The Synthesis Of Iron-based Nanocomposites And Its Electrochemical Performance

The pursuit of electrode materials with the characteristics of security,low price and higher capacity has become an important mission in the electrochemical area.Magnetite,with advantages of natural abundance,low cost,environmental compatibility and high theoretical capacity?925 mAh/g?,has emerged as alternative electrode materials for Li-ion batteries and supercapacitors.Based on this observation,we proposed a molten salt method to directly synthesize nanoparticle Fe₃O₄/C composites.In this paper,we used ferric chloride as Fe source,sodium oleate or potassium humate as carbon source and then to study their electrochemical performances.The details are as follows:Firstly,through simple and effective one-step molten-salt method to roast the mixture of iron hydroxide@oleate,self-assembled Fe₃O₄/carbon nanocomposites have been directly prepared.In the composites,highly dispersed Fe₃O₄ nanocubes are embedded in the carbon support,and the high performance applications in lithium-ion battery anodes and supercapacitor have been tested.When the composite is used as the supercapacitor electrode,S3-600 electrode material possesses a high capacitance of 253.9 F/g at current density of 1 A/g.The reasons can be attributed to carbon layer coated on the surface of metal oxide nanoparticles,which can prevent the aggregation of metal oxide particles,maintain the size of particles intrinsically.On the other hand,S3-600,as electrode of Li-ion battery,has a reversible capacitance of 3924.5 mAh/g at 100 m A/g.Specific capacitance of S3-600 can be as high as 2238.8 mAh/g after 160 cycles at 100 mA/g,and the value has a trend to increase with increasing the cycles number.When changed the current density?100?1000?100 mA/g?,capacity of S3-600 electrode gradually reduced from 3092 mAh/g to 326 mAh/g,and reached 875 mAh/g after 50 cycles.Overall,Fe₃O₄/C nanocomposites calcined at 600 oC either as a supercapacitor,or as an anode material for Li-ion battery has a good rate and cyclic performances,and have widely application prospect.Secondly,self-assembled Fe₃O₄-FexN/carbon nanocomposites have been directly prepared by a simple and effective one-step molten-salt method under ammonia atmosphere.The characterization results of two-dimensional Fe₃O₄-Fe_xN/C shown that the uniform Fe₃O₄-FexN nanocubes were embedded in the carbon films and A1-700 has a more regular morphology.A1-700 electrode combined between the Fe₃O₄-FexN and the carbon network leads to a remarkably high capacitance?707.9 F/g at current density of 500 mA/g?and good rate capability?147.4 F/g at current density of 3 A/g?of pseudocapacity.The excellent performance of sample can be attributed to three point,synergy between iron-based compounds and carbon layer,high electrical conductivity of carbon,and reduction activity of iron-based compounds.Here,carbon layer coated on the surface of Fe₃O₄-FexN can hold the integrity of Fe₃O₄-FexN particles,and increase the conductivity of electrode materials.This part work not only provides a new method for synthesis of Fe₃O₄-Fe_xN/C composites,also demonstrates that it can provide alternative path for the development of advanced energy storage devices.Thirdly,self-assembled Fe₃O₄/C nanocomposites have been prepared by roasting the mixture of iron hydroxide@oleate at Ar atmosphere,then to prepare Fe₃O₄-Fe₃N/C using molten-salt method under ammonia atmosphere.The characterization results of two-dimensional Fe₃O₄-Fe₃N/C shown that the uniform Fe₃O₄-Fe3 N nanocubes were embedded in the carbon films.B1-700,as electrode of Li-ion battery,has a first reversible capacitance of 1107.1 m Ah/g at 100 mA/g.Its specific capacitance can be as high as 931.9 mAh/g,and the device could retain 84.2% of its initial specific capacitance after 50 repeated charge-discharge cycles.When the composite is used as the supercapacitor electrode,B1-700 electrode possesses a high capacitance of 480.5 F/g at 500 mA/g.The excellent performance of sample can be attributed to the present of Fe3 N.Because Fe3 N can improve the electron transfer and mass transfer,greatly enhance the conductivity of the electrode material,and also prevent the volume change of iron oxide nanoparticles in the reaction.Moreover,the carbon layer on the surface of nanoparticles can decrease the aggregation of particles,and improve the electrochemical performances of supercapacitor.Finally,molten-salt method was adopted to directly prepare two-dimension nanoparticle Fe₃O₄/C composites.It's worth noting that the composite was obtained with potassium humate as a sole source of carbon.Self-assembled Fe₃O₄/C nanocomposites was prepared by roasting the mixture of iron hydroxide@humate under Ar atmosphere.The electrochemical performance of Fe₃O₄/C nanocomposite for reversible Li+ storage was evaluated by cyclic voltammetry and constant current charging and discharging.Due to the synergism between Fe₃O₄ and the carbon,the composites maybe have high specific capacity and good rate performances.Fe₃O₄/C-750 nanosheets exhibited a first-cycle charge capacity of 747.3 mAh/g?Li+ extraction?at 500 mA/g,and the coulombic efficiency in the first cycle can reach as high as 98%.After changing current density?100?2000?100 mA/g?,capacity of Fe₃O₄/C-750 electrode gradually reduced from 477 mAh/g to 248 mAh/g,and returned to increase to 289 mAh/g.It is clear from the results shown that 750oC-carbonized Fe₃O₄/C nanocomposites have high reversible capacity,high coulombic efficiency in the first cycle,as well as significantly enhanced cycling performance and high rate capability.When the composite is used as the electrode of supercapacitor,Fe₃O₄/C-750 has a high capacitance of 265.6 F/g at 500 mA/g.The improvements can be attributed to the carbon coating layers,which have several functions,including: increasing the electronic conductivity of electrodes,enhancing the electron-transfer rate and adjustable strain,and preventing the volume change during the reaction.