Design And Characteristic Research Of Porous Carbon Electrode Materials With High Performance

The shortage of energy supply and the deterioration of environmental conditions are one of the main difficulties faced by human society at present.There is an urgent need worldwide for sustainable and efficient energy storage systems and equipment which makes efficient use of various forms of new energy（such as wind energy,solar energy,biomass energy,etc.）.Among them,supercapacitors can not only provide rapid energy release,meet high power requirements,but also have high energy density.They also have the excellent characteristics of low maintenance cost,long service life and high stability,which have attracted great attention.Electrode is the most important core component of supercapacitor,and it is also the most critical factor affecting the performance of supercapacitor.Porous carbon materials have been widely used as electrode materials for supercapacitors because of their diverse micro morphology,high specific surface area,rich pore structure,high conductivity,simple synthesis process and low cost.In this paper,a series of functional porous carbon materials with different morphology and structure are designed and synthesized.The micro morphology,structure and composition of porous carbon materials prepared under different preparation strategies and conditions are characterized,and their electrochemical properties as supercapacitor electrode materials are studied;A variety of high-efficiency supercapacitors/hybrid supercapacitors are assembled by matching the obtained porous carbon material electrodes with different electrolytes.The electrochemical energy storage performance of the devices is studied,the influence of reaction conditions on the optimal electrochemical energy storage performance of porous carbon materials under different preparation strategies is obtained,and some electrochemical energy storage mechanisms are explored and analyzed,The design and synthesis method of high-performance porous carbon electrode materials is established,which provides useful enlightenment for the follow-up research work in this field.The major study achievement is described below:（1）Based on aminoquinone system,a novel,simple and efficient route is developed to prepare carbon nanorod materials with regular morphology,ultra-high specific surface area,N/O co-doping and reasonable micropore distribution.The polymer prepared from 1,4-bis（4’-aminophenoxy）benzene-p-benzoquinone acts as both carbon source and N/O self dopant without any complex conditions and/or time-consuming process.A series of BABQ porous carbon materials are prepared by exploring different reaction conditions（such as different solvents,different activated ratios and different carbonization/activation temperatures）,and a variety of typical materials are selected to test the relevant electrochemical properties.Through comparison,it is determined that the prepared BABQ-750-1 has typical nanorod structure,good micropore distribution,ultra-high specific surface area(2591 m² g^-1)and good N/O doping ratio（2.84/23.25 wt.%）.In 1 mol L-1 H₂SO₄ electrolyte,the electrode made by BABQ-750-1 shows the superior specific capacitance of 233 F g^-1and maintains good cycle stability(the capacitance retention rate is 78%after 2000charges and discharges at 50 A g^-1 current intensity).This research work provides a new idea and method for the structural casting and heteroatom doping of porous carbon nano materials,and it is helpful to study the relationship between polymerization and activation conditions,physical properties and electrochemical properties.（2）Using a novel polymerization strategy using p-benzoquinone and thiourea as the starting material,we design and synthesize the O/N/S ternary doped carbon nanoparticles ONSC electrode,and later prepare gel polymer electrolyte with high voltage window,which can significantly improve the energy output of supercapacitors.The highest specific surface area of ONSC materials developed and prepared is 2917m² g^-1,and the total heteroatom content is 14.85 wt.%.Among them,ONSC-700electrode has excellent electrochemical performance,including high capacitance(409F g^-1 at 1A g^-1),excellent rate performance and excellent cycle performance under three electrode system（KOH electrolyte）.The supercapacitor assembled with KOH and Na₂SO₄ electrolyte achieves excellent energy output of 11.3 and 28.8 Wh kg^-1.At the same time,we also prepare an all solid-state ionic gel electrolyte with a voltage window up to 3.5 V.We introduce EMIMBF₄ into highly porous gel polymer to prepare 3.5V ionic gel electrolyte,and assemble it with high-performance ONSC-700 electrode structure to form a high-performance solid-state supercapacitor,because the pore distribution of ONSC electrode（micropores are concentrated in the range of 0.54,0.80and 1.18 nm）can better match with the ion size of gel polymer electrolyte（EMIM⁺:0.76 nm;BF₄^-:0.48 nm）,which greatly improves the bulk energy density of the device,solid-state supercapacitor achieves high energy output up to 90.9 Wh L^-1,excellent cycle performance（over 10000 cycles,capacitance retention 91.6%）and thermal stability（0-80℃）.In addition,the energy density of the prepared flexible supercapacitor device is 76.6 Wh kg^-1.Even under 180°bending,its energy density still reaches 68.9 Wh kg^-1.This discovery provides more choices for the design and preparation of flexible wearable energy storage devices.