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Lewis NHC, Dereka B, Zhang Y, Maginn EJ, Tokmakoff A. From Networked to Isolated: Observing Water Hydrogen Bonds in Concentrated Electrolytes with Two-Dimensional Infrared Spectroscopy. J Phys Chem B 2022; 126:5305-5319. [PMID: 35829623 DOI: 10.1021/acs.jpcb.2c03341] [Citation(s) in RCA: 7] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Superconcentrated electrolytes have emerged as a promising class of materials for energy storage devices, with evidence that high voltage performance is possible even with water as the solvent. Here, we study the changes in the water hydrogen bonding network induced by the dissolution of lithium bis(trifluoromethane sulfonyl)imide (LiTFSI) in concentrations ranging from the dilute to the superconcentrated regimes. Using time-resolved two-dimensional infrared spectroscopy, we observe the progressive disruption of the water-water hydrogen bond network and the appearance of isolated water molecules interacting only with ions, which can be identified and spectroscopically isolated through the intermolecular cross-peaks between the water and the TFSI- ions. Analyzing the vibrational relaxation of excitations of the H2O stretching mode, we observe a transition in the dominant relaxation path as the bulk-like water vanishes and is replaced by ion-solvation water with the rapid single-step relaxation of delocalized stretching vibrations into the low frequency modes being replaced by multistep relaxation through the intramolecular H2O bend and into the TFSI- high frequency modes prior to relaxing to the low frequency structural degrees of freedom. These results definitively demonstrate the absence of vibrationally bulk-like water in the presence of high concentrations of LiTFSI and especially in the superconcentrated regime, while additionally revealing aspects of the water hydrogen bond network that have been difficult to discern from the vibrational spectroscopy of the neat liquid.
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Affiliation(s)
- Nicholas H C Lewis
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, United States.,Joint Center for Energy Storage Research, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Bogdan Dereka
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, United States.,Joint Center for Energy Storage Research, Argonne National Laboratory, Lemont, Illinois 60439, United States
| | - Yong Zhang
- Joint Center for Energy Storage Research, Argonne National Laboratory, Lemont, Illinois 60439, United States.,Department of Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, Indiana 46556, United States
| | - Edward J Maginn
- Joint Center for Energy Storage Research, Argonne National Laboratory, Lemont, Illinois 60439, United States.,Department of Chemical and Biomolecular Engineering, University of Notre Dame, Notre Dame, Indiana 46556, United States
| | - Andrei Tokmakoff
- Department of Chemistry, James Franck Institute, and Institute for Biophysical Dynamics, The University of Chicago, Chicago, Illinois 60637, United States.,Joint Center for Energy Storage Research, Argonne National Laboratory, Lemont, Illinois 60439, United States
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Dhattarwal HS, Kashyap HK. Heterogeneity and Nanostructure of Superconcentrated LiTFSI-EmimTFSI Hybrid Aqueous Electrolytes: Beyond the 21 m Limit of Water-in-Salt Electrolyte. J Phys Chem B 2022; 126:5291-5304. [PMID: 35819799 DOI: 10.1021/acs.jpcb.2c02822] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Abstract
Ionic liquids such as EmimTFSI (1-ethyl-3-methylimidazolium bis(trifluoromethanesulfonyl)imide) have been found to improve the solubility of LiTFSI salt in water-in-salt electrolyte (WiSE) from 21 to 60 m. However, the molecular origin of such enhancement in the solubility is still unknown. In the present work, we elucidate the microscopic structures of LiTFSI-EmimTFSI-based hybrid aqueous electrolytes and compare them with the structure of LiTFSI-based WiSE using molecular dynamics simulations. Our analysis reveals the presence of alternating water-rich clusters and TFSI-rich extended domains in the WiSE. In these clusters and domains, the Li+ ions reside such that the total number of oxygen atoms around them is conserved to four, where water contributes about three oxygen atoms. The addition of EmimTFSI in the WiSE results in removal of water from the nearest-neighbor solvation shell of TFSI- ions but not from the Li+ ions. Significant structural changes are observed when LiTFSI salt is further added to LiTFSI-EmimTFSI aqueous solution. In both the hybrid electrolytes, water and Emim+ cations are found to avoid each other. The simulated X-ray scattering structure factor reveals the presence of larger length-scale heterogeneity in the most concentrated solution of the hybrid aqueous electrolyte. We observe that this nanoscale heterogeneity originates from a water-TFSI-Emim-TFSI-water-TFSI-Emim-TFSI-like arrangement in which Li+ ions are dispersed such that the coordination number of oxygen atoms around them is enhanced to five, wherein the major contribution comes from the TFSI- ions. We envision that the enhanced LiTFSI solubility originates from the replacement of water molecules with TFSI- ions in the first solvation shell of Li+ ions.
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Affiliation(s)
- Harender S Dhattarwal
- Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India
| | - Hemant K Kashyap
- Department of Chemistry, Indian Institute of Technology Delhi, Hauz Khas, New Delhi 110016, India
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Triolo A, Di Lisio V, Lo Celso F, Appetecchi GB, Fazio B, Chater P, Martinelli A, Sciubba F, Russina O. Liquid Structure of a Water-in-Salt Electrolyte with a Remarkably Asymmetric Anion. J Phys Chem B 2021; 125:12500-12517. [PMID: 34738812 PMCID: PMC9282637 DOI: 10.1021/acs.jpcb.1c06759] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
![]()
Water-in-salt
systems, i.e., super-concentrated aqueous electrolytes,
such as lithium bis(trifluoromethanesulfonyl)imide (21 mol/kgwater), have been recently discovered to exhibit unexpectedly
large electrochemical windows and high lithium transference numbers,
thus paving the way to safe and sustainable charge storage devices.
