Superior sulfur infiltration into carbon mesosponge via chemical reaction for enhanced cycling stability in lithium–sulfur batteries

Abstract

Sulfur is a promising cathode material for secondary batteries, but its insulating nature and volume expansion during lithiation require encapsulation within carbon scaffolds. Moreover, the pronounced polysulfide shuttle effect hinders cycle stability. These issues make it difficult to achieve a sulfur content exceeding 70 wt% in typical sulfur–carbon composites, which are demanded for practical applications. This study explores a new scaffold, carbon mesosponge (CMS), featuring a single-layer graphene structure and a high mesopore volume of 3.01 cm³ g⁻¹. This unique structure allows for a sulfur content of up to 79 wt%. The S/CMS composite demonstrates superior cycling performance compared to conventional carbon scaffolds, such as KOH-activated carbon and graphene oxide. Additionally, two sulfur loading methods, physical and chemical, are compared. The chemical method facilitates sulfur deposition predominantly within the CMS pores, improving sulfur confinement and enhancing cycling stability compared to the physical method. This controlled sulfur deposition is attributed to the higher concentration of oxygen-functional groups within CMS pores, which could attract Na₂S₄, a precursor of sulfur. When used as the active material, the S/CMS composite prepared by the chemical method achieved a discharge capacity exceeding 1200 mA h g⁻¹ in a pouch cell. This research underscores the importance of CMS as a scaffold and the superior sulfur-loading method in enhancing the performance of Li–S batteries.