Dual Intercalating Molten Electrolyte Batteries

Molten salts are non-aqueous solvents which are divided into high temperature molten salts,low temperature molten salts and room temperature molten salts. Due to their unique physical and chemical properties,they are used as the reaction and electrolytic media to electrodeposit the active metal coatings that can not be obtained in aqueous solution. In recent years,the research hot spot in the field of molten electrochemistry is that it is applicable in non-aqueous reprocessing by substituting caustic molten salts for electro-deposition and separation of actinide metal ions. This article reviews the properties of actinide elements in electrochemistry,thermodynamics and physics in high temperature molten salt. The recent research progress of room temperature ionic liquids and the latest extraction advancement of actinide elements in room temperature ionic liquids are introduced. The future research trend in molten system is also given.

The extraction and purification of metals such as aluminum has relied on the electrowinning process for decades. The Hall-Héroult process, developed in 1885, utilizes a molten salt electrolyte to electrochemically produce aluminum metal (Al) and carbon dioxide (CO2) from aluminum oxide (Al2O3) and carbon.1–3 Similar molten salt techniques have been developed for a variety of other metals including the rare earth metal Neodymium (Nd). Neodymium is of particular interest recently with significant increases in demand being driven by the increased production of new technologies such as electrified vehicles and magnetic data storage that require neodymium in the form of neodymium–iron–boron (Nd–Fe–B) permanent magnets. 4,5 The state of the art procedure for neodymium processing, similar to the aluminum process, utilizes a neodymium and lithium fluoride molten salt electrolyte with a sacrificial carbon anode to convert neodymium oxide (Nd2O3) and carbon to neodymium metal and carbon dioxide.4,6 As an unfortunate byproduct of this process performed in a fluoride containing molten salt, perfluorocarbons (PFCs) can also be produced simultaneously alongside carbon dioxide from the sacrificial anode. The formation of PFCs combined with the emission of a significant amount of greenhouse gas (carbon dioxide) make the current process for neodymium electrowinning undesirable from an environmental standpoint.7 An alternative molten salt process has been proposed in which the fluoride salts have been replaced with chloride salts consisting of lithium chloride (LiCl) and potassium chloride (KCl). Rather than directly converting neodymium oxide to neodymium metal, the oxide is first converted to chloride salt form by reaction with hydrochloric acid. The neodymium salt is then dissolved into the LiCl-KCl molten salt and neodymium is electroplated via the below set of reactions.8,9 Cathode: 2NdCl3 + 6e- → 2Nd(solid) + 6Cl- Anode: 6Cl- → 3Cl2 + 6e- Overall: 2NdCl3 → 2Nd(solid) + 3Cl2 This process has several distinct advantages. Utilizing the chlorine reaction eliminates the need for a sacrificial anode material as well as the production of carbon dioxide. The chloride based molten salt also eliminates the formation of PFCs. The chlorine produced could then be recycled to make more hydrochloric acid for use in converting neodymium oxide to chloride. Our work evaluates anode and cathode behavior during this neodymium chloride molten salt process in order to determine its viability. Overpotential and stability of various anode materials are investigated in order to minimize energy consumption and ensure long life of process materials. The effect of various plating conditions such as current density and substrate material are investigated to determine impact on deposit quality, coulombic efficiency, and metal purity. Additional purification techniques such as vapor distillation procedures are developed to ensure a product that is viable for industrial use. This proof of concept work aims to develop a safe, sustainable and environmentally friendly path towards large scale production of rare earth elements. Reactor design and cathode efficiency results are based upon work supported by the U.S. Department of Energy’s Office of Energy Efficiency and Renewable Energy under the Advanced Manufacturing Office, Award Number DE-EE0009434. Anode design work was supported through a subcontract from the Ames Laboratory with funding from the Department of Energy - Energy Efficiency and Renewable Energy under contract No. DE-AC02-07CH11358; Agreement No. 26110-AMES-CMI. The views expressed herein do not necessarily represent the views of the U.S. Department of Energy or the United States Government. T. R. Beck, Electrochem. Soc. Interface, 23, 36–37 (2014).G. G. Botte, Electrochem. Soc. Interface, 23, 49–55 (2014).W. E. Haupin, J. Chem. Educ., 60, 279–282 (1983).M. F. Chambers and J. E. Murphy, Electrolytic production of neodymium metal from a molten chloride electrolyte.B. Sprecher, R. Kleijn, and G. J. Kramer, Environ. Sci. Technol., 48, 9506–9513 (2014).V. S. Cvetković et al., Met. 2020, Vol. 10, Page 576, 10, 576 (2020).H. Vogel, B. Friedrich, H. Vogel, and B. Friedrich, Int. J. Nonferrous Metall., 6, 27–46 (2017).R. Akolkar, J. Electrochem. Soc., 169, 043501 (2022).D. Shen and R. Akolkar, J. Electrochem. Soc., 164, H5292–H5298 (2017).

