Talk Christian Prehal - 7 December 2018

Combining modelling and in situ scattering to study the phase evolution in conversion type batteries



Christian Prehal



Institute for Chemistry and Technology of Materials, Graz University of Technology, Stremayrgasse 9/V, 8010 Graz, Austria



A fundamental and mechanistic understanding of reaction mechanisms is essential to improve the performance of highly complex electrochemical systems like Li-O2 or Li-S batteries. Current explanations of how (electro-)chemical reactions control the structure of reaction products and the performance of Li-O2 or Li-S batteries are contradictory1,2. To identify the main parameters determining reaction mechanisms, quantitative real-time in situ metrologies with structural information of ions, molecules and reaction products at the atomic to micron level are required.

Here in situ small and wide angle X-ray scattering (in situ SAXS/WAXS) is introduced as a suitable method to study ion rearrangements and the phase evolution of reaction products in nanoporous carbon electrodes during charging and discharging custom-built electrochemical cells3. The in situ scattering data contains rich detail of structural and kinetic information4,5. However, the complexity induced by the multi-phase character of the investigated systems makes the analysis of the scattering data challenging6.

To investigate the phase evolution of Li2O2 in Li-O2 batteries a recently published data analysis approach for nanoporous carbon supercapacitors is adapted and briefly introduced4. Involving atomistic simulation of length scale dependent ion arrangement allows a real-time quantification of ion confinement and desolvation during charging and discharging. For the analysis of the Li-O2 battery data, structural models of nanoporous carbon electrodes are derived from an analytical fit to the SAXS intensity of the empty carbon electrode using Gaussian random fields (GRF) and Boolean models7. The computer generated real-space pore structure is then filled with electrolyte and the morphology of the solid reaction product Li2O2, modelled as a function of the state of charge. Subsequent Fourier transformation yields the modelled scattering curves which are then compared with the experimental in situ SAXS measurements. The presented method allows for time-resolved detection of Li2O2 particle morphologies and locations in the carbon pore network, which are shown to conclusively determine the charge/discharge capacity.



1 Mahne, N., Fontaine, O., Thotiyl, M. O., Wilkening, M. & Freunberger, S. A. Mechanism and performance of lithium–oxygen batteries – a perspective. Chem. Sci. 8, 6716-6729 (2017).

2 Aurbach, D., McCloskey, B. D., Nazar, L. F. & Bruce, P. G. Advances in understanding mechanisms underpinning lithium–air batteries. Nat. Energy 1, 16128 (2016).

3 Prehal, C. et al. Tracking the structural arrangement of ions in carbon supercapacitor nanopores using in situ small-angle X-ray scattering. Energy Environ. Sci. 8, 1725-1735 (2015).

4 Prehal, C. et al. Quantification of ion confinement and desolvation in nanoporous carbon supercapacitors with modelling and in situ X-ray scattering. Nat. Energy 2, 16215 (2017).

5 Prehal, C., Koczwara, C., Amenitsch, H., Presser, V. & Paris, O. Salt concentration and charging velocity determine ion charge storage mechanism in nanoporous supercapacitors. Nat. Commun. 9, 4145 (2018).

6 Prehal, C. et al. A carbon nanopore model to quantify structure and kinetics of ion electrosorption with in situ small angle X-ray scattering. Phys. Chem. Chem. Phys. 19, 15549 (2017).

7 Gommes, C. J. Stochastic models of disordered mesoporous materials for small-angle scattering analysis and more. Microporous Mesoporous Mater. 257, 62-78 (2018).