Garnet-Type Fast Li-Ion Conductors with High Ionic Conductivities for All-Solid-State Batteries.

All-solid-state Li-ion batteries with metallic Li anodes and solid electrolytes could offer superior energy density and safety over conventional Li-ion batteries. However, compared with organic liquid electrolytes, the low conductivity of solid electrolytes and large electrolyte/electrode interfacial resistance impede their practical application. Garnet-type Li-ion conducting oxides are among the most promising electrolytes for all-solid-state Li-ion batteries. In this work, the large-radius Rb is doped at the La site of cubic Li _6.10 Ga _0.30 La ₃ Zr ₂ O ₁₂ to enhance the Li-ion conductivity for the first time. The Li _6.20 Ga _0.30 La _2.95 Rb _0.05 Zr ₂ O ₁₂ electrolyte exhibits a Li-ion conductivity of 1.62 mS cm ^-1 at room temperature, which is the highest conductivity reported until now. All-solid-state Li-ion batteries are constructed from the electrolyte, metallic Li anode, and LiFePO ₄ active cathode. The addition of Li(CF ₃ SO ₂ ) ₂ N electrolytic salt in the cathode effectively reduces the interfacial resistance, allowing for a high initial discharge capacity of 152 mAh g ^-1 and good cycling stability with 110 mAh g ^-1 retained after 20 cycles at a charge/discharge rate of 0.05 C at 60 °C.