Tantalum-doped
garnet (Li6.5La3Zr1.5Ta0.5O12, LLZTO) is a promising candidate to
act as a solid electrolyte in all-solid-state batteries owing to both
its high Li+ conductivity and its relatively high robustness
against the Li metal. Synthesizing LLZTO using conventional solid-state
reaction (SSR) requires, however, high calcination temperature (>1000
°C) and long milling steps, thereby increasing the processing
time. Here, we report on a facile synthesis route to prepare LLZTO
using a molten salt method (MSS) at lower reaction temperatures and
shorter durations (900 °C, 5 h). Additionally, a thorough analysis
on the properties, i.e., morphology, phase purity,
and particle size distribution of the LLZTO powders, is presented.
LLZTO pellets, either prepared by the MSS or the SSR method, that
were sintered in a Pt crucible showed Li+ ion conductivities
of up to 0.6 and 0.5 mS cm–1, respectively. The
corresponding activation energy values are 0.37 and 0.38 eV, respectively.
The relative densities of the samples reached values of approximately
96%. For comparison, LLZTO pellets sintered in alumina crucibles or
with γ-Al2O3 as sintering aid revealed
lower ionic conductivities and relative densities with abnormal grain
growth. We attribute these observations to the formation of Al-rich
phases near the grain boundary regions and to a lower Li content in
the final garnet phase. The MSS method seems to be a highly attractive
and an alternative synthetic approach to SSR route for the preparation
of highly conducting LLZTO-type ceramics.
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