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 C₆-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 cm² 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 LiFePO₄ 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.