Synergistic Enhancement\nof Biaxial Stretching and\nMultilayer Composites in All-Solid-State Polymer Electrolytes

As an important component of lithium-ion batteries, all-solid-state\nelectrolytes should possess high ionic conductivity, excellent flexibility,\nand relatively high mechanical strength. All-solid-state polymer electrolytes\n(ASSPEs) based on polymers seem to be able to meet these requirements.\nHowever, pure ASSPEs have relatively low ionic conductivity, and the\naddition of inorganic fillers such as lithium salts will reduce their\nflexibility and mechanical strength. To address the above issues, in this paper, the solvent-free method\nwas used to prepare a poly(vinylidenefluoride-<i>co</i>-hexafluoropropylene)/lithium\nbis(trifluoromethanesulfonyl) imide/poly(ethylene oxide) all-solid-state\npolymer electrolyte, which was then subjected to 4 × 4 magnification\nsynchronous bidirectional stretching. Subsequently, it was multilayered\nwith PEO-based composite polymer electrolytes to obtain multilayered\ncomposite polymer electrolytes (MCPEs). Bidirectional stretching provides\nsuperior in-plane and out-of-plane mechanical properties to MCPEs\nby inducing molecular chain orientation, which suppresses the growth\nof lithium dendrites. Concurrently, it facilitates the formation of\nthe β-crystal form of PVDF-HFP, thereby weakening the ion solvation\neffect and reducing the lithium-ion migration energy barrier. Multilayered\ncompounding improves the interfacial contact between MCPEs and electrodes,\nthereby reducing the interfacial impedance. Experiments have demonstrated\nthat the MCPEs prepared in this paper exhibit high ionic conductivity\nat room temperature (1.83 × 10<sup>–4</sup> S cm<sup>–1</sup>), low interfacial resistance (547 Ω cm<sup>–2</sup>), excellent mechanical properties (26 MPa), and excellent cycling\nrate performance (a capacity retention rate of 90% after 110 cycles\nat 0.1 C), which can meet the performance requirements of lithium-ion\nbatteries for ASSPEs.