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[en] High-temperature X-ray diffraction has been used to investigate the phase stability of lanthanum strontium cobalt oxide (LSC) for a range of materials with the formula La1-xSrxCoO3-(delta) (x = 0.7, 0.4, and 0.2). The stability of LSC increases with La content in low oxygen partial pressures at high temperature. Oxygen vacancy ordering has been observed for all three compositions in either low oxygen pressure or under reducing gas, as evidenced by the formation of the brownmillerite phase. The crystal structure of the vacancy-ordered phase was determined using Rietveld analysis of synchrotron X-ray diffraction data. The decomposition products under low oxygen pressure and in reducing conditions have been identified and characterized, including the phase transition and thermal expansion of the primary decomposition products, LaSrCoO4 and LaSrCoO3.5.
[en] The fracture of Si particles due to internal stresses formed during the intercalation of lithium ions was described by means of thermal analogy model and brittle fracture damage parameter. The stresses were calculated following the diffusion equation and equations of elasticity with appropriate volumetric expansion term. The damage parameter takes into account triaxiality of the stress state and change in elasticity upon tension and compression, and represents the probability of fracture under given stress state, - an approach suitable for brittle materials. The results were compared with the acoustic emission data from the experiments on electrochemical cycling of Li ion half-cells with silicon electrodes. A good correlation between experiment and prediction was observed.
[en] Because of their high energy efficiencies and low emissions, fuel-cell vehicles (FCVs) are undergoing extensive research and development. While hydrogen will likely be the ultimate fuel to power fuel-cell vehicles, because of current infrastructure constraints, hydrogen-carrying fuels are being investigated as transitional fuel-cell fuels. A complete well-to-wheels (WTW) evaluation of fuel-cell vehicle energy and emission effects that examines (1) energy feedstock recovery and transportation; (2) fuel production, transportation, and distribution; and (3) vehicle operation must be conducted to assist decision makers in selecting the fuel-cell fuels that achieve the greatest energy and emission benefits. A fuel-cycle model developed at Argonne National Laboratory--called the Greenhouse gases, Regulated Emissions, and Energy use in Transportation (GREET) model--was used to evaluate well-to-wheels energy and emission impacts of various fuel-cell fuels. The results show that different fuel-cell fuels can have significantly different energy and greenhouse gas emission effects. Therefore, if fuel-cell vehicles are to achieve the envisioned energy and emission reduction benefits, pathways for producing the fuels that power them must be carefully examined.
[en] In situ hard X-ray absorption spectroscopy (XAS) at metal K-edges and soft XAS at O K-edge and metal L-edges have been carried out during the first charging process for the layered Li1-xNi0.8Co0.15Al0.05O2 cathode material. The metal K-edge XAS results show that the major charge compensation at the metal site during Li-ion deintercalation is achieved by the oxidation of Ni ions, while the cobalt ions remain mostly unchanged in the Co3+ state. Ni LII,III-edge and O K-edge XAS results in both the fluorescence yield (FY) and partial electron yield (PEY) modes show that substantial amount of Ni ions at the surface of LiNi0.8Co0.15Al0.05O2 powders exist as Ni2+, whereas most of Ni ions in the bulk are in the form of Ni3+. Therefore, if the PEY mode, which is a surface-sensitive technique, is used alone, the interpretation of the results is limited to the surface structures only. In order to get the full picture of both the surface and the bulk, the FY mode and PEY mode should be used simultaneously.
[en] In a restructured electricity market, utility-scale energy storage technologies such as advanced batteries can generate revenue by charging at low electricity prices and discharging at high prices. This strategy changes the magnitude and distribution of air quality emissions and the total carbon dioxide (CO2) emissions. We evaluate the social costs associated with these changes using a case study of 500 MW sodium-sulfur battery installations with 80% round-trip efficiency. The batteries displace peaking generators in New York City and charge using off-peak generation in the New York Independent System Operator (NYISO) electricity grid during the summer. We identify and map charging and displaced plant types to generators in the NYISO. We then convert the emissions into ambient concentrations with a chemical transport model, the Particulate Matter Comprehensive Air Quality Model with extensions (PMCAMx). Finally, we transform the concentrations into their equivalent human health effects and social benefits and costs. Reductions in premature mortality from fine particulate matter (PM2.5) result in a benefit of 4.5 cents kWh-1 and 17 cents kWh-1 from displacing a natural gas and distillate fuel oil fueled peaking plant, respectively, in New York City. Ozone (O3) concentrations increase due to decreases in nitrogen oxide (NOx) emissions, although the magnitude of the social cost is less certain. Adding the costs from charging, displacing a distillate fuel oil plant yields a net social benefit, while displacing the natural gas plant has a net social cost. With the existing base-load capacity, the upstate population experiences an increase in adverse health effects. If wind generation is charging the battery, both the upstate charging location and New York City benefit. At $20 per tonne of CO2, the costs from CO2 are small compared to those from air quality. We conclude that storage could be added to existing electricity grids as part of an integrated strategy from a human health standpoint. (author)
[en] Niobium (Nb)-clad 304L stainless steel (SS) is currently under consideration for use as a bipolar plate material in polymer electrolyte membrane fuel cell (PEMFC) stacks. Because metal bipolar plates will likely be formed by stamping, the sheet metal properties of this material were characterized in both the as-rolled and an optimized annealed condition via a series of bend and quasi-static tensile tests. Results from tensile testing demonstrate that annealing significantly softens and thereby improves the ductility of the material. Bend test results indicate that springback is nearly independent of the bend direction relative to rolling direction for both the as-rolled and annealed conditions. In the as-rolled condition, springback is also nearly independent of specimen orientation (i.e. whether the cladding layer is on the inside or outside of the bend). However in the annealed condition, springback does depend on the cladding orientation relative to bending and was found in all cases to be substantially lower than that observed in the as-rolled condition. Microstructural analysis of the specimens indicates that two failure conditions can potentially arise, dependent on the thermomechanical condition of the material. In the as-rolled condition, failure initiates via fracture through the Nb cladding. In the annealed specimens, failure can occur by brittle fracture of an interfacial intermetallic layer that forms during the annealing treatment. This generates a series of crack-induced pores along the interface between the Nb cladding and the SS core, which eventually leads to ductile failure of the Nb cladding via localized necking. However the conditions required for this phenomenon to take place are fairly extreme and can be readily avoided in practice. In general, the results suggest that to achieve acceptable stamping tolerances, the material should be annealed prior to forming and the bipolar plate flow channel pattern should be designed such that extreme levels of strain at the cladding/core interface are avoided to mitigate the potential for partial delamination within the material