Localized High-Concentration Electrolytes for Sodium Batteries: Fundamentals, Challenges, and Applications

The localized high-concentration electrolyte (LHCE) has emerged as a transformative electrolyte design strategy for sodium-based batteries, effectively overcoming the limitations of conventional dilute and high-concentration systems. By constructing a locally anion-rich solvation environment through the integration of functional salts, strongly coordinating solvents, and inert diluents, LHCE simultaneously enhances interfacial stability, suppresses parasitic reactions, and improves ion transport kinetics. This review systematically outlines the fundamental principles governing LHCE solvation structures and desolvation processes, emphasizing their influence on interphase formation and electrode compatibility. Representative design strategies in sodium–sulfur batteries and sodium metal systems are highlighted, including salt-to-solvent ratio optimization, inert diluent selection, additive engineering, and anion-dominated solvation modulation. Finally, the review outlines critical challenges in achieving safer, nonfluorinated LHCE formulations and future directions to guide electrolyte innovation for next-generation sodium-ion energy storage technologies.