First-principles calculations and Yb3+ doping effects study of garnet-type solid state electrolytes

Garnet-type solid state electrolyte Li7La3Zr2O12 (LLZO) plays a critical role in enhancing the safety of all solid-state lithium batteries, but its practical applications have been seriously limited by its poor ionic conductivity at room temperature. Elemental doping is an effective strategy to address this issue and the influence of Yb3+ doping on LLZO performance was investigated in this study. The doping site of Yb3+ in LLZO was determined by first-principles calculations based on DFT for the first time, and the results revealed that the Yb3+ doping position was La3+ site. A series of Li7La3-xYbxZr2O12 (x = 0.02, 0.04, 0.06, 0.15,0.30, LLYZO) were successfully produced by solid-state reaction route. It was found that the Yb3+ doping strategy not only enhanced the ion conductivity, but also was beneficial to inhibit the abnormal grain growth by forming LiYbO2 second phase and accelerate the sintering process. The LLYZO (x = 0.15) ceramic sintered at 1200 °C for 15 h shows a highest conductivity of 2.53× 10−4 S·cm−1, the lowest activation energy of 0.294 eV and a relative density of 90.2%.