Catalyzing the Polysulfide Redox Chemistry in Lithium–Sulfur Batteries: Mechanisms Bridging First-Principles Theory and Experimental Characterization

Lithium-sulfur (Li-S) batteries are considered one of the most promising battery technologies because of the ultrahigh theoretical gravimetric energy density of sulfur cathodes (2600 Wh kg^-1). Unfortunately, their practical application is hindered by the notorious polysulfide shuttle issue. Therefore, various strategies, including the tuning of physisorption and chemisorption of polysulfides, have been proposed to mitigate this problem. Considering the "solid-liquid-solid" sulfur redox reaction, the concept of electrocatalysis has been introduced to accelerate sulfur redox kinetics, thereby effectively suppressing the polysulfide shuttle. Over the past several years, a range of electrocatalysts has been developed, and improved Li-S battery performance has been achieved. To date, although several reviews have summarized recent advances in novel electrocatalysts for Li-S batteries, a mini-review focusing on catalytic mechanisms and advanced characterization remains lacking. In this mini-review, we first introduce the charge-storage mechanism of Li-S batteries and analyze the influence of catalysts on electrochemical performance. Subsequently, we systematically summarize recent progress in first-principles theory and advanced characterization for elucidating the catalytic mechanisms in Li-S batteries. Finally, we provide perspectives and an outlook on the future development of characterization methods for Li-S batteries.