A Two-Dimensional Metal-Organic Polymer Enabled by Robust Nickel-Nitrogen and Hydrogen Bonds for Exceptional Sodium-Ion Storage.

Organic electrode materials suffer from low electronic conductivity and poor structure stability. Herein, a metal-organic polymer, Ni-coordinated tetramino-benzoquinone (Ni-TABQ), is synthesized via d-π hybridization. The polymer chains are stitched by hydrogen bonds to feature as a robust two-dimensional (2D) layered structure. It offers both electron conduction and Na+ diffusion pathways along the directions of the polymer chains and the hydrogen bonds. With both the conjugated benzoid carbonyls and imines as the redox centers for the insertion and extraction of Na+ , the Ni-TABQ delivers high capacities of about 469.5 mAh g-1 at 100 mA g-1 and 345.4 mAh g-1 at 8 A g-1 . The large capacities are sustained for 100 cycles with almost 100 % coulombic efficiencies. The exceptional electrochemical performance is attributed to the unique 2D electron conduction and Na+ diffusion pathways enabled by the robust Ni-N and hydrogen bonds.