Synergistic Regulation of Bidirectional Conversion of LiPSs and Li₂S Using Anthraquinone as a Redox Mediator

Abstract

Lithium−sulfur (Li−S) batteries are strong contenders as energy storage options in the next-generation, primarily because of their potential for delivering high energy densities. Nonetheless, their widespread commercialization faces several obstacles, including sluggish sulfur redox kinetics, the insulating properties of the Li 2 S discharge product, and significant reaction energy barriers. In this work, anthraquinone (AQ) was introduced as a redox mediator and incorporated onto Co-doped carbon materials through π−π interactions. The results showed that synergistic effect between AQ and Co atoms facilitated the bidirectional conversion of lithium polysulfides (LiPSs) and Li 2 S. During charging, AQ lowered the reaction energy barrier for Li 2 S oxidation and thereby enhanced the reversibility of sulfur redox reactions. Density functional theory (DFT) calculations showed that AQ-Li 2 S x exhibits a lower energy for the lowest unoccupied molecular orbital (LUMO) and a higher energy for the highest occupied molecular orbital (HOMO). Experimental results demonstrated that an impressive initial discharge specific capacity of 1290 mAh g −1 was achieved by the fabricated S@AQ/Co−N−C electrode at 0.1 C. After 600 cycles at 1 C, it retained 64% of this capacity and exhibited a minimal 0.06% capacity decay rate per cycle.