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

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.