Effect of the Hydrofluoroether Cosolvent Structure in Acetonitrile-Based Solvate Electrolytes on the Li+ Solvation Structure and Li-S Battery Performance

Minjeong Shin, Heng Liang Wu, Badri Narayanan, Kimberly A. See, Rajeev S. Assary, Lingyang Zhu, Richard T. Haasch, Shuo Zhang, Zhengcheng Zhang, Larry A. Curtiss, Andrew A. Gewirth

Research output: Contribution to journalArticlepeer-review

Abstract

We evaluate hydrofluoroether (HFE) cosolvents with varying degrees of fluorination in the acetonitrile-based solvate electrolyte to determine the effect of the HFE structure on the electrochemical performance of the Li-S battery. Solvates or sparingly solvating electrolytes are an interesting electrolyte choice for the Li-S battery due to their low polysulfide solubility. The solvate electrolyte with a stoichiometric ratio of LiTFSI salt in acetonitrile, (MeCN)2-LiTFSI, exhibits limited polysulfide solubility due to the high concentration of LiTFSI. We demonstrate that the addition of highly fluorinated HFEs to the solvate yields better capacity retention compared to that of less fluorinated HFE cosolvents. Raman and NMR spectroscopy coupled with ab initio molecular dynamics simulations show that HFEs exhibiting a higher degree of fluorination coordinate to Li+ at the expense of MeCN coordination, resulting in higher free MeCN content in solution. However, the polysulfide solubility remains low, and no crossover of polysulfides from the S cathode to the Li anode is observed.

Original languageEnglish (US)
Pages (from-to)39357-39370
Number of pages14
JournalACS Applied Materials and Interfaces
Volume9
Issue number45
DOIs
StatePublished - Nov 15 2017

Keywords

  • X-ray photoelectron spectroscopy
  • hydrofluoroether cosolvent
  • lithium-sulfur battery
  • solvate electrolyte
  • sparingly solvating electrolyte
  • variable-temperature NMR spectroscopy

ASJC Scopus subject areas

  • Materials Science(all)

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