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

Significance of the Topic

Ensuring quality of lithium ion battery electrolytes and solvents is critical for battery safety performance and lifespan. Discoloration of near colorless electrolyte solutions indicates contamination or degradation which can lead to safety hazards and reduced efficiency. Instrumental color measurement provides objective assessment supporting manufacturing quality control and research.

Objectives and Study Overview

This study aims to establish a reliable method for assessing color of LIB electrolytes and solvents using UV Vis spectroscopy in accordance with ASTM D5386. The method employs an Agilent Cary 3500 Flexible UV Vis spectrophotometer with Cary Sipper pump and Cary WinUV Color software to measure yellowness index and convert it to Pt Co units for production and R D quality control.

Methodology and Instrumentation

• Preparation of six Pt Co calibration standards by diluting NIST SRM 930e HAZEN 500 solution to Pt Co units 1 2 3 4 5 and 10 in ultrapure water.
• Samples included new and used bottles of two 1.0 M LiPF6 electrolytes in EC DMC and EC EMC and two spent organic solvents EMC and DMC.
• Agilent Cary 3500 Flexible UV Vis spectrophotometer with variable pathlength cell holders (2 4 5 10 cm) fitted with Cary Sipper three channel peristaltic pump for safe flow cell operation.
• Measurements performed over 400 to 700 nm using 10 mm quartz flow cell with fill hold and rinse cycles managed by Cary UV Workstation software and automated color calculations in Cary WinUV Color application.

Main Results and Discussion

• The calibration of yellowness index against Pt Co units showed excellent linearity with R2 of 1 indicating high photometric accuracy and sensitivity in the absorbance range 0.0003 to 0.0028.
• New electrolyte bottles yielded low Pt Co color values around 2.8 to 3.4 while used bottles increased to 4.8 and 5.4 reflecting subtle color changes not visible by eye.
• Used organic solvents also exhibited elevated Pt Co values around 3.5 indicating mild degradation.
• Results demonstrate that UV Vis color measurement can detect early signs of electrolyte or solvent degradation supporting quality control.

Benefits and Practical Applications

• Direct sample introduction via sipper pump ensures operator safety and high throughput for hazardous liquids.
• High sensitivity and photometric linearity enable monitoring of low absorbance samples without extensive dilution.
• Automated color calculations streamline QC workflows in production and R D laboratories.
• Method aligns with ASTM standards facilitating reproducible quality assessment for battery manufacturing.

Future Trends and Opportunities

Increasing integration of in line UV Vis sensors and flow systems for real time monitoring of electrolyte quality. Development of miniaturized portable spectrophotometers for field testing and second use battery diagnostics. Advanced chemometric models and machine learning could enhance predictive maintenance and degradation studies. Growing demand for green solvents may drive expansion of colorimetric QC in new electrolyte formulations.

Conclusion

The Agilent Cary 3500 Flexible UV Vis spectrophotometer with Cary Sipper pump and Cary WinUV Color application provides a robust and sensitive method for assessing the color quality of lithium ion battery electrolytes and solvents. By correlating yellowness index to Pt Co units the approach offers precise detection of subtle color changes indicative of contamination or degradation. The method supports safe handling high throughput and compliance with ASTM D5386 and can be deployed in both production QC and research environments to ensure battery performance safety and longevity.

Reference

1. ASTM D1209 Standard Test Method for Color of Clear Liquids Platinum Cobalt Scale 2019.
2. ASTM D5386 Standard Test Method for Color of Liquids Using Tristimulus Colorimetry 2016.
3. ASTM E308 Standard Practice for Computing the Colors of Objects Using the CIE System 2022.
4. ASTM E313 Standard Practice for Calculating Yellowness and Whiteness Indices from Instrumentally Measured Color Coordinates 2020.
5. Agilent Technologies Color Measurements by Agilent UV Vis Spectrophotometers White Paper 5994 6792EN 2023.