Study On The Preparation And Electrochemical Properties Of Carbon/Ni-Co Chalcogenides Nanocomposites

High performance energy storage equipment is the key component of electronic devices.With the upgrading of electronic products,traditional energy storage devices can no longer meet people's demands.As a new type of energy storage element,supercapacitors with higher energy density than traditional capacitors and larger power density than batteries are widely used in the situation requiring high instantaneous electric energy.Commercial supercapacitor electrode materials generally use carbon materials,which possess excellent cycling stability,highly stable microstructure and high electrical conductivity.However,the capacitance of carbon materials is low,which makes it difficult to meet the demand of high energy density in present electronic devices.Compared with carbon materials,pseudo-capacitance materials,represented by transition metal oxides and sulfides,have attracted much attention due to their higher capacitance than electrochemical double-layer capacitors.However,the irreversible electrochemical reaction in pseudo-capacitance material during the process of charging and discharging will lead to a shortened cycle life.Besides,the low conductivity of pseudo-capacitance material as the electrode material induces low electron transport efficiency and poor rate performance.In addition,pure transition metal oxide or sulfide materials suffers from severe aggregation,resulting in low utilization rate of active materials in the electrochemical reaction and consequently poor electrochemical performance.In order to obtain higher specific capacitance and stable cycling performance,this thesis focused on the synthesis and characterization of composite materials based on transition metal oxides/sulfides and carbon materials.We selected Mesocarbon microbeads?MCMB?and carbon nanotubes?CNT?as carbon matrix materials,and loaded NiCo2O4 or NiCo2S4 on the surface of carbon materials by hydrothermal or calcining methods to form the composite materials used in supercapacitor electrode materials and investigated their electrochemical properties.The main work of the research includes the following aspects:Firstly,the MCMB@NiCo₂O₄ composite material was prepared by one-step hydrothermal method followed by calcination.The NiCo₂O₄ nanoneedles were uniformly loaded on the surface of MCMB,forming urchin-like microspheres.Benefited from its unique material structure,the composite had a specific capacitance of 458 F g^-1 at 1 A g^-1 current density,and still kept 116%of specific capacitance after3000 charging-discharging cycles.Furthermore,MCMB@NiCo₂S₄ nanocomposite was prepared by two-step hydrothermal processes.The morphology of the composite was still urchin-like microsphere.Due to the excellent electrochemical properties of metal sulfide,the composite material could deliver the specific capacitance of 936 F g^-1 at 1 A g^-1 with a specific capacitance retention of 94%after 3000 charging-discharging cycles.In order to further improve the electrochemical performance of the electrode materials,we used carbon nanotubes to substitute Mesocarbon microbeads and used a two-step hydrothermal method to synthesize CNT@NiCo₂S₄ nanocomposite.NiCo₂S₄nanoclusters were dispersed in a carbon nanotube network with the intertwining support of carbon nanotubes,which rendered the composite with high conductivity and higher utilization ratio of active substances.The specific capacitance of the composite at 1 A g^-1 was as high as 1254 F g^-1,and the capacitance retention was 87%after 3000 cycles.