Mobility-viscosity decoupling and cation transport in water-in-salt lithium electrolytes

Horwitz, Gabriela; Rodríguez, Cristian; Steinberg, Paula Y.; Burton, Gerardo; Corti, Horacio R.

doi:10.1016/j.electacta.2020.136915

Cited by 30 publications

(43 citation statements)

References 54 publications

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“…One possible explanation for the surprising temperature dependence of the Nernst-Einstein ratio presented in Figure 4 is a pronounced decoupling of the conductivity and viscosity arising from ioncorrelations and non-classical ion-transport mechanisms, as discussed in prior works. 4,64 This agrees with a developing body of work that suggests alternative meanings to the free ion fraction interpretation based on ionic correlations, the presence of charge transfer events, or proton transfer in protic ionic liquids, 52,[65][66][67][68] which may contribute to different temperature dependencies of conductivity and viscosity.…”

Section: Discussionsupporting

confidence: 83%

“…Walden and Nernst-Einstein plots have been used to suggest that ionic liquids should always have lower conductivities than their viscosities imply. 4,[6][7][8] This implication is, in part, based on publications which have expanded understanding of how features such as ion-polarity, concentration, temperature, and other features influence the deviation of ionic liquids and ionic liquid solutions from conductivity-viscosity models, where measured molar conductivities are often thought to be lower than predicted conductivities. Deviation from these conductivity-viscosity scaling relationships in ionic liquids are commonly rationalized from the perspective of the ionicity framework.…”

Section: Discussionmentioning

confidence: 99%

“…Increasingly, liquid electrolytes with extremely high ion concentrations and solid-state electrolytes are explored to increase battery safety and efficiency. An emerging paradigm is that these materials enhance batteries by facilitating ion-selective transport, [1][2][3][4] which increases the reversibility of battery charge cycles. [5][6][7] Further, super-concentrated and solid state electrolytes have greatly enhanced thermal and electrochemical stability relative to conventional organic electrolytes.…”

Section: Introductionmentioning

confidence: 99%

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Bridging Database Analysis with Microrheology to Reveal Super-Hydrodynamic Conductivity Scaling Regimes in Ionic Liquids

Cashen

Donoghue

Schmeiser

et al. 2022

Preprint

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Ion transport through electrolytes critically impacts the performance of batteries and other electrochemical devices. Many frameworks used to predict and tune ion transport, such as the Nernst-Einstein model, assume hydrodynamic transport mechanisms, and hence focus on maximizing electrolyte conductivity by minimizing bulk viscosity. However, the emergence of solid-state electrolytes illustrates that selective, non-hydrodynamic ion transport provides promising avenues for enhancing ionic transport in electrolytes. Increasingly, selective ion transport mechanisms, such as hopping, are proposed for concentrated electrolytes, including ionic liquid-derived materials. Yet viscosity-conductivity scaling relationships in ionic liquids are still often analyzed with hydrodynamic models. Here, we report a data-centric analysis of how well hydrodynamic transport models describe the scaling between viscosity and conductivity in neat ionic liquids by merging three databases to bridge physical properties and chemical descriptors. With this expansive data set, we constrained our scaling analysis using ion sizes defined using simulated molecular volumes, as opposed to prior approaches that estimate sizes from activity coefficients or rely on ad-hoc estimates. Remarkably, we find that many commonly studied ionic liquids exhibit positive deviations from the Nernst-Einstein model, implying that ions move faster than hydrodynamic limitations should allow. We experimentally verify these positive deviations in a common class of ionic liquids using microrheology and conductivity measurements. Our results highlight overlooked super-hydrodynamic regimes in ionic liquid viscosity-conductivity scaling and point to opportunities to understand mechanisms of correlated ion motion in ionic liquids. We further show data science and machine learning tools can improve predictions of conductivity from molecular properties, including demonstrating predictions can be made using only computational features. Our findings reveal that many ionic liquids exhibit super-hydrodynamic viscosity-conductivity scaling, which could be harnessed to influence the behavior of electrochemical devices.

