Design And Fabrication Of Carbon Based Electrode Materials And Their Application In Energy Storage

With the growing demand of energy and the development of new energy,new energy storage devices also need to be developed.Supercapacitor has higher power density.However,its energy density is still lower than that of battery.The energy density of supercapacitor is in proportion to its specific capacitance.Thus the energy density could be enhanced by increasing specific capacitance.Furthermore,the electrode materials have great influence on the specific capacitance of supercapacitor.Hence,designing and fabricating high quality electrode materials plays a decisive role in developing high performance supercapacitors.Owing to high specific surface area,stable structure and well controlled pore size,and surface area,porous carbon materials have great potential application in energy storage.The structure and conductivity and surface chemical property have a great influence on the electrode performance.This thesis is intended to synthesis of porous carbon materials by means of simple and efficient methods.At the same time design and system study the electrode materials from the structure and surface property.The main work in this thesis is as follows:(1)Preparation of nitrogen doped graphene through artifical layered precursor is proposed.Frstly,inorganic/organic lamellar compound was synthesized through precipitation and self assembly.Secondly,the lamellar compound was carbonized and graphene was in situ formed between the layes by catalytic graphitization of Fe species.Finally,two different morphologys nitrogen doped graphene was obtained by removing inorganic metal compounds using concentrated hydrochloric acid.Bubble like graphene and sheet like graphene could be formed by using octylamine and dodecylamine,respectively.The content of nitrogen in graphene was about 5.11 percent.The specific surface area of bubble like graphen is 650 m2/g.The electrochemical performances of two kinds graphene was studied in acidic and alkaline solution conditions,respectively.It was found that the specific capacitance of bubble like graphene was higher than that of sheet like graphene.The specific capacitance of graphene in acidic solution condition was higher than that in alkaline solution condition.The specific capacitance of bubble like graphene is up to 261 F/g in 2 M H2SO4 electrolyte.(2)A mesoscale approach to synthesis of the hollow graphene nanospheres through a catalytic self-limited assembly of graphene on in-situ formed nanoparticles was proposed.Hollow structure sulfur doped graphene nanospheres was synthesized by SDS intercalating the layer of a-Ni(OH)2 and carbonizing under inert atmosphere at different temperatures.The structure and capacitance performance of hollow graphene nanospheres at different temperatures were studied and possible mechanism was proposed.The obtained hollow graphene spheres have interconnected pores and stacked graphene spheres which facilitate fast ion transport and electron transfer.The specific capacitance could up to 180 F/g at 0.5 A/g.Based on the special structure of hollow graphene spheres,the hollow graphene spheres were employed as hosts to accommodate the sulfur.A very high initial discharge capacity of 1520 mAh/g,corresponding to 91%sulfur utilization rate at 0.1 C was achieved on graphene nanosphere/sulfur composite with 64 wt%loading.A retention of 70%was maintained when the current density increased from 0.1 to 2.0 C,and a decay rate of 0.06%per cycle during 1000 cycles was detected.The decay rate is the best record based on carbon/sulfur cathode in a DOL/DME electrolyte with a routine cell configuration in reported literatures.(3)A facile and efficient strategy for preparing three dimensional flower-like hierarchical mesoporous carbon superstructures through a one-pot hydrothermal reaction was proposed.In the fabrication process of FMCS,the nickel acetate plays multifunctional roles:as inducer of flower-like hierarchical carbon,as catalyst of graphitization,and as pore-forming agent.Hierarchical porous carbon can shorten the diffusion distance of electrolyte,thus the rate capacitance of electrodes can be enhanced.Compared with the solid carbon sphere,FMCS electrode showed excellent rate capacitance.The specific capacitance of FMCS is up to 226 F/g at a current density of 0.5 A/g,and retained 82%(185 F/g)at high current density of 20 A/g,indicative of outstanding rate capability.(4)Activated carbon was prepared through microwave heating camellia oleifera shell with KOH.Microwave heating has the advantage of high heating temperature and short heating time,so a number of functional groups can be retained in the carbonization process.These functional groups not only can improve the wettability of the electrode,but also can react with electrolyte and enhance the initial capacity.The electrochemical test shows that the initial capacitance of activated carbon which prepared through microwave heating(251 F/g)is increased by 17 percent than that was prepared under high temperature(214 F/g).(5)Ni/NiO@C composite nanofibers with different metal content were prepared by electrospinning method.The morphology of Ni/NiO@C was characterized.The capacitance performance of Ni/NiO@C was also studied in alkaline solution.Based on this method,hollow structure and coaxial line Mn2O3 nanofibers were prepared by sigle nozzle electrospinning.The structure and formation mechanism of nanofibers were discussed.Electrochemical tests showed that hollow structure Mn2O3 nanofiber displayed a higher specific capacitance than coaxial line structure Mn2O3 nanofibers.