Flexible Cathode Materials Enabled by a Multifunctional Covalent Organic Gel for Lithium-Sulfur Batteries with High Areal Capacities.

Foldable lithium-sulfur (Li-S) batteries have captured considerable interest in advanced flexible energy storage systems. However, sulfur utilization, cycling stability, and mechanical durability are still not satisfactory for flexible batteries with high sulfur loadings. Herein, we present one type of new freestanding electrode material derived from a thiourea-based covalent organic gel (COG). COG can accommodate high loading of carbon nanotubes (CNTs) and sulfur with the concomitant formation of an embedded conductive CNT network. The unique performance of the COG not only facilitates ion transfer and electrolyte infiltration but also effectively confines polysulfides in the internal cavities. These advantages endow the freestanding CNT/S/COG electrodes with high reversible capacity, good rate performance, excellent cycling stability, and superior structural integrity. CNT/S/COG with an ultrahigh sulfur loading of 12.6 mg cm-2 delivers a high discharging capacity of 13.7 mA h cm-2 (1097 mA h g-1) at 0.1 C; the capacity retention is as high as 83.9% after 100 cycles. Moreover, CNT/S/COG could be processed into foldable pouch cells. This study has demonstrated great potential of COGs for the fabrication of advanced flexible energy storage devices with high energy density and long cycling life.