NANOscientific

Microscopic Characterization of sodium ion interaction into functionalized graphene by Imaging Ellipsometry

PH Thiesen  ^1,* , J. Sun  ² , V. Palermo  ³ .

¹ Park Systems GmbH - Göttingen (Germany), 

² Materials and Manufacture, Department of Industrial and Materials Science, Chalmers University of Technology - Göteborg (Sweden), 

³ Institute of Organic Synthesis and Photoreactivity (ISOF), National Research Council of Italy (CNR) - Bologna (Italy)

Graphite is already a very good material to store ions; the possibility to exfoliate graphite in graphene sheets, functionalize them and then reassemble them in less compact structures gives fantastic opportunities to create new materials for battery applications.

Operando Imaging ellipsometry [1] enable the microscopic real time imaging of the electrode material in a working cell with a lateral resolution down to 1 µm while the cell is charged/discharged or is changed under other external influences. Imaging ellipsometry in more general, combines optical microscopy and ellipsometry for spatially resolved layer-thickness and refractive index measurements of micro-structured thin-films and substrates. It is an all-optical, non-destructive measurement technique, based on the sample's interaction with polarized light. It is highly sensitive to single- and multi-layer ultrathin films, ranging from mono-atomic or monomolecular layers (sub-nm regime) up to thicknesses of several microns. The technique has been used to characterize the optical properties of graphene [2], [3], to localize flakes [4] and for atomic layer resolved imaging of 2D Materials with microscopic resolution [5].

As an example, the reversible intercalation of sodium ions into Janus graphene as novel anode for sodium ion battery was investigated, and the corresponding Delta and Psi were recorded during three charge/discharge cycles. The motivation for designing these materials is that replacing lithium by sodium in batteries is both a promising and challenging approach. The most critical step is the intercalation of Na ions into graphite. We provided a new idea using artificial graphite nanostructures based on “Janus” graphene to address this issue [1].

Acknowledgments: The research leading to these results has received funding from the European Union's Horizon 2020 research and innovation program under GrapheneCore3 881603–Graphene Flagship, FLAG-ERA project PROSPECT, and from the Swedish Research Council under project Janus 2017-04456.

References

[1] J. Sun, M. Sadd, Ph. Edenborg, H. Grönbeck, P. H. Thiesen, Z. Xia, V. Quintano, R. Qiu, A. Matic, V. Palermo, Sci. Adv. 7, eabf0812 (2021).
[2] U. Wurstbauer, Ch. Röling, U. Wurstbauer, W. Wegscheider, M. Vaupel, P.H. Thiesen, D. Weiss (2010) Appl. Phys. Lett. 97, 231901 (2010)
[3] A. Matković, A. Beltaos, M. Milićević, U. Ralević, B. Vasić, D. Jovanović, and R. Gajić J. Appl. Phys. 112, 123523 (2012).
[4] S. Funke, U. Wurstbauer, B. Miller, A. Matković, A. Green, A. Diebold, C. Röling, P. H. Thiesen, Appl. Surf. Sci. Part B. 421, 435-439, (2017)
[5] Ph. Braeuninger-Weimer, S. Funke, R. Wang, PH Thiesen, D. Tasche, W. Viöl, St. Hofmann. ACS Nano, 12, 8555–8563 (2018)