FeNiS₂ 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 1C. 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.