Combined quantitative microscopy on the microstructure and phase evolution in Li Al Ti (PO4) ceramics

Deniz Cihan GUNDUZ, Roland SCHIERHOLZ, Shicheng YUa, Hermann TEMPEL, Hans KUNGL, Rüdiger-A. EICHEL - Forschungszentrum Jülich, Institute of Energy and Climate Research, RWTH Aachen University, Institute of Physical Chemistry

Lithium aluminum titanium phosphate (LATP) is one of the materials under consideration as an electrolyte in future all-solid-state lithium-ion batteries. In ceramic processing, the presence of secondary phases and porosity play an important role. In a presence of more than one secondary phase and pores, image analysis must tackle the difficulties about distinguishing between these microstructural features. In this study, we study the phase evolution of LATP ceramics sintered at temperatures between 950 and 1100 °C by image segmentation based on energy-dispersive X-ray spectroscopy (EDS) elemental maps combined with quantitative analysis of LATP grains. We found aluminum phosphate (AlPO4) and another phosphate phase ((Lix)PyOz). The amount of these phases changes with sintering temperature. First, since the grains act as an aluminum source for AlPO4 formation, the aluminum content in the LATP grains decreases. Second, the amount of secondary phase changes from more (Lix)PyOzat 950 °C to mainly AlPO4 at 1100 °C sintering temperature. We also used scanning electron microscopy (SEM) and confocal laser scanning microscopy (CLSM) to study the evolution of the LATP grains and AlPO4, and LATP grain size increases with sintering temperature.In addition, transmission electron microscopy (TEM) was used for the determination of grain boundary width and to identify the amorphous structure of AlPO.

How Amira-Avizo Software is used

Segmentation of the different phases from single EDS elemental maps was done with Avizo Sofware.

We used Avizo also for the segmentation of CLSM and SEM micrographs and chose the thresholds that the darker levels cover the lower regions, the bright levels cover the grains, and the intermediate levels cover the secondary phase. Grains were separated with the separate object module based on a watershed algorithm, and also manual corrections were applied for this purpose when they were necessary. Analysis filter module was used to eliminate noise by excluding very small objects. Grains that are not fully inside of the analysis area were excluded from the analysis. The size of the grains reported here was retrieved via taking the square root of grain areas.