Synthesis And Properties Of Polyaniline Based Supercapacitor Electrode Materials With High Energy Density

Supercapacitor,as one of the most promising energy storage device,which possesses the unique competitive advantage of high power density,has the advantages of strong practicability,safety and efficiency,green and pollution-free,follows the trend of people pursuing low-carbon life.Therefore,supercapacitor has been favored by a large number of scientific research workers.As the core part of supercapacitor,electrode materials directly affect or even determine the performance of supercapacitor.Therefore,the development of high-performance electrode materials is important.Conductive polymers with high redox active play an important role in the field of supercapacitor electrode materials.In particular,conductive polyaniline(PANI),which has good conductivity,unique proton acid doping characteristics,and high theoretical specific capacity,is a "star" material in the research of conductive polymer electrode materials,which has great potential to be widely applied in the important areas of human life.Aiming at the problem that PANI polymer chains occur collapse and destruction during charge/discharge process,and result in internal resistance increase,rapid attenuation of specific capacity and decline of cycle performance of electrode,in this paper,conductive PANI and its composite materials with high capacity and high electrochemical stabilit prepared by improved chemical oxidation method.In the progress of polymerization,by controlling the reaction conditions,such as the types of oxidant(Mn O₂,APS,H₂O₂ and Fe Cl3),the polymerization method(emulsion polymerization,interfacial polymerization,etc.),at the same time,appropriately incorporating aminated carbon nanotubes,and home-made nano/micro carbon spheres,conductive PANI and its composite materials with high capacity,high electrochemical stability were obtained.The morphology and structure of the prepared materials were observed by SEM.The surface area and pore structure distribution of these materials were characterized by a fully automatic surface analyzer.The functional groups,chemical element composition and thermal stability of the prepared PANI and its composites were charactered by FTIR,XRD,Raman and TG,etc.Meanwhile,with the prepared PANI and its composite materials as supercapacitor electrode materials,the electrochemical performance and cycle performance of supercapacitor were evaluated by CV,GCD,EIS and cycling life test.The main work and conclusions of this paper are as follows:(1)With APS as primary oxidant,H₂O₂,?-MnO₂,?-Mn O₂ and Fe Cl3 were used as secondary oxidants,respectively,four different structures of H-PANI,B-PANI,A-PANI and F-PANI were prepared by two-step chemical oxidation method.SEM results show that H-PANI is a "coral" fiber,B-PANI is an "antenna" network fiber,A-PANI is a fine mesh fiber,and F-PANI is a mixed tubular fiber.The specific surface areas of H-PANI and B-PANI are 35.04 m2 g-1 and 28.51 m2g-1,respectively,higher than A-PANI(26.04 m2 g-1)and F-PANI(24.27 m2 g-1),meanwhile H-PANI and B-PANI have more mesoporous content.And the electrochemical properties of them were measured in 1.0 M H₂SO₄ electrolyte.The results show that both H-PANI synthesized by H₂O₂ and B-PANI synthesized by rod-Mn O₂,respectively,have better electrochemical performance.Under the current density of 0.5 A g-1,the single-electrode specific capacitance of H-PANI and B-PANI reach up to 718.8 F g-1 and 705.0 F g-1,respectively,and the capacitance of the two electrode materials are still retain 70.2% and 66.5% at 10.0 A g-1,which shows excellent rate performance.Moreover,after 1000 times galvanostatic charge-discharge tests at 1.0 A g-1,the capacity retention rates of H-PANI and B-PANI are 63.1% and 67.3%,respectively,better than 48.7% of A-PANI and 34.0% of F-PANI,demonstrating good electrochemical stability.(2)The morphology of SiO₂ spheres were controlled by the introduction of surfactant CTAB as a template by the modified St(?)ber method.The resorcinol resin was prepared through the polycondensation reaction of resorcinol and formaldehyde,and then ethyl silicate was introduced for self-assembled to synthesize highly dispersed high-dispersion SiO₂ spheres.After the process of aging,high temperature carbonization and template removal with HF,multi-pleated and monodisperse nano/micro carbon spheres were obtained(diameter at around 500 700 nm).Then with prepared nano/micro carbon spheres served as seed crystals,SDBS,CTAB as soft template and carbon sphere dispersant,acidic aqueous solution-carbon tetrachloride(CCl4)interface,three types of PANI/nano/micro carbon sphere composite materials were synthesized by emulsion polymerization and interfacial polymerization.The results of SEM,FTIR,XRD and TG analysis prove that the nano/micro carbon spheres are successfully combined with PANI.The S-PANI/CS(mosaic structure)synthesized with SDBS as template,and the T-PANI/CS(coated structure)synthesized by interfacial polymerization method,which achieve better composite effect,and also present good electrochemical performance.At a current density of 1.0 A g-1,S-PANI/CS has a maximum specific capacitance of 636.0 F g-1,T-PANI/CS has the best rate performance(the capacitance still remain 64.0% at a large current discharge density of 10.0 A g-1),and the capacity of S-PANI/CS and T-PANI/CS still retain 72.7% and 74.0% after 1000 cycles at 1.0 A g-1,which demonstrate excellent cycle stability.(3)The water-soluble aminated carbon nanotubes(N-CNTs)were prepared by chemical covalent grafting method.The in-situ chemical polymerization was used to control the orientation growth of PANI on the surface by N-CNTs,the PANI/N-CNTs composite material was successfully prepared.It was confirmed by SEM and TEM observation that PANI is coated on the surface of N-CNTs and showing a core-shell structure.PANI/N-CNTs are enhanced in terms of crystallinity and thermal stability compared to pure PANI.Then PANI/N-CNTs was used as the positive and negative electrode material,1.0 M Et4BF4/AN was used as the organic electrolyte,assembling into symmetric supercapacitor,its electrochemical performance was investigated.At a current density of 0.5 A g-1,PANI/N-CNTs has the maximum specific capacity of 146.3 F g-1,which is higher than 108.9 F g-1 of pure PANI,and the corresponding maximum energy density is 32.9 Wh kg-1,which is far higher than 10.9 Wh kg-1 of pure PANI.Morover,PANI/N-CNTs demonstrates excellent rate performance,whose capacitance is 88.8 F g-1at 10 A g-1.After 1000 cycles of charge and discharge,the capacity retention of PANI/N-CNTs is 75.7%,which is 10% higher than that of PANI,The above results show that the effective combination of PANI and N-CNTs,which not only improves the specific capacity of the PANI,but also improves the cycle performance of PANI.More importantly,the energy density is also improved.