Dynamic Balance of Partial Charge for Small Organic Compound in Aqueous Zinc-Organic Battery

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 pi-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 pi-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 degrees 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 Zn-x(CF3SO3)(y)(OH)(2x-y)center dot nH(2)O 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.

Automated summary

In this study, a small organic molecule PTONQ with extended pi-conjugated plane was designed and a partial charge regulation strategy was adopted. The Zn//PTONQ battery showed good cycling stability, fast charge transfer kinetics, and anti-freeze performance. Ex situ characterizations confirmed that the capacity mainly comes from Zn2+ insertion/removal of PTONQ and explained the formation mechanism of the by-products.