Hierarchical Carbon Structure And Its Application In Energy Storages

With the rapid development of portable electronic devices and electric vehicles,the energy storage devices towards to higher energy density and power density.Lithium-ion batteries and supercapacitors are two potential energy storage devices.For lithium-ion batteries and supercapacitors,although the storage mechanism and structure is much different between the two energy storage equipment,the electrode material is a key factor that influences their electrochemical performance.At the same time,their performance will be also influenced by other factors,such as electrolyte,diaphragm and so on.Carbon materials are one of the best anode electrode candidates for supercapacitor and lithium-ion battery.Carbonaceous materials have advantages of large surface area,good electrical conductivity,good chemical stability and low cost.Transition metal oxide nanomaterials have become a promising electrode material because of its high capacity,low cost and good stability.In this paper,hierarchical carbon structure carbon nanostructures were designed and applied to lithium-ion batteries and supercapacitors via the solventhermal and chemical vapor deposition(CVD)method.The morphologies,structures and composition of the as-prepared materials were characterized by scanning electron microscopy,transmission electron microscopy,X-ray diffraction,X-ray photoelectron spectroscopy and Raman spectroscopy.Cyclic voltammetey,galvanostatic charge/discharge test were used to research the electrochemical performance.Mainly research contents are as follows:In chapter 2,an innovative 3D-frame structure ultrathin NiO nanosheets/carbon nanotubes(CNTs)composite as anode for lithium-ion batteries(LIBs)was successfully fabricated via a facile,effective strategy.Our 3D-frame structure NiO@CNTs composite based anode for LIBs also shows ultrahigh capacity,rate,cycling and Coulombic efficiency performance for the ultrafast charge slow discharge.When using 100 mA g-1 to charge and 2000 mA g-1 to discharge(half-cell),the charge and discharge capacity of the NiO@CNTs composites reached 763 and 1000 mAh g-1 at the first cycle,respectively.From the 2nd cycle the Coulombic efficiency is higher than 95%,and after 100 cycles the capacity maintained 122.7%based on capacity of the second cycle.In chapter 3,Carbon thin film/carbon foam core-sheath structure is synthesized by chemical vapor deposition on nickel coated carbonized melamine foam.The unique structure has the highest specific capacitance of 310 F g-1 at current density of 1 A g-1.The structure shows outstanding electrochemical performance in both aqueous and "water-in-salt" electrolyte(NaTFSI).Electrochemical analysis by cyclic voltammetry and Galvanostatic charge-discharge test reveals there is high capacitive contribution up to more than 90%of its total capacitance.The core-sheath structure has advantages in ion transport as well as high utilization of electrode surface,and the synthesis process shows a way to coat carbon thin film on any substrate using nickel catalyzed chemical vapor deposition method.