A novel densification model for sintering Li₇La₃Zr₂O₁₂-based solid electrolytes for all solid-state Li-ion batteries

Abstract

Improving the safety features of traditional Li-ion batteries having a flammable liquid electrolyte is one of the current challenges that scientists have been trying to overcome. Inorganic solid ionic conductors are promising option to replace the liquid electrolytes in Li-ion batteries because of their high temperature stability. But their poor ionic conductivity is one bottleneck that prevents them in a widespread use. In order to increase the ion conduction, the electrolytes should be as dense as possible since pores have no contribution to ionic conductivity. For densification assessments during sintering of Li₇La₃Zr₂O₁₂, one of the popular inorganic solid ion conductors in the field of all solid-state Li-ion batteries, the Archimedes density measurement technique has been widely used. However, the Archimedes density itself is not sufficient enough to enlighten the densification behavior of Li₇La₃Zr₂O₁₂ since closed porosities that are very common in Li₇La₃Zr₂O₁₂ microstructures cannot be wetted by the immersed liquid. In this study, a densification model which combines Archimedes density with radial shrinkage, dilatometer, and microstructure for more accurate assessment of Li₇La₃Zr₂O₁₂ densification was offered. Optical dilatometer results showed shrinkage initiation after 980 °C. Archimedes densities were initially increased from 4.24 to 4.76 g/cm³ at the early stages of sintering and then stayed constant at 4.76 g/cm³. On the other hand, radial shrinkage showed continual increase from 7.33 to 13.20% pointing out the linking of closed porosities and grain separation.