The attached example report applies Gas Chromatography-Time of Flight Mass Spectrometry (GC-TOF-MS) to investigate the gas composition of a standard, cylindrical lithium-ion battery. It offers a preview for the kinds of results and insights Covalent can deliver with this technique.

Introduction

Understanding the internal gas composition of lithium-ion batteries is crucial for assessing their safety, performance, and longevity. This experiment dives deeper into this topic by employing advanced gas sampling techniques to identify volatile and semi-volatile compounds within a commercial 18650 lithium-ion battery. The findings shed light on the chemical environment inside these cells and provide insights into the processes occurring during cell assembly and operation.

Experiment Overview

The study focused on a Samsung SDI INR 18650-25R lithium-ion battery, a commonly used model in various electronic devices. The researchers aimed to extract and analyze the gases trapped within the battery to identify the presence of volatile organic compounds (VOCs), permanent gases, and any other potential byproducts of electrochemical reactions.

The battery was carefully punctured in an argon-filled glovebox to minimize contamination from the external atmosphere. A gas-tight syringe was then used to sample the cell atmosphere, which was analyzed using Gas Chromatography-Time of Flight Mass Spectrometry (GC-TOF-MS). This technique allowed the researchers to identify the gases based on their mass-to-charge ratios and compare them to a comprehensive library of known compounds.

Key Findings

The analysis revealed several interesting aspects of the gas composition inside the 18650 battery:

1. Primary Gases:
   • The main gases identified were nitrogen (N2), argon (Ar), carbon dioxide (CO2), and methane (CH4). The presence of argon was noted, likely due to glovebox contamination during the sampling process.
2. Electrolyte Breakdown Products:
   • Volatile compounds such as dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC), which are common electrolyte components, were detected. Additionally, the presence of light hydrocarbons like methane (CH4) to propane (C3H8) and carbon dioxide (CO2) indicates that electrolyte breakdown occurs during cell assembly and the formation of the solid electrolyte interphase (SEI).
3. Absence of Water and Hydrofluoric Acid:
   • Notably, no water (H2O) or hydrofluoric acid (HF) was detected, suggesting that these potentially harmful byproducts were either absent or below the detection limits of the analysis.
4. Trace Compounds:
   • A trace amount of a C12 hydrocarbon was detected, which could be attributed to residue from the adhesive used in the gas-sampling septum rather than an inherent component of the battery.

Conclusion

The findings of this study provide valuable insights into the chemical environment within lithium-ion batteries, particularly the volatile and semi-volatile compounds that are present. The detection of electrolyte breakdown products even in a pristine, uncycled cell suggests that these reactions occur early in the battery’s life cycle, likely during assembly and initial SEI formation. This information is crucial for improving battery design and enhancing safety measures.

This experiment exemplifies the importance of using advanced analytical techniques like GC-TOF-MS to better understand the inner workings of lithium-ion batteries. As battery technology evolves, such studies will be critical in developing safer and more efficient energy storage solutions.