One-dimensional π-d conjugated coordination polymer with double redox-active centers for all-organic symmetric lithium-ion batteries

The development of new π-d conjugated metal coordination polymers (CCPs) provides broad prospects for exploring a new generation of energy storage materials. Here, we report the synthesis, characterization and lithium-ion storage properties of carbonyl-containing π-d CCPs, which use tetraaminobenzoquinone (TABQ) as the organic ligand and M2+ (M = Co, Ni, and Cu) as the metal ligands. Among them, Ni-TABQ shows the higher conductivity and best electrochemical performance, when used as a cathode material in lithium-ion batteries (LIBs), it delivers a high initial discharge specific capacity of 318.7 mAhg-1 at 50 mA g−1 and good rate performance (even 237.2 mAhg-1 at 2 Ag-1). The reason for the superior performance of Ni-TABQ as well as its lithium-ion storage mechanism is verified by density functional theory (DFT) and spectroscopic characterization. Encouragingly, Ni-TABQ can be served as both cathode and anode materials to construct high-performance all-organic symmetric LIBs, which delivers high energy density up to 142 Wh kg−1 with stable cyclability for 100 cycles at 200 mA g−1. More importantly, the flexible all-organic pouch LIBs assembled by Ni-TABQ also show stable electrochemical properties under different bending states, demonstrating its great potential in the field of flexible wearable devices. These research results will highlight the vigorous application of π-d CCPs in LIBs and provide new insights for the rational design of similar advanced electrode materials in other energy storage systems.