Interfacial Orbital Hybridization Derived Robust Cathode-Electrolyte Interphase Enables Exceptional Sodium-Ion Storage Performance

Cathode-electrolyte interphases (CEIs) are crucial for improving battery performance, yet conventional CEIs often show poor adhesion to cathodes, particularly those undergoing pronounced volume fluctuations. Here, we demonstrate the construction of a sulfur-containing CEI (S-CEI) on iron-based Prussian blue analog (FePB) cathodes for sodium-ion batteries via interfacial orbital hybridization between Fe 3d orbitals in FePB and O sp² orbitals in 1-propene 1,3-sultone (PS). X-ray absorption near edge structure (XANES) spectroscopy combined with density functional theory (DFT) calculations reveals that this 3d-sp² orbital hybridization redistributes local electron density, altering Fe coordination in FePB and the -SO₃- environment in PS. This interaction triggers in situ formation of a uniform S-CEI rich in RSO₃Na species on FePB during battery initial cycling. These RSO₃Na species strongly coordinate surface Fe centers via the inherited 3d-sp² coupling, thereby firmly anchoring the S-CEI and stabilizing the FePB lattice. Cryogenic TEM demonstrates that the S-CEI remains chemically and structurally intact after prolonged cycling. In situ synchrotron X-ray diffraction reveals that the FePB@S-CEI exhibits a markedly suppressed cubic-to-tetragonal phase transition, with the unit-cell volume shrinkage rate reduced from 18.5 to 5.7%/V. Consequently, the FePB@S-CEI achieves stable cycling with only 0.013% capacity loss per cycle over 1500 cycles at 1C, high rate capability up to 90C, and reliable performance across -20 to 60 °C. This study presents a general strategy for designing robust CEIs through interfacial orbital hybridization to enhance battery performance.