Preparation And Eletrochemical Properities Of Composite Electrode Materials For Supercapacitor

There are two kinds of supercapacitors depending on charge storage mechanism,namely electrochemical double layer capacitors and pseudo-capacitors. The former oftenuse carbon-based materials with a high surface area and high conductivity as electrodematerials. Despite they have long cycle-life, a major shortcoming is their low specificcapacitance. On the other hand, the pseudo-capacitorsas use MnO₂/PANI as electrodematerials. They have high theoretical specific capacitances, but, low specific capacitancesare exhibited owing to their intrinsically electronic conductivity and structure.The MnO₂（PANI）/carbon-based material composites combine the excellentconducting and mechanical properties of carbon-based materials and highpseudocapacitance property of MnO₂（PANI）. However, the actual specific capacitanceand cycle performance is not ideal. There are mainly three problems:（1） the poordispersity of MnO₂/PANI;（2） the large contact resistance of the interface;（3） theunreasonable structure of the electrodes. In order to slove these problems, we developsome active composite electrodes material with high electrochemical performance, suchas MnO₂/short multi-walled carbon nanotubes （s-MWNT） composite electrode,MnO₂/Graphenes （GNs） composite electrode, Manganese（manganous oxide）/manganesecarbide/CNTs （Mn（MnO）/Mn₅C₂/CNTs） electrode, MnO₂-coated CNTs-flexible graphitesheet （FGS） electrode, PANI/CNTs/FGS electrode and PANI/G-βSiCw/FGS electrode.The specific research contents are as follows:（1） Selective etching in molten nitrate was used to cut MWNTs. MWNTs were cutinto different lengths by controlling the etching temperature and time. The cuttingproduced s-MWNTs were opened ends and rough surfaces. The present method did notintroduce any more destruction to the intrinsic graphitic structure of MWNTs. Thes-MWNTs formed more stable suspensions than did the pristine MWNTs, and showing anenhancement of the capacitive performance. MnO₂/s-MWNT composite was synthesizedby microwave irradiation. Uniform and conformal MnO₂coatings were formed on thesurfaces of individual s-MWNTs. The specific capacitance of MnO₂/s-MWNT compositewas475.8at2mV/s. After1000cycles at50mV/s, it lossed no more than0.8%of initial capacitance, showing good cycling stability.（2） GNs with the thin wrinkled structure were prepared by electrolytic exfoliationfrom FGS. The specific capacitance of GNs electrode was28.6at20mV/s and the EISwas6.75. MnO2/GNs composite electrode was synthesized by microwave irradiation.MnO₂coatings were formed on the surfaces of individual GNs. The specific capacitanceof MnO₂/GNs electrode was442.9at2mV/s. After1000cycles at50mV/s, it lossed nomore than4.5%of initial capacitance, showing good cycling stability（3）Mn（MnO）/Mn₅C₂/CNTs composite was prepared by vacuum evaporationmethod for supercapacitors. The carbide Mn₅C₂interlayer obtained by in-situ reactionprovided a low-resistance ohmic contact and a strong interface bonding between CNTsand Mn（MnO）, and consequently enhanced the conductivity and stability of thecomposite. The Mn（MnO）/Mn₅C₂/CNTs composite displayed maximum specificcapacitance of378.9F/g at2mV/s, and the EIS was5.3. The Mn（MnO）/Mn5C2/CNTselectrode also had an excellent cycling stability.（4） A flexible electrode was prepared by microwave heating deposition of MnO₂onCNTs followed by electrophoretic deposition of the MnO₂-coated CNTs on an FGS. Auniformly thin nano-scale MnO₂coating was formed on the surface of the CNTs. TheMnO₂-coated CNTs-FGS electrode showed highly capacitive behaviour with a specificcapacitance of442.9F/g at2mV/s. It exhibited an excellent cycling stability with nomore than1.1%capacitance loss after1000cycles at50mV/s.（5） Two flexible electrodes were prepared by electrophoretic deposition and directeletrodeposition of polyaniline method. The PANI/CNTs/FGS electrode displayed highspecific capacitances of521F/g at20mV/s and good cycling stability with no more than12%capacitance loss after1000cycles at50mV/s. The PANI/G-βSiCw/FGS electrodedisplayed the specific capacitance as high as190F/g at50mV/s. It exhibited an excellentcycling stability with no more than9.5%capacitance loss after1000cycles at50mV/s.