Redox-State-Dependent Interplay between Pendant Group and Conducting Polymer Backbone in Quinone-Based Conducting Redox Polymers for Lithium Ion Batteries

Conducting redox polymers (CRPs) have attracted increased interest in recent years because of the possibility of combining the favorable electron-transport properties of conducting polymers with the additional functionality provided by the redox active pendant groups (PGs). Herein we present a series of quinone-substituted PEDOT-CRPs where the quinone PGs have been substituted by electron-withdrawing substituents. Introducing electron-withdrawing substituents leads to an increase of the quinone formal potential, making, for example, CF3-substituted CRPs, a promising high-voltage cathode material for lithium ion batteries with a well-defined charge/discharge plateau around 3 V vs Li+/Li0. Interestingly, we find a shift in conductance onset potential concomitant with the quinone formal potential shift, indicating that the polymer backbone conductance is intimately associated with the PG redox chemistry. Through in situ UV–vis, electron paramagnetic resonance (EPR), and electrochemical quartz crystal microbalance experiments as well as by experiments in lithium- and tert-butyl-ammonium-based electrolytes, we show that the conductance delay is caused by the reduced lithiated quinone state, most likely by localizing the polaron charge carrier as indicated by EPR and UV–vis experiments.