Catalyzing Sulfur Redox Reactions of Li‐S Batteries by Ni/NiSe Heterojunction In Situ Encapsulated in N‐Doped CNTs

Lithium-sulfur (Li-S) batteries face two key challenges including the detrimental "shuttle effect" of long-chain lithium polysulfides (LiPSs, Li₂S_n, 4 ≤ n ≤ 8) and the slow conversion kinetics from Li₂S₄ to Li₂S. To address this, we developed a bidirectional catalyst featuring Ni/NiSe heterojunctions encapsulated within nitrogen-doped carbon nanotubes (NCNT) via an in situ CNT-encapsulation strategy to promote the conversion of sulfur species. The abundant heterointerfaces in Ni/NiSe@NCNT provide multiple active sites, which not only strongly adsorb LiPSs via chemical interactions but also serve as bidirectional catalyst to enhance the sulfur reduction reaction. In situ Raman spectroscopy and electrochemical analysis both confirmed that the Ni/NiSe@NCNT catalyst effectively suppresses the LiPSs shuttle effect and enhanced the redox reaction kinetics of sulfur. The batteries with this modified separator exhibit outstanding performance with a discharge capacity of 1406.2 mAh g^-1 at 0.1C and robust cycling stability. Furthermore, under demanding conditions of high sulfur loading (6.78 mg cm^-2) and low electrolyte/sulfur ratio, the cell delivers a reversible specific capacity of 589.9 mAh g^-1. This work provides new insights into the catalytic role of transition metals in sulfur reduction reaction and proposes an effective strategy for designing stable, high-performance bidirectional catalysts for Li-S batteries.