Electrode Potentials in Electrochemical Double-Layer Capacitors with Asymmetric Electrode Thicknesses

Electrode thickness adjustments can change the ion-migration resistances of electrodes. Since tetraethylammonium (TEA) has a higher migration resistance than tetrafluoroborate (BF4−), the negative electrode contributes more than the positive electrode to cell voltage. By reducing the thickness of the negative electrode, the contribution of inter-particle ion migration of the two ions can be equalized. At a negative to the positive thickness (N/P) ratio < 0.75, the contribution of each electrode to the cell voltage becomes independent of the current. Also, balancing the electrode thickness allows less exposure to the positive potential range, lessening the electrolyte decomposition. Cells with less electrolysis last longer at 60 °C and 1 A g-1. However, at an increased current density, 15 A g-1, the rate capability is more important than electrolysis for a longer cycle life. The fine control of the contribution of each electrode, including high-temperature cycle life, is a valuable tool for enhancing its performance.