“…The conductivity is proportional to ϖ s , where s is approximately 0.95. An onset of the ionic mobility above the glass transition of the gel has already been reported by Stallworth et al In the case of PPO−LiCF 3 SO 3 systems, Wintersgill et al could fit conductivity and data for the α relaxation with the same VTF equation and concluded that the ion transport mechanism is dominated by large-scale segmental motion of the polymer chains. 5 Real part of the conductivity at different temperatures in dependence on the frequency for a gel electrolyte on the basis of P(EG) 23 DMA with 50 wt % (EG) 11 DME and LiCF 3 SO 3 , [EG]/[LiCF 3 SO 3 ] = 75 (▵), [EG]/[LiCF 3 SO 3 ] = 25 (□) and the corresponding gel (○) and the polymer (▪) without salt. 6 Dc conductivity (▪) compared with the real part of the conductivity at 1 MHz (○) and 1 kHz (▿) in dependence on the temperature.…”
This paper reports dielectric spectroscopic studies completed by
electrochemical measurements in combination
with DSC and PFG-NMR investigations to study the charge carrier
transport in gel electrolytes, which were
prepared by photoinitiated polymerization of oligo(ethylene
glycol)23 dimethacrylate [(EG)23DMA] in
the
presence of oligo(ethylene glycol)11dimethyl ether
[(EG)11DME] as plasticizer and
LiCF3SO3. The resulting
films show a glass transition at about −60 °C and the melting of
the plasticizer around −12 °C. Below the
glass transition two relaxation processes were observed by dielectric
spectroscopy, which most likely are to
be related to the γ relaxation of the EG groups and the β
relaxation of the methacrylate groups. The high-temperature behavior of the dielectric response is dominated by the
conductivity, which is weakly dependent
on the frequency in this temperature range. The permittivity goes
through a maximum at room temperature
and decreases with further enhancement of the temperature in connection
with an increase in ionic aggregation
indicated by growing deviations from the Nernst−Einstein
relationship. These deviations expressed as a
Haven ratio are discussed as the contribution of bounded species that
do not take part in the conductivity to
the overall diffusivity, either by an enlarged content of these
species, c
b, or by an enhancement of
their
self-diffusivity, D
b.
“…The conductivity is proportional to ϖ s , where s is approximately 0.95. An onset of the ionic mobility above the glass transition of the gel has already been reported by Stallworth et al In the case of PPO−LiCF 3 SO 3 systems, Wintersgill et al could fit conductivity and data for the α relaxation with the same VTF equation and concluded that the ion transport mechanism is dominated by large-scale segmental motion of the polymer chains. 5 Real part of the conductivity at different temperatures in dependence on the frequency for a gel electrolyte on the basis of P(EG) 23 DMA with 50 wt % (EG) 11 DME and LiCF 3 SO 3 , [EG]/[LiCF 3 SO 3 ] = 75 (▵), [EG]/[LiCF 3 SO 3 ] = 25 (□) and the corresponding gel (○) and the polymer (▪) without salt. 6 Dc conductivity (▪) compared with the real part of the conductivity at 1 MHz (○) and 1 kHz (▿) in dependence on the temperature.…”
This paper reports dielectric spectroscopic studies completed by
electrochemical measurements in combination
with DSC and PFG-NMR investigations to study the charge carrier
transport in gel electrolytes, which were
prepared by photoinitiated polymerization of oligo(ethylene
glycol)23 dimethacrylate [(EG)23DMA] in
the
presence of oligo(ethylene glycol)11dimethyl ether
[(EG)11DME] as plasticizer and
LiCF3SO3. The resulting
films show a glass transition at about −60 °C and the melting of
the plasticizer around −12 °C. Below the
glass transition two relaxation processes were observed by dielectric
spectroscopy, which most likely are to
be related to the γ relaxation of the EG groups and the β
relaxation of the methacrylate groups. The high-temperature behavior of the dielectric response is dominated by the
conductivity, which is weakly dependent
on the frequency in this temperature range. The permittivity goes
through a maximum at room temperature
and decreases with further enhancement of the temperature in connection
with an increase in ionic aggregation
indicated by growing deviations from the Nernst−Einstein
relationship. These deviations expressed as a
Haven ratio are discussed as the contribution of bounded species that
do not take part in the conductivity to
the overall diffusivity, either by an enlarged content of these
species, c
b, or by an enhancement of
their
self-diffusivity, D
b.
“…4 Recently, the results obtained by these conventional techniques have been confirmed using other spectroscopies like Raman, infrared ͑IR͒, far IR, and nuclear magnetic resonance ͑NMR͒. [5][6][7][8] The development of more sophisticated diffractometric techniques like radial distribution function ͑RDF͒ allowed us to extend the range of investigations up to concentrations reaching 1-2 M, where the conductometric approach is ineffective due to the strong interactions among ions and between ions and dipoles. However, the structural information given by this approach is statistically mediated over a ''long'' time.…”
Spectroscopic ͑Raman, NMR, impedance spectroscopy͒, and thermal ͓differential scanning calorimetry ͑DSC͔͒ techniques have been used to study the solvation mechanism of lithium ions in ethylene carbonate ͑EC͒-propylene carbonate ͑PC͒ concentrated solutions. For values of N ϭ͓Li ϩ ͔/͓ECϩPC͔р0.2 all the cations are solvated by ϳ4 solvent molecules and interaction chiefly takes place between Li ϩ and the ring oxygens. For NϾ0.2 a part of Li ϩ ions begins to form complexes with two solvent molecules ͑sandwich configuration͒. At NХ0.5 nearly all cations are complexed, and a crystalline compound is formed at room temperature. For higher values of N a reassociation of the salt takes place.
“…The formers require liquid electrolytes in combination with porous or dense separators (gelled or plasticized polymer electrolytes). Following this approach, Stallworth et al investigated PAN gelled electrolytes by 23 Na NMR and Impedance spectroscopies [14], Egashira et al characterized Na tertiary liquid electrolytes incorporating a tetrafluoroborate ionic liquid, PEGDME and NaBF 4 [15]. Furthermore, Bhide et al [16] reported EC-DMC Na electrolytes, claiming that NaPF 6 /EC-DMC leads to a stable surface film on Na 0.7 CoO 2 , enabling reversible cycling.…”
Sodium-conducting solvent-free polymer electrolytes based on commercially available and inexpensive materials poly(oxyethylene), POE, and three different sodium salts (NaI, NaCF 3 SO 3 and NaClO 4 ) were prepared and exhaustively characterized. In order to minimize the environmental impact related to conventional film processing based on casting, a combination of lyophilization and hot-pressing was successfully applied. Contrary to film-casting, this new approach led to very homogeneous and pore-free films. This study suggests the obtained polymer electrolyte films as a promising route to enhance not only ionic conductivity but also mechanical properties. Furthermore, a preliminary work on salt blends hosted by POE shows that they strongly decrease melting point and crystallinity of the polymer electrolytes and paves the way for enhanced sodium-conducting materials.
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