Communication—The Ragone Plot of Supercapacitors Under Different Loading Conditions

The power-energy performance of supercapacitors is usually visualized by the Ragone plot of (gravimetric or volumetric) energy density vs power density. The energy is commonly computed from E = CV2/2, and the power from P = E/Δt, which assume RC-based models. In this study, we investigate the energy-power profiles of two commercial supercapacitors discharged with three different types of loads: (i) constant current, (ii) constant power, and (iii) constant resistive load. The energy is computed as per the definition from the time-integral of its instantaneous power, i.e. with p(t) = i(t) v(t). In doing so, we do not assume any specific model a priori, and we highlight the fact that supercapacitor performance depends on the type of load it supplies. We also model the experimental Ragone plot using a fractional-order model composed of a resistance and a constant phase element, and show its superiority over the standard RC model.