Computational and experimental investigation of Li⁺-ion transport mechanism of Eu-doped garnet solid electrolyte for Li-ion batteries

Garnet-type Li₇La₃Zr₂O₁₂ (LLZO) is one of the most preeminent solid electrolytes in all-solid-state lithium batteries (ASSLBs). To further improve the conductivity of LLZO, we synthesized a novel garnet-type solid electrolyte Li_7+xLa₃Zr_2-xEu_xO₁₂ (0 ≤ x ≤ 0.20) in which the low-valence Eu⁺³ doped at the Zr⁺⁴ site. Using density functional theory (DFT) calculation, effect of Eu³⁺ doping was also investigated. Eu³⁺ doping normalized Li⁺-ion transport by enhancing Li⁺-ion occupancy at 96 h position which reduced the Li⁺-ion diffusion barrier and enhanced the ionic conductivity. Li_7.15La₃Zr_1.85Eu_0.15O₁₂ (LLZEO) solid electrolyte exhibited highest ionic conductivity of 0.415 × 10⁻⁴ S/cm and the lowest activation energy of 0.28 eV at 25 °C. Further, a flexible composite electrolyte membrane was also prepared using LLZEO as filler into polyethylene oxide/polyethylene glycol matrix, which exhibited excellent flexibility and high ionic conductivity of 0.15 × 10⁻⁴ S/cm at 25 °C will be a promising candidate for ASSLBs.