Composition Gradients in Molten Salt Binary Mixtures during Electrolysis at High Current Density

Vallet, C. E.; Heatherly, D. E.; Braunstein, J.

doi:10.1149/1.2129617

Cited by 21 publications

(14 citation statements)

References 11 publications

(24 reference statements)

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“…First, an in situ potentiometric measurement gives (4) the composition near an electrode at the ena of electrolysis. The subsequent relaxation toward the initial composition reflects the composition profile at the end of the electrolysis (15).…”

Section: Methodsmentioning

confidence: 99%

“…The formation of anodic films at platinum electrodes at potentials above about 0.6V vs. RHE has been extensively studied (1)(2)(3)(4)(5)(6)(7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20) and reviewed in recent papers (21)(22)(23)(24)(25)(26). Following the initial adsorption of oxygen species, a thin oxide film, only about 10-15A thick, grows at potentials above 1.9V vs. RHE in both acid and alkaline solutions (4-6, 10, 11, 13, 18-20).…”

Section: Introductionmentioning

confidence: 99%

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Current‐Induced Composition Gradients in Molten AgNO3 ‐ NaNO3: A Model System for the LiCl ‐ KCl Electrolyte of an Li/S Battery

Vallet

Heatherly

Sherman

et al. 1982

J. Electrochem. Soc.

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Composition gradients, in molten AgNO3‐NaNO3 mixtures contained in silica frits, are produced by electrolysis between silver electrodes and analyzed by three methods: (i) in situ potentiometry, (ii) chemical analysis of sections of quenched electrolyte, and (iii) scanning electron microscopy with associated x‐ray fluorescence spectroscopy. The composition changes are calculated a priori from transport and thermodynamic properties independently measured in the free melt and corrected for the porosity of the frits. Since the ion flows in AgNO3‐NaNO3 are analogous to those in the normalLiCl‐normalKCl electrolyte of Li/S batteries, the former system serves as a convenient model system for the mixed electrolyte of the Li/S battery. The predicted gradients are compared to the experimental data from the three methods.

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Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Current‐Induced Composition Gradients in Molten AgNO3 ‐ NaNO3: A Model System for the LiCl ‐ KCl Electrolyte of an Li/S Battery

Vallet

Heatherly

Sherman

et al. 1982

J. Electrochem. Soc.

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“…In the event that recharging is desired, this loss of volatile sulfur will result in lower charge/discharge capacity. The migration of sulfide from the cathode can be understood in terms of the migration of all anions toward that anode (24). Reasons for the migration of iron are less obvious and may be due to the formation of a nonstoichiometric iron, sulfur, potassium, lithium complex.…”

Section: Discussionmentioning

confidence: 99%

Characterization of the Materials Comprising the Reactive Interfaces in the Li ( Si ) / FeS2 Primary Battery

Burrow

Nebesny

Armstrong

et al. 1981

J. Electrochem. Soc.

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Photomicroscopic, electron‐microscopic, and surface analytical studies have been conducted on normalLifalse(normalSifalse)/normalLiCl·normalKCl/FeS2 electrochemical cells before and after discharge, and on individual anode and cathode components. Physical and chemical compositional changes were observed at both the anode and cathode interface that have significance in the discharge mechanism. Oxygen‐rich species were found at the surface of the FeS2 cathode particles and migration of sulfur away from the cathode during discharge was also observed. Thermal shock of FeS2 single crystals confirmed the tendency for sulfur to move away from the bulk with the application of heat to the surface. Exposure of the Li(Si) alloy to atmosphere and/or thermal shock resulted in the formation of a lithium‐rich surface in the carbonate or oxide form. These findings have significance to battery systems that must be stored for long time periods, as well as the possible source of resistive interfaces in charge and discharge cycles.

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“…the electric current, as well as migrational and diffusive transport processes. This finally results in a depletion or enrichment of the electroactive species at the interfaces between electrodes and electrolyte [44,45,49]. The same authors show that current density, initial composition and differences in the mobility of the ions determine the final composition profiles [43].…”

Section: Liquid Metal Battery and Its Applicationmentioning

confidence: 95%

“…Although barely studied in LMBs, it is well known from literature that composition gradients play an important role in molten salt electrolytes. Such phenomena have been widely investigated by Braunstein and Vallet in several publications [43][44][45][46][47][48] who show that concentration gradients in molten salts can be significant. The authors predicted concentration gradients in mixed cation molten salts based on equations that did not include convection terms [43,44].…”

