Three-dimensional MXene coupled CoFe nanoalloys as sulfur host for long-life room-temperature sodium-sulfur batteries

Room-temperature sodium-sulfur (RT Na-S) batteries are potential candidates for next-generation energy storage systems because of low-cost resources, high theoretical capacity, and high energy density. However, their commercialization is hindered by the inherent shuttle effect, insulation of sulfur, and slow catalytic conversion. This study proposes a novel approach involving the design of a C/CoFe alloy catalyst coupled with Ti3C2Tx MXene substrate (C/CoFe-MXene) as a three-dimensional porous conductive sulfur host. Polysulfide adsorption/catalytic experiments and density functional theory calculation confirmed the excellent affinity and strong catalytic conversion ability of the C/CoFe-MXene composite for polysulfides. The heterostructure formed between the CoFe alloy and the MXene substrate promotes Na+ transport and accelerates reaction kinetics of sulfur species. Consequently, the assembled RT Na-S batteries with a C/CoFe-MXene sulfur host (2.0 mg cm-2) deliver a high initial specific capacity of 572 mAh g-1 at 1 C. Even at 5 C, the battery achieves ultralong-term cycling over 5,400 cycles with a capacity retention rate of 61.9%, corresponding to a slow capacity fading rate of 0.0089% per cycle, demonstrating outstanding high-rate tolerance. This work provides new insights into the preparation of three-dimensional porous sulfur cathodes with high specific surface area and excellent catalytic activity using catalysts loaded on MXene substrates in RT Na-S batteries.