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 The Li-S couple has one of the highest theoretical energy densities of
all
know
chemically reversible systems. Due to the low atomic weight of Li
and S,
the capacity
of the electrochemically active components in a Li-S
cell is 1,680
Ah/kg, and with an
average voltage of 2V, the corresponding
theoretical
specific energy is 3,360 Wh/kg.
In contrast to the metal oxide or chalcogenide systems used in some
lithium
primary and lithium ion secondary batteries, the polysulfide
electrode
is not an
insertion electrode material. Instead, it is a soluble
redox molecule
that diffuses
through the electrolyte medium to the
positive electrode
comprised of an electronically
conductive charge
transfer matrix, typically a
high surface area carbon. The electrolyte
can
be a polymeric material such as
PEO, a gelled electrolyte, or a fully liquid
electrolyte. In contrast to an
intercalation material where electrode rates
can be
limited by diffusion in the
intercalation host, polysulfide species
are limited only by
diffusion rates in the
electrolyte medium. Consequently,
very high power densities can
be realized
in Li-Li2Sx batteries.
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