Low temperature synthesis of highly ion conductive Li7La3Zr2O12–Li3BO3 composites

• A composite electrolyte of Li7La3Zr2O12 and lithium borate glass was prepared.
• The composite is proposed as a novel solid electrolyte with high lithium ion conductivity.
• The maximum process temperature for the preparation of the composite is 900°C.
• Amorphous lithium borate is formed at the grain boundaries.
• Conductivity of composite is comparable to that of Al-doped LLZ pellet sintered at 1230°C.

Highly lithium ion conductive composites with Al-doped Li7La3Zr2O12 (LLZ) and amorphous Li3BO3 were prepared from sol–gel derived precursor powders of LLZ and Li3BO3. Precursor LLZ powders with cubic phase were obtained by a heat treatment of the precursor dried gel at 600 °C. Pellets of the mixture of the obtained LLZ and Li3BO3 were first held at 700 °C, and then successively sintered at 900 °C. Density of the sintered pellet with Li3BO3 was larger than that of the pellet without Li3BO3. From the TEM observation, the pellets were found to consist of cubic LLZ and amorphous Li3BO3. Total electrical conductivity of the obtained LLZ–Li3BO3 composite was 1 × 10− 4 Scm− 1 at 30 °C.