Temperature‐Robust Interphase Enables Carboxylate‐Ester Electrolyte for Stabilizing High‐Voltage Sodium Batteries

High-voltage sodium metal batteries (SMBs) under wide temperature are fundamentally contingent upon the electrochemical stability of electrode-electrolyte interfaces. Although carboxylate esters offer a pathway to superior low-temperature performance, their inherent low oxidative stability presents a major impediment. Herein, a synergistic electrolyte engineering strategy of employing ethyl acetate (EA) with vinylene carbonate (VC) as multifunctional additives is initially pioneered. Despite its weak coordination with Na⁺, the introduced VC serves as an effective regulator that restructures the solvation shell and preferentially decomposes in synergy with PF₆^−$ anions, thereby constructing a robust cathode electrolyte interphase (CEI). As confirmed by X-ray spectroscopies and electronic microscopes, this ultrathin but gradient architecture comprises a flexible but fluorine-rich organic outer layer and a mechanically robust with ionically conductive inner layer enriched with NaF/Na₃PO₄, extending the stability of high-voltage O3-type NaNi1/3Fe1/3Mn1/3O₂ (NFM) cathode and suppressing transition metal dissolution. Consequently, the NFM | | Na cells achieve exceptional performance, demonstrating a capacity retention of 74.6% after 200 cycles under 4.5 V. Even decreasing the surrounding temperature to –20°C, a high capacity retention of 91.3% is achieved, and the NFM | | hard carbon full cells maintain the Coulombic efficiency as high as 99.3% over 100 cycles, enabling high-voltage operation and wide-temperature tolerance for high-energy-density SMBs.