Fabrication of graphene oxide and graphene foams for Li-ion batteries

Official URL: https://risc01.sabanciuniv.edu/record=b2352876 _ (Table of contents)

Graphene based materials are very promising owing to their fascinating characteristics such as extremely tunable surfaces, outstanding electrical conductance, good chemical stability and outstanding mechanical performance for energy storage applications. This project summarizes recent developments on 3D graphene network electrodes for Li-ion battery applications. A foam-like graphene material can be prepared by chemical vapor deposition and hydrothermal reduction of graphene oxide suspensions. The graphene foam has a much higher capacity than conventional graphite anode, and it possesses better rate capability as compared to powder like graphene active materials. A new super-light graphene aerogel (GA) was effectively synthesized with a high electrical technique using a low cost and accessible method. More importantly, our synthesis approach compared to the common graphene oxide (GO) reduction temperature (180 °C) involves low temperature (95°C) where the promising GO reduced with different reducing agents is achieved through freezing. In this work, we systematically investigate the effects of various reducing agents including ammonia, hydro-iodic acid, and ascorbic acid at different hydrothermal reaction time (4, 8, 24 hours) and reducing agent dosages (0, 50, 120, 200 μL) on the formation of foam, electrical conductivity, and morphology of GA. The results reveal that graphene aerogel reduced by ascorbic acid possesses the most outstanding performance on mechanical strength and reutilization but has moderate electrical conductivity (9.4 S/m). Whereas, the sample obtained with HI exhibits the highest electrical conductivity (12.1 S/m). However, this sample reveals poor mechanical strength. The graphene aerogel reduced by ammonia is very sensitive to the reaction time and temperature and has moderate mechanical strength and the lowest electrical conductivity (7.5 S/m). Therefore, ascorbic acid is a very promising reducing agent for the hydrothermal process as the resulted graphene aerogel had good electrical conductivity and great mechanical strength