The thermodynamic properties of magnesium make it a natural choice for use as an anode material in rechargeable batteries, because it may provide a considerably higher energy density than the commonly used lead-acid and nickel-cadmium systems. Moreover, in contrast to lead and cadmium, magnesium is inexpensive, environmentally friendly and safe to handle. But the development of Mg batteries has been hindered by two problems. First, owing to the chemical activity of Mg, only solutions that neither donate nor accept protons are suitable as electrolytes; but most of these solutions allow the growth of passivating surface films, which inhibit any electrochemical reaction. Second, the choice of cathode materials has been limited by the difficulty of intercalating Mg ions in many hosts. Following previous studies of the electrochemistry of Mg electrodes in various non-aqueous solutions, and of a variety of intercalation electrodes, we have now developed rechargeable Mg battery systems that show promise for applications. The systems comprise electrolyte solutions based on Mg organohaloaluminate salts, and Mg(x)Mo3S4 cathodes, into which Mg ions can be intercalated reversibly, and with relatively fast kinetics. We expect that further improvements in the energy density will make these batteries a viable alternative to existing systems.

Magnesium can be reversibly deposited from ethereal solutions of Grignard salts of the RMgX type ( R = alkyl , aryl groups, and X = halides : Cl, Br), and complexes of the Mg ( AX 4 − n R n ′ R n ″ ′ ) 2 type ( A = Al , B; X = Cl , Br; R, R ′ = alkyl or aryl groups, and n ′ + n ″ = n ) . These complexes can be considered as interaction products between R 2 Mg bases and AX 3 − n R n Lewis acids. The use of such complexes in ether solvents enables us to obtain solutions of reasonable ionic conductivity and high anodic stability, which can be suitable for rechargeable Mg battery systems. In this paper we report on the study of variety of Mg ( AX 4 − n R n ) 2 complexes, where A = Al , B, Sb, P, As, Fe, and Ta; X = Cl , Br, and F; and R = butyl , ethyl, phenyl, and benzyl (Bu, Et, Ph, and Bz, respectively) in several solvents, including tetrahydrofuran (THF), 2Me-THF, 1-3 dioxolane, diethyl ether, and polyethers from the “glyme” family, including dimethoxyethane (glyme), ( CH 3 OCH 2 CH 2 ) 2 O ( diglyme ) , and CH 3 ( OCH 2 CH 2 ) 4 OCH 3 (tetraglyme), as electrolyte solutions for rechargeable magnesium batteries. It was found that Mg ( AlCl 4 − n R n ′ R n ″ ′ ) 2 complexes (R, R ′ = Et , Bu and n ′ + n ″ = n ) in THF or glymes constitute the best results in terms of the width of the electrochemical window ( > 2 V ) , from which magnesium can be deposited reversibly. These solutions were found to be suitable for use in rechargeable magnesium batteries. A variety of electrochemical and spectroscopic studies showed that these solutions have a complicated structure, which is discussed in this paper. It is also clear from this work that Mg deposition-dissolution processes in these solutions are far from being simple reactions of Mg / Mg + 2 redox couple. The conditions for optimized Mg deposition-dissolution processes are discussed herein. © 2001 The Electrochemical Society. All rights reserved.

Mg­(N­(SO2CF3)2)2 (MgTFSI2) solutions with dimethoxyethane (DME) exhibit a peculiar behavior. Over a certain range of salt content, they form two immiscible phases of specific electrolyte concentrations. This behavior is unique, as both immiscible phases comprise the same constituents. Thus, this miscibility gap constitutes an exceptionally intriguing and interesting case for the study of such phenomena. We studied these systems from solutions structure perspective. The study included a wide variety of analytical tools including single-crystal X-ray diffraction, multinuclei NMR, and Raman spectroscopy coupled with density functional theory calculations. We rigorously determined the structure of the MgTFSI2/DME solutions and developed a plausible theory to explain the two-phase formation phenomenon. We also determined the exchange energy of the “caging” DME molecules solvating the central magnesium ion. Additionally, by measuring the ions’ diffusion coefficients, we suggest that the caged Mg2+ and TFSI– move as free ions in the solution. Knowledge of the arrangement of the solvent/cation/anion structures in these solutions enables us to explain their properties. We believe that this study is important in a wide context of solutions chemistry and nonaqueous electrochemistry. Also, MgTFSI2/DME solutions are investigated as promising electrolyte solutions for rechargeable magnesium batteries. This study may serve as an important basis for developing further MgTFSI2/ether based solutions for such an interesting use.