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Section: Discussionsupporting

confidence: 83%

Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Bridging Database Analysis with Microrheology to Reveal Super-Hydrodynamic Conductivity Scaling Regimes in Ionic Liquids

Cashen

Donoghue

Schmeiser

et al. 2022

Preprint

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“…This value is still comparable to or higher than what was expected from superconcentrated electrolytes and the values obtained for organic electrolytes [34] . This is attributed to facilitated movement of Li + within water domains, [65,66] which behave in a more pronounced non‐Gaussian manner [67] …”

Section: Macroscopic (Physicochemical) Propertiessupporting

confidence: 73%

Physicochemical and Electrochemical Properties of Water‐in‐Salt Electrolytes

Amiri

Bélanger

2021

ChemSusChem

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Aqueous electrolytes are attractive for applications in electrochemical technologies due to features like being eco‐friendly, cost effective, and non‐flammable. Very recently, superconcentrated aqueous electrolytes, such as so‐called water‐in‐salt, water‐in‐bisalt, and hydrate melt, have received a significant attention for electrochemical energy storage due to enhanced stability and much wider electrochemical stability window. This Review focuses on the physicochemical properties of the highly concentrated electrolytes that are derived from several analysis techniques and simulation. A summary of most common features such as ions‐water interactions, structure of species present in the electrolyte, conductivity, and viscosity of the electrolytes found in the literature are presented as well. In addition, this Review explains how these characteristics affect the electrochemical behavior of the electrolyte such as double layer structure and electrode/electrolyte interface leading to enhanced electrochemical stability of aqueous electrolytes.

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“…Some recent works simulating the transport properties in WIS electrolytes showed that the anions in a WIS system can form a percolating network resulting in a larger Li + transport or transference number than conventional electrolytes, while the overall diffusivities of all species decreased as electrolyte concentration increased. 19 , 21 − 23 Despite the contribution of the simulations, the transport kinetics becomes further convoluted, while another solution to increase the energy density from the engineering aspect is introduced to build a thick architecture electrode. 24 The increased thickness in thick electrodes significantly elongates the conductive pathway required of electrons across the electrode and the ionic diffusion length in the electrolyte within the electrodes’ pores.…”

Section: Introductionmentioning

confidence: 99%

Probing Kinetics of Water-in-Salt Aqueous Batteries with Thick Porous Electrodes

et al. 2021

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Aqueous electrochemical systems suffer from a low energy density due to a small voltage window of water (1.23 V). Using thicker electrodes to increase the energy density and highly concentrated “water-in-salt” (WIS) electrolytes to extend the voltage range can be a promising solution. However, thicker electrodes produce longer diffusion pathways across the electrode. The highly concentrated salts in WIS electrolytes alter the physicochemical properties which determine the transport behaviors of electrolytes. Understanding how these factors interplay to drive complex transport phenomena in WIS batteries with thick electrodes via deterministic analysis on the rate-limiting factors and kinetics is critical to enhance the rate-performance in these batteries. In this work, a multimodal approach—Raman tomography, operando X-ray diffraction refinement, and synchrotron X-ray 3D spectroscopic imaging—was used to investigate the chemical heterogeneity in LiV 3 O 8 –LiMn 2 O 4 WIS batteries with thick porous electrodes cycled under different rates. The multimodal results indicate that the ionic diffusion in the electrolyte is the primary rate-limiting factor. This study highlights the importance of fundamentally understanding the electrochemically coupled transport phenomena in determining the rate-limiting factor of thick porous WIS batteries, thus leading to a design strategy for 3D morphology of thick electrodes for high-rate-performance aqueous batteries.

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Mobility-viscosity decoupling and cation transport in water-in-salt lithium electrolytes

Cited by 30 publications

References 54 publications

Bridging Database Analysis with Microrheology to Reveal Super-Hydrodynamic Conductivity Scaling Regimes in Ionic Liquids

Bridging Database Analysis with Microrheology to Reveal Super-Hydrodynamic Conductivity Scaling Regimes in Ionic Liquids

Physicochemical and Electrochemical Properties of Water‐in‐Salt Electrolytes

Probing Kinetics of Water-in-Salt Aqueous Batteries with Thick Porous Electrodes

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