[en] Partial substitution of Mn in lithium manganese oxide spinel materials by Cu and Ni greatly affects the electrochemistry and the cycle life characteristics of the cathode. Substitution with either metal or a combination of both metals in the spinel lattice structure reduces the 3.9-4.2 V potential plateaus associated with the conversion of Mn³⁺ to Mn⁴⁺. Higher potential plateau associated with oxidation of the substituted transition elements is also observed. These substituents also significantly alter the onset of Jahn-Teller distortions in the 3 V potential plateau. Synchrotron based in situ X-ray absorption (XAS) was used to determine the exact nature of the oxidation state changes in order to explain the overall observed capacities at different potential plateaus. The studies on LiCu_0.5Mn_1.5O₄ show single phase behavior in the 4-5 V potential region with a good cycle life. Lower cycle life characteristic observed in cycling LiNi_0.5Mn_1.5O₄ and LiNi_0.25Cu_0.25Mn_1.5O₄ versus Li metal are ascribed to coexistence of several phases in this potential region. However, LiCu_0.5Mn_1.5O₄ shows onset of Jahn-Teller distortions in the 3 V potential plateau, in contrast to LiNi_0.5Mn_1.5O₄ and LiNi_0.25Cu_0.25Mn_1.5O₄ cathode materials

[en] Divalent cation doped lithiated Mn spinel with Zn and Mg as cathode materials for a lithium battery are investigated and partial reversible behavior is observed at the 5 V region. The electrochemical charge and discharge potential profiles of the Zn-doped materials indicate a close relationship between the lattice energy and lattice parameters in the Zn-doped spinel system. Lithium ions extracted from octahedral sites at the 5 V plateau during the charge cycle are partially reinserted back into the tetrahedral sites during the discharge step, which contributes to the partial reversible 5 V behavior. The significant findings reported here are that the strong tetrahedral site preference of divalent nonreactive cations such as Zn and Mg force Li cations onto octahedral sites in these materials, thus resulting in electroactivity at 5 V. In situ X-ray absorption spectroscopy measurements show that the Mn K edge is shifted to higher energy at the 4 V plateau during charge cycle and remains unchanged at the 5 V plateau. In situ Zn K-edge X-ray absorption near-edge structure measurements reveal that the valence state of zinc ions is unchanged at the 5 V plateau region. In situ Mn K-edge extended X-ray absorption fine structure studies suggest that O^2- ions in the Zn-spinel lattice are partially oxidized to O^- at the 5 V plateau during the anodic process and O- ions are reduced back to O2- during the cathodic process at the 5 V plateau. The oscillations of the lattice parameters observed at the 5 V plateau region during the anodic charge step are attributed to chemical instability of O^- ions

[en] The combination of in situ X-ray diffraction (XRD) and x-ray absorption spectroscopy (XAS) is a very powerful technique in the study of lithium battery cathode materials. XRD identifies the phase changes that occur during cycling and XAS gives information on the redox charge compensation processes that occur on the transition metal oxides. Because of its element specific nature XAS can identify the occurrence of redox processes on the various cations in doped oxide cathode materials. Since XAS probes short range order and is particularly useful in the study of amorphous tin based composite oxide anode materials

[en] In Situ x-ray diffraction studies on Li_xMn₂O₄ spinel cathode materials during charge-discharge cycles were carried out by using a synchrotron as x-ray source. Lithium rich (x = 1.03-1.06) spinel materials obtained from two different sources were studied. Three cubic phases with different lattice constants were observed during charge-discharge cycles in all the samples when a Sufficiently low charge-discharge rate (C/10) was used. There are two regions of two-phase coexistence between these three phases, indicating that both phase transitions are first order. The separation of the Bragg peaks representing these three phases varies from sample to sample and also depends on the charge-discharge rate. These results show that the de-intercalation of lithium in lithium-rich spinel cathode materials proceeds through a series of phase transitions from a lithium-rich phase to a lithium-poor phase and finally to a λ-MnO₂ like cubic phase, rather than through a continuous lattice constant contraction in a single phase

[en] The chemistry of the Fe(VI) compound, K₂FeO₄, was investigated in aqueous potassium hydroxide electrolyte for its potential use in secondary storage systems. High charge storage K₂FeO₄ material was synthesized using alkaline hypochlorite oxidation of ferric nitrate and characterized by in situ X-ray diffraction and Moessbauer spectroscopy. The discharge-charge profile of the cathode, measured versus a zinc anode, was semiquantitatively correlated with changes in Fe⁶⁺+/Fe³⁺ ratio and the nature of structural transformation at each stage by in situ Moessbauer and in situ synchrotron X-ray diffraction spectroscopy. The data in conjunction with the charge-discharge profile clearly indicates the rechargeability of K₂FeO₄ with a charge efficiency of about 36% of the total current passed under the prevailing experimental conditions. These results are potentially important to the design of Fe⁶⁺ compound analogs for use in secondary energy storage systems

