Formation mechanism of sol-gel synthesized Li7−3xAlxLa3Zr2O12 and the influence of abnormal grain growth on ionic conductivity

The development of solid-state batteries requires the optimization of ceramic electrolyte such as garnet type cubic Li 7 La 3 Zr 2 O 12 (LLZO). Exploration of powders formation mechanism and the sintering behavior of ceramics are crucial to acquire high performance LLZO electrolytes. This study adopts quantitative analysis based on X-ray adiabatic principle to investigate the formation mechanism of Li 7 − 3 x Al x La 3 Zr 2 O 12 ( x  = 0, 0.1, 0.15, 0.2, 0.25, LALZO) powders synthesized by sol-gel method. The whole calcination procedure could be divided into three stages as follows, La 2 Zr 2 O 7 (LZO) formation (<750 °C), transformation from LZO to LLZO (750 °C–850 °C) and LLZO decomposition (>850 °C). The phase, morphology and conductivity of LALZO ceramics demonstrate abnormal grain growth (AGG) caused by over-sintering leads to random orientation and conductivity deterioration. The optimal sintering condition could not only make grains bound tightly but also avoid AGG. Ceramics consist of LALZO ( x  = 0.25) exhibit better total ionic conductivity of 3.08 × 10 −4  S cm −1 (E a  = 0.27 eV) with density of 92.5% after sintering at 1100 °C for 15 h. This research provides guidance for quickly acquiring pure LLZO powders and excellent performance ceramics.