| Supercapacitors are of great interest in modern society due to their high charging efficiency,long cycle life,wide operating temperature range,long cycle life,high volumetric and specific capacitances,small volume and environmental friendliness.Carbon is currently the most widely used supercapacitor electrode material due to its wide source of raw materials,low cost,environmental protection,large surface area,good conductivity,wide operating temperature range and high stability.However,its volume energy used in commercial super capacitors is only?5 to 6 Wh L-1,which is limited in practical application.Fluorine-doped(F-doped)carbons are attractive candidates for supercapacitor electrode material owing to their high capacitance and high rate capability.However,synthesis of F-doped carbons typically requires highly hazardous or expensive fluorine-based reactants and has low efficiency due to low levels of fluorine uptake by the carbon.In the present study,we introduce an effective means to F-doped carbon using polytetrafluoroethylene(PTFE)pyrolysis.In this thesis,nickel ion exchanged resin was used as a carbon source to synthesize graphitized porous carbon.In addition,fluorine-doped carbon materials were prepared with PTFE as fluorine source and commercial activated carbon and nickel ion exchange resin as carbon source,and their applications in organic supercapacitor electrode materials were studied.The main research contents and results are as follows:(1)In the first chapter,the simple synthesis of low-temperature graphitized porous carbon material from a Ni-ion exchanged resin is described.NiCl2 is added to the carbon source as catalyst and KOH as pore-forming agent to produce highly porous graphite(HPG)at low temperature(<1000 ?).Compared with the traditional high temperature sintering method,the use of NiCl2 lowers graphitization temperature and saves the production cost greatly.Besides,the graphitized porous carbon material prepared has a larger specific surface area.(2)HPG is evaluated as an organic supercapacitor electrode material by different electrode thickness.HPG at 50-?m film thickness produced the total cell and material volumetric capacitance of 10.2 and 61 F cm-3 respectively,while the material specific capacitance was 120.5 F g-1 at volumetric current of 0.25 A cm-3.HPG exhibited the capacitance retention of 94.1%at high volumetric current of 2.5 A cm-3,undoubtedly indicating an excellent rate capability.Besides,HPG revealed good extraordinary cycling stability with the capacitance retention of 81.2%at volumetric current of 1.5 A cm'3 after 10,000 cycles.(3)In the second chapter,we demonstrate two possible means of synthesizing F-doped carbon using polytetrafluoroethylene(PTFE)pyrolysis:firstly,by directly pyrolyzing the polytetrafluoroethylene(PTFE)mixed AC in the presence of the nitrogen atmosphere under 800 ? to produce AC-F,and secondly by direct synthesis of an F-doped highly porous graphite(HPG-F)in the same environment.As supercapacitor electrode materials in organic electrolyte,both AC-F and HPG-F outperform their non-F-doped counterparts,delivering up to 40%gain in cell volumetric energy at high power cycling.Considering current collector and separator volume fractions,cells containing AC-F electrode films of 100 and 50 ?m deliver an impressive 12.9 Wh L-1 at 0.1 kW L-1 and 6.7 Wh L-1 at 2.15 kW L-1 respectively,and cells containing AC-F electrode films of 100 ?m revealed excellent extraordinary cycling stability of the capacitance retention of 97.1%at volumetric current of 1.5 A cm-3 after 10,000 cycles.F doping can effectively improve the electrochemical performance of carbon materials,which is closely related to the high electronegativity of fluorine.In addition,it is likely that simple synthesis methods will further improve other supercapacitors in the same way. |
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