Cobalt(II)-Centered Fluorinated Phthalocyanine-Sulfur SNAr Chemistry for Robust Lithium-Sulfur Batteries with Superior Conversion Kinetics

Abstract

Due to the exceptional theoretical energy density and low cost of elemental sulfur, lithium-sulfur (Li-S) batteries are spotlighted as promising post-lithium-ion batteries. Despite these advantages, the performance of Li-S batteries would need to be improved further for their wide dissemination in practical applications. Here, cobalt(II)-centered fluorinated phthalocyanine, namely, F-Co(II)Pc, is reported as a multi-functional component for sulfur cathodes with the following benefits: 1) enhanced conversion kinetics as a result of the catalytic effect of the cobalt(II) center, 2) efficient sulfur linkage via the fluorine functionality, which undergoes a nucleophilic aromatic substitution (SNAr) reaction, 3) suppression of the shuttling issue by the nitrogen atoms because of their strong affinity with polysulfides, and 4) the necessary aromaticity to engage in pi-pi interaction with reduced graphene oxide for electrical conductivity. The resulting electrode has promising electrochemical properties, such as sustainable cycling for 700 cycles and robust operation with a sulfur loading of 12 mg(sulfur) cm(-2), unveiling the promising nature of phthalocyanine and its related molecular families for advanced Li-S batteries.