Chemical and electrochemical behavior of sulfur and sulfides in electrochemical cells

The cumulative dissertation is about different possibilities to use sulfur as part of electrochemical storage devices and is based on four independent publications. One is dealing with the mobility and identity of elemental sulfur in a porous carbon matrix. The property changes of sulfur which is staying in physical contact with carbon were monitored by different analytical methods and are discussed. The relevance of the findings regarding metal/sulfur-batteries was experimentally verified. The second topic was about the (electro)-chemical stability of the Li3PS4 solid electrolyte against lithium electrodes and InLi-alloy electrodes of different stoichiometry. The article discusses the relationship between electrode potential, electrode phase composition, and electrode/electrolyte-interface stability. Further, it provides a guideline for using InLi electrodes correctly in combination with thiophosphate solid electrolytes. The last project describes the realization of a Na/polysulfide-cell with two liquid electrolyte chambers separated by a solid electrolyte. Poor cyclability characteristics were counteracted with two approaches: The use of P2S5 as additive and tetramethylurea as solvent. Moreover, Vis-spectroscopy was applied and the tetramethylurea electrolyte has been characterized. A review article presenting the different concepts of sulfur utilization in electrochemical cells is also included. Therein, advantages, disadvantages, and challenges of the concepts are discussed. Besides the publications, the dissertation contains additional material. Among them, a review on low-temperature Na/S-batteries is given, detailed descriptions of electrochemical cell assemblies are provided, and relevant parameters towards electrochemical characterization methods are explained.