Lithium plateau

S.G. Ryan The halo lithium plateau outstanding issues . In This volume. 

The observed lines gives the stellar photospheric abundance via the standard stellar atmospheric technique. For stars with a surface temperature T > 5500 K and a metallicity less than about l/20th the solar metallicity, the abundances pratically show no dispersion (the famous lithium plateau for such stars.)... 

The very metal-poor halo stars used to define the lithium plateau are very old. They have had the most time to disturb the prestellar lithium which may survive in their cooler, outer layers. Mixing of these outer layers with the hotter interior where lithium has been destroyed will dilute the surface abundance. Pinsonneault et al. (1999, 2002) have shown that rotational mixing may decrease the surface abundance of lithium in these Pop II stars by 0.1 - 0.3 dex while maintaining a rather narrow dispersion among their abundances (see also, Chaboyer et al. 1992 Theado Vauclair 2001, Salaris Weiss 2002). 

Sa.Ia.rs and Lakes. Brines having high lithium concentration are found in salars of northern Chile, southwestern Bohvia, and northwestern Argentina. Brines of lower lithium concentration are found in salars in the western United States and the Tibetan Plateau. Brines pumped from beneath the surface of the Salar de Atacama (Chile) and Silver Peak (Clayton Valley, Nevada) are used for commercial production of lithium uti1i2ing solar evaporation (see Chemicals frombrines). The concentration of selected ions in brines from salars and lakes of potential commercial interest worldwide are shown in Table 1. 

Lithium insertion in microporous hard carbons (region 3 in Fig. 2) is described in section 6. High capacity hard carbons can be made from many precursors, such as coal, wood, sugar, and different types of resins. Hard carbons made from resole and novolac resins at temperatures near 1000°C have a reversible capacity of about 550 mAh/g, show little hyteresis and have a large low voltage plateau on both discharge and charge. The analysis of powder X-ray diffraction. 

Fig. 22. The capacity of the one volt plateau measured during the second cycle of several series of samples versus the H/C atomic ratio in the samples. The solid line suggests that each lithium atom binds quasi-reversibly to one hydrogen atom.

Table 1. Plateau potentials and composition ranges of some binary lithium alloys Li v.M at400°C.

Because of the interest in its use in elevated-temperature molten salt electrolyte batteries, one of the first binary alloy systems studied in detail was the lithium-aluminium system. As shown in Fig. 1, the potential-composition behavior shows a long plateau between the lithium-saturated terminal solid solution and the intermediate P phase "LiAl", and a shorter one between the composition limits of the P and y phases, as well as composition-dependent values in the single-phase regions [35], This is as expected for a binary system with complete equilibrium. The potential of the first plateau varies linearly with temperature, as shown in Fig. 2. 

In order to achieve appreciable macro Figure 12. Plateau potentials of seven lithium alloy scopic current densities while maintaining systems at ambient temperature 42J. 

The relation between the potential-composition data for these two systems under equilibrium conditions is shown in Fig. 13. It is seen that the phase Li2hSn (Lil3Sn5) is stable over a potential range that includes the upper two-phase reconstitution reaction plateau in the lithium-silicon system. Therefore, lithium can react with Si to form the phase Li, 7 S i... 

However, there are still some drawbacks in the use of CNT that need to be solved for practical applications. Not only large reversible capacities but also large irreversible capacities have been reported on CNTs [179, 183]. Such irreversible capacity together with the lack of voltage plateau during lithium extraction (hysteresis) limits the use of nanotubes as electrode material in LI Bs. However, an active study (based on CNT treatments, surface modification, use of CNT nanocomposite matrices, etc.) is being carried out in order to overcome such difficulties [184]. 

Following a similar approach, Shu et al. used an FC/PC mixture instead of neat PC as electrolyte solvent, and their analysis of propylene gas volume corroborates the observations of Arakawa and Ya-maki. Furthermore, because FC was present in their electrolyte, the reversible lithium intercalation could occur after a long plateau at 0.8 V (representing PC decomposition), therefore a correlation between the gas volume and this irreversible process was able to be established, as shown in Figure 13. Considering Aurbach s spectroscopic observations (to be discussed later), a modified mechanism (see Scheme 10) was proposed by Shu et al., wherein a competition exists between the surface reaction leading to radical anions and the formation of ternary... 

In addition to chemical compositions, another important aspect about SEI formation that is of practical significance to the forming of lithium ion cells is the potential range in which the above reactions occur leading to the formation of the SEI. Because of the earlier observation of the plateau near 0.80 and the concurrent gas evolution, it... 

Coulombic efficiency in the first charging cycle comparable to that of the commercial electrolytes for lithium ion cells.The potential plateau at 0.80 V, characteristic of the reductive decomposition of PC, was completely eliminated due to the presence of ClEC, while a new process was observed at 1.70 V. When taking the irreversible capacity in the first cycle as a metric, the optimum concentration of ClEC was determined to be 30 vol although in a... 

Fig. 8.3. Lithium, beryllium and iron. The symbol [Fe/H] denotes the logarithm of the ratio of Fe/H for the star and Fe/H for the Sun. The evolution of lithium and beryUium in the halo [Fe/H] < — 1 is a classic example. The lithium content remains independent of the iron content in halo stars. This is known as the Spite plateau, named after the two French astronomers Monica and Fran ois Spite. It indicates a primordial origin (i.e. in the Big Bang). An upturn occurs just when the disk stars begin to take over. Berylhumis an archetypal example of elements created by spallation. Its abundance increases monotonicaUy by accumulation as time goes by.

---