A sandwich structure FPI-PEO/Celgard/FPI-PEO separator with polysulfide shuttle suppression and dendrite puncture resistance for room-temperature sodium–sulfur batteries

A commercial battery separator (Celgard) cannot inhibit the penetration of dendrites and the shuttle of sodium polysulfides (NaPSs) due to its permeable porous structure, which seriously threatens the performance and service safety of room-temperature sodium–sulfur (RT Na–S) batteries. In this work, a fluorinated polyimide and polyether copolymer (FPI-PEO) membrane was prepared by electrospinning, and then an FPI-PEO/Celgard/FPI-PEO sandwich structure was constructed using Celgard. By introducing fluorinated groups and polyether segments and constructing a fiber structure and a three-dimensional network structure, the wettability of the electrolyte was improved, and the flexibility of FPI-PEO and the mechanical strength of Celgard were combined to resist the penetration of sodium dendrites. Meanwhile, an electronegative environment was constructed on both sides of Celgard to inhibit the shuttle of sodium polysulfides (NaPSs). The results show that the FPI-PEO/Celgard/FPI-PEO separator inhibits the shuttle of NaPSs and exhibits excellent ability to resist dendrites. The battery assembled with the FPI-PEO/Celgard/FPI-PEO separator exhibits excellent cycling stability. After 2000 cycles at 3 A g⁻¹, the capacity still remained at 515 mA h g⁻¹. In addition, the FPI-PEO/Celgard/FPI-PEO separator exhibits excellent safety performance. This work provides a new and meaningful method for developing RT Na–S battery separators that resist dendrite piercing and inhibit polysulfide shuttle.