| Description |
The rechargeable Li-O2 battery is still in its infancy. More studies are required before a commercial product can be reached. My research aims at the major hurdles in current research, such as the fundamental mechanism and the high overpotential of the electrochemical reactions. In this dissertation, firstly, I demonstrated the mass and charge transport relevant to the formation of toroidal Li2O2 nanoparticles during the discharge/charge cycles in an aprotic Li-O2 cell. The accumulations of the discharge product Li2O2 not only clog the O2 pathway in the cathode, but also hinder the charge transfer process. Overfull Li2O2 requires extra energy to break its chemical bonds during charge, and causes a high charge overpotential. Electrocatalysts were employed to lower the charge overpotential. In the second part of this dissertation, atomic layer deposition (ALD) was used to deposit nanostructured palladium on porous carbon as the cathode material for Li-O2 cells. STEM showed discrete crystalline nanoparticles decorating the surface of the porous carbon support, where the size could be controlled in the range of 2-8 nm depending on the number of Pd ALD cycles performed. X-ray absorption spectroscopy at the Pd K-edge revealed that the carbon supported Pd existed in a mixed phase of metallic palladium and palladium oxide. The conformality of ALD allowed us to uniformly disperse the Pd catalyst onto the carbon support while preserving the initial porous structure. As a result, the charging and discharging performance of the oxygen cathode in a Li-O2 cell was improved. These results suggest that ALD is a promising technique for tailoring the surface composition and structure of nanoporous supports in energy storage devices. Furthermore, uniformly dispersed Pd nanoparticles on ZnO-passivated porous carbon were synthesized via an atomic layer deposition (ALD) technique, which was tested as a cathode material in a rechargeable Li-O2 battery, showing highly active catalytic effect towards the electrochemical reactions, in particular, oxygen evolution reaction. Transmission electron microscopy showed discrete crystalline nanoparticles decorating the surface of the ZnO-passivated porous carbon support, where the size could be controlled in the range of 3-6 nm depending on the number of Pd ALD cycles performed. X-ray absorption spectroscopy at the Pd K-edge revealed that the carbon supported Pd existed in a mixed phase of metallic palladium and palladium oxide. These results suggest that ALD is a promising technique for tailoring the surface composition and structure of nanoporous supports for Li-O2 batteries. |
