Density Functional Tight Binding Study on Solid Electrolyte Interface of Lithium Sulfur Battery

One of the most promising cathode materials for lithium batteries is sulfur, abundant in nature and an undesirable impurity in petroleum. It is thus very cheap. Lithium sulfur batteries, i.e. lithium batteries with a sulfur cathode, have potentially high electric capacity but so far only very poor cyclability. For practical use of lithium sulfur batteries, the poor cyclability should be overcome. However, chemical reactions at lithium and sulfur interface are barely known thus hampering the progress in this field. In particular, theoretical and simulation studies on lithium-sulfur solid electrolyte interface (SEI) at the atomic scale are highly demanding in order to accurately understand interactions between lithium and sulfur. Density functional tight binding (DFTB) approach is based on density functional theory but much more efficient thus enabling simulations of large-scale molecular systems and their long-time dynamics. One of the most severe drawbacks of DFTB approaches is lack of available parameters for lithium batteries. Here we have developed DFTB parameters for SEI of lithium sulfur batteries including electrolytes and performed long-time molecular dynamics simulations to understand kinetics of lithium insertion into sulfur electrodes. Chemical interactions of lithium electrolytes and sulfur electrodes are demonstrated and further compared with more accurate DFT calculations at a smaller system.