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

Abstract

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

Hydroxide‐Derived Nanostructures: Scalable Synthesis, Characterization, Properties, and Potential Applications

“…In a follow up paper, we showed that this prolonged stability could, in part, be attributed to the polar‐polar interactions with the NFs’ hydroxylated surfaces with polysulfides as confirmed by post‐mortem XPS analysis. [ 37 ]…”

Investigation of Ultramicroporous Structure of One-Dimensional Lepidocrocite Titanates Using Carbon Dioxide and Nitrogen Gases

“…24 We have already shown that 1DLs can be used for a large host of applications. They can be used as electrodes in lithiumion and lithium− sulfur batteries, 21,34 photochemical hydrogen production, 35 chemical cancer therapies, 21 water purification, 24 dye degradation, 25 polymer composites, 36 and perovskite solar cells. 37 Compared to the other CO 2 capturing materials, the 1DLs have several advantages.…”

Ion-Exchange Effects in One-Dimensional Lepidocrocite TiO2: A Cryogenic Scanning Transmission Electron Microscopy and Density Functional Theory Study

“…12 The authors reported good performance as an electrode for lithium-ion and lithium−sulfur batteries and an ability to reduce the viability of cancer cells. 12,48 At 4.1 eV, the band-gap energy, E g , of the resulting flakes is one of the highest, if not the highest value ever reported for titania-based nanostructures as a result of quantum confinement. 13 Despite the E g , the flakes' electronic band structure possessed visible light absorbance that was attributed to mid-band-gap energy states.…”