Academic literature on the topic 'Magnesium Batteries'

This thesis is a feasibility study of the possible application of magnesium alloys forfuture magnesium-ion batteries. It investigates dierent alloys and characterizesthem with respect to internal resistance, overpotentials and the reversibility of theelectrochemical reaction. SEM and EDS studies of used electrodes have also beencarried out. It has been showed that alloys, easier to handle and at a fraction of thecost, can be used with equal or better performance than pure Mg. The seeminglysuperior alloy, AZ61 exhibits a coloumbic eciency close to 100%, at higher chargerates than pure Mg.

This dissertation focuses on the synthesis and electrochemical testing of new electrolyte salts for rechargeable multivalent ion batteries. In chapters 2 and 3 the synthesis of Mg and Ca hexafluoropnictogenate salts as well as the electrochemical behaviour of Mg(PF6)2 is presented. Pure samples of Mg(EF6)2 (E = P, As, and Sb) can be synthesized using Mg metal and NOPF6/NOSbF6 in CH3CN or via a ammonium salt deprotonation route using Me3NHAsF6 and Bu2Mg. The NOPF6 method was extended to the Ca variant, but isolation of a pure Ca(PF6)2 material required the presence of a crown ether. Electrochemical and microscopy measurements of THF-CH3CN solutions of Mg(PF6)2 show that the electrolyte good electrochemical stability and can facilitate the plating/stripping of Mg. Further, this electrolyte system can be cycled in a full cell using the Chevrel phase Mo6S8 cathode. The electrochemical stability of the AsF6− and SbF6− salts is lower than that of the PF6− salt and electrolyte decomposition is observed when cycling on Mg electrodes. In chapter 4 the development of a series of Mg aluminates [Mg(AlOR4)2] using a general synthetic platform based on Mg(AlH4)2 and various alcohols is presented. Preliminary electrochemical studies performed on these aluminate salts in dimethoxyethane identify the phenoxy and perfluoro-tert-butoxy derivatives as promising electrolyte systems. Electrochemical cycling of these electrolytes using gold and Mg electrodes show that systems containing chloride, brought through to the product from the starting material in the form of NaCl, exhibit lower plating/stripping overpotentials and higher Coulombic efficiencies than systems from which chloride had been removed. Further, these two electrolytes can be used in Mg full cells containing the Chevrel phase cathode. Solid-state 23Na NMR analysis as well as DFT calculations show that chloride-containing electrolytes facilitate the co-insertion of Na into the cathode material. In chapter 5 the hydroboration of pyridines and CO2 in the presence of pinacolborane is presented. An optimized system employing NH4BPh4 and HBpin is developed and a mechanism of pyridine hydroboration is proposed based on multinuclear NMR spectroscopy. The catalytic reaction was found to be catalyzed by a boronium salt, which was structurally characterized in the solid-state by single crystal X-ray diffraction. This new catalytic method is shown to be tolerant to a number of functional groups in the 3-position on pyridine as well as quinoline, and CO2, producing the hydroboration products in good yields.

The importance of energy storage worldwide is increasing with the use of renewable energy sources and electric vehicles. With the intermittent nature of wind and solar power, large-scale grid storage is an extremely important progression needed to reduce the use of fossil fuels. For this to become a reality, rechargeable batteries beyond existing Li-ion technologies need consideration. The development of such batteries requires improvement of understanding their component materials. Modern computer modelling techniques enable valuable insights into the fundamental defect, ion transport and voltage properties of battery materials at the atomic level. Atomistic simulation and ab initio density functional theory (DFT) techniques have been used to study a number of potential cathode materials for Na-ion and Mg batteries. Firstly, the olivine and maricite forms of NaFePO4 are considered in terms of their defect formation energies and Na ion diffusion. The atomistic study indicates that anti-site disorder is the most favourable type of intrinsic defect. The activation energies for Na-ion migration in the olivine and maricite materials are 0.4 eV and 1.6 – 1.8 eV respectively. Moreover, molecular dynamics (MD) studies reveal that there is only substantial Na-ion diffusion in the olivine structure, with diffusion coefficients (DNa) at 300 K of 7 x 10−13 cm2s−1 for maricite and 4 x 10−9 cm2s−1 for olivine NaFePO4. The presence of anti-site defects is shown to decrease Na+ diffusion within the olivine structure, which is of relevance to its rate behaviour. Secondly, the effect of lattice strain on ion transport and defect formation in olivine-type LiFePO4 and NaFePO4 is investigated as a means to enhance their ion conduction properties. It is predicted that lattice strain can have a remarkable effect on the rate performance of olivine cathode materials, with a major increase in ionic conductivity and decrease in blocking defectsat room temperature. Thirdly, DFT techniques have been used to examinesurface and grain boundary formation in P2-NaCoO2. The coordination lossexperienced by ions present at surfaces is found to influence the resultingsurface energy. Layered oxide cathode materials were further investigated byconsidering the effect of Mg2+ doping on P2-Na2 [Ni1 Mn2 ]O2. Na vacancy 333formation energies decreased with 10% Mg2+ doping on the Ni site and an increase in Na diffusion was predicted with MD calculations. This positive effect on Na ion conductivity is caused by displacement of the Mg ions from the transition metal layer and the resulting change in electrostatic potential. Finally, Mg ion conduction, doping and voltage behaviour of MgFeSiO4 were studied. The Mg-ion migration activation energy is relatively low for an olivine-type silicate, and MD simulations predict a diffusion coefficient (DMg) of 10−9 cm2s−1, suggesting favourable electrode kinetics. Partial substitution of Fe by Co or Mn could increase the cell voltage from 2.3 V vs Mg/Mg2+ to 2.8 - 3.0 V.

