Lithium salts oxidation potentials

Poly(ethylene oxide) associates in solution with certain electrolytes (48—52). For example, high molecular weight species of poly(ethylene oxide) readily dissolve in methanol that contains 0.5 wt % KI, although the resin does not remain in methanol solution at room temperature. This salting-in effect has been attributed to ion binding, which prevents coagulation in the nonsolvent. Complexes with electrolytes, in particular lithium salts, have received widespread attention on account of the potential for using these materials in a polymeric battery. The performance of soHd electrolytes based on poly(ethylene oxide) in terms of ion transport and conductivity has been discussed (53—58). The use of complexes of poly(ethylene oxide) in analytical chemistry has also been reviewed (59). 

Kuhn s carbanion analogues, [44 ], [45 ] and [46 ], have recently been synthesized, and the precursor hydrocarbons [44]-H, [45]-H and [46J-H dissociate into the respective anions in DMSO to show deep blue colours without any added base (Kinoshita et al., 1994). A fullerene anion, Bu Qb [47 ], has also been obtained as a stable carbanion (Fagan et al., 1992) its lithium salt has been isolated in the form Li [47 ]-4MeCN or Li [47"]-3-4THF. Several stable all-hydrocarbon anions of precursor hydrocarbons with low pKa values ( 7) are listed in Table 2, along with their oxidation potentials, ox-... 

Addition of LiBr or LiCl to a solution of Sml2 in THF causes a color change from blue to purple. Oxidation potential of Sml2 in THF changes from —1.33 V to —1.98 0.01 V upon addition of I2 or LiBr (more than 1 equiv.), or to —2.11 0.01 V by addition of 12 or more equiv. of LiCl. In the presence of 4-12 equiv. of the bromide or chloride salt, the pinacol coupling reaction of cyclohexanone is accelerated. These salts should be dried before use otherwise, simple reduction to cyclohexanol occurs. The co-existing lithium cation can also act as a Lewis acid to activate the carbonyl group by coordination. ... 

Reactive electrodes refer mostly to metals from the alkaline (e.g., lithium, sodium) and the alkaline earth (e.g., calcium, magnesium) groups. These metals may react spontaneously with most of the nonaqueous polar solvents, salt anions containing elements in a high oxidation state (e.g., C104 , AsF6 , PF6 , SO CF ) and atmospheric components (02, C02, H20, N2). Note that ah the polar solvents have groups that may contain C—O, C—S, C—N, C—Cl, C—F, S—O, S—Cl, etc. These bonds can be attacked by active metals to form ionic species, and thus the electrode-solution reactions may produce reduction products that are more stable thermodynamically than the mother solution components. Consequently, active metals in nonaqueous systems are always covered by surface films [46], When introduced to the solutions, active metals are usually already covered by native films (formed by reactions with atmospheric species), and then these initial layers are substituted by surface species formed by the reduction of solution components [47], In most of these cases, the open circuit potentials of these metals reflect the potential of the M/MX/MZ+ half-cell, where MX refers to the metal salts/oxide/hydroxide/carbonates which comprise the surface films. The potential of this half-cell may be close to that of the M/Mz+ couple [48],... 

Ionically conducting polymers and their relevance to lithium batteries were mentioned in a previous section. However, there are several developments which contain both ionically conducting materials and other supporting agents which improve both the bulk conductivity of these materials and the properties of the anode (Li)/electrolyte interface in terms of resistivity, passivity, reversibility, and corrosion protection. A typical example is a composite electrolyte system comprised of polyethylene oxide, lithium salt, and A1203 particles dispersed in the polymeric matrices, as demonstrated by Peled et al. [182], By adding alumina particles, a new conduction mechanism is available, which involved surface conductivity of ions on and among the particles. This enhances considerably the overall conductivity of the composite electrolyte system. There are also a number of other reports that demonstrate the potential of these solid electrolyte systems [183],... 

In some cases, the electrode material is the limiting factor of the electrochemical stability window. In a metal salt solution, underpotential deposition (UPD) may occur. In some examples, such as gold or platinum electrodes in the presence of lithium ions, the UPD appears at potentials that are substantially higher than the bulk metal deposition [4-6], In addition, some metals may possess catalytic activity for specific reduction or oxidation processes [7-12], Many nonactive metals (distinguished from the noble metals), including Ni, Cu, and Ag, which are commonly used as electrode materials, may dissolve at certain potentials that are much lower than the oxidation potentials of the solvent or the salt. In addition, some electrode materials may be catalytic to certain oxidation or reduction processes of the solution components, and thus we can see differences in the stability limits of nonaqueous systems depending on the type of electrode used. 

Yao et al. [100] reported a pH electrode based on hthium carbonate melt-oxidized iridium oxide film with the composition of Li lrOy 11H2O. The electrode based on this oxide film exhibits promising pH sensing performance and high chemical stability, with an ideal Nemstian response 58.9mV/pH over the pH range of 1 to 13. The electrode also shows a fast potential response with a 90% response time less than 0.2 s, and a low open-circnit potential drift O.lmV/day measnred in pH 6.6 solntion. The reproducibility in terms of the Nemst slopes and the apparent standard electrode potentials has been improved among electrodes within the same batch. However, the biocompatibility due to inclusion of lithium salt was not assessed. 

FIGURE 2.20 Variation of the potential limit (a) on oxidation, onset> or (t ) in reduction, expressed by i(ep0 as a function of the anion (denoted X ) basicities expressed by their pK, values (HX/X). (Reprinted with permission from Boisset, A. et al. 2013. Comparative performances of birnessite and cryptomelane MnOj as electrode material in neutral aqueous lithium salt for supercapacitor application. Journal cf Physical Chemistry C117 7408-7422. Copyright 2013 American Chemical Society.)... 

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