Kinetics‐Mediated FeS ₂ Anodes With Selenium Doping and Sulfurized Polyacrylonitrile Catalysis Shielding: Toward Aerogenesis‐Less Sodium‐Ion Hybrid Capacitors

ABSTRACT Tackling intractable issues of FeS ₂ anodes, typically like polysulfide dissolution/shuttle, poor initial Coulombic efficiency (ICE), and severe aerogenesis, is of significance to build practical sodium (Na)‐ion hybrid capacitors (SICs). Herein, we propose a smart kinetics‐mediated/catalysis‐shielding strategy by making selenium (Se)‐doped FeS ₂ (FeS _1.75 Se _0.25 ) nano solid solutions packaged with thin conformal sulfurized polyacrylonitrile (SPAN) layers. The atomic Se doping aids in regulating FeS ₂ electronic structures and strengthening the inherent conductivity, while dense/electrochemical active SPAN shells can avert the polysulfide leakage, smooth Na ⁺ diffusion kinetics, and foremost shield catalytic sites to inhibit the adverse electrolyte decomposition/gaseous evolutions. Such SPAN‐sheltered FeS _1.75 Se _0.25 anodes demonstrate a remarkable reversible capacity of ∼540 mAh g ⁻¹ at a high current density of 10 A g ⁻¹ , long‐lasting cyclic stability (∼96.8% capacity retention after all cycles), superb ICE as high as 95.5%, and negligible self‐discharge phenomena. Systematic in situ examinations are used to unveil the reversible phase‐conversion mechanisms, and density functional theory calculations affirm their reduced band gaps and energy barriers. The assembled SICs are able to deliver an impressive energy density of 84.8 Wh kg ⁻¹ at 15 kW kg ⁻¹ without evident gases evolved upon cycling, and be fully competent as powerful energy suppliers to drive electromagnetic guns.