Curtailing Carbon Usage with Addition of Functionalized NiFe₂O₄ Quantum Dots: Toward More Practical S Cathodes for Li–S Cells

Smart combination of manifold carbonaceous materials with admirable functionalities (like full of pores/functional groups, high specific surface area) is still a mainstream/preferential way to address knotty issues of polysulfides dissolution/shuttling and poor electrical conductivity for S-based cathodes. However, extensive use of conductive carbon fillers in cell designs/technology would induce electrolytic overconsumption and thereby shelve high-energy-density promise of Li–S cells. To cut down carbon usage, we propose the incorporation of multi-functionalized NiFe₂O₄ quantum dots (QDs) as affordable additive substitutes. The total carbon content can be greatly curtailed from 26% (in traditional S/C cathodes) to a low/commercial mass ratio (~ 5%). Particularly, note that NiFe₂O₄ QDs additives own superb chemisorption interactions with soluble Li₂S_n molecules and proper catalytic features facilitating polysulfide phase conversions and can also strengthen charge-transfer capability/redox kinetics of overall cathode systems. Benefiting from these intrinsic properties, such hybrid cathodes demonstrate prominent rate behaviors (decent capacity retention with ~ 526 mAh g⁻¹ even at 5 A g⁻¹) and stable cyclic performance in LiNO₃-free electrolytes (only ~ 0.08% capacity decay per cycle in 500 cycles at 0.2 A g⁻¹). This work may arouse tremendous research interest in seeking other alternative QDs and offer an economical/more applicable methodology to construct low-carbon-content electrodes for practical usage.[Figure not available: see fulltext.].