We report the synthesis and characterization of a series of imidazolium iodide ionic liquids (ILs) containing monomethoxy-terminated poly(ethylene glycol) (mPEG), and n-alkyl groups. These PEGylated ILs contain 7, 12, or 16 ethylene glycol units in the side chains, and are designed as potential electrolytes for energy conversion and storage devices such as dye-sensitized solar cells, supercapacitors, and Li ion batteries. The thermophysical (density, viscosity, and the temperatures of glass-transition, crystallization and melting) and electrochemical (nonfaradaic window, and capacitor leakage resistance) properties of the ILs, that are critical to these targeted applications, are studied using an array of techniques. 1-Alkyl-3-methylimidazolium iodide ILs are synthesized and characterized in parallel with the PEGylated ILs, to compare how the electrolyte properties of the two systems are affected by their detailed molecular structures, and especially by the ether oxygen atoms. The mPEG side chains show strong intramolecular interactions with the imidazolium ring, weakening Coulombic interactions between the imidazolium cation and the iodide anion. The PEGylated ILs, therefore, exhibit conductivities of the order of 0.1 mS cm -1 (25 °C) despite their relatively high viscosities, and support a temperature-independent electrochemical window of about 2 V, demonstrating their suitability for extended temperature applications.

We investigate the influence of nanofiller surface chemistry and ion content on the conductivity of nanofilled PEO + LiClO 4 solid polymer electrolytes (SPEs) using dielectric spectroscopy, differential scanning calorimetry (DSC), FESEM, and quasi-elastic neutron scattering (QENS). We consider the concentration series EO/Li = 8:1, 10:1 (eutectic composition), 14:1, with both acidic α-Al 2 O 3 and neutral γ-Al 2 O 3 nanoparticles. The acidic filler is more effective at increasing conductivity at the non-eutectic compositions. In contrast, the two surface chemistries provide comparable increases at the eutectic composition. This composition maximizes the influence of nanofillers, regardless of surface chemistry. We find no significant changes in crystallinity, glass transition temperature, nanoparticle dispersion, or PEO segmental dynamics as a function of surface chemistry. In the absence of salt, acidic particles slow PEO dynamics more than neutral particles, suggesting that the PEO chains and the acidic surface sites share a favorable interaction. A rotation consistent with the crystal structure PEO 6 :LiClO 4 is observed up to 50 °C (8:1) and up to 75 °C (eutectic composition). PEO 6 rotation is hindered by nanoparticles, with the degree of restriction as a function of surface chemistry. We propose a mechanism where nanofillers stabilize the PEO 6 structure at their surface, and differences in surface chemistry and composition dictate the extent of stabilized PEO 6 and whether Li movement in this structure is facile or restricted.

A novel imidazolium iodide ionic liquid with an u-perfluoroalkyl poly(ethylene glycol) (PEG) tail attached to the imidazolium ring has been synthesized for its potential incorporation as an electrolyte in dye-sensitized solar cells. The ionic liquid molecules, with block oligomer tails, self-assembled to form a solvent-free ionic gel, without the assistance of an external gelator or an immobilizing matrix. The solidification was evidently facilitated by the generation of ionic clusters due to electrostatic interactions, as well as microphase separation of the immiscible perfluoroalkyl and PEG segments of the cation. We report herein the synthesis and electrochemical properties of this block oligomer ionogel, along with the results of self-consistent mean field calculations probing the formation of nanostructures in the ionogel. Although properties such as high viscosity and high ionic conductivity appear incompatible, it is shown that a nano-structured fluid can support high iodide diffusion at low effective fluidity, and that the formation of an organic alloy, by simple blending of two imidazolium iodide salts, can produce significant conductivity enhancements without lowering the viscosity.

The crystallinity and conductivity of nanoparticle‐filled solid polymer electrolytes (SPEs) are investigated as a function of thermal history and water content. Our objective is to evaluate how performance is affected by the conditions under which the SPEs are handled and tested. The samples consist of polyethylene oxide (PEO), LiClO4, and Al2O3 nanoparticles. At low humidity, SPEs at ether oxygen to lithium ratios of 8:1 do not crystallize immediately; instead, 3 days are required for crystallization to occur, and this does not depend strongly on the presence of nanoparticles. The conductivity is improved by the addition of nanoparticles at low humidity, but only at an ether oxygen to lithium ratio of 10:1, which corresponds to the eutectic concentration. At high humidity, the recrystallization time is delayed for 3 weeks, and the conductivity increases in both filled and unfilled SPEs beyond that of the low humidity samples. Although we observe that water amplifies the influence of nanoparticles on conductivity, we also find that nanoparticles inhibit water uptake—but only in the presence of lithium. Because Li+ strongly absorbs water, this result suggests that nanoparticles may interact directly with Li+ ions to prevent water uptake. In filled samples at the eutectic concentration (10:1), more water is absorbed compared to the nanoparticle‐filled 8:1 samples, even though less lithium is present. This suggests that nanoparticles may segregate to lithium‐poor regions in the 10:1 samples, and this scenario is supported by the morphology that would be expected at the eutectic concentration. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 49: 1496–1505, 2011