Towards quinone/pEDOT conducting redox polymers as energy storage materials

Abstract: With the increased demand for electrical energy storage devices, e.g. electric vehicles and smart grids, organic batteries have caught increasing attention due to their advantages, such as sustainability, environmental friendliness and cheap raw materials over traditional inorganic energy storage materials. Quinones, as an organic energy storage materials have high specific capacity, show fast 2e− redox reactions and provide a wide structural diversity, making them promising candidates as active battery materials. However, quinones often suffer from dissolution problem and limited electronic conductance. In this thesis, quinones are functionalized onto conducting polymer backbones to make a conducting redox polymer (CRP), where the quinone provides capacity while the conducting polymer backbone provides electronic conductance and prevents dissolution of the quinone. One fundamental requirement to make a functional CRP is that redox matching between the quinone redox potential and the conducting region of the conducting polymer is achieved. To that end, the quinone redox chemistry as well as the conductance behavior of conducting polymers must be fully understood. In this thesis, the quinone redox chemistry was firstly studied, regarding the effect of cycling cation, solvent and substituent. In this thesis, the effect of cycling cation, solvent and substitution on the quinone redox chemistry was studied and found to systematically tune the quinone redox potential, with the nature of the cycling ion showing the largest effect. Quinones were covalently attached onto 3,4-ethylenedioxythiophene (EDOT) and polymerized, the obtained CRPs were characterized. It was found that a doping threshold was required before an appreciable conductance was observed, causing a conductance delay and the loss of redox matching. In situ EQCM, in situ UV-vis and in situ EPR showed that the conductance delay was attributed to the localization of charge carriers in the CRPs as a result of the interaction between the pEDOT backbone and the reduced, lithiated quinone state. The redox matching was improved by the utilization of a high potential quinziarin. A quinizarin-CRP based lithium ion battery (LIB) was fabricated that showed improved stability compared to that of the quinone based CRP. In addition, an all CRP based organic proton battery using the quinizarin-CRP as cathode and naphthoquinone-CRP as anode was developed. Lastly, a post-deposition polymerization (PDP) method was developed and the polymerization mechanism was investigated.