Electrode potentials in electrochemical double-layer capacitors with asymmetric electrode thicknesses

Variation in the mass balance of electrodes affects the contribution of each electrode to the cell voltage in capacitors. Optimizing the mass balance is an efficient method to enhance performance and cycle life. Electrode thickness adjustments can change the ion migration resistances of electrodes. Because 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 interparticle ion migration of the two ions can be balanced. At a negative-to-positive electrode thickness (N/P) ratio < 0.75, the contribution of each electrode to the cell voltage becomes independent of the current. Furthermore, balancing the electrode thickness allows less exposure to the positive potential range, decreasing the electrolyte decomposition. Cells with less electrolysis last longer at 60 °C and 1 A g−1. However, at an increased current density of 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 is a valuable tool for enhancing its performance and high-temperature cycle life. [Display omitted]