Progress of Non-Aqueous Liquid Electrolytes for High-Voltage Sodium-Ion Batteries

Due to their significant resource-economic advantages, sodium-ion batteries are gradually becoming an important alternative to lithium-ion batteries in large-scale energy storage. However, their performance under high-voltage operation (>4.0 V vs. Na⁺/Na) is limited by various degradation mechanisms, including cathode structure evolution, electrolyte oxidation, rapid increase in interfacial resistance, and deterioration of ion transport kinetics. This paper systematically summarizes these challenges, demonstrates the trends and prospects of practical electrolyte development through computational simulations, and highlights molecularly engineered non-aqueous liquid electrolytes as a feasible solution. Advanced formulations using fluoride, nitrile, and sulfone solvents can extend the electrochemical stability window to above 4.5 V and promote the formation of a stable, inorganic-rich solid electrolyte interface (SEI/CEI). Adding functional additives containing phosphorus, boron, or silicon can further optimize the solvation structure and enhance interfacial stability, enabling the full cell to retain more than 85% of its capacity after 500-2000 cycles. Cost control and the diversity of permutations and combinations are also considered. Future research should integrate in-situ/operating state characterization, design hybrid electrolyte systems using machine learning and simulation techniques to achieve higher energy density and longer cycle life at low cost, and accelerate commercialization through interdisciplinary innovation.