The effect of limonite addition on the performance of Li7La3Zr2O12

Nowadays, Li7La3Zr2O12 (LLZO) based solid electrolytes are attracting much interest because of their enhanced safety in Li-ion batteries. However, their relatively low ionic conductivity compared to liquid electrolytes is the main factor affecting the widespread use. Fe doping of LLZO could raise the ionic conductivity values to one of the highest values measured in the field of garnet type LLZO solid electrolytes. However, high purity and cost Fe2O3 is the unique iron source used in Fe doped LLZO systems. In this study, the potential use of common and cheaper iron source α-FeOOH in the form of limonite ore as a multielement containing alternative Fe source was explored. The concept of the naturally found ore usage as a stabilizing agent in LLZO is first time reported. The results showed that the limonite addition to LLZO increased the ionic behavior and densification by modifying the open and closed porosities. Higher radial shrinkage was observed with increasing limonite content. The increasing sintering time came up with an enhancement on ionic resistance and a drop on grain boundary resistance as well as DC conductivity. The LLZO composition containing 1.250 wt % limonite sintered at 1100 °C for 18 h showed the highest ionic conductivity (0.38 mS/cm) obtained within the study.