Thesis (Ph.D. (Engineering mechanics)) --University of Limpopo, 2004<br>This thesis explores the important issues associated with the insertion of Mg2+ and Li+ into the solid materials: molybdenum sulphide and titanium disulphide. This process, which is also known as intercalation, is driven by charge transfer and is the basic cell reaction of advanced batteries. We perform a systematic computational investigation of the new Chevrel phase, MgxMo6S8 for 0 ≤ x ≤ 2, a candidate for high energy density cathode in prototype rechargeable magnesium (Mg) battery systems. Mg2+ intercalation property of the Mo6S8 Chevrel phase compound and accompanied structural changes were evaluated. We conduct our study within the framework of both the local-density functional theory and the generalised gradient approximation techniques. Analysis of the calculated energetics for different magnesium positions and composition suggest a triclinic structure of MgxMo6S8 (x = 1 and 2). The results compare favourably with experimental data. Band-structure calculations imply the existence of an energy gap located ~1 eV above the Fermi level, which is a characteristic feature of the electronic structure of the Chevrel compounds. Calculations of electronic charge density suggest a charge transfer from Mg to the Mo6S8 cluster, which has a significant effect on the Mo-Mo bond length. There is relatively no theoretical work, in particular ab initio pseudopotential calculations, reported in literature on structural stability, cations "site energy" calculations, and pressure work. Structures obtained on the basis from experimental studies of other ternary molybdenum sulphides are examined with respect to pressure-induced structural transformation. We report the first bulk and linear moduli of the new Chevrel phase structures. This thesis also studies the reaction between lithium and titanium disulfide, which is the perfect intercalation reaction, with the product having the same structure over the range of reaction 0  x  1 in LixTiS2. Calculated lattice parameters, bulk moduli, linear moduli, elastic constants, density of states, and Mulliken populations are reported. Our calculations confirm that there is a single phase present with an expansion of the crystalline lattice as is typical for a solid solution, about 10% perpendicular to the basal plane layers. A slight expansion of the lattice in the basal plane is also observed due to the electron density increasing on the sulfur ions. Details on the correlation between the electronic structure and the energetic (i.e. the thermodynamics) of intercalation are obtained by establishing the connection between the charge transfer and lithium intercalation into TiS2. The theoretical determination of the densities of states for the pure TiS2 and Li1TiS2 confirms a charge transfer. Lithium charge is donated to the S (3p) and Ti (3d) orbitals. Comparison with experiment shows that the calculated optical properties for energies below 12 eV agrees well with reflectivity spectra. The structural and electronic properties of the intercalation compound LixTiS2, for x = 1/4, 3/4, and 1, are also investigated. This study indicates that the following physical changes in LixTiS2 are induced by intercalation: (1) the crystal expands uniaxially in the c-direction, (2) no staging is observed. We also focus on the intercalation voltage where the variation of the cell potential with the degree of discharge for LiTiS2 is calculated. Our results show that it can be predicted with these well-developed total energy methods. The detailed understanding of the electronic structure of the intercalation compounds provided by this method gives an approach to the interpretation of the voltage composition profiles of electrode materials, and may now clearly be used routinely to determine the contributions of the anode and cathode processes to the cell voltage. Hence becoming an important tool in the selection and design of new systems. Keywords Magnesium rechargeable battery; Chevrel, Lithium batteries; Li and Mg-ion insertion; TiS2; Mo6S8; Charge transfer; reflectivity, intercalation, elastic constants, voltage, EOS, Moduli.<br>the National Research Foundation, the Royal Society(U.K),the Council for Scientific and Industrial Research,and Eskom

