Kinetics-Mediated FeS₂ Anodes With Selenium Doping and Sulfurized Polyacrylonitrile Catalysis Shielding: Toward Aerogenesis-Less Sodium-Ion Hybrid Capacitors

Tackling intractable issues of FeS₂ 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 FeS₂ (FeS_1.75Se_0.25) nano solid solutions packaged with thin conformal sulfurized polyacrylonitrile (SPAN) layers. The atomic Se doping aids in regulating FeS₂ 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_1.75Se_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.