Lithium Alloys at Lower Temperatures

Measurements were also made of the potential-composition behavior, as well as the chemical diffusion coefficient, and its composition dependence, in each of the intermediate phases in the Li-Sn system at 415 °C [39]. 

A smaller number of binary lithium systems have also been investigated at lower temperatures. This has involved measure- 

The lithium-tinsystem has been investigated room temperature and the influence of temperature upon the composition dependence of the potential is shown in Fig. 7. It is seen that five constant potential plateaus are found at 25 °C. Their potentials are listed in Table 4. It was also shown that the kinetics on the longest pla- 

The composition dependence of the potential of the Li44Sn phase was determined, as shown in Fig. 9. 

The chemical diffusion coefficient in that phase was also evaluated and found to 

It was found that chemical diffusion is reasonably fast in all of the intermediate phases in this system. The self-diffusion coefficients are all high and of the same order of magnitude. However, due to its large value of thermodynamic enhancement factor W, the chemical diffusion coefficient in the phase Li,Sn, is extremely high, approaching 10 cm s, which is about two orders of magnitude higher than that in typical liquids. These data are included in Table 3. 

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Chemical-process industries Even if niobium and niobium alloys are less corrosion resistant than tantalum and tantalum alloys, owing to its lower cost and its density, which is half that of tantalum, it can be used efficiently in applications handling corrosive chemicals at lower temperature and concentration. On the other hand, the niobium alloy Nb-lZr is extremely corrosion resistant to molten alkali metals such as lithium and sodium up to 1000°C, and, owing to the low capture cross section for thermal neutrons, it was extensively used for tubing and for handling liquid alkali metals in heat-transfer loops used in nuclear fast neutron breeder reactors. ... 

The physical properties of lithium metal were given in Table 4.4. Despite its obvious attractions as an electrode material, there are severe practical problems associated with its use in liquid form at high temperatures. These are mainly related to the corrosion of supporting materials and containers, pressure build-up and the consequent safety implications. Such difficulties were experienced in the early development of lithium high temperature cells and led to the replacement of pure lithium by lithium alloys, which despite their lower thermodynamic potential remained solid at the temperature of operation and were thus much easier to use. 

The terminal alloy is Li22M5, with a theoretical capacity of about 1600 mAh/g. Compared with Si-based materials, Ge exhibits a higher diffusivity for lithium ions (about 400 times greater than that in silicon at room temperature) and a lower specific volume change during the Li insertion/extraction process, which is expected to present better cycling performance at comparable capacity, and therefore shows promise as a negative electrode material for lithium-ion batteries. 

In dilute uranyl sulfate solutions the addition of sulfate salts also reduces the corrosion of stainless steel, but at temperatures of 250°C and higher the solutions are chemically unstable and complex hydrolytic precipitates form. At lower uranyl sulfate concentrations (0.04 to 0.17 m) the solutions demonstrating the greatest stability are those containing beryllium sulfate, and of the three sulfates most investigated, the least stable of the solutions were those with lithium sulfate. Sulfuric acid can be included in such solutions to prevent precipitation, but in so doing some of the effectiveness of the sulfate salt is lost. Howe cr, addition of both lithium. sulfate and sulfuric acid to dilute uranyl sulfate solutions has been found to result in improved corrosion resistance of zirconium alloys on in-pile exposure [35]. 

In the meantime, it was demonstrated that lithium can be reversibly inserted into graphite at room temperature in an organic electrolyte in 1983. Lithium-ion battery was first commercialized with this carbon-based anode in 1991. Graphite bas a capacity of 372 mAh/g, corresponding to the intercalation of one lithium atom per six carbon atoms. Though carbon bas ratber lower capacity than lithium metal and lithium alloy anodes, volume change was small and represented longer cycle performance. After this commercialization, many researchers and companies have put their effort on new carbonaceous anodes. 

Lithium which had been purified by filtration followed by gettering with titanium and yttrium at 753 K had a lower resistivity than metal purified by other methods. For the liquid, dp/dOc was positive but decreased with increasing temperature, whereas for the solid, the value increased with increasing temperature. The resistance of dissolved oxide and hydride impurities in eutectic alloys of sodium and potassium appears to be a complex function of the concentration of each impurity, which can be attributed to chemical interaction in the metal to form hydroxide. Dissolved hydride causes a considerable increase in the resistance of the alloy but hydroxide has a much smaller effect. Dissolved lithium hydride affects the resistance of the alloy more than does sodium or potassium hydride but, again, hydroxide, as lithium hydroxide, has a smaller effect. Information on the solubility of lithium salts in liquid lithium has been critically reviewed. Recommended solubilities are provided for solutions of oxide and nitride as... 

The reaction of benzene with cesium and cesium alloys to form cesium benzenide is remarkable. In contrast benzene in 0.01 M solution in 2 1 by volume of THF and 1,2-dimethoxyethane with Na-K alloy according to ESR analysis gave (59) concentrations of radical anion at equilibrium of 10 to 10" M as the temperature decreased from -20° to -83 . The superior reducing power of cesium and its alloys was perhaps to be anticipated in view of the superior reducing power of cesium over potassium in aqueous solution and the appreciably lower ionization potential of cesium compared to potassium in the gas phase. These properties will be influenced by differential solvation of potassium and cesium ions by tetrahydrofuran and by the nature of the ion pairs produced. For 9-fluorenyl salts the fraction of solvent-separated ion pairs has been shown (52) to decrease rapidly in the order Li > Na > K > Cs and is a sensitive function of the solvating power of the medium. The cesium salt of fluorene in THF at -70°C has been shown to exist essentially entirely as contact ion pairs whereas the sodium and lithium salts were completely solvent-separated. The reluctance of cesium cations to become solvent-separated from counteranions means that cesium ions are available for strong electrostatic interaction with anions. 

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