High Ionic Conductive, Mechanical Robust Solid Polymer Composite Electrolyte Achieved by Succinonitrile and Polytetrafluoroethylene Porous Fibrous Membrane for Lithium Metal Batteries

Solid polymer electrolytes (SPEs) are considered promising candidates for all-solid-state lithium metal batteries because of their easy preparation and good compatibility with lithium metal. However, their applications are restricted by their low ionic conductivity and poor mechanical properties. In this study, a composite solid polymer electrolyte composed of poly(ethylene oxide) (PEO), poly(vinylidene fluoride- co -hexafluoropropylene) (PVDF-HFP), plasticizer succinonitrile (SN), and polytetrafluoroethylene (PTFE) fibrous porous membranes was prepared. The PTFE fibrous membrane significantly enhanced the mechanical strength of the electrolyte as a supporting framework. SN reduced the crystalline regions of PEO and facilitated rapid lithium-ion transport. PVDF-HFP promoted lithium salt dissolution and improved the electrochemical stability of the electrolyte. Accordingly, the optimized PTFE/PEO/PVDF-HFP/SN polymer electrolyte exhibited a tensile strength of 3.31 MPa at 352% elongation and demonstrated an ionic conductivity of 7.6×10 −4 S·cm −1 at 60 °C. Lithium symmetric cells maintained stable cycling for over 2500 h at 0.15 mA·cm −2 , and Li//LiFePO 4 full cells showed a high capacity retention of 91.6% after 300 cycles at 0.5 C, with coulombic efficiency consistently exceeding 99.9% throughout cycling.