Ionic conduction of polymer electrolytes

Watanabe, M., Yamada, S-L, and Ogata, N., Ionic conductivity of polymer electrolytes containing room temperature molten salts based on pyridinium halide and aluminium chloride, Electrochim. Acta, 40,2285,1995. 

Table 15. Ionic conductivities of polymer electrolytes derived from cyclophosphazene pendant polymers...

In conclusion the introduction of metal oxide into the polymer matrix has significantly improved the amorphicity, mechanical, thermal and ionic conductivity of polymer electrolytes. Novel analytical devices based on nanostructured metal oxides and CPs are cost-effective, highly sensitive due to the large surface-to-volume ratio of the nanostructure, and additionally show excellent selectivity when coupled to bio-recognition molecules with simple design [99-102]. 

Wen T. C., Luo S. S., and Yang C. H., Ionic conductivity of polymer electrolytes derived from various diisocyanate-based waterborne polyurethanes. Polymer, 2000,41,6755-6764. 

Masuda Y, Seki M, Nakayama M, Wakihara M, Mita H (2(X)6) Study on ionic conductivity of polymer electrolyte plasticized with PEG-aluminate ester for rechargeable lithium ion battery. Solid State Ion 117(9-10) 843-846... 

Other kinds of copolymers include poly(vinylidene fluoride) (PVDF), poly(vinylidenefluoride-hexafluoro propylene) (P(VDF-HFP)), and polyethylene glycol dimethyl ether. The ionic conductivity of polymer electrolytes using LiCFjSOj as lithium salt can reach 10 S/cm at room temperature [1]. 

Kaskhedikar, N., Paulsdorf, J., Buijanadze, M., Karatas, Y, Wilmer, D., Rohng, B., Wiemhofer, H. D., Ionic conductivity of polymer electrolyte membranes based on polyphosphazene with oligo(propylene oxide) side chains. Solid State Ionics, 2006, 177, 703-707. 

The ionic conductivity of polymer electrolytes is typically 100 to 1000 times less than exhibited by a liquid- or ceramic-based electrolyte. Although higher conductivities are preferable, and indeed a great deal of effort has gone into improving the bulk conductivity of polymer electrolytes over the years, 100-fold or 1000-fold increases are not essential, as a thin film electrochemical cell configuration can largely compensate for the lower values. 

An interesting approach consists of the addition of nanoscale inorganic fillers, to improve the mechanical, interfacial and conductivity properties of the (gel) polymer electrolytes. Since the pioneering work by Scrosati and co-workers, addition of T102 and other nanoparticles has been extensively employed to improve the ionic conductivity of polymer electrolytes. It is well known that the presence of such nanoparticles changes the conduction mechanisms assigned to the ions introduced in the polymer however, how these nanoparticles actually act is stiU unknown. These materials can also improve the mechanical properties of gel electrolytes and ionic liquid-based electrolytes. However, their effect on the mechanical stability can result in a loss in electrolyte penetration. 

Conductivities of pure ionic liquids varied depending on the anions (3.98 for [bmim][Tf2N ], 3.55 for [bmim][BF4 ] and 0.25 for [bmim][Br ] x 10 S cm at room temperature). Ionic conductivities of all synthesized PEs were in the range 10" -10 S cm at room temperature. The conductivity decreases with increasing polymer content in the three families, being typical behaviour of other polymer electrolytes composed of ionic liquids and polymers. At high ionic liquid concentrations, the ionic conductivity reached values near to the values of the ionic liquids although the mechanical stability is compromised. The lowest ionic conductivity of polymer electrolytes is the one with bromide anion (family 3). ... 

NAN, c., LI, z., YUAN, H., et al. Enhanced ionic conductivity of polymer electrolytes containing nanocomposite Si02 particles, Phys. Rev. Lett., 2003, 91(12), 266. 

