Rapid fabrication of Ga-doped Li7La3Zr2O12 powder via microwave-assisted solution combustion synthesis

Garnet-type Li7La3Zr2O12 (LLZO) ceramics have been explored as solid-state electrolytes for energy conversion and storage applications. However, high Li volatility makes LLZO fabrication by conventional solid-state routes challenging. Here, a microwave-assisted solution combustion synthesis (SCS) process was developed to produce undoped and Ga-doped LLZO powders. Effects of two fuels, urea and glycine, on the kinetics of undoped LLZO SCS reactions were evaluated by IR camera imaging; peak temperatures were compared with adiabatic temperatures (T-ad) from thermodynamic calculations. When compared to glycine, urea was found to be a more suitable fuel for ensuring complete combustion and inducing a higher degree of crystallinity in the as-processed powder. Such a finding could possibly be attributed to the formation of more thermodynamically stable metal-glycine complexes, which lowers the reducing power of the fuel and decreases reaction exothermicity. X-ray diffraction analysis of powder fabricated with urea as the fuel showed that heat from the SCS reaction alone was sufficient to crystallize similar to 80% of the precursor into tetragonal LLZO; full crystallization was achieved after calcination at 950 degrees C for 5 h. Urea was subsequently employed to produce Ga-doped LLZO via SCS. As-processed powder was nearly 60% cubic LLZO; full crystallization was achieved upon calcination. Optimization of SCS reaction chemistry may enable synthesis of single-phase cubic LLZO without the need for a calcination step, greatly simplifying the LLZO fabrication process.

Automated summary

Microwave-assisted solution combustion synthesis (SCS) process was developed to produce undoped and Ga-doped LLZO powders. Urea was found to be a more suitable fuel, ensuring complete combustion and inducing a higher degree of crystallinity in the as-processed powder. Optimization of SCS reaction chemistry may enable synthesis of single-phase cubic LLZO without the need for a calcination step, greatly simplifying the LLZO fabrication process.