4.7 V High‐Voltage and Nonflammable Electrolyte Enabling High Energy‐Density and Long‐Lifespan Sodium Metal Batteries

Abstract Constructing sodium metal batteries (SMBs) with high safety and high energy density is an effective way to gain a cost‐competitive advantage over lithium‐ion batteries for future safe energy storage. Here, engineering the solvation structure of Na⁺ ions has been conducted in NaPF 6 ‐trimethyl phosphate‐based local high‐concentration electrolyte (PF‐LHCE) via forming more contact ion pairs and aggregates enriched with PF 6 − anions, which can effectively suppress continuous parasitic reactions and the dendrite growth on sodium anodes, enabling SMBs with long lifespans and high energy density. The optimized electrolyte not only exhibits excellent compatibility with Na anodes, but also has a higher Na⁺ transference number and expanded electrochemical window to stably match with high‐voltage cathodes, improving the interfacial transport kinetics under high current densities and reaching high energy density of full cells. With a limited negative‐to‐positive electrode capacity ratio and a broad operating voltage range of 2.0–4.7 V, this electrolyte enables full cells to exhibit a high energy density of 341.6 Wh kg −1 and high capacity retention of 91.6% after 1200 cycles. Endowed with its intrinsic nonflammability of the solvent and the abovementioned excellent performance, this designed PF‐LHCE demonstrates a promising strategy for promoting the industrialization of SMBs in the future.