Plasma-Induced NaF/C Hybrid Interphase as the Artificial Cathode-Electrolyte Interphase for Stabilizing O3-Type NaNi1/3Fe1/3Mn1/3O2 Cathodes

O3-type NaNi1/3Fe1/3Mn1/3O2 (NFM) is a promising cathode material for sodium-ion batteries, yet its practical application is hindered by interfacial instability during cycling and rapid surface degradation upon air exposure. These drawbacks stem from the high surface reactivity of the exposed lattice, which induces persistent parasitic reactions, excessive cathode-electrolyte interphase (CEI) formation, and sluggish Na+ transport. In this study, a low-temperature plasma-enhanced chemical vapor deposition strategy is employed to construct a NaF/C artificial CEI on NFM without altering the bulk structure. This approach achieves simultaneous surface chemical passivation and interfacial kinetic regulation. The NaF-rich phase stabilizes the CEI and facilitates Na+ migration, while the incorporated carbon ensures continuous electron conduction, collectively reducing polarization and accelerating Na+ diffusion. As a result, the modified NFM@NaF/C cathode delivers a capacity retention of 85.2% after 100 cycles at 1 C. Moreover, it retains 80% of its initial capacity even after 7 days of air exposure, demonstrating significantly enhanced structural and air stability.