Process Design for Effective Sintering of Garnet-Type Solid Electrolytes Toward High Density and Ion Conductivity

The oxide-based garnet-type eletrolytes in solid-state Li-metal batteries (SSLBs) is particularly promising, sector due to its high ion conductivity, excellent chemical, electrochemical stability when in contact with Li-metal. Since the density of solid electrolytes directly affects SSLBs compatibility with Li metals, oxide-based electrolytes are manufactured using a high-temperature sintering process. Previous studies have reported that the garnet-type electrolytes utilize mother powder, the same electrolyte as gas atmosphere control during sintering, which is reported to be capable of obtaining high density by suppressing lithium volatilization. To solve this problem, ultra-fast high temperature sintering methods have recently been reported, but there is a problem that it is difficult to apply to the realization of solid-state batteries due to high equipment costs and difficulty in mass production. In this study, powder pretreatment and oxygen atmosphere control during sintering were used as strategies and approaches to fabricate high-quality Li_6.4La₃Zr_1.4Ta_0.6O₁₂ (LLZT) solid electrolyte. This aims to develop efficient sintering process technology that can commercialize solid electrolytes. First, manufacturing costs were reduced by using a pressureless sintering method that enables mass production when sintering solid electrolytes and minimizing mother powder, and second, the collapse of the crystal structure and density reduction due to lithium volatilization at high temperatures were suppressed. Under these optimized sintering conditions, an LLZT solid electrolyte was produced with a high relative density of 97 %, ion conductivity of 5.88 x S/cm^-4, and critical current density (CCD) of 1.0 mA/cm². Therefore, this study will discuss the effects of the sintering process through optimized sintering atmosphere and solid electrolyte particle treatment on electrolyte properties and sintering behavior. The technology described in this study has significant potential to upgrade the high-quality solid electrolyte fabrication technology without using expensive equipment, and can greatly reduce the unit cost of materials and improve the efficiency of the electrolyte-membrane process in the battery field. These advances contribute to the further development and commercialization of solid-state battery technology.