Material Identification of Lithium‑Ion Battery Separators Using FTIR Spectroscopy

Significance of the Topic

Lithium-ion battery separators are critical to cell safety and performance, preventing short circuits and enabling ion transport. Rigorous quality control of separator materials helps ensure battery reliability, longevity and user safety. Fourier transform infrared (FTIR) spectroscopy offers a rapid, non-destructive method for polymer identification, making it well suited for routine QC and research applications.

Study Objectives and Overview

This application note demonstrates the use of the Agilent Cary 630 FTIR spectrometer fitted with a diamond ATR module and Agilent MicroLab software to identify both new and used lithium-ion battery separators. The goal is to showcase a workflow that delivers fast, accurate material confirmation with minimal user training, supporting both production QC and R&D environments.

Methodology

Two separator samples—a new multilayer device and a used film extracted from a recycling facility—were analyzed directly using attenuated total reflection FTIR. The MicroLab software’s Similarity search algorithm compared sample spectra against a user-generated polymer library. Key operating parameters included a spectral range of 4000–650 cm⁻¹, 32 sample/background scans, a resolution of 4 cm⁻¹ and air background. Hit quality index (HQI) thresholds were set to color-code results: green for HQI > 0.90, yellow for 0.80–0.90 and red for < 0.80.

Instrumentation Used

• Agilent Cary 630 FTIR spectrometer with single-reflection diamond ATR interface
• Agilent MicroLab software with internal polymer spectral library

Main Results and Discussion

The new separator matched polypropylene (PP) with HQI 0.94064, reflecting its multilayer structure and potential additives. The used separator yielded polyethylene (PE) with HQI 0.92274. Spectral overlays revealed minor contaminant bands that can lower HQI; updating the reference library with more representative spectra can improve match confidence. The MicroLab interface instantly displays color-coded results, guiding rapid decision-making without complex data interpretation.

Benefits and Practical Applications

• Rapid pass/fail material confirmation with intuitive software guidance
• Minimal training required due to picture-driven interface and color-coding
• Compact, glove box–compatible design for safe handling of sensitive materials
• Flexible library management supports both QC in manufacturing and battery materials research

Future Trends and Potential Applications

Advances may include expanded spectral libraries covering novel separator chemistries, integration of chemometric tools for compositional analysis, in situ monitoring of separator degradation, high-throughput screening workflows and further automation for smart QC systems.

Conclusion

The Agilent Cary 630 FTIR combined with Agilent MicroLab software provides a fast, reliable solution for identifying lithium-ion battery separators. High hit quality indices, ease of library updating and color-coded output enable robust QC and support ongoing R&D efforts in battery materials development.

References

1. Dutta, A. Chapter 4 - Fourier Transform Infrared Spectroscopy. In Spectroscopic Methods for Nanomaterials Characterization; Elsevier, 2017; pp 73–93.
2. Alwan, W.; Babu, S.; Zieschang, F. Quick and Easy Material Identification of Salts Used in Lithium-Ion Batteries by FTIR. Agilent Technologies Application Note 5994-6243EN, 2023.
3. Babu, S.; Alwan, W.; Zieschang, F. Quick and Easy Material Identification of Solvents Used in Lithium-Ion Batteries by FTIR. Agilent Technologies Application Note 5994-6182EN, 2023.
4. Alwan, W.; Zieschang, F. Advancing Research of Lithium-Ion Batteries Using the Agilent Cary 630 FTIR Spectrometer. Agilent Technologies White Paper 5994-6144EN, 2023.