Modulating the Overall Properties of PEO/NaTFSI Electrolytes via UiO-66 Fibrous Membranes with Different Functional Groups for Solid-State Sodium Metal Batteries

Solid-state sodium metal batteries (SSMBs) have emerged as one of the next-generation rechargeable batteries due to their low-cost, high-energy-density, and desirable safety. However, their applications mainly depend on high-performance solid-state electrolytes. Herein, a series of polymer electrolytes is developed by compositing PEO/NaTFSI electrolytes into the PAN/UiO-66-X (X = NH2, NO2, F) nanofiber membranes, and the PAN/UiO-66-X are prepared by in situ growth of UiO-66-X MOFs on the PAN electrospinning nanofiber membranes. All the recovered PEO/PAN/UiO-66-X composite electrolytes possess a highly compact structure with a thickness of around 40 μm. The continuous dense UiO-66-X coatings not only improve mechanical strength of the electrolytes but also provide continuous Na+ transport pathways for high ionic conductivity. In addition, the interconnected pore structure with abundant Lewis acidic metal sites demonstrates strong anion-trapping effects for a high ionic transfer number. As a result, all of the batteries assembled with PEO/PAN/UiO-66-X electrolytes exhibit outstanding rate performance and cycling stability. In particular, the PEO/PAN/UiO-66-X electrolyte is the best with the highest ionic transfer number of 0.87, which could deliver more than 7000 h at 0.1 mA cm–2 in Na//Na symmetric cell and more than 600 cycles at 1C in NVP//Na full cell.