1Department of Chemical & Biomolecular Engineering, Faculty of Engineering, National University of Singapore, 10 Kent Ridge Crescent, Singapore, 119260; Tel: (65) 65162186; E-mail: email@example.com.
2Key Laboratory of Organic Synthesis of Jiangsu Province, Key Laboratory of Absorbent Materials and Techniques for Environment, College of Chemical, Chemical Engineering and Materials Science, Soochow University, Suzhou, China, 215123; E-mail: firstname.lastname@example.org
In this work we combined the unique properties of graphene sheets and a hollow assembly of nanoparticles to simultaneously provide large reversible Li+ storage capacity, good rate performance and long cycle life. Specifically graphene-encapsulated ordered aggregates of Fe3O4 nanoparticles with nearly-spherical geometry and hollow interior (G-HPM) were synthesized by a simple self-assembly process. The HPM particles were first prepared by a one-pot hydrothermal synthesis. They were then modified by 3-aminopropyltriethoxysilane (KH550) to acquire a positive surface charge, which enabled electrostatic assembly with negatively charged graphene oxide. Finally, a chemical reduction was used to reduce the graphene oxide to graphene; finalizing the packaging of HPM particles in individual graphene cages. This assembly could be carried out under relatively mild conditions; thereby minimizing the perturbations to the properties of HPM. In our design, the open interior structure has adapted well to the volume change in repetitive Li+ insertion and extraction reactions; and the encapsulating graphene connects the Fe3O4 nanoparticles electronically. The composite particles showed a stable high specific reversible capacity of about 897 mA h g-1 which was nearly unvarying over 50 cycles. These graphene-Fe3O4 composites are therefore a capable reversible Li+ host with high storage capacity and good cycle life which can be cycled at high rates.