Construction Of Two-Dimensional Hierarchical Carbon Nanomaterials And Their Application In Lithium-Ion Batteries

Two-dimensional(2D)carbon nanomaterials are being extensively explored for next-generation electrochemical energy storage and conversion systems.When they are used as Li-ion battery anodes,their high surface areas can provide abundant electrochemical active sites,thus giving rise to high specific capacities.Furthermore,2D nanostructures can shorten the ion diffusion length and promote high-rate performance.In addition,their extraordinary mechanical properties enable facile strain relaxation,hence allowing for good cycling stability.However,owing to the Van dcr Waals’ interaction,2D carbon nanomaterials often suffer from serious aggregation problems,which greatly reduce the active surface area and hinder smooth Li-ion diffusion.The construction of hierarchical structures assembled by 2D nanocarbon subunits may provide an effective approach to address the above-mentioned problem,and to take full advantage of their large surface area.Moreover,optimization of pore size distribution and heteroatom functionalization also have significant meaning for improving their Li-ion storage performance.In general,the traditional methods of synthesizing hierarchical carbon nanomaterials are time-consuming and energy-consuming,and the productivities are far from satisfaction.Therefore,constructing 2D hierarchical carbon nanomaterials with eco-friendly methods is a promising research area.In this thesis,the work mainly focused on following aspects:(1)A unique 2D hierarchical carbon architecture(2D-HCA)was constructed by utilizing Mg-Al layered double hydroxide as template to adsorb a typical toxic,refractory organic anionic dye(Orange Ⅱ)as the carbon precursor.The microstructure and preparation mechanism of 2D-HCA was investigated through a series of characterization.The experiment results suggested that 2D-HCA was consisted of 2D nanocarbon subuints,and it had a porous structure which was dual-doped with N and S heteroatoms.(2)Based on the preparation route of 2D-HCA,an N-rich 2D hierarchical carbon architecture(N-2D-HCA)was synthesized with one-step doping method by utilizing melamine as the N precursor.The microstructure of N-2D-HCA,and the concentration as well as the types of the doped N,were characterized and analyzed.The characterization results showed that N-2D-HCA was also consisted of 2D nanocarbon subuints.The N concentration was 15.5%,and pyridinic N and pyrrolic N,which were electrochemically active N,accounted for 84%of total N in N-2D-HCA.(3)The electrochemical Li-ion storage performance of these two nanocarbon,including cyclic voltammetry curves,cycle performance and rate capabilities was tested with half battery system.The electrochemical testing data suggested that 2D-HCA exhibited ultra-high specific capacity,and N-2D-HCA exhibited superior capacity stability during cycling.Experimental results in this thesis proved that,constructing 2D hierarchical architecture can help to alleviate the aggregation and stacking problem of 2D nanocarbon subunits,which can enhance the surface area utilization of 2D carbon nanomaterials,and thus achieving superior Li-ion storage performance.This paper has constructed 2D hierarchical carbon architecture with excellent Li-ion storage performance by utilizing Orange Ⅱ as carbon precursor,achieving the green utilization of pollutants in wastewater.