  Li1.5Al0.5Ge1.5(PO4)3 (LAGP) is among the most promising solid electrolytes
for the next generation all-solid-state lithium batteries. However, preparing
LAGP electrolytes is timeand energy-intensive. In this work, LAGP glassy
powders were sintered and crystallized in 180 seconds by ultrafast
high-temperature sintering (UHS) under conditions attractive for continuous
industrial processes (i.e., ambient pressure and atmosphere). The fast heating
rates characteristic of UHS significantly delay crystallization, potentially
decoupling crystallization and sintering. Furthermore, EIS characterizations
reveal that LAGP sintered and crystallized by UHS has an ionic conductivity of
1.15 10-4 S/cm, slightly lower than conventionally annealed samples (1.75 10-4
S/cm). The lower conductivity can be attributed to poorer intergrain contact.
To overcome this issue, additives such as B2O3 and Li3BO3 are used, resulting
in 2 and 5 times higher grain boundary conductivity for LAGP+1 wt B2O3 and
LAGP+1 wt Li3BO3, respectively, compared to LAGP. Overall, this work provides
insights into unraveling the impact of UHS sintering on the LAGP Li+ conduction
mechanism.
