Unlocking twofold oxidation in phenothiazine polymers for application in symmetric all-organic anionic batteries

Abstract

Organic redox-active polymers stand out as electrode materials for alternative energy storage devices due to their potentially higher sustainability and the variability of their structures and charge storage mechanisms. Structural design of redox-active moieties can tune the electrochemical properties of a resulting material significantly. We showcase this strategy by synthesizing a phenothiazine (PT)-based polymer, in which the commonly inaccessible second oxidation (towards the dication) is unlocked for use in conventional carbonate electrolytes by donor-substitution of the PT-core. The resulting crosslinked polymer poly(N-styryl-3,7-dimethoxy phenothiazine) (X-PSDMPT) showed excellent performance over both oxidation processes in Li half-cells, which enabled the fabrication of a first-of-its-kind symmetric all-organic anion-rocking chair battery using the first oxidation as the reaction at the negative electrode and the second oxidation at the positive electrode. The resulting full-cell delivered a specific capacity of Cspec = 60.3 mAh/g at charging rates of 1 C and a capacity retention of 40% at ultra-high rates (100 C) as well as excellent cycling stability.