A highly stable 1.3 V organic cathode for aqueous zinc batteries designed in-situ by solid-state electrooxidation

Abstract

Aqueous zinc batteries (AZBs) with organic cathodes are attractive large-scale storage candidates thanks to the inherent safety and inexpensiveness of the AZB chemistry and sustainability and diverse redox functions offered by organic materials. Polymer type hosts are particularly appealing for their insolubility in mildly acidic aqueous electrolytes, which renders stable cycling. However, the scalability of their chemical and/or electrochemical synthesis via solution polymerization can be a concern. Moving away from the solution method, here we introduce the solid-state electrooxidation strategy for the in-situ design of a novel host - dicarbazyl - by electrooxidative coupling of N-phenyl carbazole. The electrolyte has a decisive influence on the extent of the irreversible dimerization and thus on the subsequent electrochemistry. Favorable electrode kinetics together with in-situ derived film like morphology covering the conducting nanocarbon enables an attractive ⁓100 mAh g−1 reversible capacity at 1.3 V against Zn by a reversible p-doping/de-doping charge storage mechanism, >95% capacity retention over 1000 cycles at nearly 100% Coulombic efficiency, and excellent rate capability. The oxidative formation of the host and its reversible electrochemistry is confirmed by electrochemical, spectroscopic, and density functional theory investigations. This first demonstration of the solid-state electrooxidation strategy for an organic electrode design opens a new paradigm of high performance organic electrodes development by a potentially scalable approach.