The peculiar transport features in these electrolytes are influenced
by their intrinsically nanoseparated morphology, stemming from the
anion hydrophobic nature and manifesting as nanosegregation between
anions and water domains. The underlying mechanism behind this structure–dynamics
correlation is, however, still a matter of strong debate. Here, we
enhance the apolar nature of the anions, exploring the properties
of the aqueous electrolytes of lithium salts with a strongly asymmetric
anion, namely, (trifluoromethylsulfonyl)(nonafluorobutylsulfonyl)
imide. Using a synergy of experimental and computational tools, we
detect a remarkable level of structural heterogeneity at a mesoscopic
level between anion-rich and water-rich domains. Such a ubiquitous
sponge-like, bicontinuous morphology develops across the whole concentration
range, evolving from large fluorinated globules at high dilution to
a percolating fluorous matrix intercalated by water nanowires at super-concentrated
regimes. Even at extremely concentrated conditions, a large population
of fully hydrated lithium ions, with no anion coordination, is detected.
One can then derive that the concomitant coexistence of (i) a mesoscopically
segregated structure and (ii) fully hydrated lithium clusters disentangled
from anion coordination enables the peculiar lithium diffusion features
that characterize water-in-salt systems.
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Affiliation(s)
- Alessandro Triolo
- Laboratorio Liquidi Ionici, Istituto Struttura della Materia, Consiglio Nazionale delle Ricerche (ISM-CNR), Rome 00133, Italy
| | - Valerio Di Lisio
- Department of Chemistry, University of Rome Sapienza, Rome 00185, Italy
| | - Fabrizio Lo Celso
- Laboratorio Liquidi Ionici, Istituto Struttura della Materia, Consiglio Nazionale delle Ricerche (ISM-CNR), Rome 00133, Italy.,Department of Physics and Chemistry, Università di Palermo, Palermo 90133, Italy
| | | | - Barbara Fazio
- Istituto Processi Chimico-Fisici, Consiglio Nazionale delle Ricerche (IPCF-CNR), Messina 98158, Italy
| | - Philip Chater
- Diamond House, Harwell Science & Innovation Campus, Diamond Light Source, Ltd., Didcot OX11 0DE, U.K
| | - Andrea Martinelli
- Department of Chemistry, University of Rome Sapienza, Rome 00185, Italy
| | - Fabio Sciubba
- Department of Chemistry, University of Rome Sapienza, Rome 00185, Italy.,NMR-Based Metabolomics Laboratory (NMLab), Sapienza University of Rome, Rome 00185, Italy
| | - Olga Russina
- Laboratorio Liquidi Ionici, Istituto Struttura della Materia, Consiglio Nazionale delle Ricerche (ISM-CNR), Rome 00133, Italy.,Department of Chemistry, University of Rome Sapienza, Rome 00185, Italy
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Kameda Y, Kowaguchi M, Tsutsui K, Amo Y, Usuki T, Ikeda K, Otomo T. Experimental Determination of Relationship between Intramolecular O-D Bond Length and Its Stretching Vibrational Frequency of D 2O Molecule in the Liquid State. J Phys Chem B 2021; 125:11285-11291. [PMID: 34605237 DOI: 10.1021/acs.jpcb.1c07527] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Experimental evidence has been obtained for the structure-spectra relationship of hydrogen bonds in aqueous solutions. Intramolecular O-D distance, rOD, has been determined by the least-squares fitting analysis of the neutron interference term in the high-Q region observed for pure D2O and concentrated aqueous solutions. The average O-D stretching frequency, νOD, has been obtained from the position of the center of gravity of the observed ATR-IR O-D stretching band. The linear relationship between rOD and νOD has been confirmed in the liquid state. The slope of dνOD/drOD is evaluated to be -21 000 ± 1000 cm-1 Å-1.
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Affiliation(s)
- Yasuo Kameda
- Department of Material and Biological Chemistry, Faculty of Science, Yamagata University, 1-4-12, Kojirakawa-machi, Yamagata City, Yamagata 990-8560, Japan
| | - Misaki Kowaguchi
- Department of Material and Biological Chemistry, Faculty of Science, Yamagata University, 1-4-12, Kojirakawa-machi, Yamagata City, Yamagata 990-8560, Japan
| | - Kana Tsutsui
- Department of Material and Biological Chemistry, Faculty of Science, Yamagata University, 1-4-12, Kojirakawa-machi, Yamagata City, Yamagata 990-8560, Japan
| | - Yuko Amo
- Department of Material and Biological Chemistry, Faculty of Science, Yamagata University, 1-4-12, Kojirakawa-machi, Yamagata City, Yamagata 990-8560, Japan
| | - Takeshi Usuki
- Department of Material and Biological Chemistry, Faculty of Science, Yamagata University, 1-4-12, Kojirakawa-machi, Yamagata City, Yamagata 990-8560, Japan
| | - Kazutaka Ikeda
- Institute of Material Structure Science, KEK, Tsukuba, Ibaraki 305-080, Japan
| | - Toshiya Otomo
- Institute of Material Structure Science, KEK, Tsukuba, Ibaraki 305-080, Japan
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