Volumetric and viscosity properties of water-in-salt lithium electrolytes: A comparison with ionic liquids and hydrated molten salts

Horwitz, Gabriela; Steinberg, Paula Y.; Corti, Horacio R.

doi:10.1016/j.jct.2021.106457

Cited by 8 publications

(8 citation statements)

References 56 publications

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“…This was done taking into account the partial molar volume of the water and the volume of the hypothetical supercooled salt, V 2ss . Mixtures of LiTf, LiTFSI, or LiTFSI m + LiTf m /3 with water have been shown to behave ideally regarding its volumetric properties, following the linear relation where V m is the molar volume of the solution and x is the molar fraction of the salt. By extrapolation to x = 1, the value of V 2ss , which is an intrinsic property of each salt, can be obtained.…”

Section: Resultsmentioning

confidence: 99%

“…To validate this approximation, a simple calculation can be done using the intrinsic volume of the Li + ion. Assuming that the partial molar volume of the heavy water does not significantly change by the addition of Li + ions, which is reasonable in the case of these WiS, 25 the influence of the Li + in the phase's volume can be estimated using its ionic radius. Even if we consider the extreme scenario of a 21 m solution, and we assume that all Li + ions are in the water-rich phase, which would lead to a D 2 O:Li + relation of 2.3:1, the enhancement of the molar volume of such a phase would only be around 3%.…”

Section: The Teubner−strey Modelmentioning

confidence: 99%

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The Nanostructure of Water-in-Salt Electrolytes Revisited: Effect of the Anion Size

et al. 2021

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The increasing interest in developing safe and sustainable energy storage systems has led to the rapid rise in attention to superconcentrated electrolytes, commonly called water-in-salt (WiS). Several works indicate that the transport properties of these liquid electrolytes are related to the presence of nanodomains, but a detailed characterization of such structure is missing. Here, the structural nano-heterogeneity of lithium WiS electrolytes, comprising lithium trifluoromethanesulfonate (LiTf) and bis(trifluoromethanesulfonyl)imide (LiTFSI) solutions as a function of concentration and temperature, was assessed by resorting to the analysis of small-angle neutron scattering (SANS) patterns. Variations with the concentration of a correlation peak, rather temperature-independent, in a Q range around 3.5−5 nm −1 indicate that these electrolytes are composed of nanometric water-rich channels percolating a 3D dispersing anion-rich network, with differences between Tf and TFSI anions related to their distinct volumes and interactions. Furthermore, a common trend was found for both systems' morphology above a salt volume fraction of ∼0.5. These results imply that the determining factor in the formation of the nanostructure is the salt volume fraction (related to the anion size), rather than its molality. These findings may represent a paradigm shift for designing WiS electrolytes.

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Section: Resultsmentioning

confidence: 99%

Section: The Teubner−strey Modelmentioning

confidence: 99%

The Nanostructure of Water-in-Salt Electrolytes Revisited: Effect of the Anion Size

et al. 2021

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“…LiTFSI was proposed as an electrolyte for aqueous lithium-ion batteries by Lux et al, 44 and its high concentration mixtures (c > 15 m) show interesting conductivity performances (5−10 mS/cm) 18 and an appreciable electrochemical stability, at least up to 2 V. 1 Nowadays, different options alternative to the LiTFSI-H 2 O WiS are being considered to enhance the resulting performance, including exploring Na-and K-based WiS 2,5,7,8,14,20,45−47 or exploiting asymmetric anions and anion mixtures (leading to the so-called water in bisalt systems). 6,9,12,16,24,45,48,49 Here, we explore an aqueous electrolyte system with a salt that is characterized by a remarkably asymmetric anion, i.e., a lithium salt with the anion being a member of the family of di(perfluoroalkyl-sulfonyl)imide, namely (trifluoromethylsulfonyl) (nonafluorobutylsulfonyl)imide (hereinafter indicated as [IM14]) (see Scheme 1). The high asymmetry of this anion makes it an ideal species to pair with cations that are prone to crystallization when paired with more conventional anions.…”

Section: ■ Introductionmentioning

confidence: 99%

“…LiTFSI was proposed as an electrolyte for aqueous lithium-ion batteries by Lux et al, and its high concentration mixtures ( c > 15 m) show interesting conductivity performances (5–10 mS/cm) and an appreciable electrochemical stability, at least up to 2 V . Nowadays, different options alternative to the LiTFSI-H 2 O WiS are being considered to enhance the resulting performance, including exploring Na- and K-based WiS ,,,,,,− or exploiting asymmetric anions and anion mixtures (leading to the so-called water in bisalt systems). ,,,,,,, …”

Section: Introductionmentioning

confidence: 99%

Liquid Structure of a Water-in-Salt Electrolyte with a Remarkably Asymmetric Anion

et al. 2021

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Water-in-salt systems, i.e., super-concentrated aqueous electrolytes, such as lithium bis(trifluoromethanesulfonyl)imide (21 mol/kg water ), 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 spongelike, 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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“…Therefore, free water molecules for hydrogen and oxygen evolution reactions are negligible. The absence of free water molecules resulted in an enhancement of the redox stability of aqueous LiTFSI electrolytes and a significant increase in the ESW. ,, Our study focused on widening the ESW of LiTFSI electrolytes with relatively low LiTFSI concentrations. GLY has three hydroxyl groups in its structure and is miscible with water.…”

Section: Resultsmentioning

confidence: 99%

A High-Voltage Gel Electrolyte with a Low Salt Concentration for Quasi-Solid-State Flexible Supercapacitors

et al. 2022

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Safe and eco-friendly aqueous electrolytes with wide electrochemical stability windows (ESWs) and wide temperature operating windows play a vital role in the development of high-energy and sustainable energy storage devices. In this study, we demonstrate a gel-type aqueous lithium bis-trifluoromethanesulfonimide (LiTFSI) electrolyte using glycerol as a cosolvent and polyvinyl alcohol (PVA) as a gel-forming agent. Adding watermiscible glycerol and PVA greatly decreases the number of "free" water molecules due to the H-bond interactions between water− glycerol and water−PVA molecules and suppresses the water splitting reaction. Thus, the ESW of aqueous electrolytes with low LiTFSI concentrations is significantly extended. Gel-type electrolytes with a low LiTFSI concentration of only 2m can achieve an ESW of 3.0 V, which is equivalent to an ESW value of 21m for LiTFSI aqueous solution without glycerol and PVA (superconcentrated or "water-in-salt" LiTFSI electrolyte). In addition, the temperature operating window is from −20 to +60 °C, which is much wider compared to that of the liquid 21m LiTFSI electrolyte. We assemble quasi-solid-state flexible supercapacitors using carbon nanotube sponge as the electrode and a gel-type LiTFSI electrolyte. The quasi-solid-state supercapacitors exhibit an actual operational voltage of 2.4 V, excellent flexibility, thermal stability, and good electrochemical performance at a low LiTFSI concentration in electrolytes.

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Volumetric and viscosity properties of water-in-salt lithium electrolytes: A comparison with ionic liquids and hydrated molten salts

Cited by 8 publications

References 56 publications

The Nanostructure of Water-in-Salt Electrolytes Revisited: Effect of the Anion Size

The Nanostructure of Water-in-Salt Electrolytes Revisited: Effect of the Anion Size

Liquid Structure of a Water-in-Salt Electrolyte with a Remarkably Asymmetric Anion

A High-Voltage Gel Electrolyte with a Low Salt Concentration for Quasi-Solid-State Flexible Supercapacitors

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