Preparationof Porous Carbons With Hierarchical Structure And Their Electrochemical Energy Storage Performance

Porous carbons arevery promising materials for electrochemical energy storage due to their high specific surface area,good physicochemical stability and low cost.In recent years,their complex pore structures,surface properties and poor electric conductivity limit their wide applications.In this research,we designed and prepared porous carbon materials with hierarchical structure,including hierarchical porous structure,hierarchical surface property and hierarchical crystalline structure to fulfill high-capacity and high-rate energy storage.Hierarchical porous structure was designed.Firstly,carbon nanospheres with hierarchical porosity were preparedviaa low-concentration hydrothermal reaction with block copolymer F127 as a soft template.Its interconnected hierarchical porous structure and nanoscale ion diffusion pathgreatly promoted the fast charge/discharge process.Secondly,the above-mentioned carbon nanosphereswere employed as raw material and KOH as chemical activation agent to prepare activated carbon nanosphereswith hierarchical porous structure and enhanced porosity.It shows high specific capacitywith gravimetric capacitance of 243 F g-1,volumetric capacitance of 198 F cm-3 and good rate capability with 67% capacitance retention at a high current density of 20Ag-1.Based on the construction of hierarchical porous structure,porous carbon materials with hierarchical surface propertieswere designed.To be specific,the porous surface was modified with abundant nitrogen doping in this research.Firstly,two-dimensional graphene was employed as matrix,and F127 as a soft template to prepare hierarchical porous carbon nanosphere/graphene composite.Subsequent NH3 treatment revealed the surface modification with rich nitrogen functionalities.When used as electrode materials in supercapacitor and lithium-ion hybrid capacitor,it shows superior high-rate performance.It maintains 48% capacitance at an ultrahigh current density of 80 Ag-1 as supercapacitor electrode and shows a maximum power density as high as 336 kWkg-1 in hybrid capacitor.Then,magnesium citrate was used as carbon source and hard template simultaneously to prepare hierarchical porous carbon,and nitrogen doping was fulfilled through NH3 treatment as well.The as-prepared nitrogen-doped hierarchical porous carbon can be well applied in three energy storage systems.In lithium-sulfur battery,it unique microstructure enables high sulfur loading as well as high reversible capacity and good rate performance.As supercapacitor and hybrid capacitor electrode,it also shows high specific capacitance and good rate capability.Further,the mixture of magnesium citrate and potassium citrate were employed as the raw materials to prepare nitrogen-doped hierarchical porous carbon nanosheets through direct pyrolysis and subsequent NH3 treatment.As-prepared two-dementional porous carbon shows excellent performance in both lithium-sulfur battery and supercapacitor.At last,porous carbons with hierarchical crystalline structurewere designed.Cobalt ions were employed as the catalyst for graphitization to achieve partial graphitized carbon.Meanwhile,nitrogenous organic compound was also employedas carbon source to realize nitrogen doping and zinc source as hard template to get hierarchical porous structure.As-prepared porous carbon with hierarchical pore,surface and crystalline structure shows high specific capacity and superior rate performance in lithium-sulfur batteries.