Pore Engineering of Covalent Organic Frameworks Boosts Chlorine Confinement and Electrochemical Performance in Li─Cl₂...

The development of high-energy-density Li─Cl₂ batteries is hindered by insufficient Cl₂ storage in cathodes. Although porous host materials have been preliminarily explored, the effect of pore size on Cl₂ confinement and electrochemical behavior still remains unclear. Herein, two novel covalent organic frameworks (COFs) with distinct pore sizes, namely TH-COF (mesoporous, 2.7 nm) and HH-COF (microporous, 0.9 nm), were fabricated by reacting triphenylene-2,3,6,7,10,11-hexacarboxylic acid with 3- and 6-connected amines, respectively, to serve as a model system for elucidating the pore-size effect in Li-Cl₂ batteries. Owing to its smaller pore size and resultant stronger spatial confinement, the microporous HH-COF enables superior Cl₂ capture and markedly enhanced battery performance, as exemplified by a high capacity of 4500 mAh g^-1, a high current density of 10 000 mA g^-1, and a Coulombic efficiency (CE) above 94% for each of the 500 cycles, outperforming its mesoporous TH-COF counterpart and all previously reported electrodes. Density functional theory calculations reveal stronger host-guest interactions between Cl₂ and the microporous HH-COF than its mesoporous counterpart TH-COF. This study not only clarifies the pivotal role of pore-size engineering in Li-Cl₂ batteries but also establishes a rational design principle for developing high-performance Cl₂ host cathodes.