FeNiS ₂ quantum dot integration boosts enhanced reaction kinetics and cycle stability of SPAN nanofiber cathode for Li-S batteries

Sulfurized polyacrylonitrile (SPAN) has been regarded as one of the most competitive cathode candidates for lithium-sulfur (Li-S) batteries, owing to its outstanding theoretical energy density, excellent structural durability, and minor self-discharge. Nevertheless, the intrinsically slow reaction kinetics of SPAN results in insufficient active sulfur utilization at high current rates, which severely restricts its rate performance and long-cycle stability. This study introduces FeNiS2 Quantum Dots (QDs) as catalyst embedding in SPAN nanofibers (FeNiS2 QDs@SPAN). Taking advantages of the ultra-small size, superior dispersibility and abundant catalytic sites of FeNiS2 QDs, the redox kinetics and cycle performance of SPAN are significantly enhanced. Kinetic analyses and theoretical calculation demonstrate the uniformly dispersed FeNiS2 QDs effectively reduce charge transfer resistance and facilitate conversion reaction. FeNiS2 QDs@SPAN material exhibits high reversible capacity of 1,213 mAh g-1 and an ultralow capacity decay of 0.034% per cycle over 1,000 cycles at 1 C. Remarkably, even at high rate of 5 C (8.37 A g-1), it delivers a stable long-cycle capacity of 720 mAh g-1 and demonstrates excellent cycling capability with a low fade rate of 0.029% per cycle over 450 cycles. FeNiS2 QDs@SPAN material maintains good performance even under lean electrolyte conditions and a wide temperature range. This work underscores the significant potential of FeNiS2 QDs as catalyst for achieving high performance sulfur cathode and advanced Li-S batteries.