Degradation Characteristics of Electric Double-Layer Capacitors Consisting of High Surface Area Carbon Electrodes with Organic Electrolyte Solutions

Aging characteristics of electric double-layer capacitors (EDLCs) comprising high surface area carbon electrodes with organic electrolyte solutions have been examined under high-voltage (high cell-potential) and high-temperature cycling conditions. The influences of the electrolyte components on decreasing the capacitance were investigated for cells using different electrolyte compositions. The use of acetonitrile (AN) as the electrolyte solvent in the cell led to higher cycling capacitance than those using alkyl carbonate solvents, such as propylene carbonate or ethylene carbonate mixed with dimethyl carbonate, under moderate cycling conditions. However, when the cycling was done with a higher operating voltage (>3.5 V), significant capacitance degradation was observed for the cells using AN-based electrolytes. The EDLC cells using carbonate-based electrolytes showed moderate degradation behavior even at higher operating voltages. With respect to the electrolytic salt, cells using LiBF4 generally showed lower durability than cells using tetraethylammonium salt, TEABF4, especially at high operating voltages (>3.5 V). The mechanism of the decreasing capacitance with repeated cycle is discussed.