Activating Ferroelectric‐Magnetic Synergistic Effects at Cathode‐Electrolyte Interfaces Toward Superfast and Stable Sodium Storage

Abstract Layered oxides are promising cathode candidates for sodium‐ion batteries due to their high energy density. However, the rate and cycling performances are hindered by severe interfacial side reactions and sluggish kinetics. Using NaNi 0.5 Mn 0.5 O 2 (NM) as a model material, ferroelectric‐magnetic synergistic effects are activated at the NM‐electrolyte interfaces via constructing a multiferroic layer on the NM surface, significantly realizing the superfast and stable sodium storage. First, the nucleation and growth of interfacial layers are regulated by ferroelectric‐magnetic synergistic effects, resulting in the formation of a thin interfacial layer enriched with NaF. Second, a uniform sodium‐ion distribution at the NM‐electrolyte interfaces is established, boosting the charge transfer kinetics. Third, the distortion of NiO 6 local structure is reduced, minimizing the structural change and improving the cycling stability. As a result, superior cycling (82.1% retention after 1000 cycles) and rate capabilities (up to 50–100C) in half cells, as well as high energy densities (340.7 Wh kg −1 ) and fast‐charging properties (≈113 s per charge with ≈240.0 Wh kg −1 input) in full cells, are achieved. This work presents a novel strategy for improving rate and cycling capabilities by harnessing ferroelectric‐magnetic synergistic effects, offering a pathway for designing advanced electrodes in secondary batteries.