Building‐Block Design of Nonflammable Quasi‐Solid Electrolytes for Ampere‐Hour‐Scale Sodium‐Ion Batteries

Sodium‐ion batteries (SIBs) are emerging as a competitive technology for large‐scale energy storage; however, their commercial viability remains severely hindered by the inherent flammability and high volatility of liquid electrolytes (LEs). Herein, we propose a modular assembly strategy inspired by the building‐block principle to architect a quasi‐solid electrolyte (QSE). By synergistically integrating vinylene carbonate (VC) and 2,2,3,4,4,4‐hexafluorobutyl acrylate (HFBA) monomers, we modulate the electron density distribution within the polymer matrix. The resulting PVH QSE lowers the Na + desolvation barrier and provides continuous ion migration pathways, thereby achieving exceptional ionic conductivity of 5.60 mS cm −1 and a sodium‐ion transference number of 0.58. Furthermore, the spatially locked polymer architecture drives the formation of ion‐solvent aggregates and a robust NaF‐rich solid electrolyte interphase, synergistically suppressing solvent decomposition and eradicating sodium dendrite growth. Consequently, the Na||Na 3 V 2 (PO 4 ) 3 cells exhibit an outstanding capacity retention of 94.9% after 3000 cycles alongside superior temperature adaptability. To demonstrate practical feasibility, the hard carbon||NaNi 0.33 Fe 0.33 Mn 0.33 O 2 pouch cells maintain stable cycling over 200 cycles. Crucially, nail penetration and accelerating rate calorimetry (ARC) tests verify the exceptional safety of the pouch cells. By linking molecular microenvironment regulation to macroscopic battery safety, this work illuminates a viable pathway toward the commercialization of intrinsically safe SIBs.