Conducting Polymers Doped with Bifunctional Copolymers for Improved Organic Batteries

We propose a simple yet very versatile method to functionalize conducting polymers by the use of a bifunctional copolymer that can act as a redox-active dopant. A copolymer composed of 4-vinylcatechol and styrenesulfonic acid moieties was used as both the source of ions and the dopant for poly(3,4-ethylenedioxythiophene) (PEDOT) electropolymerization. The composite polymer shows an improvement in capacity which originates from the catechol faradaic reaction (52 mAh g–1 vs 18 mAh g–1) compared to PEDOT:poly(styrenesulfonate) (PSS). The active material utilization in the composite polymer was further investigated by using HClO4 as a secondary dopant and by increasing the ratio of neutral 4-vinylcatechol in the bifunctional copolymer to obtain a higher energy density electrode. Characterization by X-ray diffraction and atomic force microscopy hints at phase separation between PEDOT and the doping copolymer. Consequently, 4-vinylcatechol electronic connection to PEDOT is weakened at the microscale which prevents its complete utilization. These findings show the complex interaction between a conducting polymer and its dopant. The possibility to further tune the bifunctional copolymer composition, structure, and polymerization strategy should lead to improved energy storage performances and other new functional materials that explore properties imbedded in molecular units.