| As the unique electronic structure,the carbon materials such as the graphene and carbon nanotubes（CNT）possess remarkable physical and chemical properties,which make them have a great prospect application in the nanoscale electronic devices,biological sensors,fuel cell,lithium battery,supercapacitor and other fields.While the chemical inertness,van der Waals forces of attraction or entanglement between molecules make the graphene sheets and carbon nanotubes easily re-aggregate,which dramatically decreases their properties and hinders them extensive application.Self-assembly of 2D graphene sheets into 3D porous architectures or simultaneous assembly of 2D graphene sheets and 1D CNTs into 3D graphene-CNTstructurehavebecomecentralissuesinscience research fields.Preparing the carbon materials such as graphene and carbon nanotubes into a liquid-like fluid could solve the aggregation problem of them.In this thesis we first adopted long-chain organic ions to modify the surfaces of CNT and graphene synthetizing these two kinds of solvent-free carbon nanofluids.Then resultant product was carbonized at high temperature under inert atmosphere obtaining two different kinds of three dimension（3D）carbon nanomaterials,and the structures and morphologies of them was in-depth and systematic studied.Finally,the obtained materials were used in the supercapacitor and lithium-silicon batteries to significantly improve their electrochemical properties.The main contents and results of this thesis were listed as follow:1.Eighteen tertiary amine polyoxyethylene ether（abbreviate as PEG-TA）was used to modify the oxide graphene（GO）through chemical reaction with oxygen groups on the surface of the oxide graphene,preparing the solvent-free oxide graphene nanofluids（GOF）.The carbonized products was studied and characterized by X-ray diffraction（XRD）,Raman spectrum,Fourier translation infrared spectrum（FT-IR）,scanning electron microscopy（SEM）and transmission electron microscopy（TEM）,et al.The results were as follows:the carbonized products were formed into 3D porous architectures of graphene under the different temperature.As the carbonization process at 700oC temperature was not completed and the introduction of defects is more,the degree of graphitization is lower and the stacking between layer and layer of graphene is closely,the structure is not very ideal.While under the 800oC temperature,the PEG-TA polymer chain grafted on oxide graphene could be carbonized completely,simultaneously the oxide graphene itself was reduced,the flaws could be healed up,so the degree of graphitization is higher.But it still remained a small amount of oxygen functional groups.For the microstructure,the morphology of product carbonized at 800oC is much well,forming the ideal porous"3D graphene architecture".The architecture is very beneficial to ions and electrons transfer.Comprehensive analysis concluded that 800oC is the best temperature of carbonization of GOF.2.The obtained products carbonized at different temperature were used in the supercapacitor,and the electrochemical performance was measured.The results were as follows:the electrochemical performance of carbonized products was notably improved comparing with that of GO.There were still a small quantity of O and N elements in the carbonized products,the O and N elements could take place oxidation-reduction,so the pseudocapacitance was existed at low current density during charge/discharge process,leading to poorer reversibility.By comparison,it is found that the electrochemical performance of product carbonized at 800oC was the best.At the 0.5 A/g current density,the specific capacitance of it was as high as 278F/g,which is about 12 times of that of GO at the same current density.When the current density increased to 10 A/g,the specific capacitance of CGOF-700 still remained 198 F/g.The composite formed by the product carbonized at 800oC and nano-silicon particles was used in lithium ion battery.It can effectively alleviate the volume expansion of silicon.Compared to the bare silicon,the specific capacity of CGOF/Si electrode has been improved,and the cycling life has been extended.3.The carbon nanotube（CNT）was modified by using long-chain organic silane（DC5700）and poly（ethyleneglycol）（PEG）-tailed sulfonate anion（NPES）,synthetizingthesolvent-freeoxideCNTnanofluids（CNTF）.The carbonized products were in-depth and systematic studied by SEM,TEM,atomic force microscopy（AFM）,XRD,Raman spectrum,et al.The follow results were confirmed.Under the 700oC carbonizing temperature,the DC5700 and NPES long-chain organic ions were converted into few layers of graphene（FLG）with the minimum thickness of 1 nm,forming 3D CNT-FLG architecture with plenties of free-standing space.The specific surface area of this architecture reached as high as 2250 m2/g.The generating mechanism of this structure are further discussed and analyzed,and a series of electrochemical performance of supercapacitor using the obtained 3D CNT-FLG materials as working electrode was measured.It showed that the CNT-FLG working electrode has a good double capacitance characteristics,cycle stability and rate capacity.At the 0.8 A/g current density,the specific capacitance of it was as high as 531 F/g,which is about 5 times of that of p-MCNTs at the same current density.After cycling 10000 times,CNT-FLG electrode capacity retention is still as high as 96%under the current density of 5 A/g.4.Si nanoparticles were first mixed with the prepared CNTF,obtaining Si/CNT-FLG composite.Then the composite was used in lithium ion battery.And the structure and electrochemical performance of it was in-depth and systematic studied.The results were as follows:Si nanoparticles were well dispersed in the CNTF system before carbonization.After carbonization,the Si nanoparticles were encapsulated in the formed CNT-FLG and there was still enough empty space to accommodate the volume expansion of silicon.It is basically consistent with the desired architecture.Si/CNT-FLG battery also shows a very excellent electrochemical performance.The first reversible capacity was as high as 1945 mAh g-11 at 0.1 C.The reversible capacity still remained approximately 1350 mAh g-11 with96%capacity retention after 300 charge/discharge cycles at 0.5 C,demonstrating an outstanding cycling stability performance.Based on the principle of CNT-FLG applying to silicon anode materials in lithium ion battery,the PEG/CNT/Si composite electrodes were prepared by mixing different molecular weight ofpolyethylene glycol（PEG）with CNT and Si nanoparticles.And their electrochemical performances were tested.The results showed that the specific capacity of PEG/CNT/Si composite electrodes obtained by carbonizing the mixture of PEG with different molecular weight,CNT and Si nanoparticles could be reached more than 3000 mAh g-1.The specific capacity showed a gradually increased trend with the increase of cycling times.After cycling a certain number of times,the specific capacity reached maximum,subsequently it began to decay.The molecular weight of PEG had a little effect on the electrochemical performance of the battery.The above results showed that,the 3D carbon nano-materials formed by carbonizing the mixture of PEG with different molecular weight and CNT showed a great potential promising application in improving the electrochemical performance of silicon-based anode materials. |
