High lithium ion conductive Li7La3Zr2O12 by inclusion of both Al and Si

High lithium-ion (Li+) conductive garnet-structured lanthanum lithium zirconate (LLZ) solid electrolyte is prepared by incorporation of appropriate amounts of silicon (Si) and aluminum (Al). The resultant pelletized LLZ obtains total Li+ conductivity of 6.8 × 10− 4 S cm− 1 at 298 K. This improved conductivity is nearly identical with the bulk Li+ conductivity of the LLZ reported earlier, suggesting that the grain boundary resistance is effectively reduced by the incorporation of Si and Al. Microanalyses by transmission electron microscopy coupled with energy-dispersive X-ray microanalysis and electron energy-loss spectroscopy revealed the presence of amorphous Li–Al–Si–O with nano crystalline LiAlSiO4 at grain boundaries. Fast lithium-ion transport around the amorphous Li–Al–Si–O/LiAlSiO4 interface will facilitate Li+ transport between the LLZ particles, resulting in the improvement of the total Li+ conductivity of LLZ.

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► Total lithium ionic conductivity of lanthanum lithium zirconate (LLZ) is reported.
► The value at 298 K reaches to 6.8×10–4 S cm–1 by inclusion of both Si and Al.
► Removal of grain boundary resistance is the main reason.
► The resultant LLZ maintains the stability with lithium metal.