Electrospinning Preparation And Electrochemical Performance Of CoFe₂O₄ Composite Nanofibers

As the non-renewable resources,the storage of fossil energy has been decreased gradually by the development of industry.Meanwhile,the combustion process of fossil energy will also release large amounts of sulfur dioxide and smoke dust,leading to the deterioration of the environment.Hence,developing clean renewable energy and safe power storage devices with high efficiency became one hot topic in the world energy study field.Lithium-ion battery is one of the most common power storage devices with the great electronic capability and environment-friendly,which is the efficient way to solve the storage problem of renewable energy.However,with the increasing material and cultural demands of human,lithium-ion batteries have gradually been hard to meet the requirement of the electronic devices with efficient and long cycle life on currently market.Anode material is one of the important elements which could affect the performance of lithium-ion battery.The transition metal oxide anode material has many advantages,such as high specific capacity,low cost and environment-friendly,which has a wide application prospect in anode materials.Based on this idea,CoFe₂O₄ nanofibers,CoFe₂O₄/PPy composite nanofibers and CoFe₂O₄/rGO composite nanofibers were prepared through the electrospinning technique,in-situ polymerization and hydrothermal method,respectively.The synthesis process,modification and electrochemical performance were studied in this paper.The main points of this work are summarized as follows:（1）PAN/Co（CH₃COO）₂/Fe（NO₃）₃ nanofiber mats with uniform diameter were fabricated by electrospinning technique at first,and then calcined at 600 ^oC and 800 ^oC to prepare CoFe₂O₄ nanofibers.The characterization of CoFe₂O₄ nanofibers were evaluated by thermogravimetric analysis（TGA）,X-ray diffraction（XRD）,scanning electron microscopy（SEM）and transmission electron microscopy（TEM）.XRD results indicated that the CoFe₂O₄nanofibers obtained at 800 ^oC exhibited higher crystallization and bigger grain than that of prepared at 600 ^oC.SEM images showed the CoFe₂O₄ nanofibers has a rough surface,good orientation and spatial network structure.The BET results demonstrated the CoFe₂O₄nanofibers possessed large surface area,which could increase the contact area with electrolyte and good for the diffusion of Li⁺and electronics.The CoFe₂O₄ nanofibers are used as potential anode material for lithium-ion batteries.Electrochemical performance exhibited that the initial discharge capacities of CoFe₂O₄ nanofibers is 696 mAh/g,and the stabilized capacity is 412 mAh/g after 50 cycles at 50 mA/g.About 59.5%of the capacity is maintained.After cycled at higher current density,the capacity of electrode could still recover to 400mAh/g,exhibited good cyclic stability and rate performance.（2）In order to further improve the electrochemical performance of CoFe₂O₄ nanofibers,CoFe₂O₄/PPy composite nanofibers with different proportion pyrrole were prepared by in-situ polymerization method.The electrochemical results exhibited that the cyclic performance and rate capacity of Co Fe₂O₄ nanofibers which coated by polypyrrole have all been improved,demonstrated that the polypyrrole could buffer the volume expansion during discharge/charge process,keep the anode material structure stable and improve the conductivity of anode material.CP2 composite nanofibers（n（CoFe₂O₄）:n（Py）=2:1）showed the best electrochemical performance between three different proportion composite nanofibers,the initial discharge and charge capacities is 1285 and 810 mAh/g at a current density of 50 mA/g,respectively.The columbic efficiency of first cycle is about 63.0%.The discharge capacity is 649 mAh/g after 50 cycles,which is still higher than that of other proportion CoFe₂O₄/PPy composite nanofibers.（3）CoFe₂O₄/rGO composite nanofibers were synthesized by electrospinning technique combined with hydrothermal reduction and freeze-drying method.The initial discharge capacity of CoFe₂O₄/rGO composite nanofibers is 1243 mAh/g at 50 mA/g,the discharge capacity could still retained about 865 mAh/g after 200 cycles.The CoFe₂O₄/rGO composites nanofibers also exhibited excellent rate capability.The excellent electrochemical performance could be ascribed to the following reasons:the conductivity of CoFe₂O₄/rGO composites nanofibers was improved by rGO additive;the volume expansion during the extraction/insertion process can be relieved,which ensure the structure stability of composites nanofibers;the graphene sheets as conductive network could effectively restrain the agglomeration of CoFe₂O₄ nanopaiticals.