Author(s): Joanna Maria Maratos, Luke Severson
Mentor(s): Jason Porter
Institution BYU
Lithium-sulfur (Li-S) batteries have the potential to revolutionize energy storage for electric vehicles and renewable energy systems due to their high energy density, low cost, and abundant raw materials. However, widespread adoption of Li-S batteries is hindered by rapid capacity fading during use, a challenge primarily attributed to the “polysulfide shuttle effect.” In this process, sulfur compounds, or polysulfides, dissolve in the electrolyte and migrate between the battery’s electrodes, where they repeatedly form and break down. This cycle accelerates chemical degradation in the electrolyte, reducing the battery’s stability and lifespan. This research aims to understand how thermal and chemical factors contribute to electrolyte degradation in Li-S batteries, with a specific focus on the role of polysulfides. Electrolytes were prepared by mixing tetraethylene glycol dimethyl ether (TEGDME) with lithium bis(fluorosulfonyl)imide (LiFSI) and adding increasing concentrations of lithium polysulfides. The prepared electrolytes were heated to temperatures up to 200°C and monitored using Fourier Transform Infrared (FTIR) Attenuated Total Reflectance (ATR) spectroscopy. FTIR, a technique that detects how chemical bonds absorb infrared light, enabled tracking of molecular changes in the electrolyte. As the samples were heated to temperatures that might be encountered in real-world applications, such as electric vehicles, we observed shifts in the infrared absorption peaks of the electrolyte. Absorption peak shifts indicate molecular changes that may result from thermal degradation over time. By varying the concentration of polysulfides, we were able to assess how these compounds accelerate degradation under thermal stress. Data analytics were then applied to analyze the FTIR spectra, specifically observing shifts in the absorption peak wavenumbers, which reveal the electrolyte’s molecular transformations over time. Findings from this analysis illuminate how a combination of high temperatures and elevated polysulfide concentrations may increase the rate of degradation. This study aims to identify factors driving capacity fade in Li-S batteries, particularly in the context of high-performance applications like electric vehicles that require stability across a wide temperature range. By mapping degradation trends, this research contributes to the development of predictive models that can guide the design of more durable Li-S batteries. Ultimately, this work supports the broader goal of improving energy storage technologies for a sustainable future.