Advanced Li-Ion Conducting pathways in Polymer-in-Filler composite solid electrolytes Utilizing Pre-Percolated bimetallic UiO-66 networks

Composite solid electrolytes (CSEs) are imperative for advancing Li metal batteries due to their strategic integration of polymer matrices and inorganic fillers. However, widespread commercialized adoption of CSEs is hampered by challenges such as low ionic conductivity and inefficient ion transport. In this work, we address these issues by refining filler design, specifically for enhancing their intrinsic properties and facilitating the formation of a highly interconnected three-dimensional (3D) structure within the polymer matrix to maximize the CSE performance. To achieve this, bimetallic UiO-66(Zr/Ti) (BMU) fillers with strong Lewis acid properties are synthesized into densely interconnected 3D structures. Specifically, the polymeric backbone of electrospun polyacrylonitrile (PAN) fibers is thermally modified to generate a ladder-like chemical configuration through reactions such as cyclization and oxidative uptake, facilitating a dense and robust coating of the BMU. The resulting bimetallic UiO-66(Zr/Ti)-coated 3D nanofiber (3DBMU) is then embedded into a poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-hfp) polymer matrix. Consequently, the pre-percolated Lewis acidic filler establishes continuous, fast, and efficient Li-ion transport channels, enabling the PVDF-hfp-based CSEs to achieve a Li-ion transference number of 0.701 and an ionic conductivity of 0.808 mS cm⁻¹ at 30 °C. Moreover, unlike the CSEs employing BMU particles, the CSEs incorporating 3DBMU effectively suppress Li dendrite growth throughout the Li metal surface. Overall, this approach suggests that both the intrinsic performance of the filler and the control of its secondary structure are essential for realizing high-performance CSEs. Therefore, the advanced CSE design introduce in this research marks a significant advancement in the evolution of next-generation CSEs.