Regulating the Metal Nodes of In Situ Electropolymerized Metal–Organic Coordination Polymers for High Performance LIBs

Metal-organic coordination polymers (MOPs) comprised of redox-active organic moieties and metal ions emerge as an important class of electroactive materials for battery applications. The bipolar two transition metal-based (Fe and Co) coordination complexes bearing terpyridine-triphenylamine ligand are used as models to investigate the relationships between structure and electrochemical performance. It turned out that the choice of central metal atom has a profound influence on the practical voltage window and specific capacity. The high-performing poly(FeL)_n electrode exhibits a reversible capacity of 272.5 mAh g^-1 after 100 cycles at 50 mA g^-1, excellent cycling stability up to 4000 cycles at 5A g^-1 (capacity ration:83.1%), and excellent rate capacity. The poly(CoL)_n electrode exhibits a significantly lower capacity of 107 mAh g^-1 at the 100th cycle and inferior stability (54 mAh g^-1 after 4000 cycles at 5A g^-1, capacity retention: 38.7%). DFT analysis indicates that the metal center directly influences the electron cloud density of the metal-terpyridine structure, which in turn affects the redox activity of the polymer by varying the affinity to lithium ions and the charge transfer efficiency. These findings highlight the importance of metal centers in coordination polymers, providing direct guidance for the exploration of MOPs as novel resource-friendly cathode materials.