Theoretical Interpretation of Ion Velocities in Concentrated Electrolytes Measured by Electrophoretic NMR

Timachova, Ksenia; Newman, John; Balsara, Nitash P.

doi:10.1149/2.0591902jes

Cited by 22 publications

(33 citation statements)

References 22 publications

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“…In Newman's concentrated solution theory, the species velocity obtained due to the presence of an electric field or a salt concentration gradient is governed by the following equations: [35]…”

Section: Diffusion and Migration Under Electric Fieldsmentioning

confidence: 99%

“…At finite salt concentrations where the terms containing +− are no longer negligible, expressions for the net species velocities at t = 0 + are given by: [35] Figure 9. The velocities of (a, b) ions and (c) polymer as a function of potential gradient as measured by eNMR.…”

Section: Ion Migrationmentioning

confidence: 99%

“…These coefficients in combination with the thermodynamic factor can be used to quantify the performance of the electrolytes in practical batteries and predict parameters like the limiting current. They also enable prediction of migration velocities of the ions[35]. Polymer segmental dynamics QENS is a powerful that exploits the large incoherent neutron scattering cross-section of hydrogen atoms and quantifies the motion of hydrogen-containing compounds on short time scales.…”

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confidence: 99%

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Diffusion and migration in polymer electrolytes

Choo

Halat

Villaluenga

et al. 2020

Progress in Polymer Science

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128

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Mixtures of neutral polymers and lithium salts have the potential to serve as electrolytes in next-generation rechargeable Li-ion batteries. The purpose of this review is to expose the delicate interplay between polymer-salt interactions at the segmental level and macroscopic ion transport at the battery level. Since complete characterization of this interplay has only been completed in one system: mixtures of poly(ethylene oxide) and lithium bis(trifluoromethanesulfonyl)imide (PEO/LiTFSI), we focus on data obtained from this system. We begin with a discussion of the activity coefficient, followed by a discussion of six different diffusion coefficients: the Rouse motion of polymer segments is quantified by Dseg, the self-diffusion of cations and anions is quantified by Dself,+ and Dself,-, and the build-up of concentration gradients in electrolytes under an applied potential is quantified by Stefan-Maxwell diffusion coefficients, 0+ , 0− , and +−. The Stefan-Maxwell diffusion coefficients can be used to predict the velocities of the ions at very early times after an electric field is applied across the electrolyte. The surprising result is that 0− is negative in certain concentration windows. A consequence of this finding is that at these concentrations, both cations and anions are predicted to migrate toward the positive electrode at early times. We describe the controversies that surround this result. Knowledge of the Stefan-Maxwell diffusion coefficients enable prediction of the limiting current. We argue that the limiting current is the most important characteristic of an electrolyte. Excellent agreement between theoretical and experimental limiting current is seen in PEO/LiTFSI mixtures. What sequence of monomers that, when polymerized, will lead to the highest limiting current remains an important unanswered question. It is our hope that the approach presented in this review will guide the development of such polymers.

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Section: Diffusion and Migration Under Electric Fieldsmentioning

confidence: 99%

Section: Ion Migrationmentioning

confidence: 99%

mentioning

confidence: 99%

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Diffusion and migration in polymer electrolytes

Choo

Halat

Villaluenga

et al. 2020

Progress in Polymer Science

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128

113

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“…where 𝑣 ! , 𝑣 ' and 𝑣 " are the averaged species velocities of the cation, anion, and solvent, respectively, 𝐹 is the Faraday constant, c is salt concentration and E is the applied electric field [18]. The ionic conductivity and transference number at dilute concentrations can be determined using the Nernst-Einstein equation [19].…”

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confidence: 99%

Electric-Field-Induced Spatially Dynamic Heterogeneity of Solvent Motion and Cation Transference in Electrolytes

et al. 2022

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While electric fields primarily result in migration of charged species in electrolytic solutions, the solutions are dynamically heterogeneous. Solvent molecules within the solvation shells of the cation will be dragged by the field while free solvent molecules will not. We combine electrophoretic NMR measurements of ion and solvent velocities under applied electric fields with molecular dynamics simulations to interrogate different solvation motifs in a model liquid electrolyte. Measured values of the cation transference number (𝑡 ! " ) agree quantitatively with simulation-based predictions over a range of electrolyte concentrations. Solvent-cation interactions strongly influence the concentration-dependent behavior of 𝑡 ! " . We identify a critical concentration at which most of the solvent molecules lie within solvation shells of the cations. The dynamic heterogeneity of solvent molecules is minimized at this concentration where 𝑡 ! " is approximately equal to 0.

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“…An emerging technique involves applying a large electric field to PFG-NMR, known as electrophoretic NMR. The measured instantaneous velocity between species is then used to interpret transport properties [215,216,186].…”

Section: Spectroscopic Techniquesmentioning

confidence: 99%

Parameterising continuum level Li-ion battery models & the LiionDB database

Wang,

O'Kane,

Planella

et al. 2021

Preprint

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The Doyle-Fuller-Newman framework is the most popular physics-based continuum-level description of the chemical and dynamical internal processes within operating lithium-ion-battery cells. With sufficient flexibility to model a wide range of battery designs and chemistries, the framework provides an effective balance between detail, needed to capture key microscopic mechanisms, and simplicity, needed to solve the governing equations at a relatively modest computational expense. Nevertheless, implementation requires values of numerous model parameters, whose ranges of applicability, estimation, and validation pose challenges. This article provides a critical review of the methods to measure or infer parameters for use within the isothermal DFN framework, discusses their advantages or disadvantages, and clarifies limitations attached to their practical application. Accompanying this discussion we provide a searchable database, available at www.liiondb.com, which aggregates many parameters and state functions for the standard Doyle-Fuller-Newman model that have been reported in the literature.

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Theoretical Interpretation of Ion Velocities in Concentrated Electrolytes Measured by Electrophoretic NMR

Cited by 22 publications

References 22 publications

Diffusion and migration in polymer electrolytes

Diffusion and migration in polymer electrolytes

Electric-Field-Induced Spatially Dynamic Heterogeneity of Solvent Motion and Cation Transference in Electrolytes

Parameterising continuum level Li-ion battery models & the LiionDB database

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