Dual-active sites and reversible-structural covalent organic framework for highly stable alkali metal-ion batteries

Organic materials are promising candidates for energy storage due to their sustainability, environmental friendliness, and structural designability. However, their application is severely limited due to short lifespan and sluggish kinetics caused by low redox stability, solubility, and low electronic conductivity. Here, we designed a polyimide-conjugated covalent organic framework (NAA-COF). Its highly covalent framework cannot only endow the organic material with strong pi-pi interactions and robust network ensuring its structure stability, but also offer open channels for rapid ions/electrons transfer inside. Additionally, the introduction of multiple redoxactive sites can significantly enhance ion-storage capacity. Consequently, when evaluated as a cathode for Li-ion batteries, NAA-COF exhibits large capacity of 220mAh/g, superb initial coulombic efficiency (90 %), good voltage platform, long lifespan (10000 cycles), and high-rate performance (110 mAh/g at 10 A/g). More importantly, even for Na-/K-ion batteries, the exceptional electrochemical performances can still be maintained. In situ transmission electron microscopy (TEM) and in/ex situ spectroscopy further elucidate the low volume expansion (12.2 %) during the lithiation process and 8-electron reaction mechanism for the NAA-COF cathode. This work provides a high-performance universal COF cathode material that can simultaneously satisfy the requirements of alkali metal-ion batteries.