Multifunctional separator engineering via FeCo₂O₄ nanosheets and conductive additives for high-rate Li-S batteries

The growing demand for energy storage has driven significant research interest in lithium-sulfur (Li-S) batteries. However, the commercialization of Li-S batteries has been hindered by several challenges, among which the polysulfide shuttle effect is especially prominent. In this study, we synthesized binary transition-metal oxide FeCo₂O₄ nanosheets (FCO) via a hydrothermal precipitation reaction followed by high-temperature calcination. By simply coating FCO and Super P (SP) onto a polypropylene separator, we developed a modified separator (FCOSP) to enhance the battery performances. The FCO surface is abundant in catalytic and adsorptive active sites, effectively mitigating the polysulfide shuttle effect and thereby improving the battery performances. Meanwhile, SP not only enhances the conductivity of the coating but also contributes to the adsorption of polysulfides. The Li-S batteries assembled with FCOSP exhibit a decay rate of 0.083% after 1000 cycles at 1C. More remarkably, the capacity decay rate is as low as 0.07% after 1000 cycles at 5C. The effectiveness of FeCo₂O₄ in adsorbing and catalytically converting polysulfides is demonstrated, thus providing a viable approach for the commercialization of Li-S batteries.