3D Printing of Solid-State Electrolytes for Li-Ion Batteries: Processing and Morphology Optimization

Solid-state batteries promise substantially higher energy densities and improved safety compared to traditional Li-ion batteries due to the replacement of flammable liquid electrolyte with solid-state materials. These advantages make them excellent candidates for next generation energy storage, but many processing and performance challenges must first be addressed. While several different types of solid-state electrolytes have been proposed, inorganic materials such as Li6.4La3Zr1.4Ta0.6O12 (LLZTO) have attracted much interest due to their high ionic conductivities and good mechanical and electrochemical properties. However, these materials are brittle and prone to large interfacial resistance, and many of the current fabrication techniques are difficult to scale up for manufacturing. 3D printing is an excellent tool to help solve some of these challenges, since it is scalable and capable of creating tailored architectures and compositions that can facilitate Li+ transport and reduce interfacial resistance. We report the development and optimization of ink formulations and processing conditions for 3D printed solid-state electrolytes. Since the electrolyte must be sintered after printing to densify the structure and achieve good ionic conductivity, initial particle size is an important consideration for both ink rheology and sintering success. We investigated the effect of milling solvent on particle size and lithium loss, both of which can affect the final ionic conductivity. In addition, while samples are traditionally mechanically pressed to aid densification during sintering, this technique cannot be used with printed architectures. Therefore, we explored other strategies to facilitate densification, including incorporating additional materials to act as sintering aids and optimizing ink composition and active material volume fraction. Samples were analyzed by SEM, XRD, and EIS to correlate processing and sintering conditions with electrochemical performance. Our results demonstrate significant progress toward 3D printing architected solid-state electrolytes with good ionic conductivity for high-energy-density solid-state batteries.