Dynamic balance of partial charge for small organic compound in aqueous zinc-organic battery

Abstract

Organic cathodes for aqueous zinc-ion batteries (AZIBs) feature intrinsic flexibility and favorable kinetics, but they suffer from high solubility. Herein, a partial charge regulation strategy is deployed by designing a small organic molecule with extended π-conjugated plane, namely benzo[i]benzo[6′,7′]quinoxalino[2′,3′:9,10]phenanthro[4,5-abc]phenazine-5,10,16,21-tetraone (PTONQ). The charge equalization of active sites induced by the extended π-conjugated plane of the PTONQ molecule combined with high aromaticity renders the molecule low solubility, fast charge transfer, and high structural stability. The fabricated Zn//PTONQ battery cycles more than 500 h at 175 mA g−1 with small capacity reduction, fast charged/discharged kinetics, and anti-freeze performance (below -20°C). By a series of ex situ characterizations, it is attested that the capacity originates mainly from Zn2+ insertion/removal of PTONQ without H+ incorporation, which also accounts for the formation of Znx(CF3SO3)y(OH)2x-y·nH2O by-products. This result benefits the understanding of the by-product formation mechanism of organic cathode and paves a new way to advance the aqueous Zn-organic batteries.