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Anode: Carbon compound, graphite
Cathode: Lithium oxide
Electrolyte:
Applications: Laptops, cellular phones, electric
vehicles
Lithium batteries that use lithium metal
have safety disadvantages when used as secondary (rechargeable) energy sources.
For this reason a series of cell chemistries have been developed using lithium
compounds instead of lithium metal. These are called generically Lithium ion
Batteries.
Cathodes consist of a a layered crystal (graphite) into
which the lithium is intercalated. Experimental cells have also used lithiated
metal oxide such as LiCoO2,
NiNi0.3Co0.7O2, LiNiO2,
LiV2O5, LiV6O13,
LiMn4O9, LiMn2O4,
LiNiO0.2CoO2.
Electrolytes are usually LiPF6, although this
has a problem with aluminum corrosion, and so alternatives are being sought.
One such is LiBF4. The electrolyte in current production batteries
is liquid, and uses an organic solvent.
Membranes are necessary to separate the electrons from the
ions. Currently the batteries in wide use have microporous polyethylene
membranes.
Intercalation (rhymes with relation—not inter-cal,
but in-tercal-ation) is a long-studied process which has finally found a
practical use. It has long been known that small ions (such as lithium, sodium,
and the other alkali metals) can fit in the interstitial spaces in a graphite
crystal. Not only that, but these metallic atoms can go farther and force the
graphitic planes apart to fit two, three, or more layers of metallic atoms
between the carbon sheets. You can imagine what a great way this is to store
lithium in a battery—the graphite is conductive, dilutes the lithium for
safety, is reasonably cheap, and does not allow dendrites or other unwanted
crystal structures to form. |
