Binder-Free Manganese Iron Nitrides/N-Doped CNT Cathode for Lithium-Sulfur Batteries

Lithium-sulfur batteries (LSBs) hold promise due to their high energy density for commercialization. However, in lab-scale research, sulfur loading has typically remained below 2 mg cm⁻², far below the practical application requirements. The pressing need to increase sulfur loading inevitably intensifies a host of challenges, including poor conductivity, volume expansion, and notably, the shuttle effect. In this work, we present an innovative approach to address these formidable challenges. Our strategy involves the utilization of a composite composed of manganese iron nitrides and reduced graphene oxide (rGO). Manganese and iron are selected as host elements for their cost-effectiveness and substantial potential for cathode modification. Fe-N co-doped carbons demonstrate high adsorption–catalysis effectiveness for long-chain polysulfide reactions (LPR), while Mn-(O, N) coordination exhibits a strong adsorption effect for short-chain polysulfide reactions (SPR) and reduces charge-transfer resistance for Li₂S. Manganese iron nitrides are prepared by deriving the manganese-iron bimetallic metal-organic framework (MOF), which possesses high surface area and abundant active sites to adsorb the polysulfide and catalyze the conversion reactions. These bimetallic nitrides are assembled on a low tortuosity reduced graphene oxide (rGO) aerogel. The rGO aerogel, created through directional freeze drying, offers flexibility to accommodate volume expansion, high porosity to house sulfur, and creates direct pathways for fast charging of ions. By employing this directional rGO aerogel as the sulfur scaffold, manganese iron nitrides significantly mitigate the shuttle effect associated with various states of the polysulfides. Through the implementation of the S/rGO aerogel without additives as the cathode for LSBs, we can achieve a higher areal capacity while simultaneously preserving cycle stability. This advancement holds the potential to expedite the realization of LSBs for real-world applications.