Liquid Crystals as Ion Conductors in Solid Polymer Electrolytes for Lithium Metal Batteries

Details

Supervisors

Gohy, Jean-François

Faculty

Faculté des sciences

Degree label

Master [120] en sciences chimiques, à finalité spécialisée: chimie de l'industrie

Abstract

Over the next few decades, our society will be forced to transition to more carbon-neutral methods of energy production. The problem with this transition is that storage systems are not sufficiently developed to meet current energy needs. The solution that offers the best energy density is the Lithium metal battery. However, Lithium metal batteries require improvements in safety. The search for optimisation of all-solid-state Lithium metal batteries is at the heart of this study, and more specifically the development of solid polymer electrolytes. The major challenge is to achieve good ionic conductivity at room temperature for solid polymer electrolytes. The advantages linked to the use of such electrolytes are potentially numerous: mechanical strength, resistance to flammability, limitation of dendrite formation. However, they suffer from poor ionic conductivity, especially at room temperature. With the hope of improving their conductivity, liquid crystals are added to solid polymer electrolytes to form a hybrid material. Indeed, liquid crystals have the property of forming self-organized mesophases that may contain channels that facilitate the passage of ions through the material. The objective is to identify the hybrid material giving an improved conductivity close to that of liquid electrolytes at room temperature for their application in the field of solid electrolytes. This work started with the synthesis of monomers, liquid crystals, and polymers. Their thermal properties were characterised. Then, different solid polymer electrolytes were made and analysed by electrochemical impedance spectroscopy. For one of the investigated systems, the conductivity is of the order of 10^-3 S cm^-1, which agrees with the objective of this study. An analysis of the thermal and electrochemical stability of the solid polymer electrolytes was performed. A catholyte with the selected solid polymer electrolyte was formed and integrated in an all-solid-state battery. This catholyte proved to be effective despite a significant capacity loss with the solid polymer electrolyte. In addition to the achieved goal, several ways of improvement are envisaged for future work.