Ligand Engineering Toward Robust Sodium Storage in Self-Supported Metal-Organic Frameworks

Sodium-ion batteries capable of charging and discharging rapidly and durably are eagerly demanded to replace current lithium-ion batteries. However, large Na⁺ ions need more space to accommodate them. Metal-organic frameworks are promising anode materials, and their structure and performance are governed by organic ligands. Herein, we report a ligand engineering to design metal-organic frameworks with large conjugated naphthalene-2,6-dicarboxylic acid. Self-supported arrays of metal-organic frameworks reveal robust sodium storage when used as a binder-free anode. The uniquely long and conjugated aromatic ligands endow the metal-organic frameworks with rich sites to accommodate Na⁺ ions, thus enabling a high reversible capacity for sodium storage. As a result, such metal-organic frameworks exhibit a high capacity of 330 mAh g^-1 at 1000 mA g^-1 with remarkable rate capability and cycling performance. This work provides an exciting ligand strategy to design high-capacity metal-organic framework materials and would find extensive applications in various energy storage systems.