UnsaturatedCoordination Co-BDC Nanosheets with NumerousPotential Binding Sites for Sodium Ions

Since the radius of sodium ions is larger compared to that of lithium ions, it is more likely to lead to the structural instability of the electrode material during the embedding and de-embedding process or even trigger the structural collapse. Due to the ability of unsaturated coordination metal–organic framework materials to expose more metal active centers and provide additional sodium-ion binding sites, these materials have great potential as anode materials for sodium-ion batteries. In this study, we obtained unsaturated coordinated Co-terephthalic acid materials via a simple hydrothermal method using an adjusted metal-to-ligand ratio. The rigid structure of the benzene ring and the presence of the –COO^– group ensures both the high-strength stability of the material and the increase in the intercalation sites for Na ions. Therefore, the electrode based on this MOF demonstrates a long lifespan and a high capacity of 191 mA h g^–1 at 100 mA g^–1. The preparation of pure MOF materials by constructing unsaturated sites provides ideas for the application of MOF-based materials in sodium-ion batteries.