Manipulating Polysulfide Conversion with Strongly Coupled Fe₃O₄ and Nitrogen Doped Carbon for Stable and High Capacity Lithium–Sulfur Batteries

Li–S batteries are among the most promising energy storage technologies but their commercialization faces substantial challenges, largely due to difficulties in controlling their reaction pathways under practical conditions. Here, the synthesis of strongly coupled Fe₃O₄ and N-doped carbon directly in flexible carbon cloth is demonstrated, as well as their novel use for hosting sulfur with outstanding performance for Li–S batteries. It is discovered that the synergistic effects of Fe₃O₄ and N-carbon bring strong adsorption toward lithium polysulfide, and ensure nearly complete conversion of short-chain polysulfide to Li₂S during discharge. The Li₂S solids generated on these novel hosts are extremely reactive and can be readily charged back to S without a noticeable overpotential. The critical roles of Fe₃O₄ and N-doped carbon are studied and direct correlations are established between their surface concentration/crystallinity and the Li₂S₄ to Li₂S conversion capacity. This novel manipulation of polysulfide conversion allows to fabricate freestanding and flexible sulfur cathodes that deliver a specific capacity of 1316 mAh g⁻¹ at 0.1C and stable cycling for 1000 cycles at 0.2C under a high sulfur loading of ≈4.7 mg cm⁻².