Solid-State Transformations of Active Materials in the Pores of Sulfurized-Polyacrylonitrile Fiber Membranes via Nucleophilic Reactions for High-Loading and Free-Standing Lithium–Sulfur Battery Cathodes

Sulfurized polyacrylonitrile (SPAN) has emerged as an excellent cathode material for lithium–sulfur batteries (LiSBs), and it addresses the shuttle effect through a solid‒solid reaction. However, the actual sulfur loadings in SPAN often remain below 40 wt%. Due to the susceptibility of polysulfides-to-nucleophilic reactions with electrolytes, achieving physical encapsulation of elemental sulfur is a challenging task. In this study, a free-standing cathode material with a high sulfur/selenium (S/Se) loading of 55 wt% was fabricated by introducing SeS_x into the unique lotus root-like pores of porous SeS_xPAN nanofiber membranes by electrospinning and a two-step heat treatment. Insoluble compounds were formed due to nucleophilic interactions between lithium polyselenosulfides (LiSeS_x) and the electrolyte, which potently blocked the existing lotus root-like pores and facilitated the creation of a thin cathode–electrolyte interphase on the fiber surface. This dual functionality of LiSeS_x safeguarded the active material embedded within the porous structure. The SeS₁₅PAN cathode exhibited remarkable cycling stability with almost no degradation after 200 cycles at 0.2 C, along with a high discharge capacity of 580 mAh/g. This approach presents a solution for addressing the insufficient sulfur content in SPAN.

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