Unravelling the Role of Speciation in Glyme:Ionic Liquid Hybrid Electrolytes for Na−O₂ Batteries

Abstract

The morphology and size of the discharge products in Na−O2 batteries are largely dominated by the interactions of the electrolyte with superoxide and sodium ions; therefore, an in‐depth understanding is essential for achieving high performance batteries. Herein, we report a framework designed to understand solvation and coordination in the recently discovered hybrid electrolytes, based on glyme and a pyrrolidinium ionic liquid. FTIR and NMR spectroscopic techniques, coupled with molecular dynamics simulations, have been used to characterize these systems. We demonstrate that the presence of ionic liquid in the hybrid electrolyte affects the superoxide coordination environment by weakening the glyme‐Na+ interactions, and generating solvent separated ion pairs. All these factors lead to different deposition mechanisms, which will determine the battery performance. The Na+ solvation shell compositions, anion conformers and relative free glyme content are also evaluated. The combinatorial approach used in this study‐experimental and computational – can be applied for further design of these hybrid electrolytes and other metal – O2 chemistries and electrochemical systems.

NaFSI and NaTFSI Solutions in Ether Solvents from Monoglyme to Poly(ethylene oxide)—A Molecular Dynamics Study

“…Vibrational (infrared or Raman) spectroscopy is commonly used to experimentally assess interactions between ions and solvents in Na-conducting electrolytes. 20 , 21 , 24 , 27 − 29 , 31 , 33 , 34 , 37 These findings are supplemented by the results of quantum-chemical calculations. 13 , 20 , 21 , 25 , 28 , 38 Early works performing molecular dynamics (MD) for polymer electrolytes with Na + ions were focused on glyme–NaI 39 , 40 or PEO–NaI 41 , 42 systems.…”

“… 11 − 13 , 15 , 16 Among the electrolytes using molecular liquids are the systems based on diglyme 17 − 19 or other short glymes as solvents—usually from mono- to pentaglyme. 20 − 31 There are also studies on polymer-based systems, offering several advantages, such as better mechanical properties and safety. However, conductivity of solid polymer electrolytes is lower than that of liquid systems.…”

“…Nowadays, classical and ab initio MD simulations are routinely applied to support and elucidate measurements of transport properties and structure of electrolytes. 15 , 24 , 29 , 31 , 36 , 37 , 43 − 45 …”

“…Similarly to the Li-based devices, systems investigated as possible electrolytes for Na-ion batteries are sodium salt solutions in molecular solvents, ionic liquids, or mixed solvents. − Several of those works are aimed at the study of highly concentrated salt solutions in search for better performing systems. − ,, Among the electrolytes using molecular liquids are the systems based on diglyme − or other short glymes as solventsusually from mono- to pentaglyme. − There are also studies on polymer-based systems, offering several advantages, such as better mechanical properties and safety. However, conductivity of solid polymer electrolytes is lower than that of liquid systems.…”

“…Vibrational (infrared or Raman) spectroscopy is commonly used to experimentally assess interactions between ions and solvents in Na-conducting electrolytes. ,,,− ,,,, These findings are supplemented by the results of quantum-chemical calculations. ,,,,, Early works performing molecular dynamics (MD) for polymer electrolytes with Na + ions were focused on glyme–NaI , or PEO–NaI , systems. Nowadays, classical and ab initio MD simulations are routinely applied to support and elucidate measurements of transport properties and structure of electrolytes. ,,,,,,− …”