Molten Salt Electrolyte Research Articles

First-Principles Computational and Experimental Investigation of Molten-Salt Electrolytes: Implications for Li–O2 Battery

Nitrate-based molten salts have been the most stable electrolytes in Li–O2 electrochemical systems. While the high temperature of operation is a disadvantage, the molten-salt electrolytes offer a c...

Ceramic coating on Ti-6Al-4V by plasma electrolytic oxidation in molten salt: Development and characterization

The plasma electrolytic oxidation (PEO) method is one of the most promising methods for the formation of oxide coatings on metallic substrates. This process is usually conducted in an aqueous solution electrolyte; however, it has several disadvantages, such as heating-up of the system and the formation of the undesired chemical components. This study addresses these disadvantages by conducting the process in a molten salt electrolyte. The surface morphology, phase composition, hydrophobicity, and the effects of process current frequency were examined. Thin titanium oxide, rutile and anatase, coating of 2–2.5 μm was formed on the treated Ti-6Al-4V alloys. The potentiodynamic polarization test evaluated the highest polarization polarization resistance for the alloy obtained using current frequency of 150 Hz which was 364×10 4 Ω·cm 2 in comparison with the pristine alloy which was 6.93×10 4 Ω·cm 2 . Electrochemical impedance spectroscopy revealed the same behavior. Morphology evaluation revealed that the structure of this coating contained uniform sub-micron porosity and its surface exhibited the highest hydrophobicity. • TiO 2 coating was developed by plasma electrolytic oxidation in nitrate salt. • Effect of PEO current frequency on structure and performance was examined. • The highest PEO coating properties were obtained using current frequency of 150 Hz. • The highest contact angle was obtained on the most compact titanium oxide coating. • The highest corrosion resistance was obtained on the most uniform coating.

The Suppression Effect of Functional Gradient Design on Concentration Polarization of Multiple Cations Molten Salt Electrolyte for Thermal Batteries

The energy density of traditional Li−Si/FeS2 thermal batteries, which multiple cations are contained in molten salt electrolyte, is limited by the deficiency of Li+ in cathode when a high discharge current is applied. To address this issue, LiCl−KCl is taken as an example to build a functional gradient structure through Li−Si/FeS2 thermal batteries. By levering the Li+ concentration in cathode and preventing the formation of high concentration polarization resistivity as well as molten salt precipitation, the energy density of Li−Si/FeS2 single cell with a discharge current of 500 mA cm−2, increase from 157.0 Wh kg−1 to 218.4 Wh kg−1 at 450 °C (with an increase ratio of 39.1%), compared with the original one. Similarly, a 25.6% raise is observed at 525 °C. Moreover, the effects of LiCl-rich electrolyte and the functional gradient structure on the electrochemical performance of Li−Si/FeS2 single cells are discussed and classified.

A low-charge-overpotential lithium-CO2cell based on a binary molten salt electrolyte

A eutectic molten mixture was introduced to Li-CO2 battery as electrolyte to realize a low charge overpotential and better reversibility. The overall performance could be further promoted by ruthenium catalyst.

Electrodeposition of Aluminum Coatings from AlCl3-NaCl-KCl Molten Salts with TMACl and NaI Additives.

The Al coatings achieved via electrodeposition on a Cu electrode from AlCl3-NaCl-KCl (80–10–10 wt.%) molten salts electrolyte with Tetramethylammonium Chloride (TMACl) and Sodium Iodide (NaI) additives is reported. The effect of the two additives on electrodeposition were investigated by cyclic voltammetry (CV), chronopotentiometry (CP), scanning electron microscopy (SEM) and X-ray diffraction (XRD). Results reveal that compact and smooth Al coatings are obtained at 150 °C by the electrodeposition process from the electrolyte with 1% TMACl and 10% NaI. The Al coatings exhibit great corrosion resistance close to that of pure Al plate, with a corrosion current of 3.625 μA. The average particle size is approximately 2 ± 1 μm and the average thickness of the Al layer is approximately 7 ± 2 μm. The nucleation/growth process exhibits irrelevance with TMACl or NaI during the electrodeposition of Al. TMACl cannot affect and improve the electrodeposition effectively. However, the addition of TMACl and NaI can intensify the cathodic polarization, producing an inhibition of Al deposition, and contribute to form uniform Al deposits. This can increase the conductivity and facilitate in refining the size of Al particles, contributing to forming a continuous, dense and uniform layer of Al coating, which can be used as effective additives in molten salts electrolyte.

