Transference of lithium ions

This type of Li battery has already widely diffused in the electronic consumer market, however for automotive applications the presence of a liquid electrolyte is not considered the best solution in terms of safety, then for this type of utilization the so-called lithium polymer batteries appear more convenient. They are based on a polymeric electrolyte which permits the transfer of lithium ions between the electrodes [21]. The anode can be composed either of a lithium metal foil (in this case the device is known as lithium metal polymer battery) or of lithium supported on carbon (lithium ion polymer battery), while the cathode is constituted by an oxide of lithium and other metals, of the same type used in lithium-ion batteries, in which the lithium reversible intercalation can occur. For lithium metal polymer batteries the overall cycling process involves the lithium stripping-deposition at the anode, and the deintercalation-intercalation at the anode, according to the following electrochemical reaction, written for a Mn-based cathode ... 

In its most common configuration, this battery is formed by a graphite anode, a lithium metal oxide cathode (e.g., LiCo02) and a porous separator soaked with a liquid solution of a lithium salt (typically LiPFg) in an organic solvent mixture (ethylene carbonate-dimethylcarbonate mixture). The electrochemical mechanism of this battery is the back-and-forth transfer of lithium ions between the two electrodes ... 

Lithium ion batteries, based on a carbonaceous anode and a lithium metal oxide cathode, are high-energy power sources that are well established in the consumer electronics market. The lithium ion concept, however, can be extended to any electrode combination that assures a cyclic transfer of lithium ions across the cell. In general, a lithium ion cell can be considered as based on a lithium-rich L M Y electrode and a lithium-accepting electrode. The electrochemical process is ... 

Fig. 7.2 Schematic of a lithium-ion battery which consists of an anode and a cathode separated by electrolyte containing dissociated lithium salts, enabling transfer of lithium ions between the two electrodes. Reproduced with permission from Ref. [16] Copyright 2007 Elsevier...

The lithium metal-free sulphur battery concept was confirmed by using a lithiated silicon-carbon anode, an HCS-S (hard carbon spherules-sulphur composite) cathode (cfr. Figure 3.29) and a LiCFgSOgTEGDME liquid electrolyte (see Figure 3.31) [50]. The electrochemical process involves the transfer of lithium ions from the anode to the cathode Li Si-C -f S Lij.S + xSiC + HCS (HCS hard carbon spherules). The battery delivers a capacity of 500 mAh g g at an average voltage of 1.8 V (see Figure 3.31). 

It is worth mentioning that single-ion conductivities of lithium ions and anions at infinite dilution, and transference numbers of ligand-solvated lithium ions estimated therefrom, increase due to the replacement of more than one (generally four) solvent molecules. Table 6 demonstrates this beneficial feature. 

The synthesis of a variety of lithium ion conducting borosiloxane polymers have been reported.51 The incorporation of the Lewis acidic boron and silicon into the polymer backbone was expected to facilitate their interaction with anions and thereby increase the T+ (transference numbers) of the resulting polymers.52... 

This sharp decline in cell output at subzero temperatures is the combined consequence of the decreased capacity utilization and depressed cell potential at a given drain rate, and the possible causes have been attributed so far, under various conditions, to the retarded ion transport in bulk electrolyte solutions, ° ° - ° ° the increased resistance of the surface films at either the cathode/electrolyte inter-face506,507 Qj. anode/electrolyte interface, the resistance associated with charge-transfer processes at both cathode and anode interfaces, and the retarded diffusion coefficients of lithium ion in lithiated graphite anodes. - The efforts by different research teams have targeted those individual electrolyte-related properties to widen the temperature range of service for lithium ion cells. 

Reduction then proceeds by successive transfers of hydride ion, H e, from aluminum to carbon. The first such transfer reduces the acid salt to the oxidation level of the aldehyde reduction does not stop at this point, however, but continues rapidly to the alcohol. Insufficient information is available to permit very specific structures to be written for the intermediates in the lithium aluminum hydride reduction of carboxylic acids. However, the product is a complex aluminum alkoxide, from which the alcohol is freed by hydrolysis ... 

Trimethyltrifluoromethylsilane, which is now generally referred to as Ruppert s reagent [92], has been widely investigated [93-96] as an intermediate for transferring the trifluoromethyl group as a nucleophile, thus compensating for the deficiencies of poly-fluoroalkyl Grignard or lithium derivatives. This approach also complements other methods for transfer of trifluoromethide ion. A variety of procedures have now been developed for the synthesis of this compound but the electrochemical procedure [93]... 

TABLE XLIV. TRANSFERENCE NUMBER OF LITHIUM ION IN LITHIUM CHLORIDE AT 25°... 

We are already familiar with the facile transfer of hydride from carbon to carbon within a single molecule (hydride shift in reanangements), and between molecules (abstraction by carbonium ion. Sec. 6.16). Later on we shall encounter a set of remarkably versatile reducing agents (hydrides like lithium aluminum hydride LiAlH4, and sodium borohydride, NaBH4) that function by transfer of hydride ion to organic molecules. 

A number of metal hydrides have been employed as reducing agents in organic chemistry, but the most commonly used are lithium aluminium hydride and sodium borohydride, both of which are commercially available. These reagents are nucleophilic and as such they normally attack polarized multiple bonds such as C=0 or C=N by transfer of hydride ion to the more-positive atom. They do not usually reduce isolated carbon-carbon double or triple bonds. 

With both reagents all four hydrogen atoms may be used for reduction, being transferred in a stepwise manner (7.58). For reductions with lithium aluminium hydride, each successive transfer of hydride ion takes place more slowly than the one before, and this has been exploited for the preparation of modified reagents that are less reactive and more selective than lithium aluminium hydride itself (for example, by replacement of two or three of the hydrogen atoms of the anion by alkoxy groups). 

Yamada, Y. Itiyama, Y. Abe, T Ogumi, Z. Kinetics of lithium ion transfer at the interface between graphite and liquid electrolyte effects of solvent and surface film, Langmuir 2009, 25, 12766-12770. 

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