Design of slurries for 3D printing of sodium-ion battery electrodes

Additive manufacturing of battery electrodes, using syringe deposition 3D printing or direct ink writing methods, enables intricate microstructural design. This process differs from traditional blade or slot-die coating methods, necessitating tailored physical properties of composite slurries to ensure successful deposition. Inadequately optimised slurries result in non-uniform extrusion, and challenges such as nozzle swelling or slumping, result in compromised structural integrity of the print, limiting the resolution. This study focuses on developing slurry design principles by thoroughly characterising the rheology of several water-based hard carbon anode slurry, both in shear and extension. Hard carbon is chosen as a material of significant importance for future sodium-ion batteries, and an example for this optimisation. The slurry composition is tailored to introduce yield stress by incorporating network-forming binder (carrageenan) and additive (carbon nanotubes), effectively reducing spreading, and preserving the printed coating's structure. Validation is performed through printing a large width line and evaluating spread. The same slurry is deposited on a smaller 150 μm nozzle, which introduces die swell and spreading effects. This offers insights for further optimization strategies. The strategies developed in this research for characterizing and optimizing the rheology through formulation lay the groundwork for the advancement of detailed 3D printed electrodes, contributing to the progress of additive manufacturing technologies in the field of battery manufacturing.