The findings, published in ACS Nano, could help understand the fundamental factors that determine the composition and stability of solid electrolyte interphase, or SEI. "A robust SEI is key to the performance and safety of Li-ion batteries used to power electric vehicles," said researcher Jagjit Nanda at ORNL.
The researchers used surface enhanced Raman spectroscopy to evaluate how the lithium-salt interacts between the liquid electrolyte and electrode 20nm from the membrane. The plasmonic coupling between the gold nanoparticles produces strong electromagnetic field enhancement in the gap region, leading to a 5 orders of magnitude increase in Raman intensity for the lithium hexafluorophosphate, fluoroethylene carbonate, ethylene carbonate and diethyl carbonate in the electrolyte. This was compared to the lithium-ion solvation number derived from SERS, standard Raman spectroscopy, and Fourier transform infrared spectroscopy experiments.
"We found that the ion-solvation at the interface differs from what we observed in the bulk liquid electrolyte," said Nanda. Understanding this phenomenon could lead to improved electrolytes resulting in batteries with higher performance and better stability.