Abstract
Correlative microscopy has been used to investigate the relationship between Li-ion conductivity and the microstructure of lithium aluminum titanium phosphate (Li1.3Al0.3Ti1.7(PO4)3, LATP) with high spatial resolution. A key to improvement of solid state electrolytes such as LATP is a better understanding of interfacial and ion transport properties on relevant length scales in the nanometer to micrometer range. Using common techniques, such as electrochemical impedance spectroscopy, only global information can be obtained. In this work, we employ multiple microscopy techniques to gain local chemical and structural information paired with local insights into the Li-ion conductivity based on electrochemical strain microscopy (ESM). Scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX) have been applied at identical regions to identify microstructural components such as an AlPO4 secondary phase. We found significantly lower Li-ion mobility in the secondary phase areas as well as at grain boundaries. Additionally, various aspects of signal formation obtained from ESM for solid state electrolytes are discussed. We demonstrate that correlative microscopy is an adjuvant tool to gain local insights into interfacial properties of energy materials.
Highlights
Solid state electrolytes (SSE) of the NASICON-type exhibit a high ionic conductivity and are in this respect becoming comparable to conventional organic electrolytes commonly used in lithium-ion batteries (LIBs) [1,2,3,4,5]
As it can already be seen from the results of different lithium-ion conductivities for grain and grain boundary structures in comparison to the overall ionic conductivity, it is of utmost importance to understand the electrochemical and ion-transport properties of promising SSEs such as LATP at the length scale of the grain size, local defects and structural inhomogeneities, that is, on the nanometer to low-micrometer scale [10,11]
Sasano et al have reported about the qualitative relation between grain orientation and Li-ion mobility in Li0.33La0.56TiO3 using scanning electron microscopy (SEM) with electron backscatter diffraction (EBSD) and electrochemical strain microscopy (ESM) [21]
Summary
Solid state electrolytes (SSE) of the NASICON-type exhibit a high ionic conductivity and are in this respect becoming comparable to conventional organic electrolytes commonly used in lithium-ion batteries (LIBs) [1,2,3,4,5]. The SEM image (Figure 2a) illustrates the grain structure of the sample and reveals the existence of primary phase and secondary phase represented by different colors.
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