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Direct Observation of SEI Formation and Lithiation in Thin-Film Silicon Electrodes via in Situ Electrochemical Atomic Force Microscopy

Silicon is a very promising anode material for Lithium-Ion Batteries based on the theoretical capacity that is about 10-times higher compared to state-of-the-art graphitic counterparts. Within this work we visualize the initial states of lithium intercalation and s(olid)-e(lectrolyte)-i(nterface) formation, a protective layer on silicon, by means of electrochemical in-situ atomic force microscopy. We find that the RMS roughness is only weakly fluctuating above a lithiation state of about 25%. Silmultaneous measurements of the surfaces Youngs Modulus show a drastical decrease during SEI formation. With increasing lithiation state the samples stiffness raise as well. The broad distribution of obtained values indicates a heterogeneous lithiation of the electrode.

ACS Applied Energy Materials 2 (9), 6761-6767