Understanding the charge storage mechanism of conductive polymers as hybrid battery-capacitor material in ionic liquids by in-situ atomic force microscopy and electrochemical quartz crystal microbalance

Abstract

Safe and sustainable energy storage systems with the ability to perform efficiently during large number of charge/discharge cycles with minimum degradation, define the main objectives of the near future energy storage technologies. Closing the gap between high power and energy per unit weight, demands new materials acting as battery and capacitor at the same time. Conductive polymers attracted attention as hybrid battery-capacitor material. However, their potential impact has not been fully investigated, as their behaviour, especially in non-aqueous electrolytes such as ionic liquids, is not completely understood. Here, we aim to clarify the fundamental functionality of the hybrid characteristics while studying the interaction between a conductive polymer and an ionic liquid by in-situ atomic force microscopy and electrochemical quartz crystal microbalance. The main achievement is the visualisation of morphological modifications of the conductive polymer depending on the state of charge. These modifications influence the viscoelastic material properties of the polymer, significantly. The combination of the findings provides a model, which is able to explain why conductive polymers behave like a (pseudo)-capacitor at a high and as battery at a low state of charge. This understanding enables the application-orientated synthesis and the use of conductive polymers as high-performance energy storage material.

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ORCID for Carlos Ponce De Leon Albarran: orcid.org/0000-0002-1907-5913

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