Synthesis And Modification Of Iron Compounds/Carbon Nanomaterials And Basic Research On Electrochemical Energy Storage

Iron is one of the most abundant metals on the earth.Iron compounds are widely used in metallurgy,construction,machinery and other fields.In recent years,researchers have tried to apply iron compounds to electrochemical energy storage and have made great achievements.Transition metal oxides,sulfides and their composite materials have attracted many attentions.They have extensive application prospects in the fields of energy conversion and storage.Iron-based oxides and iron-based sulfides are potential electrode materials due to their high theoretical capacity,rich resources,low cost and non-pollution.However,their low electrical conductivity severely limits the charge conduction in the electrode material.In addition,the volume expansion effect of iron-based oxides and iron-based sulfides during charging/discharging can seriously reduce the capacity and cycle life of the secondary battery.In this work,the iron-based oxides,iron-based sulfides and manganese-based oxides are prepared through electrospinning,calcination,hydrothermal and other technologies.Their electrochemical properties are studied in supercapacitors and sodium batteries.This doctoral dissertation mainly consists of four parts content as follows:(1)Fabrication and electrochemical energy storage performances of polyaniline/hydroxylferric oxide/graphene electrode materials by interfacial polymerizationThe polyaniline/hydroxyl ferric oxide/graphene nanocomposites are successfully prepared by simple interfacial polymerization under acidic conditions.The effect of the addition(graphene and polyanilne)on the electrochemical properties of electrodes such as conductivity and specific capacity is investigated.The effects of polymerization time on nanostructure,morphology,grain size and electrochemical properties of electrodes are studied.The influence mechanism of stacking structure on cycling stability is researched.The results show that when the polymerization time is 48 h,the PFG48 nanocomposites exhibit the best electrochemical performance.Its specific capacitance is 417 F·g^-1at 1A·g^-1.Meanwhile,its capacitance retention is 71.2%after 5000 cycles.(2)Fabrication and electrochemical energy storage performances of FeS₂/three-dimensional porous carbon by hydrothermal approachAlthough the cycling stability of iron compounds supported by graphene is improved,the volume of some iron compounds still expands after cycling.In order to further improve the cycling stability of electrode materials,the iron compounds/carbon materials with an embedded structure are designed and synthesized.Three-dimensional porous carbon(3DPC)decorated with FeS₂nanospheres nanocomposites(FeS₂/3DPC)are developed as electrode material for supercapacitors and sodium ion batteries through a facile hydrothermal approach.The effect of the FeS₂content on the electrochemical properties of FeS₂/3DPC is studied.The influence mechanism of embedded structure on cycling stability of electrodes is investigated.The effect mechanism of three-dimensional porous carbon on conductivity of electrodes is explored.The results show that the FeS₂/3DPC supercapacitor has a highest specific capacitance of 254.1 F·g^-1at 2 A·g^-1.After 5000 cycles,the capacitance retention is as high as 84.8%.For the sodium ion battery,the initial charging capacity of 50%FeS₂/3DPC is 500 m Ah·g^-1at 500 m A·g^-1.And the capacity remains 430 m Ah·g^-1after 200 cycles.(3)Fabrication and electrochemical energy storage performances of Fe₃O₄/C nanofiber by electrospinningThe embedded iron compounds/carbon composites synthesized by above method still have some volume expansion after cycling,so the new structure which covers the iron compound has been designed.Fe₃O₄/carbon nanofibers(Fe₃O₄CNFs)with encapsule structure are prepared by electrospinning and calcination.The effect of the Fe₃O₄content on the electrochemical properties of Fe₃O₄CNFs is studied.The influence mechanism of encapsule structure on cycling stability of Fe₃O₄CNFs electrodes is researched.The influence mechanism of synergistic effect of carbon nanofibers and Fe₃O₄on electrochemical properties of electrodes is elucidated.As electrode materials of supercapacitors and sodium ion batteries,Fe₃O₄CNFs show excellent electrochemical performances.The synergistic effect of Fe₃O₄and carbon fiber can effectively improve the conductivity of nanocomposites.The encapsule structure can inhibit the volume expansion of Fe₃O₄during charging and discharging.The results show that the specific capacitance of 4Fe₃O₄CNFs//AC supercapacitor is 203.3 F·g^-1at 1 A·g^-1.And the capacitance retention is 86.2%at 2 A·g^-1after 5000 cycles.4Fe₃O₄CNFs also have a good cycle stability as the anode material of sodium ion battery.It can maintain 358.1 m Ah·g^-1at 500 m A·g^-1after200 cycles.(4)Fabrication and electrochemical energy storage performances of FeS₂/C nanofiber by electrospinningFor improving electrical conductivity of iron compounds/carbon composites,Fe₃O₄/C nanocomposites are doped with in-situ sulfur to obtain FeS₂/carbon nanofibers.The effect of in-situ sulfur doping on conductivity of FeS₂/carbon nanofibers is researched.The influence mechanism of synergistic effect of FeS₂and carbon nanofibers on electrochemical performances is explored.The results show that the FeS₂CNFs supercapacitor is 206.2 F·g^-1at 1 A·g^-1.And the capacitance retention is 87.5%after 5000cycles.As the anodes of sodium battery,FeS₂CNFs also have a good cycle stability.It can maintain 490.6 m Ah·g^-1at 500 m A·g^-1after 200 cycles.