Lawrence Berkeley National Laboratory

Tape casting is an attractive technology for the scalable manufacturing of thin lithium garnet electrolyte (LLZO) layers for solid state battery applications. Processing of LLZO is complicated by many factors including lithium volatilization, abnormal grain growth, and phase instability, which are exacerbated by high surface area to volume ratios. In this work a sintering protocol for commercially available Li6.25Al0.25La3Zr2O12 (Al-LLZO) powder was developed that requires no mother-powder covering or externally applied pressure. MgO was investigated as a sintering additive to improve density and ionic conductivity of the Al-LLZO sheets and produce a fine-grained microstructure. Al-LLZO sheets with 5 wt % MgO had densities of >90% and ionic conductivity > 2 × 10-4 S/cm. The optimized ceramic composition and sintering protocol were used to compare several tape casting binder systems. A "green"water-based system using methylcellulose as a binder was developed with green and final properties comparable to those obtained with solvent-based systems.