Nonflammable Polyfluorides‐Anchored Quasi‐Solid Electrolytes by Chemical‐Crosslinking for High‐Safety Sodium Metal Battery

Abstract The combustion risks of flammable organic solvents and polymer matrices in liquid and polymer electrolyte systems, coupled with critical challenges such as inadequate ionic conductivity at room temperature (RT) and poor sodium dendrite suppression capability, significantly hinder the practical application of sodium metal batteries (SMBs). Therefore, developing flame‐retardant or non‐combustible electrolyte systems represents a critical pathway to overcome their safety limitations. To address these challenges, this study develops a fluorinated polymer membrane (PCUF), which integrates sodium salt loading, enhanced ion dissociation, and flame retardancy functions, and is compatible with high‐safety sodium metal battery systems. The presence of the electron‐withdrawing fluorine atom enhances the dissociation of lithium/sodium perchlorate and promotes efficient ion transport. The PCUF membrane exhibits remarkable ionic conductivity ( σ _Na ^⁺ = 2.590 × 10⁻⁴ S cm⁻¹, σ _Li ^⁺ = 2.413 × 10 ^‐ ⁴ S cm ^‐ ¹) and transference numbers ( t _Na ^⁺ = 0.910, t _Li ⁺ = 0.804). The Na|PCUF|Na₃V₂ (PO₄) ₃ battery exhibits a robust specific capacity of 81.3 mAh g⁻¹ after 2000 cycles at 1 C and maintains stable performance over a wide temperature range (> 400 cycles from 25 to 85 °C. Meanwhile, the battery assembled with PCUF demonstrates excellent cycling stability after 4000 cycles at a charge–discharge rate of 0.5 C. Furthermore, thermal runaway testing reveals that the PCUF membrane exhibits both a higher onset temperature and enhanced flame‐retardant performance compared to the PCU membrane. This improvement stems from fluorine‐containing free radicals (F·) generated during PCUF's thermal decomposition, which effectively suppress the migration of highly reactive radicals from chain reactions into the gas phase. This work highlights a rational design strategy for constructing a stable SEI and enhancing the ionic conductivity of the electrolyte for safe and long‐life sodium‐metal battery applications.