Polymer electrolytes conducting polymers

Table 1. Some imide ions and carbanions used in salts to enhance polymer electrolyte conductivity and reduce crystallinity...

The response to the applied perturbation, which is generally sinusoidal, can differ in phase and amplitude from the applied signal. Measurement of the phase difference and the amplitude (i.e. the impedance) permits analysis of the electrode process in relation to contributions from diffusion, kinetics, double layer, coupled homogeneous reactions, etc. There are important applications in studies of corrosion, membranes, ionic solids, solid electrolytes, conducting polymers, and liquid/liquid interfaces. 

Polymer Repeat unit Glass-transition temperature, Ts (°C) Melting point, Tm (°C) Typical polymer electrolyte Conductivity (S/cm at 25°C)... 

Polymer electrolytes conduct cations by segmental motions of the polymer backbone that carry the cations from one complexation site to the next.60-62 Since this requires significant fluidity, the polymers are conductive only in the amorphous state, i.e. above the crystalline to gel transition temperature. For the bulk polymer of PHB, this temperature is in the range of 0° to 10 °C. Accordingly, single molecules of PHB dissolved in fluid lipid bilayers should be capable of considerable segmental motions at physiological temperatures. 

Figure 18.2 A cutaway view displaying the coated electrode system with electrolyte, conducting polymer, metal electrodes, and substrate. The current path across the interface between the electrolyte and the polymer determines the impedance.

An alternative to lithium batteries with liquid electrol5des are those with solid polymer electrolytes. Solid polymer electrodes are generally gel type electrolytes which trap solvent and salt in pores of the polymer to provide a medium for ionic conduction. Typical polymer electrolytes are shown in Table 15.8. 

Acrylic polyesters are also used by the polymer industry to produce fibers. However, the blends and composites of this class of polymers with conductive polymers were systematically prepared in the form of films One of the first attempts involved the electrochemical polymerization of 3-methylthiophene using an electrolyte solution containing poly(methyl methacrylate) [92]. By this method poly(methyl methacrylate) is codeposited on the electrode with the conductive polymer, forming a self-supported film. The conductivity of the film on the electrode side was two orders of magnitude higher than on the electrolyte side. Cyclic voltammetry and the visible spectra of the blend reproduce exactly the curves for the pure conductive polymer. This one-step synthesis is an alternative to the electrode coating method, provided that the insulating polymer host is soluble in the electrolyte solution. 

Qelik, S. tJ., Bozkurt, A., Hosseini, S. S., Alternatives toward proton conductive anhydrous membranes for fuel cells Heterocyclic protogenic solvents comprising polymer electrolytes. Prog. Polym. Sci. 2012, 37 (9), 1265-1291. 

Varying amounts of nanoscale rutile T102 with particle size ranging from 10 to 70 wt% were used by Kim and colleagues (2003) in the preparation of PVdF-HFP-based porous polymer electrolytes. A polymer electrolyte with 40 wt % rutile T1O2 showed the maximum ion conductivity of more than 10 S/cm at room temperature and potential to apply in the rechargeable lithium batteries. 

Doyle et al. [2] examine the tradeoffs involved with using a higher salt concentration in polymer electrolytes. Conductivity in polymer electrolytes generally displays a maximum at about 1 to 15 M salt concentration. One might then choose to use a salt concentration which yields this maximum conductivity. 

Gasa, J. V. Weiss, R. A. Shaw, M. T., Inflnence of blend miscibility on the proton conductivity and methanol permeability of polymer electrolyte blends,/. Polym. Sci. Part B Polym. Phys., 44,2253-2266 (2006) DOI 10.1002/polb.20865. 

Reversible oxidation and reduction of polymers is commonly used to increase conductivity in these systems. Ions from the electrolyte are usually incorporated into the polymer as part of this process (see Electrically conducting polymers). 

Polymer Electrolyte Fuel Cell. The electrolyte in a PEFC is an ion-exchange (qv) membrane, a fluorinated sulfonic acid polymer, which is a proton conductor (see Membrane technology). The only Hquid present in this fuel cell is the product water thus corrosion problems are minimal. Water management in the membrane is critical for efficient performance. The fuel cell must operate under conditions where the by-product water does not evaporate faster than it is produced because the membrane must be hydrated to maintain acceptable proton conductivity. Because of the limitation on the operating temperature, usually less than 120°C, H2-rich gas having Htde or no (

The successfiil synthesis of a transparent soHd polymer electrolyte (SPE) based on PEO and alkoxysilanes has been reported (41). The material possessed good mechanical properties and high electrical conductivity (around 1.8 x 10 S/cm at 25°C) dependent on the organic—inorganic ratio and PEO chain length. 

Polypyrroles. Highly stable, flexible films of polypyrrole ate obtained by electrolytic oxidation of the appropriate pyrrole monomers (46). The films are not affected by air and can be heated to 250°C with Htde effect. It is beheved that the pyrrole units remain intact and that linking is by the a-carbons. Copolymerization of pyrrole with /V-methy1pyrro1e yields compositions of varying electrical conductivity, depending on the monomer ratio. Conductivities as high as 10 /(n-m) have been reported (47) (see Electrically conductive polymers). 

A second class of important electrolytes for rechargeable lithium batteries are soHd electrolytes. Of particular importance is the class known as soHd polymer electrolytes (SPEs). SPEs are polymers capable of forming complexes with lithium salts to yield ionic conductivity. The best known of the SPEs are the lithium salt complexes of poly(ethylene oxide) [25322-68-3] (PEO), —(CH2CH20) —, and poly(propylene oxide) [25322-69-4] (PPO) (11—13). Whereas a number of experimental battery systems have been constmcted using PEO and PPO electrolytes, these systems have not exhibited suitable conductivities at or near room temperature. Advances in the 1980s included a new class of SPE based on polyphosphazene complexes suggesting that room temperature SPE batteries may be achievable (14,15). 

Electrogenerated conducting polymer films incorporate ions from the electrolyte medium for charge compensation (182). Electrochemical cycling in an electrolyte solution results in sequential doping and undoping of the polymer film. In the case of a -doped polymer, oxidation of the film results in the... 

An example of an ionically conductive polymer is polyethylene oxide containing LiC104, which is used as a solid phase electrolyte in batteries. 

A completely separate family of conducting polymers is based on ionic conduction polymers of this kind (Section 11.3.1.2) are used to make solid electrolyte membranes for advanced batteries and some kinds of fuel cell. 

Figure 11.9. Conductivity vs temperature plot for two ionically conducting crystals and for a polymer electrolyte, LiTf-aPtO40, which is based on amorphous poly(ethylene) oxide (after Ratner...

---