Carbon Nanotube Supported Fluorine Substituted Iron Phthalocyanine Enabling Boosted Polysulfide Redox Conversion Kinetics and Cyclic Stability.

Abstract

The sluggish transition and shuttle of polysulfides (LiPS) significantly hinder the application and commercialization of Li-S batteries. Herein, carbon nanotubes (CNTs) supported 10 nm sized iron Hexadecafluorophthalocyanine (FePcF₁₆/CNTs) are prepared using a solid synthesis approach. The well-exposed FePcF₁₆ molecular improve the LiPS capture efficiency and redox kinetics by its central Fe-N₄ units and F functional groups. The strong electron withdraw F groups significantly promote the conjugate effect and decrease the steric hindrance during mass migration procedure. Distribution of relaxation time (DRT) analysis shows that the Fe-N₄ units exhibit strong affinity towards LiPS and the F groups further improve the Li⁺ diffusion rate in Li₂S nucleation and oxidation procedure, accomplishing a porous surface on cathode. As a result, the FePcF₁₆/CNTs separator exhibits a high initial capacity of 1136.2 mAh g^-1 at 0.2 C, outstanding rate capacity of 624.9 mAh g^-1 at 5 C and superior long-term stability at 2 C surviving 300 cycles with a low capacity decay of 0.43 ‰ per cycle.