Side-Chain Modulation in Diketopyrrolopyrrole-Based Covalent Organic Frameworks for Fast and Durable Lithium-Ion Batteries.

Abstract

The development of high-performance anode materials is essential for next-generation rechargeable batteries. Herein, a series of pyrene-linked diketopyrrolopyrrole (DKP)-based covalent organic frameworks (COFs) is reported through systematic side-chain engineering using methyl and ether functionalities. A stepwise synthetic strategy employing unsubstituted, methylated, and ether-functionalized DKP monomers enabled precise tuning of pore environments, ion coordination, and electrochemical behavior. Among these materials, the ether-modified Py-DKPOMe COF exhibited outstanding lithium storage performance, delivering an initial reversible capacity of 265 mA h g^- ¹ and retaining over 100 mA h g^- ¹ at an ultrafast 20C rate, with 60 mA h g^- ¹ maintained at 25C. Remarkably, it achieved 80% state of charge within 61.7 s and exhibited excellent long-term cycling stability, while the high lithium-ion diffusion coefficient (7.12 × 10^-10 cm² s^-1) confirmed the rapid ion transport facilitated by the ether-functionalized chains. Interestingly, density functional theory (DFT) and nudged elastic band (NEB) calculations revealed enhanced Li⁺ adsorption affinity and reduced migration barriers in Py-DKPOMe COF. In addition, Py-DKPOMe COF also demonstrated promising sodium-ion storage (138 mA h g^- ¹). Full-cell tests with a Li-rich LNMO cathode verified its practical applicability, highlighting molecular-level COF design as a powerful strategy for fast, durable organic electrodes.