Electrochemical polarization and reduction experiments are reported which were performed with a three-terminal cell and a molten salt electrolyte consisting of calcium chloride with additions of calcium oxide. Employing a metal cathode, a graphite anode and a pseudo-reference electrode also made from graphite, polarization measurements were carried out with the aim to validate the performance of the pseudo-reference electrode and to assess the stability of the electrolyte. Using a chromium sesquioxide cathode in conjunction with a graphite anode and a graphite pseudo-reference electrode, electrochemical reduction experiments were conducted under potentiostatic control. The key results are: a graphite pseudo-reference electrode has been shown to be appropriate in the present type of molten salt electrochemical experiments that take place on a time scale of many hours; the conversion of chromium oxide into chromium metal has been accomplished under cathodic potential control and in the absence of calcium metal deposition; a significant amount of calcium oxide in the calcium chloride has been found necessary to preclude anodic chlorine formation throughout the entire experiment; a considerable overpotential has been identified at the anode.

Low temperature molten salts are a new class of electrolytes for battery applications (e.g. [1]). Viscosity measurements of low temperature molten salts based on mixtures of aluminium or copper halide and alkylpyridinium or dialkylimidazolium halide have been reported [1-5]. They have shown strong dependences of viscosity with changes in composition in basic (i.e. organic-rich) melts [1, 2, 4, 5]. Further, 'gaps' in the liquidus lines, i.e. regions where fusion does not occur, only a glass transition at very low temperatures, have been shown for binary melts containing 1-methyl-3-ethylimidazolium chloride (MEIC) [1] and bromide [2] as the organic salt. Finally, measurements of chemical shifts for proton and carbon nuclear magnetic resonance spectra of basic MEICA1C13 melts have been explained in terms of oligomeric structures [6, 7]. All of these measurements used viscometers based on variations of Cannon-Fenske devices [1-3, 5] or the falling ball method [4]. These methods do not provide shear stress-shear rate data, which could be used to determine whether the melts behave like non-Newtonian fluids. This paper reports viscosity measurements of MEIC-A1CI3 binary melts using a plate and cone viscometer (in order to obtain shear stress-shear rate data) and compares the viscosities measured using this technique with those of previous investigators.

The effective separation of aluminum (Al) foil and cathode materials is a critical issue for the recycling of spent lithium-ion batteries (LIBs). Previous studies have shown that the strong binding force provided by the organic binder polyvinylidene fluoride (PVDF) between the cathode materials and the Al foil of spent LIBs makes it difficult to peel off the cathode materials from the Al foil, reducing the effectiveness of the metal recovery process. This study reports on a low-temperature molten salt technology for melting the organic binder PVDF. The results showed that an aluminum chloride-sodium chloride (AlCl3-NaCl) system—a nontoxic reaction medium—could melt PVDF efficiently and is environmentally friendly as well, because of the phase transformation of molten salt caused by heat storage. The optimal conditions for peeling off cathode materials were a temperature of 160 °C, molten salt:cathode electrode mass ratio of 10:1, and holding time of 20 min. The highest peeling off percentage of cathode materials was 99.8 wt %. The purpose of this study was to provide an environmentally friendly, low-cost, and effective solution for the separation of cathode materials and Al foil from spent LIBs.

