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

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.

Authors:
; ; ; ; ; ; ; ; ; ;
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science - Office of Basic Energy Sciences - Materials Sciences and Engineering Division; USDOE Office of Science (SC); USDOE Office of Science - Office of Basic Energy Sciences - Joint Center for Energy Storage Research (JCESR)
OSTI Identifier:
1420080
DOE Contract Number:
AC02-06CH11357
Resource Type:
Journal Article
Resource Relation:
Journal Name: ACS Applied Materials and Interfaces; Journal Volume: 9; Journal Issue: 45
Country of Publication:
United States
Language:
English
Subject:
X-ray photoelectron spectroscopy; hydrofluoroether cosolvent; lithium-sulfur battery; solvate electrolyte; sparingly solvating electrolyte; variable-temperature NMR spectroscopy

Citation Formats

Shin, Minjeong, Wu, Heng-Liang, Narayanan, Badri, See, Kimberly A., Assary, Rajeev S., Zhu, Lingyang, Haasch, Richard T., Zhang, Shuo, Zhang, Zhengcheng, Curtiss, Larry A., and Gewirth, Andrew A. Effect of the Hydrofluoroether Cosolvent Structure in Acetonitrile-Based Solvate Electrolytes on the Li+ Solvation Structure and Li-S Battery Performance.. United States: N. p., 2017. Web. doi:10.1021/acsami.7b11566.
Shin, Minjeong, Wu, Heng-Liang, Narayanan, Badri, See, Kimberly A., Assary, Rajeev S., Zhu, Lingyang, Haasch, Richard T., Zhang, Shuo, Zhang, Zhengcheng, Curtiss, Larry A., & Gewirth, Andrew A. Effect of the Hydrofluoroether Cosolvent Structure in Acetonitrile-Based Solvate Electrolytes on the Li+ Solvation Structure and Li-S Battery Performance.. United States. doi:10.1021/acsami.7b11566.
Shin, Minjeong, Wu, Heng-Liang, Narayanan, Badri, See, Kimberly A., Assary, Rajeev S., Zhu, Lingyang, Haasch, Richard T., Zhang, Shuo, Zhang, Zhengcheng, Curtiss, Larry A., and Gewirth, Andrew A. 2017. "Effect of the Hydrofluoroether Cosolvent Structure in Acetonitrile-Based Solvate Electrolytes on the Li+ Solvation Structure and Li-S Battery Performance.". United States. doi:10.1021/acsami.7b11566.
@article{osti_1420080,
title = {Effect of the Hydrofluoroether Cosolvent Structure in Acetonitrile-Based Solvate Electrolytes on the Li+ Solvation Structure and Li-S Battery Performance.},
author = {Shin, Minjeong and Wu, Heng-Liang and Narayanan, Badri and See, Kimberly A. and Assary, Rajeev S. and Zhu, Lingyang and Haasch, Richard T. and Zhang, Shuo and Zhang, Zhengcheng and Curtiss, Larry A. and Gewirth, Andrew A.},
abstractNote = {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.},
doi = {10.1021/acsami.7b11566},
journal = {ACS Applied Materials and Interfaces},
number = 45,
volume = 9,
place = {United States},
year = 2017,
month =
}
  • Li-S batteries are a promising next-generation battery technology. Due to the formation of soluble polysulfides during cell operation, the electrolyte composition of the cell plays an active role in directing the formation and speciation of the soluble lithium polysulfides. Recently, new classes of electrolytes termed "solvates" that contain stoichiometric quantities of salt and solvent and form a liquid at room temperature have been explored due to their sparingly solvating properties with respect to polysulfides. The viscosity of the solvate electrolytes is understandably high limiting their viability; however, hydrofluoroether cosolvents, thought to be inert to the solvate structure itself, can bemore » introduced to reduce viscosity and enhance diffusion. Nazar and co-workers previously reported that addition of 1,1,2,2-tetrafluoroethyl 2,2,3,3-tetrafluoropropyl ether (TTE) to the LiTFSI in acetonitrile solvate, (MeCN) 2-LiTFSI, results in enhanced capacity retention compared to the neat solvate. Here, we evaluate the effect of TTE addition on both the electrochemical behavior of the Li-S cell and the solvation structure of the (MeCN) 2-LiTFSI electrolyte. Contrary to previous suggestions, Raman and NMR spectroscopy coupled with ab initio molecular dynamics simulations show that TTE coordinates to Li + at the expense of MeCN coordination, thereby producing a higher content of free MeCN, a good polysulfide solvent, in the electrolyte. Furthermore, the electrolytes containing a higher free MeCN content facilitate faster polysulfide formation kinetics during the electrochemical reduction of S in a Li-S cell likely as a result of the solvation power of the free MeCN.« less
  • X-ray absorption edge and EXAFS spectra of the acetonitrile, dimethyl sulfoxide, pyridine and tetrahydrothiophene solvated copper(I) ions and the acetonitrile and dimethyl sulfoxide solvated copper(II) ions have been measured in solution. Analysis reveals that the copper(I) solvates are most probably tetrahedral, and the following Cu-solvate bond distances have been found: Cu-N = 1.99(2) [angstrom] in acetonitrile, Cu-O = 2.09(4) [angstrom] in dimethyl sulfoxide, Cu-N = 2.06(1) [angstrom] in pyridine, and Cu-S = 2.30(1) [angstrom] in tetrahydrothiophene. The copper(II) solvates are most probably Jahn-Teller distorted octahedrons, and the following equatorial Cu-solvate bond distances have been found: Cu-N = 1.99(1) [angstrom] inmore » acetonitrile, and Cu-O = 1.98(1) [angstrom] in dimethyl sulfoxide. An 1.0 M solution of copper(II) trifluoromethanesulfonate in acetonitrile has been studied by means of the large-angle X-ray scattering technique, and the following Cu-N and Cu-C distances have been found for the Cu(CH[sub 3]CN)[sub 4][sup 2][sup +] complex: 1.99(1) and 3.12(1) [angstrom], respectively. No solvate molecules in the axial positions could however be seen by any of the technique used. The structure of the tetraaquacopper(I) ion has been assumed to be tetrahedral, and from a correlation between the difference in bond length between the copper(I) and copper(II) solvates and the disproportionation constants of copper(I) in the solvent, the Cu-O bond distance is predicted to be approximately 0.14 [angstrom] longer than the equatorial Cu-O distances in the Jahn-Teller distorted hexaaquacopper(II) complex, thus about 2.13 [angstrom].« less
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