In-situ investigation of solid-electrolyte interphase formation on the anode of Li-ion batteries with Atomic Force Microscopy

•In-situ AFM is used to study SEI formation on the surface of graphite Li-ion electrode.•It is observed that SEI is composed of a top particle layer and a bottom insertion layer.•A top particle layer and a second layer underneath the top layer were observed in SEI.•A dynamic competition mechanism between two layers of SEI is proposed.

Solid-electrolyte interphase (SEI) formation at highly ordered pyrolytic graphite (HOPG) surface has been studied with in-situ AFM. The morphology and thickness of both the top particle layer of the SEI and the bottom layer of the SEI that was caused by lithium insertion were investigated. The formation mechanism of the SEI was proposed accordingly. Ex-situ FESEM and EDS were also used to analyze the composition of the electrode after cycling to confirm the proposed mechanism.