Improving the Li-ion conductivity and air stability of cubic Li7La3Zr2O12 by the co-doping of Nb, Y on the Zr site

The elements Nb and Y were simultaneously substituted to the Zr sites of an Li7La3Zr2O12 (LLZO) electrolyte to improve its Li-ion conductivity and air stability. Samples of Li7La3Zr2-2xNbxYxO12 were fabricated using a solid-state reaction method. The results show that the introduction of Nb and Y can stabilise cubic-phase LLZO. The total conductivity of Li7La3ZrNb0.5Y0.5O12 electrolyte can reach 8.29 × 10−4 S cm−1 at 30 °C when sintered at 1230 °C for only 15 h. Surprisingly, the conductivity of Li7La3ZrNb0.5Y0.5O12 can be maintained at 6.91 × 10−4 S cm−1 after exposure to air for 1.5 months, indicating excellent air stability. Furthermore, a LiFePO4/Li7La3ZrNb0.5Y0.5O12/Li cell displayed stable charge/discharge and cycling performance at ambient temperature, suggesting there is potential to use Li7La3ZrNb0.5Y0.5O12 electrolyte in Li-ion batteries. Additionally, the effects of varying the co-doping amount and dwelling time on the Li-ion conductivity of Li7La3Zr2-2xNbxYxO12 were investigated.