product, formed a stable hexagonal morphology in the lithium-oxygen battery upon discharge process by scanning electron microscopy and X-ray diffraction techniques. Also, it leads to improved oxygen mobility at high temperature since a molten salt was used as the electrolyte in lithium-oxygen batteries. In addition, we found that kinetics are improved with increasing operating temperature in molten salt electrolyte cells.ope
