Synthesis of a low Li to Zr mole ratio of lithium lanthanum zirconate Li0.5xLa0.5xZr1−xO12−δ

Abstract

In this research, a low mole ratio formula Li to Zr of Li_0.5xLa_0.5xZr_1−xO_12−δ(LLZO*) with various x = 0.1, 0.3, and 0.6 was synthesized. The research aims to understand the crystal structure and the electrochemical properties of the new formula of Li_0.5xLa_0.5xZr_1−xO_12−δ, in which the Li to Zr mole ratio is smaller than the common cubic garnet of Li₇La₃Zr₂O₁₂ (LLZO). A different sintering treatment was also applied to understand whether the material properties are only a matter of chemical formula or are also affected by the sintering method. The first sintering method was firing at 1230 °C for 6 h under air to produce LLZO*(A), and the second method was firing at 900 °C for 6 h under Ar flows to produce LLZO*(B). The XRD analysis found that the LLZO*(A) was crystallized mainly to tetragonal structure, and cubic pyrochlore secondary phase, with a small amount of cubic structure. Meanwhile, the LLZO*(B) was crystallized mainly into cubic and tetragonal structure. The impedance analysis found that LLZO*(B) shows a higher ionic conductivity than LLZO*(A), i.e., 7.573 × 10⁻⁵ S.cm^−1. A full-cell impedance measurement of LiFePO₄-LLZO*(B)-mcmb shows that LLZO*(B) x = 0.1 has the lowest Li⁺ migration resistance of 223.8 Ω confirming the promising material for solid electrolyte.