Structural, electronic, and Li-ion mobility properties of garnet-type Li₇La₃Zr₂O₁₂ surface: An insight from first-principles calculations

Garnet-type Li₇La₃Zr₂O₁₂ (LLZO) is a promising solid-state electrolyte for Li-ion batteries, but Li-dendrite’s formation greatly limits the applications. In this paper, we systematically investigate the stability, electronic properties, and Li-ion mobility of the LLZO surface by the first-principles calculations. We consider the (110) and (001) slab structures with different terminations in the t- and c-LLZO. Our results indicate that both (110) and (001) surfaces prefer to form Li-rich termination due to their low surface energies for either t- or c-LLZO. Moreover, with the decrease of Li contents the stability of Li-rich surfaces is improved initially and degrades later. Unfortunately, the localized surface states at the Fermi level can induce the formation of metallic Li on the Li-rich surfaces. In comparison, Li/La-termination has a relatively low metallic Li formation tendency due to its rather low diffusion barrier. In fact, Li-ion can spontaneously migrate along path II (Li3 → Li2) on the Li/La–T(001) surface. In contrast, it is more difficult for Li-ion diffusion on the Li–T(001) surface, which has a minimum diffusion barrier of 0.50 eV. Interestingly, the minimum diffusion barrier decreases to 0.34 eV when removing four Li-ions from the Li–T(001) surface. Thus, our study suggests that by varying Li contents, the stability and Li-ion diffusion barrier of LLZO surfaces can be altered favorably. These advantages can inhibit the formation of metallic Li on the LLZO surfaces.