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

The development of new pi-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 pi-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 pi-d CCPs in LIBs and provide new insights for the rational design of similar advanced electrode materials in other energy storage systems.