High Performance Supercapacitors Based On Distinctivepolymer-derived Carbon Nanomaterials

Supercapacitors are a new type of electrochemical energy storage devices with the ultrahigh output power,fast charge/discharge process and the advantages of long cycle life.As a result,supercapacitors have been widely applied to hybrid electric vehicles,portable electronic devices,emergency equipment system and so on.However,the energy density of commercial supercapacitors is still lower than that of lithium-ion batteries and fuel cells.Therefore,the supercapacitors are still restricted for further widely application in various fields.To improve the energy density?E?of supercapacitors and maintain their intrinsic high power density,both the device capacitance?C,dependent on the inherent properties of electrode materials?and the operating voltage?V,dependent on the decomposition voltage of electrolytes and construction of asymmetric device structure?should be improved according to the equation of E=1/2 CV².In order to improve the energy density of supercapacitors,we first analysed the factors on the properties of supercapacitors,and then designed and prepared cheap conductive polymer and polymer-derived carbon nanomaterials as the electrode material,simultaneous match the appropriate electrolytes to construct the novel symmetric/asymmetric supercapacitors.The main research contents and results are as follows:1.Two-dimensional mesoporous carbon nanosheets?CNSs?have been prepared via simultaneous activation and catalytic carbonization route using macroporous anion exchange resin?AER?as carbon precursor,ZnCl₂ and FeCl₃ as activating agent and catalyst,respectively.The iron catalyst in the skeleton of the AER may lead to carburization to form a sheet-like structure during the carbonization process.The obtained CNSs have a large number of mesoporous,a maximum specific surface area of 1764.9 m² g^-1 and large pore volume of 1.38 cm³ g^-1.As an electrode material for supercapacitor application,the CNSs electrode possesses a large specific capacitance and excellent rate capability.Furthermore,CNSs symmetric supercapacitor exhibits specific energies of 17.2 Wh kg^-1 at a power density of 224 W kg^-1 operated in the voltage range of 0-1.8 V in Na₂SO₄ aqueous electrolyte,and outstanding cycleability.2.We developed a facile one-step activation and nitrogen-doped combination method using AER as carbon precursor,the combination of Ca?OH?₂ and NH₄Cl as an activator and nitrogen source for preparation of nitrogen-doped graphene-like carbon nanosheets?N-CNSs?.The N-CNSs have abundant wrinkled structures and ultrahigh pore volume(3.19 cm³ g^-1)as a high-performance electrode material for supercapacitors.Based on the above results,in order to form advanced 2D carbon nanosheets,we further incorporate urea as a nitrogen source and expansive agent,CaCl₂ acts as an activating agent,with AER as carbon source to prepare the highly crumpled nitrogen-doped graphene-like nanosheets?CN-GLSs?.The CN-GLSs contain highly crumpled morphology,high surface area(1169 m² g^-1)and effective nitrogen doping?about 4.25 wt%?.Benefiting from the unique structure,the CN-GLSs exhibit high capacity,excellent rate capability,high energy density and extraordinary long cycle performance.3.High-performance aqueous asymmetric supercapacitors?ASCs?are designed and assembled based on pseudocapacitance in both positive and negative electrodes to obtain the large working voltage and high energy density,while maintaining a high power density and long cycle life.?1?High energy density ASC is assembled based on polyaniline?PANI?nanotubes positive electrode and MoO₃ nanobelts negative electrode in 1 M H₂SO₄ aqueous electrolyte.The assembled novel PANI//MoO₃ ASC device with an extended operating voltage window of 2.0 V in spite of the use of aqueous electrolyte and exhibits excellent performance,reaching an energy density as high as 71.9 Wh kg^-1 at a power density of 254 W kg^-1.?2?A novel CNF//WO₃ ASC is assembled based on carbon nanofibers?CNF?network positive electrode and WO₃nanorod bundles negative electrode.Polyaniline-based CNF are prepared by direct carbonization of polyaniline nanofibers,while the WO₃ nanorod bundles are synthesized via a simple NaCl assisted hydrothermal process.The CNF//WO₃ ASC device operates with a voltage of 1.6 V and achieved a high energy density of 35.3Wh kg^-1 at a power density of 314 W kg^-1.Furthermore,the device shows an excellent cycling performance with capacitance retention of 88%after 1000 cycles.4.A facile integrated oxidation polymerization of poly?p-phenylenediamine?and catalytic carbonization method was used to prepare three-dimensional porous nitrogen-doped carbon networks?3D N-CNWs?with high specific surface area and high nitrogen content?about 8.4 wt%?.The N-CNWs electrode exhibit high specific capacitance of 304 F g^-1 at a current density of 0.5 A g^-1,and excellent rate capability in KOH aqueous solution.Moreover,the as-assembled N-CNWs symmetric supercapacitor exhibits a considerably high energy density(15.8 Wh kg^-1)and large operating voltage?1.8 V?in Na₂SO₄ aqueous solution.In addition,in order to match the N-CNWs negative electrode materials,a novel aqueous asymmetric supercapacitor was constructed,which can further improve the energy density of supercapacitor.The petal-like cobalt selenide(Co_0.85Se)nanosheets positive electrode is synthesized via a simple low-temperature solvothermal method without any template and surfactant.Thanks to their unique structures and high capacitive performance,the as-assembled Co_0.85Se//N-CNWs ASC device possesses an extended operating voltage window of 1.6 V,high energy density of 21.1 Wh kg^-1 at a power density of 400 W kg^-1,and outstanding cycling stability in aqueous KOH electrolyte.