PAN@UiO66 Nanofibers with Fast Li⁺ Transfer and Outstanding Mechanical Performance for Composite Solid Polymer Electrolytes

The liquid electrolytes (LEs) in traditional lithium batteries present safety concerns. Solid polymer electrolytes (SPEs) have garnered increasing attention due to their nonvolatility, ease of processing, excellent mechanical properties, and stability. However, the performance of PEO-based solid-state batteries is often constrained by low ionic conductivity and poor mechanical strength. Therefore, we fabricated a nanofiber scaffold (PAN@UiO66) using electrospinning technology and then cast a solution containing zirconia (ZrO₂) fillers and bis(trifluoromethane)sulfonimide (LiTFSI), dispersed in poly(ethylene oxide) (PEO), onto the electrospun PAN@UiO66 scaffold to obtain a composite solid polymer electrolyte (CSPE, PZ/PAN@UiO66). The synergistic effect of the PAN@UiO66 scaffold and zirconia creates an amorphous-enriched region in the CSPE, providing uniform and abundant Lewis acid–base interaction sites, which reduce the crystallinity of the PEO-based solid electrolyte and enhance the diffusion and migration of lithium ions within the polymer. The components were physically characterized and electrochemically tested by using Fourier-transform infrared spectroscopy (FT-IR), thermogravimetric analysis (TGA), X-ray diffraction (XRD), and energy-dispersive spectroscopy (EDS). The results indicate that the incorporation of PAN@UiO66 optimizes the lithium-ion transport behavior of PEO-based solid electrolytes and enhances their cycling stability. Specifically, at 60 °C, the lithium-ion transference number of the PAN@UiO66 nanofiber-enhanced composite solid polymer electrolyte (CSPE) increased from 0.20 to 0.40, the electrochemical voltage window expanded from 4.58 to 5.10 V, and the Li||Li symmetrical cell assembled with CSPE exhibited stable plating and stripping for over 670 h at a current density of 0.1 mA cm^–2. The assembled LFP||Li coin cell delivered an initial discharge capacity of 149.81 mAh g^–1 at 0.5C, with a capacity retention of 101.53% after 200 cycles. The LFP||Li pouch cell assembled with CSPE exhibited a discharge capacity of 113.21 mAh g^–1 at 0.5C and stable cycling for 100 cycles, demonstrating the commercial potential of the composite solid-state electrolyte.