Surfactant-assisted synthesis of Fe2O3 nanoparticles and F-doped carbon modification toward an improved Fe3O4@CFx/LiNi0.5Mn1.5O4 battery.

A simple surfactant-assisted reflux method was used in this study for the synthesis of cocklebur-shaped Fe2O3 nanoparticles (NPs). With this strategy, a series of nanostructured Fe2O3 NPs with a size distribution ranging from 20 to 120 nm and a tunable surface area were readily controlled by varying reflux temperature and the type of surfactant. Surfactants such as cetyltrimethylammonium bromide (CTAB), polyvinylpyrrolidone (PVP), poly(ethylene glycol)-block-poly(propylene glycol)-block-poly(ethylene glycol) (F127) and sodium dodecyl benzenesulfonate (SDBS) were used to achieve large-scale synthesis of uniform Fe2O3 NPs with a relatively low cost. A new composite of Fe3O4@CFx was prepared by coating the primary Fe2O3 NPs with a layer of F-doped carbon (CFx) with a one-step carbonization process. The Fe3O4@CFx composite was utilized as the anode in a lithium ion battery and exhibited a high reversible capacity of 900 mAh g(-1) at a current density of 100 mA g(-1) over 100 cycles with 95% capacity retention. In addition, a new Fe3O4@CFx/LiNi(0.5)Mn(1.5)O4 battery with a high energy density of 371 Wh kg(-1) (vs cathode) was successfully assembled, and more than 300 cycles were easily completed with 66.8% capacity retention at 100 mA g(-1). Even cycled at the high temperature of 45 °C, this full cell also exhibited a relatively high capacity of 91.6 mAh g(-1) (vs cathode) at 100 mA g(-1) and retained 54.6% of its reversible capacity over 50 cycles. Introducing CFx chemicals to modify metal oxide anodes and/or any other cathode is of great interest for advanced energy storage and conversion devices.