In‐Plane Exposed Metal Sites in Covalent Organic Frameworks for High‐Performance Lithium Sulfur Batteries

Covalent organic frameworks (COFs), featuring structural tunability and high porosity, have attracted great interest and are being developed into metal-COFs (M-COFs) by introducing metal atoms to boost their electrocatalytic performance. However, current M-COFs in Li-S batteries are fully metal coordinated in-plane environments, showing less exposed metal sites due to eclipsed (AA/AA') stacking modes. Here, a bottom-up molecular design strategy is proposed to construct M-COFs with in-plane exposed metal sites by precisely incorporating pyridine N atom pairs into the COF framework. Comprehensive experimental characterizations and theoretical calculations demonstrate that the in-plane exposed active sites significantly reduce activation barriers for polysulfides conversion, thereby achieving excellent rate performance (1412 mAh g^-1 at 0.5 C, 842 mAh g^-1 at 5 C) and cycle stability (0.027% capacity fade per cycle over 2000 cycles at 1 C).