Mathematical Modeling of Hybrid Asymmetric Electrochemical Capacitors

Electrochemical capacitors may be ideal energy storage devices for applications ranging from renewable energy storage to transportation. Electrochemical capacitors are characterized by high power density and cycle life, and can be classified based on the properties of their electrodes. Symmetric capacitors have two electrodes that exhibit the same behavior, while asymmetric capacitors have two electrodes that exhibit different behavior. A hybrid asymmetric capacitor is a device that has two electrodes that behave differently because of different processes occurring in them. In this paper, we present a mathematical model of hybrid asymmetric capacitors made up of a redox couple electrode and a double-layer electrode. We show that, because of the different behavior of each electrode, the hybrid asymmetric capacitor possesses higher energy and power density than the symmetric capacitor. Our model is generic and can be extended to any device so long as the properties of the electrodes are known.