High‐Temperature Formation of a Functional Film at the Cathode/Electrolyte Interface in Lithium–Sulfur Batteries: An In Situ AFM Study

Abstract Lithium–sulfur (Li–S) batteries have been attracting wide attention for their promising high specific capacity. A deep understanding of Li–S interfacial mechanism including the temperature (T) effect is required to meet the demands for battery modification and systematic study. Herein, the interfacial behavior during discharge/charge is investigated at high temperature (HT) of 60 °C in an electrolyte based on lithium bis(fluorosulfonyl) imide (LiFSI). By in situ atomic force microscopy (AFM), dynamic evolution of insoluble Li 2 S 2 and Li 2 S is studied at the nanoscale. An in situ formed functional film can be directly monitored at 60 °C after Li 2 S nucleation. It retards side reactions and facilitates interfacial redox. The insight into the interfacial processes at HT provides direct evidence of the existence of the film and reveals its dynamic behavior, providing a new avenue for electrolyte design and performance enhancement.