Metallic FeCo clusters propelling the stepwise polysulfide conversion in lithium-sulfur batteries

Catalytic conversion of polysulfides is considered to be an important way to improve the kinetics and inhibit the shuttle effect of lithium-sulfur batteries (LSB). In this work, a 3D FeCo/PNC composite was prepared by in situ anchoring of the sulfiphilic compound FeCo on a lithiophilic N-doped porous carbon (PNC) substrate. Uniquely, the sulfiphilic FeCo clusters and lithiophilic N species active sites in the FeCo/PNC tend to form strong interactions of “Fe/Co-S, Li-O or Li-N” bonding, simultaneously enhancing the chemisorption and conversion ability toward polysulfides. More importantly, this strategy utilizes bi-metallic FeCo clusters to selectively catalyze the long-chain polysulfide conversion (S₈ ↔ Li₂S₄) and short-chain polysulfide conversion reactions (Li₂S₄ ↔ Li₂S), respectively. As a result, the prepared S@FeCo/PNC-based electrode with 70 wt% S-loading delivered a high mass capacity (1405 mA h g⁻¹ at 0.1C) and an excellent cycling stability (99.55% retention rate after 500 cycles at 1C). Apparently, the combination of the stepwise catalysis of the bi-metallic clusters and the synergistic anchoring of the dual active sites (bi-metallic clusters and N) plays an important role in accelerating the polysulfide conversion and suppressing the “shuttle effect” in high-performance Li-S batteries.