Void Formation, Growth, and Shrinkage in Lithium Metal in contact with an LLZO Electrolyte

Titelangaben

Lang, Sabrina ; Hennerici, Lukas ; Kramer, Dominik ; Avadanii, Diana ; Linz, Mario ; Kita, Jaroslaw ; Moos, Ralf ; Mönig, Reiner:
Void Formation, Growth, and Shrinkage in Lithium Metal in contact with an LLZO Electrolyte.
2025
Veranstaltung: 76th Annual Meeting of the International Society of Electrochemistry , 7.9.-12.9.2025 , Mainz, Germany.
(Veranstaltungsbeitrag: Kongress/Konferenz/Symposium/Tagung , Poster )

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Abstract

Solid-state batteries (SSB) with lithium metal anodes promise higher energy densities compared to conventional lithium-ion batteries. Interfacial processes such as the growth of voids and dendrites are the key mechanisms leading to capacity loss and short circuits in SSBs. Here, we report on observations of voids in metal electrodes during cell operation. Our experiments are performed on cells that contain Li7La3Zr2O12 electrolyte layers with thicknesses of ~30 μm. The electrolyte layers were fabricated using powder-aerosol-deposition (PAD). With this technique, nanocrystalline ceramic films are deposited by accelerating ceramic powder particles onto copper substrates at room temperature. We press lithium electrodes with diameters as small as 200 μm on LLZO to create Li|LLZO|Cu cells and use heat treatments (< 230°C) to generate different microstructures in the lithium. We operate our cells without stack pressure under galvanostatic conditions inside a scanning electron microscope (SEM) at low current densities of 20 μA/cm2. The metal electrode is investigated using optimized imaging conditions to generate contrast from voids that are located underneath the surface of the thin and small lithium electrodes.
We investigated dissolution and deposition of lithium metal on more than 15 lithium metal electrodes. Our results indicate that electrochemistry ends directly at the interface and that mechanical stresses take over as the driving force for lithium metal motion to and from the interface. Diffusion along the inner Li surface of voids as well as along grain boundaries are suggested as main transport pathways for metal atoms. We present results that highlight the strong effect of the microstructure of the Li electrode on the growth and shrinkage of voids at the Li|LLZO interface. We suggest that flux divergences of atoms at the intersections of voids and grain boundaries govern the shape of growing and shrinking voids in polycrystals. These complex interactions of voids and grain boundaries limit the reversibility of the shape of voids. Nevertheless, our observations also prove that voids that are located inside large grains can reversibly grow and shrink without massive shape changes of the metal electrode. Furthermore, we found that cell operation under the presence of cracks in the solid electrolyte as a result of Li deposition at the LLZO|Cu interface is possible.
In principle, all-solid-state batteries based on Li-LLZO can be quite reversible, but they are strongly affected by the microstructure of the Li electrode. Our results indicate that reliable cells may become feasible by tailoring the microstructure of the lithium and optimizing the electrochemical interface. Further operando SEM investigations will be needed in order to better characterize, understand, and eventually minimize the degradation of metal electrodes in SSB.