Anionic conduction, polymer-salt

This distribution causes a problem the best-described conducting polymers interchange anions with the electrolyte, and the Li electrode liberates Li+during discharge. The salt accumulates in the electrolyte [Fig. 32(a)], requiring a great volume and mass in order to avoid the precipitation of the salt. This fact reduces the specific energy of the battery to impractical values. 

Tens of conductive LB films have been developed so far, including metallic and superconductive LB films. These LB films are classified into the categories anion radical salt, charge-transfer complex, cation radical salt, conducting polymer, and transition metal complex in this section. The LB films, with metallic temperature dependences of conductivity, and the fullerene LB films, which exhibit a superconducting transition, are discussed separately. 

Ambient temperature molten salt can be obtained by several methods. One effective way to obtain a room-temperature molten salt is by the introduction of polyether chains to ions. The term polyether/salt hybrid is used in this chapter as a common name for polyether oligomers having anionic or cationic charge(s) on the chain (Figure 22.1). Polyethers, such as poly-(ethylene oxide) (PEO), are known as representative ion conductive polymers [1]. Polyether/salt hybrids have been studied as a kind of room-temperature molten salt apart from the development of onium-type ionic liquids [2]. The preparation of ionic liquids consisting of metal ions has been one of the important goals in this research field. Polyether/salt hybrid derivatives give one such solution for this task. 

Electrochemistry in RTILs has recently been reviewed, and a book has been published on the topic. a large number of metals have been deposited from ionic liquids (Table 6.5) and a book has also been published on electrodeposition from these media. Alloys, semiconductors and conducting polymers have also been deposited from ionic liquids. The key advantages of ionic liquids for electrodeposition and electrochemical applications are their wide potential window, the high solubility of metal salts, the avoidance of water and their high conductivity compared to non-aqueous solvents. There are numerous parameters that can be varied to alter the deposition characteristics including temperature, the cation and anion used, diluents and additional electrolytes. ... 

For polypyrroles and polythiophenes, n is usually ca. 3 for optimal conductivity, ie. there is a positive charge on every third or fourth pyrrole or thiophene along the polymer chain, near which the dopant anion A is electrostatically attached. For polyanilines, the ratio of reduced (amine) and oxidised (imine) units in the polymer is given by the y/( 1 - y) ratio. The conducting emeraldine salt form of polyaniline has y = 0.5, i.e. there are equal numbers of imine and amine rings present. 

The next group of materials comprises conducting polymers (ICP). Systems with identical polymers have often been reported for polyacetylene. It is known that this ICP forms insertion compounds of the A and D types (see Section 6.4, and No. 5 in Table 12). Cells of this Idnd were successfully cycled [277, 281-283]. However, the current efficiency was only 35% heavy losses were observed due to an overoxidation of the PA [284]. In other cases as for polypyrrole (PPy), the formation of D-PPy was anticipated but did not occur [557, 558]. Entry (6) in Table 12 represents some kind of ideal model. A PPy/PPy cell with alkyl or aryl sulfates or sulfonates rather than perchlorates is claimed in [559]. Similar results were obtained with symmetric polyaniline (PANI) cells [560, 561]. Symmetric PPy and RANI cells yield about 60% current efficiency, much more than with PA. An undoped PPy/A-doped PPy combination yields an anion-concentration cell [562, 563], in analogy to graphite [47], (cf. No. 7). The same principle can be applied with the PPy/PT combination [562, 563] (cf. No. 8). Kaneto et al. [564] have reported in an early paper the combination of two pol54hiophene (PT) thin layers (< 1 pm), but the chargeability was relatively poor (Fig. 40, and No. 9 in Table 12). A pronounced improvement was due to Gottesfeld et al. [342, 343, 562, 563], who employed poly[3-(4-fluoro-phenyl)thiophene], P-3-FPT, in combination with a stable salt electrolyte (but in acetonitrile cf. Fig. 40 and No. 10 in Table 12). In all practical cases, however, Es.th was below 100 Wh/kg. 

Methylmagnesium chloride is used to deprotonate CH2(S02Cp3)2. The anion is then alkylated with CF3SO2F [37 Eq. (30)]. Subsequent treatment with LiOFI gives the lithium salt that is used as an electrolyte in conducting polymer films. 

FTIR spectroscopy has been used to monitor the conducting states of a conducting polymer as well as to know if a doping experiment is successful [86, 87], The FTIR and UV-Vis spectra of unsubstituted PANI is similar to that of substituted PANI though with slight band shifts. Doped PANI and its derivatives exist in the emeraldine salt forms which are essentially delocalized polysemiquinone radical cations whose stability is maintained by the presence of dopant anions. The degree of electron delocalization in the polysemiquinone forms of the doped PANI manifests itself in the form of an electronic-like band at ca. 1100 cm 1 associated with polarons [86], The structures of emeraldine base and emeraldine salt form of PANI are presented in Figure 6. 

A dramatic impact on chemical properties is achieved by the appropriate choice of counterion. The counterion employed during synthesis can have a marked effect on the anion-exchange selectivity series of conducting polymers.54 Table 3.4 shows the anion-exchange selectivity series obtained for both polypyrrole chloride and polypyrrole perchlorate. As illustrated, polypyrrole salts do not behave similar to conventional ion-exchange resins. 

A conductive polymer film of polypyrrole doped with polymolybdate anions was electrodeposited onto steel and found to provide corrosion protection in neutral and acidic 3.5% NaCl solution [152]. The anodic codeposition of polypyrrole and Ti02 onto mild steel in an oxalic acid medium has been described [153,154]. The PPy and Ti02 composite showed a considerable improvement in anticorrosion properties with respect to PPy films in salt spray and weight-loss tests. It was suggested that these composite films could be applied as a primary coating replacement for the phosphatized layers on mild steel [154]. 

In terms of crystalline structure, this means that a channel of sufficient size must link the accessible sites in order that ion diffiision is not hindered if channels are too large with respect to the ion radius, ions can be trapped. In polymers, the region of high conductivity is found in the homogeneous, elastomeric amorphous phase and the presence of partial crystallinity inhibits conduction. The motion of mobile ions is strongly linked to that of polymer segments and ionic conductivity drops to extremely low values below 7 where the chain segment motions are frozen. Both anions and cations are mobile in many polymer/salt electrolytes. 

---