Modulating Electronic Structure with Linearly Fused Pyrazine Units for High-Voltage and Stable Zinc-Organic Batteries Cathode

Abstract

High-voltage n-type organic cathode materials are critical for constructing zinc-organic batteries (ZOBs) with high energy density and long cycle life. However, the intrinsically unfavorable electronic structures and relatively high LUMO energy levels of most n-type materials often lead to sluggish kinetics, high solubility, and suboptimal discharge voltages (< 0.8 V). Here, we design a small molecule, quinoxalino[2',3':5,6]pyrazino[2,3-f][1,10]phenanthroline (DPQP), as a ZOB cathode by introducing locally electron-deficient motifs into the conjugated backbone of aromatic compounds. The linearly fused pyrazine units extending the pyrazine-benzene framework effectively optimize the electronic structure, thereby significantly enhancing the discharge voltage. Meanwhile, the expanded π-conjugated plane suppresses dissolution and accelerates charge-transfer kinetics. Benefiting from these features, the DPQP electrode exhibits an exceptional increase in average operating voltage from 0.61 V to 1.07 V (vs. Zn²⁺/Zn) at 0.1 A·g^-1, with an overpotential of only 140 mV. Notably, no discernible voltage decay occurs as the current density increases, indicating rapid and highly reversible redox kinetics. Furthermore, the DPQP cathode delivers outstanding cycling stability, maintaining over 2000 h of continuous operation at 0.1 A·g^-1 and retaining 82.5% of its capacity after more than 10,000 cycles at 10 A·g^-1. Remarkably, the DPQP electrode also demonstrates excellent tolerance to extreme temperatures, achieving stable electrochemical performance across a wide temperature range from -20 °C to 60 °C. In addition, a series of spectroscopic and microscopic characterizations confirm the highly reversible redox behavior and Zn²⁺ storage mechanism of the DPQP cathode.

Keywords

Aqueous zinc batteries / Organic cathode / n-type material / Electronic structure design / High voltage

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