Superconcentrated aqueous electrolytes have recently emerged as a new class of electrolytes, called water-in-salt electrolytes. They are distinguished, in both weight and volume, by a quantity of salt greater than water. Currently, these electrolytes are attracting major interest, particularly for application in aqueous rechargeable batteries. These electrolytes have only a small amount of free water due to an ultrahigh salt concentration. Consequently, the electrochemical stability window of water is wider than the predicted thermodynamic value of 1.23 V. Hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) have been shown to be shifted to more negative and positive potentials, respectively. The decrease in free water population is recognized as being involved in the increase in the electrochemical stability window of water. Here, we study the quantitative contribution of the decrease in the free water molecule concentration to the permittivity of the solution and of the activity of water to the OER and HER overpotentials when the salt concentration increases. We compare our model with that of Kornyshev and get three types of electrolyte structures: diluted, gradient of water contents, and aggregation. The theoretical calculation of the redox potentials of the OER and HER is compared with the experimentally determined electrochemical properties of aqueous LiTFSI electrolytes.
REFERENCES
1.
M.
Marcinek
et al, “Electrolytes for Li-ion transport – Review
,” Solid State Ionics
276
, 107
–126
(2015
).2.
K.
Xu
, “Nonaqueous liquid electrolytes for lithium-based rechargeable batteries
,” Chem. Rev.
104
(10
), 4303
–4418
(2004
).3.
Y.
Yamada
and A.
Yamada
, “Review—Superconcentrated electrolytes for lithium batteries
,” J. Electrochem. Soc.
162
, A2406
–A2423
(2015
).4.
L.
Suo
et al, “A new class of Solvent-in-Salt electrolyte for high-energy rechargeable metallic lithium batteries
,” Nat. Commun.
4
, 1481
(2013
).5.
L.
Suo
et al, “‘Water-in-salt’ electrolyte enables high-voltage aqueous lithium-ion chemistries
,” Science
350
(6263
), 938
–943
(2015
).6.
L.
Suo
et al, “‘Water-in-salt’ electrolytes enable green and safe Li-ion batteries for large scale electric energy storage applications
,” J. Mater. Chem. A
4
, 6639
–6644
(2016
).7.
W.
Sun
et al, “‘Water-in-salt’ electrolyte enabled LiMn2O4/TiS2 lithium-ion batteries
,” Electrochem. Commun.
82
, 71
–74
(2017
).8.
A.
Eftekhari
, “High-energy aqueous lithium batteries
,” Adv. Energy Mater.
8
, 1801156
–1801171
(2018
).9.
C.
Yang
et al, “4.0 V aqueous Li-ion batteries
,” Joule
1
(1
), 122
–132
(2017
).10.
L.
Smith
and B.
Dunn
, “Opening the window for aqueous electrolytes
,” Science
350
(6263
), 918
(2015
).11.
Y.
Yokoyama
et al, “Origin of the electrochemical stability of aqueous concentrated electrolyte solutions
,” J. Electrochem. Soc.
165
(14
), A3299
–A3303
(2018
).12.
J.
Zheng
et al, “Research progress towards understanding the unique interfaces between concentrated electrolytes and electrodes for energy storage applications
,” Adv. Sci.
4
(8
), 1700032
(2017
).13.
L.
Coustan
, G.
Shul
, and D.
Bélanger
, “Electrochemical behavior of platinum, gold and glassy carbon electrodes in water-in-salt electrolyte
,” Electrochem. Commun.
77
, 89
–92
(2017
).14.
L.
Coustan
, K.
Zaghib
, and D.
Bélanger
, “New insight in the electrochemical behaviour of stainless steel electrode in water-in-salt electrolyte
,” J. Power Sources
399
, 299
–303
(2018
).15.
N.
Dubouis
et al, “The role of the hydrogen evolution reaction in the solid–electrolyte interphase formation mechanism for “Water-in-Salt” electrolytes
,” Energy Environ. Sci.
11
, 3491
–3499
(2018
).16.
R.
Bouchal
et al, “Competitive salt precipitation/dissolution during free-water reduction in water-in-salt electrolyte
,” Angew. Chem., Int. Ed.
59
, 15913
–15917
(2020
).17.
Y.
Yamada
and A.
Yamada
, “Superconcentrated electrolytes to create new interfacial chemistry in non-aqueous and aqueous rechargeable batteries
,” Chem. Lett.
46
(8
), 1056
–1064
(2017
).18.
Z.
Li
et al, “Transport properties of Li-TFSI water-in-salt electrolytes
,” J. Phys. Chem. B
123
(49
), 10514
–10521
(2019
).19.
W. J.
Hamer
and Y. C.
Wu
, “Osmotic coefficients and mean activity coefficients of uni‐univalent electrolytes in water at 25 °C
,” J. Phys. Chem. Ref. Data
1
(4
), 1047
–1100
(1972
).20.
E.
Glueckauf
, “The influence of ionic hydration on activity coefficients in concentrated electrolyte solutions
,” Trans. Faraday Soc.
53
, 305
(1957
).21.
M.
Krummen
, D.
Gruber
, and J.
