Polar Bilayer Cathode for Advanced Lithium-Sulfur Battery: Synergy between Polysulfide Conversion and Confinement

Despite possessing 5-fold higher specific energy density compared to commercial lithium-ion batteries, the insulating nature of sulfur and its reductive derivatives along with the uncontrollable migration of polysulfides hinder the commercialization of lithium-sulfur technology. Herein a bilayer cathode consisting of nitrogen sulfur codoped porous carbon network and titanium carbide has been introduced and investigated methodically. The porous sulfur host promotes uninterrupted diffusion of electrolyte and ions whereas titanium carbide acts as polysulfide trapping material. The superiority of this bilayer cathode over the conventional interlayer approach has been highlighted in terms of the diffusivity of lithium ions and the overall ohmic resistance. Variation in interfacial charge transfer resistance during charging and discharging has been investigated using dynamic electrochemical impedance spectroscopy. Discharge capacity reaches as high as 1300 mA h g-1 at 0.1 C with a Coulombic efficiency of 99%. Theoretical studies reveal that the polar nature and improved interfacial charge transfer between the TiC and polysulfides result in excellent binding strength and faster redox kinetics during operation, respectively. This work provides an experimental as well as theoretical evidence of the bifunctional mechanism of TiC toward polysulfide confinement and conversion.