Alloying-driven 3d orbital charge transfer for enhanced polysulfide adsorption and conversion in room temperature sodium-sulfur batteries

Abstract

The severe shuttle effect and sluggish reaction kinetics in room-temperature sodium-sulfur (RT Na-S) batteries have been major bottlenecks hindering their practical application. To overcome these challenges, a straightforward reduction approach was employed to design three bimetallic alloy nanoparticles (FeNi, FeCo, and NiCo) supported on multistage porous carbon substrates. Experimental and theoretical calculations reveal that the charge transfer within the alloy catalyst influences the position of its d-band center and its degree of hybridization with sodium polysulfides (NaPSs). An increased charge transfer leads to a shift of the alloy’s d-band center closer to the Fermi energy level, thereby enhancing its adsorption and catalytic capabilities. Among the three alloy compositions, the FeNi alloy exhibits the highest charge transfer. Consequently, the FeNi alloy demonstrates the superior electrochemical performance, achieving a high reversible specific capacity of 848.2 mA h g⁻¹, with an average capacity degradation rate of only 0.037 % per cycle over 1000 cycles at 1.2 C. The S/FeNi/NC cathode exhibits a low electrolyte-to-sulfur (E/S) ratio of 6.6 µL mg⁻¹, while maintaining a high reversible specific capacity of 568.1 mA h g⁻¹. This offers valuable insights for the application of alloy catalysts in the S/FeNi/NC cathode of RT Na-S batteries.