Speaker
Description
% TITLE
{\large{\bf Theoretical Simulations of Li-S Battery Materials and X-ray Spectroscopic Analysis} }
% AUTHORS
\vskip0.5\baselineskip{\bf \underline {Ayda Gholamhosseinian}$^{1}$, Michael Walter$^{1}$ }
% AFFILIATION
\vskip0.5\baselineskip{\em$^{1}$(Presenting author underlined) Freiburg Center for Interactive Materials and Bioinspired Technologies (FIT), University of Freiburg, Georges-Köhler-Allee 105, 79110 Freiburg, Germany.\
\end{center}
\noindent
% ABSTRACT
Lithium–sulfur (Li–S) batteries are promising candidates for energy storage systems due to having a high theoretical capacity (1675 mAh/g)\,\cite{marmorstein2000electrochemical, ji2010advances}, but also face some challenges, such as the polysulfide shuttle effect, which causes the battery capacity to decrease during charge and discharge cycling. There are different approaches to overcoming these challenges \,\cite{li2019comprehensive}, one way is to covalently bond sulfur chains to organic structures\,\cite{li2019comprehensive, simmonds2014inverse} such as Naphthalene Diimide (NDI), and N-methylpyrrolidone (NMP). This covalent C–S bonding not only anchors sulfur, reduces the shuttle effect, but also provides additional redox-active sites from the organic backbone. Furthermore, by controlling the sulfur chain length through inverse vulcanization, we can balance high capacity (longer chains) with improved cycling stability (shorter chains).
In the present study, to have a comprehensive picture of the electronic states, we simulate X-ray absorption spectroscopy (XAS), X-ray emission spectroscopy (XES), and resonant inelastic X-ray scattering (RIXS) with density functional theory (DFT) performed using the GPAW code\,\cite{mortensen2024gpaw, johnsen2025explicit}.
XAS probes unoccupied electronic states, while $\alpha$-XES corresponds to a core-to-core transition (S $2p \rightarrow 1s$). In contrast, $\beta$-XES involves valence-to-core transitions and therefore provides information on occupied valence states and is more sensitive to the chemical environment \,\cite{ribson2025}. XES spectra are usually measured in the non-resonant region at incident energies around 2800 eV\,\cite{qureshi2021,ribson2025}, much higher than the sulfur K-edge absorption energy of about 2470 eV.
In RIXS, the energy of incident and emitted photons is correlated, allowing us to study both occupied and unoccupied states, as well as provide information on sulfur species within complex chemical environments.
We compare our simulations to X-ray spectroscopy measurements from our experimental
collaborators.
Our calculations indicate that variations in the dihedral angle of the sulfur chains and changes in the S–S bond length lead to shifts in the core-excitation energies in the XAS spectra. This combined experimental–theoretical approach provides insight into structure–property relationships and supports the rational design of stable, high-capacity polymer-based cathodes for next-generation Li–S batteries.