Preparation And Electrochemical Properties Of ZnFe₂O₄ Composite Nanofibers

Nowadays, environmental pollution and serious energy crisis have attracted widespread concerns. Compared to other batteries, lithium-ion batteries were regarded as the effective way to solve the shortage of fossil fuels due to the advantages of the excellent electrochemical performance and eco-friendly, etc. However, the development of electrical/hybrid vehicles and portable electronic devices created great challenge for the lithium-ion battery,researchers have been focusing on the development of the anode material which was as the critical part for the performance. Transition metal oxides were particularly attractive owing to their high theoretical capacities, as well as the electrospun nanofibrous mats, which due to the high specific surface area and high porosity, they all have good prospects in the field of lithium-ion battery. Based on the above idea, we prepared ZnFe₂O₄ nanofibers?ZnFe₂O₄/G composite nanofibers and ZnFe₂O₄/PANI composite nanofibers by nanotechnology and composite technology with grapheme or conducting polymers. ZnFe₂O₄ nanofibers was the main body of the lithium storage, the study managed to research the modification of ZnFe₂O₄ nanofibers, as well as the electrochemical performance of the composite nanofibers after modifying as the anode materials of lithium-ion batteries. The main contents of this work are as follows:?1? ZnFe₂O₄ nanofibers were prepared by electrospinning followed by carbonization technique at 600 ? and 800 ? respectively. The XRD results showed that the crystallization of ZnFe₂O₄ prepared under 800 ? was higher than 600 ?, SEM pictures show that ZnFe₂O₄ nanofibers own rough sucface and good orientation, possesse an average diameter of 150 nm. and then the morphology, composition and electrochemical performance of sample nanofibers were characterized by BET, TG, FTIR and electrochemical tests. The results showed ZnFe₂O₄ nanofibers not only displayed high initial discharge capacity of around 1278 mAh g-1, but also maintained a stable capacity of 550 mAh g-1 after 50 cycles. It proved that nanfibers did a great improvement to electrochemical performance attributed to the high specific surface area and abundant Pores, which also accelerated lithium ion diffusion and lithium Storage Performance.?2? In order to further improve the performance of ZnFe₂O₄ nanofibers, ZnFe₂O₄/G composite nanofibers were synthesized via electrospinning and in situ polymerization with adding graphene oxide. The graphene sheets which owned flexible lamellar structure coated on ZnFe₂O₄ nanofibers could effectively prevented ZnFe₂O₄ from agglomeration, guaranteed the whole structural by preventing the contact between the electrode and electrolyte. The good electrical conductivity of graphene well makes up for the performance deficiency of single nanofibers, and the ZnFe₂O₄ nanofibers and graphene sheet all play their roles effectively, the tested results indicated that the nanocomposites materials could remarkable improve the electrochemical performance. The results showed ZnFe₂O₄/G composite nanofibers present a superior reversible capacity of 900 mAh g-1 after 100 cycles at the current density of 300 mA g-1, and obtain reversible capacitie of 711 mAh g-1 at the high current rates of 5000 mA g-1.?3? We combine electrospinning with in situ polymerization methods to successfully prepare the ZnFe₂O₄-PANI composite nanofibers?ZP-10 ? ZP-15 and ZP-20?. The electrochemical tests results showed that the ZP-15 electrode shows the most excellent electrochemical performance among the samples. The ZP-15 electrode delivered an initial specific discharge capacity of 1469.7 mAh g-1 and remained reversible capacity of 1180 mAh g-1 after 50 cycles, even at at the high current of 2000 mA g-1, it also showed high reversible capacity of about 738 mAh g-1, the rate performance was promoted greatly. The PANI enhanced the conductivity and provided more active sites during electrochemical reaction, the special porous structure of cladding also acted as the protective barrier for ZnFe₂O₄ nanoparticals to aggregation during cycling.