The Renaissance of Liquid Metal Batteries

Next-generation batteries with long life, high-energy capacity, and high round-trip energy efficiency are essential for future smart grid operation. Recently, Cui et al. demonstrated a battery design meeting all these requirements—a solid electrolyte-based liquid lithium-brass/zinc chloride (SELL-brass/ZnCl2) battery. Such a battery design overcomes some inherent problems of conventional ZEBRA batteries and lithium ion batteries.

Molten Salt Electrolytes: Computational Analysis of Transport, Electrochemical Properties and Designing New Mixtures

Electric aircraft propulsion has gained traction over the last decade due to possible high-energy density electrochemistries with reasonable cycle life and identification of non-flammable chemistries that can guarantee much better safety. Commercial Li-ion batteries cannot reach such high capacities because of weight limitations that arise from the widely used intercalation electrodes. Also, use of organic electrolytes make them highly susceptible to fire on exposure to air and humidity. Currently, use of Lithium metal anode along with conversion electrochemistries such as Li-O2 and Li-S are being pursued to achieve such high energy densities. Safer inorganic solid-state electrolytes, recently discovered Water-in-Salt electrolytes, molten salt electrolytes are some of the alternatives being pursued for a safer/non-flammable battery.Of these safer alternatives, molten-salt electrolytes offer some attractive properties: liquid at operating temperatures resulting in better electrode-wetting, stable interface with Li-metal anodes and good ionic conductivity; their only drawback being high operating temperatures. In this talk, we will discuss some of the computational studies, driven via atomistic simulations, of the properties of molten-salt electrolytes including transport mechanism and interface stability. We will also discuss predicting electrochemical properties of these high-temperature electrolytes. Further, we will discuss a thermodynamic approach to predicting new molten-salt eutectics with lower melting points.

Recovery of Nickel and Cobalt By Electrowinning from Spent Lithium-Ion Batteries Using Molten Salt Electrolytes

Electrodeposition of metals is of wide interest with application in several fields such as electroplating, electrorefining and electrowinning (EW). Particularly, electrowinning is used in the fabrication of commercially pure copper and zinc, with approximately 20% of the world refined copper (Cu) produced by this process. One of the main advantages of EW is the high purity achieved of the final product. Electrowinning has been implemented recently as one of the final steps in the hydrometallurgical recycling process of lithium-ion batteries (LIBs) to recover some of the valuable metals present in the battery such as cobalt and nickel.This work describes advances in the recovery of metals from spent LIBs, by using a two-phase molten salt of sodium borate/sodium chloride at high temperature. The study takes advantage of the versatility of the molten salts used as electrolytes - sodium borate’s easiness for dissolving metal oxides, and sodium chloride as the chosen electrolysis media. For the study, two different cathode chemistries were used, NMC 111 and NCA. The electrolytic cell comprises of a gas-tight vertical tube furnace under argon atmosphere, possible in a single-vessel configuration by utilizing the immiscibility of the two liquid phases used (see Figure 1). The experiments are conducted in a three-electrode setup, using graphite (C) as counter electrode, and tungsten (W) as pseudo-reference and working electrodes. The process operates within the temperature range of 800-900℃, where both salts are in liquid state. The reduction potentials were applied stepwise using chronoamperometry to record the current output. Cyclic voltammetry was used beforehand to corroborate the reduction potential for each metal, and to compare it to the reported ones by Amietszajew et. al. The plating potentials and recovered metals quality are reported (see Figures 2-3), indicating successful process proof-of-concept.Evaluation of the energy efficiency of the process and purity of the deposited metals is compared with the current commercial processes for metal recovery employed to recycle batteries from portable devices. The system demonstrates stability, and gives the possibility to be used in joint with other metal recycling sources and process. It has the possibility to solve some of the issues related to the hydrometallurgical methods including significant amounts of water waste, sulphates by-products presence and toxic acids resulting in highly detrimental effects on the environment. The reduction in energy consumption and hazardous gases generation that the common pyrometallurgical process adds to the advantages. Furthermore, the method developed is inclusive of a range of metals, which is of high importance considering the growing and future complexity of the battery waste stream. Figure 1

