Development of Metal & Metal Oxides Decorated Graphene-Based Electrode Materials for Next Generation Li-ion and Li-O2 Batteries
Adnan Taşdemir
Materials Science and Engineering, PhD Dissertation, 2020
Thesis Jury
Prof. Dr. Selmiye Alkan Gürsel (Thesis Advisor),
Asst. Prof. Dr. Alp Yürüm (Thesis Co-Advisor),
Prof. Dr. Ayşe Gül Gürek
Assoc. Prof. Dr. Fevzi Çakmak Cebeci
Asst. Prof. Dr. Mustafa Kemal Bayazıt
Date & Time: September 3rd, 2020 – 10:30 AM
Place: FENS G032
Zoom link: https://zoom.us/j/92322524548?pwd=aUwvQ1NteGg3VGl2c0F4eVltbXBjUT09
Keywords: Lithium-oxygen batteries, Li-ion batteries, air cathode, anode, CeO2 nanorods, silicon, TiO2-B, lithium iodide, nitrogen doped reduced graphene oxide, high cycle performance
Abstract
The graphene oxide (GO) utilized in this study was synthesized by the improved Hummers’ method. Then a straightforward, one-step thermal route has been established to fabricate reduced- (rGO) and nitrogen-doped reduced graphene oxide (NrGO) electrodes with remarkable lithium-ion storage properties. The electrochemical properties of the rGO and NrGO electrodes have been extensively comparedin a Li-ion half-cell. The NrGO electrodes exhibited a reversible capacity of 240 mAhg-1 at a high current of 10 Ag-1 after 500 cycles of operation with 90 % capacity retention.
Further, we have investigated the synergistic effect of NrGO and nanotubular TiO2 to achieve high rate capabilities with high discharge capacities through a simple, one-step and scalable method. First, hydrogen titanate nanotubes were hydrothermally grown on the surface of NrGO sheets and then converted to a mixed phase of TiO2-B and anatase by thermal annealing. The prepared anode showed a stable discharge capacity of 150 mAhg-1 at 1C current rate after 50 cycles.
Moreover, we introduced a simple and cost-effective spray-drying method to fabricate a layered (sandwich-like) anode structure using Si nanoparticles (NPs) and rGO. The Si NPs were synthesized by the magnesiothermic reduction of SiO2 nanoparticles. By a scalable and straightforward spraying/drying method, we embedded Si NPs between two layers of rGO sheets. The sandwich-like structure, which successfully contains the expansion of Si particles, protects the anode from detrimental conditions. With this new and uncomplicated production technique, the rGO-Si-rGO anode after 50 cycles, shows a high specific capacity of 1089 mAhg-1 at 1C with 97% coulombic efficiency and a stable cycling performance at current densities up to 5C.
Lastly, cerium (IV) oxide (CeO2) nanorods were synthesized by hydrothermal treatment and supported on NrGO by another hydrothermal step. Herein, CeO2/NrGO catalyst materials were studied as an Li-O2 cathode using an aprotic electrolyte, which includes lithium iodide (LiI) as a redox mediator. The results showed that the novel catalyst hybrid of CeO2 and NrGO with LiI directly increased the electrochemical performance of Li-O2 battery. Their synergetic effect improved the kinetics of OER and ORR. The impact of LiI on CeO2/NrGO by comparing bare NrGO air cathode was investigated for the first time in this study. The addition of LiI decreased the overpotential up to 0.78 V in CeO2/NrGO air cathode. CeO2/NrGO were tested at the different current densities and revealed a maximum capacity of 5040 mAhg-1 at 25 mAg-1 current density.