Thermal Stability of the HOPG/Liquid Electrolyte Interphase Studied by In Situ Electrochemical Atomic Force Microscopy

Abstract

In situ atomic force microscopy (AFM) was used to follow temperature‐dependent morphological changes at a highly oriented pyrolytic graphite (HOPG)/electrolyte interface. Cyclic voltammetry was performed on an HOPG crystal covered with an electrolyte [, ethylene carbonate/β‐butyrolactone (EC/γ‐BL) 2:1] with a 0.5% water content. Water reduction was observed at 1.4 V vs. . A solid electrolyte interphase (SEI) formation occurred at 0.8 V, and lithium‐ion intercalation began at 0.2 V. In situ AFM measurements were made at 25, 40, 50, 60, and 70°C. Destruction or melting of the SEI layer, causing a growth of small blisters spread on the surface, could be detected at 50°C. At higher temperatures, reaction products concentrate at the HOPG edge planes. X‐ray photoelectron spectroscopy characterization of HOPG cells stored at 20 and 80°C support the in situ AFM observations. Graphite powder electrodes show similar thermal SEI breakdown behavior, generating a thick carbon‐oxygen layer on the electrode surface at temperatures above 60°C. The influence of the lithium salt (here, ), organic solvent and water are discussed. © 2000 The Electrochemical Society. All rights reserved.