Insight into the Interfacial Process and Mechanism in Lithium–Sulfur Batteries: An In Situ AFM Study

Lithium–sulfur (Li–S) batteries are highly appealing for large‐scale energy storage. However, performance deterioration issues remain, which are highly related to interfacial properties. Herein, we present a direct visualization of the interfacial structure and dynamics of the Li–S discharge/charge processes at the nanoscale. In situ atomic force microscopy and ex situ spectroscopic methods directly distinguish the morphology and growth processes of insoluble products Li 2 S 2 and Li 2 S. The monitored interfacial dynamics show that Li 2 S 2 nanoparticle nuclei begin to grow at 2 V followed by a fast deposition of lamellar Li 2 S at 1.83 V on discharge. Upon charging, only Li 2 S depletes from the interface, leaving some Li 2 S 2 undissolved, which accumulates during cycling. The galvanostatic precipitation of Li 2 S 2 and/or Li 2 S is correlated to current rates and affects the specific capacity. These findings reveal a straightforward structure–reactivity correlation and performance fading mechanism in Li–S batteries.