Abstract text (incl. figure legends and references)

Due to the growing need for sustainable, rechargeable energy storage systems, efforts are made towards the development and improvement of battery electrode components based on organic compounds. Electron donor-acceptor metalloporphyrin complexes like [5,15-bis(ethynyl)-10,20-diphenylporphinato]copper(II) (CuDEPP) are promising materials for rechargeable lithium[1], sodium[2] and magnesium batteries[3].

In this study we demonstrate that structural changes of composite CuDEPP electrode material (50 wt.% CuDEPP active material, 40 wt.% carbon black and 10 wt.% poly(vinylidene difluoride)) for Li/ LiPF₆/CuDEPP batteries can be visualized including the initial self-conditioning step during the first charge-discharge cycle and changes of the active material after longer charge-discharge cycles via focused ion beam/scanning electron microscopy (FIB/SEM) and energy dispersive/wavelength dispersive X-ray spectroscopy (EDX/WDX) measurements.

Pristine CuDEPP electrode and electrodes cycled for 1, 200 and 2000 times in Li half-cell with LiPF₆ electrolyte were treated with OsO₄ vapor and embedded in silicone resin. After staining and embedding, the samples were investigated using FIB/SEM cross-sectioning and tomography (Helios Nanolab600), EDX measurements using a Quanta 3D FEG (both Thermo Fisher) equipped with a SDD Apollo XV (EDAX) and WDX measurements obtained with a JXA-8530FPlus (JEOL).

For the pristine sample, EDX and WDX measurements show no uptake of Os, as the aromatic conjugated double and triple bonds that occur in pristine CuDEPP are not affected by OsO₄ staining. However, all cycled samples show a gradient in grey values in BSE images with highest values at the edges of each grain due to the incorporation of Os. The occurrence of Os coincides with increased P content (Fig.1) and therefore with the penetration of electrolyte (LiPF₆) into the CuDEPP particles during cycling. As OsO₄ does not react with the pristine material, a measurable Os content within the cycled CuDEPP directly indicates structural changes of CuDEPP (degradation) given the fact that Os enrichment is related to the formation of non-aromatic double bonds [4].

Fig.1: BSE image (a) and WDX map of P (c) and Os (d) of CuDEPP particles after 200 cycles. (b) show intensity profiles of BSE, P and Os signal along the yellow line. Two CuDEPP particle marked by red line in (a).

[1] P. Gao et al. Angew. Chemie Int. Ed. 56 (2017) 10341–10346.

[2] X. Chen et al. Nano-Micro Lett. 13 (2021) 71.

[3] E. Abouzari-Lotf et al. ChemSusChem. 14 (2021) 1840–1846.

[4] T. Philipp et al. J. Power Sources. 522 (2022) 231002.