An all-solid-state Li battery was fabricated using a NaI-based Li+ conductor as the solid electrolyte. The formation of the solid solutions was confirmed for 9(15NaI center dot NaBH4)center dot LiI with no significant inclusion of LiBH4. The Li+ conductivity of 9(15NaI center dot NaBH4)center dot LiI was 1.5 x 10(-5) S/cm at 30 degrees C. The activation energy for Li+ conduction was estimated as 0.28 eV for 9(15NaI center dot NaBH4)center dot LiI. This compares well to the activation energy of the conventional high Li+ conductors with a single alkali cation. Furthermore, the charge-discharge performances of the Li/TiS2 cell using 9(15NaI center dot NaBH4)center dot LiI were excellent. It was shown that the charge-discharge capacity of 175 mAh/g can be maintained for 60 cycles under 0.05C. The Coulombic efficiencies of each cycle were over 99.
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