Hydrofluoric acid

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Dry room

A production room whose air is kept extremely dry — dew points around −30 °C to −60 °C — so that no moisture reaches the cell while the electrolyte goes in. Water would react with the salt LiPF₆ to form hydrofluoric acid.

Lithium salt

The dissolved salt that supplies the mobile lithium ions in a liquid electrolyte, almost always lithium hexafluorophosphate, LiPF₆, at about one mole per litre. It reacts with traces of water to form hydrofluoric acid, which is why cells are filled in a dry room.

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.

Transition-metal dissolution

Manganese, nickel or cobalt ions leaching from the positive electrode into the electrolyte, especially at high voltage and temperature or when HF is present. They migrate to the negative electrode and poison the SEI there, accelerating lithium loss.

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. Thermal runaway mechanism of lithium ion battery for electric vehicles: A review

   Xuning Feng et al. · Energy Storage Materials · 2018

   Topic background · Electrical, mechanical and thermal abuse; thermal-runaway mechanisms and propagation.