Lithium/sulfur (Li/S) batteries are a promising solution for future energy storage systems, due to their high energy density, and to the abundance, non-toxicity and low cost of sulfur as an active material. This type of battery does not rely on the same cycling mechanisms as conventional commercialised Li-ion batteries, and current performances do not yet meet application requirements, in particular, in terms of cyclability. The study of morphological changes in Li/S cells is thus essential to understand the degradation phenomena occurring in the battery and to advance the move toward commercialisation.
In this work, an advanced electrochemical cell (Figure 128a) was designed  and characterised operando while undergoing electrochemical cycling using a combination of multimodal X-ray techniques at beamline ID15A: absorption tomography to study the morphological evolution of a 3D sulfur electrode, and X-ray diffraction computed tomography
Fig. 129: Evolution of the sulfur active material through the depth of the electrode while discharging a Li/S cell, based on XRD-CT data. The graph shows the integrated intensity of 20 µm (the vertical resolution) slices; inset images show the distribution in the plane, with 300 µm resolution. Reprinted from principal publication with kind permission from Elsevier.
(XRD-CT) to probe locally the structural modification of the crystalline sulfur active materials.
In particular, XRD-CT made it possible to study the dynamic processes at the positive electrode with high spatial resolution (300 x 300 µm2 in the x,y plane, 30 µm in the z plane). The use of XRD-CT enables a significant reduction in noise and improves the quality of the XRD patterns (Figure 128b), in order to determine, voxel by voxel, the presence of crystalline phases in the battery electrode operando, and to map these phases in three dimensions (Figure 129). The combination of electrochemical methods and tomography techniques made it possible to characterise the heterogeneous behaviour of the sulfur electrode during cycling, with faster kinetics at the top of the electrode observed with respect to the bulk. This characterisation methodology is a valuable tool for optimising sulfur positive electrodes in order to move towards commercialisation.
Operando investigation of the lithium/ sulfur battery system by coupled X-ray absorption tomography and X-ray diffraction computed tomography, G. Tonin (a,b,c), G.B.M. Vaughan (b), R. Bouchet (c), F. Alloin (c,d),
M. Di Michiel (b) and C. Barchasz (a), J. Power Sources 468, 228287 (2020); https://doi.org/10.1016/j. jpowsour.2020.228287. (a) Univ. Grenoble Alpes, CEA-LITEN, DEHT, STB, Grenoble (France)
(b) ESRF (c) Univ. Grenoble Alpes, Univ. Savoie Mont Blanc, CNRS, Grenoble INP, LEPMI, Grenoble (France) (d) Réseau sur le Stockage Electrochimique de l Energie (RS2E), CNRS, Amiens (France)
 G. Tonin et al., Sci. Rep. 7, 2755 (2017).
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