Electrochemical characterization of supercapacitors with glass wool separator

Abstract

Supercapacitor, also known as ultracapacitor exhibits higher power density, greater rapid charging and discharging rates, and superior life cycle than a rechargeable battery. The major drawback of supercapacitor is its relatively lower energy density. Previous researchers have proved that the specific capacitance of supercapacitor increases with the increment of electrolyte concentration, which contributes to the improvement of its energy density. Commercial separator, such as cellulose paper, is incapable of withstanding high concentration of electrolyte. A corrosive-resistant material, glass wool has been previously introduced as a potential material for the separator. Nonetheless, studies of the electrochemical performance of supercapacitors with glass wool separator under different types of electrolytes with different concentrations are very limited. This thesis aims to electrochemically evaluate glass wool-based supercapacitor under three types of electrolytes; 1 mol/dm3 sulfuric acid (H2SO4), 6 mol/dm3 potassium hydroxide (KOH) and 1 mol/dm3 tetraethylammonium tetrafluoroborate (TEABF4) and compare the performance to an identical supercapacitor with cellulose separator. A systematic study on the effect of high concentrated electrolytes coupled with the glass wool separator was also carried out. The electrochemical performance of the constructed supercapacitors was evaluated through cyclic voltammetry, galvanostatic charge-discharge, electrochemical spectroscopy, and cyclability charge-discharge tests using a symmetrical two-electrode test cell. It is found that the glass wool separator has outperformed cellulose in terms of its internal resistance and power density under the acidic, basic, and organic electrolytes. Interestingly, the glass wool-based supercapacitor coupled with high concentrated H2SO4 (18 mol/dm3) electrolyte exhibits 23% increment of specific capacitance and energy density with almost 100% retention throughout 3000 cycles of charge-discharge process as compared to the one with 1 mol/dm3 H2SO4 electrolyte. The optimum concentration for basic electrolyte KOH suggested is 10 mol/dm3 which gives 5.3% increment in energy density, 13% increments in power density and excellent cyclability compared to that of 6 mol/dm3 KOH electrolytes. The application of 2.5 mol/dm3 concentration of TEABF4 improves the energy and power density by 153% and 3821%, respectively compared to 1 mol/dm3 TEABF4.