Combining 3D Printing and Field Assisted Sintering to Process Garnet-based Solid-state Electrolyte and Composite Cathode

Garnet-based lithium-ion conductors have been investigated as a promising solid electrolyte material exhibiting superior conductivity and stability compared to sulfur- and polymer-based ones. However, the fabrication of garnet-based solid-state batteries is challenging due to the high temperature (1000-1250 ^oC) and long duration (~12 hr) necessary for densification as well as the brittle nature of ceramics when processing thin layers below millimeters. To achieve thin and dense garnet layers using an energy efficient approach, we combine two advanced manufacturing technologies, digital light processing (DLP) and field assisted sintering (FAS), to produce Li₇La₃Zr₂O₁₂(LLZO) electrolyte layer and LiCoO₂ (LCO)–LLZO composite cathode.<br/><br/>DLP is a unique 3D printing technology capable of layer-by-layer printing of multiple components in a single print [1]. In this work, we demonstrate that LLZO layer and LLZO/LCO composite cathode stacks printed with controllable solid mass loading, dimension, and composition. The ceramic prints are subsequently densified using FAS, during which an electric field is applied to the sample to create local Joule heating that aids densification to near theoretical density [2]. Using FAS, LLZO can be densified with a significantly shorter dwell time (&lt;10 min) and lower temperature (900-1100 ^oC) compared to conventional routes. DLP-printed workpieces with controlled mass and homogeneous distribution of ceramic particles also enable FAS to produce objects thinner than its traditional limit at a millimeter-scale. By establishing the DLP-FAS process flow, we produce free-standing, sub-millimeter-thick LLZO layers. The thickness is further reduced when co-sintered with LLZO-LCO composite cathode serving as a support layer. The LLZO/cathode stack is then coupled with Li metal anode and full battery performance is evaluated.<br/><br/>This DLP-FAS workflow not only saves the energy and time during sintering, but also introduces several other advantages in solid-state battery processing, including reduced number of processing steps, preservation of grain and interface structures, and minimizing interdiffusion during co-sintering of LLZO and cathode material. Using DLP, fine adjustments of layer thickness and compositions, such as multi-layer structures or graded mixtures, are also achievable. In the future, this DLP-FAS process flow will provide more opportunities to fabricate various designs and chemistries of solid-state batteries.<br/><br/>[1] Chaudhary, R., Fabbri, P., Leoni, E., Mazzanti, F., Akbari, R., & Antonini, C. (2022). Additive manufacturing by digital light processing: a review. <i>Progress in Additive Manufacturing</i>, 1-21.<br/>[2] Zhu, H., & Liu, J. (2018). Emerging applications of spark plasma sintering in all solid-state lithium-ion batteries and beyond. <i>Journal of Power Sources</i>, <i>391</i>, 10-25.