Gmehling
, “Measurement of activity coefficients at infinite dilution in solvent mixtures using the dilutor technique
,” Ind. Eng. Chem. Res.
39
(6
), 2114
–2123
(2000
).22.
H.
Maki
et al, “Quantitative analysis of water activity related to hydration structure in highly concentrated aqueous electrolyte solutions
,” Electrochemistry
87
(3
), 139
–141
(2019
).23.
J. B.
Hasted
, D. M.
Ritson
, and C. H.
Collie
, “Dielectric properties of aqueous ionic solutions. Parts I and II
,” J. Chem. Phys.
16
(1
), 1
–21
(1948
).24.
J.-B.
Cazier
and V.
Gekas
, “Water activity and its prediction: A review
,” Int. J. Food Prop.
4
(1
), 35
–43
(2001
).25.
M. J.
Blandamer
et al, “Activity of water in aqueous systems; A frequently neglected property
,” Chem. Soc. Rev.
34
(5
), 440
–458
(2005
).26.
Y.
Zhu
et al, “Exploring the role of redox mediator within mesoporous carbon using Thionine and LiTFSI water-in-salt electrolytes
,” Energy Storage Mater.
55
, 808
–815
(2023
).27.
F.
Miomandre
et al, Électrochimie: Des concepts aux applications - Cours et exercices corrigés
, 3 éme ed
(DUNOD
, 2014
).28.
T. F.
Burton
et al, “Water-in-salt electrolytes towards sustainable and cost-effective alternatives: Example for zinc-ion batteries
,” Curr. Opin. Electrochem.
35
, 101070
(2022
).29.
S.
Schlumpberger
and M.
Bazant
, Simple Theory of Ionic Activity in Concentrated Electrolytes
arXiv:1709.03106
(2017
).30.
Nobel Foundation
, Nobel Lectures, Chemistry 1901–1921
(Elsevier Publishing Company
, Amsterdam
, 1966), p. 196
.31.
W. R.
Fawcett
, Liquids, Solutions, and Interfaces: From Classical Macroscopic Descriptions to Modern Microscopic Details
(Oxford University Press
, 2004
), p. 621
.32.
Q.
Nguyen
et al, “Comparative analysis of fluorinated anions for polypyrrole linear actuator electrolytes
,” Polymers
11
, 849
(2019
).33.
G.
Orädd
, L.
Edman
, and A.
Ferry
, “Diffusion: A comparison between liquid and solid polymer LiTFSI electrolytes
,” Solid State Ionics
152–153
, 131
–136
(2002
).34.
L.
Wang
et al, “Anion effects on the solvation structure and properties of imide lithium salt-based electrolytes
,” RSC Adv.
9
(71
), 41837
–41846
(2019
).35.
A.
von Wald Cresce
et al, “Anion solvation in carbonate-based electrolytes
,” J. Phys. Chem. C
119
(49
), 27255
–27264
(2015
).36.
Y.
Zhang
et al, “Investigation of ion–solvent interactions in nonaqueous electrolytes using in situ liquid SIMS
,” Anal. Chem.
90
(5
), 3341
–3348
(2018
).37.
S. B.
Rempe
et al, “The hydration number of Li+ in liquid water
,” J. Am. Chem. Soc.
122
(5
), 966
–967
(2000
).38.
Y.
Zeng
et al, “Solvation structure and dynamics of Li+ ion in liquid water, methanol and ethanol: A comparison study
,” Chem. Phys.
433
, 89
–97
(2014
).39.
P.
Lannelongue
et al, “‘Water-in-salt’ for supercapacitors: A compromise between voltage, power density, energy density and stability
,” J. Electrochem. Soc.
165
(3
), A657
–A663
(2018
).40.
L.
Suo
et al, “Advanced high-voltage aqueous lithium-ion battery Enabled by ‘water-in-bisalt’ electrolyte
,” Angew. Chem.
55
(25
), 7136
–7141
(2016
).41.
G. G.
Stokes
, Trans. Cambridge Philos. Soc.
9
, 5
(1856
).42.
43.
M.
Salomon
, “Conductance of solutions of lithium bis(trifluoromethanesulfone)imide in water, propylene carbonate, acetonitrile and methyl formate at 25 °C
,” J. Solution Chem.
22
(8
), 715
–725
(1993
).44.
J.
Vincze
, M.
Valiskó
, and D.
Boda
, “The nonmonotonic concentration dependence of the mean activity coefficient of electrolytes is a result of a balance between solvation and ion-ion correlations
,” J. Chem. Phys.
133
(15
), 154507
(2010
).45.
B.
Pal
et al, “Electrolyte selection for supercapacitive devices: A critical review
,” Nanoscale Adv.
1
(10
), 3807
–3835
(2019
).46.
D. E.
Goldsack
, R.
Franchetto
, and A.
Franchetto
, “Solvation effects on the conductivity of concentrated electrolyte solutions
,” Can. J. Chem.
54
(18
), 2953
–2966
(1976
).47.
L.
Wang
, K.
Uosaki
, and H.
