Fusion of nitro isomers of naphthoquinone enhances capacity and cyclability in Zn-ion batteries†

Abstract

Aqueous Zn-ion batteries (ZIBs) are promising alternatives to lithium-ion batteries because of their inherent safety, raw material abundance (e.g., 10 million metric tons of available zinc in India, and Australia is the second largest zinc producer), and cost-effectiveness. This study focuses on utilising redox-active organic materials with quinone moieties, namely, 5- and 6-nitro 2,3-dichloro 1,4-naphthoquinone (5-DCNNQ) and (6-DCNNQ), and their mixtures in a 3 : 1 ratio as cathode materials for aqueous ZIBs. Although the introduction of the nitro group reduced the solubility of the active material in the electrolyte, the isomer mixture DCNNQmix cathode, with the high voltage characteristic of 5-DCNNQ and the high capacity characteristic of 6-DCNNQ, exhibited a higher capacity and cyclability than either material. The battery retained its capacity even after 9600 charge–discharge cycles.