Single-ion conductor

The single-ion conductor, PAGSOa Na (m/n = 0.4 or 1.0, in which m and n are the number of siloxy units in the structure), was made by consecutive hydrosilylation of PHMS with AM PEG and allyl glycidyl ether. The neutral polymer was sulfonated with aqueous NaHSOa, which quantitatively converted the epoxy group into -CH(0H)CH2S03". Excess NaHSOa was removed by repeated ultrafiltration of the polymer solution with a cutoff membrane having a Mw of 1000. The poly sulfonate was azeotropically dried with benzene and finally in vacuum at 50 °C for several days. 

This is directly evidenced by the echo attenuation of the proton resonance in PFG-NMR experiments of phosphonic acid functionalized oligomer [104], Only the echo of the phosphonic protons is attenuated ivhile the echo of the oligomer protons is only slightly affected by the magnetic field gradient (Fig. 23.9). The reader may recall that complexation of phosphoric acid and a basic polymer does not show any sign of this effect (see Fig. 23.7), which opens the way to the development of true single ion conductors. 

Fig. 7.18 A comparison of the lithium diffusion coefficient in PEO-based single ion conductors (Fig. 7.14) and PEO-based binary comb-branch polymer electrolytes (Fig. 7.10) from simulations...

Figure 7.18 shows the lithium diffusion coefficient in a PEPE binary (free anion) SPE (Fig. 7.13) and single ion conductors (Fig. 7.17) from unpublished simulations for various EO Li ratios. Simulation reveals that the lithium diffusion coefficient in the single ion conductor is about a factor of 2-6 lower than in the binary PEO SPEs. Note that unlike the binary PEO SPEs, the PEPE-based single ion conductor does not show a maximum in conductivity around EO Li = 20, but increases... 

Dou S, Zhang S, Klein RJ, Runt J, Colby RH (2006) Synthesis and characterization of poly (ethylene glycol)-based single-ion conductors. Chem Mater 18 4288-4295... 

Copolymer system A simple example for the single ion conductor can be proposed by the copo1ymerization of oligo(oxyethylene) methacrylate and methacrylic acid salt [9-12]. The present copolymer is a typical single ion conductor without any added salt. Generally, the conductivity for single ion conductor is very low, in the range of 10 - 10 S/cm. This can be improved by this copolymerization. 

To fix the anions to the macromolecular main chain by covalent bonds, and obtain a single ion conductor, one or more of the following methods may be used ... 

Blending a polymer electrolyte with a polymer matrix that is beneficial to ionic conduction. For example, a single ion conductor mixture is prepared by blending a high molecular weight PEO with a polymer electrol5de, poly(lithium 2-(4-carboxyl hexafluorobutyl acyloxy) ethyl methacrylate). However, the ionic conductivity is low, 4 x 10 S/cm at 30°C. 

A single-ion conductor containing a PEO unit can also be prepared for gel polymer electrolytes. For example, the lithium salt prepared as shown in Figure 11.3 is plasticized with EC or PC solvent, though the LP-ion transference number decreases with the amount of solvent added. When the number of EO units is greater than three, it behaves as a single-ion conductor and follows the VTF equation. The ionic conductivity remains relatively constant with varying numbers of EO units. 

AUcock, H. R., Welna, D. T., Maher, A. E., Single ion conductors—Polyphosphazenes with sulfonimide functional groups. Solid State Ionics, 2006, 177, 741-747. 

Single-ion conductors can be obtained by the intercalation of PEO on clay due to the presence of cation charge at the silicate surface. The conductivity values of electrolytes based on POEM with the addition of 2 and 5 wt% clay were found to be around 4 x 10 S/cm at 70 °CF The conductivity obtained can be anisotropic. Molecular dynamic simulation has shown that the Li" ions are solvated preferentially by the silicate oxygen atom rather than PEO. The conductivity is too low for practical applications, even with a cationic transference number equal to one. In order to increase conductivity, but with a cationic transference number different from one, lithium salts were added to PEO/clay nanocomposites. At room temperature, the nanocomposite electrolyte exhibited higher ionic conductivity than unfilled polymer due to the larger content of the PEO amorphous phase. The improvement in conductivity depends on the nature of the clay. Fan et al. have shown that 250-Li-MMT, i.e. Li-MMT heated to 250°C, was more effective in enhancing the conductivity of (PE0)i6LiC104 than Org-MMT, dodecylamine modified Li-MMT, and Li-MMT, since 250-Li-MMT forms an exfoliated structure in the PEO matrix. 

For a single ion conductor, D = can be used and in case both cations and anions are mobile, an effective D value may be used [17,18]. Anyhow, by using equation (18) one can obtain ... 

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