FeCoN ₆ Sites Unlock Superior Sodium‐Ion Storage Through Synergizing Capture‐Release and Orbital‐Mediated Charge Delocalization

Abstract

ABSTRACT Sodium‐ion hybrid capacitors (SHCs) are severely hindered by sluggish sodiation kinetics in conventional anodes. Single‐atom sites, though promising, suffer from localized d ‐orbitals that induce overly strong Na + binding, creating a kinetic bottleneck. Herein, we design heteroatomic FeCo dual‐atom sites (FeCoN 6 ) that unlock a dual‐mechanism synergy for fast and durable Na + storage. Theoretical‐experimental evidence confirms that strong d–d orbital coupling induces an orbital‐mediated charge‐delocalization (OMCD) effect, which downshifts the d ‐band center to moderate Na + binding affinity. Meanwhile, the intrinsic heteroatomic nature of the FeCoN 6 sites provides a stepped energy landscape for optimized Na + capture‐release pathways. This synergy between electronic OMCD modulation and the kinetic capture‐release model significantly lowers the diffusion barrier. Consequently, the FeCo dual‐atom nitrogen‐doped carbon anode exhibits dominant pseudocapacitive kinetics, superior rate capability (225 mAh g −1 at 10 A g −1 ), and exceptional durability. The full SHC delivers a high energy density of 165 Wh kg −1 at 23 W kg −1 , retains 108 Wh kg −1 at 9424 W kg −1 , and achieves 90% capacity retention over 10,000 cycles. This study establishes that engineering heteroatomic sites to leverage both intrinsic functional heterogeneity and electronic delocalization is a powerful strategy to overcome kinetic limitations in energy storage.