The Research On Electrospinning Synthesis For Supercapacitor And Li,Na Ion Battery Applications

The demand for high efficiency energy storage device systems gradually increase due to the growing necessity of electrical grid storage to convert the intermittent renewable sources?such as solar and wind?into electricity.Over the last two decades,high performance Lithium-Ion Batteries?LIBs?have attracted a great deal of attention as a promising candidate for future green energy.LIBs are a kind of low cost and environmentally friendly devices.They are regarded as crucial power sources and used in many field such as portable electronic consumer devices,hybrid electric vehicles and implantable medical devices due to their high energy density,high voltage,and light weight.While Supercapacitors?SCs?,as a new class of energy storage devices,have also attracted much attention for their high power density,fast charging/discharging rate,long cycle life and high reliability.As we all known the the main performance of the energy storage device is decided by the electrode material.Therefore,finding the suitable electrode material is the key to the study of electrochemical energy storage.Electrospinning is the most facile and highly versatile approach to produce one-dimensional nanomaterials with a small diameter and controllable morphology.Electrospun nanofibers have a shorter diffusion path for the ion relative to the commonly employed powder materials due to their high specific surface area.Hence,electrospun nanofibers is regarded as ideal candidates for various kinds of electrochemical energy storage devices.The main content of the study are as follows:?1?In chapter 2,novel RuO₂@Co₃O₄ heterogeneous nanofibers?HNFs?were synthesized by a simple technique of electrospinning method followed by calcination.PossibleformationmechanismofRuO₂@Co₃O₄HNFsispresented.For supercapacitor application,due to the synergetic effect between RuO₂ and Co₃O₄ as well as the unique feature of heterostructure,the composite exhibited high reversible capacities(1103.6 F g^-1at a current density of 10 A g^-1),high-rate capability(500.0 F g^-1at a current density of 100 A g^-1)and excellent cycling performances(the capacities could be maintained at 93.0,91.8,and 88.0%after 1000,2000 and 5000cycles at a current density of 10 A g^-1).Our work confirms the as-prepared RuO₂@Co₃O₄ HNFs can serve as advanced supercapacitors?SCs?materials.It is highly expected this simple method of electrospinning can be extended to prepare other new type of heterostructure materials which could be used in the field of electrochemical energy storage.?2?In chapter 3,we firstly synthesized Co?NO₃?₂@PVP nanofibers by a facile electrospinning method.Then,the spun fibers were annealed in air to get porous Co₃O₄ nanotubes.The scanning electron microscopy?SEM?and transmission electron microscope?TEM?image showed that it has a good porous tubular structure.We prepared the Co₃O₄ nanotubes electrode and studied the electrochemical properties when used as the anode for LIBs.Due to the porous tubular structure,Co₃O₄nanotubes exhibited high high specific surface area,which increased the contact area between the electrode and electrolyte.As a result,the efficiency of ion and electron transfer was improved during the electrochemical reaction process.The porous tubular structure can also provide space for the huge volume expansion of the materials during the charging and discharging processes.The Co₃O₄ electrode exhibited a first specific discharge capacity of 1294.4 mA h g^-1at the current density of 0.1 A g^-1.It showed stable cycle performance,with the specific capacitance of887.6 mA h g^-1after 60 cycles.When the current density increased to 1 A g^-1,a reversible capacity of 498.4 mA h g^-1could still be obtained.?3?In chapter 4,we firstly prepared Fe₂O₃ nanotubes by electrospinning and calcination.Then,we synthetized the core-shell Fe₂O₃@TiO₂ nanotubes by using the atomic layer deposition technology and studied its performance of lithium storage when used as the anode for LIBs.Compared to the pure Fe₂O₃ electrode,the core-shellFe₂O₃@TiO₂nanotubeselectrodeexhibitssignificantlyimproved electrochemical performance.The core-shell Fe₂O₃@TiO₂ nanotubes electrode exhibited a first specific discharge capacity of 1078,6 mA h g^-1at the current density of 0.2 A g^-1and maintained a high discharge capacity of 774.8 mAh g^-1after 100cycles.While the specific discharge capacity of the pure Fe₂O₃ electrode decreased significantly from the 40th cycle and only showed a capacity of 607.6 mAh g^-1.The SEM image after the cyclic test proved that the amorphous TiO₂ played a key role for maintaining morphology of the electrode.The design of combining Fe₂O₃ with TiO₂ is not only make full use of the high capacity of the Fe₂O₃,but also take full advantage of the amorphous TiO₂ to maintain the stability of the structure,thereby improving the cycle stability of the pure Fe₂O₃ electrode.?4?In chapter 5,rechargeable sodium-iodine batteries represent a promising scalable electrochemical energy storage alternative as sodium and iodine are both low cost and widely abundant elements.Here,we demonstrate a rechargeable sodium-iodine battery that employs free-standing iodine quantum dots?IQDs?decorated reduced graphene oxide?IQDs@RGO?as the cathode.The battery exhibits high capacity,outstanding cycle stability(with a reversible specific capacity of 141mAh g^-1after 500 cycles at current density of 100 mA g^-1)and high rate performance(170,146,127,112 and 95 mAh g^-1at current densities of 100,200,400,600 and1000 mA g^-1,respectively).Notably,even after 500 cycles the morphology and structure of the IQDs exhibit no noticeable change implying their use as a stable cathode material for sodium-iodine batteries.Moreover,the IQDs based flexible full-cells also exhibited high capacity and long cycle life(the capacity with 123 mAh g^-1at current density of 100 mA g^-1after 100 cycles).