Supercapacitor Degradation: Understanding the Mechanisms of Cycling-Induced Deterioration and Failure of a Pseudocapacitor

Supercapacitors (SCs) have generated widespread interest in the field of energy storage because of their unique characteristics of high-power density, good reversibility and rapid rate of charge/discharge.¹ Their degradation, however, has traditionally been overlooked owing to their widely accepted reputation of having a long lifetime and an excellent cycle stability which has hindered the development of high-performance, next-generation systems.<br/><br/>SC degradation has thus far mainly been studied from an impedance perspective and mathematically modeled in numerous RC (resistor-capacitor) circuit configurations.^2–4 Studies such as this, however, do not account for variables such as dynamic voltage fluctuations and other deviations from ideality that inevitably occur in realistic use. More importantly, they do not actually explain why the supercapacitor is degrading; whether through chemical changes, mechanical stress, poor device engineering, or other mechanisms.<br/><br/>In this work, we utilize a multiscale characterization approach that pairs electrochemical analysis with X-ray computed tomography and complimentary spectroscopic, microscopic and diffraction analysis to reveal the modes of degradation in commercial SCs over their full charge/discharge cycle lifetime. Importantly, while the pseudocapacitor system studied was rated for long lifetimes of up to 100,000 cycles, it was found to suffer from extreme degradation linked to severe material degradation at the cathode after only 2000 cycles.<br/><br/>These findings therefore provide new insights into the aging processes of pseudocapacitors and highlight how essential it is to develop an in-depth knowledge of supercapacitor degradation before these devices become even more widely utilized in commercial applications.<br/><br/>1 D. P. Dubal, O. Ayyad, V. Ruiz and P. Gómez-Romero, <i>Chem. Soc. Rev.</i>, 2015, <b>44</b>, 1777–1790.<br/>2 F. Rafik, H. Gualous, R. Gallay, A. Crausaz and A. Berthon, <i>J. Power Sources</i>, 2007, <b>165</b>, 928–934.<br/>3 M. Ayadi, O. Briat, R. Lallemand, A. Eddahech, R. German, G. Coquery and J. M. Vinassa, in <i>Microelectronics Reliability</i>, Elsevier Ltd, 2014, vol. 54, pp. 1944–1948.<br/>4 O. Bohlen, J. Kowal and D. U. Sauer, <i>J. Power Sources</i>, 2007, <b>172</b>, 468–475.