Section: Liquid Metal Battery and Its Applicationmentioning

confidence: 99%

Modeling Potential and Species Distribution in a Li||Bi Liquid Metal Battery Using the Finite Volume Method

et al. 2022

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To match the growing demand for grid scale energy storage in order to balance out renewable energies, the liquid metal battery (LMB) technology is highly promising. Key elements of these batteries are the liquid electrodes, which require LMBs operating at elevated temperatures. Hereby, the electrolyte can be liquid or solid state. Based on density differences, the battery is self-assembling since the components self-segregate when the system is heated. Additionally, many of the possible materials are earth-abundant and not expensive. This results in a very cost effective technology. Moreover, the molten electrodes feature superior kinetics and transport properties as well as high voltage efficiencies at high current densities. Otherwise, the liquidity has the disadvantage that high operating temperatures are necessary. Further, there is a risk of corrosion, self-discharge and short-circuiting. The latter makes the battery not applicable for portable applications [Kim, H. et al. Chem. Rev. 113 (3) (2013)]. Among all LMBs, the Li||Bi cell has been investigated to a large extend and therefore, most material properties are readily available. This is the reason why the present study focuses on this material pairing. A schematic of this cell during discharge is shown in figure 1a. Here, the anode metal Lithium is oxidized and the ion crosses the electrolyte layer. Then it alloys with the molten Bismuth. At charge, this process is reversed. A picture of a real cell can be found in figure 1b. Nevertheless, there are other very promising cell chemistries such as NaZn batteries [Xu, J. et al. J. Power Sources 332 (2016)]. For theoretical investigations and numerical simulations, electromagnetic fields, electrochemistry and fluid dynamics need to be considered. Coupling of the corresponding fundamental equations and the different regions in the battery is challenging. Further, there are multiple fluid flow phenomena – like surface instabilities, Tayler instability, electro-vortex flow, thermal convection,solutal convection or Marangoni convection [Kelley, D. H. and Weier, T. Appl. Mech. Rev. 70 (2) (2018)] – that might occur when the battery is operated. To determine the operating voltage of a cell, overpotentials need to be investigated. Generally, there are three types of overpotentials: the ohmic loss, the mass transfer and the charge transfer overpotential. However, the latter can be neglected [Newhouse, J. M. Ph.D. thesis, MIT (2014)]. Determining the ohmic overpotential is quite straightforward using Ohm’s law, while the concentration overpotential requires the calculation of the species distribution in the electrolyte and the positive electrode. The present study will focus on the electrochemical behavior of an all liquid Li||Bi battery and neglects fluid flow. Hereby, the whole cell is modeled using the parent-child-mesh technique from Weber et al. [Weber, N. et al. Computers & Fluids 168 (2018)]. This implies that the species distribution in the electrolyte and the distribution of the dissolved species in the cathode are calculated locally and the potential and current density distribution are calculated globally. The equations to solve are coupled between the used meshes. To account for the potential distribution, it is necessary to consider the electrochemical double layer at the electrode-electrolyte interfaces. Macroscopically, the latter can be described as a potential jump at both interfaces in accordance to the Nernst equation. Weber et al. [Weber, N. et al. Electrochim. Acta 318 (2019)] introduced to model this jump using a source term. In the present study, the approach to use internal jump boundary conditions for modeling the potential jump is proposed. To the best knowledge of the authors, species distributions in the electrolyte have not been investigated previously. When there is no mixing of the electrolyte of LMBs, concentration gradients of each species might be significant [Vallet, C. E. et al. J. Electrochem. Soc. 130 (12) (1983)]. Based on the solution for the species distribution, the potential jump at each interface can be calculated. Further, the charge transfer overpotentials can be obtained. The equations are solved quasi-one-dimensional using the finite volume method and are implemented in the open source library OpenFOAM. To validate this new approach, a comparative study with Comsol is performed. Lastly, an application case is simulated, which confirms that concentration layers in the electrolyte are indeed present. This is, for the case of an Li+ ion in a LiCl-KCl eutectic molten salt, exemplarily shown in figure 1d. Further, as it can be seen in figure 1c, the simulation is able to solve the potential distribution in the cell with respect to the potential jump at the interface. Acknowledgment: This project has received funding from the European Union’s Horizon 2020 research and innovation program under grant agreement No 963599. Figure 1

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Composition Gradients in Molten Salt Binary Mixtures during Electrolysis at High Current Density

Cited by 21 publications

References 11 publications

Current‐Induced Composition Gradients in Molten AgNO3 ‐ NaNO3: A Model System for the LiCl ‐ KCl Electrolyte of an Li/S Battery

Current‐Induced Composition Gradients in Molten AgNO3 ‐ NaNO3: A Model System for the LiCl ‐ KCl Electrolyte of an Li/S Battery

Characterization of the Materials Comprising the Reactive Interfaces in the Li ( Si ) / FeS2 Primary Battery

Modeling Potential and Species Distribution in a Li||Bi Liquid Metal Battery Using the Finite Volume Method

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