Research On The Synthesis And Lithium Stroage Performance Of The Micro-nano Composite Magnesium Ferrite

Recently,lithium ion batteries?LIBs?have become more and more attractive due to their high energy density,long life,environment friendly,no memory effect and so on.However,as the potential power supply for electric vehicles,the cost,energy density and safety should be substantially improved.While adoption of more security electrode materials with higher energy density and lower cost will contribute to the commercialized application of LIBs.As the current commercial anode material for LIBs,the theoretical specific capacity of graphite is only 372mAhg-1,and the safety issues is also noticeable caused by the formation of lithium dendrite during the charge/discharge process.Transition metal oxides?TMOs?with high theoretical specific capacity are one of the most promising alternative anode materials for LIBs.However,the fast capacity fading and poor rate performance,which caused by the high volume expansion and intrinsic low electrical conductivity,hamper its applications.Through preparing nanostructured material,reasonable structure design and compositing with othercomponents,the performance of TMOs can be improved greatly.The spinel structure MgFe₂O₄ isusually used as magnetic materials,catalyst and humiditysensor.And recently,it is found MgFe₂O₄ can be used as anodematerial in lithium ion battery.MgFe₂O₄ consists of high electrochemical active Fe₂O₃ and inactive MgO.Mg O acts as a skeleton structure during the conversion reaction of MgFe₂O₄,which can alleviate volume expansion to a certain extent.In this paper,MgFe₂O₄ and its modified product are the main research objects.Through adjusting its composition,and constructing binder-free integrated electrode,to improve its conductivity and structural stability,and then,improve its electrochemistry performance.Details are as follows:1.Synthesis of Fe₂O₃/MgFe₂O₄ complexes by a simple gel-cast methodFe₂O₃/MgFe₂O₄ complexes were synthesized by adding a certain proportion of magnesium nitrate and ferric nitrate with polyacrylamide polymer gel network as template.Fe₂O₃/MgFe₂O₄ complexes show the excellent cycling and rate performance.At a current density of 1Ag-1 for 500 cycles,its capacity still maintains at 1800mAhg-1,even cycling at an ultra-high current density of 20Ag-1,the capacity keeps 761mAhg-1.The excellent performances may be attributed to the enlarged crystal lattice and the relatively lower cloud density of Fe-O bond.Furthermore,capacity rise phenomenon of the Fe₂O₃/MgFe₂O₄ composite was studied.Results show that both interfacial lithium storage and the polymeric/gel-like layer contribute to that.2.Synthesis of graphene coated Mg Fe₂O₄ by a solvothermal methodVesicle-like MgFe₂O₄/graphene 3D network anode material was synthesized via a simple one-step in-situ growth of solvothermal technique.The as-obtained unique 3D nanostructure consists of MgFe₂O₄ particles randomly anchored on mutual crosslinking graphene sheets,functioning as a mechanical support and an efficient electron conducting pathway.The as-synthesized anode material shows an excellent cycling and outstanding rate performance.A specific capacity of 1300 mAh g-1 can be maintained at 1 A g-1 in a prolonged charge-discharge process?200 cycles?.When cycling at a high current density of 10000 mA g-1,a specific capacity of 597 mAh g-1 can still be achieved.The superior battery performance can be attributed to the unique 3D network structure,which provides an efficiently conductive network,buffers the volume expansion,and improves the structure integrity of the electrode.3.Constructing binder-free integrated electrodeThe superior 3D architectures integrative electrode with porous MgFe₂O₄ nonosheet directly grown on Ni foam are firstly designed and synthesized via a simple hydrothermal method as the binder free anode material for LIBs.The spheroidicity-like MgFe₂O₄ about 100 nm are connected with each other to form porous nanosheet which is directly grown on Ni foam substrate with good conductivity.As expected,the integrative electrode exhibits high lithium-storage capacity,superior cycle stability and impressive rate capability.At a current density of 5Ag-1,the capacity maintains at 780 mAh g-1 for 1000 cycles.The integrative electrode not only simplifies the processing technology of the electrode,but also reduces the polarization and accommodates volume expansion during Li+ insertion/deinsertion process,thus enhance the cycling and rate performance.