A New Class of 2D Materials - Quaternary Derived Nanostructures - and Their Polysulfide Anchoring Capabilities in Lithium Sulfur Batteries

Metal-sulfur battery chemistries have garnered a lot of interest due to their 5-10 fold higher theoretical energy densities compared to state-of-the-art lithium-ion batteries, in addition to the abundance and environmental benignity of sulfur. However, the insulating nature of sulfur, the formation and shuttling of polysulfides, are still major drawbacks. In this work we started with quaternary ammonium salts or quat derived nanostructures (QDNs), synthesized using a facile bottom-up reaction, directly from commercial 3D bulk solids1. This approach leads to better functionalization, facile tunability, and higher active sites. Moreover, these materials self-assemble into a plethora of microstructures – from individual anatase-based 1D nanoribbons 6x102 Å in cross-section to 2D flakes to mesoscopic particles, both comprised of 1D nanoribbons - depending on the synthesis and washing parameters. Here we use QDNs made from commercial titanium carbide (TiC) reacted at 50℃ for 5 days, washed with 5M lithium chloride, and freeze dried after filtration. These TiC QDNs are simply hand ground with sulfur in a 50:50 ratio by weight, to create a sulfur TiC QDN composite. This composite was then used to make a slurry with carbon black and binder, in a ratio of 70:20:10 respectively. We obtain specific capacities of 800 mAh.g-1 at 0.5 C after 300 cycles seen in Figure 1. The anatase-based 1D nanoribbons, that assemble into 2D layers, traps the polysulfides by forming thiosulfate species and Lewis acid-base interactions with the titanium, confirmed by post-mortem X-ray photoelectron spectroscopy. Additionally, these interactions were confirmed visually with the 2D QDNs adsorbing polysulfides, after 7 days the 0.5mM solution of polysulfides appeared clear in comparison to the still yellow hue of the polysulfides seen with carbon black seen in Figure 2. These interactions are further enhanced with the added functionalization of the 2D materials using non-polar di(hydrogenated tallow)benzyl methyl ammonium chloride (DHT) surfactant molecules. 1. H. O. Badr et al., Materials Today, S1369702121003813 (2022). Figure 1