A High-Voltage Organic Cathode Enabled by a Continuous Electronegativity Zone in Aqueous Zinc-Organic Batteries

Abstract

N-type organics serve as cathode materials for aqueous zinc-ion batteries, exhibiting high theoretical capacity. However, their operating voltage is typically lower than 1 V (vs Zn²⁺/Zn), which significantly restricts the enhancement of the energy density and the practical application of these batteries. To address this issue, an imine compound 3-5,6,11,12-tetraazanaphthacene (3TANC) is designed, characterized by a continuous negative electrostatic potential region. This feature results in lower lowest unoccupied molecular orbital (LUMO) energy levels and enables a high average discharge voltage of 1.05 V (vs Zn²⁺/Zn). The elevated operating voltage allows 3TANC to achieve an energy density of 215 Wh kg⁻¹ at 0.1 A g⁻¹. Furthermore, the capacity is maintained at 94.38% after 1000 cycles at 2 A g⁻¹. Additionally, 3TANC demonstrates the ability for NH₄⁺ storage, exhibiting a high average discharge voltage of −0.1 V (vs SCE) and offers a specific discharge capacity of 267.84 mAh g⁻¹ at 0.1 A g⁻¹. Moreover, 3TANC's ammonium-ion half-cells maintain 100% capacity after 2100 cycles at 5 A g⁻¹. The Zn||3TANC hybrid ion cell exhibits exceptional cycling stability in 2 m (NH₄)₂SO₄ electrolyte, achieving 90.23% capacity retention over 13800 cycles at 2 A g⁻¹. This work presents a novel approach for designing high-voltage organic cathodes.