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Chun-Han Lai1 Bing-Ang Mei1 Laurent Pilon1 Bruce Dunn1

1, University of California, Los Angeles, Los Angeles, California, United States

Batteries and electrochemical capacitors (ECs) represent the most widely used types of electrochemical energy storage devices. The fact that carbon-based ECs can deliver greater power, have much faster response times and longer cycle life than batteries makes this approach very attractive for a number of applications. An important limitation to this technology is its low energy density. For this reason, there is widespread interest in pseudocapacitance, a faradaic process involving surface or near-surface redox reactions, that can lead to high energy density at high charge-discharge rates. While there has been considerable progress in identifying pseudocapacitive materials as well as nanoscale materials that exhibit some of these responses, the fact remains that these redox materials are usually wide band gap semiconductors whose low electronic conductivity limits their kinetics when prepared in thick electrodes. The present paper provides guidance towards the development of pseudocapacitive materials for high rate energy storage. An analysis based on time-dependent multi-dimensional simulations was applied to an architecture in which a pseudocapacitive material was deposited on a conductive scaffold. The computed faradaic capacitance, which arises from reversible faradaic reactions, gave values consistent with experimental results as it decreased continuously with increasing sweep rate and pseudocapacitive layer thickness. Our research on Li+ insertion into Nb2O5 and reduced MoO3 is in good agreement with these simulations. This analysis provides guidance on the design of electrodes for high rate energy storage and identifies the key factors for attaining increased loading of the redox material.

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