Melanin comes in several molecular structures, each of
which causes it to behave in a slightly different way. When
its molecules form matches the structure of a polymer, the
polymers can be arranged into that of a battery’s material. Specifically, researchers discovered the tetramer structure, which
is a four-membered ring made up of bigger molecules. This
structure matches the model of melanin macromolecules.
“Only the tetramer structure had the correct number of ex-
posed nitrogens to bind with the sodium,” says Bettinger. “The
voltage signals we received are consistent with what you would
observe if you believe that the tetramer is the correct structural
One big challenges Bettinger and his team encountered
was identifying the right combination of electrode configura-
tion and complementary cation pairs, he told Digital Trends.
“If you use melanin the wrong way or use the wrong
type of cation, you get a very different, often worse, level of
performance in terms of both capacity and voltage,” he says.
“Only after understanding something about the fundamental
function of melanin in the body and leveraging that knowl-
edge appropriately could we design a battery that would
There were several candidate materials found inside of the
body which could be used for the battery’s other electrode. The
most promising ones included magnesium, sodium, titanium
phosphate, and copper. Magnesium was finally chosen by the
team because it is better at creating a boundary within the
“Magnesium (Mg) is more ‘sticky’ than sodium (Na) because
the charge-to-mass ratio is much larger. This means that it’s
harder for Mg to move in and out of the battery electrodes
(both positive and negative) very efficiently because the high
charge of Mg (relative to Na) makes it interact with the material
more strongly,” explains Bettinger.
“This impacts the operation of the battery and limits how
many times the battery can be charged and re-charged. With
melanin, we speculate that it has a specific chemistry that is
designed to attach to ions with a charge of + 2 (like Mg). Therefore, melanin electrodes can exchange these ions very efficiently
where other traditional electrode materials do this very poorly.