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.

Solid-state Li-metal batteries with solid-state electrolytes have attracted increasing attention due to their high energy density and intrinsically high safety. Among diverse available solid-state electrolytes, cellulose-based solid polymer electrolytes (CSPEs) are particularly attractive and have showcased great promise because of their multiple merits including abundant reserves, abundant polar groups, chemical stability and high flexibility. This review surveys currently-developed solid electrolytes based on modified cellulose and its composites with diverse organic and inorganic fillers. Common preparation methods for solid electrolyte membranes are discussed in detail, followed by a sequential overview of various modification and compositing strategies for improving Li-ion transport in CSPEs, and a summary of the current existing challenges and future prospects of CSPEs to achieve high-performance solid batteries.