Origin of Unusual Acidity and Li+ Diffusivity in a Series of Water-in-Salt Electrolytes
Abstract
Super-concentrated aqueous electrolytes (‘water-in-salt’ electrolytes, or WiSE) enable various aqueous battery chemistries beyond the voltage limits imposed by the Pourbaix diagram of water. However, their detailed structural and transport properties remain unexplored and could be better understood through added studies. Here, we report on our observations of strong acidity (pH = 2.4) induced by lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) at super-concentration (at 20 mol/g). Multiple nuclear magnetic resonance (NMR), pulsed-field gradient (PFG) diffusion NMR experiments, density functional theory (DFT) calculations, and molecular dynamics (MD) simulations reveal that such acidity originates from the formation of nanometric ion-rich structures. The experimental and simulation results indicate the separation of water-rich and ion-rich domains at salt concentrations = 5 m and the acidity arising therefrom are due to deprotonation of water mole-cules in the ion-rich domains. As such, the ion-rich domain is composed of hydrophobic -CF3 (of TFSI-) and hydrophilic hydroxyl (OH-) groups. At 20 m concentration, the tortuosity and radius of water diffusion channels are estimated to be ~10 and ~1 nm, respectively, which are close to values obtained from hydrated Nafion® membranes that also have hydrophobic polytetrafluoroethylene (PTFE) backbones and hydrophilic channels consisting of a SO3- ion cluster networks providing for the transportmore »
- Authors:
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[1];
[2];
[2];
[1];
[1];
[2];
[2];
[1];
[1]
- Pacific Northwest National Lab. (PNNL), Richland, WA (United States); Argonne National Lab. (ANL), Argonne, IL (United States). Joint Center for Energy Storage Research (JCESR)
- Argonne National Lab. (ANL), Argonne, IL (United States). Joint Center for Energy Storage Research (JCESR)
- Argonne National Lab. (ANL), Argonne, IL (United States). Joint Center for Energy Storage Research (JCESR); Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Argonne National Lab. (ANL), Argonne, IL (United States). Joint Center for Energy Storage Research (JCESR); Army Research Lab., Adelphi, MD (United States)
- Publication Date:
- Research Org.:
- Argonne National Lab. (ANL), Argonne, IL (United States); Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
- Sponsoring Org.:
- USDOE Office of Science (SC), Basic Energy Sciences (BES)
- OSTI Identifier:
- 1635536
- Alternate Identifier(s):
- OSTI ID: 1646623
- Report Number(s):
- PNNL-SA-151945
Journal ID: ISSN 1520-6106; 160701
- Grant/Contract Number:
- AC02-06CH11357; AC05-76RL01830
- Resource Type:
- Accepted Manuscript
- Journal Name:
- Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical Chemistry
- Additional Journal Information:
- Journal Volume: 124; Journal Issue: 25; Journal ID: ISSN 1520-6106
- Publisher:
- American Chemical Society
- Country of Publication:
- United States
- Language:
- English
- Subject:
- 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; Salts; Diffusion; Electrolytes; Molecules; Ions
Citation Formats
Han, Kee Sung, Yu, Zhou, Wang, Hui, Redfern, Paul C., Ma, Lin, Cheng, Lei, Chen, Ying, Hu, Jian Zhi, Curtiss, Larry A., Xu, Kang, Murugesan, Vijayakumar, and Mueller, Karl T. Origin of Unusual Acidity and Li+ Diffusivity in a Series of Water-in-Salt Electrolytes. United States: N. p., 2020.
Web. doi:10.1021/acs.jpcb.0c02483.
Han, Kee Sung, Yu, Zhou, Wang, Hui, Redfern, Paul C., Ma, Lin, Cheng, Lei, Chen, Ying, Hu, Jian Zhi, Curtiss, Larry A., Xu, Kang, Murugesan, Vijayakumar, & Mueller, Karl T. Origin of Unusual Acidity and Li+ Diffusivity in a Series of Water-in-Salt Electrolytes. United States. https://doi.org/10.1021/acs.jpcb.0c02483
Han, Kee Sung, Yu, Zhou, Wang, Hui, Redfern, Paul C., Ma, Lin, Cheng, Lei, Chen, Ying, Hu, Jian Zhi, Curtiss, Larry A., Xu, Kang, Murugesan, Vijayakumar, and Mueller, Karl T. Tue .
"Origin of Unusual Acidity and Li+ Diffusivity in a Series of Water-in-Salt Electrolytes". United States. https://doi.org/10.1021/acs.jpcb.0c02483. https://www.osti.gov/servlets/purl/1635536.
@article{osti_1635536,
title = {Origin of Unusual Acidity and Li+ Diffusivity in a Series of Water-in-Salt Electrolytes},
author = {Han, Kee Sung and Yu, Zhou and Wang, Hui and Redfern, Paul C. and Ma, Lin and Cheng, Lei and Chen, Ying and Hu, Jian Zhi and Curtiss, Larry A. and Xu, Kang and Murugesan, Vijayakumar and Mueller, Karl T.},
abstractNote = {Super-concentrated aqueous electrolytes (‘water-in-salt’ electrolytes, or WiSE) enable various aqueous battery chemistries beyond the voltage limits imposed by the Pourbaix diagram of water. However, their detailed structural and transport properties remain unexplored and could be better understood through added studies. Here, we report on our observations of strong acidity (pH = 2.4) induced by lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) at super-concentration (at 20 mol/g). Multiple nuclear magnetic resonance (NMR), pulsed-field gradient (PFG) diffusion NMR experiments, density functional theory (DFT) calculations, and molecular dynamics (MD) simulations reveal that such acidity originates from the formation of nanometric ion-rich structures. The experimental and simulation results indicate the separation of water-rich and ion-rich domains at salt concentrations = 5 m and the acidity arising therefrom are due to deprotonation of water mole-cules in the ion-rich domains. As such, the ion-rich domain is composed of hydrophobic -CF3 (of TFSI-) and hydrophilic hydroxyl (OH-) groups. At 20 m concentration, the tortuosity and radius of water diffusion channels are estimated to be ~10 and ~1 nm, respectively, which are close to values obtained from hydrated Nafion® membranes that also have hydrophobic polytetrafluoroethylene (PTFE) backbones and hydrophilic channels consisting of a SO3- ion cluster networks providing for the transport of ions and water. Thus we have discovered the structural similarity between WiSE and hydrated Nafion® membrane on the nano-meter scale.},
doi = {10.1021/acs.jpcb.0c02483},
journal = {Journal of Physical Chemistry. B, Condensed Matter, Materials, Surfaces, Interfaces and Biophysical Chemistry},
number = 25,
volume = 124,
place = {United States},
year = {Tue Jun 02 00:00:00 EDT 2020},
month = {Tue Jun 02 00:00:00 EDT 2020}
}
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