Improving the Performance of Lithium Sulfur Batteries Employing First Principles Guided Approaches

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Lithium batteries are widely used. They consist typically in a lithium-graphite anode and an oxide cathode. Lithium sulfur batteries represent a new concept in the development of batteries. An advantage is the extremely high energy density. A disadvantage is the limited number of charge and discharge cycles. In the present project, using ab-initio molecular dynamics, we want to investigate the basic chemical reactions which lead step-wise to the formation of lithium sulfide and byproducts. Ab-initio molecular dynamics uses a quantum mechanical description of the electronic cloud and a classical description of the nuclei, which allows to describe any chemical reactions on physical grounds. This approach is limited by limited CPU time. Since, in electrochemical applications, we can trigger the reactions by charge transfer, it is possible to observe chemical reactions with moderate CPU time. The result can be presented in the form of movies, which allows to transport a lot of information. In particular, using movies, we can demonstrate how every single atom moves from A to B during a chemical reaction. Hence, ab-initio molecular dynamics allows to understand in principle the mechanisms of arbitrary chemical reactions. In the course of the project we want to start with rather simple model structures and then proceed step-by-step to more realistic hetero structures consisting of more than 1000 atoms.