Monitoring Changes in Electrolyte Composition of Commercial Li-Ion Cells after Cycling using NMR Spectroscopy and Differential Thermal Analysis

Abstract

We illustrate a simple and effective electrolyte extraction methodology from commercial 18650 lithium-ion cells. This methodology is based on a liquid-liquid extraction step, which is highlighted for robustness, reproducibility, and reliability. We assess the consumption of electrolyte by tracking compositional changes using liquid-state nuclear magnetic resonance (NMR) spectroscopy, supported by differential thermal analysis (DTA) before and after cell cycling. An analysis method that monitors compositional dynamics is presented and shows the impact of these changes throughout a cell's lifetime. Such methodology can be employed in the understanding of electrolyte degradation mechanisms to enhance the understanding of performance fade in commercial cells. Moreover, it will help build robust mathematical models that are able to predict the drive of cell degradation and ultimate failure.