| With the continuous development of science and technology,the energy problem in the society received more and more widespread attentions.The electrochemical supercapacitor is a new type of energy storage device,which displays high power density,excellent transient charge-discharge performance,high efficiency,long cycle life and high safety.It has attracted great attentions in the hybrid power supply application.Metal sulfides are promising electrode materials for next-generation supercapacitors due to their high theoretical specific capacitance,good electrochemical reversibility and environmentally benignity.However,electronic conductivity of many transition metal sulfides is low,which leads to low capacitance and poor rate capability at high current densities.Based on the above analysis,method to improve their electrochemical performance was discribed in this thesis from chapter three to the chapter five via doping metal sulfides with conductive graphene.A noval carbon materials/sulfur composite applied in lithum-sulfur battery was also introdced in appendix part.1.NiS/reduced graphene oxide(NiS/rGO)nanocomposites were prepared by a hydrothermal method.Electron microscope observation revealed that the NiS was thin sheet-like structure and X-ray diffraction indicated the NiS of high-purity were on the graphene nanosheets.Nitrogen adsorption at 77 K showed the BET surface area of the composite is 35.7611 m2 g-1.Such materials exhibited high specific capacitance of 978.2 F g'1 at 1 A g-1 in 3 M KOH and good capacitance retention of 76%over 1000 cycles at 5 A g'1.The results suggest that NiS/rGO nanocomposites are promising for applications in supercapacitors with enhanced properties.2.Hierarchically nanoporous CuCo2S4/reduced graphene oxide(CuCo2S4/rGO)composites of nano-belt structure were synthesized with a facile hydrothermal method.The samples were characterized with field emission scanning electron microscopy,transmission electron microscopy,X-ray diffraction and nitrogen adsorption at 77 K.The materials had micropores of 0.7-1.2 nm widths and mesopores of 2-10 nm widths,with a total pore volume of 0.1 cm3 g-1.Such materials showed a good performance as electrodes in supercapacitors,which showed enhanced capacitance and desirable rate performance(The capacitance can reach 525 F g-1 at 1 A g-1 and 304 F g-1 at 20 A g-1)and the specific capacitance retained 83%after 1000 cycles at 4 A g-1.Such electrochemical properties identify the CuCo2S4/rGO nanocomposites as a promising electrode material for supercapacitors.3.CoNi2S4/reduced graphene oxide(CoNi2S4/rGO)nanocomposites were prepared by a hydrothermal method.Electron and Transmission microscope observation revealed that the materials were 10-20 nm cube-like structure and X-ray diffraction indicated the CoNi2S4 is high purity.Nitrogen adsorption at 77 K indicated BET surface area is 83.6238 m2 g-1.Such pseudo-active materials exhibited high specific capacitance of 1065 F g-1 at 1 A g-1 and good capacitance retention of 79.3%over 1000 cycles at 4 A g-1.The results suggest that CoNi2S4/rGO nanocomposites are promising for applications in supercapacitors with enhanced properties.4.We synthesized graphene/single wall carbon nanohorn xerogel firstly,then heating with sulfur to obtain graphene-single wall nanohorn xerogel/sulfur composites.Nitrogen adsorption at 77 K showed the BET surface area is 10.8764 m2 g-1.With the loading of 70 wt.%sulfur,the composites had a specific capacity of 1070.3 mAh g-1 in 100 mA g-1,but for composites without single wall nanohorn,the specific capacity is only 922.4 mAh g-1 in the same condition,which suggests that minimum amount of single wall carbon nanohorn could improve the capacity of sulfur electrode. |
PDF Full Text Request