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 CO/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.