Rational Design of Ultrafine Co, Fe, Ni, and Cu on Fluorine-Free Nitrogen-Doped MXene via a Molten Salt Etching Strategy for the Adsorption–Barrier–Catalyst Functions of Polysulfides toward High-Energy Lithium–Sulfur Batteries

Designing electrocatalysts with high catalytic activity and strong adsorption capacity is crucial for overcoming the key challenges in lithium-sulfur batteries. In this paper, a nitrogen-functionalized MXene loaded with cobalt nanoparticles is prepared via a fluoride-free molten salt etching method. The N-functional groups were introduced via an in situ substitution strategy, while maintaining the layered character of MXene. The resulting cobalt nanoparticles from the etching process were retained in the composite, synergizing with nitrogen to enhance the chemical anchoring of polysulfides and accelerate the redox reaction kinetics. Electrochemical tests demonstrate that Co/N-MX exhibits outstanding catalytic ability and adsorption capacity. Benefiting from the synergistic effect, lithium-sulfur batteries with a Co/N-MX modified separator exhibit improved electrochemical performance. Importantly, this strategy can be extended to other metals such as Cu, Fe, and Ni, with nitrogen functional groups simultaneously introduced onto the MXene surface, demonstrating its versatility and broad applicability.