Low-sintering-temperature garnet oxides by conformal sintering-aid coating

Abstract Garnet-type solid electrolytes have attracted an extensive attention for high-energy solid-state lithium batteries. However, the high processing temperature up to 1200°C with high cost limits the large-scale production. Here, we report a simple approach to reduce the sintering temperature by a conformal coating of nanoscale amorphous alumina, without sacrificing ionic conductivity. The ceramic sintered at 980°C shows a high ionic conductivity of 0.13 mS cm− 1 at room temperature. It reveals that the second phase segregated at grain boundaries can promote Li-ion transport, block electronic conduction, and improve mechanical property. The Li symmetry cells using this garnet electrolyte indicate a long-term 2500 cycle life and a high critical current density of 0.52 mA cm− 2. The garnet electrolyte enables the high-voltage cells using Li1.2Ni0.2Mn0.6O2 to deliver a high specific capacity of 248 mAh g− 1 at 0.05 C-rate. This work provides a new clue to lower sintering temperature for garnet electrolytes, which can extend to other ceramics towards practical applications.