Regensburg 2019 – scientific programme

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MM: Fachverband Metall- und Materialphysik

MM 22: Materials for Energy Storage and Conversion

MM 22.8: Talk

Wednesday, April 3, 2019, 12:15–12:30, H43

Cage-hopping mechanism of lithium cation diffusion in liquid thiophene-derivatives as revealed by AIMD simulations — •Pouya Partovi-Azar and Daniel Sebastiani — Martin-Luther Universität Halle-Wittenberg

Unraveling the diffusion mechanism of Li⁺ in thiophene-based liquids is of great importance in reaching optimal electrolyte compositions for Li-based energy-storage devices. However, the dynamics of Li⁺ in thiophene-based electrolytes is barely known at an atomistic level, which makes it hard to reveal the actual mechanism of the diffusion. Here, we report on DFT-based ab initio molecular dynamics simulations performed to study the fundamental processes occurring in the Li⁺/thiophene-based systems. We consider Li⁺ ions at 1M concentration in thiophene and 3,4-ethylenedioxythiophene (EDOT) liquids in the condensed phase. Our simulations reveal a cage-hopping mechanism for Li⁺ diffusion in both liquids. Each Li⁺ is surrounded by four liquid molecules in a cage structure, while being coordinated by four sulfur and four oxygen atoms in the case of thiophene and EDOT, respectively. The liquid molecules in a cage form a slightly deformed tetrahedron, where a “weak” part is formed due to repulsive interaction between two closer sulfur atoms, allowing the Li⁺ ion to escape the cage. This finding can be directly used to define proper collective variables for metadynamics or kinetic Monte-Carlo simulations. The thermal energy at 300K is found to be enough to trigger a Li⁺ hopping in the thiophene liquid, but falls short in the case of EDOT liquid, which possesses a stronger molecular network due to H bonding.