A magnetic field assisted self-assembly strategy towards strongly coupled Fe3O4 nanocrystal/rGO paper for high-performance lithium ion batteries

Quantum sized nanocrystals (NCs) have theoretically provided higher electrochemical activity for lithium ion batteries than their bulk counterparts due to their large surface area and short diffusion distance for Li+ ions. With ever-increasing interest in the development of next-generation, high-performance and flexible LIBs, reduced graphene oxide (rGO)/quantum sized NC hybrid papers are being considered to be one of the promising configurations for these special needs. However, one of the challenges regarding this kind of hybrid paper is how to control the uniform size distribution and monodispersibility, as well as keeping it on rGO sheets individually separated. In this work, a remarkably high reversible capacity (1140 mA h g(-1) at a current density of 1 C) and long-term stability (at least 220 cycles) for lithium storage over a flexible rGO/Fe3O4 NC (similar to 2 nm) paper have been achieved. A viable polyelectrolyte-assisted synthesis of strongly coupled rGO/Fe3O4 hybrids has demonstrated the self-assembled magnetite hybrid paper at the air/liquid interface, with the help of an external magnetic field. Crystallographic and microscopic characterizations revealed that the Fe3O4 nanocrystals still retained high-crystallinity, well-dispersibility and original size after long-term cycles, with negligibly slight aggregation.