Air sensitivity remains a substantial barrier to the commercialization of sodium (Na)–layered oxides (NLOs). This problem has puzzled the community for decades because of the complexity of interactions between air components and their impact on both bulk and surfaces of NLOs. We show here that water vapor plays a pivotal role in initiating destructive acid and oxidative degradations of NLOs only when coupled with carbon dioxide or oxygen, respectively. Quantification analysis revealed that reducing the defined cation competition coefficient (η), which integrates the effects of ionic potential and sodium content, and increasing the particle size can enhance the resistance to acid attack, whereas using high-potential redox couples can eliminate oxidative degradation. These findings elucidate the underlying air deterioration mechanisms and rationalize the design of air-stable NLOs.

Hard carbon stands out as an auspicious anode material for commercial sodium-ion batteries, yet the correlation between plateau-potential capacity and its pore architecture remains poorly understood. In this study, we systematically investigated the sodium-ion storage behavior in hard carbons with tailored pore architecture. The plateau-potential capacity of hard carbon is attributed to the filling of sodium clusters within closed nanopores and open nanopores that are impervious to the solvent molecules of the electrolyte. Small-angle X-ray scattering (SAXS) has been shown to be an effective method for estimating the volume of nanopores that can store sodium clusters. A rapid and user-friendly butanol pycnometry technique is designed to assess the volume of nanopores available for sodium-ion storage. This method has established a linear correlation between the nanopore volume detected and the plateau-potential capacity measured experimentally. We identified two scenarios where the plateau-potential capacity deviates from the congruence linear relationship established by SAXS and butanol pycnometry techniques. First, sodium clusters are unable to fill nanopores larger than 4 nm and could only partially fill those larger than 2 nm. Second, the diffusion of Na⁺ ions is impeded in graphene nanodomains with tight interlayer spacing and extended crystalline planes.

TA is employed as a reducing agent to supply electrons in the hydrothermal reaction, followed by brief annealing to restore the Li ⁺ diffusion pathways along the [010] direction and facilitate the re-intercalation of Li ⁺ in spent LFP.

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.