Beschreibung:
<jats:p> Lithium-sulfur batteries represent a promising alternative to the classical Li-ion technology, particularly due to the high specific energy density combined with the good environmental sustainability of sulfur. Compared to state-of-the-art cathode materials for Li-ion batteries (LiB), which usually contain cobalt and/or manganese, sulfur is less toxic and much more abundant [1]. Additionally, the theoretical capacity of 1.675 mAh g<jats:sup>-1</jats:sup> is more than eight times higher than typical cathode materials as Lithium-Nickel-Mangan-Cobalt-Oxide (NMC), Lithium-Cobalt-Oxide (LCO) or Lithium-Iron-Phosphate (LFP) [1,2]. One of the main challenges of sulfur is the so-called “shuttle effect” [1,3]. During lithiation soluble intermediates (polysulfides) migrate to the anode side, further react and precipitate, resulting in a continuous loss of active material and capacity. Next to that, the poor electrical conductivity (5∙10<jats:sup>-30</jats:sup> S cm<jats:sup>-1</jats:sup>) does not allow the utilization of pure sulfur as cathode material [1].</jats:p>
<jats:p>To improve the low conductivity, carbon-containing composites have been proposed as cathode material for Li-S batteries for several decades. One possible carbon matrix material is reduced graphene oxide (rGO) [4]. The reduced form of partially oxidized graphite (graphite oxide; GO) is a graphene-like material with high potential for a scale-up to mass production.</jats:p>
<jats:p>In our group, we have developed a new synthesis method to rapidly reduce GO using a reactive spray drying technique, where most functional groups can be removed from GO within seconds. The rapid thermal processing leads to a reduced and exfoliated rGO, which still contains small amounts of epoxy groups within the carbon lattice. These remaining oxygen atoms influence the conjugated π-bonds of the graphene-like matrix and thus change the polarity of the surface. A thermal post-treatment for 2 h in Ar/H<jats:sub>2</jats:sub> can further reduce the remaining functional groups leading to a highly non-polar surface.</jats:p>
<jats:p>It is assumed that oxygen-containing groups (e.g. epoxy and hydroxy) result in a varying adsorption behavior of the polysulfides, affecting the unwanted “shuttle effect” and thus influencing the electrochemical performance [5]. Here, we show the impact of remaining functional groups in rGO on the electrochemical performance of S-rGO composites as cathode material vs. Li/Li<jats:sup>+</jats:sup>. We compare untreated GO to reactive spray dried and additionally (thermally) post-treated rGO. Furthermore, we analyze the composites in terms of asymmetric and symmetric bonding vibrations as well as crystallinity using FT-IR, RAMAN and XRD.</jats:p>
<jats:p>[1] Baikalov, N. et al., <jats:italic>Frontiers Energy Research</jats:italic>
<jats:bold>2020</jats:bold>, 8, 207</jats:p>
<jats:p>[2] Su, Y.-S. et al., <jats:italic>Nature Communications</jats:italic>
<jats:bold>2013</jats:bold>, 4, 2985</jats:p>
<jats:p>[3] Ren, W. et al., <jats:italic>Energy Storage Materials</jats:italic>
<jats:bold>2019</jats:bold>, 23, 707-732</jats:p>
<jats:p>[4] Shastri, M. et al., <jats:italic>Ceramics International</jats:italic>
<jats:bold>2021</jats:bold>, 47, 10, B, 14790-14797</jats:p>
<jats:p>[5] Ji, L. et al., <jats:italic>Journal of the American Chemical Society</jats:italic>
<jats:bold>2011</jats:bold>, 133, 18522-18525 </jats:p>