Influence Of Surface Structure Of Carbon Materials On Performance Of Supercapacitors

Carbon materials have become the most commercially valuable and practical electrode materials for supercapacitors due to their excellent electrical conductivity,high physical and chemical stability,and low cost.Meanwhile,the surface structures of carbon materials are important factors in capacitance of supercapacitor.At present,the adjustment of surface structure is an important method to improve performance of electrode materials.However,it is difficult to quantitatively describe the contribution of basal-,edge-and defect-surfaces of carbon materials on the specific capacitance of supercapacitors.In order to solve this problem,we herein proposed a series of research programs to deeply explore the relationship between the surface structure of carbon materials and the performance of supercapacitors.In this paper,various contents of surface structures such as basal-,edge-,defect-surface,were created in graphite powders through ball-milling.Then,the surface areas of basal-,edge-,and defect-surfaces were quantitatively calculated by the modified non-local density functional theory（MNLDF）according to the Ar adsorption data.Meanwhile,the ball-milling samples were applied as electrode of supercapacitors and their capacitances were systematically studied in 1M TEABF4/PC electrolyte.The results show that the contribution capacitance of defect-surface is higher than the basal-and edge-surface,which can reach 5.24μFcm^-2 at 1 V.This can be attributed to the high chemically active sites on the defect surface,which facilitates the absorption of ions in the electrolyte at the interface and increases the specific capacitance,during the charge and discharge process.Then,we used the characteristics of organic electrolytes with a wide electrochemical window to further study the influence of the voltage on the specific capacitance of the three surface structures and its regularity.The results shown that as the voltage increases,the base-surface exhibits a higher growth rate than the defect-surface.It is benefit that the basal-surface can provide large specific surface area and high electronic conductivity under high voltage to improve capacitance.Finally,different contents of Fe were loaded on purified activated carbon（Fe@C composites）synthesized by impregnation process in an effort to establish a correlation between SDC process and contents of Fe impurities in SCs.The results show that a small amount of Fe doping（<1.12 wt.%）changed surface structure of active carbon,reducing voltage loss of self-discharge.In summary,we believe that the surface structure of carbon materials is important role in the construction of high-performance supercapacitors.Meanwhile,the defect structure has a great influence on the energy storage of carbon materials.To adjust the surface structure of carbon materials is crucial role for low-cost and high-performance of electrode materials,and is also an important means to develop large-scale commercial supercapacitors in the future.