Additive Manufacturing of Redox-Active Covalent Organic Frameworks for High-Areal-Capacity Lithium-Sulfur Batteries.

Covalent organic frameworks (COFs) have emerged as promising sulfur hosts for lithium-sulfur batteries; however, most studies rely on conventional two-dimensional cast cathodes, which restrict practical sulfur loading levels and areal capacity. Here, we report a 3D direct ink writing (DIW) strategy for fabricating metal-free, redox-active COF-based cathodes that enable electrodes with practical sulfur loadings essential for achieving high areal capacity. This study addresses the long-standing processing challenges associated with COF-based DIW to fabricate sulfur cathodes by carefully optimizing the ink rheology, printing parameters, and postprocessing conditions. A porous anthraquinone COF (DAAQ-TFP), synthesized via a scalable terracotta method, was used as the sulfur host and further formulated as a printable ink with shear-thinning behavior suitable for DIW. The free-standing 3D-printed cathodes delivered high sulfur loadings (up to 10 mg cm-2) and areal capacities (up to 11.1 mAh cm-2) at 0.05 C. Furthermore, battery cycling studies of a 5.1 mg cm-2 sulfur-loaded cathode-based coin cell demonstrated good cycling stability over 300 cycles with >95% Coulombic efficiency. These results support advancement in battery technology by offering promising solutions to improve active-site accessibility and enhance performance and reliability in metal-sulfur batteries under higher loading conditions.