Quality Control of Lithium-Ion Battery Electrolytes and Solvents by UV-Vis Spectroscopy

Importance of the Topic

Quality control of lithium-ion battery electrolytes and solvents is essential for ensuring safety, performance, and longevity of energy storage devices. Discoloration of near-colorless electrolyte solutions can signal contamination or degradation, impacting battery reliability.

Objectives and Study Overview

This study aims to establish a sensitive and high-throughput UV-Vis spectroscopic method, compliant with ASTM D5386, for instrumental color measurement of LIB electrolytes and solvents using the Agilent Cary 3500 Flexible UV-Vis with Cary Sipper pump.

Methodology and Instrumentation

A platinum-cobalt (Pt-Co) color scale (0–500 units) was used to quantify yellowness. Six calibration standards (1 to 10 Pt-Co units) were prepared from NIST SRM 930e by dilution. Samples comprised new and used 1.0 M LiPF6 in EC/DMC and EC/EMC electrolytes and used dimethyl carbonate and ethyl methyl carbonate solvents. Measurements were performed over 400–700 nm with 2 nm bandwidth, using a 10 mm quartz flow cell and Cary Sipper pump to handle hazardous liquids. Yellowness index (YI) was calculated via Agilent Cary WinUV Color application.

Main Results and Discussion

A calibration curve of YI versus Pt-Co units exhibited excellent linearity (R2=1), demonstrating high photometric sensitivity (absorbance range 0.0003–0.0028). New electrolyte samples showed low Pt-Co values (2.8–3.4), while used bottles increased to 4.8–5.4, indicating subtle degradation not visible to the eye. Used solvents exhibited Pt-Co values of ~3.53–3.57. These findings underscore the method’s capability to detect minor color changes critical for QC.

Benefits and Practical Applications

• Direct sampling via flow cell and peristaltic pump ensures operator safety and efficient handling of hazardous liquids.
• High sensitivity and reproducibility support reliable monitoring of electrolyte quality in production and R&D.
• Automated data processing through Cary WinUV Color application streamlines QC workflows.

Future Trends and Applications

Future developments may include inline process analytical technology (PAT) integration for real-time monitoring, compact and portable UV-Vis instrumentation for field use, and AI-driven data analysis for predictive maintenance of battery materials.

Conclusion

The Agilent Cary 3500 Flexible UV-Vis spectrophotometer with Cary Sipper pump provides a robust, precise, and safe method for QC of LIB electrolytes and solvents. Its superior photometric performance and automation capabilities make it valuable for ensuring consistent battery quality and advancing R&D efforts.

Instrumentation

• Agilent Cary 3500 Flexible UV-Vis spectrophotometer
• Agilent Cary Sipper three-channel peristaltic pump
• 10 mm quartz flow cell (Agilent part number 5061-3398)

References

1. ASTM D1209-19 Standard Test Method for Color of Clear Liquids (Platinum Cobalt Scale).
2. ASTM D5386-16 Standard Test Method for Color of Liquids Using Tristimulus Colorimetry.
3. ASTM E308-22 Standard Practice for Computing the Colors of Objects by Using the CIE System.
4. ASTM E313-20 Standard Practice for Calculating Yellowness Index.
5. Agilent Cary WinUV Color Application User Guide (publication 5994-6792EN).