Geometrical effects on ionic diffusion in carbon-carbon symmetric supercapacitors

There is a great need to understand the structural dependence of supercapacitors for the development of advanced electrode materials that can be used to improve the electrochemical performance and structural integrity. In this work, we investigate the effects of the size and pore width/size of activated carbon microspheres (ACMSs) with diameter in a range of 2.7 ± 0.54 to 9.45 ± 1.81 μm and average pore width in a range of 1.60 to 2.0 nm on the electrochemical impedance characteristics of carbon-carbon symmetrical supercapacitors. Both the size and pore width/size of the ACMSs have negligible effects on contact resistance. The activation energy for the migration/diffusion of electrolyte ions in the supercapacitors made from the ACMSs of nearly same porous structure increases nonlinearly with the increase of the average size of the ACMSs, which is likely associated with overscreening effect. The activation energy for the migration/diffusion of electrolyte ions in the supercapacitors made from the ACMSs of nearly same size increases first and then decreases as the pore width/size increases.