Exploring hindered glymes as electrolyte solvents for sodium–oxygen batteries: impact on electrochemical performance and discharge product stability
Abstract
Sodium–oxygen (Na–O2) batteries are a promising alternative for high-energy storage applications, but their practical use is limited by electrolyte instability and poor cycling performance. This study investigates the role of hindered glymes—ether-based solvents with bulky tert-butyl groups—in improving the electrochemical behaviour of Na–O2 batteries. We compare hindered glymes with conventional glymes in terms of discharge capacity, cycling stability, electrolyte interactions, and solid electrolyte interphase (SEI) composition. Although hindered glymes exhibit higher overpotentials, they outperform conventional glymes in cycle life. Post-mortem analysis confirms sodium superoxide (NaO2) as the primary discharge product, but hindered glymes promote a greater formation of hydrated sodium peroxide, likely due to differences in the exposed surface area of discharge products. Molecular dynamics simulations reveal that steric hindrance in hindered glymes weakens Na+–solvent interactions, facilitating Na+ desolvation, which improves cycling stability. This steric effect also reduces Na+ solvation, increases molecular rigidity, and limits discharge product stabilization, leading to higher polarization and smaller NaO2 cubes during discharge. However, the improved Na+ desolvation in hindered glymes enhances cycling performance, with hindered monoglyme (H-G1) showing a more pronounced effect due to its shorter chain. X-ray photoelectron spectroscopy (XPS) analysis demonstrates that weakened Na+–solvent interactions lead to a more inorganic SEI, which contributes to improved interfacial stability. These results position hindered glymes as a promising electrolyte solution for Na–O2 batteries, offering enhanced thermal and electrochemical stability while improving cycling performance.
- This article is part of the themed collection: Green and Sustainable Batteries