CoS/V₃S₄ heterostructures wrapped by nitrogen-sulfur co-doped carbon for ultra-fast-charging sodium-ion batteries

Metal sulfides are attractive anodes for sodium-ion batteries due to their high capacity and low polarization. However, single metal sulfides suffer from severe volume changes and sluggish kinetics. Constructing heterostructures offers a promising strategy, yet rational designs that achieve genuine ultra-fast charging capability remain scarce. Herein, we report metallic disc-like CoS/V₃S₄ heterostructures encapsulated in nitrogen‑sulfur co-doped carbon (CoS/V₃S₄@NSC). When evaluated with an ether-based electrolyte, the optimized CoS/V₃S₄@NSC exhibits high initial Coulombic efficiency (>90%), high reversible capacity (622.6 mAh g^-1 at 0.5 A g^-1), excellent stability (291.5 mAh g^-1 after 300 cycles at 15 A g^-1), and remarkable ultra-fast charging capability (143.1 mAh g^-1 at 40 A g^-1 within 12 s). Combined in situ/ex situ studies and density functional theory calculations reveal metallicity, enhanced Na⁺ diffusion, and a pseudocapacitive-dominated conversion mechanism. Full cells assembled with Na₃V₂ (PO₄)₃@rGO cathodes further demonstrate long-term stability (414.1 mAh g^-1 after 1500 cycles at 1 A g^-1) and outstanding rate capability (324.8 mAh g^-1 at 5 A g^-1). This work highlights a rational heterostructure design that enables practical ultra-fast sodium-ion storage.