A Highly Crystalline 2D Conjugated Metal–Organic Framework for Superior Sodium Storage

A highly crystalline 2D conjugated metal–organic framework (Cu-TBP) with dual active centers has been synthesized from an octahydroxyl tetrabenzophenazine ligand. Cu-TBP exhibits superior sodium storage capability with a high reversible capacity, outstanding rate performance, and remarkable long-term cyclability due to its abundant redox-active sites, prominent conductivity, and excellent stability.

Abstract

Two-dimensional conjugated metal–organic frameworks (2D c-MOFs) have emerged as promising electrode materials for sodium-ion batteries (SIBs). However, developing 2D c-MOFs with multiple redox-active sites and well-defined structures to enhance the performance of SIBs and elucidate the structure–property relationship remains challenging. Herein, a 2D c-MOF single crystal (Cu-TBP) with dual active centers was synthesized using an octahydroxyl tetrabenzophenazine (8OH-TBP) ligand. Three-dimensional electron diffraction (3D ED) analysis reveals the atomic-level crystal structure of Cu-TBP, characterized by a planar 2D rhombus network and a unique slipped AA layer-stacking. Cu-TBP exhibits typical semiconducting behavior with a high electrical conductivity (7.69 × 10⁻³ S m⁻¹ at 298 K) and a low thermal activation energy. Owing to its abundant redox-active sites and superb electrical conductivity, Cu-TBP shows remarkable electrochemical performance as a SIB anode, achieving a high reversible capacity of 369.7 mAh g⁻¹ at 0.25 A g⁻¹, exceptional rate capability, and extraordinary cyclability (82.6% capacity retention after 800 cycles at 0.25 A g⁻¹). Experimental studies combined with theoretical calculations further elucidate the Na⁺ storage mechanism.

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