High Temperature Batteries for Venus Surface Missions

In-situ exploration of Venus is seriously hampered by its severe environment, which is benign (28oC) at an altitude of 55 km, but rapidly becomes hostile, with increasing temperature and CO2 pressure at lower altitudes, eventually reaching ~465°C and 90 bars at the surface.1 These challenging conditions have limited the previous Venus surface missions, e.g., the Russian Venera series and Vega-2 Landers,2 to barely two hours after deployment with lithium-primary batteries, despite the use of considerable insulation, phase-change materials, and similar heat sinks to isolate batteries and avionics from high surface temperatures. The recent decadal survey, ‘Vision and Voyages for Planetary Science in the Decade as well as the more recent Venus Exploration and Analysis Group (VEXAG) study3 emphasized the need to gather basic information on the crust, mantle, core, atmosphere/exosphere, and bulk composition of Venus, to understand the evolutionary paths of Venus in relation to Earth and recommended long-duration landers and probes for future missions.In order to enable extended surface missions on Venus, e.g., landers, probes and seismometers, NASA has initiated the development of high temperature electronics and power technologies, under its ‘Hot Operating Temperature Technology’ (HOTTech) program. Under this program, we have been developing advanced primary batteries resilient to the hostile conditions on the Venus surface and operational for several days with high specific energy (>100 Wh/kg) and energy density (>150 Wh/l). Here, we will describe the development of high temperature batteries based on lithium alloy (e.g., Li-Al) anodes, molten salt electrolytes containing binary/ternary mixtures of alkali metal halides, cathodes consisting of transition metal sulfides, and designs similar to the aerospace thermal batteries.4 With FeS cathode and appropriate changes in the electrolyte, binder and active material ratios, we have demonstrated the operation of the high temperature battery in prototype cells for 30 days in primary mode, and >150 days in rechargeable mode at 475oC. Further, with suitable thin coatings of inorganic compounds, e.g., Al2O3, AlF3 and AlBO3 on the cathode particles, the utilization of the cathode, and hence the operational life of the cells have been improved by another 50%.AcknowledgementsThe work described here was carried out at the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration (NASA) and supported by the NASA’s HOTTech project. The information in this document is pre-decisional and is provided for planning and discussion only.References Basilevsky, J. W. Head, "The surface of Venus". Rep. Prog. Phys. 66, 1699 (2003).Gilmore, et al., “Venus Surface Composition Constrained by Observation and Experiment”, Space Sci. Rev. 212, 1511–1540 (2017); doi:10.1007/s11214-017-0370-8.A. Bullock, et al., “A Venus Flagship Mission: Report of the Venus Science and Technology Definition Team," 40th Lunar and Planetary Science Conference (Lunar and Planetary Science XL), The Woodlands, TX, March 23-27 (2009).E. Glass, J.P. Jones, A. V. Shevade, D. Bhakta, E. Raub, R. Sim, R. V. Bugga, “High temperature primary battery for Venus surface missions”, J. Power Sources. 449, 227492 (2020). doi:10.1016/j.jpowsour.2019.227492.

