Ultrathin Polymer Composite Electrolyte With Dual‐Scale Reinforcement: Integrating <scp>PTFE</scp> Framework and In Situ Silica

ABSTRACT Developing ultrathin yet mechanically robust polymer electrolytes remain a key challenge for enabling practical solid‐state lithium batteries. Here, we report a scalable engineering strategy to construct an ultrathin (~19 μm) composite polymer electrolyte (PPLS) by integrating a macroporous polytetrafluoroethylene (PTFE) scaffold with an in situ formed silica (SiO 2 ) nanonetwork within a poly(ethylene oxide) (PEO) matrix. The PTFE framework provides macroscopic dimensional stability and mechanical reinforcement, while the SiO 2 network, generated via a controlled in situ hydrolysis process, effectively reduces polymer crystallinity and enhances ionic transport. The resulting PPLS membrane exhibits a tensile strength of approximately 75 MPa, an ionic conductivity of 1.6 × 10 −4 S cm −1 at 60°C, and a Li + transference number of 0.60. This electrolyte enables stable L//Li cycling for more than 700 h and demonstrates excellent rate capability in both LiFePO 4 and NCM523 full cells. The hierarchical PTFE/SiO 2 architecture exemplifies how rational multi‐scale design can simultaneously achieve structural robustness and efficient ionic mobility, providing a promising and scalable pathway for the development of high‐performance polymer composites for energy storage applications.