Hydrogen Bonding Stabilizing Sodium Metal Interfaces: Toward Ultralong‐Life, High‐Rate, and Heatless Quasi‐Solid‐State Batteries

Abstract Severe interfacial instability limits the practical deployment of succinonitrile (SN)‐based deep eutectic solvent (DES) in sodium metal batteries (SMBs). Although fluoroethylene carbonate (FEC) has demonstrated effectiveness in mitigating side reactions, the fundamental understanding of FEC‐SN interaction mechanisms and the chemical evolution of solid electrolyte interphase (SEI) remain largely unexplored. Here, it is revealed that the C─F···H─C hydrogen bonding between FEC and SN plays a pivotal role in enhancing the stability of SN with sodium metal (Na). Moreover, FEC competitively coordinates with Na ⁺ against SN, effectively suppressing SN's coordination tendency while promoting the decomposition of both FEC and anion at the electrode‐electrolyte interface. Therefore, the fabricated quasi‐solid‐state polymer electrolyte (QSPE) based on SN‐DES‐FEC exhibits excellent electrochemical stability. The quasi‐solid‐state Na||Na ₃ V ₂ (PO ₄ ) ₃ (NVP) cells maintain stable operation even at an ultrahigh rate of 120 C (16.17 mA cm ⁻² ), and demonstrate a breakthrough long‐term cycling stability even at 50 C (30 °C) within 20 000 cycles, and 3 C (0 °C) within 3000 cycles. More importantly, the pouch cells demonstrate superior safety under mechanical deformation and shear, with only 33% of temperature rise of the conventional liquid batteries during overcharging. This work represents a significant step toward enabling SMBs to operate effectively under high‐power and harsh working conditions.