Electrochemical Purification of Molten Chloride/Fluoride Salt for Silicon Electrorefining

With the ever-increasing demand for solar modules nowadays, there is a growing interest in developing an alternative, eco-friendly and low-cost manufacturing process for solar-grade silicon. Silicon electrorefining in a molten salt is a promising technique for producing solar-grade silicon directly from metallurgical-grade silicon with low carbon emission and low energy consumption. Due to the stringent requirement in the purity of the silicon for solar applications (at least 99.9999% or 6N), a high-purity molten salt electrolyte is necessary for the solar-grade silicon electrorefining process. In this report, an electrochemical purification process for the eutectic CaCl2-CaF2 (CaCl2:CaF2 = 86.2:13.8 by weight) molten salt at 900℃ has been studied. The impurity level in the salt was in-situ examined by cyclic voltammetry (CV). After the electrochemical purification process, a decrease in peak current of the CV is observed, indicating the removal of the impurities. According to energy-dispersive x-ray spectroscopic results, Fe, Mn, Mg and Al were successfully extracted from the salt. This electrochemical purification process and in-situ salt purity examination technique are useful for purity control of the molten salt in the solar-grade silicon electrorefining process.

Printable Ink Development for Molten Salt Battery Electrodes

Thermal batteries are important power sources in applications requiring a long shelf life, fast activation, and reliable power delivery. They operate at high temperatures and utilize molten salt electrolytes, typically eutectic mixtures, which are inert solids at ambient temperatures and provide fast ionic conductivity above the melting point of the salt. The size, energy density, and mechanical properties of thermal batteries are limited by the current manufacturing processes, which are slow and labor-intensive. The development of printable, coated-film electrodes and components will lead to batteries with increased energy density, a more efficient production process, and form factor flexibility.The electrolyte salt (LiCl-KCl eutectic) and MgO separator materials are combined in a single ‘electrolyte binder’ mixture (EB). Slurries were prepared with the EB using DMSO as the carrier solvent and additional dissolved LiCl as a binder for the printed film. The slurries show a large change in viscosity as a portion of the electrolyte dissolves during the mixing process. The initial coarse slurry mixture quickly increases in apparent viscosity before smoothing out into highly shear-thinning suspension with a small overall particle size (<25 µm). The slurries can be easily printed directly on coated cathode substrates, using a slot-die or tape casting coating method. After drying, the film provides a stable separator layer, which can be cut or punched into the desired form and assembled into battery cells. Micro-CT imaging shows the resulting multi-layer film with a distinct cathode layer, and separator layers with a final dry film thickness on the order of 220 µm.Thermal analysis data indicates that neither the modified salt content nor the dissolution and re-crystallization process significantly alter the melting behavior of the electrolyte salts and separator coatings when compared to the standard thermal battery separator mixtures. Thermogravimetric analysis (TGA) indicates that the solvent is sufficiently removed from the printed films during the drying process, and differential scanning calorimetry (DSC) measurements show that the melting point of the electrolyte in the coated separator film shifts by less than 5ºC, in comparison to the standard LiCl-KCl eutectic mixture. Single-cell electrochemical tests using the combined multi-layer separator/cathode films yielded voltages of >1.9 V delivering a capacity >100 mAh/g and with a lower internal resistance than standard thermal battery cells.Figure 1. Cross-sectional micro-CT image of printed multi-layer electrode, consisting of carbon fiber support with cathode film and separator/electrolyte overcoat. Sandia National Laboratories is a multimission laboratory managed and operated by National Technology & Engineering Solutions of Sandia, LLC, a wholly owned subsidiary of Honeywell International Inc., for the U.S. Department of Energy’s National Nuclear Security Administration under contract DE-NA0003525.This paper describes objective technical results and analysis. Any subjective views or opinions that might be expressed in the paper do not necessarily represent the views of the U.S. Department of Energy or the United States Government. SAND No. SAND2020-5349 A Figure 1

