Contributed Talk  - Thursday, 16 September I 14:30 PM (CEST)

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Philipp Veelken: "Investigating local ionic conductivity in solid-state electrolytes by Electrochemical Strain Microscopy"

P. Veelken1,2, M. Wirtz ¹ ², R. Schierholz ¹, H. Tempel ¹, H. Kungl ¹, Rüdiger-A. Eichel ¹ ² ³, F. Hausen ¹ ² ³

¹ Institute of Energy and Climate Research, IEK-9, Forschungszentrum Jülich, Jülich, Germany

² Institute of Physical Chemistry, RWTH Aachen University, Aachen, Germany

³ Jülich-Aachen Research Alliance, Section: JARA-Energy, Germany

The interest in all-solid-state lithium-ion batteries increased, because of enhanced safety and capacity in comparison to batteries baes on liquid electrolytes. Hybrid solid-state electrolytes are used to substitute the liquid electrolytes and are composed of ion conducting polymers with lithium salt and ion conducting ceramics.[1] Polyethylene oxide (PEO) with lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and Li6.4La3Zr1.5Ta0.6O12 (LLZO:Ta) are promising materials, combining the flexibility of the polymeric electrolyte and the superior ion conductivity of a ceramic electrolyte. However, with the introduction of multiple materials into one system, different ionic conduction mechanisms have to be considered, especially the ion transport across interfaces between two materials should be investigated on the nanoscale.[2]

Electrochemical Strain Microscopy (ESM) is employed to investigate the local ionic conductivity inside hybrid solid-state electrolytes. Of particular importance to understand percolation paths for Li-Ions is the conductivity at the interface between the polymer PEO-LiTFSI and thee ceramic LLZO:Ta, because of different conduction mechanisms inside the different materials. An increased ESM signal is observed at the interface between polymer and ceramic indicating a higher ion concentration or an enlarged ion mobility. Hence, in order to further explore the ion mobility and conduction pathways a modified ESM method is employed, based on recent work by Simolka et al.[3] A force volume method with a defined hold time of the tip on the sample is used. During the hold time a DC pulse is applied to measure the expansion and relaxation of the different materials. The aim is to relate the obtained relaxation times to the diffusivity of lithium ions inside different materials. The applicability of this method and the resulting signal will be critically discussed.

[1]   M. Wirtz, M. Linhorst, P. Veelken, H. Tempel, H. Kungl, B. M. Moerschbacher, R.-A. Eichel, Electrochem. Sci. Adv. 2021, 1, e2000029.

[2]   M. Keller, A. Varzi, S. Passerini, Journal of Power Sources 2018, 392, 206.

[3]   M. Simolka, H. Kaess, K. A. Friedrich, Beilstein journal of nanotechnology 2020, 11, 583.