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

Garnet-type solid electrolytes have attracted extensive attention for solid-state lithium (Li) batteries. However, the high processing temperature of up to 1,200°C limits large-scale production. Here, we report a simple approach reduce sintering by using conformal nanoscale amorphous alumina coating. The ceramic sintered at 980°C shows room ionic conductivity 0.13 mS cm?1. It reveals that second phases segregated grain boundaries are ionically conductive but electronically blocking, which can block electronic conduction and improve mechanical property. Li symmetry cells indicate long-term 2,500-cycle life critical current density 0.52 mA cm?2. garnet electrolyte enables high-voltage Li1.2Ni0.2Mn0.6O2 deliver specific capacity 248 mAh g?1 0.05 C. This work provides new clue lowering electrolytes, extend other ceramics toward practical applications.