Kyoto University (京都大学)<br>0048<br>新制・課程博士<br>博士(人間・環境学)<br>甲第19071号<br>人博第724号<br>新制||人||174(附属図書館)<br>26||人博||724(吉田南総合図書館)<br>32022<br>京都大学大学院人間・環境学研究科相関環境学専攻<br>(主査)教授 内本 喜晴, 教授 田部 勢津久, 准教授 藤原 直樹<br>学位規則第4条第1項該当

Les objectifs de cette thèse sont d’une part, de développer de nouveaux électrolytes par la conception de nouveaux sels de magnésium non dangereux ou par l’utilisation d’additifs aromatiques comme l’anthracène et d’autre part de synthétiser un polymère organique ayant des propriétés redox adaptées à son utilisation comme électrode positive dans des batteries au Magnésium.La première méthodologie a été la synthèse de plusieurs sels de magnésium obtenus par la réaction de phénol substitués ou de thiophénol avec l’anion tetrahydroborate. Les meilleurs résultats ont été obtenus avec le sel obtenu par réaction du thiophénol et du tétrahydroborate. L'impact de ce nouveau sel sur l’amélioration de l'interface Mg/électrolyte a été caractérisé par des électrochimie. En outre, les performances de la cellule complète Mg/Mo6S8 ont été évaluées, et une capacité de 75 mAh/g a été obtenue après 20 cycles, avec une faible polarisation de l'électrode de Mg. La deuxième méthodologie a consisté à étudier l'effet d’additifs aromatiques sur le processus de dépôt/dissolution du Mg, et ainsi permettre d’approfondir notre compréhension du mécanisme assisté sous-jacent. La deuxième partie de cette thèse présente les performances électrochimiques de matériaux organiques utilisés comme électrode positive pour les batteries au lithium et au magnésium. Le polybenzoquinonedisulfure (PBQDS) a été synthétisé avec un rendement très élevé de façon écologique et facile. Les performances obtenues en cellule Li sont intéressantes, alors qu’en cellule Mg, une perte de capacité importante est obtenue associée au piégeage des ions Mg2+ au sein de l’électrode, due à une forte interaction oxygène/Mg2+. L'utilisation d'un additif solvatant, un éther couronne, dans l'électrolyte atténue partiellement ce comportement, proposant ainsi des pistes d'amélioration intéressantes<br>The objectives of this thesis are, on the one hand, to develop new electrolytes by the design of new non-hazardous magnesium salts or by the use of aromatic additives such as anthracene and, on the other hand, to synthesize an organic polymer with redox properties suitable for its use as a positive electrode in magnesium batteries. The first methodology was the synthesis of several magnesium salts obtained by the reaction of substituted phenol or thiophenol with the tetrahydroborate anion. The best results were obtained with the salt obtained by the reaction of thiophenol and tetrahydroborate. The impact of this new salt on the improvement of the Mg/electrolyte interface was characterized by chronoamperometry and impedance spectroscopy measurements. In addition, the performance of full cell Mg/Mo6S8 was evaluated, a capacity of 75 mAh/g was obtained after 20 cycles, with a weak polarization of the Mg electrode. The second methodology several π-rich compounds were used. The best promising molecule is the 2-(tert-butyl)anthracene with an improvement in the Mg plating/stripping process reversibility. The second part of this thesis will present the electrochemical performance of organic material using as positive electrode for both lithium and magnesium batteries. Polybenzoquinonedisulfide (PBQDS) was synthesized with very high yield in a green and easy way. After the particle size reduction using ball milling technique, the discharge capacity reaches a stable value of 140 mAh/g at C/20 in sulfolane based electrolyte. In Mg cell, even if similar capacity is obtained in the first cycles, a large capacity fading is observed associated with the trapping of Mg2+ in the active material, due to strong oxygen/Mg2+ interaction. The use of solvation additive (crown ether) in the electrolyte mitigates partially this behaviour, given some interesting leads of improvement