[en] There is an increasing interest in lithiated transition metal oxides because of their use as cathodes in lithium batteries. LiCoO₂, LiNiO₂ and LiMn₂O₄ are the three most widely used and studied materials, At present, although it is relative expensive and toxic, LiCoO₂ is the material of choice in commercial lithium ion batteries because of its ease of manufacture, better thermal stability and cycle life. However, the potential use of lithium ion batteries with larger capacity for power tools and electric vehicles in the future will demand new cathode materials with higher energy density, lower cost and better thermal stability. LiNiO₂ is isostructural with LiCoO₂. It offers lower cost and high energy density than LiCoO₂. However, it has much poorer thermal stability than LiCoO₂, in the charged (delithiated) state. Co, Al, and other elements have been used to partially replace Ni in LiNiO₂ system in order to increase the thermal stability. LiMn₂O₄ has the highest thermal stability and lowest cost and toxicity. However, the low energy density and poor cycle life at elevated temperature are the major obstacles for this material. In order to develop safer, cheaper, and better performance cathode materials, the in-depth understanding of the relationships between the thermal stability and structure, performance and structure are very important. The performance here includes energy density and cycle life of the cathode materials. X-ray diffraction (XRD) is one of the most powerful tools to study these relationships. The pioneer ex situ XRD work on cathode materials for lithium batteries was done by Ohzuku. His XRD studies on LiMn₂O₄, LiCoO₂, LiNiO₂, LiNi_0.5Co_0.5O₂, and LiAl_xNi_1-xO₂ cathodes at different states of charge have provided important guidelines for the development of these new materials. However, the kinetic nature of the battery system definitely requires an in situ XRD technique to study the detail structural changes of the system during charge and discharge. The in situ XRD technique was used by Reimers, Li,and Dahn to study the LiCoO₂, LiNiO₂, and LiMn₂O₄ systems. Their results of these studies have demonstrated that in situ XRD can provide more detailed information about the cathode material structural changes during charge-discharge. Conventional x-ray sources were used in these studies and the beryllium windows were used in the in situ cells. Provisions were made to prevent corrosion of the beryllium windows during charge-discharge. For this reason, the in situ cells were often designed quite differently than a real battery. More seriously, the problem of beryllium corrosion restricted the voltage range of the cell below 4.5 V. This limited the use of this technique to study the effects of overcharge which is very important to the thermal stability of the cathodes. Using the plastic lithium battery technology, Amatucci, Tarascon, and Klein constructed an in situ XRD cell, which allows structural investigations at voltages greater than 5 V without any beryllium window corrosion. However, all of these in situ XRD studies using conventional x-ray sources probe the cell in reflection geometry. Therefore, the observed structural changes are predominantly from the top few microns of the electrode coating, which might not be representative for the whole coating during charge-discharge especially when the rate is high

[en] This was a study of electrode degradation mechanisms and the reaction kinetics of LaNi_4.7Sn_0.3, La_(1-x) Y_xNi_4.7Sn_0.3 (x = 0.1, 0.2, and 0.3) and La_0.7Y_0.3Ni_4.6Sn_0.3Co_0.1 metal hydride electrodes. Alloy characterization included x-ray diffraction (XRD), x-ray absorption (XAS), hydrogen absorption in a Sieverts apparatus, and electrochemical cycling of alloy electrodes. The atomic volume of H was determined for two of the alloys. Electrochemical kinetic measurements were made using steady state galvanostatic measurements, galvanodynamic sweep, and electrochemical impedance techniques. XAS was used to examine the degree of corrosion of the alloys with cycling. Alloying with Y decreased the corrosion rate. The results are consistent with corrosion inhibition by a Y containing passive film. The increase in the kinetics of the hydrogen oxidation reaction (HOR) with increasing depth of discharge was much greater on the Y containing alloys. This may be due to the dehydriding of the catalytic species on the surface of the metal hydride particles

[en] We have measured the XAFS spectra of tin-based composite oxide (TCO) glass with nominal composition of Sn_1.0B_0.56P_0.40Al_0.42O₃ during the discharge and charge cycles in a non-aqueous cell. Our results confirm the amorphous nature of TCO material and show that Sn in TCO is coordinated with 3 oxygen atoms at a distance of 2.12 Angstrom. Upon discharge (i.e., Li insertion), initially, Li interacts with the electrochemically active Sn-O center forming metallic Sn, most likely in the form of highly dispersed clusters, and Li₂O. Upon further discharge, our results are consistent with a model in which additional Li alloys with Sn forming various alloys with composition dependent on the amount of Li inserted. The formed alloys appear to be in the form of highly dispersed clusters and/or amorphous in nature. Their local structure differs somewhat from the crystalline structure of the known Li-Sn alloys such as LiSn, Li₇Sn₃, or Li₇Sn₂. Upon charging (i.e., Li removal), metallic Sn is reversibly produced with a Sn-Sn distance intermediate to those of gray and white Sn. (au)

[en] This paper describes the design and the development progress of a 3 to 5 auxiliary power unit (APU) based on a gasoline fueled solid oxide fuel cell (SOFC). This fuel cell was supplied reformate gas (reactant) by a partial oxidation (POx) catalytic reformer utilizing liquid gasoline and designed by Delphi Automotive Systems. This reformate gas consists mainly of hydrogen, carbon monoxide and nitrogen and was fed directly in to the SOFC stack without any additional fuel reformer processing. The SOFC stack was developed by Global Thermoelectric and operates around 700^oC. This automotive APU produces power to support future 42 volt vehicle electrical architectures and loads. The balance of the APU, designed by Delphi Automotive Systems, employs a packaging and insulation design to facilitate installation and operation on-board automobiles. (author)

[en] In recent years there is a revival of interest in the Molten Salt Breeder Reactors (MSBR). MSBRs are inherently safe reactors with several other advantages like online reprocessing of spent fuel, potential to achieve self sustainable ²³³U/Th cycle, reliability, proliferation resistance etc. LiF, ThF₄ and UF₄ salt mixture is one among the probable candidates for MSBR application. Information on the physico-chemical properties like viscosity of molten coolant, blanket and fuel salt is an important parameter required for successful design and operation of these reactors. In the present work, viscosity of three fluoride based salt eutectic systems such as: fuel salt (LiF = 78 mole %, ThF₄ = 20 mole%, UF₄ = 2 mole%), blanket salt (LiF =77.5 mole %, ThF₄ = 22.5 mole %) and coolant salt (LiF = 46.5 mole %, NaF = 11.5 mole %, KF = 42 mole %) is reported