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 degrees 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 m(2) 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(-2). 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. (C) 2014 Elsevier Ltd. All rights reserved.