Synthesis Of Porous Carbon Derived From Polymer And Their Composites For The Application Of Supercapacitors

As an important electrochemical energy storage system,supercapacitors（SCs）possess advantages of high power density,long cycling life and great safety to meet the requirements of particular applications.Porous carbon materials have been widely utilized of the commercial supercapacitors due to the large specific surface,high electrical conductivity,abundant sources,excellent chemical stability and environmental friendliness.The electrochemical performance of carbon materials are determined by specific surface area,pore size distribution,conductivity,micromorphology and heteroatoms doping,which directly affect the energy density of carbon-based supercapacitors.Polymer-derived porous carbon materials have tunable chemical composition,porosity and self-assembling（nanometer）structure,which maximize the utilization and function of carbon materials,thus achieving optimal electrochemical performance.In this thesis,a series of novel polymer-derived porous carbon materials and their composite are developed to improve the specific capacitance.Besides,hybrid LICs and asymmetric supercapacitors are constructed by using organic electrolyte and ionic liquid to broaden the working voltage,which can remarkably enhance the energy density of carbon-based supercapacitors.The main researches are as follows:（1）The mesoporous hollow carbon spheres（MHCSs）were synthesised by using SiO₂as templeta and phenolic resin as carbon source.To introduce pseudocapacitance,an effective encapsulation strategy was used to prepare a core-shell structured Mo S₂@MHCSs,which is used as an excellent electrode material for aqueous supercapacitors.The results indicate that mesoporous hollow carbon spheres shell not only effectively confines the growth of Mo S₂nanosheets inside shells,but also improve significantly the conductivity and structural stability of the nanocomposite,which alleviate the volume expansion and reduce ion diffusion paths.The nanocomposite electrode delivers a high specific capacitance(613.4 F g^-1 at 1 A g^-1)and good rate performance(358.2 F g^-1 at 10 A g^-1)as well as excellent cycle performance.（2）To enhance the energy density of supercapacitors,a hybrid Lithium ion capacitors（LICs）in Li PF₆-containing organic electrolyte was designed and fabricated,which used the Mo S₂@MHCSs nanocomposite as the anode and polyaniline active carbon（PAC）as the cathode.The results show that the Mo S₂@MHCSs composite material is an excellent hybrid capacitor negative electrode material with high specific capacitance(1160 m A h g^-1 at 0.1 A g^-1).Furthermore,combined with the ideal double-layer energy storage stability of PAC materials,the developed Mo S₂@MHCSs-based hybrid LICs deliver an outstanding specific energy density value of 82 Wh kg^-1 at 10000Wkg^-1,which successfully constructs a novel energy storage device with high energy output.（3）Because of the expensive template,complicated procedures and low yield,a free-template/self-doping method combined with Cu Cl₂-activation strategy were used to prepare high N/O co-doped porous carbon spheres（CS）derived from a facilely-synthesized quinone-amine polymer precursor.The as-prepared N/O-doped CS exhibit a uniform nanosphere-like geometry with hierarchical porosity,large surface area(as high as 2957.8 m² g^-1)and ultrahigh N/O dopants（as high as 14.9/10.6 at.%）.Owing to these combined merits,the optimal CS-Cu Cl₂-800 exhibits a high specific capacitance(273 F g^-1 at 0.5 A g^-1)and excellent cycle stability in aqueous supercapacitor.Furthermore,the solid-state supercapacitors based on the ionic liquid gel electrolyte can not only deal with the leakage problem,but also maintain a high energy density of 71.3 Wh kg^-1 at 350 W kg^-1,successfully realized the application of carbon nanospheres in high energy output all-solid supercapacitors.（4）To achieve various structural morphologies,a new type of N-doped porous carbon nanorods with large surface area and high N/O level were prepared from a N/O-rich polymer precursor.The polymer precursor were synthesized by the condensation of two low-cost comonomers（3,3’-diaminobenzidine and 2,5-dihydroxy-1,4-benzoquinone）.Utilizing the mild activation agent of Cu Cl₂to fulfill one-step carbonization/activation not only can maintain the natural morphology of the precursor and reduce the release of heteroatoms,but also can achieve high-yield synthesis of N-doped porous carbon with high specific surface area.The best-performed C-Cu Cl₂-800exhibits a delightful capacitance of 271 F g^-1 at 0.5 A g^-1 and 180.2 F g^-1at 20 A g^-1.The capacitance retention of the supercapacitor is 97%after 10 000 charge/discharge operations at 5.0 A g^-1 in aqueous electrolyte.Moreover,a high energy density of 64.5Wh kg^-1 at 350 W kg^-1 is also demonstrated for the ionic-liquid-based supercapacitor.（5）In order to introduce the high pseudocapacitance of polymer-derived carbon nanorods（CNR）,a facile hydrothermal reaction was presented to prepare Ni Co₂S₄@CNR composite materials.Studies from structural characterization and electrochemical measurements show that a nanosheet-like Ni Co₂S₄ uniformly grow on the surface and the inner pores of CNR.The composite maintain the nanorod-like morphology and display the character of cubic Ni Co₂S₄.The Ni Co₂S₄@CNR composite electrodes show larger specific capacitances(1138.8 F g^-1 at 0.5 A g^-1)than that of CNR electrodes and higher rate capability(941.5 F g^-1 at 20 A g^-1,82.4%)than that of Ni Co₂S₄（47.7%）.The energy density of asymmetric supercapacitors（ASCs）assembled by Ni Co₂S₄@CNR composite materials and CNR is as high as 23.9 Wh Kg^-1 at the power density of 145 W Kg^-1.Besides,the capacitance retention of ASCs remained 86.7%after 5000 cycles at 1 A g^-1.