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Chemical Synthesis of K2S2 and K2S3 for Probing Electrochemical Mechanisms in K–S Batteries
journal contribution
posted on 2018-10-16, 00:00 authored by Sichen Gu, Neng Xiao, Feng Wu, Ying Bai, Chuan Wu, Yiying WuUnderstanding the
properties of polysulfide intermediates is crucial
for explaining and optimizing metal–sulfur batteries. Unlike
the unstable or inseparable low-order polysulfide intermediates in
Li–S systems, the K–S phase diagram displays a series
of stable phases of K2Sn (n = 1, 2, 3, 4, 5, 6), which provides the accessibility
of an individual polysulfide to investigate the mechanism using pure-phase
polysulfides. Herein, we synthesized two key intermediate polysulfides,
K2S2 and K2S3, and probed
their electrochemical pathways. When K2S2 and
K2S3 are coated directly on a current collector,
both species can be further reduced. However, when K2S2 and K2S3 are electrically isolated
from the current collector, no further reduction is observed, showing
the reduction occurs through a solid-state conversion pathway. Interestingly,
K2S2 and K2S3 can be charged
even when they are electrically isolated from the current collector,
proving solution-mediated charging pathways. Only K2S is
the “dead” sulfur species that cannot be charged.