Preparation And Energy Storage Of Carbon Nanofibers Regulated By Zn/Co Metal Oxides

The development of high-performance and flexible energy storage devices matching wearable electronics has become a research hotspot in today's world.And the design and preparation of high-energy-density and highly-flexible electrodes is the key to achieve flexible energy storage devices.Thanks to its high conductivity and inherent flexibility,carbonaceous textile fibers have great potential in the preparation of high performance flexible electrodes.According to the design concept of functional fibers in textile dyeing and finishing,the study aim to endow electrospun carbon nanofibers?CNFs?in outstanding energy storage performance and flexibility through combining Zn/Co transition metal oxides,which possess high energy densities and various reactions between C.To meet the requirements of the flexible electrodes,strategies for designing and modifying the fine structure of carbon nanofibers were employed to improve the energy density and flexibility of CNFs.Based on the analysis of the relationship between the composition,structure and energy storage properties of the as-prepared CNFs,the lithium storage mechanisms were discussed.Chapter 1 briefly introduced the basic situation of lithium-ion battery and the storage applications of carbon-based textile fiber material.Subsequently,a particular summary was provided on the research status and challenges of the electrospun PAN-based carbon nanofibers.Then,a brief introduction of the Zn/Co based transition metal oxides applied in the field of energy storage and carbon materials processing was provided.Finally,research significance and content of this paper was proposed.In chapter 2,we demonstrate the preparation of CNFs anchored with ZnCo₂O₄?ZCO?nanocubes to improve energy density of CNFs by hydrothermal method.ZnCo₂O₄ nanocubes in ZCO/CNF-10 fabricated by 1.0 mmol urea were moderate in size and coated the CNF uniformly.Serving as a binder-free anode material for LIBs,ZCO/CNF-10 composite maintained a high reversible capacity of 600 mAh g^-1 when cycled at a current density of 0.5 C for 300 times.However,the specific capacities of pristine CNFs are low since its inherent heavy weight,which restrict the overall capacity of the electrodes.In chapter 3,to enhance CNFs own specific capacity,we design a novel porous and graphitized CNFs fabricated by"activating catalyzed-graphitization"induced by ZnCo₂O₄.The ZnCo₂O₄ nanoparticles were added to PAN solution followed by electrospinning-carbonization to prepare sponge-like porous CNFs?SLCNFs?with a series of well-interconnected graphitized mesopores.Serving as conductive agent-free anode materials for LIBs,SLCNFs can maintain a high reversible capacity of 900mAh g^-1 when cycled 100 times at a current density of 100 mA g^-1.Furthermore,after cycled at a high current density of 1670 mA g^-11 for 2000 cycles,SLCNFs can deliver a reversible capacity of 460 mAh g^-1.In chapter 4,drawing on the preparation methods of high-performance carbon fiber?CF?,we enhanced the flexibility of CNFs through promoting the preoxidation process by adding Zn?Ac?₂,and we fabricated a flexible FCNF-3/4 and a strong FCNF-1/2.During electrospinning-preoxidation-carbonization procedure,Zn?Ac?₂played three roles of plasticization,catalysis and activation to enhance the flexibility of FCNFs.A systematic flexible mechanism of FCNFs containing fabric texture,fiber structure,and microstructure was first proposed.Serving as self-supported anodes for half-cells,the FCNF-3/4 maintained a capacity of 630 mAh g^-1 when cycled 100 times at a current density of 200 mA g^-1.Furthermore,a metal-conductor-free foldable full cell consisting of a commercial flexible LiCoO₂/CNT cathode and a FCNF-3/4 anode is also assembled,which can deliver an initial discharge capacity of 572 mAh g^-1 and can light an LED even it is folded twice.Finally,in chapter 5,we systematically summarized the overview and deficiency of this thesis.And some prospects on the possible future research are presented.