Integration of Low Melting Temperature Electrolyte in Thermal Batteries

Thermal batteries usually operate at temperatures higher than 400 °C. This high operating temperature requires a complex thermal and mechanical design of the battery components and hermetically sealed casing. Reduced operating temperature thermal cells can benefit from the majority of intrinsic characterizations of thermal batteries such as safety, robustness, and infinite shelf life while mitigating the challenges related to the high operating temperature batteries such as exotic thermal insulation materials, complicated internal pyrotechnic heat source, and heavy packaging. To integrate the thermal batteries into a wider range of applications such as bore-hole probes, smart grid energy storage, and geothermal energy applications, operating temperatures of these batteries should be reduced.The most common design for thermal batteries is pellet stacks. The pellet pressing fabrication method inherently causes issues due to the fragility of the pellets, making handling and assembly of the cells arduous. Additionally, due to the liquid nature of molten salt electrolyte used in these batteries, a structure to immobilize the electrolyte layer during the operation of the battery is required. The role of the immobilizing component is also to prevent short circuiting while the battery is affected by severe physical shock or vibration. The most commonly used binder material in today’s thermal batteries is magnesium oxide (MgO). Extensive investigations were conducted on the properties and the electrochemical effect of using MgO as the binding material, besides, its fabrication process is well optimized. However, using MgO is not without its drawbacks. To prevent short-circuiting during the cell operation especially in the presence of an external shock to the system, approximately 30 vol.% of the separator layer should be dedicated to MgO, resulting in lower than desired energy density. Ceramic felts showed promising results in recent studies. High level of porosity (e.g. 96% bulk porosity), outstanding stability at elevated temperatures, and mechanical stiffness could be the key to make batteries that can operate for a longer time.Our research group has previously developed a novel eutectic electrolyte mixture using potassium bifluoride and different lithium salts such as lithium fluoride as the low melting point electrolytes. In this research, initially, the integration of this electrolyte mixture in a thermal cell was tested. Consequently, aluminum oxide (Al2O3) and yttria-stabilized zirconia (YSZ) ceramic felts were loaded with the low melting electrolyte as an alternative to the current pellet-based separator layer. Finally, (i) the assembly of the cell, (ii) the thermal analysis of the components by differential scan calorimetry (DSC) method, (iii) the new electrolyte/ceramic-felt combination’s loading level, wetting properties, infiltration, and leakage, and (iv) electrochemical behavior of the new thermal battery such as discharge capability and energy density were investigated.

Understanding the Structure and Speciation of Molten LiCl-KCl Using Raman and Ultraviolet-Visible-Near IR Spectroscopic Techniques

Pyrochemical reprocessing (pyroprocessing) of used nuclear fuel (UNF) is a promising pathway towards closing the nuclear fuel cycle by recycling actinides into new fuel and providing the means to generate durable wasteforms for portions of the UNF that are not able to be recycled. One of the most significant challenges in the advancement of this technology is developing a more complete understanding of the chemistry of the electrolyte molten salts used in the electrorefining process, where fission products, transuranic elements and fuel elements are anodically dissolved into a LiCl-KCl electrolyte, forming a chemically complex mixture. To enhance our understanding of the chemistry of the mixture of molten salt electrolyte and UNF we are studying the structure and speciation of lanthanide and actinide elements dissolved in LiCl-KCl using Raman and ultraviolet-visible-near infrared (UV-Vis-NIR) spectroscopy. These techniques are starting to provide information on the coordination, symmetry, and electronic structure of the dissolved species, which will result in a more complete understanding of the chemistry of these solutions. Results of a Raman spectroscopy study of mixtures of NdCl3, SmCl3, CeCl3, and EuCl3 with LiCl-KCl and LiCl-KCl-UCl3 and the development of a system to conduct Raman and UV-Vis-NIR spectroscopy and spectroelectrochemistry will be presented.Acknowledgements: This work was performed under the auspices of the Department of Energy (DOE) under contracts DE-NE0008889, and the US Nuclear Regulatory Commission (NRC) under contracts NRC-HQ-13-G-38-0027 and 31310018M0032. Dr. Kenny Osborne and Ms. Nancy Hebron-Isreal serve as the program managers for the DOE and NRC awards, respectively. For support of furnace design and fabrication work at INL, RG and WCP acknowledge the Laboratory Directed Research & Development (LDRD) Program under DOE Idaho Operations Office Contract DE-AC07-05ID14517 and a subcontract under LDRD (INL) to University of Nevada, Reno via award number 204471 (UNR award AWD-01-00001719); this design served as starting iteration for this work. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1447692. One of the authors, JM, acknowledges the Graduate Research Fellowship from the US National Science Foundation.

