Synthesis Of Heterogeneous Carbon Nano-composite Materials And Their Application For Energy Storage

Carbon nano-materials have achieved much attention in the field of supercapacitors and lithium-ion batteries?LIBs?because of their unique structure and excellent physical and chemical performances,including high specific surface areas,great conductivity and superior mechanical property.At present,many kinds of carbon nano-materials have been used in the energy storage such as 0D carbon naon-onions?CNOs?,1D carbon nanotubes?CNTs?and 2D graphene.Different dimentions have their own advantages.Therefore,the composite of different dimensional structures is the key to promote the application of carbon nano-materials in the energy storage.This study has used the chemical vapor depositon?CVD?method to design and synthesize the carbon nano-composite materials including the carbon nano-chains with the self-assembly of carbon nano-onions,the carbon films composed of hollow nano-micro spheres and the sandwiched graphene sheets which were filled with yolk-shell?-Fe₂O₃nanoparticlesencapsulatedbygrapheneshells?YS-?-Fe₂O₃@G-GS?.The preparation processes,the growth mechanism and their electrochemical performances have been investigated.This study aimed to lay a foundation for the deveiopment of LIBs and supercapacitors with excellent performance.1)The study reports the use of Fe-Ni catalyte on MgO substrate for the growth of the carbon nano-chains?CNCs?by chemical vapor deposition?CVD?.The influence of growth conditions?growth temperature,time and gas ratio?on the carbon structures and the growth mechanism of the CNCs were investigated.Moreover,the CNCs has been activated with KOH and the activation parameters,including the KOH content,temperature and duration,were investigated.The mechanism was also discussed.The results indicated that the CNCs are in favor to grow at 750? with CH₄ is 60 mL min^-1.The growth mechanism combining the dissolution-precipition of carbon and the diffusion of catalyte has also been discussed.After activation,the CNCs have much improved specific surface area and porous structure.The electrochemical performance investigations showed that the activated CNCs have a power density of 159.6 kW kg^-1 and an energy density of15.5 Wh kg^-1,as well as excellent cycle stability,which is very superior to the original CNCs and due to the improved surface and micro-mesoporosity without sacrificing their electronic transmission properties.2)The study has developed a colloidal film-assisted CVD method to synthesize the carbon films composed of hollow nano-micro spheres.The influence of growth conditions?pressure,growth temperature and time?during CVD process on the carbon structures and the growth mechanism of the carbon films were investigated.The binder-free carbon film is flexible and tough,advantaged for the assembly of all solid-state supercapacitors.Under the low press,the carbon nano-micro sphere film can be synthesized at 600? for 10 min.Benefitting from the composite of nano-micro 0 D structures,the performance of the carbon nano-micro sphere film in supercapacitors is remarkably improved,which exhibits the ultrahigh area specific capacity.At the current density of 5 mA cm^-2,the area specific capacity can be 903mF cm^-2.When the current density increased to 500 mA cm^-2,the area specific capacity can be 729 mF cm^-2.3)In the study,A convenient and scalable in-situ CVD method is developed for one-step fabrication of sandwiched graphene sheets which were filled with yolk-shell?-Fe₂O₃nanoparticlesencapsulatedbygrapheneshells?YS-?-Fe₂O₃@G-GS?.The influence of growth temperature has been tested.In the aid of the first principle calculation,the formation mechanism has also been found,which is about the carbon shell suppports the nucleation site for Fe₂O₃ and makes the yolk form.As a result,long-term cyclic stability at high rates and superior rate capability can be obtained when YS-?-Fe₂O₃@G-GS were used as an LIBs anode.