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Detailed and Direct Observation of Sulfur Crystal Evolution During Operando Analysis of a Li–S Cell with Synchrotron Imaging
journal contribution
posted on 2020-07-02, 15:07 authored by Sebastian Risse, Anika Juhl, Simone Mascotto, Tobias Arlt, Henning Markötter, André Hilger, Ingo Manke, Michael FröbaHerein,
we present a detailed investigation of the electrochemically
triggered formation and dissolution processes of α- and β-sulfur
crystals on a monolithic carbon cathode using operando high-resolution synchrotron radiography (438 nm/pixel). The combination
of visual monitoring with the electrical current response during cyclic
voltammetry provides valuable insights into the sulfur formation and
dissolution mechanism. Our observations show that the crystal growth
process is mainly dictated by a rapid equilibrium between long-chain
polysulfides on one side and solid sulfur/short-chain polysulfides
on the other side, which is consistent with previous studies in this
field. The high temporal and spatial resolution of synchrotron imaging
enables the observation of different regimes during the sulfur formation
and dissolution process. The appearance of short-chain polysulfides
after the first anodic CV peak initiates a rapid dissolution process
of α-sulfur crystals on the cathode. The increase in the long-chain
lithium polysulfide concentration at the cathode surface during charge
results in an increased crystal growth rate, which in turn produces
imperfections in α- and β-sulfur crystals. There are strong
indications that these defects are fluid inclusions, which may trap
dissolved polysulfides and therefore reduce the electrochemical cell
capacity.