The Analysis of Swelling Gas in Lithium-Ion Batteries with an Agilent 990 Micro GC

Significance of the Topic

Swelling gases generated in lithium-ion batteries during charge–discharge cycles pose critical safety and performance challenges. Understanding the composition of these gases helps optimize electrolyte formulations, prevent capacity loss, and improve overall battery reliability.

Objectives and Study Overview

This application note demonstrates a rapid, small-volume analytical approach for characterizing swelling gas from lithium-ion batteries using an Agilent 990 Micro GC. The study aims to resolve permanent gases and light hydrocarbons, quantify their concentrations, and evaluate method repeatability.

Methodology

Sample collection involved puncturing the bulged battery enclosure with a gas-tight syringe to withdraw 10 mL of swelling gas. The gas was manually injected into the Micro GC with a controlled dispensing rate of 10–20 mL/min. Repeatability was assessed over ten consecutive injections of a multi-component calibration standard.

Instrumentation

Agilent 990 Micro GC equipped with a manual injection accessory and four analytical channels:

• Channel 1: 10 m CP-Molsieve 5Å (backflush) for H₂, CH₄, CO
• Channel 2: 10 m CP-PoraPLOT U (backflush) for C₂ hydrocarbons and CO₂
• Channel 3: 10 m CP-Al₂O₃/KCl (backflush) for C₃–C₅ hydrocarbons and combined C₆/C₆+
• Channel 4 (optional): 6 m CP-Sil 5 CB (straight) for detailed C₃–C₆ separation

Carrier gas: helium. Calibration standard comprised H₂, N₂, CH₄, CO, CO₂, C₂H₆, C₂H₄, C₂H₂, C₃H₈, i-C₄H₁₀, n-C₄H₁₀, i-C₅H₁₂, n-C₅H₁₂, n-hexane in defined molar ratios.

Key Results and Discussion

Chromatograms showed baseline resolution of permanent gases on CP-Molsieve, C₂ species on CP-PoraPLOT, and C₃–C₅ on CP-Al₂O₃/KCl, with C₆+ eluting as a combined peak. The optional CP-Sil 5 CB channel separated propane through n-hexane, facilitating fingerprinting of heavier components. Area repeatability across ten injections yielded RSDs below 3% and retention time RSDs under 0.03%. Analysis of a real swelling gas sample identified H₂ (12.9 mol%), CH₄ (46.5 mol%), CO (1.65 mol%), CO₂ (2.94 mol%), C₂H₄ (0.31 mol%), C₂H₆ (6.74 mol%), C₂H₂ (2.35 mol%), C₃H₈ (0.086 mol%), and C₆/C₆+ (1.79 mol%). Unidentified peaks beyond propane indicated heavier or novel decomposition products.

Benefits and Practical Applications

The Agilent 990 Micro GC method enables:

• Rapid analysis: full cycle in under 150 s
• Low sample requirement: 5–10 mL per run
• High repeatability and sensitivity
• Compact footprint suited for on-site or laboratory environments

Applications include battery R&D, quality control in production, safety diagnostics, and formulation screening.

Future Trends and Applications

Advancements may include integration of real-time online monitoring in battery packs, expansion to next-generation electrolytes, coupling with mass spectrometry for structural identification, and development of automated sampling modules for field deployment.

Conclusion

The Agilent 990 Micro GC, configured with multiple chromatographic channels and a manual injection accessory, provides a robust, fast, and low-volume solution for comprehensive analysis of swelling gases in lithium-ion batteries. Its high repeatability and modular design support diverse analytical needs in battery research and manufacturing.

References

1. Van Loon R.; Amarasinghe S.; Ahmed K. Fuel Cell Development and Testing Using an Agilent Micro GC. Agilent Technologies Application Note 5991-3364EN, 2011.
2. Fast Analysis of Natural Gas Using the Agilent 990 Micro GC Natural Gas Analyzer. Agilent Technologies Application Note 5994-1040EN, 2019.