（3）Using 1,5-diaminonaphthalene and glyoxal as monomers,utilizing an efficient custom strategy of solvent-precursor interaction,we design porous heteroatom modified carbon nanomaterials with specified physicochemical properties.By adjusting the solubility of solvent polymer,the polymerization kinetics and growth behavior of oligomers can be adjusted,so that the prepared carbon nanomaterials have a variety of geometric configurations（block,particle,sphere and sheet）,highly adjustable specific surface area(33-1022 m² g^–1)and customizable N/O functional doping ratio（2.78/10.17to 6.01/6.03 wt.%）.In this series of materials,C_{Et OH} materials have the highest nitrogen content,reaching 6.01 wt.%,the most balanced N/O high-level doping（N/O content is～6 wt.%）,and the largest specific surface area(1022 m² g^–1).These properties significantly increase the possibility of heteroatoms on the surface of cetoh contacting with solute ions.By establishing solubility parameter diagram,introducing a series of parameters and indicators such as|δ|、R_a and RED,building an intuitive Hansen solubility ball model,and conducting molecular dynamics simulation calculation,the results show that ethanol has the best matching with the polymer precursor,and the obtained polymer precursor has the highest stability.Through further theoretical calculation,it is also found that the solvent ethanol and the precursor have the characteristics of low binding energy barrier(-5.93 kcal mol^–1)and strong interaction(-151.4 kcal mol^–1).It is indicated that ethanol is the best solvent in this system,so carbon nano materials with the best performance are synthesized.Under the condition of the best C_{Et OH} nano material as cathode and zinc foil as anode,the assembled zinc ion hybrid supercapacitor achieves a reversible capacity of 170 m Ah g^-1 at a current density of 1 A g^-1.It has energy density of 92.8 Wh kg^–1（cathode）as battery level,power density of 28.3 k W kg^–1 as capacitor level,excellent cycle performance(more than 40000 cycles at 40 A g^–1,energy retention rate of 93.5%).In addition,the systematic characterization also confirmes that the N heteroatom doped structural sites can produce strong adsorption capacity and chemical reaction of hydroxyl/carboxyl surface groups to Zn ions.These characteristics provide fast ion reaction kinetics and superior charge storage capability for the device.This work provides useful enlightenment for the design and electrochemical mechanism of high efficiency zinc-based hybrid supercapacitor.（4）A precursor self-assembly strategy is adopted to form carbon superstructure materials,which can effectively control the pore size and the doping ratio of hetero elements.The process of self-assembly to form carbon superstructure after polymerization using 2,4,6-tricholoro-1,3,5-triazine（TCT）and 2,6-Diaminoanthraquinone（DAQ）as monomer molecules is deduced,and the"tenon"role of the key structural unit-NH₂⁺Cl^--is speculated,revealing its important role in the process of self-assembly to form rigid superstructure andπ-πmulti-facet combination to build a solid rigid skeleton.In addition,the carbon superstructure material TCT-DAQ sample achieves a high doping amount of N and O heteroatoms,and the distribution is uniform.The possible reason is that the reaction monomer TCT contains a highly stable C=N bond(bond energy of 615 k J mol^-1),and DAQ contains a more stable C=O bond(bond energy of 799 k J mol^-1),even after high-temperature carbonization/activation process,the formed carbon superstructure still retains the original chemical structures in a high proportion,it is reduced the loss of heteroatoms during carbonization/activation.Chemical defects and redox active sites of heteroatom motifs can effectively improve the pseudocapacitive activity of carbon materials.The solvent-precursor effect predicts that tetrahydrofuran（THF）is the best suitable solvent in the synthesis process.When the prepared TCT-DAQ carbon superstructure material is used as the electrode of supercapacitor,the specific capacitance reaches an ultra-high level of 426 F g^-1.Even at a high current density of 50 A g^-1,it still has good electrochemical performance of300 F g^-1.At the same time,the electrode has good cycle stability.After 20000 cycles at 20 A g^-1,the device still has 103.5%capacitance retention,which is attributed to the increase of redox active centers brought by the superstructure.The assembled supercapacitor can provide a high energy density of 14.8 Wh kg^-1at a power density of250 W kg^-1.When the power density increases to 25000 W kg^-1,the energy density of the supercapacitor remains at 10.4 Wh kg^-1,the retention rate is more than 70%.It drives a variety of electronic devices in different working conditions with various forms,and has great application potential.Through the research in this chapter,the effectiveness of the application of solvent-precursor effect in carbon superstructure materials is verified.It also provides a new strategy for the functionalization and pore structure design of carbon super structure materials.