Templated Synthesis of 2D Polyimide Covalent Organic Framework for Rechargeable Sodium-Ion Batteries

Covalent organic frameworks (COFs) hold great promise for electrochemical energy storage because of their high surface area, readily accessible redox-active sites, and environment-friendly chemical composition. In this study, the synthesis of a redox-active pyrene-containing polyimide COF (PICOF-1) by linker exchange using an imine-linked COF as a template is reported and its performance in sodium-ion batteries (SIBs) is demonstrated. The reported synthetic route based on linker exchange mitigates the challenges typically encountered with crystallizing chemically stable polyimide COFs from typical condensation reactions; thus, facilitating their rapid synthesis and purification. Using this approach, PICOF-1 exhibits high crystallinity with very low refinement parameters R_P and R_WP of 0.415% and 0.326%, respectively. PICOF-1 has a high Brunauer-Emmette-Teller (BET) surface area of 924 m²  g^-1 and well-defined one-dimentional (1D) channels of 2.46 × 1.90 nm, which enable fast ion transport and charge transfer, reaching a capacity at 0.1 C of almost nearly as its theoretical capacity and maintaining 99% Coulombic efficiency over 175 cycles at 0.3 C. The study demonstrates that imine-linked COFs are effective templates for integrating carbonyl-rich polyimide moieties into high-surface COFs to advance electrochemical energy storage applications.