Lowering the sintering temperature of Li<sub>7</sub>La<sub>3</sub>Zr<sub>2</sub>O<sub>12</sub> electrolyte for co-fired all-solid-state batteries via partial Bi substitution and precise control of compositional deviation
Ken Watanabe, Ayumu Tashiro, Yoshihiro Ichinose, Shinichi Takeno, Koichi Suematsu, Kazutaka Mitsuishi, Kengo Shimanoe
Abstract
Li7La3Zr2O12 (LLZ) has great potential as a solid electrolyte for co-fired all-solid-state Li-ion secondary batteries. However, to realise a solid-state battery using LLZ, the sintering temperature of LLZ should be reduced to one that can suppress the formation of a high-resistance reaction layer at the interface between LLZ and the electrode. In this study, we demonstrate an effective method for reducing the sintering temperature of Li6La3ZrTaO12 by combining partial Bi-substitution for Ta and precise control of the compositional deviation. The intentional tuning of the La deficiency in Li6La3ZrTa0.8Bi0.2O12 (LLZTB0.2) promoted the formation of a liquid phase based on Li2O–Bi2O3 at the grain boundary, resulting in its densification at 775 °C. Furthermore, we fabricated a co-fired all-solid-state half-cell based on an LLZTB0.2 electrolyte attached to a LiCoO2 + LLZTB0.2 composite electrode and a half-cell operated at 60 °C. From these results, it was found that the proposed concept is effective in reducing the sintering temperature of LLZ and is applicable for co-firing an all-solid-state battery.