A “seat-squatting” strategy via lithium substitution to suppress Fe-migration in Na layered oxide cathodes†

Na-ion batteries (NIBs) are emerging as a promising alternative to Li-ion batteries (LIBs). To align with sustainability principles, the design of electrode materials must incorporate considerations for abundant and environmentally friendly elements, such as redox-active Fe. Despite its appeal, the enduring challenge of Fe migration in layered cathodes remains inadequately addressed over decades. Here, we propose a “seat-squatting” strategy via Li-substitution to fundamentally suppress Fe migration. Li is strategically introduced to migrate first, occupying available migration sites without inducing structural damage and effectively raising the activation energy for Fe migration. Experimental and theoretical validation using O3-Na_0.83Li_0.17Fe_0.33Mn_0.5O₂ (NaLFM) demonstrates a robust suppression of irreversible Fe migration. As a result, the NaLFM cathode delivers enhanced structural and electrochemical cycling stability. This work illustrates a compelling strategy to curb irreversible Fe migration in NIBs, offering a pathway for the development of stable and cost-effective layered oxides based on Fe redox centers.