Direct Observation of Cycle and Temperature Effects on Surface Film Morphology of Graphite Negative Electrode by In-situ Electrochemical AFM

Abstract

This study investigated the stability of the surface film of the negative electrode by investigating how temperature affects the morphology of the surface film of the negative electrode using in-situ electrochemical atomic force microscope (AFM) in LiPF₆-based electrolytes with the addition of vinylene carbonate (VC) or by replacing LiPF₆ with lithium bis(fluorosulfonyl)imide (LiFSI). AFM measurements revealed that, in the case of the LiPF₆-based electrolyte, blisters were generated by the reductive decomposition of the electrolyte at the step edge of the negative electrode, grew larger as the storage temperature increased up to 45 °C, and collapsed at 55 °C. The surface film with blisters was partially broken down at 65 °C. Conversely, with VC addition or LiFSI substitution, no blister collapse and film dissolution were observed, even when the temperature was raised to 65 °C.