Combined quantitative microscopy on the microstructure and phase evolution in Li1.3Al0.3Ti1.7(PO4)3 ceramics

Deniz Cihan Gunduz,Hans Kungl,Roland Schierholz,Hermann Tempel,Shicheng Yu,Rüdiger-A Eichel

doi:10.1007/s40145-019-0354-0

Abstract

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)PyOz at 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 AlPO4.

Highlights

Inorganic solid Li-conducting electrolytes are consideredJ Adv Ceram 2020, 9(2): 149–161 multi-scale challenge [2]
The microstructural properties of lithium aluminum titanium phosphate (LATP)-pellets sintered at temperatures from 950 to 1100 °C with 50 °C steps were studied
An image analysis and reconstruction method based on energy-dispersive X-ray spectroscopy (EDS) elemental maps revealed that with increasing temperature, (Lix)PyOz is consumed while more AlPO4 is formed

Summary

Introduction

Inorganic solid Li-conducting electrolytes are consideredJ Adv Ceram 2020, 9(2): 149–161 multi-scale challenge [2]. Various types of Li-ion conducting solid-state electrolytes have been reported in Ref. Promising ionic conductivities have been reported for Li3N [10], perovskite-type La2/3−xLixTiO3 [11], garnet type Li7La3Zr2O12 [12,13], thio LISICON-type Li10GeP2S12 [14], B2S3–Li2S–LiI glass [15], and NASICON-type Li1+xMxTi2–x(PO4)3 [6,16]. Focusing on solid electrolytes that can be processed under dry-room conditions, NASICON-type Li1+xMxTi2–x(PO4) are the materials of choice, as they combine high Li-ion conductivity with stability under air [17] and electrochemical stability window from 2.17 to 4.21 V [18]. The increase in Li-ion conductivity on substituting Ti by Al in Li1+xAlxTi2–x(PO4) was shown independently on microstructural effects on single crystals by using micro-contacting reaching a maximum at x = 0.4, where x was tracked via atomic emission spectroscopy [22]. Impedance measurements give a grain ionic conductivity that exceeds the grain-boundary ionic conductivity by almost three orders of magnitude [24]

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Conclusion