Construction Of Hierarchical Carbon/Nickel Nanostructures And Study Of Their Capacitive Property

As a new type energy storage device with high storage and conversion capacity,supercapacitors have fast charge-discharge speed,long cycle life and high power density.However,the low energy density of supercapacitors limits their large-scale application,and the electrode directly determines the performance of supercapacitors.Electric double layer capacitor(EDLC)materials and pseudocapacitive materials have been extensively studied as electrode materials for supercapacitors.Owing to their high electrical conductivity,and large specific surface area,carbon-based materials have been successfully commercialized,but they still face the problem of low specific capacity.Despite the pseudocapacitive materials with relatively high theoretical capacity,the structure is easily to be destroyed in the charge-discharge process resulting in poor rate performance.The above problems restrict the development of high energy density energy supercapacitors.In order to develop high-performance electrode materials,on the one hand,we can upgrate the specific surface area,electron transmission rate and chemical stability of materials by means of designing structure;on the other hand,we can develop novel electrode materials which have high specific capacity.In addition,constructing an asymmetric capacitor to expand the operating voltage window facilitates the increase in energy density,thus obtaining a high specific energy supercapacitor device.In recent years,the development trend of electronic devices is lightweight and wearable,which also put forward higher requirements for flexible energy storage devices.In this paper,we deeply investigated the relationship among the synthesis mechanism,structure-activity relationship,and electrochemical performance by designing the microstructure of the electrode material with various methods.Meanwhile,we aim to construct asymmetric capacitor devices simply and efficiently.We synthesized a hierarchical carbon/nickel composite and studied its electrochemical properties for the supercapacitors.The ethanol vapor was used as carbon source and Nickel as catalyst to grow carbon nanotubes by annealing in inert gas atmosphere.During this process,Ni nanoparticles were ultra-uniformly distributed in the carbon nanotubes skeleton,which then were converted into nickel hydroxide with pseudo capacitance character by in-situ electrochemical oxidation.The synergistic effect of carbon materials and pseudocapacitive materials effectively improved the electrochemical properties of a single material.Moreover,the introduction of flexible,self-supporting carbon fiber as both current collector can avoid using binder,but also make the electrode directly used for flexible supercapacitors.Based on the prepared advantage of hierarchical carbon/nickel composites,we proposed a new concept of “one for two”,this is,asymmetric supercapacitors are assembled by only using the same electrode materials as both positive and negative electrodes which facilitates the simple construction of asymmetric supercapacitors.