Stabilization of Hexaaminobenzene in a 2D Conductive Metal–Organic Framework for High Power Sodium Storage

TLDR

Redox‑active organic materials are promising battery electrodes but suffer from low conductivity and instability under redox conditions. The authors aim to create a cobalt‑based 2D conductive metal‑organic framework, Co‑HAB, that stabilizes hexaaminobenzene for high‑power sodium‑ion storage. Co‑HAB is assembled by conjugative coordination of HAB linkers to Co(II) centers, yielding dense, accessible active sites and a bulk conductivity of 1.57 S cm⁻¹. Co‑HAB achieves a reversible three‑electron redox per HAB, delivering 214 mAh g⁻¹ in 7 min (152 mAh g⁻¹ in 45 s) and 2.6 mAh cm⁻² at 9.6 mg cm⁻² loading, demonstrating high rate capability and scalable capacity.

Abstract

Redox-active organic materials have gained growing attention as electrodes of rechargeable batteries. However, their key limitations are the low electronic conductivity and limited chemical and structural stability under redox conditions. Herein, we report a new cobalt-based 2D conductive metal-organic framework (MOF), Co-HAB, having stable, accessible, dense active sites for high-power energy storage device through conjugative coordination between a redox-active linker, hexaaminobenzene (HAB), and a Co(II) center. Given the exceptional capability of Co-HAB for stabilizing reactive HAB, a reversible three-electron redox reaction per HAB was successfully demonstrated for the first time, thereby presenting a promising new electrode material for sodium-ion storage. Specifically, through synthetic tunability of Co-HAB, the bulk electrical conductivity of 1.57 S cm-1 was achieved, enabling an extremely high rate capability, delivering 214 mAh g-1 within 7 min or 152 mAh g-1 in 45 s. Meanwhile, an almost linear increase of the areal capacity upon increasing active mass loading up to 9.6 mg cm-2 was obtained, demonstrating 2.6 mAh cm-2 with a trace amount of conducting agent.