Accelerating polysulfides conversion by constructing Lewis acidic Mn-N4 single atomic sites for Li-S battery with high sulfur loading

Abstract

The shuttle effects of lithium polysulfides (LiPSs) and the sluggish conversion reaction between LiPSs and Li2S significantly limit the electrochemical performance of Li-S batteries. In this study, a unique structured single atomic Mn anchored on nitrogen-doped carbon black (SAMnN@C) is developed to address above challenges. Physical characterizations confirmed atomically dispersed Mn atoms were anchored on carbon by 4 N atoms forming a typical structure of planar Mn-N4. Li-S battery assembled by as-prepared SAMnN@C displayed a discharge capacity of 1400 mA h g-1 at 0.1C, and outstanding stability with a capacity decay rate of 0.052 % per cycle during 1000 cycles at 1C. Moreover, excellent electrochemical performances could be preserved even if the S mass loading increased to 5.7 mg cm−2 with ∼ 5 μL (mg S)-1 electrolyte. The mechanism studies revealed that SAMnN@C exhibited a unique Lewis acid-base interaction between Mn-N4 site and S atom, which significantly lowered the decomposition energy barrier of Li2S2, and eventually accelerated the sluggish solid-state conversion reaction of Li2S2 to Li2S. This study is believed to shed light on the mechanism of SACs for high performance Li-S batteries.