Nanofibrous Interlayers with Ultrafine Decoration of Titanium Oxide to Intercept Lithium Polysulfides in Lithium–Sulfur Batteries

This is a study on developing interlayers to address the redox shuttling of lithium polysulfides (LiPSs) in lithium-sulfur batteries. Carbon nanofiber mats with ultrafine decoration of titanium oxide (CNF-TiO₂) and stabilized polyacrylonitrile-TiO₂ (Sta. PAN-TiO₂) nanofiber mats are fabricated, and the discharge–charge cycling performance of lithium-sulfur cells assembled with them as interlayers confirms the effectiveness of CNF-TiO₂ nanostructure.

Li–sulfur (LiS) batteries are potential alternatives to Li-ion batteries due to the ampleness of the sulfur and their higher gravimetric energy density. However, in conventional LiS batteries, the dissolution and redox shuttling of the formed lithium polysulfide species (LiPSs) pose disadvantages regarding capacity retention. Herein, free-standing nanofiber mats are fabricated using polyacrylonitrile (PAN) and titanium tetraisopropoxide (TTIP) to address the shuttling of LiPSs. After the subsequent heat treatment of the nanofiber mats, denoted as stabilization and carbonization, they are introduced into the LiS cells between the sulfur electrode and the separator as an interlayer to intercept the shuttling LiPSs. Material characterizations confirm an ultrafine distribution of TiO₂ in the fibers and also the formation of a thin layer of SiO₂ on them after carbonization. Constant-current discharge/charge cycling shows that using each of the developed interlayers leads to higher capacity retention compared to the case without any interlayer (100th cycle discharge capacity of 695 mAh g_S ⁻¹ for stabilized PAN-TiO₂ and 749 mAh g_S ⁻¹ for CNF-TiO₂ compared to 495 mAh g_S ⁻¹ for the cell without an interlayer). The improved cycling performance with interlayers is attributed to the adsorption and conversion of LiPSs thanks to their nanocomposite structures.

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