A Microporous Gel Polymer Electrolyte for Sodium Batteries

Room-temperature sodium batteries have the potential to meet the growing worldwide demand for electrical energy storage, thanks to the widespread availability and low cost of sodium. Compared with traditional liquid electrolytes, gel polymer electrolytes (GPEs) offer higher safety and adaptability to be designed as flexible energy storage devices without sacrifice of conductivity. In this work, we have successfully synthesized furan-based hypercrosslinked microporous polymers (Fu-HCPs) by using a solvothermal method. The prepared Fu-HCPs demonstrate a high surface area ≈ 500 m2 g‒1 with a pore-size distribution of 5−15 Å. A novel porous membrane consisting of a double polymer network of microporous Fu-HCPs and macroporous poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) is fabricated via a phase-inversion technique. The corresponding polymer electrolyte is prepared by immersing the porous membrane into a sodium liquid electrolyte. The macroporous and microporous nature of the prepared polymer membrane allows for an electrolyte uptake up to 200 wt. %. The polymer electrolyte saturated with sodium liquid electrolyte exhibits high conductivities (e.g., > 10‒3 S cm−1 at 25 °C) with great electrochemical (up to 4.2 V vs Na) and mechanical stability. If the microporous polymer electrolyte is applied in a full-cell sodium-ion battery with metallic sodium as an anode and Na3V2(PO4)3 as a cathode, the cycling performance and coulombic efficiency are significantly improved relative to the cell with liquid electrolyte. The results suggest that the microporous/macroporous furan-based polymer host with immobilized-liquid electrolyte inhibit sodium dendrite growth and allow the use of a metallic sodium anode for large-scale applications.