The performance of lithium-ion battery (LIB) electrodes is closely related to their microstructure. For the analysis of LIB cathodes, commonly focused ion beam - scanning electron microscopy (FIB-SEM) tomography is used due to its high resolution in the nm-range and excellent contrast mechanisms . In recent years, also X-ray tomography or even correlative approaches combining both techniques are applied on LIB cathodes, in order to additionally benefit from the larger volumes analyzable by X-ray tomography . For LIB anodes consisting of graphite, FIB-SEM tomography is not feasible as the energy from the ion source is not sufficient to adequately mill the graphite. Hence, all anode reconstructions reported in literature are based on X-ray tomography. These studies allow the analysis of large volumes with resolutions in the range of several hundreds of nm. However, due to the lower resolution and the lower contrast mechanism of X-ray compared to FIB-SEM tomography, details of the graphite structure cannot be observed from X-ray tomography analysis.
In this contribution, a novel method for the 3D reconstruction of graphite anodes is presented. It is realized using a TriBeam system , which has integrated an ultrashort pulse femtosecond lasers into a FIB-SEM system. In contrast to FIB-SEM tomography, the milling is conducted by a laser beam instead of an ion beam, though the imaging is still be done by an electron beam. Thus the milling is much faster, while the excellent contrast mechanisms and resolution of the consecutive images retain, which so far was characteristic only for FIB-SEM tomography.
The reconstruction of a graphite anode obtained from this new laser tomography method will be analyzed and microstructural parameters such as volume fractions, surface area, particle and pore sizes as well as tortuosity values will be presented. The results gained from laser tomography will be compared to results obtained on the same anode using X-ray tomography. Finally, the differences, possibilities and limits of both methods will be discussed.
1. M. Ender, J. Joos, T. Carraro, E. Ivers-Tiffée, J. Electrochem. Soc., 159 (7), p. A972 (2012)
2. R. Moroni, M. Börner, L. Zielke, M. Schröder, S. Nowak, M. Winter, I. Manke, R. Zengerle, S. Thiele, Sci. Rep., 6, p. 30109 (2016).
3. M. Echlin, A. Mottura, C. Torbet, T. Pollock, Review of Scientific Instruments, 83, p. 023701 (2012)