Experimental and numerical studies of slurry-based coextrusion deposition of continuous carbon fiber micro-batteries to additively manufacture 3D structural battery composites

Carbon fiber structural battery composites have recently attracted growing interests due to their potentials of simultaneously carrying mechanical loads and storing electrical energy for lightweight application. In this study, we present a slurry-based coextrusion deposition method to additively manufacture 3D structural battery composites from carbon fiber micro-batteries. Cathode slurry is coextruded together with solid polymer electrolyte-coated carbon fibers in a single deposition. A network of carbon fiber micro-batteries is achieved within the fabricated structural battery composites. Electrochemical tests show a stable charge-discharge performance up to 100 cycles. The rheological behavior of the cathode slurry is found to govern the coextrusion process and the obtained electrochemical-mechanical properties. The rheological measurements are first used to identify printability windows in terms of solid loadings and binder contents in the cathode slurry. Increasing binder contents improve the mechanical properties, with maximum 1.1 GPa and 124 GPa obtained for tensile strength and modulus, respectively, but lowers the obtained electrochemical performance. Lowering solid loadings improves printability, simultaneously increasing electrochemical capacity (by 106%) and tensile modulus (by 108%) and strength (by 40%). Further microstructural characterization shows that residual voids play a major role in the obtained electrochemical and mechanical properties. A meso-scale computational fluid dynamics simulation is used to understand void formation during the coextrusion process. The cathode slurry rheology mainly affects degree of impregnation. The findings help understand the effects of the cathode slurry on 3D printing and how to further improve multifunctional performance for electrically powered structural systems where lightweight materials are in strong demands.