Immobilizing Poly(vinylphenothiazine) in Ketjenblack-Based Electrodes to Access its Full Specific Capacity as Battery Electrode Material

Tengen, Bärbel; Winkelmann, Timo; Ortlieb, Niklas; Perner, Verena; Studer, Gauthier; Winter, Martin; Esser, Birgit; Fischer, Anna; Bieker, Peter

Abstract

Organic batteries are considered as environmentally friendly alternative to lithium-ion batteries due to the application of transition metal-free redox-active polymers. One well-established polymer is poly(3-vinyl-N-methylphenothiazine) (PVMPT) with a fast reversibility of the electrochemical redox reaction at a potential of 3.5 V versus Li|Li+. The oxidized PVMPT is soluble in many standard battery electrolytes, which diminishes its available specific capacity but at the same time can lead to a unique charge/discharge mechanism involving a redeposition process upon discharge. Herein, the influence of different conductive carbon additives and their properties, e.g., specific surface area, pore size distribution, and electrical conductivity, on the dissolution behavior of oxidized PVMPT is investigated. Compared to the state-of-the-art conductive carbon Super C65 employed in many organic battery electrodes, Ketjenblack EC-300J and EC-600J reduce the dissolution of the oxidized PVMPT due to better immobilization on the carbon additive and in the resulting 3D structure of the electrode, as assessed by N2-physisorption, electrochemical, UV–vis spectroscopy and scanning electron microscopy investigations. The studies demonstrate that a dense packing of the carbon particles in the electrode is decisive for the stable immobilization of PVMPT while maintaining its long-term cycling performance.