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MoS2 nanosheets as interlayer in Li-S batteries
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This work has investigated the use of MoS2 nanosheets acting as an interlayer to effectively
block polysulfide shuttling (movement from cathode to the anode) in Li-S batteries.
In the first part of the work we exfoliated bulk MoS2 into a few layered MoS2 flakes, resulting
in increased surface area and improved electric properties, to achieve a better interlayer
performance by effectively trapping polysulfide (PS) in the cathode. This was done through
solvothermal lithium intercalation followed by water sonication, creating a reaction between
water and intercalated lithium to promote exfoliation.
In the second part was explored the electrochemical characterization of distinct Li-S test cells
(each with different interlayers), and compared to a standardized Li-S test cell. The afore
mentioned interlayers were spread either on to the cathode or the separator. Furthermore,
carbon black, bulk and exfoliated MoS2, were compared as active materials of the interlayers.
Bulk MoS2 exfoliation into thinner flake, resulted in a size reduction up to 56 times and a
decrease in the number of layers. The results of optical spectroscopy suggest effects of quantum
confinement. Furthermore, with XRD, was analytically demonstrated successful intercalation and
exfoliation. Then, through Raman and SEM analysis demonstrated evidence of thinner MoS2
structures.
On another hand, exfoliated MoS2 was spread on a sulfur cathode creating the interlayer that
successfully trapped polysulfides. This was showed through a 4 percentage points increase in
sulfur utilization for the first cycle, and an improvement of sulfur loss by cycle of 0.02%
retaining a good 99.4% coulombic efficiency. In addition a ΔE decreased of 45%, a result of
improved battery kinetics. Nonetheless a simple carbon black DL interlayer was also made using
a different solvent. However was observed a increase of sulfur utilization by 9% in the first cycle
and the same degradation of sulfur per cycle as the standard battery with an impressive CE of
99.7%.