The Woodruff School

SUMMARY

Graphene, a two-dimensional honeycomb carbon layer, has drawn an intensive attention as a promising electrode material for rechargeable batteries and supercapacitors due to its high electrical conductivity and, chemical and physical stability. Recent progress of a large-scale synthesis of graphene oxide (GO) from graphite has boosted more investigation for conversion of GO to graphene. For energy storage applications, role of graphene can be largely categorized into two groups; A) A component for build-up of composite with various active materials. B) Graphene itself as an active material for charge storage. In the first group, graphene does not involved in electrochemical reaction to store charge or contribute to the amount of charge storage with very limited capacity or capacitance. In the first group, two sub topics, graphene-encapsulated submicron Si and two-dimensional functional carbon synthesis using graphene-template, were studied. The graphene-encapsulated submicron Si showed enhanced cycling stability up to 100 cycles with a capacity retention of 84%. The two-dimensional functional carbon exhibited high capacity of ~250 mAh g-1 in Li-cell due to the ultrathin functional carbon deposition on the graphene (less than 15 nm). In the second group, graphene actively participates in charge storage and thus graphene can be identified as an active material. It is known that an irreversible restacking of GO sheets during electrode preparation has limited the accessible surface area (ASA) to store ions, resulting in a low gravimetric capacity of ~100 mAh/g. In this section, crumpled graphene, which has an aggregation-resistive characteristic, was investigated as cathode material for Li-ion batteries. In addition, the crumpled graphene was studied as anode material for Na-ion batteries by controlling the oxygen functional groups on the crumpled graphene. To increase density of graphene electrodes, cabbage-like graphene was also prepared using pre-stacking process. The results in various applications using graphene would provide insights how graphene play an role for high performance energy storage.

SUBJECT:	Ph.D. Dissertation Defense

BY:	Byeongyong Lee

TIME:	Monday, July 30, 2018, 10:00 a.m.

PLACE:	MRDC Building, 3315

TITLE:	Graphene-Based Electrodes for High-Performance Electrochemical Energy Storage

COMMITTEE:	Dr. Seung Woo Lee, Chair (ME) Dr. Peter Hesketh (ME) Dr. Hailong Chen (ME) Dr. Seung Soon Jang (MSE) Dr. Thomas Fuller (CHBE)

SUMMARY Graphene, a two-dimensional honeycomb carbon layer, has drawn an intensive attention as a promising electrode material for rechargeable batteries and supercapacitors due to its high electrical conductivity and, chemical and physical stability. Recent progress of a large-scale synthesis of graphene oxide (GO) from graphite has boosted more investigation for conversion of GO to graphene. For energy storage applications, role of graphene can be largely categorized into two groups; A) A component for build-up of composite with various active materials. B) Graphene itself as an active material for charge storage. In the first group, graphene does not involved in electrochemical reaction to store charge or contribute to the amount of charge storage with very limited capacity or capacitance. In the first group, two sub topics, graphene-encapsulated submicron Si and two-dimensional functional carbon synthesis using graphene-template, were studied. The graphene-encapsulated submicron Si showed enhanced cycling stability up to 100 cycles with a capacity retention of 84%. The two-dimensional functional carbon exhibited high capacity of ~250 mAh g-1 in Li-cell due to the ultrathin functional carbon deposition on the graphene (less than 15 nm). In the second group, graphene actively participates in charge storage and thus graphene can be identified as an active material. It is known that an irreversible restacking of GO sheets during electrode preparation has limited the accessible surface area (ASA) to store ions, resulting in a low gravimetric capacity of ~100 mAh/g. In this section, crumpled graphene, which has an aggregation-resistive characteristic, was investigated as cathode material for Li-ion batteries. In addition, the crumpled graphene was studied as anode material for Na-ion batteries by controlling the oxygen functional groups on the crumpled graphene. To increase density of graphene electrodes, cabbage-like graphene was also prepared using pre-stacking process. The results in various applications using graphene would provide insights how graphene play an role for high performance energy storage.