Nonflammable Succinonitrile‐Based Deep Eutectic Electrolyte for Intrinsically Safe High‐Voltage Sodium‐Ion Batteries

Abstract Intrinsically safe sodium‐ion batteries are considered as a promising candidate for large‐scale energy storage systems. However, the high flammability of conventional electrolytes may pose serious safety threats and even explosions. Herein, a strategy of constructing a deep eutectic electrolyte is proposed to boost the safety and electrochemical performance of succinonitrile (SN)‐based electrolyte. The strong hydrogen bond between S═O of 1,3,2‐dioxathiolane‐2,2‐dioxide (DTD) and the α‐H of SN endows the enhanced safety and compatibility of SN with Lewis bases. Meanwhile, the DTD participates in the inner Na⁺ sheath and weakens the coordination number of SN. The unique solvation configuration promotes the formation of robust gradient inorganic‐rich electrode–electrolyte interphase, and merits stable cycling of half‐cells in a wide temperature range, with a capacity retention of 82.8% after 800 cycles (25 °C) and 86.3% after 100 cycles (60 °C). Correspondingly, the full cells deliver tremendous improvement in cycling stability and rate performance.