Polymer electrolytes liquids

In this chapter, attention is focused on a number of polymers that are either themselves characterized by special properties or are modified for special uses. These include high-temperature and fire-resistant polymers, electroactive polymers, polymer electrolytes, liquid crystal polymers (LCPs), polymers in photoresist applications, ionic polymers, and polymers as reagent carriers and catalyst supports. 

The first use of ionic liquids in free radical addition polymerization was as an extension to the doping of polymers with simple electrolytes for the preparation of ion-conducting polymers. Several groups have prepared polymers suitable for doping with ambient-temperature ionic liquids, with the aim of producing polymer electrolytes of high ionic conductance. Many of the prepared polymers are related to the ionic liquids employed for example, poly(l-butyl-4-vinylpyridinium bromide) and poly(l-ethyl-3-vinylimidazolium bis(trifluoromethanesulfonyl)imide [38 1]. 

Noda and Watanabe [42] reported a simple synthetic procedure for the free radical polymerization of vinyl monomers to give conducting polymer electrolyte films. Direct polymerization in the ionic liquid gives transparent, mechanically strong and highly conductive polymer electrolyte films. This was the first time that ambient-temperature ionic liquids had been used as a medium for free radical polymerization of vinyl monomers. The ionic liquids [EMIM][BF4] and [BP][Bp4] (BP is N-butylpyridinium) were used with equimolar amounts of suitable monomers, and polymerization was initiated by prolonged heating (12 hours at 80 °C) with benzoyl... 

The aim of this chapter is to give a state-of-the-art report on the plastic solar cells based on conjugated polymers. Results from other organic solar cells like pristine fullerene cells [7, 8], dye-sensitized liquid electrolyte [9], or solid state polymer electrolyte cells [10], pure dye cells [11, 12], or small molecule cells [13], mostly based on heterojunctions between phthaocyanines and perylenes [14], will not be discussed. Extensive literature exists on the fabrication of solar cells based on small molecular dyes with donor-acceptor systems (see for example [2, 3] and references therein). 

It is now well established that in lithium batteries (including lithium-ion batteries) containing either liquid or polymer electrolytes, the anode is always covered by a passivating layer called the SEI. However, the chemical and electrochemical formation reactions and properties of this layer are as yet not well understood. In this section we discuss the electrode surface and SEI characterizations, film formation reactions (chemical and electrochemical), and other phenomena taking place at the lithium or lithium-alloy anode, and at the Li. C6 anode/electrolyte interface in both liquid and polymer-electrolyte batteries. We focus on the lithium anode but the theoretical considerations are common to all alkali-metal anodes. We address also the initial electrochemical formation steps of the SEI, the role of the solvated-electron rate constant in the selection of SEI-building materials (precursors), and the correlation between SEI properties and battery quality and performance. 

It is not clear why <2IR is twice as large [6, 76, 96] (or more) in polymer electrolytes than it is in liquid electrolytes. This may result from larger <2SP and larger <2SE] due to partial exfoliation. 

The major differences between polymer and liquid electrolytes result from the physical stiffness of the PE. PEs are either hard-to-soft solids, or a combination of solid and molten in phases equilibrium. As a result, wetting and contact problems are to be expected at the Li/PE interface. In addition, the replacement of the native oxide layer covering the lithium, under the... 

Since this is a new field, little has been published on the LiXC6 /electrolyte interface. However, there is much similarity between the SEIs on lithium and on LixC6 electrodes. The mechanism of formation of the passivation film at the interface between lithiated carbon and a liquid or polymer electrolyte was studied by AC impedance [128, 142]. Two semicircles observed in AC-impedance spectra of LiAsF6/EC-2Me-THF electrolytes at 0.8 V vs. Li/Li+ [142] were attributed to the formation of a surface film during the first charge cycle. However, in the cases of LiC104 or LiBF4 /EC-PC-DME (di-... 

A plasticized electrolyte, usually obtained by the addition of small amounts of a liquid of high dielectric constant to a solving polymer electrolyte in order to enhance its conductivity. 

