A 50 µm‐Thick Fiber‐Reinforced Fluorinated Polymer Plastic Crystal Electrolyte Enabling High Ionic Conductivity and Voltage Stability for Advanced Solid‐State Sodium Batteries

ABSTRACT Low room‐temperature conductivity, narrow electrochemical stability window, and insufficient mechanical strength restrict the further application of solid polymer electrolytes in solid‐state sodium metal batteries (SMBs). Here, we reported a 50 µm‐thick fiber‐reinforced fluorinated polymer plastic crystal electrolyte (PPCE) prepared via in‐situ polymerization. The fluorinated polymer effectively disrupts the ordered structure of the plastic crystal, thus increasing the proportion of amorphous phase that provides rapid Na + transport pathways. Meanwhile, the fluorohydrocarbon and ether units within polymer weaken its binding energy with Na + , which facilitates Na + dissociation and achieves high room‐temperature conductivity (2.34 mS cm − 1 ). Furthermore, the fluorine‐rich groups enhance PPCE's oxidation resistance and deliver a robust, inorganic F‐rich interphase, which stabilize the electrode/electrolyte interface and extend high‐voltage tolerance (4.83 V). The integration of a 34 µm‐thick polyethylene fiber‐reinforced substrate (tensile strength: 8.50 MPa) and the copolymer skeleton provides critical mechanical support. When paired with various cathodes, including Na 3 V 4 (PO 4 ) 3 , Prussian white, Na 3 V 2 (PO 4 ) 2 F 3 , or NaNi 0.33 Fe 0.33 Mn 0.33 O 2 , the cells deliver high capacity, stable cyclability, and excellent rate performance. This work demonstrates a highly compatible and robust PPCE design, highlighting its broad application prospects in advanced solid‐state sodium batteries.