WCPS: High Accuracy Standard Addition ICP-MS Analysis of Elemental Impurities in Electrolyte Used for Lithium-Ion Batteries

Significance of the Topic

The performance, safety and lifetime of lithium-ion batteries are critically affected by trace elemental impurities in the electrolyte salts. Even low‐level contaminants can alter electrode reactions, reduce cycle life, and pose safety risks. As the industry moves toward higher power densities and stricter quality specifications, reliable quantification of sub‐µg/kg levels of metal and nonmetal impurities becomes essential for raw material suppliers and battery manufacturers.

Objectives and Overview of the Study

This study developed and validated a high‐accuracy standard addition calibration method using single‐quadrupole ICP‐MS for the simultaneous determination of 68 elements in four common Li‐salt matrices: lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4) and lithium bis(fluorosulfonyl)imide (LiFSI). Key aims included overcoming ionization suppression by the high Li matrix, achieving sub‐µg/kg detection limits in the original solid salts, and demonstrating robust long‐term operation under high‐matrix conditions.

Methodology

Sample Preparation and Standard Addition Calibration:

• Weighed 5 g of each Li salt into PFA containers and dissolved in ultrapure water to achieve 10× dilution (5% TDS).
• Prepared nine standard addition levels by spiking aliquots of each dissolved matrix with a mixed multi‐element intermediate standard (67 elements) and a separate sulfur stock.
• Applied an overall 20× dilution with 2% HNO3 to minimize matrix effects while reaching required MDLs.
• Used the unspiked matrix as the sample blank and acquired calibration curves across 1–500 µg/kg for most elements, 0.5–10 µg/g for S, and 0.05–5 µg/kg for Hg.

Used Instrumentation

Analyses were carried out on an Agilent 7900 ICP‐MS equipped with:

• PFA inert sample introduction kit and HF-resistant PFA nebulizer.
• Pt-tipped sampling and Ni skimmer cones for corrosion resistance and reduced salt deposition.
• Fourth‐generation ORS4 collision/reaction cell configured for:
• Helium (standard and high‐energy) for polyatomic interference removal.
• Hydrogen for resolving ArO and other overlaps on Si, Fe, Ca and Se.
• Agilent MassHunter autotune for optimized tuning in each mode.

Main Results and Discussion

• Linearity: All analytes showed calibration coefficients ≥ 0.999 using standard addition calibration.
• Detection Limits: Method detection limits (MDLs) in the solid salts were sub‐µg/kg for most trace elements after correction for dilution factors.
• Accuracy: Spike recoveries between 80–120% (n=3) with RSDs < 12% for all elements except those present at high native concentrations (B, Si, P, S).
• Matrix Tolerance: The Pt cones exhibited minimal salt deposition after a 6-hour run; simple ultrasonic cleaning in 0.5% citric acid fully restored performance.
• Long-Term Stability: QC recoveries remained within ±15% over 6 hours with a QC sample analyzed every 10 injections.

Benefits and Practical Applications

The presented ICP-MS protocol delivers:

• Accurate, low-level quantification of a broad range of metallic and nonmetallic impurities in Li salts without excessive dilution.
• Robust tolerance to high‐matrix samples, reducing re-analysis and downtime.
• Applicability to quality control of electrolyte raw materials and final battery products to meet stringent industry and regulatory standards.

Future Trends and Opportunities

Emerging approaches and directions include:

• Triple quadrupole ICP-MS (e.g., Agilent 8900) for even lower detection limits and enhanced interference control.
• Integration of automated sample prep and on-line monitoring for real-time quality assurance in battery manufacturing.
• Extension of methodology to novel electrolyte chemistries and solid‐state battery precursors.

Conclusion

A robust standard addition ICP-MS method on the Agilent 7900 enables accurate, sensitive, multi-element analysis of high-matrix lithium‐salt electrolytes. The approach effectively mitigates ionization suppression, achieves sub-µg/kg detection limits, and demonstrates excellent long‐term stability, meeting the evolving needs of lithium-ion battery quality control.

References

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3. Encyclopedia of Analytical Chemistry, John Wiley & Sons, Ltd. (2016).
4. ISO/WD 10655: Methods for analysis of lithium hexafluorophosphate—Determination of metal ions by ICP-OES, 1st ed. (2022).
5. Enhanced Helium Collision Mode with Agilent ORS4 Cell, Agilent publication 5994-1171EN.
6. Proper, W.; McCurdy, E.; Takahashi, J., Performance of the Agilent 7900 ICP-MS with UHMI for high salt matrix analysis, Agilent publication 5991-4257EN.
7. Plasma Robustness and Matrix Tolerance, Agilent Technology Brief 5994-1173EN.
8. Zou, A.; Li, S.; Ang, C.H.; McCurdy, E., Accurate ICP-MS Analysis of Elemental Impurities in Electrolyte Used for Lithium-Ion Batteries, Agilent publication 5994-5363EN.