Graphene-Based and Other Electrochemical Double Layer Capacitors for Energy Harvesting Systems

Abstract

A piezoelectric energy harvesting system that generates energy from the oscillation of a mass-spring and stores the energy on a capacitor is being developed for replacing batteries in some applications. Typically, this energy is stored in an electrolytic capacitor. Here, we explore a number of electrolytic- and electrochemical double layer capacitors (EDLCs, aka supercapacitors), including a graphene-array-based EDLC, for storing this energy. EDLCs are of interest because they are potentially smaller, lighter, and more reliable than conventional capacitors and batteries. One issue with using EDLCs in this application is that the piezoelectric voltage output can greatly exceed the EDLC electrolyte breakdown voltage of a single cell, and the oscillation frequency greatly exceeds the frequency response of most commercial EDLCs. We find that electrolyte breakdown is not a serious limitation with transient overvoltage, as electrolyte breakdown is kinetically limited, and further, any breakdown is self-healing. In this study, we report results from capacitors of different sizes and response times, and find that capacitors of similar size store similar quantities of energy, with faster capacitors charging more quickly.