Sodium Bis(fluorosulfonyl)imide/Poly(ethylene oxide) Polymer Electrolytes for Sodium-Ion Batteries

Sodium-ion batteries (SIBs), a promising substitute for lithiumion batteries (LIBs), are considered to have the potential to be employed in large-scale energy storage systems with lower cost and enhanced safety as primary concerns. Solid polymer electrolyte (SPE)-based SIBs will more likely meet these demands, because of their good flame resistance and excellent flexibility compared with conventional organic liquid-electrolyte-based SIBs. Here, we describe an SPE composed of sodium bis(fluorosulfonyl) imide (NaFSI) and poly(ethylene oxide) (PEO). The NaFSI/PEO (molar ratio of EO/Na+ = 20) blended polymer electrolyte exhibits a low glass transition temperature (i.e. -37.9 8 degrees C), relatively high ionic conductivity (i.e. & 4.1 V 10(-4) Scm(-1) at 808 degrees C), and enough electrochemical and thermal stability for application in SIBs. Most importantly, the NaFSI/PEO blended polymer electrolyte displays excellent interfacial stability with Na metal in Na/Na cells and good cycling performance in prototype cells with Na0.67Ni0.33Mn0.67O2 as the cathode material. All of these properties make NaFSI-based SPEs promising candidates for use in SIBs.