A gold interlayer was introduced into the interface between Li6.25Al0.25La3Zr2O12 (Al-LLZ) and lithium metal anode to decrease their interfacial resistance. The interfacial resistance was decreased to 150 ohm from 1200 ohm by the introduction of gold interlayer with a heat-treatment at 150°C, in which Li-Au alloy formation occurred. The interfacial resistance decreases with increasing the thickness of gold interlayer until 50 nm. Li/Au/Al-LLZ/Au/Li symmetric cell with the heat-treatment showed smaller overpotential for dissolution and deposition of lithium than Li/Al-LLZ/Li symmetric cell, due to difference in the interfacial resistance. From this result, it can be concluded that the gold interlayer is effective to decrease the interfacial resistance.

Thermal stability of LiCoO 2 , LiMn 2 O 4 and LiFePO 4 with Li 6.25 Al 0.25 La 3 Zr 2 O 12 (Al-LLZ) solid electrolyte was investigated at 300-800°C. In the case of LiCoO 2 /Al-LLZ mixture, the XRD patterns and charge-discharge behavior did not change after the heat treatment at 800°C. In contrast, the formation of impurities and degradation of cathode performance were observed for LiMn 2 O 4 /Al-LLZ mixture and LiFePO 4 /Al-LLZ mixture. The decomposition of Al-LLZ and the formation of some impurities were observed from 600°C for LiMn 2 O 4 /Al-LLZ mixture, leading to decrease in the discharge capacity. In the case of LiFePO 4 /Al-LLZ mixture, the decomposition of both materials was started at 400°C. These results indicate that the limit of heat treatment temperature for the formation of electrode/solid electrolyte system strongly depends on the kind of electrode material.

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A cubic boracite with substituted boron sites,