Boosting Lithium–Sulfur Battery Performance by Integrating a Redox-Active Covalent Organic Framework in the Separator

Lithium–sulfur batteries are getting more attention in energy storage and conversion fields due to their high theoretical capacity and specific energy density. Nevertheless, the dissolution of polysulfides results in their poor cycle stability, which is the major issue in practical use. To overcome the challenge, we report a new strategy by employing a redox-active covalent organic framework as the separator in lithium–sulfur batteries. The one-dimensional pore channels of the covalent organic framework provide a fast transport pathway for the lithium ion. And the pyridine units of the framework not only enhance the chemical adsorption of sulfur but also catalyze the charge and discharge processes. By virtue of these features, the specific capacity at 0.2 C is 977 mAh g–1 after 100 cycles, which is 5.2 times higher than that of the pristine separator-based battery. Additionally, the specific capacity achieves 826 mAh g–1 at 1 C after 250 cycles.