Aiding Lithium Ion Secondary Battery Electrolyte Design via UPLC-MS and APGC-MS Analysis on a Single High-Resolution Mass Spectrometer Platform

Importance of the Topic

The performance, lifetime and safety of lithium-ion secondary batteries depend critically on the chemical composition of their electrolyte solutions and proprietary additives. Understanding how charge–discharge cycling alters both volatile and non-volatile components enables battery developers to identify degradation pathways, optimize additive formulations, and improve overall battery robustness.

Study Objectives and Overview

This study demonstrates a unified high-resolution mass spectrometry (HRMS) workflow that combines ultra-performance liquid chromatography-mass spectrometry (UPLC-MS) with atmospheric pressure gas chromatography-mass spectrometry (APGC-MS) on a single Xevo G2-XS QTof platform. The goal is to monitor changes in electrolyte composition after defined numbers of charge–discharge cycles and to discover and elucidate chemical markers of electrolyte degradation.

Methodology and Instrumentation

Sample Preparation:

• Dimethyl carbonate (DMC)–based electrolyte containing diethyl carbonate, ethyl-methyl carbonate, fluoroethyl carbonate (FEC), LiPF6 and proprietary additives.
• Battery packs subjected to 0 (control), 1, 40, 180 and 200 charge–discharge cycles at fixed voltage; electrolytes extracted in DMC.

Instrument Parameters:

• APGC-MS inlet (GC): DB-5 MS column, He carrier, APGC corona ionization for softer ionization and molecular ion preservation.
• UPLC-MS inlet (LC): ACQUITY UPLC HSS T3 column, gradient elution with ammonium formate/water and methanol, ESI positive ion mode.
• Mass spectrometer: Xevo G2-XS QTof, high resolution, accurate mass in both inlet modes.
• Data analysis: UNIFI Scientific Information System with embedded multivariate and structural elucidation workflows.

Main Results and Discussion

The dual-inlet configuration captured both volatile and non-volatile species in a single run, ensuring comprehensive coverage. Total ion chromatograms showed distinct profiles for low-cycle (1×, 40×) versus high-cycle (180×, 200×) samples.

Principal component analysis (PCA) separated control and cycled samples into two clusters: early (1×/40×) and late (180×/200×) cycles, confirming cycle-dependent chemical changes. Orthogonal partial least squares discriminant analysis (OPLS-DA) further pinpointed discriminating ions. A key marker at m/z 131.0336 emerged after 40 cycles and increased through 200 cycles.

UNIFI’s elemental composition prediction (C5H6O4) and database search suggested this marker arises from FEC degradation, replacing the fluorine moiety with carbon monoxide. Fragment matching via MassFragment validated the proposed structure. Concurrently, FEC abundance decreased in parallel, confirming its role as precursor.

Benefits and Practical Applications

By integrating GC- and LC-HRMS on a single platform and leveraging automated informatics, researchers can rapidly identify and track degradation products in battery electrolytes. This approach accelerates additive optimization, enables quality control in manufacturing, and supports the design of longer-lived, safer batteries.

Future Trends and Applications

• Real-time reaction monitoring using direct MS interfaces and inline sampling.
• Expansion of high-resolution ion mobility separations to resolve isomeric degradation products.
• Machine-learning-driven multivariate analysis for predictive lifecycle modeling.
• Integration with electrochemical cells for in situ MS investigation of charge/discharge processes.

Conclusion

This application note showcases a powerful, unified UPLC-MS and APGC-MS workflow for in-depth characterization of lithium-ion battery electrolytes. Comprehensive HRMS data combined with multivariate and structural elucidation tools enabled discovery of a novel FEC degradation marker. Such insights can guide formulation improvements and advance next-generation battery technologies.

Reference

1. OECD. Climate Futures: Policy Highlights; 2020.
2. UK Parliament. Electric Vehicle Transition Report; 2019.
3. Gür TM. Review of Electrical Energy Storage Technologies. Energy Environ. Sci. 2018;11:2696–2767.