It has recently been shown that sulfur, a solid material in its elementary form S8, can stay in a supercooled state as liquid sulfur in an electrochemical cell. We establish that this newly discovered state could have implications for lithium–sulfur batteries. Here, through in situ studies of electrochemical sulfur generation, we show that liquid (supercooled) and solid elementary sulfur possess very different areal capacities over the same charging period. To control the physical state of sulfur, we studied its growth on two-dimensional layered materials. We found that on the basal plane, only liquid sulfur accumulates; by contrast, at the edge sites, liquid sulfur accumulates if the thickness of the two-dimensional material is small, whereas solid sulfur nucleates if the thickness is large (tens of nanometres). Correlating the sulfur states with their respective areal capacities, as well as controlling the growth of sulfur on two-dimensional materials, could provide insights for the design of future lithium–sulfur batteries.
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The data that support the plots within this paper and other findings of this study are available from the corresponding author upon reasonable request.
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We acknowledge support from the Department of Energy, Office of Basic Energy Sciences, Division of Materials Science and Engineering under contract DE-AC02-76SF00515. Part of this work was performed at the Stanford Nano Shared Facilities (SNSF) and Stanford Nanofabrication Facilities (SNF), supported by the National Science Foundation under award ECCS-1542152. R.A.V. acknowledges support from the National Academy of Sciences Ford Foundation Fellowship and the National Science Foundation Graduate Research Fellowship Program (NSF GRFP, grant number: DGE – 1656518). We acknowledge C. Su and J. Li from MIT for performing the DFT calculations. A.Y. acknowledges D. Zakhidov for his assistance with polarized Raman measurements and Y. Ye, Z. Wang and R. Xu for helpful discussions.
The authors declare no competing interests.
Peer review information Nature Nanotechnology thanks Yuyan Shao, Guoxiu Wang and Reza Shahbazian-Yassar for their contribution to the peer review of this work.
Publisher’s note Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
Supplementary Figs. 1-21 and Table 1.
Sulfur generation on MoS2 shows distinct growth behaviors on the basal plane and the edges. Specifically, liquid sulfur droplets were generated on the basal plane of the MoS2 while solid sulfur crystal was generated on the edges of the MoS2 flake. Play speed is 3× of the actual speed.
Cryogenic electron microscopy (Cryo-EM) Selected Area Electron Diffraction (SAED) of solid sulfur indicates its high crystallinity. The sample was tilted between -30° and 30°. Play speed is 5× of the actual speed.
Liquid and solid sulfur generation on the edges of 2D flake. Liquid droplets were observed on the edges at the initial stage and quickly turned into solid by the emerging crystals from the edges. Play speed is 5× of the actual speed.
Sulfur generation on monolayer MoS2. Liquid droplets were dynamically generated on monolayer MoS2 without crystallization. The MoS2 flake in the middle was not connected to the Ti electrode, so no sulfur was generated. Play speed is 20× of the actual speed.
Liquid sulfur generation on MoS2 window. The edges of the MoS2 flake were completely covered to suppress crystal growth. Play speed is 10× of the actual speed.
Solid sulfur generation on MoS2 window. The edges of the MoS2 flake were partially left open to initiate crystal growth. Play speed is 10× of the actual speed.
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Yang, A., Zhou, G., Kong, X. et al. Electrochemical generation of liquid and solid sulfur on two-dimensional layered materials with distinct areal capacities. Nat. Nanotechnol. 15, 231–237 (2020). https://doi.org/10.1038/s41565-019-0624-6
Nature Nanotechnology (2020)