Study On Preparation Process And Capacitive Properties Of The Supercapacitors Based On Four Activated Carbons

Activated carbons are the most common used electrode materials in double layer supercapacitor.The performance of the activated carbon is directly affected by the carbon sources,activation method,and particle size distribution and so on.Meanwhile,the assembly process and method also have a deep impact on the electrochemical behavior.In this paper,different activated carbons were characterized;and the effects of assembly process,as well as the graphene/activated carbon composite on capacitive behaviors were systematically studied to achieve high performance supercapacitor.The results showed that the specific surface area of alkali activated carbon was bigger than that of water vapor activated carbon.And the specific surface area of petroleum coke was larger than that of coconut shell activated carbon under the same activation method.All these 4 kinds of activated carbon showed good capacitance properties.although the petroleum coke/alkali exhibited the best specific capacitance as well as the lowest equivalent resistance,the cycling stablity of the petroleum coke/alkali is poor(the attenuation reached 16%).However,coconut shell/alkali showed a moderate specific capacifitance and the best cycling stability(only 12% of attenuation),leading to the best comprehensive performance.The L16(44)orthogonal test of four factors and four levels was also performed to study the influence of the content of conductive agent,the thickness of the electrode,electrolyte content and drying time on the electrochemical performance.The results showed that the electrode thickness had the greatest effect on the specific capacitance.While the drying time produced minimal effect on the specific capacitance.Moreover,the equivalent resistance was also closely related to the electrode thickness.The content of conductive agent content had the least effect on the equivalent resistance.Therefore,the optimum preparation process was proposed as follows: the content of conductive agent content,electrode thickness,electrolyte content and the drying time must be 8%,150?m,5g,and 12 h respectively.Compared with the wet electrode,the dry electrode showed better specific capacitance and higher cycling stability.Although the internal resistance was about 10% higher than that of wet electrode,the internal resistance increase of the dry electrode was comparative to that of the wet electrode.According to the SEM,TEM,XRD,and the Raman spectra analysis,the layer number of the as fabricated graphene was about 2-5 layers with a low concentration of structural defect.The graphene/activated carbon composites with the graphene content of 1%,3% and 5% were prepared using dry electrode process.When the content of graphene reached 5%,the minimum internal resistance of 10.57 m? was achieve.However,the introduction of graphene had an adverse effect on the specific capacitance.Although the introduction of graphene had little influence on the cycling stability,the increase of internal resistance was inhibited during the cycling,that the increasing rate of internal resistance dropped by 48% when 5% of graphene was introduced compared with the pure activated carbon.