Impacts of GeO2 modification on microstructure, electrical and interface performance of Ta-doped garnet electrolytes

Li6.4La3Zr1.4Ta0.6O12 (LLZTO) electrolytes have attracted tremendous attentions in recent years. In this work, a novel strategy is proposed to simultaneously address their grain boundary problems and the interface issues with Li anode by introducing GeO2 additive in sintering of LLZTO ceramics. GeO2 consumes Li2O, forming Li4(Ge5O12)/Li2O eutectic melt phase in grain boundary regions. Li-Ge-O melt contributes primarily in (i) regulating growth and combination of LLZTO grains, (ii) constructing consecutive Li+ conduction pathways within the electrolytes, (iii) promoting Li wettability on ceramic’s surface and (iv) suppressing growth of lithium dendrites. Therefore, the ionic conductivity is increased to 6.23 × 10−4 S·cm−1 and the activation energy is reduced to 0.29 eV. The compact bonding without any modification layer is formed between Li and the electrolyte. The Li|LLZTO@Li4(Ge5O12)/Li2O|Li symmetrical cell cycles stably for over 400 h at the current density of 0.1 mA·cm−2 and 300 h at the current density of 0.2 mA·cm−2. [Display omitted] •GeO2 additive is introduced in sintering of LLZTO electrolyte.•Microstructure is optimized by GeO2 regulation on grain boundary migration.•Consecutive Li+ conduction pathways are constructed by Li-Ge-O phase.•Wettability of Li anode on surface of electrolyte is promoted by Li-Ge-O phase.•Stable cycle of Li/electrolyte bonded interface for more than 400 h is achieved.