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Title: Electrolyte Stability and Discharge Products of an Ionic-Liquid-Based Li–O2 Battery Revealed by Soft X-Ray Emission Spectroscopy

Abstract

Here, we explore the electrolyte stability and discharge products of an ionic-liquid-based Li–O2 battery through soft X-ray emission spectroscopy (XES) experiments, which offer unique site specificity for detecting subtle changes in the local nitrogen and oxygen environment. We benchmark the valence electronic structures of the molecules composing the electrolyte, namely the solvent PP13(TFSI), the salt LiTFSI, and the PP13 cation. Then, the transformation of the electrolyte is shown using cathodes stopped at different discharge and charge stages. We provide experimental evidence that the nitrogen site of the salt is unstable during electrochemical operation. The chemical environment of the nitrogen atoms is gradually changed during the electrochemical cycle, indicating the breaking of S–N bonds. The ionic liquid solvent remains mostly as an ion pair, but some decomposition into PP13 cations and TFSI anions cannot be ruled out. These findings and detailed analysis also show that the discharge products in our cell consist of lithium peroxide with some amount of hydroxide; however, no carbonate is observed.

Authors:
ORCiD logo [1];  [1];  [2]; ORCiD logo [3]; ORCiD logo [4]; ORCiD logo [1]; ORCiD logo [1];  [5]; ORCiD logo [5]
  1. Karlsruhe Inst. of Technology (KIT) (Germany)
  2. Univ. of Nevada, Las Vegas, NV (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Advanced Light Source (ALS)
  3. Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States). Advanced Light Source (ALS)
  4. Helmholtz-Zentrum Berlin (HZB), (Germany). German Research Centre for Materials and Energy; Helmholtz-Inst. Erlangen-Nürnberg for Renewable Energy (HI ERN), Berlin (Germany); Univ. of Erlangen-Nuremberg (Germany)
  5. Karlsruhe Inst. of Technology (KIT) (Germany); Univ. of Nevada, Las Vegas, NV (United States)
Publication Date:
Research Org.:
Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
OSTI Identifier:
1594943
Grant/Contract Number:  
AC02-05CH11231
Resource Type:
Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. C
Additional Journal Information:
Journal Volume: 123; Journal Issue: 51; Journal ID: ISSN 1932-7447
Publisher:
American Chemical Society
Country of Publication:
United States
Language:
English
Subject:
25 ENERGY STORAGE; Salts; Electrodes; Solvents; Electrolytes; Lithium

Citation Formats

Léon, Aline, Fiedler, Andy, Blum, Monika, Yang, Wanli, Bär, Marcus, Scheiba, Frieder, Ehrenberg, Helmut, Heske, Clemens, and Weinhardt, Lothar. Electrolyte Stability and Discharge Products of an Ionic-Liquid-Based Li–O2 Battery Revealed by Soft X-Ray Emission Spectroscopy. United States: N. p., 2019. Web. doi:10.1021/acs.jpcc.9b08777.
Léon, Aline, Fiedler, Andy, Blum, Monika, Yang, Wanli, Bär, Marcus, Scheiba, Frieder, Ehrenberg, Helmut, Heske, Clemens, & Weinhardt, Lothar. Electrolyte Stability and Discharge Products of an Ionic-Liquid-Based Li–O2 Battery Revealed by Soft X-Ray Emission Spectroscopy. United States. doi:10.1021/acs.jpcc.9b08777.
Léon, Aline, Fiedler, Andy, Blum, Monika, Yang, Wanli, Bär, Marcus, Scheiba, Frieder, Ehrenberg, Helmut, Heske, Clemens, and Weinhardt, Lothar. Thu . "Electrolyte Stability and Discharge Products of an Ionic-Liquid-Based Li–O2 Battery Revealed by Soft X-Ray Emission Spectroscopy". United States. doi:10.1021/acs.jpcc.9b08777. https://www.osti.gov/servlets/purl/1594943.
@article{osti_1594943,
title = {Electrolyte Stability and Discharge Products of an Ionic-Liquid-Based Li–O2 Battery Revealed by Soft X-Ray Emission Spectroscopy},
author = {Léon, Aline and Fiedler, Andy and Blum, Monika and Yang, Wanli and Bär, Marcus and Scheiba, Frieder and Ehrenberg, Helmut and Heske, Clemens and Weinhardt, Lothar},
abstractNote = {Here, we explore the electrolyte stability and discharge products of an ionic-liquid-based Li–O2 battery through soft X-ray emission spectroscopy (XES) experiments, which offer unique site specificity for detecting subtle changes in the local nitrogen and oxygen environment. We benchmark the valence electronic structures of the molecules composing the electrolyte, namely the solvent PP13(TFSI), the salt LiTFSI, and the PP13 cation. Then, the transformation of the electrolyte is shown using cathodes stopped at different discharge and charge stages. We provide experimental evidence that the nitrogen site of the salt is unstable during electrochemical operation. The chemical environment of the nitrogen atoms is gradually changed during the electrochemical cycle, indicating the breaking of S–N bonds. The ionic liquid solvent remains mostly as an ion pair, but some decomposition into PP13 cations and TFSI anions cannot be ruled out. These findings and detailed analysis also show that the discharge products in our cell consist of lithium peroxide with some amount of hydroxide; however, no carbonate is observed.},
doi = {10.1021/acs.jpcc.9b08777},
journal = {Journal of Physical Chemistry. C},
number = 51,
volume = 123,
place = {United States},
year = {2019},
month = {11}
}

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