Engineering of Electrolyte Solution in Governing the Stability of Sodium Metal Anode for Room Temperature Sodium-Sulfur Batteries

Abstract

The charge storage properties of room temperature sodium-sulfur (Na-S) batteries are dependent on the electrolyte chemistry, which dictates the interfacial stability between electrode and electrolyte. Here, we introduce a localized high-concentration electrolyte (LHCE) consisting of 6 M sodium bis(fluorosulfonyl)imide in 1,2-dimethoxyethane and diluted with bis(2,2,2-trifluoroethyl)ether in a 1:1.5 molar ratio for Na-S batteries. This LHCE consists of a highly aggregated solvation shell over strongly interacting Na+-FSI- ion pairs and minimal free solvent. Such a solvation structure enables the formation of an inorganic-rich solid electrolyte interphase on the Na metal anode, which suppresses dendrite growth. Moreover, the LHCE shows compatibility with sulfurized polyacrylonitrile (SPAN) cathode without dissolution of soluble Na-polysulfides during cycling. Coupled with a SPAN cathode and 50 mu m of Na metal anode, the pouch-type Na-S battery using the LHCE delivers an areal capacity of 2.6 mAh cm-2 and cycling stability after 300 cycles at 1 C.