Preparation of Nano- and Microstructured Garnet Li₇La₃Zr₂O₁₂ Solid Electrolytes for Li-Ion Batteries via Cellulose Templating

Lithium lanthanum zirconate (LLZO) is a promising Li⁺ ion conductor for applications as a ceramic solid electrolyte in all-solid-state lithium batteries. However, the tetragonal and cubic phases of LLZO differ in lithium ionic conductivity by several orders of magnitude with extrinsic dopants or nanostructuring often required to stabilize the high conductivity cubic phase at room temperature. Here, we show that nanostructured LLZO can be prepared by templating onto various cellulosic fibers, including laboratory Kimwipes, Whatman filter paper, and nanocellulose fibrils, followed by calcination at 700-800 °C. The effect of templating material, calcination temperature, calcination time, and heating ramp rate on the LLZO crystal structure and morphology were thoroughly investigated. Templating was determined to be an effective method for controlling the LLZO size and morphology, and low calcination times and ramp rates were found to favor the formation of small ligaments. Furthermore, it was verified that cubic phase stabilization occurred for LLZO with ligaments of size less than 1 μm on average without the use of extrinsic dopants. This work provides more information regarding the size dependence of cubic LLZO stabilization that was not previously investigated in detail, and cellulosic templating is shown to be a viable route toward the scalable, sustainable synthesis of LLZO solid electrolytes.