Influence of cold sintering process on the structure and properties of garnet-type solid electrolytes

Li-stuffed garnet oxides are one of the most promising solid electrolytes for Li batteries, but their development is impeded by the overly high sintering temperature (above 1000 degrees C), which causes uncontrollable Li evaporation and poor repeatability of synthesis. The present study evaluates the possibility of addressing this issue using a recently developed technique called cold sintering process (CSP). We demonstrates that CSP can easily realize a high density of 87.7% at an extremely low temperature of 350 degrees C. However, the material becomes air sensitive after CSP, and the conductivity is degraded. Detailed structural and chemical analyses reveal that such detrimental effects arise from the inter-granular phase induced by the preferential dissolution of Al and Li. Therefore, in order to take full advantage of CSP during solid-electrolyte fabrication, the incongruent dissolution issue must be the focal point of improvement. Our results suggest that CSP is a promising solution to the overly high sintering temperature of garnet electrolytes, and deserves more attention in future studies.