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Electrolyte solutions of magnesium organo-halo-aluminates in ethers are suitable for rechargeable magnesium batteries as they enable highly reversible electrodeposition for magnesium while they possess a wide electrochemical window ͑Ͼ2.2 V͒. Adding LiCl or tetrabutylammonium chloride to these solutions considerably improves their ionic conductivity, the kinetics of the Mg deposition-dissolution processes, and the intercalation behavior of Mg x Mo 6 S 8 Chevrel cathodes. The dissolution of both salts in the electrolytic solutions involves acid-base reactions with complex species. Multinuclei nuclear magnetic resonance and Raman spectroscopy were used in conjunction with electrochemical techniques to study these systems. The nature of these reactions, their products, and the way they influence the various properties of these solutions, are discussed herein.There is ongoing interest in the study of electrolyte solutions from which magnesium can be deposited reversibly, mainly for developing rechargeable magnesium batteries. Magnesium deposition from solutions of conventional Mg salts in nonaqueous aprotic solvents is impossible due to complete electrodes passivation. 1 Over the years, scientists found that Mg can be deposited reversibly from ethereal solutions of Grignard reagents ͑RMgX, R = alkyl, aryl X = Cl, Br͒. However, these solutions exhibit a narrow electrochemical window ͑Ͻ1 V͒. 2,4-7 There have also been few attempts to develop improved solutions, of which the best system, ethereal solutions of Mg͑BR 4 ͒ 2 ͑R = alkyl, aryl͒ were presented Gregory et al. 3 These solutions enabled highly reversible Mg deposition and possessed wider electrochemical windows ͑Ϸ1.8 V͒. 3 A few years ago we developed improved electrolyte solutions comprising complexes that can be represented nominally as MgAlR n Cl 3−n ͑0 Ͻ n Ͻ 3, R = alkyl, aryl͒, from which Mg is deposited reversibly. 8 The substitution of a few of the organic ligands around the Lewis acid by chloride enabled solutions with wide electrochemical window, Ͼ2.2 V. 9 This paved the way for the first demonstration of feasible rechargeable Mg-based batteries with Mg x Mo 6 S 8 ͑0 Ͻ x Ͻ 2͒ Chevrel-phase cathode. 10 One of the drawbacks of these solutions is their relatively low ionic conductivity, 1-1.3 mS/cm at 25°C. Thus, it was important to explore directions for increasing their ionic conductivity. In this paper we report on the improvement of the ionic conductivity by the addition of R 4 NCl and LiCl. ExperimentalAll chemical preparations and electrochemical measurements were carried out under pure argon atmosphere in M. Braun, Inc., glove boxes ͑less than 1 ppm of water and oxygen͒. The typical preparation of a complex salt solution was described elsewhere. 11 The standard solution for this work comprised tetrahydrofuran ͑THF͒ and a complex with the formal formula Mg͑AlCl 2 R 2 ͒ 2 denoted as THF/DCC. Triethylaluminum ͑Aldrich, 97%͒, diethylaluminumchloride ͑Aldrich, 97%͒, and ethylaluminumdichloride ͑Ald-rich, 97%͒, were used as received. Chevrel-phase ͑CP͒ Mo 6...

Slow-scan rate cyclic voltammetry ͑SSCV͒ and chronopotentiometry were used for a quantitative comparison of the thermodynamic and kinetic characteristics of Li ϩ and Mg 2ϩ -ion insertion into the Mo 6 S 8 chevrel phase compound. The Li-insertion process consists mainly of three stages with the relative stoichiometries 1:2:1, corresponding to the formation of , respectively. The kinetics of the intercalation is relatively fast. Mg-ion insertion was found to have the stoichiometry 2:2, i.e., Mg 1 Mo 6 S 8 and Mg 2 Mo 6 S 8 are formed. The initial magnesiation and the final demagnesiation of the chevrel phase (Mo 6 S 8 ↔ Mg 1 Mo 6 S 8 ) reveal intrinsically slow kinetics, accompanied by a substantial decrease in the intercalation level. This probably results from a low ionic conductivity of the electrode bulk caused by both small concentration and low mobility of the Mg ion in this potential region, related to the sites that the Mg intercalants occupy in the Mg x Mo 6 S 8 phase. A moderate increase in temperature results in a drastic increase of ion mobility. In Mg͑AlCl (4Ϫn) R n ) 2 solution, the difference of the two sequential insertions of Mg ion into the chevrel phase was found to be 0.26 V, i.e., by 0.08 V lower than that for the insertion of Li ion.The ability of molebdenum cluster chalcogenides, such as the chevrel Mo 6 S 8 phase, to insert reversibly ͑both chemically and electrochemically͒ different types of metal ions has been known for years due to important contributions made et al., 8 etc. The structure of this phase can be presented as a threedimensional array of Mo 6 S 8 units consisting of distorted Mo 6 -octahedra, which, in turn, are surrounded by S 8 cubes 2 ͑see Fig. 1͒. Intersecting, three-dimensional channels of the crystal structure of the chevrel phase facilitate the occupation of vacant sites by guest ions during its reduction. It is known that small guest ions ͑below 1 Å͒ do not occupy the exact center of the S 8 -hole but shift away from it, 2 as seen in Fig. 1. Moreover, due to a peculiar thermal motion of ions in the hole, small cations are delocalized within the hole. Li ions have the radius close to 0.74 Å, and thus belong to the class of small cations. They were proven 2 to be distributed randomly in six inner and six outer sites ͑Fig. 1͒. The stoichiometry of the Li insertion reaction in the chevrel phase has been previously studied by Gocke et al. 4 using chronopotentiometry and 7 Li nuclear magnetic resonance ͑NMR͒. Combination of these techniques allowed for a reasonable conclusion on the nature of the sites appropriate for Li accommodation and the character of their bonding in the host material as a function of the intercalation level, x in Li x Mo 6 S 8 . In another paper, Gocke et al. 5 studied the thermodynamics and kinetics of the electrochemical intercalation of closed shell (d 10 ) metallic ions (Zn 2ϩ , Cd 2ϩ , radii 0.74 and 0.97 Å͒ and s 0 ions such as Na ϩ having formally an ionic radius 0.95 Å, which is similar to Cd 2ϩ . This study demonstrated the competition between...

