Mass and Charge Transport in the Polymer-Ionic-Liquid System PEO-EMImI: From Ionic-Liquid-in-Polymer to Polymer-in-Ionic-Liquid Electrolytes.

Conventional polymer electrolytes based on inorganic salts are commonly characterized and utilized over a small salt-poor composition range because of phase transitions accompanied by loss of ion conductivity at high salt concentrations. By contrast, well-chosen polymer-ionic-liquid (IL) systems offer the possibility to vary the IL content from the IL-in-polymer to the polymer-in-IL domain. We have investigated the temperature-dependent ionic conductivity in PEOyEMImI systems consisting of poly(ethylene oxide) complexed with 1-ethyl-3-methylimidazolium iodide for y = EO/IL ratios ranging from 0.

Ion transport effects in a solid polymer electrolyte due to salt substitution and addition using an ionic liquid.

We investigated mass and charge transport in amorphous salt-in-poly(ethylene oxide) (PEO) electrolytes with NaI and/or the ionic liquid (IL) EMImTFSI (1-ethyl-3-methylimizadolium bis(trifluoromethylsulfonyl)imide) as salt component. Combining the results of ion conductivity, pulsed field gradient nuclear magnetic resonance, and radiotracer diffusion measurements, it is found that over wide temperature ranges both the cation and anion diffusion coefficients and the charge diffusivity are distinctly larger in PEO(20)EMImTFSI than in PEO(20)NaI complexes, where the monomer-to-salt mole ratio equals 20. In the mixed-salt complexes PEO(20)NaI(1)EMImTFSI(1) and PEO(20)NaI(0.

Ionic transport in polymer electrolytes based on PEO and the PMImI ionic liquid: effects of salt concentration and iodine addition.

We find a strong impact of ion pairing on ionic transport in potential Grätzel-cell electrolytes based on poly(ethylene oxide) (PEO) and 1-propyl-3-methylimidazolium iodide (PMImI). Furthermore, the addition of free iodine enhances both mass and charge transport, which can be explained by the reduced pair-formation tendency of the bulky triiodide ion. These results arise from conductivity and diffusion measurements on amorphous complexes with EO/PMImI molar ratios of 20 and 30 and their evaluation in a comprehensive ion-transport model.

What can we learn from ionic conductivity measurements in polymer electrolytes? A case study on poly(ethylene oxide) (PEO)-NaI and PEO-LiTFSI.

We explore in detail what information on ionic diffusivity and ion pairing can be exclusively gained from combining accurate direct-current conductivity data in polymer electrolytes with a novel evaluation model. The study was performed on two prototype systems based on poly(ethylene oxide) (PEO) with known disparate ion-association properties, which are due to the dissimilar salt components being either sodium iodide (NaI) or lithium bis(trifluoromethane-sulfonyl)imide (LiN(CF(3)SO(2))(2) or LiTFSI). The temperature dependence of the conductivity can be described by an extended Vogel-Tammann-Fulcher (VTF) equation, which involves a Boltzmann factor containing the pair-formation enthalpy ΔH(p).

Rubidium impurity diffusion in a poly(ethylene oxide)-sodium iodide polymer electrolyte.

Diffusion of the radioisotope (86)Rb in an amorphous polymer-salt complex consisting of poly(ethylene oxide) and sodium iodide was found to be faster at all temperatures investigated than tracer self-diffusion of the smaller alkali metal cation (22)Na. This is the striking result of the first study on impurity diffusion in a polymer electrolyte system and a comparison with ionic self-diffusion and conductivity data previously obtained from the same system. The experimental findings can be rationalized within an ion transport model based on the occurrence of charged single ions and neutral ion pairs.