A novel modified PI separator with enhanced dendrite suppression, puncture prevention and improved size stability for room-temperature sodium–sulfur batteries†

Commercial battery separators (Celgard) have poor wettability, limited heat resistance, and low needle-punching strength, and the growth of sodium dendrites can easily pierce the separators, posing significant risks to the cycle life and safety of room-temperature sodium–sulfur batteries (RT Na–S). In this work, a polyimide copolymerized with polyether (PI–PEO) membrane was prepared using an electrospinning method. By incorporating polyether segments into the polyimide molecular chain and constructing a nanofiber structure, the polarity and fiber structure of the material improved the wettability of the electrolyte. The toughness of the membrane was improved while maintaining its size stability, effectively resisting the puncture of sodium dendrites. As a result, the battery assembled with the PI–PEO separator exhibited excellent cycle stability, with a capacity maintained at 450 mA h g⁻¹ after 2000 cycles at 3 A g⁻¹. Additionally, the PI–PEO separator demonstrated higher ionic conductivity (1.48 mS cm⁻¹), better size stability and improved electrolyte wettability than Celgard. This work provides a novel and effective method for developing durable room temperature sodium–sulfur batteries.