Hydrogen sulfite ion functionalized cationic covalent organic framework nanosheets as a separator boosted the energy storage performance of Li–S batteries

Abstract

Lithium–sulfur (Li–S) batteries are among the most promising new-generation energy storage devices due to their abundant reserves, low price, and high theoretical specific capacity (1675 mA h g⁻¹). However, Li–S batteries still face challenges such as the “shuttle effect” and slow redox kinetic reactions during charging and discharging. Here, we report a covalent organic skeleton with a bisulfite (EB-COF:HSO₃) modified separator, which is capable of mitigating the shuttle effect of polysulfide anions and accelerating Li–S transport. Specifically, negatively charged sulfate groups can inhibit identically charged polysulfide anions through electrostatic repulsion, thereby improving the cycling stability of the battery. At the same time, positively charged lithium ions are promoted to pass through the separator. As a result, the EB-COF:HSO₃-modified separator exhibited excellent electrochemical performance at a current density of 1C, with an initial specific capacity of 968 mA h g⁻¹, and maintained a capacity of 785 mA h g⁻¹ after 500 cycles with a decay rate of only 0.04%. In comparison, EB-COF under the same conditions has an initial capacity of 813 mA h g⁻¹ and a high decay rate of 0.12%.