Over the last century, anthropogenic activity has led to a significant increase in the concentration of carbon dioxide in the Earth's atmosphere. Today, the annual increase in CO2 is 3200-3600 million tons. Carbon dioxide together with other greenhouse gases (water vapor H2O, methane CH4, nitrous oxide N2O, sulfur hexafluoride SF6, etc.) causes global warming, which leads to serious environmental degradation - increasing the acidity of sea water, melting glaciers, strengthening the water cycle, which in some regions leads to heavy rainfall and floods, and in others - to extreme droughts. Therefore, the effective carbon dioxide utilization is becoming an urgent scientific and environmental task.One of the ways of carbon dioxide utilization is the electrochemical method. It consists in the electrochemical reduction of CO2 at the cathode. Depending on the conditions of electrolysis (composition of the electrolytic bath, temperature, current density, voltage in the bath, electrode materials), the chemical composition of cathode products changes dramatically.Report is a review of the present state of research concerning the electrochemical conversion of carbon dioxide from conducting liquid and solid media of different chemical composition. They include solid, aqueous, non-aqueous (organic and ionic liquids), and molten salt electrolytes. It contains a comparative analysis of the effectiveness of using these electrolytes, as well as products obtained by the electrochemical splitting of CO2 and the prospects for their use. Special emphasis has been made on the electrochemical decomposition of carbon dioxide from molten salts, several variants of decomposition have been considered, the advantages and disadvantages of each variant have been analyzed. An analysis of literature data on this subject as well as research results of the author on the direct electrochemical conversion of CO2 into valuable solid-phase chemicals with added value is presented.A feature of the electrochemical reduction of CO2 dissolved in molten salts, in contrast to aqueous, organic, solid electrolytes and ionic liquids is the possibility of forming a solid carbon phase at the cathode. Knowledge of the laws of electrode processes involving CO2 is necessary to create a scientific basis and control for the processes of electrochemical synthesis of nanosized carbon-containing inorganic compounds - nanotubes, nanofibers, graphene, amorphous carbon, carbides of refractory metals and numerous composites based on them.The voltammetric study of carbon electrowinning mechanism from carbon dioxide under excessive pressure and lithium carbonate in different gas media (air, argon, carbon dioxide) dissolved in chloride melts at temperatures of 550–800 °С was conducted. The characterization of the chemical and phase compositions, morphological and structural features of nanosized carbon phases obtained by electrolysis in the studied melts has been carried out; a correlation between the structure of the products and the synthesis conditions is established.Thermodynamic analysis of possible ways of electroreduction of CO2 and carbonates of alkali and alkaline earth metals in the temperature range 700 - 1000 K showed that the cathode product can be: (1) - solid carbon phase; (2) - carbon monoxide; (3) - carbide phase. At temperatures below 1000 K, the first path will be thermodynamically advantageous.Electrochemical behavior of CO2 in molten salt mixtures NaCl–KCl (0.5: 0.5 mol%); NaCl–KCl–CsCl (0.3: 0.245: 0.455 mol%); NaCl–KCl–NaF (0.423: 0.423: 0.154 mol.%) under gas excess pressure (1-17 atm.) was studied by cyclic voltammetry at different potential scan rates (0.02-10 Vs-1) and reverse potentials at Pt, Au and GC electrodes. It was established that CO2 electroreduction takes place in two stages, the electrode process is controlled by the charge transfer rate and the rate of CO2 diffusion in the melts. The solubility of CO2 in the melts of Na,K|Cl and Na,K|Cl,F was determined and the implementation of Henry's law in the studied pressure range was shown. An ECE (electrochemical–chemical–electrochemical) mechanism of cathodic reaction has been proposed for the cathode discharge of CO2. Oxidation of oxide- and carbonate- anions takes place at the anode, with the release of oxygen.Electrochemical reduction of Li2CO3 in molten equimolar mixture of Na,K|Cl in various gaseous media (air, argon, CO2) was studied by CV. Reduction of Li2CO3 to carbon in air occurs through the stage of preliminary chemical reaction of acid-base type with the formation of two electrochemically active particles of CO2 and {LixCO3}2-x at potentials -0.8 and -1.7 V, respectively, relative to Pb|PbCl2 reference electrode . Both processes are irreversible, and the limiting stage of reduction {LixCO3}2-x is the diffusion of the depolarizer to the electrode surface. In the atmosphere of argon and CO2, only {LixCO3}2-x participates in the electroreduction process.Promising areas of application of electrolytic carbon are presented.

Calcium batteries (CaBs) fundamentally offer a promise of sustainable high energy density storage. However, the development of functional CaB electrolytes remains a key challenge. Here, molecular simulations are used to investigate structural and dynamic properties of solvent‐free molten salt electrolytes (MSEs) containing Ca2+ and alkali cations (Li+, Na+, K+), paired with either FSI or TFSI anions. Two equimolar MSEs, [Li, Na, K, Ca]FSI and [Li, Na, K, Ca] TFSI, are examined across a range of temperatures to better understand cation–anion interactions, coordination and local structure, and ion mobility, in particular with respect to Ca2+. The interplay between cation charge density, anion structure, and thermal effects provides valuable insights into the MSEs’ macroscopic behavior. These insights inform the design of advanced electrolytes that enhance Ca2+ mobility, supporting the development of next‐generation CaBs.

