Room temperature bulk ionic conductivity

Figure 1. The room temperature bulk ionic conductivity, along z, of KTP crystals as a function of the reciprocal of their midpoint growth temperatures., Philips flux , DuPont flux O Airtron high temperature hydrothermal , Airtron low temperature hydrothermal.

Bulk ionic conductivities of the samples were measured by impedance analysis between room temperature and 545°C. The extrapolated ionic conductivity could be as high as 0.14-0.16 S/cm at 800°C. This value is very promising, however, caution should be exercised in interpreting this extrapolated ionic conductivity value. A change in the slope of log(cjT) versus 1/T plot is suspected in the literature above 550°C. 

Monomer II is also a polymerizable IL composed of quatemized imidazoliimi salt, as shown in Figure 29.1. This monomer is liquid at room temperature and shows a Tg only at —70°C. Its high ionic conductivity of about 10 S cm at room temperature reflects a low Tg. Although the ionic conductivity of this monomer decreased after polymerization as in the case of monomer I, it was considerably improved by the addition of a small amount of LiTFSI. Figure 29.3 shows the effect of LiTFSI concentration on the ionic conductivity and lithium transference number ( Li ) for polymer II. The bulk ionic conductivity of polymer II was 10 S cm at 50°C. When LiTFSI was added to polymer 11, the ionic conductivity increased up to 10 S cm After that, the ionic conductivity of polymer II decreased gradually with the increasing LiTFSI concentration. On the other hand, when the LiTFSI concentration was 100 mol%, the of this system exceeded 0.5. Because of the fixed imidazolium cations on the polymer chain, mobile anion species exist more than cation species in the polymer matrix at this concentration. Since the TFSI anions form the IL domain with the imidazolium cation, the anion can supply a successive ion conduction path for the lithium caiton. Such behavior is not observed in monomeric IL systems, and is understood to be due to the concentrated charge domains created by the polymerization. 

Figure 5 is the plot of log(cT) vs 1/T for LSGM samples with 15% and 17% Mg between room temperature and 545°C. Data for both compositions lie on straight lines Along with the experimental data, best linear fits to the data for the two samples are also shown. From these linear fits the ionic bulk conductivities for LSGM at 800°C were estimated by extrapolating to be 0.14-1.16 S/cm for 17% and 15% Mg containing samples, respectively. 

Park and co-workers, reported a series of polymer electrolytes based on the blend of P(VdF-HFP) and poly(vinylacetate) (PVAc), and the maximum ion conductivity reached 2.3 x 10 S/cm at room temperature (Kim et al., 1998).The mobility and concentration of the free lithium ions in the polymer electrolyte were reduced with increasing PVAc content, leading to the decrease in the ionic conductivity. The bulk and interfacial resistance of the P(VdF-HFP)-based polymer electrolyte used for the lithium symmetric cell were gradually increased with storage, while those of the P(VdF-HFP) PVAc (7 3)-based ones were relatively stable during storage. 

---