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

ABSTRACT 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 PF 6 − 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/Na 3 PO 4 , extending the stability of high‐voltage O3‐type NaNi 1/3 Fe 1/3 Mn 1/3 O 2 (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.