Solvated intercalation reaction

Apart from reactions with the electrolyte at the carbon surface, the irreversible specific charge is furthermore strongly affected by the possible co-intercalation of polar solvent molecules between the graphene layers of highly graphitic matrices [139]. This so-called "solvated intercalation reaction" depends (i) on the crystallinity and the morphology of the parent carbonaceous material, which will be discussed in Sec. 

The overall current-producing reaction (11.8) describes the process of cell discharge only approximately. The intermediate product of cathodic polyfluorocarbon reduction is assumed to be a certain solvated intercalation compound C-F-Li decomposed in the course of discharge. 

Whereas the electrochemical decomposition of propylene carbonate (PC) on graphite electrodes at potentials between 1 and 0.8 V vs. Li/Li was already reported in 1970 [140], it took about four years to find out that this reaction is accompanied by a partially reversible electrochemical intercalation of solvated lithium ions, Li (solv)y, into the graphite host [64], In general, the intercalation of Li (and other alkali-metal) ions from electrolytes with organic donor solvents into fairly crystalline graphitic carbons quite often yields solvated (ternary) lithiated graphites, Li r(solv)yC 1 (Fig. 8) [7,24,26,65,66,141-146],... 

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. 

Reactions (5.5.30) and (5.5.31) proceed prevailingly during intercalation from solid or polymer electrolytes (cf. Section 2.6) or melts. When using common liquid electrolyte solutions, a co-insertion of solvent molecules (and/or intercalation of solvated ions) very often occurs. The usual products of electrochemical intercalation are therefore ternary compounds of a general composition ... 

Whatever the precursor, the formation of an intermediate solid phase was always observed. It can be inferred from X-ray diffraction (Fig. 9.2.7) and infrared spectroscopy that this intermediate phase shows a lamellar, incompletely ordered structure (turbostratic structure) built up with parallel and equidistant sheets like those involved in the lamellar structure of the well-crystallized hydroxides Ni(OH)2 or Co(OH)2, these sheets are disoriented with intercalation of polyol molecules and partial substitution of hydroxide ions by alkoxy ions (29). The dissolution of this solid phase, which acts as a reservoir for the M(I1) solvated species, controls the concentration of these species and then plays a significant role in the control of the nucleation of the metal particles and therefore of their final morphological characteristics. For instance, starting from cobalt or nickel hydroxide as precursor in ethylene glycol, the reaction proceeds according to the following scheme (8) ... 

When the circuit is complete, lithium metal from the lithium electrode dissolves giving solvated ions, and solvated ions in the solution are deposited in the titanium disulfide. These ions intercalate into the disulfide, and electrons from the external circuit balance the charge. Thus, the two electrode reactions are ... 

Intercalation of both cationic and neutral (solvated) molecular species in MXj is particularly important when the reaction occurs in the presence of polar solvents, especially at low temperatures (Fig. 8.8). A simplified scheme of reactions which explains this type of intercalation has been proposed by Schollhorn (1980) ... 

On the basis of these properties, the three approaches summarized in Figure 3 have been elaborated specifically for the introduction of photoactive M—— M cores into layered phosphate host structures. These are (1) the direct intercalation of solvated M—— M cores into layered phosphates wherein the phosphate groups of the layers form the ligation sphere for the bimetallic core (2) acid-base reaction of specially functionalized ligands on the bimetallic core with protons from the layers and (3) replacement of the phosphate groups with functionalized phosphonates that offer well-defined coordination sites for the M—M core. We now discuss each of these methodologies. 

Table IV compares for a series of dienes the yields of 1,2 addition products obtained with Rh(NBD)(dppe)+ as the catalyst precursor under intercalated and homogeneous reaction conditions. The yields of terminal olefins are consistently higher for the intercalated catalyst. The deviation from solution yields are larger when the intercalated catalyst is solvated with methanol than with acetone.0 Methanol swells the interlayers to an average thickness of 12 A, whereas acetone swells the interlayers to w 15 A. Since the more constricted methanol solvated interlayers provide the higher yields of terminal olefins, spacial factors as well as polarization effects induced by the charged silicate sheets may be contributing to the deviations from solution behavior. In this reaction system polarization effects may well be more important than spacial factors in directing hydrogenation transfer because the spacial requirements of the transition states derived from or r 3 allyl intermediates should be very similar.

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