Molten salt electrolytes have been considered to be the most promising electrolytes for next-generation lithium secondary batteries, owing to their high safety and wide electrochemical windows. Perfluorosulfonylamide-based lithium salts exhibit the lowest melting temperatures among all of the lithium salts. Nevertheless, their melting point is above 100 °C, and lowering their melting point is still a considerable challenge for their application as secondary battery electrolytes. In this study, we prepared binary lithium salts by mixing lithium bis(fluorosulfonyl)amide (LiFSA, Li[F–SO2–N–SO2–F]) and lithium (fluorosulfonyl)(trifluoromethylsulfonyl)amide (LiFTA, Li[F–SO2–N–SO2–CF3]) using a ball mill and revealed a eutectic composition ratio of 35:65, a eutectic point of 76 °C, and a viscosity of 20800 mPa s–1 at 100 °C. This binary lithium molten salt electrolyte exhibited a low melting point, a wide electrochemical potential window of 5.1 V, no Li+ concentration gradient, and successful charge and discharge of a conventional graphite negative electrode with high Coulombic efficiency at a 0.05C rate. Our findings further advance the development of high-voltage and high-power lithium secondary batteries.

As the operating period of a nuclear power plant increases, the demand for dismantling of nuclear facilities has been rising, and the dismantling market is expected to continue to expand steadily. The Inconel 600, which was used as a material for the steam generator, has problem with crack and corrosion, and it is currently replaced with a steam generator of Inconel 690. It has been reported that if this steam generator is corroded or cracked, the cooling water contaminated with radioactive elements such as cobalt, strontium, may penetrate into the cracks. Therefore, development of decontamination technology for radioactive metal waste is essential to minimize waste during dismantling process.This study investigates the decontamination possibility of Inconel 600 in LiCl-KCl-CoCl2-NiCl2 molten salt electrolyte. Inconel 600 – cobalt alloy was used for anode as a simulated radioactive metal waste. After electrorefining process, the cobalt remains in the molten salt. Therefore, CoCl2 was added to the electrolyte to imitate the case when the radioactive metal waste was dissolved and concentrated in the electrolyte. Electrochemical analysis was performed by cyclic voltammetry (CV) to confirm the redox behavior of Ni ions in molten salt electrolytes. Decontamination experiments were performed by chrono potentiometry (CP) to analyze the oxidation behavior of Inconel 600 – cobalt alloy (anode) and the reduction behavior of Ni on Ni plate electrodes (cathode). Decontamination factor(DF) of the deposits produced by electrorefining was analyzed by ICP.

Electrochemical separation is one of the most promising methods for recycling used nuclear fuel, in which uranium is isolated from other fission products using a molten salt electrolyte1. The used fuel is immersed in molten salt electrolyte in an electrochemical cell referred to as an electrorefiner. In an ideal electrorefiner cell the used fuel is dissolved anodically, releasing uranium ions into a ternary chloride salt (LiCl-KCl-10wt%UCl3). The uranium ions are then reduced at an inert cathode, forming uranium metal for reuse in new uranium fuel pellets2. However, in actual electrorefiner systems, uranium is not the only element from the used fuel that is oxidized into the electrolyte. Alkali/alkaline-earth elements, such as cesium, barium, and strontium, are also oxidized because they have lower standard reduction potentials than uranium in the chloride system3. As alkali/alkaline-earth elements accumulate in the electrolyte, they change the physical and chemical properties of the electrolyte due to their short half-lives and high heat densities. The electrolyte is periodically removed from the electrorefiner to maintain the recycling process, thereby generating excessive volumes of nuclear waste. Lichtenstein et al. have demonstrated that alkali/alkaline-earth elements exhibit low thermodynamic activity (6.6 × 10-16 at x Ba = 0.05, 773 K) in liquid metals such as bismuth, implying strong atomic interactions4. These interactions cause a shift in the elements’ reduction potentials and can be leveraged to selectively remove the accumulated elements from the electrolyte by depositing them into liquid metal electrodes. To determine the viability of removing alkali/alkaline-earth elements using liquid metals such as lead, the thermodynamic properties of Sr-Pb alloys were determined by electromotive force (emf) measurements using a solid state electrolyte (binary CaF2-Sr­F­2, 97-3 mol%). Emf values were measured at 723 K-1073 K using a Sr(s)|CaF2-SrF­2|Sr(in Pb) electrochemical cell and were used to determine the thermodynamic properties of Sr-Pb, including activity, partial molar entropy, and partial molar enthalpy for x Sr = 0.05-0.75. At 973 K, activity values of Sr in Pb were as low as 5 × 10-9 at xSr = 0.05, implying strong atomic interactions between Sr and Pb. According to Okamoto et al., the liquid-state solubility of Sr in Pb is approximately 37 mol% at 973 K5. With the high solubility of Sr in Pb in the liquid state, combined with strong Sr-Pb atomic interactions, Pb has demonstrated promise for use as a liquid metal electrode material to remove Sr2+ ions from molten salt electrolytes. [1] Electrometallurgical Techniques for DOE Spent Fuel Treatment: Final Report, National Academy Press Washington, D.C, 2000.[2] Willit, J. L., Miller, W.E., Battles, J.E. Electrorefining of uranium and plutonium – A literature review, J. Nucl. Mater. 195 (3), 229-249 (1992). [3] Roine, A., Outokumpu HSC Chemistry® 5.1; Chemical Reaction and Equilibrium Software with Extensive Thermochemical Database, (2002). [4] Lichtenstein, T., Smith, N.D., Gesualdi, J., Kumar, K., Kim, H. Thermodynamic Properties of Barium-Bismuth Alloys Determined by emf Measurements, Electrochim. Acta. 228, 628-635 (2017). [5] Okamoto, H. Sr-Pb (Strontium-Lead), 2nd ed., ASM International, Materials Park, (1990).

