Dynamic Self‐Optimizing Interfaces via Cu Corrosion and Anion‐Vacancy Synergy in SnSSe @ Recycled Graphite Anodes for High‐Performance Sodium‐Ion Batteries

Abstract Tin sulfide (SnS 2 ) anodes for sodium‐ion batteries (SIBs) exhibit high theoretical capacity (1136 mAh g −1 ) but face sluggish kinetics and structural instability due to volume expansion and poor conductivity. This work proposes a dual‐defect strategy combining anion vacancies and dynamic interfacial optimization. Selenium (Se)‐doped, anion vacancy‐rich tin sulfoselenide (SnSSe) nanosheets anchored on recycled graphite (RG) are synthesized (SnSSe@RG). Electrochemical tests and density functional theory calculations jointly demonstrate that Se doping enhances sodium ion (Na + ) diffusion kinetics. Crucially, a copper (Cu)‐driven interfacial evolution mechanism is further uncovered: sodium polysulfides/selenides formed during the charge/discharge react with the Cu current collector, triggering in situ copper sulfide (Cu 2 S)/copper selenide (Cu 2 Se) formation. Ab initio molecular dynamics simulations reveal spontaneous decomposition of Na 2 S 6 /Na 2 Se 6 at the Cu interface, forming new Cu─S/Cu─Se bonds. These self‐optimized interfaces synergize with anion vacancies to mitigate the volume expansion and accelerate charge transport. Consequently, SnSSe@RG anode delivers high cycling stability (540 mAh g −1 after 300 cycles at 1 A g −1 ) and rate capability (440 mAh g −1 at 5 A g −1 ). Paired with an Na 3 V 2 (PO 4 ) 3 @C cathode, the resultant sodium‐ion full cell retains 125.5 mAh g −1 after 500 cycles at 0.2 A g −1 , demonstrating high viability. This work provides profound mechanistic insights into defect‐coupled current collector engineering and establishes a paradigm for designing self‐adaptive electrodes in high‐performance SIBs.