Constructing nickel-cobalt bimetallic sulfide nanoparticles embedded in N/ S co-doped carbon nanofibers with enhanced reaction kinetics for superior sodium-ion batteries

Sodium-ion batteries (SIBs) have garnered significant attention as a feasible alternative in the field of energy storage due to their cost-effectiveness and abundant resource availability. Nevertheless, it remains an ongoing challenge to develop suitable anode materials to fulfill the high energy density demands of SIBs. In this work, a novel bimetallic sulfide (Ni 0.33 Co 0.67 ) 9 S 8 nanoparticles uniformly embedded in N/S co-doped carbon nanofibers (NSCFs) has been successfully synthesized by an electrospinning technique followed by a sulfurization treatment. The N/S co-doped carbon nanofibers framework can effectively improve the electrical conductivity, and alleviate the volume variation during the discharge-charge process. As an anode material for SIBs, (Ni0.33C- o0.67)9S8@NSCFs electrode exhibits a remarkable rate performance (414.9 mAh/g at 5 A/g) and outstanding cycling stability (405.4 mAh/g after 1150 cycles at 1 A/g with a capacity retention of 84.1 %), all of which are superior to that of monometallic sulfide Co9S8@NSCFs. Density functional theory calculations demonstrates that (Ni 0.33 Co 0.67 ) 9 S 8 exhibits a reduced barrier energy for Na+ diffusion, enhanced binding ability with NSCFs, and increased adsorption energy of Na+ compared to monometallic sulfide Co9S8. The proposed multicomponent design and nanostructural configuration provide a promising approach for the development of high-performance anode materials based on bimetallic sulfide in sodium-ion batteries.