Carbon optimization for asymmetric capacitor configuration

摘要

In the present study, different carbon materials have been applied as electrode for asymmetric supercapacitors working in neutral medium, e.g., aqueous lithium sulfate solution. Specially modified carbon played the role of negative electrode whereas delithiated LiMn_2O_4 spinel served as a positive one. However, in the case of lithium sulphate electrolyte, hydrated lithium ions with a large radius should be taken into account during charging/discharging of the carbon electrode. Ultramicropores which are mainly responsible for hydrogen capacity can be hardly or non-accessible for other ions. The challenge is to find convenient porous carbon materials for application in this particular electrolytic medium. Previous investigations pointed out that not only the porosity of carbon but also the amount and nature of surface functional groups affect the reversible lithium sorption from aqueous solution. For optimization of carbon, a special treatment with various oxidants has been performed. Such parameters as the porous texture (surface area, pore size distribution), surface functionality, hydrophobic/hydrophilic character, wettability have been studied, In order to establish the effect of physico-chemical properties of carbon on the electrochemical properties of the negative electrode as well as on the total asymmetric system, cyclic voltammetry, galvanostatic charge/discharge and impedance spectroscopy measurements have been applied.