Green and scalable synthesis strategy for garnet type solid electrolyte using in-situ thermally decomposed nanocrystalline zirconia as raw material

Garnet-type Li 7 La 3 Zr 2 O 12 (LLZO) is a premier solid electrolyte candidate, offering high ionic conductivity, a broad electrochemical stability window, and exceptional chemical stability against lithium metal. However, its performance is constrained by synthesis routes, which dictate crystal phase purity, microstructure, and Li-ion vacancy concentration. Traditional high-temperature solid-state reactions face challenges such as high sintering temperatures and potential impurities, while wet-chemical methods struggle with reproducibility and toxic gas emissions. This work introduces a green, low-cost, and industrially scalable one-step improved solid-state reaction synthesis strategy for aluminum-doped cubic-phase LLZO powders. The highly reactive intermediates of nano-crystalline zirconia with monoclinic phase are skillfully in-situ transformed from low-cost zirconium hydroxide during the thermal decomposition process and covered on the surface of lanthanum oxide particles, and the phase formation temperature is significantly reduced. Cubic phase target powders with good sintering performance are prepared at 850–900 °C, and pellets sintered at 1150–1200 °C exhibit pure garnet-type LLZO phase. The L1200 sample achieves the highest grain conductivity (9.86×10 −4 S cm −1 ) and apparent total conductivity (7.57×10 −4 S cm −1 ). Optimal sintering temperatures (1150–1200 °C) are identified based on shrinkage rate, grain size, density, and ionic conductivity. This method establishes an efficient aluminum-doped LLZO synthesis precursor engineering strategy. • LLZO solid electrolyte was prepared by a green and low-cost synthesis strategy. • Highly reactive intermediates of nano-zirconia was skillfully in-situ transformed. • Target powders with good sintering performance was prepared at low temperature. • The sample achieves a high grain conductivity and apparent total conductivity.