Identification of lithium-ion battery degradation products using GC Orbitrap mass spectrometry

Significance of the topic

Lithium-ion battery performance and safety are closely linked to the stability of the electrolyte, which undergoes complex degradation during cycling and storage. Detailed identification of degradation products enables chemists and engineers to understand aging mechanisms, design targeted additives, and improve battery lifetime, reliability, and cost.

Objectives and study overview

This work demonstrates the use of gas chromatography coupled with high-resolution accurate-mass Orbitrap mass spectrometry (GC-HRAM-MS) to identify characteristic carbonate substructures and solvent degradation products in aged lithium-ion battery electrolytes. The study focuses on confirming known methyl and ethyl carbonate dimers and discovering related unknown oligomeric species in a battery electrolyte matrix.

Methodology and sample preparation

Sample collection and treatment were performed as follows:

• Aged electrolyte was extracted from battery separators and negative electrodes by centrifugation.
• Conducting salt LiPF6 was precipitated by diluting the electrolyte with dichloromethane (1:100 v/v) and cooling at 3 °C overnight.
• The clarified supernatant was used for GC-MS analysis.

GC-MS analysis employed two ionization modes to balance structural information and molecular ion detection:

• Electron ionization (EI) at 70 eV for fragmentation patterns and substructure confirmation.
• Positive chemical ionization (PCI) using ammonia reagent gas to generate [M+H]+ and [M+NH4]+ adducts and reveal molecular formulas.

Instrumentation

The analytical workflow utilized Thermo Fisher Scientific instrumentation:

• TriPlus RSH autosampler for automated injection (1 µL split, split ratios 100:1 in EI, 10:1 in PCI).
• TRACE 1310 GC system with TraceGOLD TG-5SilMS 30 m × 0.25 mm column (0.25 µm film) and a temperature program from 40 °C to 260 °C in two ramps.
• Orbitrap Exploris GC mass spectrometer operated at 60 000 resolving power (FWHM at m/z 200) for full-scan acquisition (35–500 Da in EI, 50–500 Da in PCI).
• Data processing via FreeStyle software for accurate-mass extraction and elemental composition assignment.

Main results and discussion

Targeted EI extracted ion chromatograms for fragments m/z 103.0389 (C4H7O3+), 77.0233 (C2H5O3+), and 63.0076 (CH3O3+) selectively revealed peaks corresponding to dimethyl, ethyl-methyl, and diethyl carbonate dimers in the aged electrolyte. High mass resolution enabled narrow extraction windows, removing complex background interferences.

Unknown peaks at retention times 13.9, 14.1, and 14.4 min displayed similar EI fragmentation patterns, suggesting related oligomeric carbonates. PCI spectra acquired with ammonia reagent gas furnished clear [M+H]+ and [M+NH4]+ ions. For the 13.9 min peak, ions at m/z 267.07106 and 284.09761 were assigned to C9H15O9 adducts (< 1 ppm mass error). Subsequent peaks yielded formulas C10H17O9 and C11H19O9, consistent with carbonate trimers.

A comparison of candidate elemental formulas at varied mass accuracy thresholds showed that sub-1 ppm accuracy restricts possibilities to two or fewer, drastically reducing identification workload and boosting confidence.

Benefits and practical applications

• High-resolution GC-HRAM-MS enables selective detection of low-level degradation species in complex electrolyte matrices without reference standards.
• Combined EI and PCI acquisitions allow both substructure confirmation and definitive molecular formula assignment within minutes.
• Mass accuracy better than 1 ppm streamlines elemental composition proposals, supporting targeted screening of aged and new electrolyte formulations.

Future trends and potential applications

Advances may include coupling Orbitrap GC-MS with alternative soft ionization reagents or tandem MS for deeper structural elucidation. Integration with automated data-mining and machine learning could accelerate profiling of complex electrolyte degradation pathways. The approach can be extended to novel solvent systems, solid-state electrolytes, and additive screening to optimize battery performance.

Conclusion

The benchtop Orbitrap Exploris GC-MS platform delivers a robust workflow for detailed characterization of lithium-ion battery electrolyte degradation products. Its combination of high resolving power, mass accuracy, and rapid switching between EI and PCI modes enables confident identification of known and unknown carbonate substructures, informing electrolyte design and battery longevity strategies.

References

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