Accurate ICP-MS Analysis of Elemental Impurities in Electrolyte Used for Lithium-Ion Batteries

Importance of the Topic

Lithium-ion batteries are central to portable electronics, electric vehicles, and renewable energy storage. Electrolyte purity directly influences battery performance, safety, and lifetime. Accurate monitoring of trace metal impurities in lithium salts is essential for consistent battery manufacturing and quality assurance.

Objectives and Overview of the Study

This study introduces a single quadrupole ICP-MS method to quantify 68 elemental impurities in four commercial lithium salts (LiPF6, LiBF4, LiClO4, and LiFSI). The aim was to achieve low detection limits, high accuracy, and robust control of matrix effects by using a standard addition calibration approach.

Methodology and Used Instrumentation

• Sample Preparation: Solid salts (5 g) were dissolved in ultrapure water, ultrasonicated, and diluted to 5 % total dissolved solids. Further dilution and standard addition spiking yielded calibration levels from sub-µg/kg to ppm.
• Calibration Strategy: Standard addition minimized ionization suppression and reduced reliance on internal standards, allowing direct matrix matching.
• Instrumentation: Agilent 7900 ICP-MS with HF-resistant PFA sample introduction, PFA nebulizer, platinum-tipped sampling and skimmer cones, and ORS4 collision/reaction cell.
• Cell Gas Modes: Helium KED mode for most analytes; enhanced helium mode for P and S; hydrogen reaction mode for Si, Ca, Fe, and Se to remove specific polyatomic interferences.

Main Results and Discussion

• Linearity: Calibration curves for all 68 elements achieved R² ≥ 0.999.
• Detection Limits: Sub-µg/kg MDLs were obtained for most trace elements in the original solid salts, demonstrating high sensitivity.
• Accuracy and Precision: Spike recoveries ranged from 80 % to 120 % with RSDs below 12 % for the majority of analytes.
• Robustness: A six-hour continuous run in high-matrix samples yielded QC recoveries within ±15 % and minimal cone fouling, which was easily removed by citric acid cleaning.

Benefits and Practical Applications of the Method

• Rapid multi-element screening of lithium salt electrolytes for battery production quality control.
• Effective elimination of matrix-induced suppression via standard addition calibration.
• Low detection limits meeting stringent impurity specifications.
• High throughput with minimal maintenance and long-term stability.

Future Trends and Applications

Emerging directions include the use of triple quadrupole ICP-MS for even lower detection limits, extension to novel electrolyte chemistries, integration of automated sample preparation, and coupling with speciation techniques to deepen understanding of impurity behavior in battery systems.

Conclusion

The Agilent 7900 ICP-MS method with standard addition calibration delivers sensitive, accurate, and robust analysis of 68 trace elements in lithium salt matrices. It meets critical quality control requirements for lithium-ion battery manufacturing and supports ongoing research into advanced battery materials.

References

• A. Zou et al., J. Electrochem. Soc. 164 (2017) A5019–A5025.
• M. Armand and J.M. Tarascon, Nature 451 (2008) 652–657.
• Encyclopedia of Analytical Chemistry, John Wiley & Sons, Ltd., 2016.
• ISO/WD 10655, Draft method for LiPF6 metal content by ICP-OES.
• Agilent 5994-1171EN, Enhanced Helium Collision Mode with ORS4 Cell.
• Agilent 5991-4257EN, 7900 ICP-MS performance with UHMI for high-salt analysis.
• Agilent 5991-6116EN, Trace element determination in steel using Agilent 7900 ICP-MS.