Medium‐Entropy‐Alloy FeCoNi Enables Lithium–Sulfur Batteries with Superb Low‐Temperature Performance

Lithium‐sulfur battery suffers from sluggish kinetics at low temperatures, resulting in serious polarization and reduced capacity. Here, this work introduces medium‐entropy‐alloy FeCoNi as catalysts and carbon nanofibers (CNFs) as hosts. FeCoNi nanoparticles are in suit synthesized in cotton‐derived CNFs. FeCoNi with atomic‐level mixing of each element can effectively modulate lithium polysulfides (LiPSs), multiple components making them promising to catalyze more LiPSs species. The higher configurational entropy endows FeCoNi@CNFs with extraordinary electrochemical activity, corrosion resistance, and mechanical properties. The fractal structure of CNFs provides a large specific surface area, leaving room for volume expansion and Li2S accumulation, facilitating electrolyte wetting. The unique 3D conductive network structure can suppress the shuttle effect by physicochemical adsorption of LiPSs. This work systematically evaluates the performance of the obtained Li2S6/FeCoNi@CNFs electrode. The initial discharge capacity of Li2S6/FeCoNi@CNFs reaches 1670.8 mAh g−1 at 0.1 C under ‐20 °C. After 100 cycles at 0.2 C, the capacity decreases from 1462.3 to 1250.1 mAh g−1. Notably, even under ‐40 °C at 0.1 C, the initial discharge capacity of Li2S6/FeCoNi@CNFs still reaches 1202.8 mAh g−1. After 100 cycles at 0.2 C, the capacity retention rate is 50%. This work has important implications for the development of low‐temperature Li‐S batteries. A self‐supporting 3D porous film with in situ growth of FeCoNi alloy nanoparticles is designed. FeCoNi medium‐entropy‐alloy as an efficient catalyst to prevent polysulfides accumulate, accelerate kinetics, and enhance adsorption‐conversion ability at low temperature. The results show that lithium‐sulfur battery has excellent low‐temperature performance. After 100 cycles under −20 °C and 0.2 C, the capacity can reach 1250.1 mAh g‐1.