Molecular Interactions and Dynamics in Lithium Conducting Electrolytes

Doctoral thesis, 2002

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.