Abstract: Carbonate-based electrolytes, represented by ethylene carbonate (EC)/ethyl methyl carbonate (EMC), have been widely and long-term utilized in conventional lithium-ion batteries, primarily due to their excellent overall performance and high electrochemical stability compatible with electrode materials. However, with the increasing demand for high-energy-density and high-safety lithium batteries, carbonate-based electrolytes gradually reveal shortcomings in terms of wide-temperature adaptability, flame retardancy, and compatibility with high-voltage cathodes and lithium metal anodes. Ether-based electrolytes, as another important system for lithium batteries, demonstrate potential in wide-temperature performance and safety owing to their low viscosity, high ionic conductivity, and favorable interfacial compatibility with lithium metal anodes. Nevertheless, their poor oxidation stability (<4.0 V vs Li⁺/Li) limits their application in high-voltage cathode materials. To address this issue, this study systematically investigated the influence of polyethylene glycol ether molecular chain structures on electrolyte physicochemical properties and interfacial behavior by comparing seven ether solvents with varying chain lengths, ultimately identifying a diethylene glycol dimethyl ether-based electrolyte with outstanding comprehensive performance. Building on this, functional lithium salts and film-forming additives were introduced to further enhance the interfacial stability of the electrolyte under high-voltage conditions. The optimized diethylene glycol dimethyl ether-based electrolyte achieved an ionic conductivity of 5.9 mS·cm⁻¹ at room temperature, an electrochemical window of 5.8 V, and excellent flame retardancy. Electrochemical tests showed that the electrolyte achieved a Coulombic efficiency of 92.6% in Li||Cu cells and maintained a capacity retention of 75.2% after 500 cycles at a 3C rate in NCM811||Li cells. These results indicate that, through rational optimization, polyethylene glycol ether-based electrolytes can serve as a promising high-performance electrolyte solution.