A potential working electrode based on graphite and montmorillonite for electrochemical applications in both aqueous and molten salt electrolytes

Ionic liquids (ILs) are low temperature molten salts, that is, a salt in the liquid state. ILs used to present a very low vapour pressure and this property makes of the ILs key materials for the development of a wide variety of emerging technologies. The stability of ILs at high temperatures (several hundred degrees), low combustibility, and even the relatively high viscosity of some of them compared to conventional solvents, are characteristic of interest for some applications. Due to the large diversity of ILs components, they may present wide structural variations which can be used to design the IL with more adequate properties for a particular application. These applications might include new types of lubricants and fluids for thermal engines, electrodeposition, energy and CO2 capture devices, biomimetics, double layer capacitors,.....in fact, the scientific and technological importance of the ILs spans nowadays to a wide range of applications [1-5]. Among the energy devices, polymer-electrolyte membranes for fuel cell application are under development as a way to reduce global warming and energy cost and ILs incorporation in the structure of Nafion, a typical membrane for fuel cell use, is under study [6-8]. Since transport properties of porous and dense membranes can be modified with the addition of substances which could favour/reject the pass of some of the particles or ions in a mixture, the incorporation of a particular IL in the structure of a membrane may increase its selectivity and/or specificity. Chemical characterization and determination of electrical parameters for different ILs as well as the changes associated to water incorporation, a subject of interest for different electrochemical applications, is considered in this work. Moreover, due to the importance that membrane separation technology has nowadays, modification of membranes with different structures by incorporation of RTILs or IL-cations and their effect on mass and charge transport is also presented. Ionic liquids, membranes and membranes/IL-modified samples were chemically characterized by X-ray photoelectron spectroscopy (XPS). This technique allows the

In this work, a low-temperature electro-deoxidation strategy of solid SeO2 was proposed for the first time in neutral NaCl-AlCl3 molten salt. Based on thermodynamic and electrochemical means, the deoxidation of SeO2 was confirmed to be a two-step two-electron process. Besides, the electro-deoxidation products and their morphology evolution processes were revealed along with the change of potential. It is hoped that the deep understanding of preparing metal Se by direct electrolytic reduction can offer key insights into short-process and green metallurgy of other characteristic scattered metals.

Electrodeposition behavior of aluminum from urea-acetamide-lithium halide low-temperature molten salts

Zirconium is widely used in the nuclear industry as a cladding material for nuclear reactors and loading nuclear fuel. From the perspective of safety and the economy, the recovery of zirconium from cladding waste at low temperatures is of strategic significance for nuclear energy. This work studied the electrochemical behavior of Zr(IV) and the separation of Zr metal in a low-temperature LiCl–KCl–CsCl molten salt system at 573 K (300 °C). Zr(IV) ion was reduced to metallic Zr through a two-step four-electron reaction process Zr(IV) → Zr(III) → Zr on the W electrode. The diffusion coefficients of Zr(IV) on the W electrode calculated by cyclic voltammetry and chronoamperometry were 5.805 × 10−5 cm2 s−1 and 2.861 × 10−5 cm2 s−1, respectively. Furthermore, the reaction activation energy of the Zr(III)/Zr(0) pair was measured to be 34.52 kJ mol−1 by the Tafel method. Then, the electrochemical recovery of Zr was accomplished on the W electrode by potentiostatic electrolysis at −2.0 V or galvanostatic electrolysis at 0.01 A, and two zirconium-containing products with the dendritic and flakes morphologies were obtained accordingly. This study provides a new low-temperature molten salt system for the reprocessing of zirconium cladding and shows the application potential of low-temperature molten salts LiCl–KCl–CsCl for spent fuel reprocessing.