Analysis of Main Components of Lithium Salts in Lithium-Ion Battery Electrolytes Using Ion Chromatography-Quadrupole Time-of-Flight High-Resolution Mass Spectrometry

Significance of the Topic

Electrolytes are a critical component in lithium-ion batteries, influencing charge-discharge efficiency, stability, and lifespan. Identifying main salt anions and their degradation products is essential for improving battery performance and understanding aging mechanisms.

Objectives and Overview of the Study

This work aimed to develop and validate a combined ion chromatography and high-resolution mass spectrometry method for comprehensive analysis of lithium salt anions in battery electrolytes. The study focused on separating key anions and detecting both known and unknown species.

Methodology and Instrumentation

Sample Preparation

• Electrolyte samples were diluted in acetonitrile and filtered.
• Direct injection of prepared solutions into the chromatography system.

Chromatographic Conditions

• Column: Metrosep A supp 5–250/4.0 anion exchange.
• Mobile phase: aqueous 3.2 mmol/L Na2CO3 with 1.0 mmol/L NaHCO3 mixed with 40% acetonitrile.
• Flow rate 0.5 mL/min, injection volume 20 µL, column temperature 30 °C.
• Detection: suppressed conductivity.

Mass Spectrometry Conditions

• Instrument: Agilent 6546 LC/Q-TOF with Dual AJS ESI source.
• Ionization: negative ESI, mass range m/z 50–1100.
• Acquisition: 6 spectra per second, collision energies at 20, 40, and 60 V for fragmentation.

Main Results and Discussion

The method achieved baseline separation of six anions (F–, PF2O2–, BF4–, PF6–, F2NS2O4–, and C2HO4–) within 45 minutes, with resolution values above 1.5 and retention time RSDs below 0.8%. High-resolution mass data enabled confident identification of each anion. For example, bisfluorosulfonimide (m/z 179.9243) was confirmed by accurate mass (0.09 ppm error) and characteristic fragment ions from S–N bond cleavage. Detection of oxalate indicated LiODFB hydrolysis under ambient conditions.

Benefits and Practical Applications of the Method

• Combines high-efficiency IC separation with accurate mass MS for unknown anion screening.
• Overcomes poor retention and coelution of highly polar anions on conventional columns.
• Enables routine quality control and mechanistic studies in battery research.

Future Trends and Potential Applications

• Automation of sample handling and data processing to increase throughput.
• Extension to other battery chemistries and degradation studies.
• Integration with tandem MS and ion mobility for deeper structural characterization.
• Application in real-time monitoring of electrolyte aging.

Conclusion

The presented IC–Q-TOF approach provides a robust tool for comprehensive analysis of lithium salt anions and their degradation products in battery electrolytes. It delivers high resolution, accurate identification, and practical applicability for both research and quality control in battery development.

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