CoFe Alloy-Decorated Interlayer with a Synergistic Catalytic Effect Improves the Electrochemical Kinetics of Polysulfide Conversion.

Good electrical conductivity, strong catalytic activity, high interaction with lithium polysulfides (LIPSs), simple method, and low cost should be considered for the design and preparation of high-performance electrochemical catalysts that catalyze the conversion of LIPSs. In this work, we designed a bimetallic alloyed multifunctional interlayer with multiple adsorption/catalysis sites. The interwoven carbon fibers derived from bacterial cellulose (BC) not only contribute to reducing metal ions to metals but also confine the growth of Co-Fe alloys formed in situ. The metal supported on carbon is very effective for the conversion of LIPSs due to its high adsorption and catalytic sites. In addition, the synergistic effect between Fe and Co species leads to excellent bifunctional catalytic activity. Through detailed electrochemical analysis and theoretical calculations, we revealed that CoFe@CNFs has superior electrocatalytic activity, and the lithium-sulfur (Li-S) batteries with a catalytic interlayer can deliver satisfactory rate and cycle performance. At a high current density of 2C, the discharge capacity can still reach 627 mAh g. At a current density of 1C, the Coulombic efficiency is maintained at a level close to 100% during the whole cycle process and a satisfying low capacity decay of 0.08% per cycle. More importantly, even if the ambient temperature drops to 0 °C, the Li-S battery using the interlayer can still be charged and discharged normally and shows acceptable discharge capacity, which shows that it has good rate kinetics.