Supercapacitor leakage in energy-harvesting sensor nodes: Fact or fiction?

Abstract

Abstract-As interest in energy-harvesting sensor nodes continues to grow, the use of supercapacitors as energy stores or buffers is gaining popularity. The reasons for their use are numerous, and include their high power density, simple interfacing requirements, simpler measurement of state-ofcharge, and a greater number of charging cycles than secondary batteries. However, supercapacitor energy densities are orders of magnitude lower. Furthermore, they have been reported to exhibit significant leakage, and this has been shown to increase exponentially with terminal voltage (and hence stored energy). This observation has resulted in a number of algorithms, designs and methods being proposed for effective operation of supercapacitor-based energy-harvesting sensor nodes. In this paper, it is argued that traditional 'leakage' is not as significant as has commonly been suggested. Instead, what is observed as leakage is in fact predominantly due to internal charge redistribution. As a result, it is suggested that different approaches are required in order to effectively utilize supercapacitors in energy-harvesting sensor nodes.

Flexible Piezoelectric Energy Harvesting Circuit With Printable Supercapacitor and Diodes

“…The sudden drop is probably related to slow movement of the electrolyte ions in the porous electrodes (high ESR), which restricts the available power, according to (4). The following recovery of the voltage could be due to charge redistribution within the device [24].…”

Energy Harvesting Sources, Storage Devices and System Topologies for Environmental Wireless Sensor Networks: A Review

“…However, the use of supercapacitors is often affected by self-discharge—a problem related to the terminal voltage of the energy stored in the element [ 52 ]. The magnitude of the problem depends on device capacity, but also differs among manufacturers and even among individual production batches.…”

“…Initially, it was assumed that all energy losses in supercapacitors are due to leakage. However, a study by Merret et al [ 52 ] expanded this view in two important ways. First, they observed that voltage drops considerably faster with shorter charge times.…”

Perspectives on Energy Storage for Flexible Electronic Systems

“…needed to operate micropower electronics [12]. In spite of its practical impact, leakage information is not always disclosed in some recent high energy density EC capacitor reports, although, self-discharge time constants ranging tens to hundreds of hours from small commercial supercapacitors and ECs have been disclosed [12], [13], [15].…”