Preparation Of Fe₃O₄Particles And Research On Performances Of Lithium Ion Battery Of Fe₃O₄/Graphene Composite

Recently, our energy needs continue to grow with the development of technology. Increasing attention has been paid on lithium ion battery, a common and convenient energy storing device. How to improve the stability、capacity and efficiency of Lithium Ion Battery is the basic problem in current research. Fe3O4have high theoretical capacity、low cost and environment friend. It has been used as cathode material in the fields of lithium ion battery. Graphene and graphene-based materials have been considered as one of the promising alternatives as electrode materials in energy-related devices, because these materials have superior electrical conductivities, high surface area, chemical tolerance, high transparency and a broad window of electrochemical.Our work is mainly focused on study of the structural, morphological and magnetic properties of solid and hollow Fe3O4microspheres prepared by solvent-thermal method. The effects of reaction time and content of urea are also researched. On this basis, Fe3O4/graphene composite materials are fabricated by three different methods. The properties of lithium ion battery of Fe3O4and Fe3O4/grapheme composite are also examined.The main results and conclusions are:(1) Hollow Fe3O4microsphere was prepared by solvent-thermal method in the absence of template. The diameter and interior diameter of the microsphere is400nm and230nm, respectively. And they both have good surface topography and dispersion. By VSM measurement, the obtained particles exhibit room temperature ferrimagnetism.(2) With increasing time of reaction, the particles develop into hollow structure gradually. When the reaction time is8h, the particles have solid structure; when the reaction time is20h, the particles have hollow structure. (3) The content of urea can affect the morphology of particles. When the content of urea is1.0g, the diameter of the particles is about800nm. With increasing content of urea, the diameter becomes smaller and its morphology becomes irregular. When the content of urea is2.0g, the microsphere has the best morphology.(4) The research on the microwave absorption of solid and hollow Fe3O4microsphere shows that the hollow structure can improve the microwave absorption ability. For the hollow Fe3O4microsphere, the minimal return loss is-42.6dB at5.7GHz which is higher than the solid Fe3O4microsphere (-29.1dB at3.2GHz).(5) We have fabricated the Fe3O4/graphene composite materials by graphene coating solid and hollow Fe3O4microsphere. Results show that Fe3O4microsphere can hold its original morphology and graphene is reduced better. The performance of lithium ion battery is also improved.(6) At the same time, we found that the surface modification of Fe3O4microsphere with KH550can improve the bonding capacity between Fe3O4and graphene. The graphene can protect Fe3O4microsphere much better and correspondly the composite shows higher lithium ion battery performance. Compared with Fe3O4/graphene composite that without KH550modification, the discharge capacity of modified Fe3O4/graphene composite increases15%after50recycles, this is due to the better dispersion of particles and strong protection of graphene.