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In the OPINCHARGE Scientific Publications series, we highlight research that advances the understanding of battery materials, degradation processes and next-generation energy storage technologies. This study focuses on one of the key challenges facing solid-state batteries — the formation and accumulation of lithium within solid electrolytes.
The publication “Investigation of Li accumulations in LLZO based solid state batteries via operando neutron imaging and ex-situ correlative structural and chemical analysis” was authored by Luca Cressa, Pierre Boillat, Mathieu Gerard, Yanyan Sun, Sayantan Sharma, Olivier De Castro, Maryam Nojabaee, Guido Schmitz, Tom Wirtz and Santhana Eswara, bringing together researchers from the Luxembourg Institute of Science and Technology, University of Stuttgart, Paul Scherrer Institute, German Aerospace Center and University of Luxembourg.
Read the publication: https://zenodo.org/records/14999833
Solid-state batteries offer significant potential for safer and more efficient energy storage, but their long-term performance can be limited by lithium dendrite formation.
During battery operation, lithium can penetrate and accumulate within the solid electrolyte. These localised deposits may eventually create conductive pathways between the electrodes, causing short circuits and battery failure. Understanding where, when and how these lithium accumulations develop is therefore essential for improving the safety and lifetime of solid-state batteries.
The researchers investigated a solid-state half-cell using the garnet-type electrolyte Li₇La₃Zr₂O₁₂ (LLZO). The cell was cycled until short-circuit failure while being continuously examined using operando neutron imaging.
This technique makes it possible to monitor changes inside the battery while it is operating. After cycling, the researchers complemented the neutron measurements with scanning electron microscopy (SEM) and secondary ion mass spectrometry (SIMS), providing high-resolution structural images and chemical maps of lithium within the electrolyte.
By combining these techniques, the study connects what happens during battery operation with detailed evidence of where lithium ultimately accumulates inside the material.
The results revealed that lithium accumulation is highly localised and strongly influenced by the microstructure of the LLZO electrolyte.
In dense regions of the material, lithium was found mainly along grain boundaries, forming intergranular accumulations. In lower-density regions containing pores and cracks, the researchers identified different lithium morphologies, including thin whisker-like dendrites and larger lithium deposits.
Operando neutron imaging detected regions where excess lithium increased by up to 3.6 vol.-%, particularly near the LLZO/lithium interface. At the same time, the subsequent SEM/SIMS analysis confirmed much smaller lithium dendrites within the bulk electrolyte that were below the spatial resolution of neutron imaging.
No single analytical method can capture the complete picture of lithium dendrite formation.
Neutron imaging provides a valuable way to track lithium dynamically and non-destructively during cycling, while SEM and SIMS reveal much finer structural and chemical details after the experiment. Combining these approaches therefore bridges the gap between real-time observation and high-resolution post-mortem analysis.
The study demonstrates how correlative characterisation can reveal degradation mechanisms that might remain hidden when relying on only one analytical technique.
By showing where lithium accumulates and how different forms of dendrites develop within LLZO, this research provides important insights into one of the major challenges facing solid-state battery technology.
A better understanding of the relationship between material microstructure, lithium transport and dendrite formation can support the development of solid electrolytes that are more resistant to short circuits and degradation — contributing to safer, more reliable and longer-lasting solid-state batteries.
