Molecular engineering of interplanar spacing via π-conjugated phenothiazine linkages for high-power 2D covalent organic framework batteries

Abstract

<h2>Summary</h2> Two-dimensional covalent organic frameworks (2D-COFs) represent an attractive platform for organic electrodes, yet they suffer from inferior power capability caused by poor Li⁺ intercalation in densely π-π stacked interlayers. Herein, featuring nonplanar π-conjugated heteroaromatic linkages, phenothiazine with "butterfly" conformation is integrated as a structural scaffold to instantly tune packing topology and interplanar distance. Corrugated 2D-COF maintaining aromaticity and crystallinity is formed with good electroactivity, enlarged d-spacing, and accessibility to interior Li⁺-interactive sites, which results in remarkable capacity of 220–773 mAh g⁻¹ at high rates ranging from 100 to 3,200 mA g⁻¹ with a good cycle life, bridging the performance gap between power and energy. Mechanistic studies reveal a dual storage mechanism with dominating capacitive storage promoted by π-Li⁺ interactions, as well as enhanced redox activity of carbonyls for better chemical accessibility. These findings elucidate inherent effects of molecular-level d-spacing regulation enabled by heteroaromatics, presenting a new design concept of interlayer engineering for organic porous energy storage materials.