Abstract: Miniaturized batteries are widely utilized in microscale devices, and 3D printing technology has great advantages in the manufacture of miniaturized battery electrodes. Lithium–nickel–cobalt–manganate material (LiNi_0.5Co_0.2Mn_0.3O₂) is gradually becoming a mainstream cathode material for lithium-ion batteries due to its high energy density, high rate of performance, high stability, and low cost. In this study, we prepared lithium-ion-battery electrodes using extrusion-based three-dimensional (3D) printing technology, and we selected ternary nickel–cobalt–manganese hydride as the positive active material. Subsequently, using deionized water, hydroxyethyl cellulose, and other additives, positive inks was prepared for the lithium-ion battery that exhibited stable performance and adequate 3D printing. The effects of thickener type and content, ink viscosity, and the printing process on the rheological properties and printability of the ink were investigated using a rheometer, X-ray diffraction, a battery tester, and ANSYS simulation analysis. The results show that when the mass ratio of hydroxyethyl cellulose/hydroxypropyl cellulose is 1∶1 and the mass fraction is 3%, the viscosity of the prepared ink is 20.26 Pa·s, and it shows good rheology and uniformity in printing. At present, the printing electrode has good rheology, steady ink outflow, and a smooth surface, which satisfies the printability requirements of the ink. Additionally, the simulation results show that the fluidity of the ink is significantly influenced by its viscosity. The electrode preparation process, e.g., ultrasonic dispersion, printing, or sintering, does not lead to a change in the crystal structure of the electrode material. The first-charge and discharge capacities of the electrodes are 226.5 and 119.4 mA·h·g⁻¹, respectively. After 20 cycles, the change rates of the charge and discharge capacities in the battery decrease and then tend to become stable. Lastly, the 3D printed electrode exhibits good cycle stability.