Research On Preparation And Electrochemical Performance Of Graphene Modified PAN-based Carbon Fiber Electrode Materials

Lithium-ion batteries is the highest energy density of secondary energy storagebatteries at present,widely used in electronic equipment,electric vehicles and other fields.In order to meet the new era of clean energy requirements,the development of higher energy density lithium-ion battery has become a research hotspot.Iron oxide shows high theoretical capacity in electrode materials,and has many advantages such as rich resources,environmental friendliness,which is an ideal substitute for lithium ion anode materials.By combining with carbon materials（carbon fiber and graphene）,it can effectively overcome the inherent defects of iron oxide and is an effective means to improve the electrochemical performance of the material.The subject is based on electrospinning combined with other methods,including sol-gel and multi-step impregnation.By a variety of methods of cross and fusion,different structure of Fe₂O₃/C composite fiber materials have been prepared,and modified with graphene.The resulting composite electrode material was evaluated in terms of reversible capacity,capacity retention and rate performance.The main research contents are as follows:（1）Graphene/Fe₂O₃-loaded carbon fibers（G-Fe₂O₃-CNFs）were prepared by electrospinning process.The precursors consisted of Fe₂O₃nanoparticles,graphene sheets and polyacrylonitrile.Graphene nanosheets wrapped nano-Fe₂O₃evenly distributed in CNFs.The results show that G-Fe₂O₃-CNFs,as anodes for lithium-ion batteries,have high reversible capacity and rate performance as well as good cycle stability.The enhanced electrochemical performances of G-Fe₂O₃-CNFs were attributed to the introduction of graphene sheets,which not only prevented the aggregation of Fe₂O₃nanoparticles during electrospun process and thermal treatment,but also accommodated the volume change upon cycling and further improved the electrical conductivity of materials.Therefore,the comprehensive performance of G-Fe₂O₃-CNFs is better than that of Fe₂O₃-CNFs.（2）The Fe₂O₃/C fiber composites were prepared by sol-gel method.Through orthogonal experiment,the impact of the Fe₂O₃content in composite materials on the morphology and the influence of the morphology on the electrochemical performance were studied.The results show that the capacity degradation during cycling is associated with the content of Fe₂O₃in composite materials.Comparative study of three composite samples with different Fe₂O₃contents revealed that the best electrochemical performance with good cycling stability,high reversible capacity and improved rate capability was exhibited by the Fe₂O₃@CF sample.After 150 cycles at a constant current density of 50m A g^-1,a high reversible discharge capacity of 634 m Ah g^-1can be achieved,which is comparable to its theoretical value of 607 m Ah g^-1.Even after 50 cycles of long charge/discharge process,the one-dimensional nanofibrous structure of the composite was well maintained,demonstrating robust structural stability of the composite.The morphological stability and excellent electrochemical performance of Fe₂O₃/C fiber composites are suitable for anode materials of high performance lithium-ion batteries.（3）Graphene was introduced to modify the above Fe₂O₃@CF composites.The graphene was coated on the outside of Fe₂O₃@CF（G@Fe₂O₃@CF）by sequential impregnation in PAH,GO and hydrazine hydrate,and its electrochemical performance as a anode material for lithium ion was studied.The results show that the cycle capacity,stability and rate performance of G@Fe₂O₃@CF are greatly improved due to the physical and chemical properties and the protective effect of graphene and the synergistic effect of the components,which makes G@Fe₂O₃@CF The electrochemical performance was significantly higher than that of Fe₂O₃@CF.The research shows that carbon fiber and iron oxide complex effectively improve the reversible capacity of carbon fiber,and graphene,as a promising electrode material modifier,successfully modifies the electrochemical properties of carbon fiber composites,improving the rate performance of carbon fiber composites greatly and increasing reversible capacity and capacity retention rates to a certain extent.