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

Abstract

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 Li7+xLa3Zr2-xEuxO12 (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. Li7.15La3Zr1.85Eu0.15O12 (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.