(Invited) Understanding the Corrosion of SS316L in Molten LiCl-Li2O-Li Using 3D Transmission X-Ray Microscopy and 3D XANES

Pyrochemical reprocessing (pyroprocessing) of used nuclear fuel (UNF) is a promising pathway towards closing the nuclear fuel cycle and providing the means to generate durable wasteforms for portions of the UNF that are not able to be recycled. To incorporate commercial UNF (UO2) into the pyroprocessing scheme, the ceramic UNF must be converted to a metallic form at the head end of the process, which can be accomplished via electrolytic reduction of the UNF in LiCl-Li2O molten salt electrolyte. During the electrolytic reduction of UO2 at the cathode, metallic Li is inevitably co-reduced from the electrolyte due to the proximity of the reduction potential of the U4+ in UO2 and Li+ in the electrolyte. Metallic Li disperses into the LiCl electrolyte and can then interact with the process vessel and other apparatus in contact with the electrolyte, altering the rate and mechanism of the degradation of those materials.Our group has previously shown that the presence of metallic Li in the electrolyte creates a reducing condition where the surface oxide layer of SS316 is removed, and extensive intergranular corrosion takes place. To further the understanding of the mechanism and morphology of the intergranular corrosion, transmission X-ray microscopy (TXM) at Brookhaven National Laboratory’s National Synchrotron Light Source II (NSLSII) beamline 18-ID was used to examine ~20 μm diameter focused-ion beam (FIB) milled pillars of the cross-section of SS316L exposed to LiCl-Li2O-Li with 0 wt.%, 0.3 wt.%, 0.6 wt.% and 1 wt.% Li. Computed Tomographic (CT) images were obtained at X-ray energies above and below the absorption edges of alloying elements of interest, providing insight into the distribution of alloying elements after exposure to the molten salt. 3D X-ray absorption near edge spectroscopy (XANES) tomography at the Cr K-edge was also attempted. This analysis provided additional evidence of the formation of Cr-rich intermetallic phases and 3D CT images of the void structure of the exposed samples, strengthening the evidence that the sensitization of SS316L at process temperatures and the subsequent dissolution of the Cr carbide precipitates into the electrolyte is the primary driver of the deep intergranular corrosion of SS316L in LiCl-Li2O-Li. To our knowledge, this is the first application of this FIB milling technique and TXM imaging of the FIB-milled pillars to corrosion samples and lessons learned regarding the sample preparation and analysis will be presented.Acknowledgements: The authors thank Zachary Karmiol, research scientist at Materials Characterization Nevada, for technical assistance with the FIB sample preparation. This work was performed under the auspices of the Department of Energy (DOE) under contracts DE- NE0008236, and the US Nuclear Regulatory Commission (USNRC) under contract NRC-HQ-13-G-38-0027. Dr. Kenny Osborne and Ms. Nancy Hebron-Isreal serve as the program managers for the DOE and NRC awards, respectively. This research used beamline 18-ID of the National Synchrotron Light Source II, a U.S. Department of Energy (DOE) Office of Science User Facility operated for the DOE Office of Science by Brookhaven National Laboratory under Contract No. DE-SC0012704. This work was supported as part of the Molten Salts in Extreme Environments Energy Frontier Research Center, funded by the U.S. Department of Energy (US-DOE), Office of Science, Basic Energy Sciences, at Idaho National Laboratory under contract DE-AC07-05ID14517. This material is based upon work supported by the National Science Foundation Graduate Research Fellowship under Grant No. DGE-1447692. One of the authors, JM, acknowledges the Graduate Research Fellowship from the US National Science Foundation.

