In situ atomic force microscopy study of dimensional changes during Li+ ion intercalation/de-intercalation in highly oriented pyrolytic graphite

The knowledge of dimensional changes during the electrochemical intercalation of Li+ ions in a secondary Li+ ion battery is of fundamental importance for a comprehensive understanding of the degradation mechanism of the negative electrode. In this work in situ electrochemical atomic force microscopy was used to measure the step height change during the intercalation/de-intercalation of Li+ into the graphene layers of highly oriented pyrolytic graphite (HOPG). During the first intercalation/de-intercalation cycle an irreversible increase of graphene layer spacing of about 24 ± 7% was evidenced. During consecutive repetitive scanning between 3 and 0.005 V vs. Li/Li+, a reversible change of the step height of the HOPG of about ±17% could be observed in 1 M LiClO4 in ethylene carbonate and dimethyl carbonate in a 1:1 (w/w) ratio. The statistical procedure to determine the height changes introduced in the present study is superior to the evaluation of single line scans.