Polymer electrolytes ionic conductivity

Key words multivalent polymer electrolytes, ionic conductivity, cationic... 

Pradhan, D.K. et al.. Effect of plasticizer on microstructure and electrical properties of a sodium ion conducting composite polymer electrolyte. Ionics, 2005.11(1) 95-102. 

Ramesh, S. and K. Wong, Conductivity, dielectric behaviour and thermal stability studies of lithium ion dissociation in poly (methyl methacrylate)-based gel polymer electrolytes. Ionics, 2009.15(2) 249-254. 

For the composite polymer electrolytes, the conductive carbonaceous filler must be below the electrical percolation threshold, due to the need to obtain an electronically insulating material with suitable ionic conductivity. These fillers are also used to improve the thermal stabilization and serve as mechanical reinforcement to improve the electrolyte/ electrode compatibility. CNT/P(VDF-TrFE) composites showed higher porosity and electrolyte uptake compared to the pristine polymer. CNT also contributed to increase ionic conductivity (2.6 xlO S cm , 0.1 wt.% CNT) and diminished its variations with temperature. 

Agar gels have been used for many decades although it may seem strange to consider these systems as examples of solid polymer electrolytes, we will see that they share many properties with most polymer-based, ionically conducting systems. A variety of other polymers, both synthetic and natural product derivatives, will gel aqueous solutions. 

The motion of ions (i.e. conductivity) in polymer electrolytes appears to occur by a liquid-like mechanism in which the movement of ions through the polymer matrix is assisted by the large amplitude segmental motion of the polymer backbone. Ionic conductivity primarily occurs in the amorphous regions of the polymer [4,5]. The temperature dependence of the conductivity of polymer electrolytes is best related by the Vogel-Tamman-Fulcher (VTF) equation... 

Khiar ASA, Arof AK. 2010. Conductivity studies of starch-based polymer electrolytes. Ionic 16(2) 123-129. Kim DH, Kwon OJ, Yang SR, Park JS. 2007. Preparation of Starch-based Polyurethane Films and Their... 

Quasi-solid-state electrolytes include gel polymer electrolytes, ionic liquids, and plastic crystal systems. It is important to distinguish polymer electrolytes and gel polymer electrolytes. In polymer electrolytes, charged cationic or anionic groups are chemically bonded to a polymer chain, while gel polymer electrolytes are solvated by a high dielectric constant solvent and are free to move. In a classical gel electrolyte, polymer and salts are mixed with a solvent, usually having a concentration above 50 wt%, and the role of the polymer is to act as a stiffener for the solvent, creating a three-dimensional network, where cations and anions move freely in the liquid phase [88]. The solid polymer electrolyte includes poly(ethylene oxide) (PEO)-based lithium ion conductors that typically show conductivities of 10 S cm while the gel polymer electrolytes have semisolid character with much higher ionic conductivities of the order 10 —10 S cm . ... 

Multivalent polymer electrolytes that use PEO as the polymer base are usually multiphase systems consisting of salt-rich crystalline phases, another crystalline phase of pure polymer, and amorphous phases with dissolved salts. Conductivity is thus often affected by factors such as slow crystallisation and salt redistribution processes between the phases, which result in values dependent on the thermal history, preparation methods, etc. The morphological and crystallographic structures of these polymeric systems are presented, and the influence of factors such as crystallisation of the pure polymer on ionic conduction, and the factors that influence them in turn, are highlighted. Discussion of conduction takes into account the two possible mechanisms of mobility of charged ionic clusters and exchange of... 

Some polymer electrolytes show conductivity temperature dependence that falls outside the three types described above, with neither the Arrhenius law nor the VTF (or WLF) law being followed in the temperature ranges studied." Here, if there are no phase changes, effects associated with ionic aggregate equilibria are likely, superimposed on the simple variation in ionic mobility. In all cases, it is important to consider not only this parameter, but also the number and types of charge carriers, which are influenced by the ionic association that probably exists in ionic transport. ... 

In another work, poly(l-oligo(ethylene glycol) methacrylate-3-methyUmidazolium chloride) was synthesized as the ionic liquid polymer, exhibiting ionic conductivity of 1.0 x 10 S cm at room temperature. Ionic liquid-based electrolytes were prepared by the addition of the ionic polymer poly(l-oligo(ethylene glycol) methacrylate-3-methylimidazolium chloride) to a binary ionic liquid mixture and Lil/E. It was shown that the ionic conductivity decreases with increasing polymer content, and the maximum conductivity achieved (2.0 x 10 S cm ) was obtained at a polymer content of 10 vt%. DSSC assembled with the optimized electrolyte presented overall efficiency conversion of 6.1%. ... 

The GPE was composed of a PEG-based acrylate macromonomer, photoinitiator, plasticiser, glass beads and the electrolyte to compensate for the charge injected into or extracted from the conducting polymer. The ionic conductivity of lithium-PEO has been reported to be at a maximum for a Li/O ratio of 0.04 and hence the composition of the GPE with no plasticiser was prepared with this ratio. The different compositions of the GPEs used in this study are shown in Table 12.1. 

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). 

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

By the time the next overview of electrical properties of polymers was published (Blythe 1979), besides a detailed treatment of dielectric properties it included a chapter on conduction, both ionic and electronic. To take ionic conduction first, ion-exchange membranes as separation tools for electrolytes go back a long way historically, to the beginning of the twentieth century a polymeric membrane semipermeable to ions was first used in 1950 for the desalination of water (Jusa and McRae 1950). This kind of membrane is surveyed in detail by Strathmann (1994). Much more recently, highly developed polymeric membranes began to be used as electrolytes for experimental rechargeable batteries and, with particular success, for fuel cells. This important use is further discussed in Chapter 11. 

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...

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... 

Electrolyte a substance, liquid or solid, which conducts electrical current by movement of ions (not of electrons). In corrosion science, an electrolyte is usually a liquid solution of salts dissolved in a solvent, or a molten salt. The term also applies to polymers and ceramics which are ionically conductive. 

---