SUMMARY

Graphene, a two-dimensional honeycomb carbon layer, has drawn an intensive attention for a promising electrode materials for Li- and Na-ion batteries (LIBs and NIBs) 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 graphene and GO. Utilization of graphene in energy storage systems can be mostly classified into two categories:1) graphene electrode 2) a component material for composites.

First, in the graphene electrode, an irreversible restacking of graphene oxide sheets during the preparation of the graphene electrode has limited the accessible area to store ions, resulting in a limited gravimetric capacity. In recent, crumpled graphene (CG) has introduced and CG has strong aggregation- and compression-resistive characteristics due to its unique 3D ball morphology, potentially proposing a solution to avoid the restacking issue and enhance the electrochemical performance. Thus, in my research, crumpled graphene oxide (CGO) was firstly introduced as cathodes in LIBs and anodes in NIBs by controlling functional groups on its surface.

Second, the graphene can be a good protection gear for large volume change materials, such as Si and Sn. It is known that Si shows dramatic volume variation up to 400% in LIBs, resulting in poor cycling stability. Although improved cycling stability can be achieved by employing nano-sized Si, nano-sized Si have scalability issues since the nano-sized Si is often synthesized by costly process. Herein, the carbon-coated submicron Si encapsulated with graphene was firstly investigated.