Anions and Additives for Lithium Battery Electrolytes

Licentiate thesis, 2008

Based on the atomic postulate, which is now more than 2400 years old, scientists have developed very advanced tools for studying the material world. With the potential realized with modern computers, more and more sophisticated methods are available for predicting real material properties, even from simple theoretical model systems. Often these predictions are made in conjunction with practical experiments, to assist in the interpretation of experimental data. In this thesis work, a combination of experimental and computational techniques has been applied to study individual components of lithium battery electrolytes. More specifically molecular interactions between anions, and either lithium ions or neutral additives, have been explored by Raman spectroscopy and ab initio computations. With the main aim to predict new suitable anions for lithium salts that will improve the properties of future lithium batteries. In the first of three papers a pure computational study predicts the electrochemical stability and lithium ion pair dissociation energies of two closely related families of heterocyclic anions. Small structural modifications are made by varying the degree and positions of substituent groups; modifications that turn out to have a large effect on the investigated properties. In the second paper a similar approach is taken, but here a single anion is in focus. Properties of this anion and its lithium ion pairs are predicted by computations, while spectroscopic investigations are made of a novel ionic liquid comprising the same anion. In the third and final paper the scientific work of this thesis is concluded with a combined experimental and computational study. The role of a neutral molecular additive in solid polymer electrolytes is explored; an additive designed to improve lithium ion conductivity by trapping anionic species. The anion preferences of the additive are predicted and experimental signs of anion-additive interactions are searched for.