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Lithium loss indicated formation of microcracks in LATP ceramics

: Wätzig, Katja; Rost, Axel; Langklotz, Ulrike; Schilm, Jochen


Ohji, Tatsuki (Hrsg.) ; American Ceramic Society -ACerS-, Westerville/Ohio:
Advanced processing and manufacturing technologies for nanostructured and multifunctional materials III : A collection of papers presented at the 40th International Conference on Advanced Ceramics and Composites, January 24-29, 2016 Daytona Beach, Florida
Hoboken/NJ: Wiley, 2017 (Ceramic engineering and science proceedings 37.2016, Nr.5)
ISBN: 978-1-119-32170-5
ISBN: 978-1-119-32173-6
International Conference and Exposition on Advanced Ceramics and Composites (ICACC) <40, 2016, Daytona Beach/Fla.>
Fraunhofer IKTS ()
LATP; microcracks; Li-Sulfur battery; solid electrolyte; Li-Air battery

Lithium ion conducting ceramics are investigated as candidates for use as solid electrolytes in Lithium-Sulfur and Lithium-air battery concepts. LiTi2(PO4)3 have to provide a high Li-ion conductivity and a hermetical tightness for separating the liquid electrolyte of the cathode and anode side. A partial substitution of Ti4+ by Al3+ improves the conductivity up to 3.0.10-3 S/cm for the composition Li1.3Al0.3Ti1.7(PO4)3 (LATP). LATP exhibits a high thermal expansion anisotropy and cracks are a result of grain growth during the sintering. At least, it was described, that the formation of microcracks can be inhibited by reducing the critical grain size (<1.6 μm). In this study, the LATP ceramics were prepared by melting and milling of a glass frit to a powder with a d50-value of 0.7 μm. Sintering at temperatures (Ts) between 800 and 1050 °C was performed by SPS. The phase composition, density, porosity, ionic conductivity, He leakage rate and grain size of the specimens were measured. The highest density (2.82 g/cm³) and ionic conductivity (~1.10-4 S/cm) was reached at Ts between 900 and 1000 °C. The formation of microcracks was observed at Ts=950°C in AlPO4 secondary phase (caused by Li loss during the preparation). With higher sintering temperatures coarse grains and cracks dominate the microstructure. Two different mechanisms of crack formation are found and an explanation of observed phenomena is given.