Controlled Synthesis And Electrochemical Properties Of Fe₂O₃/SWNT Composite Films

Carbon nanotubes?CNTs?with many unique properties,such as high specific surface area,thermal conductivity,mechanical properties,electron mobility and stable cyclability,can be widely used as electrode material for lithium ion batteries,supercapacitors,solar cells and so on.However,the theoretical capacity of CNTs is only 372 mAh/g,which cannot fully meet the requirement of high power and energy densities,so the development of novel energy storage materials with better performance is an important concern.Up to now,various of composite materials have been reported,such as polymers and oxides were introduced into the CNT network to improve specific capacity.Among various transitional metal oxides,Fe₂O₃ has been considered as a potential anode material owing to its low cost,abundance,non-pollution and high theoretical specific capacitance.Here,we presented a simple and controllable method to produce Fe₂O₃/Single-walled carbon nanotube composite and uniform distribution of Fe2O3 nanoparticles among a highly conductive SWNT network.The SWNT films were synthesized by the chemical vapor deposition technique,and we could control the content of Fe particles in as-grown SWNT films by controlling ferrocene concentration of reaction source and convert it into Fe₂O₃ by annealing at predefined temperature.The loading capacity of Fe₂O₃ could be tuned by changing the temperature of anneal.At the temperature of600^oC,the ratio of Fe₂O₃ reached 96%with high specific capacitance,and the composite film could still maintain the network structure.Furthermore,the composite film could be used as electrode material with no addition of carbon additive or binder to tailor into any shape for electrode to match the device requirement and exhibit high storage capacity.As an electrode material for supercapacitors,the performance of composite was improved consistently with the increasing Fe2O3 loading by increasing annealing temperature.In a three-electrode cell system,the Fe₂O₃/SWNT-600^oC shown a specific capacitance of 1204.4 F/g at the scan rate of 2 mV/s,and the specific capacitance was still as high as 1144.6 F/g at 20 mV/s.In addition,the Fe₂O₃/SWNT-600^oC electrode expressed cycling ability with 62%capacitance retention after 5000 cycles of charge-discharge at current density of 5 A/g.Additionally,as anode material of lithium ion batteries,Fe₂O₃/SWNT-600^oC film also exhibited excellent lithium storage performance with the discharge capacity up to1006.6 mAh/g after 100 cycles at the current density of 200 mA/g,excellent rate capability?384.9 mAh/g at 5 A/g?and stable cycling performance with the discharge capacity up to 567.1 mAh/g after 600 cycles at 2 A/g.These results demonstrated that the high-loading Fe₂O₃/SWNT composite films obtained by our method have potential applications for various energy devices.