The Design And Capacitive Performance Of Nickel Based Oxide/Carbon Composite Electrode Materials

As a new type of energy storage device,supercapacitor has become one of the research hotspots due to its high charging-discharging speed,high power density and good cycle performance.Electrode materials play a decisive role in the performance of supercapacitors.The carbon materials with double layer capacitance energy storage are good in conductivity and cycle performance,but the specific capacitance is lower,and the metal oxides in the form of pseudocapacitance have higher specific capacitance,but the cycle performance is poor.Combining metal oxide with carbon to form composite materials can further improve storage performance and meet the development requirements of supercapacitors.Therefore,in the thesis,three kinds of metal oxide/carbon composite electrode materials are designed and prepared with the carbon materials derived from the metal organic framework（MOF）.The main content is the following:1.Hexagonal NiO/mesoporous carbon nanodisks（NiO/MCN）are facilely and controllably synthesized via constructing nickel-zinc trimesic acid heterobimetallic metal-organic framework（HMOF）disks by a self-assembly method before solid state transformation.The study showed that only when the reaction time was 1 min,and the Ni/（Zn+Ni）molar ratio was 0-1.0%,the normalized NiO/MCN nanodisk composites could be obtained NiO/MCN-0₅%have good conductivity,high graphitization degree,high porosity and properly populated NiO nanocrystals by comparing different NiO/MCN samples.Therefore,it is used as electrode material of the double electric layer capacitor that shows the high quality specific capacitance（261 F/g）,the good rate capability and superior cycle stability（the specific capacitance is lost by 2%after 8000 cycles）in electrochemical tests.2.In order to improve the utilization rate of pseudocapacitance components,the OCNF@NiCO2O4 composite material were prepared by loading nickel-cobalt hydroxide in the oxygen functionalized carbon fiber（OCNF）derived from the MOF before annealed.Scanning electron microscopy（SEM）and transmission electron microscopy（TEM）demonstrate the successful construction of core-shell structured OCNF@NiCo2O4 architectures,and NiCo2O4 nanosheet were distributed evenly on OCNF.Comparative study of its analogue CNF@NiCo2O4 bearing unmodified carbon nanofibers and pure NiCo2O4,OCNF@NiCo2O4 reveals more dense NiCo2O4 nanosheets,and possess a stronger interaction with the carbon matrix.It is considered that the carbon surface functionalities are crucial to render such a highly efficient OCNF@NiCo2O4 electrode,which shows higher specific capacity of 1142 F/g,excellent rate capability and superior cycling stability up to 5000 cycles within a larger capacitance retention ratio of 94.5%.3.A series of NiCo2O4/CNF composites were obtained after the annealing of the loaded nickel-cobalt hydroxide in the different support,just using zinc-trimesic acid-derived carbon nanofibers（CNF）originated from different pyrolytic temperatures.The results showed that increasing the carbonization temperature leads to a transformation in NiCo2O4 shape from nanoparticles to nanosheets but a decrease in NiCo2O4 content from 95%to 55%.The resultant NiCo2O4/CNF-450,with highly dispersed nanosheets and proper NiCo2O4/CNF weight ratio,exhibits the best capacitive performance with a large specific capacitance of 870 F/g at a scan rate of 1 mV/s,and a high energy density of 39.3 Wh/kg in the case of power density of 300 W/kg.The elaborately fabricated NiCo2O4/CNF-450 also shows lower resistance,superior rate capability and excellent charge-discharge stability（up to 5000 cycles）probably owing to the strong interaction between NiCo2O4 and carbon nanofiber.