Process intercalation

The electrochemical performance of lithiated carbons depends basically on the electrolyte, the parent carbonaceous material, and the interaction between the two (see also Chapter III, Sec.6). As far as the lithium intercalation process is concerned, interactions with the electrolyte, which limit the suitability of an electrolyte system, will be discussed in Secs. 5.2.2.3,... 

Figure 5. The complexity of the first intercalation process into graphite (after Refs. [6, 25J.

The smaller ion may intercalate faster into the graphite galleries. Reaction (5) may be the rate-determining step for the solvent co-intercalation process, and if so, molecules that form large and stable solvated lithium cations will have a smaller tendency for co-intercalation into the graphite. 

Changes in electrical resistivity (V3) and mechanical properties (V3, V4) of graphite fibers upon nitration have been studied. Increases in elastic modulus, and decreases in tensile strengths, have been related to removal of boundary dislocations by the intercalation process proposed elsewhere iN4). 

The reaction of iodine heptafluoride is accompanied by reduction to the pentavalent state (S15). The intercalation process can thus be described in terms of the reaction... 

At this time, no all-inclusive rule can be given that will predict whether a given compound will intercalate or not. Most of the information available seems to have been obtained empirically. Such analogies as similar chemical properties have been helpful. The many factors that infiuence the intercalation process have been surveyed by Herold (H14). In Tables II-VI are listed metal halides considered to intercalate into graphite, together with some structural information (S2J, i 9). Several general characteristics have been ascribed to intercalat-... 

The HF-SbFs system is known to be a superacid H34). The possible relevance of this to the intercalation process was pointed out by Vogel V12), who first reported on the extremely high electrical conductivity of graphite-SbFj measured normal to the crystallographic c-axis. The measured conductivity was approximately 40 times that of pristine graphite, and 50% greater than that of pure copper. Other workers... 

Novel room-temperature-vulcanized silicone mbber-organo-MMT nanocomposites were prepared by a solution intercalation process by Wang et al. [104]. A new strategy was developed by Ma et al. [105] to prepare disorderly exfoliated nanocomposites, in which a soft siloxane surfactant with a weight-average molecular weight of 1900 was adopted to modify the clay. 

Investigation of these properties should be one of the significant directions of future development of these compounds, especially worthwhile are the exploration of the possibility of removing the templates from the channels of the hon-eycomb-like material [Tl5(Ti2Cl9)][(Nb6Cli204)3(Ti3CL. )2] and the studies of this and other oxychloride materials as hosts in redox intercalation processes. 

Nylon-6-clay nanocomposites were also prepared by melt intercalation process [49]. Mechanical and thermal testing revealed that the properties of Nylon-6-clay nanocomposites are superior to Nylon. The tensile strength, flexural strength, and notched Izod impact strength are similar for both melt intercalation and in sim polymerization methods. However, the heat distortion temperature is low (112°C) for melt intercalated Nylon-6-nanocomposite, compared to 152°C for nanocomposite prepared via in situ polymerization [33]. 

Later electrochemical smdies on sputtered, amorphous MoOyS films showed that the Li intercalation process strongly depends on the composition of these films... 

The intercalation compounds of lithium with graphite are very different in their behavior from intercalation compounds with oxides or halcogenides. Intercalation processes in the former compounds occur in the potential region from 0 to 0.4 V vs. the potential of the lithium electrode. Thus, the thermodynamic activity of lithium in these compounds is close to that for metallic lithium. For this reason, lithium intercalation compounds of graphite can be used as negative electrodes in batteries rather than the difficultly of handling metallic lithium, which is difficult to handle. 

At present, intercalation compounds are used widely in various electrochemical devices (batteries, fuel cells, electrochromic devices, etc.). At the same time, many fundamental problems in this field do not yet have an explanation (e.g., the influence of ion solvation, the influence of defects in the host structure and/or in the host stoichiometry on the kinetic and thermodynamic properties of intercalation compounds). Optimization of the host stoichiometry of high-voltage intercalation compounds into oxide host materials is of prime importance for their practical application. Intercalation processes into organic polymer host materials are discussed in Chapter 26. 

Another factor also contributed to the appearance of new concepts in electrochemistry in the second half of the twentieth century The development and broad apphca-tion of hthium batteries was a stimulus for numerous investigations of dilferent types of nonaqueous electrolytes (in particular, of sohd polymer electrolytes). These batteries also initiated investigations in the held of electrochemical intercalation processes. 

The most stable base sequences (67 7M are the pyrimidine(p) purine ones TpA, TpG and CpG. For binding to N2(G), N6(a), 06(g) and NH(c) these lead to 5% 5% Y and 3 type binding for receptor sites. The 3 and 5 type binding for (pu) and (py) base atoms, respectively, require the use of receptor sites which are less stable. These binding orientations are less likely to occur if the intercalation process precedes covalent bond formation. 

The desirability of using a non-invasive in-situ probe has already been discussed. There is, however, a problem, in that standard characterisation techniques are unable to penetrate bulky reaction vessels. As a result of this, little is known about the reaction dynamics or kinetics of intercalation reactions. A non-invasive probe which can interrogate a typical intercalation process is required. It is also necessary to employ short data collection times in order that kinetic information may be obtained. X-ray powder diffraction is a highly appropriate tool. It is non-invasive, and is a powerful characterisation technique when used in combination with ex-situ analyses. 

The activation energy for the intercalation process was calculated using the Arrhenius relationship. 

The influence of the nature of the anion on the intercalation process was also studied. The intercalation of 5 M solutions of liX (with X = Br, NO3, OH and ISO4) were followed at 120 °C. The extent of reaction plots vary greatly between the different salts (Fig. 9). The plots shown in Fig. 8 are reduced time plots, in which the time is divided by the half-life of the reaction. 

Experiments were performed with various LiAl-X LDHs, with X = Br, NO3 and ISO4. As with the intercalation process, the nature of the anion exerts a powerful influence on the reaction. In the case of sulfate, the deintercalation reaction does not go to completion - only 40% of the available lithium sulfate was released. The deintercalation reaction initially proceeds very quickly, but the process is then halted. The rate of deintercalation is NOs" > Cl > Br . This series does not correspond with data on the anion selectivity for intercalation into Al(OH)3, which is S04 > Cl" > Br" > NO3". Neither is there a correlation of the release data with the heats of hydration of the anions. The series observed arises because the intercalation and deintercalation processes are a balance of a number of factors, including interactions between the guest ions and the host matrix. 

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