Quantum-Size FeS₂ with Delocalized Electronic Regions Enable High-Performance Sodium-Ion Batteries Across Wide...

Wide-temperature applications of sodium-ion batteries (SIBs) are severely limited by the sluggish ion insertion/diffusion kinetics of conversion-type anodes. Quantum-sized transition metal dichalcogenides possess unique advantages of charge delocalization and enrich uncoordinated electrons and short-range transfer kinetics, which are crucial to achieve rapid low-temperature charge transfer and high-temperature interface stability. Herein, a quantum-scale FeS₂ loaded on three-dimensional Ti₃C₂ MXene skeletons (FeS₂ QD/MXene) fabricated as SIBs anode, demonstrating impressive performance under wide-temperature conditions (- 35 to 65 °C). The theoretical calculations combined with experimental characterization interprets that the unsaturated coordination edges of FeS₂ QD can induce delocalized electronic regions, which reduces electrostatic potential and significantly facilitates efficient Na⁺ diffusion across a broad temperature range. Moreover, the Ti₃C₂ skeleton reinforces structural integrity via Fe-O-Ti bonding, while enabling excellent dispersion of FeS₂ QD. As expected, FeS₂ QD/MXene anode harvests capacities of 255.2 and 424.9 mAh g^-1 at 0.1 A g^-1 under - 35 and 65 °C, and the energy density of FeS₂ QD/MXene//NVP full cell can reach to 162.4 Wh kg^-1 at - 35 °C, highlighting its practical potential for wide-temperatures conditions. This work extends the uncoordinated regions induced by quantum-size effects for exceptional Na⁺ ion storage and diffusion performance at wide-temperatures environment.