Graphene-encapsulated hollow Fe 3O 4 nanoparticle aggregates as a high performance anode material for lithium ion batteries

Abstract

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 Fe 3O 4 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. Inour 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 Fe 3O 4 nanoparticles electronically. The composite particles showed a stable high specific reversible capacity of about 897 mA h g -1 which was nearly unvaryingover 50 cycles. These graphene-Fe 3O 4 composites are thereforea capable reversible Li + host with high storage capacity and good cycle life which can be cycled at high rates.