No abstract

State-of-the-art poly͑ethylene oxide͒ ͑PEO͒-based polymer electrolytes have a t Liϩ much lower than 1; it is typically around 0.2-0.3. Thus, the development of single-cation-conductive, solvent-free polymer electrolytes is considered of prime importance for the progress of the technology of lithium batteries. Attempts mainly directed at immobilization of the anion in the polymer architecture have been reported in the past, but with only modest success because this approach generally depresses the conductivity to unacceptably low values. In this work, we report an alternative, new approach based on the addition to the PEO-LiX blend of an anion-trapping supermolecular component. In this way, polymer electrolytes with unity values of t Liϩ but still maintaining a true solid configuration combined with appreciable conductivity have been obtained. To our knowledge, this strategy has never been used, and we believe that this breakthrough result is associated with the immobilization of the anion (X Ϫ ) by the additive and, possibly, by an ordering of the PEO-LiX system.

In the present paper, a novel lithium-conducting polymer electrolyte, based on the low molecular weight dimethoxy poly(ethylene oxide) matrix as well as high molecular weight poly(ethylene oxide), is studied. New calixarene derivatives have been designed, synthesized, and successfully applied as neutral anion-binding receptors in the electrolytes, what could be of interest in the search for new sensors as well as for enhancing electrolytic functionality in energy-storage devices. Herein, details regarding synthesis and structural properties of all compounds incorporated in the polyether system are presented and discussed. The effect of supramolecular additives on physical (e.g., the charge-carriers transport mechanism, mechanical and thermal properties, or degree of crystallinity) and chemical (e.g., ion-receptor ion-matrix interactions) characteristics of polymer electrolyte is investigated in terms of differential scanning calorimetry, Fourier-transform IR spectroscopy, and impedance spectroscopy results. In particular, it was established that binding anions by some of the receptors under study may enhance ionic dissociation and after all increase the relative fraction of mobile lithium cations, leading to a transference number close to 1. Iodide anions complexing by the supramolecular additive were also found to be responsible for stabilization of the solid electrolyte−electrode interface. Its nature is discussed.

In poly͑ethylene oxide͒-based solid electrolytes, ionic conduction can occur by cations moving inside the helix ͑along the helix axis͒ and by anions moving on its envelope. This particular mode of ion transport can be enhanced by alignment of the polymeric structural units. We describe a procedure for orienting the helices in the perpendicular direction, the result of which is a oneorder-of-magnitude increase in polymer electrolyte ͑PE͒ conductivity and a similar decrease in PE/electrode interphase resistance. This procedure could also be of importance in the orientation of polymers in the nanoscale for various applications. Manipulation of large molecules like polymers and the ability to position them in the desired orientation is of great importance in various fields, including thin-film-based devices, microelectromechanical systems, and nanotechnology. Thin-layer technology includes liquid crystal displays ͑LCDs͒, sensors, electrochromic displays, advanced high-energy-density batteries, and fuel cells. In these devices, a thin ͑0.02-0.1 mm͒ polymer electrolyte ͑PE͒ is sandwiched between two electrodes. PE, are generally semicrystalline materials, most commonly derived from the archetypal helical poly͑ethylene oxide͒ ͑PEO͒. The common preparation process for the PEO-based PEs is that of casting from solution. This leads to a preferential planar orientation of helices in the parallel-to-thecasting plane, denoted as XY. As a result, the longitudinal conductivity is much higher than that in the perpendicular Z direction. However, in most practical applications, especially in solid thin-film batteries, the conductivity of PE films in the Z direction is crucial. Another factor contributing to high internal resistance ͑and thus to low power͒ in lithium-PE batteries is the too-high electrode/PE interphase resistance. To complete the conduction path, ions must at some time jump from helix to helix through the helix ''envelope.'' This is a slow process that adds yet another resistance to the system. We denote this resistor as R inter or R GB ͑grain boundaries͒.Until now, to get maximum conductivity, the strategy has been to reach the maximum amorphicity of the polymer and the lowest glass-transition temperature (T g ). 1-3 Molecular-level approaches employed to effectively suppress crystallinity in PEO have included architectural modifications such as branched polyethoxy systems, 4,5 linear random copolyethers, 6 and comb copolymers. 7-9 Despite strenuous efforts over some 20 years involving the preparation of highly amorphous polymer electrolytes with low T g , the maximum conductivity of such electrolytes remains around 10 Ϫ5 S/cm at room temperature.10 Theoretical models [11][12][13] have been proposed to explain the mechanism responsible for ionic conductivity in these systems, and molecular dynamic ͑MD͒ and Monte Carlo ͑MC͒ simulations have been carried out for PEO:salt complexes. 14-18Recently, we found a way [19][20][21][22][23][24] to increase the ionic conduction of PEs in one direction by a longitudinal align...

The complex interplay between the ionic conductivity and structure of the LiCF 3 SO 3 :PEO polymer electrolyte, induced by the calix͓6͔pyrrole anion receptor, has been investigated by different experimental methods, including ac impedance, calorimetry, X-ray diffraction, and Fourier-transform infrared spectroscopy. It was found that calix͓6͔pyrrole, even at low concentrations, can form stable bidentate complexes with triflate anions, thus making cation transport dominating, which results in t + close to unity. It should be noted that the incorporation of an anion trap does not suppress the bulk ionic conductivity of polymer electrolytes at above 60°C. We attribute this effect to the dissociation of ion aggregates and structural changes imposed by the additive. Stable solid electrolyte interface resistance was achieved in the polymer electrolytes containing calix͓6͔pyrrole.