Fast and low-temperature densification of highly conductive Li7La3Zr2O12 ceramic electrolytes for solid-state batteries

Garnet-type electrolyte like Li7La3Zr2O12 (LLZO) is a promising candidate for solid-state batteries (SSBs) due to its high Li + conductivity. Obtaining a dense microstructure for their practical use typically requires 1200 degrees C, which often lead to structural issues in addition to concerns on the scale up at industrial level.In this study, we propose a two-step process to fabricate LLZO electrolytes with a high relative density under low temperature. During the first step, a high quasi-isostatic pressure of 5.5 GPa was applied at temperatures below 500 degrees C (high pressure and low temperature, HPLT), reaching a density of over 97% with absence of grain growth. Then, a brief treatment at moderate temperature below 800 degrees C was applied to promote grain growth, leading to an ionic conductivity of 3.10-4 S cm -1. A relationship between the microstructure obtained under key parameters: temperature, pressure, and time; and the ionic transport of LLZO electrolytes has been established. Besides the high ionic conductivity obtained via HPLT, stripping and plating of lithium in a symmetric cell demonstrated the practical application.This work provides guidelines on the control of the microstructure of LLZO from processing parameters and contributes to the understanding of the correlations between microstructure and conductivity.