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

Abstract

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.