Magnesium-sulfur (Mg-S) batteries represent a very promising emerging cell chemistry. However, developments in Mg-S batteries are in an early stage, and the system exhibits problems similar to those of early lithium-sulfur batteries (Li-S). The significant challenges are the low coulombic efficiency and short cycle life of Mg-S batteries, mainly associated with the well-known polysulfide shuttle. An obvious result of this phenomenon is the rapid self-discharge of Mg-S batteries. In this article, we present a multiscale simulation framework for metal-sulfur batteries. In our approach, we provide a continuum description of chemical and electrochemical processes at the positive and negative electrodes. In combination with a 1D model for the transport of dissolved species in the electrolyte, this approach allows us to reproduce and interpret experimental data measured on Li-S and Mg-S batteries. We focus on the common properties of Li-S and Mg-S batteries as well as on the key differences causing the much more rapid self-discharge of the Mg system. We identify side reactions on the anode surface as a limiting process, while other factors, such as the mobility of dissolved species and solid phase kinetics, play a minor role.
Various intermetallic compounds harbor subtle electronic correlation effects. To elucidate this fact for the Fe-Al system, we perform a realistic many-body investigation based on the combination of density functional theory with dynamical mean-field theory in a charge self-consistent manner. A better characterization and understanding of the phase stability of bcc-based D03-Fe3Al through an improved description of the correlated charge density and the magnetic energy is achieved. Upon replacement of one Fe sublattice by V, the Heusler compound Fe2VAl is realized, known to display bad-metal behavior and increased specific heat. We here document a charge-gap opening at low temperatures in line with previous experimental work. The gap structure does not match conventional band theory and is reminiscent of (pseudo)gap charateristics in correlated oxides.
Oxide delafossites represent natural heterostructures with often rather different electronic characteristics in their constituting layers. The design of novel heterostructure architectures highlighting the competition between such varying characteristics appears promising from the viewpoint of basic research as well as for future technological applications. By means of the combination of density functional theory and dynamical mean-field theory, we here unveil the formation of highly correlated electron states in delafossite heterostructures build from metallic PdCrO2 and insulating AgCrO2. Due to the sophisticated coupling between layers of strong and of weak internal interaction, correlation-induced semimetals at ambient temperature and doped Mott-insulators at low temperature are predicted in this study.
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