Template-Free Method Preparation And Supercapacitive Properties Investigation Of Three-Dimensional Hierarchically Porous Carbons

Supercapacitors,as novel electrochemical energy storage devices,are characterized by high power density,rapid charge/discharge ability and excellent cycling stability,which show great potential application in new energy vehicles,renewable power integration and rail transit.In this dissertation,aiming at the low energy density and the limitation of ion transportation under high power in supercapacitor,the free-templated self-growing hierarchically porous nanocarbons with sheet-or tubular-like were designed.This work mainly focuses on the effect of hierarchical pores designed by sheet-and tubular-like morphologies and modified by heteroatoms to improve electrolyte ions transportation and the enhanced mechanism of capacitance.The detailed research contents are as follows:1.Hierarchically porous sheet-like nanocarbons?HPSNCs?were prepared by the convertion of polytetrafluoroethylene?PTFE?and graphene oxide?GO?under the positive effect of the graphene oxide self-limitation feature and KOH chemical etch.Benefit from the unique hierarchical micro-,meso-and macro-pores and the sheet layer structure design,the electrolyte ions achieve fast ion transportation and migration in HPSNCs.The HPSNC-based supercapacitors achieved both high power density of 35 kW kg^-1 and high energy density of51.7 Wh kg^-1.2.Based on chlorination etching TiC_0.5N_0.5 technique,N and Cl co-doped hierarchically porous sheet-like nanocarbons?CDCs-N/Cl?were in situ synthesized.CDCs-N/Cl in deionized water showed no obvious sedimentation phenomenon after standing above one month,indicating superior hydrophilicity.The CDC-N/Cl electrodes achieve specific capacitance of 277.7 F g^-1 in KOH electrolyte,which is the highest value among the reported CDC materials.The assembled asymmetrical supercapacitors can achieve 74.1%capacitance retention when the current density increase by 300 times,and 97%initial capacitance can be retained after sustaining charge/discharge 20000 cycles at a current density of 2 A g^-1,which unambiguously demonstrated that the superior power performance and cycling durability.3.Controllable construction of hierarchical porous tubular nanocarbons?hCTNs?on various conductive substrates controlled through magnesium thermal reduction method based on solid-gas interface reaction.The as-prepared hCTN networks structure can be tuned and possess good mechanical flexible.The assembled solid-state flexible supercapacitor delivered an areal capacitance of 80 mF cm^-2,and almost no capacitance decay under bended,folded and twisted different strain state.Moreover,the flexible solid-state supercapacitor is liable to connection in series and in parallel,thus can achieve the controlled output of voltage and current,showing potential application in novel flexible energy storage devices.