착체중합법에 의해 제조된 Li3BO3 분말이 첨가된 Li7La3Zr2O12 고체전해질의 소결특성 및 이온전도도

Abstract

All-solid-state lithium ion secondary batteries with solid-state electrolytes are drawing significant attention owing to their excellent safety, reliability, and energy density. Among solid-state electrolytes, Li7La3Zr2O12(LLZ), which has a cubic garnet structure, has a high bulk ionic conductivity and low grain boundary resistance. Additionally, it exhibits excellent thermal and chemical stability against lithium metal and commercial electrodes. In order to achieve high ionic conductivity, the densification process is critical, since porous solid-state electrolytes exhibit low ionic conductivity and undergo mechanical failure. A liquid phase sintering process is utilized for densifying LLZ at low temperatures. In this process, a sintering additive, which has a low melting point and forms a liquid phase at temperatures below the solid-phase sintering temperature, is added. In this study, Li3BO3(LBO) glass prepared by a polymeric complex method was used as a sintering additive for low-temperature sintering of garnet-type LLZ solid electrolyte. The shrinkage and wetting behaviors of the LLZ-LBO composite powder during thermal treatment were analyzed by dilatometry. The sintering shrinkage of the LLZ-LBO composite powder occurred in two stages and was related to the densification of the composite. It was also closely related to the wetting behavior of the LBO. The sintering of LLZ-LBO from approximately 700°C is driven by the viscous sintering of LBO, while sintering above 850°C is due to particle rearrangement in LLZ and the solid-state sintering of LLZ after the melting of LBO. The density of the LLZ-16wt.%LBO composite sintered for 8h at 1100°C was found to be substantially higher (88%) than that of pure LLZ(58%). The ion conductivity of the former is 1.28×10−4Scm-1 at 28°C.