An Ultrathin Composite Polymer Electrolyte Dual‐Reinforced by a Polymer of Intrinsic Microporosity (PIM‐1) and Poly(tetrafluoroethylene) (PTFE) Porous Membrane

Abstract The performances of solid‐state polymer electrolytes are urgently required to be further improved for high energy density lithium metal batteries. Herein, a highly reinforced ultrathin composite polymer electrolyte (PLPP) is successfully fabricated in a large scale by densely filling the well‐dispersed mixture of polyethylene oxide (PEO), Li‐salt (LiTFSI) and a polymer of intrinsic microporosity (PIM‐1) into porous poly(tetrafluoroethylene) (PTFE) matrix. Based on the macro‐plus‐micro synergistic enhancement of the PTFE with excellent mechanical properties and the soluble PIM‐1 with suitable functional groups, the PLPP electrolyte exhibits excellent properties including mechanical stress, thermal stability, lithium‐ion transference number, voltage window and ionic conductivity, which are all superior to the typical PEO/LiTFSI electrolytes. As a result, the Li/PLPP/Li symmetric cell can stably cycle for > 2000 h, and the LiFePO₄/PLPP/Li full cell exhibits excellent rate performance (>10 C) and high cycling stability with an initial capacity of 158.8 mAh g⁻¹ and a capacity retention of 78.8% after 300 cycles. In addition, the excellent mechanical properties as well as the wide voltage window reasonably result in the stable operation of full cells with either high‐loading cathode up to 28.1 mg cm⁻² or high voltage cathode with high energy density.