Preparation Of Heteroatom-doped Carbon/Carbon Composite Material And Application In Lithium Ion Battery

New carbon materials such as graphene,amorphous carbon,and biomass-derived carbon are used as anode materials for lithium-ion batteries,overcoming the disadvantages of traditional graphite anodes,such as low theoretical specific capacity(372 mAh g^-1),slow lithium ion transmission speed,and poor performance.However,when single carbon material is used as anode electrode material for lithium ion battery,it has also existed some limitations.Therefore,it is particularly important to modify these new carbon materials.In this thesis,the heteroatom-doped carbon/carbon composite material prepared by modifying pyrolytic ionic liquids（ILs）with different morphology of carbon substrates combine the advantages of two carbon materials and have good electrochemical performance properties when used as anode materials for lithium-ion batteries.The main research contents are as follows:（1）Based on melamine foam pyrolyzed carbon（CMF）as the substrate,and1-ethyl-3-methylimidazole hydrogen sulfate（[EMIm]HSO4）pyrolyzed nitrogen-sulfur co-doped carbon NSDC and CMF were synthesized to prepare NSDC@CMF composite.The effects have been investigated of salt template and melamine carbon foam substrate on the structure and morphology of NSDC@CMF composite material.The results showed that NSDC grew on the CMF substrate.NSDC@CMF was used as anode material for lithium-ion batteries,with a discharge/charge specific capacity of 1843.7/861.1mAh g^-1 in the first cycle at a current density of 0.5C,and a reversible specific capacity of 539.4 mAh g^-1 after 750cycles.（2）Based on cotton pyrolysis carbon fibers（CCFs）as the substrate,and1-hexyl-3-methylimidazolium dinitrile salt（[HMIm]N（CN）2）pyrolyzed nitrogen-doped carbon NC and CCFs were synthesized to prepare NC@CCFs composite material.The microscopic morphology,structure and element distribution of NC@CCFs composite material have been studied.The results showed that the NC was evenly coated on CCFs,and the nitrogen doping amount reached 14.85%.When the NC@CCFs composite material was used as anode material for lithium ion battery,the discharge/charge specific capacity is 1256.9/789.8 mAh g^-1 for the first cycle at a current density of 0.5C,and it still has a reversible specific capacity of 614.3 mAh g^-1after 250 cycles.It has a reversible specific capacity of 220.2 mAh g^-1 at a large rate of 10C.（3）Based on reduced graphene oxide（rGO）as the substrate,and1-ethyl-3-methylimidazole dinitrile amine salt（[EMIm]N（CN）2）pyrolyzed nitrogen-doped carbon NDC and rGO were synthesized to prepare sandwich-like rGO@NDC composite material.The microscopic morphology,structure and element distribution of composite materials have been studied by SEM,TEM,XRD,Raman,FTIR and XPS.The results showed that the sandwich-like composite rGO@NDC was composed of NDC particles covering the surface of rGO and NDC particles between the rGO layers,and the nitrogen doping content reached 7.68%.When the composite material was used as anode material for for lithium ion battery,in the first cycle the discharge/charge specific capacity was reached 1392.9/790.1 mAh g^-1 at a current density of 0.5C,and it showed a high discharge specific capacity of 409.4 mAh g^-1after 50 cycles.It maintained a discharge specific capacity of 222.8mAh g^-1 after 1200cycles under a large current density of 10C and almost with no capacity decay.