Advantageous electrolytic solutions for rechargeable magnesium batteries are obtained by dissolving in THF the reaction products of EtAlCl 2 and Bu 2 Mg, in various stoichiometric proportions. The components of these solutions are identified by multinuclear NMR ( 1 H, 13 C, 27 Al, and 25 Mg) and conductivity measurements for the closely related system where the organomagnesium species is Et 2 Mg. The system with the highest electrochemical stability and relatively high ionic conductivity, denoted as a "2:1 complex", is obtained from a 2:1 ratio of EtAlCl 2 and Et 2 Mg and is shown to be composed of a chloride-bridged species, Et 2 -ClAl-Cl-AlClEt 2 -, and of MgCl + , the result of transmetalation reactions.

ures 1a,b, the nanotubes are in contact with each other, providing a high resistance path for electron travel. On the creation of the space charge layer due to hydrogen adsorption, these tube-to-tube contact points become highly conducting relative to the rest of the nanotube. For a bulk conductivity constant with nanotube diameter the greater the number of contact points the greater will be the resistance change upon exposure to hydrogen. Therefore, the smaller diameter tubes, with thinner walls and greater number of contact points will exhibit higher sensitivities than their larger diameter counterparts.Out results show titania nanotubes can be used as extremely sensitive, drift-free, and robust hydrogen sensors. Hydrogen sensing applications include industrial process control, combustion control, clinical use where hydrogen is an indicator of certain types of bacterial infection, and will certainly be of critical importance to a hydrogen-based fuel economy. Agreement between our experimental results and chemisorption isotherms indicate chemisorption as the fundamental mechanism of hydrogen interaction with the nanotubes. The nanoscale morphology of the nanotubes, not simply surface area, is responsible for the variation in hydrogen sensitivity with nanotube diameter as the space charge layers are significantly modified at this length scale. There is no doubt that one of the greatest challenges of modern electrochemistry is the development of high energy density, rechargeable batteries, which are composed of materials as environmentally and abandon-friendly as possible. An excellent candidate as an anode material for batteries is magnesium, which is an active metal, easily obtained in the earth's crust, and safe for handling and use. In the field of lithium batteries, [1] Major efforts are invested in the development of rechargeable polymer lithium batteries. Replacement of liquid electrolyte solutions by solid-state electrolytes should have great advantages in terms of ease of fabrication, flexibility in dimensions and geometry of the batteries (e.g., production of flat thin batteries with light plastic cases), and safety features. There are continuous attempts to develop polymers that can dissolve lithium salts, and hence, form freestanding solid matrices that can conduct lithium ions. [2,3] However, so far the most practical solid electrolytes that are being developed for lithium batteries are gel systems, which contain a polymeric matrix, lithium salt, and polar aprotic solvents (mostly cyclic alkyl carbonates), which are trapped in the matrix, solvate the lithium salts, and hence, enable high conductivity to be achieved at low temperatures. [4,5] Following the interest and achievements in the field of lithium electrochemistry, there have been attempts over the years to develop rechargeable magnesium batteries. [6] There are reports on a search for non-aqueous electrolyte systems from which magnesium can be reversibly deposited [7] and on the study of cathode materials that reversibly intercalate mag...