Fluorinated Benzimidazole-Linked Highly Conjugated Polymer Enabling Covalent Polysulfide Anchoring for Stable Sulfur Batteries

Abstract

Sulfur is one of the most abundant and economical elements in the p-block family and highly redox active, potentially utilizable as a charge-storing electrode with high theoretical capacities. However, its inherent good solubility in many electrolytes inhibits its accessibility as an electrode material in typical metal-sulfur batteries. In this work, the synthetically designed fluorinated porous polymer, when treated with elemental sulfur through a well-known nucleophilic aromatic substitution mechanism (SNAr), allows for the covalent integration of polysulfides into a highly conjugated benzimidazole polymer by replacing the fluorine atoms. Chemically robust benzimidazole linkages allow such harsh post-synthetic treatment and facilitate the electronic activation of the anchored polysulfides for redox reactions under applied potential. The electrode amalgamated with sulfurized polymer mitigates the so-called polysulfide shuttle effect in the lithium-sulfur (Li−S) battery and also enables a reversible, more environmentally friendly, and more economical aluminum-sulfur (Al−S) battery that is configured with mostly p-block elements as cathode, anode, and electrolytes. The improved cycling stabilities and reduction of the overpotential in both cases pave the way for future sustainable energy storage solutions.