A new Na[(FSO2)(n-C4F9SO2)N]-based polymer electrolyte for solid-state sodium batteries

Abstract

To improve the safety of sodium (Na) batteries, we first report a new solid polymer electrolyte (SPE), composed of sodium (fluorosulfonyl)(n-nonafluorobutanesulfonyl)imide (Na[(FSO₂)(n-C₄F₉SO₂)N], NaFNFSI) and poly(ethylene oxide) (PEO), which is prepared by a facile solution-casting method. The NaFNFSI/PEO (EO/Na⁺ = 15) blended polymer electrolyte exhibits a relatively high ionic conductivity of 3.36 × 10⁻⁴ S cm⁻¹ at 80 °C, sufficient thermal stability (>300 °C) and anodic electrochemical stability (≈4.87 V vs. Na⁺/Na) for application in solid-state Na batteries. Most importantly, the NaFNFSI-based SPE can not only deliver excellent chemical and electrochemical stability with Na metal, but can also display good cycling and current-rate performances for the Na|SPE|NaCu_1/9Ni_2/9Fe_1/3Mn_1/3O₂ cell. All of these outstanding properties would make the NaFNFSI-based SPE promising as a candidate for application in solid-state Na batteries.