Electrochemical performance of NiCl2 with Br-free molten salt electrolyte in high power thermal batteries

NiCl2 with high theoretical voltage and thermal decomposition temperature attracts much attention as cathode material for thermal batteries with the requirement of high power density, high energy density and long work time. Unfortunately, the practical utilization of thermal batteries with NiCl2 cathode is limited by their poor electrochemical performance under large current, even with the conventional LiF-LiCl-LiBr all-lithium molten salt electrolyte which proposes ultrahigh lithium ion conductivity. In this work, an unexpected ionic exchange reaction between NiCl2 and LiBr in LiF-LiCl-LiBr was found, which would be the main reason for the poor electrochemical behavior of thermal batteries with NiCl2 cathode and LiF-LiCl-LiBr molten salt. On this basis, LiF-LiCl-Li2SO4, another all-lithium molten salt free of LiBr, was investigated as the new electrolyte for NiCl2 cathode. For the single cell of Li(Si)/LiF-LiCl-Li2SO4/NiCl2, a discharge capacity of 377 mA h g−1 (with a cut-off voltage of 1.2 V) was achieved with large current density (500 mA cm−2) applied at 520°C, which is almost twice of that of Li(Si)/LiF-LiCl-LiBr/NiCl2(190 mA h g−1) at the same conditions.

Corrosion of Metallic Materials in the Molten FLiNaK

Molten fluoride salts can be used as the fuel and coolant for molten salt reactors (MSR) and electrolytes for spent nuclear fuel (SNF) reprocessing. 46.5%LiF-11.5%NaF-42%KF (FLiNaK) melt is the prospective media for these purposes due to their desirable thermophysical and nuclear properties. Finding construction materials with sufficient corrosion and mechanical resistance is the most challenging task for practical implementation of MSR concept.In the present study the corrosion and mechanical properties of different types of construction materials were investigated. The materials included various low carbon Ni-Cr-Fe-Mo, Ni-Cr-Mo, and Ni-Mo alloys, and metals with relatively positive electrode potentials.The corrosion experiments were performed in FLiNaK melt at different temperatures (from 550 to 750 °C) in the specially designed stainless steel cells under high-purity argon atmosphere. Corrosion properties of studied materials were investigated under static conditions, and the duration of each test was 100 h to enable the comparison of the experimental data. In a special series of experiments fluorides of typical fissile nuclides and fission products were added to the salt electrolyte to estimate the influence of the red-ox potential on the corrosion resistance of the materials.Corrosion rates were determined from the weight loss measurements and chemical analysis of quenched melts. Surface and microstructure of corroded samples was examined by various microscopic techniques. Mechanical properties of investigated materials were also studied at the ambient temperature and at 600 °C.Advantages and limitations of different types of construction materials were evaluated on the basis of data obtained. The effect of temperature on corrosion and mechanical properties of the studied materials were determined. Possible mechanisms of corrosion of various materials in fluoride melts were proposed.The alloys based on Ni-Cr-Mo and Ni-Mo systems, and molybdenum and its alloys were selected for further long-time tests under dynamic conditions to determine the resource of materials in contact with molten fluorides for MSR and SNF recycling technologies.

