at least keep up with the consumption by electrochemical reduction.This increase is fueled by both the dissolution of solid sulfur and
the subsequent reduction of S2-x
species producing shorter, but also more numerous
molecules.Once no more sulfur dissolves into the electrolyte (or only at comparatively
low rates, see above), the total concentration of polysulfides levels off.The continuous
precipitation of Li2S from the electrolyte is balanced by the progressive reduction of
longer S2-x
species down to S2-4
.Later during the dis charge, when less longer species are available, most reduction products precipitate
immediately, reducing the total amount of dissolved polysulfides.5.23 contains the most relevant
information about the liquid electrolyte system, which is also confirmed by various
experimental characterization techniques, see e.g. Ref.Hence, there is
a constant flow of sulfur in its highest oxidation state into the electrolyte, stabilizing a
steady-state equilibrium, which in turn results in a constant cell voltage.In that situation, the voltage decreases continuously as does the
average oxidation state of the dissolved S2-x polysulfide species.Therefore, each electron extracted from the system directly
lowers all concentrations simultaneously, in the end precipitating 1/16 molecule of S8
per electron.The shorter polysulfides are very short lived; they
are fully reduced to S2- and rapidly precipitate as solid Li2S.Depending on the
discharge cutoff voltage, the total concentration may either become as low as that of a
fully charged cell or remain close to the plateau level.As indicated by the
solid lines in Fig.[P4].