Browsing by Author "Köhn, Andreas"

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    The quasi-binary acetonitriletriide Sr3[C2N]2
    (2019) Clark, William P.; Köhn, Andreas; Niewa, Rainer
    The first quasi-binary acetonitriletriide Sr3[C2N]2 has been synthesised and characterised. The nearly colourless crystals were obtained from the reaction of Sr metal, graphite, and elemental N2, generated by decomposition of Sr(N3)2, in a sealed Ni ampoule with the aid of an alkali metal flux. The structure of this compound was analysed via single-crystal Xray diffraction and the identity of the [C2N]3- anion was confirmed by Raman spectroscopy and further investigated by quantum-chemical methods. Computed interatomic distances within the [C2N]3- anion strikingly match the obtained experimental data.
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    The reduction behavior of sulfurized polyacrylonitrile (SPAN) in lithium-sulfur batteries using a carbonate electrolyte : a computational study
    (2024) Klostermann, Sina V.; Kappler, Julian; Waigum, Alexander; Buchmeiser, Michael R.; Köhn, Andreas; Kästner, Johannes
    Lithium–sulfur batteries (LSBs) have attracted attention due to their high theoretical energy density. This and various other advantages, such as the availability and non-toxicity of sulfur, raise interest in LSBs against the background of the energy revolution. However, a polysulfide shuttle mechanism can adversely affect the electrochemical performance of the cell. The sulfur redox properties are influenced, for example, by the electrolyte and the cathode material. Here, a computational study of the discharge process of an LSB with sulfurized poly(acrylonitrile) (SPAN) as the cathode material in combination with a carbonate electrolyte is presented. The nucleation of produced solid Li2S is compared to soluble Li2S. Dominating species are determined by comparing the Gibbs free energy of several species. We found that multiple lithiation steps occur before each Li2S detachment, preventing longer-chain polysulfide cleavage and a polysulfide shuttle. Through nucleating on the nitrogen-rich backbone of SPAN, Li2S units are stabilized by interactions with each other and with the nitrogen atoms. Experimental data show a potential drop and plateau during discharge, which is consistent with the calculated discharge profiles of SPAN with both soluble and nucleated Li2S, and hints at a direct solid-solid transition in the Li-SPAN cell during discharge when using carbonate-based electrolytes.