Direct electrochemical generation of supercooled sulfur microdroplets well below their melting temperature

Nian Liu; Guangmin Zhou; Ankun Yang; Xiaoyun Yu; Feifei Shi; Jie Sun; Jinsong Zhang; Bofei Liu; Chun-Lan Wu; Xinyong Tao; Yongming Sun; Yi Cui; Steven Chu

doi:10.1073/pnas.1817286116

Direct electrochemical generation of supercooled sulfur microdroplets well below their melting temperature

Proc Natl Acad Sci U S A. 2019 Jan 15;116(3):765-770. doi: 10.1073/pnas.1817286116. Epub 2019 Jan 2.

Authors

Nian Liu^{1

2

3}, Guangmin Zhou², Ankun Yang², Xiaoyun Yu², Feifei Shi², Jie Sun², Jinsong Zhang², Bofei Liu², Chun-Lan Wu², Xinyong Tao^{2

4}, Yongming Sun², Yi Cui^{5

6}, Steven Chu^{1

7}

Affiliations

¹ Department of Physics, Stanford University, Stanford, CA 94305; nian.liu@chbe.gatech.edu yicui@stanford.edu schu@stanford.edu.
² Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305.
³ School of Chemical & Biomolecular Engineering, Georgia Institute of Technology, Atlanta, GA 30332.
⁴ College of Materials Science and Engineering, Zhejiang University of Technology, 310014 Hangzhou, China.
⁵ Department of Materials Science and Engineering, Stanford University, Stanford, CA 94305; nian.liu@chbe.gatech.edu yicui@stanford.edu schu@stanford.edu.
⁶ SLAC National Accelerator Laboratory, Stanford Institute for Materials and Energy Sciences, Menlo Park, CA 94025.
⁷ Department of Molecular and Cellular Physiology, Stanford University, Stanford, CA 94305.

Abstract

Supercooled liquid sulfur microdroplets were directly generated from polysulfide electrochemical oxidation on various metal-containing electrodes. The sulfur droplets remain liquid at 155 °C below sulfur's melting point (T_m = 115 °C), with fractional supercooling change (T_m - T_sc)/T_m larger than 0.40. In operando light microscopy captured the rapid merging and shape relaxation of sulfur droplets, indicating their liquid nature. Micropatterned electrode and electrochemical current allow precise control of the location and size of supercooled microdroplets, respectively. Using this platform, we initiated and observed the rapid solidification of supercooled sulfur microdroplets upon crystalline sulfur touching, which confirms supercooled sulfur's metastability at room temperature. In addition, the formation of liquid sulfur in electrochemical cell enriches lithium-sulfur-electrolyte phase diagram and potentially may create new opportunities for high-energy Li-S batteries.

Keywords: Li-S batteries; crystallization; in situ optical microscopy; liquid sulfur droplets; supercooled liquids.

Publication types

Research Support, U.S. Gov't, Non-P.H.S.