| Supercapacitor is considered an electrochemical capacitor,which can fall into electrical double layer capacitor?EDLC?and pseudocapacitor in accordance with different working mechanisms.In EDLC,charges are separately stored in the electric double layer formed at the interface between electrode and electrolyte.By contrast,the pseudocapacitor is often accompanied with reversible redox reactions associated with a typical Faradic charge transfer process at the electroactive sites of the electrode.The physical mechanism of EDLCs enables fast charge-discharge process,long cycle life,better rate capability and high power density(>10kW kg-1),which make this kind of supercapacitor a great potential candidate to power portable electronic devices,cold-starting assistants and electric vehicles.This paper focuses on the electrode materials of double layer capacitors.In EDLCs,carbon materials are considered the most promising electrodes by virtue of their merits of high specific surface area,excellent electrical conductivity,good stability,and abundant sources.Mesoporous carbon,activated carbon,carbon nanotubes and graphene have been widely used in EDLCs.In recent years,the development and application of supercapacitor technology have made people put forward higher requirements for performance of carbon materials.Therefore,a kind of solid carbon sphere?SCS?with diameter of 400 nm was prepared for supercapacitor.The electrochemical behavior of the electrode material was characterized by cyclic voltammetry,constant current charge-discharge and electrochemical impedance.The specific capacitance of this carbon sphere in acidic electrolyte is up to 166.5 F g-1.In order to improve the electrochemical performance of SCS,solid carbon spheres with different diameters were synthesized by changing the experimental conditions.It is found that with the decrease of particle size,the specific capacity of SCS increases,and the specific capacity of SCS with diameter of250 nm reaches 207.5 F·g-1.In addition,the performance of carbon sphere was improved by morphology regulation and element doping.Hollow carbon spheres with Surface opening?SO-HCS?,hollow carbon spheres?HCS?and nitrogen-doped carbon spheres?NCS?were synthesized and their capacitive behaviors in acidic electrolyte were characterized.The specific capacitance of SO-HCS,HCS and NCS were 272.2,252.8 and 235.6 F·g-1,respectively,which were much higher than those of SCS.The high activity of SO-HCS comes from this unique surface opening structure.The opening of the surface provides a loose channel for the electrolyte,which enables it to diffuse smoothly into the interior of the carbon ball and contact the electrolyte more fully,thus providing more active sites for the charge storage.In addition,after 10000cycles of charge and discharge,both SO-HCS,NCS and SCS electrodes showed good cycle stability,which exceeded 90.0%of their initial capacitance,and the retention rate of SO-HCS reached 96.9%.In conclusion,a carbon sphere electrode material has been developed for supercapacitors.It is proved that the electrode performance can be effectively improved by particle size regulation,special structure design and element doping.The research results are of great significance to the design of new and efficient carbon electrode materials for supercapacitors. |
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