A Functional Separator Enabling Safe and High-performance Sodium Metal Batteries under Elevated Temperature

Abstract

Sodium metal batteries (SMBs) are considered to have promising application prospects in large-scale energy storage systems owing to the abundant resources and low cost of sodium (Na). However, Na metal anodes suffer from dendrite growth and intensified interfacial reactions at high temperatures due to their high reactivity, undermining battery safety. Conventional polyolefin separators are also unsuitable for high-temperature operation owing to their low thermal stability and tendency to shrink. Herein, a composite functional layer consisting of a Na superionic conductor (Na3Zr2Si2PO12) and a sulfonated metal-organic framework (UiO-SO3Na) is constructed on the surface of a polyimide (PI) separator, resulting in the development of a N-Us@PI multifunctional separator. The N-Us@PI separator is endowed with excellent thermal stability (withstanding temperatures up to 300 °C) and high ionic conductivity (1.75 mS cm -1 at 60 °C). The strongly electronegative sulfonate groups on N-Us@PI effectively promote Na + desolvation and facilitate the formation of a stable solid electrolyte interphase (SEI). Electrochemical tests demonstrate that Na|N-Us@PI|Na3V2(PO4)3 full cells exhibit a capacity retention of 93.2% after 930 cycles at 60 °C and 5 C, while pouch cells also show good cycling stability under high-temperature conditions.This study provides an effective separator design strategy for enhancing the electrochemical performance and safety of SMBs operating under high-temperature environments.