Engineering the Li-ion conductivity in solid-composite electrolytes

Battery issues such as limited lifetime and slow charging rate are related to poorly controlled interfaces (so-called solid-electrolyte interface) and to the use of liquid electrolytes which poses safety concerns. Therefore, solid electrolytes are being explored to replace the flammable liquid electrolyte. Next to solving the issues with safety, the transition to a solid-state electrolyte would mean significant improvements in the battery performance as well: higher energy density, longer battery lifetime and wider temperature range of operation. In order to develop a technological relevant all-solid-sate battery, it is of key importance to gain fundamental insights in the working principles of the active components in this battery, i.e. the solid-state electrolyte and the positive and negative electrodes. Indeed, the battery performance strongly depends on the conductivity of lithium ions and electrons in these materials, and on the capacity of the electrodes to intercalate lithium ions. An interesting approach to engineer the ionic conductance can be done by the composite electrolyte approach. Here, the enhanced ion transport at the interface between an insulator (such as silica or alumina) and an ordinary lithium salt (such as lithium carbonate) is exploited to make new materials with high ion conductivity. The meso- or nano-porous insulators provide the high effective surface area for sufficient conduction paths and the lithium salt provides the necessary Li+ ions. Important are the conduction promoters which are needed to achieve sufficient conductivity (target of 10-2 S/cm). Little is known about these conduction promoters. They typically need to act as ligand for the Li+ but it is their effect on the interface layer that will eventually determine the interface conductivity. This approach can be used for any ion-system and is thus relevant also for post Li-ion battery chemistries such as sodium or calcium. In this PhD thesis, the synergistic surface effects of dielectric, salt, mediator on the ion conductivity in the interface region will be investigated. The new insights will lead to new material combinations for future solid composite electrolytes in Li-ion batteries.

Accessibility:Open