Over the last decade there has been a sizeable effort within the battery community to improve upon the safety and performance of conventional Li-ion batteries to satisfy market demand. A large fraction of that effort has been devoted to solid-state garnet-type Li-conducting electrolytes, due to their inherent nonflammability, relatively high Li⁺ conductivity (~1 mS/cm), and stability to both lithium metal anodes and high voltage cathodes. Recently, improved materials properties and a paradigm shift in electrolyte microstructure have begun to make solid-state electrolytes competitive with liquid electrolyte counterparts in terms of performance [1,2]. Specifically, researchers have demonstrated 3 mA/cm²current density in Li|LLZ|Li symmetric cells and successfully cycled full cells using a porous-dense-porous multilayered LLZ solid electrolyte framework which dramatically reduces the bulk and interfacial impedance of the battery and increases the energy density by reducing excess electrolyte materials [2]. It is clear then that the solid electrolyte microstructure can have a substantial impact on cell electrochemical performance. However, the effect of the electrolyte microstructure on the cell properties has yet to be investigated, properties which are critical to ensuring high battery performance, long-lifetime of the battery and tolerance to abuse. An optimized solid electrolyte microstructure will need to balance electrochemical and mechanical properties for a marketable battery design.

In this work, we utilize 3D-printing to rapidly explore the relationship between solid electrolyte microstructure and resulting electrolyte and cell properties (e.g. mechanical strength). Specifically, we 3D-print a variety of different solid electrolyte geometries, including columns (Figure 1), grids, and stacked geometries using recently developed LLZ inks, and correlate the structure type and characteristics (e.g., aspect ratio) with properties of the electrolyte. First, we investigate the properties of the 3D-printed solid electrolyte itself, followed by a study including infiltration of electrode materials which is more representative of the final battery design. This study will help inform the best solid electrolyte microstructure, ensuring the structure of solid-state batteries will be suitable for a wide variety of real-world applications.

[1] J. van den Broek, S. Afyon, J. L. M. Rupp, Adv. Energy Mater., 2016, 6, 1600736.

[2] G. T. Hitz, D. W. McOwen, Y. Wen, Y. Gong, J. Dai, X. Han, T. R. Hamann, A. L. Ruth, P. C. Latorre, L. Hu, E. D. Wachsman, submitted.

Figure 1. 3D-printed LLZ columns.