The ionic conductivity of polymer electrolytes, however, is by far lower than that of liquid phase electrolytes. Gelled polymer electrolytes (GPEs), which are composed of polymer matrices and solvents or plasticizers, have been developed in place of genuine polymer electrolytes to improve ionic conductivity. And in the end of 1990s, LIBswith GPEs, which will be called lithium polymer batteries (LPBs) hereafter for convenience s sake, were put on the market. 

Table 1 WLF Parameters for Ionic Conductivity of Polymer Electrolytes from PPO Network and LiC104...

The ionic conductivity of polymer electrolytes is affected not only by the ionic mobility, but also by the number of carrier ions. It is unlikely that salts incorporated at such high concentrations dissociate completely in these media of relatively low polarity. Thus, a part of an incorporated salt may dissociate to free ions, which function as carrier ions, but we cannot deny the possibility of the presence of aggregated ions, so-called ionic multiplets. The energetics for the formation of ionic aggregates have been studied as a function of the dielectric constant of the solvent and of the salt concentration in electrolyte solutions [64]. If the incorporated salts are partially dissociated, the number of carrier ions will be influenced by the incorporated salt species, its concentration, temperature, and the polymer structure. 

Hammond and DeLongchamp [255] reported the development of a highly ionic, conductive, solid polymer electrolyte film from hydrogen bonding LBL... 

Of course an appropriate ionic conductivity in the active layer is important as well. Organic solid polymer electrolytes (SPEs) provide only k = 0.1-1 mS/cm, and liquid organic electrolytes k — 1-lOmS/cm. But aqueous electrolytes have much better values in the order of lO-lOOmS/cm. One of the consequences of the low ionic conductivities of organic electrolytes is a minimization of transport length L (cf. Vetter s model [64]), or the capillary gap cell in organic electrosynthesis [4]. 

A third type of ionic conduction occurs in polymer electrolytes, such as polyethylene oxide. The mechanism of ionic conduction in polymer electrolytes is not entirely understood. However, it is believed to involve rapid polymer segmental motion which creates regions of an elastomeric nature. These elastomeric regions have relaxation times similar to liquids, and, thus, allow a higher ionic mobility than would be concluded from the polymer s macroscopic properties [2]. 

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. 

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... 

Hayamizu K, AUiara Y, Price W (2000) Correlating the NMR self-diffusion and relaxatirai measurements with ionic conductivity in polymer electrolytes composed of cross-linked poly (ethylene oxide-propylene oxide) doped with LiN(S02CF3)(2). J Chem Phys 113(11) 4785 793... 

Kelly, M.J., et al. 2005. Conductivity of polymer electrolyte membranes by impedance spectroscopy with microelectrodes. Solid State Ionics 176 2111-2114. 

The basic setup of polymer electrolyte membrane fuel cells (PEMFC) as well as direct methanol fuel cells (DMFC) is in line with the standard fuel cell setup the two electrodes are separated by means of an electrically insulating but ionically conductive membrane (polymer electrolyte). In a PEM fuel cell, the anodic reactant is hydrogen, which is oxidized to form protons on the cathode, oxygen is reduced and forms water with protons that are transported through the proton conductive membrane. The overall reaction is... 

Jing, F., Hou, M., Shi, W, Fu, J., Yu, H., Ming, P. and Yi, B. (2007) The effect of ambient contamination on PEMFC performance. J. Power Sources 166, 172-176 Kadirov, M. K., Bosnjakovic, A. and Schlick, S. (2005) Membrane-derived fluorinated radiceds detected by electron spin resonance in UV-irradiated Nafion and Dow ionomers Effect of counterions and H O - J- Phys. Chem. B 109, 7664-7670 Kelly, M. J., Egger, B., Fafilek, G., Besenhard, J. O., Kronberger, H. and Nauer, G. E. (2005a) Conductivity of polymer electrolyte membranes by impedance spectroscopy with microelectrodes. Solid State Ionics 176, 2111-2114... 

---