Copper and conjugated carbonyls of metal-organic polymers as dual redox centers for Na storage.

ABSTRACT

Metal-organic polymers (MOPs) are fascinating electrode materials for high-performance sodium-ion batteries due to their multiple redox centers and low cost. Herein, a flower-like π-d conjugated MOP (Cu-TABQ) was synthesized using tetramino-benzoquinone (TABQ) as an organic ligand and Cu2+ as a transition metal node under the slow release of Cu2+ from [Cu(NH3)4]2+ and subsequent dehydrogenation. It possesses dual redox centers of Cu2+/Cu+ and C[double bond, length as m-dash]O/C-O to render a three-electron transfer reaction for each coordination unit with a high reversible capacity of 322.9 mA h g-1 at 50 mA g-1 in the voltage range of 1.0 to 3.0 V. The flower-like structure enhances fast Na+ diffusion and highly reversible organic/inorganic redox centers. This results in excellent cycling performance with almost no degradation within 700 cycles and great rate performance with 198.8 mA h g-1 at 4000 mA g-1. The investigation of the Na-storage mechanism and attractive performance will shed light on the insightful design of MOP cathode materials for further batteries.