CoFe Alloy Coated with Nitrogen-Doped Porous Carbon as both the Electrocatalyst and Lithium-Ion Accelerator for Lithium–Sulfur Batteries

The development of lithium–sulfur (Li–S) batteries with high capacity has been limited by the shuttle effect from slow kinetics of sulfur species and limited lithium-ion migration, leading to rapid capacity decay. Here, a CoFe alloy coated with nitrogen-doped porous carbon (CoFe@NPC) is designed as a separator modification material for Li–S batteries to enhance reaction kinetics and promote lithium-ion transportation. CoFe alloy prolongs the S–S and Li–S bonds of polysulfides, which lowers the reaction energy barrier during the reduction of polysulfides and oxidation of Li₂S, facilitating the deposition and dissociation of Li₂S. Moreover, the NPC layer and highly conductive CoFe alloy ensure timely lithium-ion sources during the polysulfide conversion process. Consequently, the CoFe@NPC-modified separator can effectively utilize active material and suppress polysulfide shuttle, bringing about improved performance of Li–S batteries. These batteries demonstrate a high initial discharge specific capacity of 1242.94 mA h g^–1 at 0.5 C and excellent long-term cycling stability with a capacity decay of only 0.033% per cycle over 400 cycles. Furthermore, the pouch cell with an initial capacity of 178.8 mAh shows stable cycling for over 60 cycles, highlighting the potential practical application of Li–S batteries. This work provides a proposal for the design of separator modification materials for practical Li–S batteries.