None-Mother-Powder Method to Prepare Dense Li-Garnet Solid Electrolytes with High Critical Current Density

Cubic Li-garnet Li7La3Zr2O12 (c-LLZO) is a promising Li+ ion conductor for applications as a ceramic solid electrolyte in next generation high safety lithium batteries. The sintering temperature of c-LLZO is usually higher than 1100 °C, where Li-loss is severe, especially in conventional air ambient sintering method. Covering the green body with "mother powder" is often adopted for compensating the Li-loss. The mother powder having the same composition as the green body cannot be repeatedly use, which raises the cost of the c-LLZO ceramics. A self-compensating Li-loss method without mother powder is proposed and investigated to prepare high-quality c-LLZO ceramics. In this method, excess lithium is added to c-LLZO green pellets to self-compensate Li-loss at high temperature. The impact of different amounts of excess Li and crucible material, such as Pt, MgO, Al2O3, and ZrO2 is studied. With optimized such sintering method, Ta doped LLZO pellets with 10% excess Li can be well sintered inside low-cost MgO crucible without mother powder at 1250 °C for only 40 min and laboratory scale production is demonstrated. The ceramics have relative densities of ∼96%, conductivities of ∼6.47 × 10–4 S cm–1 and critical current density of 1.15 mA cm–2 at 25 °C, which is fundamental for further researches on solid-state batteries.