Effects of current distribution on mass transport in the positive electrode of a liquid metal battery

Liquid metal electrodes are one of the key components of different electrical energy storage technologies. The understanding of transport phenomena in liquid electrodes is mandatory in order to ensure efficient operation. In the present study we focus our attention on the positive electrode of the Li||Bi liquid metal battery. Starting from a real experimental setup, we numerically investigate the charge transfer in a molten salt electrolyte and the mass transport in the positive electrode. The two phenomena are tightly coupled, because the current distribution influences the concentration field in the positive electrode. The cell is studied during charging when compositional convection becomes apparent. First results of compositional convection from a non-uniform current distribution are presented, highlighting its capability to affect the flow in the positive electrode and the cell performance.

An Electrochemical Approach toward the Metastable Type II Clathrate Germanium Allotrope.

By using an anodic conversion process at 280 °C, the type II clathrates Na1.7(6)Ge136 and Na23.0(5)Ge136 were obtained from Na12Ge17 as the starting material. An alkali-metal iodide molten-salt electrolyte complied with the reaction conditions, allowing for the formation of microcrystalline products. Characterization by powder X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy also revealed Na4Ge13 as an intermediate and α-Ge and Cs8–xGe136 as byproducts, with the latter likely resulting from cation exchange between the starting material and electrolyte. Taking such minor side reactions and a small contribution of material without suitable electrical contact into account, anodic conversion of Na12Ge17 to Na1.7Ge136 proved to proceed without parasitic processes and to comprise the material bulk. The hitherto existing preparation method for Nax→0Ge136 by gas–solid oxidation of Na12Ge17 has thus been translated into a scalable high-temperature electrochemical approach with enhanced tools for reaction control, promising access to pure Ge(cF136) and Na24Ge136 after process optimization.

A high-performance graphite-graphite dual ion battery based on AlCl3/NaCl molten salts

A novel double graphite dual ion battery (DIB) based on low-temperature inorganic molten salt (AlCl3/NaCl) electrolytes is first investigated. As a result, it is found that chloroaluminate ions are intercalated/de-intercalated at the cathode and metallic aluminum are dissolved and deposited at the anode. In addition, the self-discharge phenomenon of the DIB is systematically studied and found that it has obvious self-charging phenomenon due to the adsorption of the charged ions when standing at low voltage. Due to low cohesion and the relatively high working temperature for the inorganic molten salt, the DIB exhibits unexpected electrochemical performance. The initial capacity is 183.8 mAh g−1 at 1 A g−1, and the capacity is 132 mAh g−1 even at 4 A g−1. After 700 cycles, the capacity retention rate is 79.5% and the coulombic efficiency increase from 85.1% to 93.9%. Given the advantages of cost-effectiveness and environmental friendliness, the DIB will play a decisive role in the future of aluminum-based batteries.

An ultra stable and efficient bifunctional cathode catalyst for iron molten air batteries

Iron molten air battery possesses cost-efficiency and high theoretical specific energy density merits, and is one of the promising battery systems for future application in energy storage. Although substantial efforts and significant progress have been made in recent years, it is still one of the major challenges to explore a stable and efficient bifunctional catalyst in high-temperature molten salt environments. Herein, the NiMnO3–La2O3 composite is synthesized on porous nickel foam substrates by a hydrothermal method and used as a cathode catalyst for the iron molten air battery. The results show that the NiMnO3–La2O3 composite has excellent stability and durability. After 250 cycles in a 500 °C molten salt electrolyte, the microscopic morphology of the catalyst is almost the same as that before using. Moreover, the NiMnO3–La2O3 composite exhibits excellent oxygen evolution reaction (OER)/oxygen reduction reaction (ORR) activity, less discharge polarization, and excellent rate performance. The iron molten air battery with NiMnO3–La2O3 composite cycles stably over 250 cycles with the highest Coulombic efficiency of 99.8% and the average discharge potential of 1.14 V at 500 °C in the air. This work opens a new avenue toward developing a stable and efficient bifunctional cathode catalyst for the iron molten air batteries.