The research activity described in this thesis has been focused on the development and study of novel electrolyte and electrode materials for application in Lithium and Magnesium secondary batteries. The proposed materials belong to the “beyond Li-ion” class of compounds, where systems exceeding the energy density values of classic Li-ion batteries or completely innovative chemistries are presented. Three different classes of electrolytes have been prepared and studied. A solid polymer electrolyte has been obtained by a lithium functionalization of a poly(vinyl alcohol-co-vinyl acetate), forming lithium alkoxide functional groups. In this way, the counter anion of Li+ was the overall polymer chain, giving rise to a single lithium ion conductivity. However, the room-temperature conductivity value observed for this material was quite low (4.6·10-10 S·cm-1). By ionic liquid (IL) doping of the solid polymer electrolyte, we have obtained a double effect: i) lithium cations have been exchanged by the cations of IL, enhancing the mobility of the active species; and ii) the flexibility of polymer chains has been increased by the plasticizing effect of the IL. Thus, a room temperature conductivity of 1.3·10-5 S·cm-1 has been reached, maintaining a high value of Li transference number (0.59). By reacting glycerol with different quantities of lithium hydride, a new family of lithium-ion conducting electrolytes has been synthetized. In these electrolytes the lithium glycerolate component acts as a large and flexible macro-anion which is able to provide a singleion conductivity to the material (2.0∙10-4 at 30 °C and 1.6∙10-2 S∙cm-1 at 150 °C). In the last class of electrolytes, ionic liquid-based materials for magnesium batteries, the cation and anion replacement effect on the structure, conductivity mechanism, and electrochemical performances has been studied. The proposed materials have exhibited a conductivity value between 10-3 and 10-4 S∙cm-1, an overpotential in the magnesium deposition lower than 50 mV vs. Mg/Mg2+, an anodic stability up to +2.35 V vs. Mg/Mg2+, and a coulombic efficiency up to 99.94 %. In the second part of this Ph.D. project, the improvement of the electrochemical features of various cathode materials has been studied. In the first case, it has been found that, by adding CuCO3 to the precursors, segregated CuO particles have been formed. The presence of these particles has improved the charge-transfer kinetics during the charge/discharge processes of the cathode material. On the other hand, graphite addition to the precursors has been found to improve the elasticity of the 3D structure of the cathode backbone. Thus, an increased structural flexibility that facilitates the percolation of lithium ions along the 1D channels of the cathode material has been observed. In the second approach, the improvement of the electron conductivity of a high-voltage cathode has been gauged by V, Nb, or Ta insertion within its olivine structure. This approach has allowed for an improved kinetic and reversibility of Li+ insertion reaction. The specific capacity reached by these cathodes was equal to 149 mAh∙g-1. The last cathode material has been implemented in a magnesium secondary battery device. A graphene oxide surface functionalization of vanadium-based nanoparticles has been obtained thanks to electrostatic interactions through ammonium bridges. This functionalization has allowed for the obtaining of a material able to: a) sustain extremely high current rates (1000 mA∙g-1, 1700 mW∙g-1 of specific power); and b) give reasonable specific capacity values (72 mAh∙g-1).

With the growing global population comes the ever-increasing consumption of energy in powering cities, electric vehicles, and portable devices such as cell-phones. While the power grid is used to distribute energy to consumers, the energy sources needed to power the grid itself are unsustainable and inefficient. The primary energy sources powering the grid, being fossil fuels, natural gas, and nuclear, are unsustainable as the economically-accessible reserves are continually depleted in exchange for detrimental emissions and air-pollutants. Cleaner, renewable sources, such as solar, wind, and hydroelectric, are intermittent and unreliable during the peak hours of energy usage, that is dawn and dusk. However, during waking hours and nighttime sleeping hours, energy consumption plummets resulting in substantial losses of potential energy as these intermittent energy providers do not have the infrastructure to store unused energy. Therefore, the research and development of efficient energy storage materials and renewable energy sources is critical to meet the needs of society in their fundamental operation while reducing harmful emissions. The research presented in this thesis focuses on selected energy storage materials and electrocatalysts as attractive technology for sustainable and benign renewable energy chemistry. Specifically, (1) theoretical studies on magnesium chloride / aluminum chloride electrolytes provide insight for further development of Mg batteries; (2) theoretical and experimental studies on viologen derivatives for organic redox flow batteries advance the development of these two-electron storage systems; and (3) a new iron(II) polypyridine catalyst that was found to electrochemically reduce CO2 to produce renewable fuels such as carbon monoxide (CO), hydrogen (H2), and methane (CH4), as well as promote the photochemical CO2-to-methane conversion with visible light.