Figure 1 shows the temperature variation of the ionic conductivities for several polymer-electrolyte systems. At room temperature they are typically 100 to 1000 times less than those exhibited by a liquid or the best ceramic- or glass-based electrolytes [6,8], Although higher conductivities are preferable, 100-fold or 1000-fold... 

The polymer electrolytes discussed so far suffer from a number of disadvantages. Firstly, they exhibit low conductivities in comparison with liquid or solid (crystalline or glassy) electrolytes at or below room temperature. The best all-amorphous systems have conductivities less than 10"4 S cm-1 at room temperature. These ambient... 

The difficulties engendered by a hypothetical liquid standard state can be eliminated by the use of unsymmetrically normalized activity coefficients. These have been used for many years in other areas of solution thermodynamics (e.g., for solutions of electrolytes or polymers in liquid solvents) but they have only recently been employed in high-pressure vapor-liquid equilibria (P7). 

The electrocatalytic oxidation of methanol has been widely investigated for exploitation in the so-called direct methanol fuel cell (DMFC). The most likely type of DMFC to be commercialized in the near future seems to be the polymer electrolyte membrane DMFC using proton exchange membrane, a special form of low-temperature fuel cell based on PEM technology. In this cell, methanol (a liquid fuel available at low cost, easily handled, stored, and transported) is dissolved in an acid electrolyte and burned directly by air to carbon dioxide. The prominence of the DMFCs with respect to safety, simple device fabrication, and low cost has rendered them promising candidates for applications ranging from portable power sources to secondary cells for prospective electric vehicles. Notwithstanding, DMFCs were... 

We have already referred to the Mo/Ru/S Chevrel phases and related catalysts which have long been under investigation for their oxygen reduction properties. Reeve et al. [19] evaluated the methanol tolerance, along with oxygen reduction activity, of a range of transition metal sulfide electrocatalysts, in a liquid-feed solid-polymer-electrolyte DMFC. The catalysts were prepared in high surface area by direct synthesis onto various surface-functionalized carbon blacks. The intrinsic... 

Arico AS, Creti P, Antonucci PL, Antonucci V. 1998. Comparison of ethanol and methanol oxidation in a liquid-feed solid polymer electrolyte fuel cell at high temperature. Electrochem Sol Lett 1 66-68. 

In polymer electrolytes (even prevailingly crystalline), most of ions are transported via the mobile amorphous regions. The ion conduction should therefore be related to viscoelastic properties of the polymeric host and described by models analogous to that for ion transport in liquids. These include either the free volume model or the configurational entropy model . The former is based on the assumption that thermal fluctuations of the polymer skeleton open occasionally free volumes into which the ionic (or other) species can migrate. For classical liquid electrolytes, the free volume per molecule, vf, is defined as ... 

The ion solvating polymers have found application mainly in power sources (all-solid lithium batteries, see Fig. 2.19), where polymer electrolytes offer various advantages over liquid electrolyte solutions. 

Polymer gels and ionomers. Another class of polymer electrolytes are those in which the ion transport is conditioned by the presence of a low-molecular-weight solvent in the polymer. The most simple case is the so-called gel polymer electrolyte, in which the intrinsically insulating polymer (agar, poly(vinylchloride), poly(vinylidene fluoride), etc.) is swollen with an aqueous or aprotic liquid electrolyte solution. The polymer host acts here only as a passive support of the liquid electrolyte solution, i.e. ions are transported essentially in a liquid medium. Swelling of the polymer by the solvent is described by the volume fraction of the pure polymer in the gel (Fp). The diffusion coefficient of ions in the gel (Dp) is related to that in the pure solvent (D0) according to the equation ... 

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 ... 

Polymeric conducting systems were also prepared by in situ polymerization of vinyl monomers in ionic liquids [22], with a conductivity of 1 mS/cm. A conductive polymer electrolytes were also prepared by polymerization in liquid EMIm(HF)nF leading to a composite poly(2-hydroxyethyl methacrylate)-EMIm(HF)nF. Recently, polymer electrolytes were prepared in the form of thin foils, by incorporating ionic liquids in a polymer matrix [13-15], Conductivities of polymer-IL or polymer-IL-solvent systems are collected in Table 4. 

Similar or even better capacity was obtained in systems with polymer electrolytes based on ionic liquids. A series of electrochemical... 

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