Fe3O4-decorated hollow graphene balls prepared by spray pyrolysis process for ultrafast and long cycle-life lithium ion batteries

Fe3O4-decorated graphene balls were prepared by a spray pyrolysis process. Analysis by Raman spectroscopy and X-ray photoelectron spectroscopy indicated that the spray pyrolysis at 800 °C resulted in the complete reduction of graphene oxide sheets containing oxygen functional groups into graphene sheets, leading to the formation of Fe3O4-decorated graphene balls. The graphene content in the composite ball was 27 wt%. The Brunauer–Emmett–Teller surface area of the Fe3O4-decorated graphene balls was as high as 130 m2 g−1. The initial discharge and charge capacities of the Fe3O4-decorated graphene balls at a high current density of 7 A g−1 were 1210 and 843 mAh g−1, respectively, and the discharge capacity was as high as 690 mAh g−1 even after 1000 cycles. The stable reversible discharge capacities of the Fe3O4-decorated graphene balls decreased from 1040 to 540 mAh g−1 with the increase in current density from 1 to 30 A g−1. The Fe3O4-decorated graphene balls with a uniform distribution of ultrafine Fe3O4 nanocrystals below 15 nm showed superior electrochemical properties as anode materials for lithium ion batteries. The overall structure of the Fe3O4-decorated graphene balls was maintained even after long-term cycling.