Low-Sintering-Temperature Garnet Oxides by Conformal Sintering-Aid Coating

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 phases segregated at grain boundaries are ionically conductive but electronically blocking, which can 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.