Controllable Fabrication Of Two-Dimensional Carbon Materials And Their Electrochemical Applications

Owing to the high surface area,high conductivity,good stability and the ability to binding various organic/inorganic active components,two-dimensional?2D?carbon materials have been widely applied in diversified energy storage and conversion devices such as lithium ion battery?LIB?,sodium ion battery?SIB?,supercapacitor and fuel cells.In the last decades,the rapid development of portable and wearable electronics including cell phones,unmanned aerial vehicles,electric vehicles and smart watches has boost the demand on high performance energy devices.Among these devices,LIB is the most developed secondary battery,which has high energy density,no memory effect,high output voltage and long cycling life.As the potential substituent for LIB,SIB doesn't only have the advantages of LIB.The low cost of sodium resources is also one attractive feature of SIB.On the other hand,supercapacitor is also a highly attractive energy storage device,which has high power density and fast charge/discharge ability.Nowadays,the development of the electrode materials in aforementioned energy devices is still not satisfying and the following points are what people concern most:?1?The electrode materials in commercial LIBs have low capacity.The generally used cathode material,LiFePO₄,only has a theoretical capacity of 170 mA h g^-1.And the graphite anode can just delivery a theoretical capacity of 372 mA h g^-1.?2?The huge demand on LIBs from the electric vehicle market caused the rapid increasing on the price of Li mineral.?3?The commercial supercapacitors have low capacity,which prohibit the practical application of them.In this thesis,we designed different routes for the controllable fabrication of several 2D carbon materials.Their applications as the electrode materials in LIB,SIB and supercapacitor are also investigated.The detailed research contents including:?1?The fabrication of the composites with graphene oxide?GO?and perylene diimide?PDI?as the cathode materials in LIB:In this part,the most often used organic LIB cathode,PDI was selected to construct composites with GO sheets.During the solvothermal treatment process,the?-?interactions between the aromatic parts of PDI and GO and the ionic interactions between negatively charged GO and positively charged PDI enable PDI to bind on the surface of GO.The following thermal treatment can reduce GO and remove the positively charged groups in PDI,which will further enhance the interactions between the two components and improve the stability and conductivity of the composites.The applications of the composites as the cathode materials in LIB and SIB were further studied.The different electrochemical performances of pure PDI,the intermediates after solvothermal treatment and the final products were compared,which discloses the effects of GO composition and thermal treatment on the performances of PDI in LIB/SIB cathodes.The sample obtained after solvothermal treatment,which is named as G-P,showed a high capacity of 262 mA h g^-1 as the LIB cathode at the charging rate of 25 mA g^-1,which is much higher than that of LiFePO₄.On the other hand,G-P also manifested a capacity of 101 mA h g^-1 at 50mA g^-1 when it was used as the cathode in SIB.G-P-300,the sample after thermal treatment delivered a capacity of 166 mA h g^-1 at 50 mA g^-1,much higher than most of the known PDI composites in SIB cathode.More importantly,the fabrication strategy can be utilized to build up the composites of organic aromatic molecules and GO,leading to enhanced conductivity,rate performance and capacity for the resulting composites.?2?Fabrication of hexagonal nitrogen doped carbon nanosheets with LDHs as templates:In this part,a“melting warp-cooling-carbonization”method was applied to combine the polymerization of monomer and the carbonization of the resulting polymer in one step.Firstly,melted1,2-diaminobenzene was mixed with LDH at 110 ^oC.After cooling to room temperature,crystalized 1,2-diaminobenzene can form uniform layers over the surface of LDHs.The following thermal treatment enable the polymerization of 1,2-diaminobenzene and the carbonization of the obtained polymers.Hexagonal nitrogen doped carbon nanosheets were then produced after the LDH templates were etched.Compared with solution polymerization process,this method doesn't need any solvent and other can also be used.Diversified carbon materials can be obtained in this way by selecting different polymerizable nitrogen containing monomers and polymerization-carbonization temperatures.As the anode materials in LIB,the carbon sheets fabricated in this work manifested a high capacity of 829.6 mA h g^-1 at 100 mA g^-1,much better than graphite.As the electrode materials in supercapacitor,the carbon sheets also gave a high capacitance of 249.5 F g^-1 at the charging rate of 1.0 A g^-1.