Enhanced Sodium Metal/Electrolyte Interface by a Localized High-Concentration Electrolyte for Sodium Metal Batteries: First-Principles Calculations and Experimental Studies

The applications of Na metal batteries (SMBs) are restricted owing to the capacity attenuation and safety hazards during the cycling process, while a rational design of the electrolyte is critical on solving this problem. In this work, an electrolyte is designed by adding 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropylether (TTE) into a 3.8 M sodium bis(fluorosulfonyl)imide/1,2-dimethoxyethane (NaFSI/DME) electrolyte, forming the localized high-concentration electrolyte (LHCE) for constructing a stable solid electrolyte interface (SEI) for SMBs. Ab initio molecular dynamics (AIMD) results indicate that the solvation degree of Na+ ions with DME molecules in LHCE is lower than that in HCE, which leads to more FSI– anions but less DME molecules to decompose on the Na metal anode. And the TTE could also decompose on the Na metal anode, which synergistically builds a NaF-rich compact SEI with low surface resistance and good mechanical property so that it is favorable for the transportation of Na+ ions and suppression of the Na dendrite growth. Therefore, the optimized LHCE electrolyte in SMBs exhibits an outstanding electrochemical performance. This study provides an updated perspective on the understanding and design of localized high-concentration electrolytes for SMBs.