Anion intercalated graphite: a combined electrochemical and tribological investigation by in situ AFM

Abstract

The intercalation of graphite by electrochemical methods is an efficient strategy to produce massive graphene flakes. In fact, when graphite is biased inside an acidic solution, anions enter inside the stratified structure of the electrode and reduce the layer-to-layer interaction. Consequently, a gentle sonication is sufficient to disperse the graphene flakes inside the electrolyte. In view of an optimisation of the production protocol, a detailed analysis of the intercalation mechanism at the molecular length scale is mandatory. In the last 30 years, electrochemical (EC) scanning probe microscopies (e.g. EC-STM and in situ AFM) have been widely exploited in this research topic. In fact, these techniques have the possibility of combining the EC characterisation (e.g. cyclic-voltammetry, CV) with mechanical characterisation (e.g. adhesion and friction) and topography acquisition with high (molecular) lateral resolution. In this work, we investigate the tribological properties of the basal surface of graphite before and after the anion intercalation. By comparing the results acquired after the extraction of the graphite electrode from the EC cell with those collected inside the EC cell during the CV by an in situ AFM, we show how some features deriving from anisotropic friction can be exploited to unveil the very early stage of graphite exfoliation.

Review—Multiscale Characterization of Li-Ion Batteries through the Combined Use of Atomic Force Microscopy and X-ray Microscopy and Considerations for a Correlative Analysis of the Reviewed Data

“…By means of EC-AFM and EC-STM coupled with cyclic voltammetry it has been also demonstrated that the early stages of anion intercalation are highly affected by a number of factors like surface faceting, step erosion, terrace damages, and nanoprotrusions. [97,98] From these studied it emerged that AFM resulted particularly sensitive in detecting the very early stage of intercalation. Once SEI is formed, the subsequent process of intercalation/deintercalation of lithium cations within the graphite layers is basically reversible.…”

Preface to StSPM2019EV special issue

“…The present special issue comprises 10 papers, showing to the interested reader a wide variety of excellent work presented at the extended version of the StSPM workshop. Atomic Force Microscopy (AFM) was employed in the graphene framework, aiming to study the exfoliation of large flakes of this 2D material from graphite via electrochemical approaches characterised by in situ AFM, 4 and to characterise graphene deposition on silicon surfaces that were nanostructured by lowenergy oxygen ion irradiation. 6 AFM was employed by Canino et al 5 to evaluate the surface roughness and image the surface morphology of Al + ion implantation of hexagonal silicon carbide (4H-SiC), a key process in the realisation of power electronic devices.…”