Analysis of Electrolyte and Electrode in LIB Degraded by Overcharge and High Temperature

Significance of the topic

Modern lithium-ion batteries (LIBs) are critical for electric vehicles and energy storage systems, yet their performance and safety depend on understanding degradation processes under extreme conditions. Analyzing dissolved metal ions and organic breakdown products in electrolytes, as well as deposited elements on electrodes, reveals mechanisms that lead to capacity loss, internal short circuits, and potential fire hazards. This multifaceted approach supports improvements in cell design and operational protocols.

Study Objectives and Overview

This work examines pouch cells subjected to overcharge and elevated temperature cycling to simulate real-world stress. The goals are to quantify transition metals dissolved into the electrolyte, identify organic degradation species, and map element deposition on electrodes. By combining ICP-AES, GC-MS, and EDXRF analyses, the study provides a comprehensive assessment of battery aging under varied voltage and thermal conditions.

Methodology and Instrumentation

Cells were assembled with NCM523 cathodes, graphite anodes, standard carbonate solvents (EC/EMC/DEC) containing LiPF6 salt and additives, and PP separators. Cycle tests (0.2 C, 100 cycles) were conducted under five conditions varying cutoff voltage (4.0–5.6 V) and ambient temperature (40–60 °C). After disassembly, electrolytes were diluted and analyzed by ICP-AES (Shimadzu ICPE-9820) to quantify Ni, Co, Mn. Organic byproducts were profiled by GC-MS (Shimadzu GCMS-QP2050 with AOC-30i) in SIM mode. Extracted electrodes were examined directly by EDXRF (Shimadzu EDX-8100) to measure deposited transition metals, fluorine, and phosphorus.

Main Results and Discussion

Under higher cutoff voltages, electrolyte metal concentrations rose sharply: Ni reached hundreds of mg/kg, confirming cathode dissolution. Elevated temperature had a minor effect on metal leaching. GC-MS revealed that organophosphate derivatives and dioxahexane carboxylates increased markedly at 5.0 V and above, indicating accelerated solvent decomposition. EDXRF demonstrated corresponding metal deposition on the anode, along with increased phosphorus and fluorine migration from electrolyte to electrode surfaces. Temperature stress enhanced phosphorus accumulation but did not cause significant metal deposition.

Benefits and Practical Applications

• Early detection of transition-metal dissolution helps optimize cathode formulations and additives to improve cycle life.
• Identification of specific organic degradation markers guides the development of more stable solvent blends and interphase modifiers.
• Rapid EDXRF screening of electrode surfaces enables routine quality control of assembled cells without extensive sample prep.

Future Trends and Opportunities

Combining elemental and molecular analyses offers a pathway toward real-time monitoring of battery health. Future work may integrate online sampling of electrolyte and nondestructive electrode scanning in module assemblies. Advanced data analytics and machine learning could correlate multi-modal degradation signatures with remaining useful life, supporting predictive maintenance for large battery systems.

Conclusion

This study demonstrates a robust analytical workflow using ICP-AES, GC-MS, and EDXRF to unravel complex degradation phenomena in lithium-ion batteries under overcharge and high-temperature stress. The insights into metal dissolution, solvent breakdown, and element migration are instrumental for improving cell longevity, safety, and performance in demanding applications.

Reference

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