“One stone-two birds”: reviving waste-activated carbon for stable polysulfide shuttle-free room-temperature Na-S batteries

Room-temperature sodium-sulfur batteries offer great potential for large-scale energy storage due to their high energy density, remarkable affordability, and abundant resources. However, its practical application is significantly hampered by the shuttle effect of Na2Sx (x = 1, 2, 4, 6), which leads to the irreversible loss of active sulfur species and parasitic reactions, resulting in low reversible capacity and rapid capacity degradation. In this study, we propose a sustainable approach that utilizes waste activated carbon to transform the conventional glass-fiber separator into a functional separator. The functional separator effectively mitigates the polysulfide shuttle effect through the synergistic effects of physical adsorption and chemical bonding, as supported by both experimental observations and density functional theory calculations. Consequently, the cell utilizing the functionalized separator delivers an enhanced capacity of 698.2 mAh g-1 and superior stability (degradation rate 0.08%/cycle during 260 cycles). This design represents a promising pathway toward sustainable, room-temperature sodium-sulfur batteries, while also introducing an innovative method for the repurposing of industrial waste.