A sustainable molten-salt synthesis of S-terminated Ti₂C MXene/FeSe₂ heterostructures toward exceptionally stable and high-capacity sodium-ion batteries

HF-free synthesis of FeSe₂@S-Ti₂C via Lewis acidic molten-salt etching. • Simultaneous Ti₂C termination, etching, and FeSe₂ anchoring in one step. • Strong interfacial coupling endows Ti₂C/FeSe₂ with metallic conductivity. • Ti₂C/FeSe₂ delivers high capacity, long life, and high rate for SIBs. • Synergistic Na-storage mechanism of FeSe₂@S-Ti₂C revealed by DFT and in situ EIS/DRT analyses. The development of high-performance anode materials is critical for advancing sodium-ion batteries (SIBs) toward practical applications. Herein, we report a novel FeSe 2 @S-Ti 2 C heterostructure synthesized via a safe and straightforward Lewis acidic molten salt etching strategy followed by in-situ selenization. This approach enables simultaneous etching of Ti 2 AlC MAX phase, surface termination with sulfur-containing groups, and uniform anchoring of FeSe 2 nanoparticles within the Ti 2 C MXene matrix, eliminating the need for hazardous HF or post-synthesis metal removal. The resulting heterostructure integrates multiple advantageous features: The highly conductive Ti₂C MXene framework accelerates the transport of Na + , while its structural robustness effectively accommodates the volume expansion caused by Na + deintercalation. S-containing surface terminations provide additional active sites that enhance Na + adsorption. Ultimately, the FeSe₂@S-Ti₂C anode demonstrates exceptional sodium-storage performance, characterized by a high reversible capacity of 397.6 mAh g −1 after 350 cycles at 1 A g −1 , superior rate capability (227.8 mAh g −1 at 5 A g −1 ), as well as robust full-cell performance with an initial Coulombic efficiency of 91.2% and a reversible capacity of 493.6 mAh g −1 following 500 cycles at 1 A g −1 . Density functional theory calculations further elucidate the underlying mechanism, revealing metallic conductivity, reduced Na + diffusion barrier (0.30 eV), and enhanced Na adsorption energy (−2.43 eV) in the heterostructure. This work presents a versatile and scalable strategy for constructing advanced MXene-based heterostructures, offering promising avenues for high-performance SIB anodes. Description : Lewis acidic molten salt etching enables one-pot synthesis of FeSe₂@S–Ti₂C heterostructures; the conductive MXene framework with S-terminations and interfacial coupling deliver fast Na + diffusion and robust sodium storage. Download: Download high-res image (203KB) Download: Download full-size image