| Carbonaceous materials have been extensively used as an electrode in electrochemical energy storage,which is due to its unique structure.However,the behavior of energy storage for carbon materials is more complex due to the hybrid of sp2 and sp3 in practical applications.It is generally believed that the capacitance performance is mainly determined by the specific surface area and pore size distribution for carbonaceous materials.But the relationship of capacitance and specific surface area can be not accurately expressed in the quantitative study.For example,the capacity of carbonaceous material with large specific surface is low than that of low specific surface.Therefore,for this phenomenon,we will prepare the pore wall surface with different proportion of carbon materials by mechanical grinding,and quantitatively describe the relationship of capacity performance and the surface area of carbonaceous materials.In this paper,planetary ball mill and three-dimensional vibration ball mill are used to grind graphite powder,respectively,where Na Cl was added as a grinding medium.Under the condition of constant rotation speed,we researched the structure changes of graphite by the change of grinding time.It is found that planetary ball mill will not seriously damage the structure in a short period of time,which is due to the weaken van der Waals force,leading to the interlayer separation of graphite.However,for the three-dimensional vibration ball mill,it will destroy the graphite structure and produce a certain pore structure even in a short time by the impact force.Therefore,the planetary ball mill is a relatively mild grinding method compared with the three-dimensional vibration ball mill,and it can protect the integrity of graphite structure in the grinding process.In the quantitative study of the correlation between wall area and capacity,we choose planetary ball mill to grind the commercial graphite powder,which can introduce different types of edges and defects,resulting in different proportions of wall surfaces to and avoiding to generate abundant microporous structures.In addition,a modified non-local density functional theory（MNLDFT）was used to quantitatively evaluate wall surface areas by fitting adsorption isotherms.Then,the linear regression method is applied to establish the relationship between capacitance and wall surface.The results reveal that the basal-,edge-and defect-surfaces contributed an areal capacitance of 0.04μF cm-2,1.65μF cm-2 and 7.95μF cm-2,respectively.Hence,the capacitance is mainly provided by defect-surfaces. |
