Research progress of low-concentration electrolytes for sodium-based batteries

• This review offers a timely update on the latest research progress in low-concentration electrolytes for sodium-based batteries. • The design principle of solvents, salts and additives in low-concentration electrolyte is discussed with typical examples. • The manipulation of solvation structures and interphase chemistry in low-concentration electrolyte is discussed. • Current challenges and future prospects for the design of high-performance low-concentration electrolytes are presented. Sodium-based batteries (SBBs) have shown tremendous potential in large-scale energy storage applications due to their cost-effectiveness and natural abundance of sodium. Conventional views hold that low-concentration electrolytes (LCEs) struggle to achieve stable charge/discharge performance because of reduced ionic conductivity caused by low Na⁺ concentrations. The research progress, performance regulation, and development prospects of low-concentration electrolytes have not been fully summarized. Low-concentration electrolytes (LCEs, typically <1 M) have presented significant potential for SBBs electrolytes owing to their advantages of cost-effectiveness, low viscosity and wide-temperature tolerance. However, they are confronted with critical challenges, specifically regarding low ionic conductivity and inadequate interfacial stability. This paper presents a systematic review of the recent advances in LCEs for SBBs, focusing on the regulatory mechanisms of solvent engineering, additive design, and salt systems and their concentrations on electrode/electrolyte interface (EEI) chemistry, and analyzes the synergistic effect between ion transport and interfacial stability under low-salt concentration. Finally, this paper analyzes the current challenges and prospects the future directions of multifunctional electrolyte design, providing new ideas for the low-cost and high-reliability development of SBBs. The high-performance low-concentration electrolyte is important for the industrialization of sodium-based batteries.