| Facing the increasingly severe energy crisis and environmental pollution problems,it is particularly important to vigorously develop new and efficient renewable energy sources.As a new energy storage device,supercapacitors have attracted widespread attention from researchers due to its high-power density,short charging and discharging time,long service life,and environmental protection.The quality of the electrode material determines the comprehensive energy storage performance of the device.In recent years,electrodes based on nickel-cobalt-based hydroxides have great potential for development due to their extremely high theoretical specific capacities,large reserves,and ease of preparation.However,the relatively poor conductivity of this type of material limits its further application,and the agglomeration of particles during preparation and electrode reaction also reduces the cycle stability of the electrode.In order to solve these problems,this thesis explores various synthetic methods to prepare nickel-cobalt-based hydroxide composite electrodes with special morphology.The structure,morphology,and composition of the electrode were analyzed through systematic characterization.And it is assembled with a carbon material into a hybrid supercapacitor to achieve a joint increase in energy and power density.First,a nano flower-like nickel hydroxide(NNH)electrode containing nitrate and carbonate intercalation was synthesized by a hydrothermal method.Subsequently,micro/nano-scale Co(OH)2 particles were compounded with them without destroying the original morphology.The prepared composite electrode has excellent electrochemical performance.Among them,the NNH/Co(OH)2-6 electrode with the best comprehensive performance shows a specific capacity of 967.5 C·g-1 at a current density of 1 A·g-1,which is about 22.2%higher than that of a pure NNH electrode.When the current density is increased to 10 A·g-1,the capacity retention rate is84.4%.And after 5000 cycles,the capacity retention rate is 70.7%.In addition,the assembled NNH/Co(OH)2//AC hybrid supercapacitor also has good performance.Further,the flower-like nickel hydroxide used in the previous work is used as a substrate.And the Ni-Co double metal layered hydroxide(NCLDH)electrode was synthesized by doping Co element into Ni(OH)2 by one-step hydrothermal method.For hydroxides prepared with different nickel-cobalt ratios,there are differences in structure and morphology.The system's electrochemical test results show that the double metal hydroxide with a nickel/cobalt ratio of6/4 has the best performance.It has a specific capacity of 871 C·g-1 at a current density of 1A·g-1,and the capacity retention rate is still 73.0%at a current density of 20 A·g-1.Next,the N6C4LDH electrode material and carbon quantum dots were ultrasonically compounded to further improve the electrochemical performance of the material.The fabricated NCLDH/CQDs composite material electrode has a high specific capacity of 994 C·g-1,and the NCLDH/CQDs//AC hybrid capacitor assembled at the same time has considerable energy density.Finally,nickel-cobalt hydroxide was selected as the research object,and the rate and cyclic stability of the electrode were improved by changing its morphology and structure,while a small amount of high-conductivity metallic silver was selected to improve its conductivity.The Ag@NCOH nanoparticle electrodes with core-shell structure were constructed by using template-assisted etching to encapsulate silver nanoparticles in amorphous nickel-cobalt hydroxide.The obtained electrode has excellent electrochemical comprehensive performance,it has a specific capacity of 718.1 C·g-1 at 1 A·g-1,a capacity retention rate of 71.9%at 30 A·g-1.The assembled hybrid supercapacitor(Ag@NCOH//AC)can achieve an energy density of39.88 Wh·kg-1 at a power density of 375 W·kg-1,and also has excellent cycle stability. |
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