Cobalt’s function is to provide the battery with a good cycling ability,
because of its tight molecular structure that it has in the cathode.
Nickel is being more commonly used throughout the world because of a shortage
on cobalt. The common belief is that the more nickel is used in a cathode,
the more energy that cathode will have. However, this is not true. The more
nickel is used in the cathode, the overall voltage decreases. Many researchers
are trying to find a cathode with zero cobalt composition, but cobalt must
be used to counteract the effects of nickel.

Many batteries are using a “333” composition. This represents 1/3 nickel, 1/3
cobalt, and 1/3 manganese. The industry is trying to optimize safety, power,
performance and price by moving towards compositions like 523, 622, & 811.
(The first digit representing nickel, second cobalt, and third as
manganese.) The furthest scientists have gotten is at least 10% cobalt, which
means that it is still required but less is needed, hopefully improving the
world’s amount of cobalt.

More about Cobalt:

Group: 9 – Melting point: 1495°C, 2723°F, 1768 K
Period: 4 – Boiling point: 2927°C, 5301°F, 3200 K
Block: d – Density: (g cm−3) 8.86
Atomic number: 27 – Relative atomic mass: 58.933
State at 20°C: Solid – Key isotopes: 59Co
Electron configuration: [Ar] 3d74s2 – CAS number: 7440-48-4

Other uses:

Cobalt, like iron, can be magnetized and so is used to make magnets.
It is alloyed with aluminum and nickel to make particularly powerful magnets.

Other alloys of cobalt are used in jet turbines and gas turbine generators,
where high-temperature strength is important.

Cobalt metal is sometimes used in electroplating because of its
appearance, hardness and resistance to corrosion.

Cobalt salts have been used for centuries to produce brilliant blue colors
in paint, porcelain, glass, pottery and enamels.

Radioactive cobalt-60 is used to treat cancer and, in some countries,
to irradiate food to preserve it.

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-Taylor