Aluminum fluoride intercalation in graphite for rechargeable batteries design.

Rechargeable batteries based on graphite are considered as promising alternatives for energy storage applications. The charge/discharge mechanisms of these batteries results from the intercalation and de-intercalation driven electrochemically by the atoms or molecules of the electrodes in contact with a liquid electrolyte. These solutions are often complex systems engineered to stabilize and allow the transport of the evolving moieties. In this article, we isolate the effect on the graphite structure of a chemical component of novel electrolytes, the aluminum fluoride (AlF 3), by dosing this pure compound in the gas phase over high oriented pyrolitic graphite (HOPG) substrates at 10−9 mbar and 300 K. We performed an extensive experimental study involving surface characterization and beam analysis techniques, and developed a model of the sorption substantiated in ab-initio calculations. We found a preferential interlaminar absorption when dosing in the direction transversal to the carbon planes. The intercalation in the HOPG is spontaneous and non-reactive, and increases the interplanar spacing by 20%. A charge transfer of 0.65 e− per formula from graphite to AlF 3 is calculated for the intercalate. Since the absorption depends on the roughness of the substrate we may infer that the intercalation proceeds through the step-edges. These features may contribute to the development of novel quasi-2D devices for special applications. [Display omitted] ● We isolate the effects of the AlF 3 over the crystalline structure and chemistry of HOPG by studying the system AlF 3 /HOPG in UHV by STM, XPS, RBS, and using DFT calculations to build an absorption model. ● The AlF 3 aggregates diffuse into the substrate, separating the carbon layers locally, and in turn generate changes in the density of electronic states of neighboring regions. ● The AlF 3 and HOPG retain their chemical identity ruling out the formation of metallic Al formation on the surface and any type of covalent bond between C and AlF 3 ● Surface defects and rsubstrate roughness are parameters that control the thickness of the fluoride intercalates. ● The calculated intercalation energy favours this process over adsorption, predicting a value of 4.41 V for its deintercalation potential. [ABSTRACT FROM AUTHOR]