A normal lithium ion cell doesn't contain any metallic (elemental) lithium.
The chemicals are usually a lithium salt like lithium perchlorate or
lithium hexafluorophosphate dissolved in a suitable organic solvent mixture
such as ethylene carbonate and dimethyl carbonate. The electrodes are
typically lithium cobalt oxide (positive) and graphite(negative) but vary
widely. None of the above chemicals is particularly air-sensitive. The
danger comes from two things: the high energy density of the cell such that
even a tiny short circuit internal to the cell can cause extreme heating
and also the flammability of the electrolyte. The lithium compounds play
only a minor role in the combustion (they can turn the flames bright red
from the characteristic emission spectrum of Li(+) ions)
It is a very active area of research to find a suitable non-flammable
solvent for lithium ion battery electrolyte - to substitute for the organic
carbonates and other solvents used now. Unfortunately the solvent needs to
have certain properties which greatly reduce the number of suitable
solvents. Water cannot be used - not because of reaction with lithium - but
because the cell voltage is too high and it would immediately begin
breaking the water apart into hydrogen and oxygen. In fact, you absolutely
should consider using water to put out a lithium ion battery fire, as long
as there is no high voltage present (such as a line-powered battery
charger) which could cause a shock hazard to the person pouring the water.
Some of the confusion in this topic comes from the existence of lithium
primary batteries. These are non-rechargable and DO contain elemental
lithium. Examples of these are 3V button cells (like the CR-series) and
long-term memory or clock backup batteries. Some critical medical or
military equipment can contain fairly large lithium primary cells - like
some automated external defibrillators. The chemistry also varies greatly
but the traditional main example is the lithium manganese dioxide cell,
which has lithium metal as the anode, MnO2 as the cathode, and a solution
of lithium perchlorate in an organic solvent as the electrolyte. These will
react violently if the inside of the cell is exposed to water. They will
also react with oxygen in air (if the seal is broken) but much more slowly.
However, their lithium anode can certainly burn in air with a very hot
flame if it is ignited and the electrolyte is once again very flammable,
too.
Post by smplxPost by Richard PopeJames, Ryan,
What has happened is a cascade failure. Remember that a battery is
made of several cells. When one of these cells failed it overheated the
cells around it. This caused these cells to fail and this overheated
surrounding cells and so forth. The lithium in the batteries would react
in a violent manner to the oxygen in the air when the cells were
breached. Once this type of failure starts there is no way to stop it.
Actually, if I remember correctly, it's not the oxygen in the air that's
the problem but the composition of the electrolyte. Some chemistries are
happy to oxidise the lithium without the need for atmospheric oxygen.
Regards
Sergio Masci
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