Synergistic effect of Ga and Yb co-doping on the structure and ionic conductivity of Li7La3Zr2O12 ceramics

Li7La3Zr2O12 (LLZO) has shown excellent electrochemical performance and chemical stability. In this work, Li6.4Ga0.2La3-xYbxZr2O12 (0 ≤ x ≤ 0.1) has been synthesized by solid-state reaction method. The effect of Ga and Yb co-doping on the crystal structure, morphology, densification, and electrical performance was investigated. The doping with Ga3+ stabilized the cubic phase while the doping with Yb3+ optimized Li+ transport channel size and accelerated the densification of the ceramics. Li6.4Ga0.2La2.95Yb0.05Zr2O12 (relative density 94.8%) exhibited the highest total conductivity (8.96 × 10−4 S·cm−1 at 30 °C) and the lowest activation energy of 0.28 eV. Meanwhile, Li6.4Ga0.2La2.95Yb0.05Zr2O12 showed high mobility (1.36 × 10−6 cm2 V−1 s−1), diffusion coefficient (3.18 × 10−8 cm2 s−1) and high hopping rate of lithium ions (5.0 × 106 rad s−1) at 0 °C. The high discharge capacity and capacity retention of LiFePO4/Li6.4Ga0.2La2.95Yb0.05Zr2O12/Li solid-state batteries indicate that Ga and Yb co-doped Li7La3Zr2O12 ceramic should be a promising electrolyte.