Transforming Mesoporous Covalent Organic Polymers into Efficient 18‐Electron‐Redox Anodes via Redox Site Engineering for Superior Li‐Ion Storage

Redox‐active covalent organic polymers (COPs) have emerged as appealing renewable electrode materials for next‐generation Li‐ion batteries, but their performance is limited by insufficient redox sites and inadequate Li‐ion diffusion. Here, we develop a novel class of mesoporous covalent organic polymer (namely TF‐Azo‐COP) bearing multiple redox sites and explore its first use as efficient 18‐electron‐redox anodes for superior Li‐ion storage in both coin‐type and fiber‐type batteries. The newly produced TF‐Azo‐COP involves three types of active sites including C=N in triazines and imines, N=N in azo, and C 6 ‐ring aromatics to enable 18‐Li‐ion storage on one repeatable segment, while affording extended π‐conjugation for fast electron transfer and a pore size of ~2.5 nm for facilitated ion diffusion with a high coefficient up to ~10 −10 cm 2 s −1 —superior to some reported organic electrodes. Meriting from the above, pairing TF‐Azo‐COP with metal Li endows a coin cell with good cycling stability and a large reversible capacity of 795.4 mAh g −1 at 0.1 A g −1 —representing one of the best performances among reported organic electrodes. When coupled with fiber‐shaped LiFePO 4 cathodes, the assembled fiber cell delivers an excellent combination of linear capacity (0.23 mAh cm −1 ), energy density (0.55 mWh cm −1 ), cycling stability (250 cycles), and good flexibility.