Synthesis of sulfur-rich copolymers using the inverse vulcanization reaction is a practical approach to modify the sulfur active material for enhanced stability in Li–S batteries. However, to effectively design such polymers, a thorough understanding of the underlying redox mechanisms is critical. Here, we study electrochemical behavior of sulfur-rich copolymers using in operando FTIR spectroscopy with attenuated total reflection. We used sulfur-diisopropenylbenzene copolymers [poly­(S-co-DIB)] as the active material in Li–S batteries and monitored the evolution of the C–S peak position and cyclic changes in the S–S bond stretching at different potentials during discharge and charge. Moreover, we synthesized various copolymers with sulfur wt % of 80 and 30 wt % and compared the electrochemical behavior and their corresponding IR response during cyclic voltammetry sweep. Our results indicated that the C–S bond in sulfur copolymers is not active in the voltage window of Li–S batteries. Moreover, we showed that the shift in the C–S peak position becomes smaller with increase in the monomer wt %. In addition, the S–S stretching peak at ∼500 cm–1 diminishes when the sulfur wt % is decreased from 80 to 30 wt %, highlighting a significant change in electrochemical behavior of the copolymers.

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

Lithium-sulfur batteries (LSBs) have garnered interest recently due to their 8-fold increase in theoretical capacity compared to state-of-the-art Li-ion batteries (LIBs), the affordability of sulfur at $100/ton, and the low environmental impact of sulfur. However, just like LIBs, LSBs suffer from anode instability due to dendrite formation and an unstable solid electrolyte interface (SEI). In this work, we address anode stability via a facile, polymer and lithium salt interfacial layer. Stable SEI formation was achieved by using a fluorinated polymer and lithium salt. A conventional Celgard separator was used for mechanical support and the polymer:salt ratio was tuned. To confirm the effectiveness of the interfacial layer for anode stability, it was used as a standalone gel polymer electrolyte in a Li-Li symmetric cell. It showed remarkable stability beyond 700 hours at an energy density of 1 mA cm-2 and capacity of 1 mAh cm-2, with a steady polarization voltage of 16mV. By comparison, a Li-Li symmetric cell with a Celgard separator began to show increasing polarization voltage after just 100 hours, with a polarization voltage that gradually increased to beyond 500mV (Figure 1). This stability was achieved by a robust SEI layer that contained LiF and Li2O, hindering the formation of the dead lithium layer. The presence of these compounds was confirmed by post-mortem X-ray photoelectron spectroscopy. Dendrite formation was also physically inhibited by the presence of the polymer matrix that had a uniform morphology and pore diameter around 1 μm. Additionally, using this interfacial layer in a lithium-sulfur coin cell provided a capacity of 866 mAh g-1 at 200 cycles, a 26% improvement over lithium-sulfur cells without the interfacial layer. Figure 1