Thermal analysis, nuclear magnetic resonance spectroscopy, and impedance spectroscopy of N,N-dimethyl-pyrrolidinium iodide: An ionic solid exhibiting rotator phases

N,N-dimethyl-pyrrolidinium iodide has been investigated using differential scanning calorimetry, nuclear magnetic resonance (NMR) spectroscopy, second moment calculations, and impedance spectroscopy. This pyrrolidinium salt exhibits two solid-solid phase transitions, one at 373 K having an entropy change, Delta S, of 38 J mol(-1) K-1 and one at 478 K having Delta S of 5.7 J mol(-1) K-1. The second moment calculations relate the lower temperature transition to a homogenization of the sample in terms of the mobility of the cations, while the high temperature phase transition is within the temperature region of isotropic tumbling of the cations. At higher temperatures a further decrease in the H-1 NMR linewidth is observed which is suggested to be due to diffusion of the cations. (C) 2005 American Institute of Physics

Molecular Interactions and Dynamics in Lithium Conducting Electrolytes

Lithium conducting electrolytes, suitable for battery applications, have been characterized on a molecular level using Raman spectroscopy, ab initio calculations and nuclear magnetic resonance spectroscopy, in order to better understand molecular and ionic interactions and dynamics in the systems. Three different types of electrolytes have been investigated; polymer gel electrolytes, solid polymer electrolytes and plastic crystal materials, with the main focus on the polymer based electrolytes. Polymer gel electrolytes, comprised of a polymer swelled with a liquid electrolyte, are now replacing liquid electrolytes in lithium ion batteries. Extensive research efforts are still needed in order to optimize the performance of these materials. The molecular dynamics and ionic interactions in a series of gel electrolytes based on a co-polymer with an "inert" backbone, poly(methyl methacrylate), PMMA, and "active" side-chains, ethylene oxide, EO, are reported in this thesis. Furthermore, the effects of the addition of ceramic filler nano-particles to gel electrolytes based on PMMA, have been studied. An all solid-state-battery is a future goal, and solid polymer electrolytes show great potential. However, the ionic conductivity of these materials is still too low. Recently, the addition of nano-sized ceramic particles to solid polymer electrolytes has attracted considerable interest due to observed increases in conductivity, approaching values suitable for battery applications. The molecular interactions and dynamics have been investigated for different nanocomposite solid polymer electrolytes as a function of filler type and concentration. Other types of materials are also explored in the field of solid-state electrolytes. Plastic crystal materials have a number of advantageous properties, and it is possible to achieve high molecular/ionic diffusivities, as well as high conductivities. In this thesis the structure and vibrational properties of the different phases of an ionic plastic crystal material has been studied

Amphiphilic polymer gel electrolytes. II. Influence of the ethylene oxide side-chain length on the gel properties

Amphiphilic polymers consisting of copolymethacrylates carrying about 26 wt % ethylene oxide [(EO)(n)] side chains of different lengths were used as matrices in gel electrolytes. The gel electrolytes were composed of 30 wt % copolymer and 70 wt % 1 M LiPF6 in a mixture of ethylene carbonate and gamma -butyrolactone (2/1 w/w). The coordination of lithium ions by the (EO)(n) side chains in competition with the solvent was studied by Raman spectroscopy. A significantly stronger lithium coordination was observed when the gel electrolyte was based on a copolymer carrying (EO)(9) units in comparison with copolymers having (EO)(1), (EO)(2), and (EO)(4) units. Despite the observed stronger lithium coordination by (EO)(9) units in the gel, the ion conductivity was not significantly lower with respect to the gels based on the other copolymers

LiI-doped N,N-Dimethyl-Pyrrolidinium iodide, an archetypal rotator-phase ionic conductor

N,N-Dimethyl-pyrrolidinium iodide, and the effect of doping with LiI, has been investigated using DSC, NMR, and impedance spectroscopy. It was found that the addition of a small amount of LiI enhances the ionic conductivity by up to 3 orders of magnitude for this ionic solid. Furthermore, a slight decrease in phase transition onset temperatures, as well as the appearance of a superimposed narrow line in the 1H NMR spectra with dopant, suggest that the LiI facilitates the mobility of the matrix material, possibly by the introduction of vacancies within the lattice. 7Li NMR line width measurements reveal a narrow Li line width, decreasing in width and increasing in intensity with temperature, indicating mobile Li ions.<br /

Unusual phase behaviour of the organic ionic plastic crystal N,N-dimethylpyrrolidinium tetrafluoroborate

Analysis of N,N-dimethylpyrrolidinium tetrafluoroborate by 1H and 11B NMR, Raman spectroscopy and powder XRD shows that this organic ionic plastic crystal material exhibits unusual phase behaviour. 1H NMR analysis indicates that the mobility of the pyrrolidinium cation decreases when the material is heated into phase I, while the X-ray diffraction pattern changes from a simple, one peak structure in phase II to a more complex pattern in phase I. The possible origins of these unusual transitions are discussed.<br /

Plastic crystal behaviour in tetraethylammonium dicyanamide

The plastic crystal tetraethylammonium dicyanamide ([N2,2,2,2][dca]) has been investigated with an emphasis on structure and dynamics in the plastic phase. It was found that almost all of the volume expansion occurs at the II &rarr; I transition, with no volume expansion at the melt transition (as normally observed for crystals). The conductivity of this material shows a rapid increase at temperatures below the II &rarr; I transition, reaching values ~ 10&minus; 3 S/cm in Phase I, and 0.1 S/cm in the melt. The NMR measurements show that there is a sudden onset of rotational motions of the cations at the plastic transition; below this temperature the cations appear static. The rotational motion of the cation in Phase I has been discussed in terms of isotropic tumbling.<br /