On Hierarchical Engineering Of Pore Structure For Polypyrrole-Based Activated Carbon And Its Capacitance Performance

Supercapacitors?SCs?are a new type of energy storage device between batteries and capacitors with high power,high safety and long life,etc..They have been widely used in defense military industry,aerospace,transportation and photoelectric energy storage.However,the specific capacitance of current activated carbon electrode for SCs is still less than 300 F g^-11 in high voltage ionic liquids,which severely limits the application of SCs under conditions of higher energy density.Therefore,in order to improve its energy density,researches on high specific capacitance porous activated carbon electrode materials,high voltage electrolyte and the optimization of device structure have become the focus of current research.In the present work,polypyrrole is used as a precursor,and the carbonization-activation process is used to synthesize polypyrrole-based porous activated carbon.Through the study of material morphology,pore structure and distribution,doping elements and content,and with the help of density functional theory?DFT?calculation and analysis,systematically discuss its electrochemical performance and capacitance storage mechanism under different electrolyte systems.Obtaining the following research results.?1?3D Pomegranate-like hierarchical porous carbon for aqueous supercapacitors with high gravimetric and volume capacitanceA new strategy is provided for designing pore structures to enhance the volume,gravimetric capacitance as well as rate performance of SCs.It is proposed to prepare3D Pomegranate-like hierarchical porous carbon with co-doped high content of N,O heteroatoms.The novel porous carbon structure can effectively maximize the gravimetric and volume specific capacitance of supercapacitors in aqueous electrolytes.DFT theoretical calculation results show that the contribution of pseudocapacitance comes from the increase of effective N,O functional groups.At the same time,the hierarchical porous channels with high packing density and ions are beneficial to increase the volume capacitance and maintain a high retention rate under the high mass loading of the electrode.Electrochemical characterization shows that in H₂SO₄,3D hierarchical porous carbon can provide excellent volume(278.6 F cm^-3)and gravimetric capacitance(398 F g^-1).In addition,under the high mass loading,79%retention of the above gravimetric capacitance can be achieved.?2?Slit mesoporous activated carbon for ionic liquid supercapacitors with high energy densityIIIA new strategy is provided for designing and developing novel pore structures to enhance the specific energy of ionic liquid SCs.A two-step synthesis process of carbonization and activation using polypyrrole as a precursor was proposed to prepare a new type of porous carbon material with slit pore structure.With the high voltage ionic liquid EMIMBF₄ as the electrolyte,the SCs have maximum specific capacitance of 310 F g^-11 and maximum energy density of 171.5 Wh kg^-11 at 0.5 A g^-1.Combined with DFT calculations,slit mesoporous activated carbon has a maximum cation volume utilization rate of 74%,which can effectively enhance the ion storage capacity and better interact with the ions in the ionic liquid electrolyte,demonstrating excellent specific capacitance.?3?Hollow nanospheres activated carbon for ionic liquid supercapacitors with high power densityA new method is developed for preparing hollow activated carbon spheres that significantly improves the high rate performance of ionic liquid SCs.It is proposed that aniline-pyrrole copolymer nanospheres are used as precursors and activated by KOH to prepare a 3D porous network structure consisting of interconnected hollow spheres with high specific surface areas of 1796 m² g^-1.The interconnected microstructure of Macropore-mesopore-micropore and the effective co-doping of N and O atoms make the supercapacitor with this material as the active material has the highest specific capacitance of 290 F g^-1?60??at 1 A g^-1,and when the current density is expanded by 20 times,it can still maintain a specific capacitance of 82%.After 10,000 cycles at a high rate of 10 A g^-1,it still has a capacity retention rate of83%.?4?Nanowire porous activated carbon for high performance lithium ion capacitorsA novel method is provided for developing porous carbon as a high-performance asymmetric lithium-ion capacitors?Li-HEC?cathode application.It is proposed to prepare nanowire porous carbon with high specific surface area(3268 cm² g^-1),micro-,mesoporous and N,O co-doped.The asymmetric lithium ion capacitor?Li-HEC?composed of nanowire porous carbon and Li₄Ti₅O₁₂2 has a maximum energy density of about 87 Wh kg^-11 and an initial discharge specific capacity of 90.2%after 3,000charge-discharge cycles.