Noguchi
, “Effect of electrolyte concentration on the solvation structure of gold/LITFSI–DMSO solution interface
,” J. Phys. Chem. C
124
(23
), 12381
–12389
(2020
).48.
J.
Tong
et al, “The effect of concentration of lithium salt on the structural and transport properties of ionic liquid-based electrolytes
,” Front. Chem.
7
, 945
(2020
).49.
M.
Ue
, “Mobility and ionic association of lithium and quaternary ammonium salts in propylene carbonate and γ-butyrolactone
,” J. Electrochem. Soc.
141
(12
), 3336
(1994
).50.
J.
Chidiac
, L.
Timperman
, and M.
Anouti
, “Salt and solvent effect on physicochemical properties and species organisation of Lithium fluorosulfonyl imide (FSI and TFSI) based electrolytes for Li-ion battery: Consequence on cyclability of LiNi0.8Co0.15Al0.05 (NCA) cathode
,” J. Taiwan Inst. Chem. Eng.
126
, 88
–101
(2021
).51.
M. T.
Ong
et al, “Lithium ion solvation and diffusion in bulk organic electrolytes from first-principles and classical reactive molecular dynamics
,” J. Phys. Chem. B
119
(4
), 1535
–1545
(2015
).52.
R.
Evans
et al, “Quantitative interpretation of diffusion-ordered NMR spectra: Can we rationalize small molecule diffusion coefficients?
,” Angew. Chem., Int. Ed.
52
(11
), 3199
–3202
(2013
).53.
R.
Evans
, “The interpretation of small molecule diffusion coefficients: Quantitative use of diffusion-ordered NMR spectroscopy
,” Prog. Nucl. Magn. Reson. Spectrosc.
117
, 33
–69
(2020
).54.
H.
Moon
et al, “Solvent activity in electrolyte solutions controls electrochemical reactions in Li-ion and Li-sulfur batteries
,” J. Phys. Chem. C
119
(8
), 3957
–3970
(2015
).55.
A.
Levy
, M.
Bazant
, and A.
Kornyshev
, “Ionic activity in concentrated electrolytes: Solvent structure effect revisited
,” Chem. Phys. Lett.
738
, 136915
(2020
).56.
W. R.
Fawcett
and A. C.
Tikanen
, “Role of solvent permittivity in estimation of electrolyte activity coefficients on the basis of the mean spherical approximation
,” J. Phys. Chem.
100
(10
), 4251
–4255
(1996
).57.
R.
Buchner
, G. T.
Hefter
, and P. M.
May
, “Dielectric relaxation of aqueous NaCl solutions
,” J. Phys. Chem. A
103
(1
), 1
–9
(1999
).58.
R.
Renou
et al, “Concentration dependence of the dielectric permittivity, structure, and dynamics of aqueous NaCl solutions: Comparison between the drude oscillator and electronic continuum models
,” J. Phys. Chem. B
118
(14
), 3931
–3940
(2014
).59.
A. C.
Tikanen
and W. R.
Fawcett
, “The role of solvent permittivity in estimation of electrolyte activity coefficients for systems with ion pairing on the basis of the mean spherical approximation
,” Ber. Bunsengesellschaft Phys. Chem.
100
(5
), 634
–640
(1996
).60.
I. Y.
Shilov
and A. K.
Lyashchenko
, “The role of concentration dependent static permittivity of electrolyte solutions in the Debye–Hückel theory
,” J. Phys. Chem. B
119
(31
), 10087
–10095
(2015
).61.
P.
Wang
and A.
Anderko
, “Computation of dielectric constants of solvent mixtures and electrolyte solutions
,” Fluid Phase Equilib.
186
(1–2
), 103
–122
(2001
).62.
A. A.
Kornyshev
, “Nonlocal screening of ions in a structurized polar liquid—new aspects of solvent description in electrolyte theory
,” Electrochim. Acta
26
(1
), 1
–20
(1981
).63.
M.
McEldrew
et al, “Theory of ion aggregation and gelation in super-concentrated electrolytes
,” J. Chem. Phys.
152
(23
), 234506
(2020
).64.
Y.
Yamada
et al, “Hydrate-melt electrolytes for high-energy-density aqueous batteries
,” Nat. Energy
1
, 16129
(2016
).65.
F.
Moučka
, I.
Nezbeda
, and W. R.
Smith
, “Molecular simulation of aqueous electrolytes: Water chemical potential results and Gibbs-Duhem equation consistency tests
,” J. Chem. Phys.
139
(12
), 124505
(2013
).66.
R. H.
Stokes
and R. A.
Robinson
, “Ionic hydration and activity in electrolyte solutions
,” J. Am. Chem. Soc.
70
(5
), 1870
–1878
(1948
).67.
G.
Feng
et al, “Water in ionic liquids at electrified interfaces: The anatomy of electrosorption
,” ACS Nano
8
(11
), 11685
–11694
(2014
).68.
S.
Bi
et al, “Minimizing the electrosorption of water from humid ionic liquids on electrodes
,” Nat. Commun.
9
(1
), 5222
(2018
).69.
W. M.
Haynes
, CRC Handbook of Chemistry and Physics
(CRC Press
, 2022), p. 97
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