Promoting the Transformation of Li₂S₂ to Li₂S: Significantly Increasing Utilization of Active Materials for High‐Sulfur‐Loading Li–S Batteries

Abstract

Abstract Lithium–sulfur (Li–S) batteries with high sulfur loading are urgently required in order to take advantage of their high theoretical energy density. Ether‐based Li–S batteries involve sophisticated multistep solid–liquid–solid–solid electrochemical reaction mechanisms. Recently, studies on Li–S batteries have widely focused on the initial solid (sulfur)–liquid (soluble polysulfide)–solid (Li 2 S 2 ) conversion reactions, which contribute to the first 50% of the theoretical capacity of the Li–S batteries. Nonetheless, the sluggish kinetics of the solid–solid conversion from solid‐state intermediate product Li 2 S 2 to the final discharge product Li 2 S (corresponding to the last 50% of the theoretical capacity) leads to the premature end of discharge, resulting in low discharge capacity output and low sulfur utilization. To tackle the aforementioned issue, a catalyst of amorphous cobalt sulfide (CoS 3 ) is proposed to decrease the dissociation energy of Li 2 S 2 and propel the electrochemical transformation of Li 2 S 2 to Li 2 S. The CoS 3 catalyst plays a critical role in improving the sulfur utilization, especially in high‐loading sulfur cathodes (3–10 mg cm −2 ). Accordingly, the Li 2 S/Li 2 S 2 ratio in the discharge products increased to 5.60/1 from 1/1.63 with CoS 3 catalyst, resulting in a sulfur utilization increase of 20% (335 mAh g −1 ) compared to the counterpart sulfur electrode without CoS 3 .