Systematic Study of Aluminum Corrosion in Ionic Liquid Electrolytes for Sodium-Ion Batteries: Impact of Temperature and Concentration

The development of sodium-ion batteries utilizing sulfonylamide-based electrolytes is significantly encumbered by the corrosion of the Al current collector, resulting in capacity loss and poor cycling stability. While ionic liquid electrolytes have been reported to suppress Al corrosion, a recent study found that pitting corrosion occurs even when ionic liquids are employed. This study investigates the effects of temperature and Na salt concentration on the Al corrosion behavior in different sulfonylamide-based ionic liquid electrolytes for sodium-ion batteries. In the present work, cyclic voltammetry measurements and scanning electron microscopy showed that severe Al corrosion occurred in ionic liquids at high temperatures and low salt concentrations. X-ray photoelectron spectroscopy was employed to identify the different elemental components and verify the thickness of the passivation layer formed under varied salt concentrations and temperatures. The differences in the corrosion behaviors observed under the various conditions are ascribed to the ratio of free [FSA]- to Na+-coordinating [FSA]- in the electrolyte and the stability of the newly formed passivation layer. This work aims at augmenting the understanding of Al corrosion behavior in ionic liquid electrolytes to develop advanced batteries.