Analysis of battery electrolytes and N-methyl-2- pyrrolidone (NMP) via headspace GC-FID

Significance of the Topic

The proliferation of portable electronic devices and electric vehicles has intensified the need for rigorous monitoring of lithium-ion battery materials.
Analysis of N-methyl-2-pyrrolidone (NMP) purity and electrolyte composition is crucial for ensuring electrode performance and battery longevity.

Objectives and Study Overview

• Develop a headspace GC-FID method to assess NMP purity with minimal sample preparation.
• Quantify trace levels of NMP in battery electrolytes and profile major volatile components.
• Demonstrate the performance of the Nexis GC-2030 with HS-20NX sampler for battery-related analyses.

Methodology

Headspace sampling was applied to avoid extensive sample preparation. Sample volumes: 5 µL of NMP solution in a 20 mL vial for purity testing; 20 µL of electrolyte solution for NMP trace quantification with a five-point calibration (14–342 mg/L); 1 µL of electrolyte solution for volatile profiling.
Carryover tests were performed after a 650 mg/L NMP injection to evaluate system inertness.

Used Instrumentation

• Nexis GC-2030 gas chromatograph.
• HS-20NX headspace autosampler.
• FID-2030 flame ionization detector.
• Automatic gas selector for carrier gas flexibility and consumption control.

Main Findings and Discussion

• NMP purity reached 99.82 %, with four impurities totaling less than 0.18 %.
• Electrolyte analysis revealed four major volatile compounds at area percentages of 36.9 %, 35.1 %, 2.7 %, and 25.4 %; reproducibility was high (%RSD < 2.4 %).
• Calibration curves exhibited excellent linearity and carryover was negligible (0.01 %).
• Real electrolyte samples contained negligible NMP residues under standard conditions.

Benefits and Practical Applications

• Headspace GC-FID eliminates tedious sample preparation, enhancing throughput and reducing contamination risk.
• Automated gas selection improves flexibility and optimizes gas usage during routine analyses.
• High sensitivity and reproducibility support quality control in electrode manufacturing and electrolyte formulation.

Future Trends and Potential Applications

• Integration of mass spectrometric detectors for comprehensive volatile profiling.
• Automation and real-time monitoring for battery production quality assurance.
• Portable headspace systems for field diagnostics of battery health.
• Extension to emerging electrolyte solvents and solid-state battery materials.

Conclusion

The combined Nexis GC-2030 and HS-20NX system offers a robust platform for NMP purity assessment and electrolyte volatile analysis, enabling efficient, high-throughput battery quality control without extensive sample preparation.

References

[1] Bauer W, Nötzel D, Rheological properties and stability of NMP based cathode slurries for lithium ion batteries, Ceram. Int., 40(3), 4591–4598 (2014).
[2] Sliz R et al., Suitable cathode NMP replacement for efficient sustainable printed Li-ion batteries, ACS Appl. Energy Mater., 5(4), 4047–4058 (2022).
[3] Recharge, Eurobat, Recommendation about n-methyl-pyrrolidone (NMP; CAS no. 872-50-4) proposal for inclusion in Annex XIV for authorization, Position Paper, May 2017.