Morphology and modulus evolution of graphite anode in lithium ion battery: An in situ AFM investigation

We investigated the interfacial electrochemical processes on graphite anode of lithium ion battery by using highly oriented pyrolytic graphite (HOPG) as a model system. In situ electrochemical atomic force microscopy experiments were performed in 1 M lithium bis(trifluoromethanesulfonyl)imide/ethylene carbonate/diethyl carbonate to reveal the formation process of solid electrolyte interphase (SEI) on HOPG basal plane during potential variation. At 1.45 V, the initial deposition of SEI began at the defects of HOPG surface. After that, direct solvent decomposition took place at about 1.3 V, and the whole surface was covered with SEI. The thickness of SEI was 10.4 +/- 0.2 nm after one cycle, and increased to 13.8 +/- 0.2 nm in the second cycle, which is due to the insufficient electron blocking ability of the surface film. The Young's modulus of SEI was measured by a peak force quantitative nanomechanical mapping (QNM). The Young's modulus of SEI is inhomogeneous. The statistic value is 45 +/- 22 MPa, which is in agreement with the organic property of SEI on basal plane of HOPG.