The Importance of Doping Elements on Improving the Interphase Properties of Garnet-Type Solid Electrolytes with a Lithium Metal Anode

The garnet-type solid electrolyte Li₇La₃Zr₂O₁₂ (LLZO) is considered the most compatible with the Li anode, which has the highest theoretical energy density (3860 mAh g^–1). However, there are various challenges at the Li/LLZO interface, such as the formation of residual alkali, low ionic conductivity, and the growth of lithium dendrites. Therefore, in this work, four elements (Ti, Nb, Al, and Ga) are selected as representative elements to investigate the effect and mechanism of element doping at the Li/LLZO interface on improving electrochemical performance through first-principles calculations. We found that doping elements substituting for Zr sites, especially Ti, facilitate the formation of O vacancies on the interface, resulting in a lower Li⁺ diffusion barrier (0.16 eV) and thus enhancing the trans-phase boundary ionic conductivity while suppressing the adsorption of CO₂, thereby reducing the tendency of residual alkali formation. However, element doping cannot improve the wettability of the interface and has a limited effect on inhibiting the growth of lithium dendrites. Based on the coordination relationship and electronic structure characteristics in the local chemical environment, the mechanism of doping with the Ti element on improving the comprehensive electrochemical performance of the phase boundary was clarified.