Gas chromatography–mass spectrometry

Example

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Connect results with scale and specimen preparation.

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Differential electrochemical mass spectrometry

Feeding gas from an operating cell straight into a mass spectrometer, so each species is identified and quantified as it forms. It shows ethylene from ethylene carbonate reduction during formation, and the oxygen and carbon dioxide released by layered oxides at high state of charge, tying each gas to the voltage that made it.

Electrolyte decomposition

Reduction of the electrolyte at the negative electrode and oxidation at the positive, outside its stability window. A little is useful — it builds the SEI — but continued decomposition consumes lithium, dries the cell and makes gas.

Gas generation

Formation of gases — ethylene, hydrogen, carbon monoxide and carbon dioxide — by electrolyte decomposition, mostly during formation and later under high voltage or temperature. In a pouch cell it shows as swelling; in a can it raises pressure until the vent opens.

Off-gas

The mixture released when a cell vents: electrolyte vapour, hydrogen, carbon monoxide, carbon dioxide and hydrocarbons, with hydrogen fluoride. It is flammable and toxic, and gas sensors detect it before smoke or heat in a storage container.

Post-mortem analysis

Opening an aged or failed cell in an inert glovebox and examining its electrodes by microscopy, diffraction and chemical analysis. It confirms which degradation mechanisms actually occurred rather than inferring them from voltage.

References & further reading

Further reading on this topic

These sources provide broader context; they are not presented as citations for every statement in this entry.

1. Advanced characterization techniques for solid state lithium battery research

   Yuxuan Xiang, Xia Li, Yongqiang Cheng, Xueliang Sun, Yong Yang · Materials Today · 2020

   Topic background · X-ray, solid-state NMR and neutron methods in solid-state battery research.