Preparation And Electrochemical Performance Of Porous Carbons

Supercapacitors have prefect reversibility,high power density,long service life and few self discharge,and also possess advantage on energy density and environmental protection,which have been payed more attention in area of maintaining power.Generally,electrode materials are the decisive factor of performance in supercapacitors.Owning to sustainable precursors,low cost,strong stability and good electrical conductivity,porous carbon is an ideal candidate for supercapacitors electrode materials.In this thesis,we prepared porous carbon materials from ionic liquids,coal liquefaction pitch and tea by different methods.The specific surface area,pore structure,the surface chemical state,and the degree of graphitization correlating to their electrochemical performance were studied.The main contents and results of this thesis are shown as follows:?1?Nitrogen doped porous carbons?NPCs?,were prepared from precursor of a soluble and easily dispersive cross-linked poly?ionic liquid?copolymer of 1-vinyl-3-butylimidazolium bromide?VBImBr?and divinylbenzene?DVB?,and with SiO₂?from tetraethyl orthosilicate?as a template.The specific surface area and pore structure of NPCs were depended on the precursors,the SiO₂/VBImBr ratios and carbonization temperature.Under the optimized condition,the NPC_{P?IL-DVB?-0.2-900}?IL-DVB?-0.2-900 prepared from P?VBImBr-0.1DVB?gave high specific surface area up to 1324 m²·g^-1.The amorphous and disordered graphitic layers were dominant in NPCs.The nitrogen contents were about 4-5 wt%in NPCs,and nitrogen bonding state on surface was mainly pyridinic-and pyrrolic-N.Meanwhile,the specific capacitance of NPC_{P?IL-DVB?-0.2-900}?IL-DVB?-0.2-900 was up to 243 F·g^-1at 0.1 A·g^-1and 192 F·g^-1at 2 A·g^-1,and the retention ratio was nearly 100%after being cycle charge-discharge 2400 times at 2 A·g^-1 in three-electrode with 6M KOH as electrolyte.?2?Porous carbons were prepared through a protic ionic liquid1-hydrogen-3-butylimidazolium hydrogen sulfate?HVImHSO₄?as main precursor and another ionic liquid as assistant through one-step carbonization process.The specific surface area and pore structure of PCs were depended on the type of assistant ionic liquid and the assistant ionic liquid/HVImHSO₄ ratios.Nitrogen,phosphorus and sulfur co-doped porous carbons could be gained in the specific surface area up to above 1000 m²·g^-1 with BMImPF₆ assistant under the optimized condition.The amorphous and disordered graphitic layers were dominant in PCs.Nitrogen bonding state was mainly N-Q?N substituted groups of aromatic graphite structure?,phosphorus was mainly in P-O type groups,and sulfur was attributed to C-S-C type sulfur.Meanwhile,the specific capacitance of PC_-BMImPF6-0.5BMImPF6-0.5 was 138 F·g^-1 at 0.5 A·g^-1 and 100 F·g^-1 at10 A·g^-1,the retention ratio was 95.8%after being cycle charge-discharge 10000 times at 2A·g^-1 in three-electrode with 6 M KOH as electrolyte.?3?Activated carbons?ACs?were prepared from coal liquefaction pitch?soft point 243??and tea through carbonization and activation method.The CLP/tea ratios,activating agent type,activating agent/carbon ratios and activating temperature influenced specific surface area,pore structure,surface chemical state,and degree of graphitization of ACs,and affected their electrochemical performance further.ACs activated by steam gave lower specific surface area and specific capacitance.AC_1/3-2.5-700/3-2.5-700 prepared under conditions of CLP/tea ratio of 1/3,KOH/carbon ratio of 2.5/1 and 700?,gave high specific surface area up to 2184 m²·g^-1,surface nitrogen content 2.1 at%and oxygen content 6.98 at%.The specific capacitance of AC_1/3-2.5-700was up to 323 F·g^-1 at 0.5 A·g^-1 and 215 F·g^-1 at 50 A·g^-1 in three-electrode with 6 M KOH as electrolyte.Meanwhile the energy density was 2.9 Wh·kg^-1 at power density of 6936 W·kg^-1,the retention ratio was above 95%after being cycle charge-discharge 10000 times at 10 A·g^-1in simulative button supercapacitors with 6 M KOH as electrolyte.?4?Spherical activated carbons?SACs?were prepared from coal liquefaction pitch?soft point 110??through carbonization with high temperature spray drying and activation with steam,CO₂ and KOH.The balling and carbonization of coal liquefaction pitch were completed in single-step of high temperature spray drying,meanwhile spherical carbons with size of 0.5-3?m were gained.SAC_KOH-800-1OH-800-1 prepared from spherical carbons with KOH as activating agent,gave high specific surface area up to 1739 m²·g^-1 and oxygen content 6.59 wt%.SAC_KOH-800-1had better wettability than SACs activated by steam and CO₂.The specific capacitance of SAC_KOH-800-1OH-800-1 was up to 266 F·g^-1at 0.5 A·g^-1and 161 F·g^-1at 50 A·g^-1in three-electrode with 6M KOH as electrolyte.Meanwhile the energy density was 3.1 Wh·kg^-1 at power density of 7020W·kg^-1,the retention ratio was 100%after being cycle charge-discharge 10000 times at 10 A·g^-1in simulative button supercapacitors with 6 M KOH as electrolyte.