A nitrogen–sulfur co-doped porous graphene matrix as a sulfur immobilizer for high performance lithium–sulfur batteries

Abstract

Owing to their overwhelming advantage of theoretical energy density, lithium–sulfur (Li–S) batteries are considered as one of the most promising candidates for next-generation electrochemical energy storage systems. The primary challenges in the development of Li–S batteries include the suppression of the polysulfide shuttle effect and maintenance of high sulfur loading. Herein, we report a strategy of strong chemisorption for polysulfides utilizing a chemically activated graphene matrix co-doped with nitrogen and sulfur. The dopant N and S atoms act as electron attracting atoms, leading to the nearby C atoms and causing oxygen functional groups to be polarized and more active for anchoring sulfur and polysulfides. Meanwhile, highly developed defects and edges, as well as the porous structure derived from graphene chemical activation, not only achieve a high sulfur loading in a well dispersed amorphous state, but also serve as polysulfide reservoirs to alleviate the shuttle effect. When applied as cathode hosts for lithium–sulfur batteries, the nitrogen–sulfur co-doped porous graphene architecture exhibited a high specific capacity of 1178 mA h g⁻¹ at 0.2C, 1103 mA h g⁻¹ at 0.5C, and 984 mA h g⁻¹ at 1C rate, and excellent cycling stability for 600 cycles with a retained capacity of 780 mA h g⁻¹ (0.2C).