Differential electrochemical mass spectrometry

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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.

Formation

The first controlled charge and discharge cycles of a newly assembled cell, during which the SEI forms. It is part of cell production, before aging and grading.

Gas chromatography–mass spectrometry

Separating the volatile components of a sample in a heated column and identifying each by its mass spectrum. It measures electrolyte composition and aging products such as transesterified solvents and oligomers; with thermal-conductivity detection it also quantifies hydrogen, carbon monoxide, carbon dioxide and hydrocarbons in cell and vent 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.

Operando and in-situ measurement

Measuring a cell inside its working environment rather than after taking it apart (ex situ): in situ means within the cell or its surroundings, operando means while it is actually charging or discharging. Operando methods catch transient states, such as phases or plated lithium that vanish during rest or disassembly.

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.