Dual‐Additive‐Driven Boron‐Enriched Interphases Stabilize Tetrahydrofuran‐Based Electrolytes for High‐Voltage Sodium‐Ion Batteries

Abstract The advancement of energy storage systems heavily relies on the development of high‐performance electrolytes. Nonetheless, conventional electrolytes often struggle with interfacial stability, ionic conductivity, and electrochemical compatibility. Cyclic ether solvents, such as tetrahydrofuran (THF), despite their superior ionic conductivity and solvation kinetics, are plagued by intrinsic oxidative instability at high potentials (>4.0 V vs Na + /Na), which undermines their cycling durability with high‐voltage cathodes. This study introduces a boron‐rich dual‐additive electrolyte that resolves the voltage‐stability paradox of THF‐based systems, by preferentially adsorbing onto the cathode and decomposing to form a robust, boron‐enriched interfacial layer that precisely regulates interfacial chemistry and stabilizes high‐voltage operation. Consequently, the optimal electrolyte significantly enhances the performance of high‐voltage Na 0.75 Ni 0.25 Fe 0.25 Mn 0.5 O 2 (NFM) cathodes, achieving 82.9% capacity retention after 150 cycles at a 4 V cut‐off and delivering a remarkable rate capability of 80.4 mAh g −1 at 1 A g −1 . Additionally, full cells with hard carbon anodes maintain 69.3% capacity over 150 cycles with an average Coulombic efficiency of 99.5%. This work establishes a general paradigm for designing oxidation‐resistant electrolytes through targeted interface engineering, representing a fundamental leap toward high‐voltage sodium‐ion batteries.