Synthesis of graphen-supported MnO2-based hybrid nanocomposides and characterization of electrochemical properties

Technological devices that have completely changed our lifestyle have brought the need for energy. John B. Goodenough, M. Stanley Whittingham and Akira Yoshino were awarded the 2019 Nobel chemistry prize for their contributions to the development of rechargeable lithium-ion battery technology, which is the energy source that most affects our daily lives. However, lithium-ion batteries have to be developed in order to be used not only in portable devices, but also in electric vehicles and sustainable energy sources. A typical commercial lithium-ion battery uses a graphite anode with a specific capacity of 372 mAh/g and a lithium cobalt oxide cathode with a specific capacity of 137 mAh/g. Higher energy capacity, lower cost, use of environmentally friendly materials and harmless production methods are demanded from lithium-ion batteries, which are aimed to be used as the energy source of the future. In this doctoral thesis, MnO2 was chosen as the active material in order to produce durable and high-performanced cathodes for lithium-ion batteries at low cost. Different MnO2 polymorphs were produced by the mild chemical method, microwave assisted hydrothermal method. Graphene with superior properties was chosen as the support material. Graphene was obtained by using two different methods, by chemical and thermal reduction of graphene oxide produced by the modified Hummers method. The produced MnO2 polymorphs were combined with reduced graphene oxides to form free electrodes. The electrochemical tests of the free electrode form cathodes were carried out in a half cell and the cathode with the best performance was determined as AKİGO (321 mAh/g). Cathode performance is improved by applying Co doping and carbon coating processes to the selected cathode. The optimized cathode is combined with the LTO anode, resulting in an initial discharge capacity of 324 mAh/g in full-cell performance. After the full-cell tests, the battery was opened and the post-cycle cathode and anode structure was examined.