The development of supercapacitors with enhanced energy and power densities has driven significant interest in nanostructured electrodes. Among fabrication methods, 3D printing offers precise control over electrode architecture, enabling tailored porosity and improved electrochemical performance. This article examines the materials, printing techniques, and structural advantages of 3D-printed nanostructured supercapacitor electrodes, along with challenges and emerging applications.

Ink formulation is critical for achieving both printability and electrochemical functionality. Graphene-based inks are widely used due to their high conductivity and surface area. A typical formulation involves dispersing graphene oxide (GO) or reduced graphene oxide (rGO) in water or organic solvents, combined with rheological modifiers such as cellulose nanocrystals or Pluronic surfactants to adjust viscosity and shear-thinning behavior. Carbon nanotubes (CNTs) are another popular additive, enhancing mechanical strength and electrical percolation networks. Hybrid inks incorporating metal oxides like MnO2 or RuO2 further improve pseudocapacitance. The balance between solid loading and printability is crucial; excessive nanoparticle concentration can lead to clogging, while insufficient loading reduces electrode conductivity. Optimal formulations often contain 5-15 wt% active material, with viscosities ranging from 10 to 1000 Pa·s for direct ink writing (DIW).

Printing techniques determine the electrode’s microstructural precision. DIW, or robocasting, is the most common method, allowing layer-by-layer deposition of viscous inks through fine nozzles (50-500 µm diameter). Shear-thinning behavior ensures smooth extrusion, while rapid solvent evaporation or gelation maintains shape fidelity. DIW excels in creating porous lattices, such as gyroid or honeycomb designs, which facilitate electrolyte penetration. Stereolithography (SLA) offers higher resolution (down to 10 µm) by photopolymerizing resin-based inks containing suspended nanomaterials. SLA-produced electrodes exhibit finer pore structures but require careful optimization of UV curing to prevent nanoparticle aggregation. Both techniques enable programmable porosity, with pore sizes ranging from 20 to 500 µm, directly influencing ion transport kinetics.

3D-printed architectures enhance supercapacitor performance through several mechanisms. Hierarchical porosity—combining macropores from printed designs with mesopores from nanoparticle packing—reduces ion diffusion resistance, leading to higher power densities. For example, electrodes with ordered pore channels exhibit 30-50% lower ionic resistance compared to conventional slurry-cast electrodes. Additionally, lattice geometries improve mechanical robustness. Triply periodic minimal surface (TPMS) structures, such as Schwarz-P designs, distribute stress evenly, enabling load-bearing capabilities in structural energy storage devices. The interplay between porosity and mechanical strength is quantified by the Gibson-Ashby model, which predicts stiffness scaling with relative density.

Despite these advantages, challenges persist in resolution, binder content, and post-processing. Nozzle-based methods like DIW face limitations in feature size, often constrained by particle agglomeration at sub-100 µm scales. Binders, necessary for ink cohesion, can hinder conductivity if not removed properly. Thermal annealing or chemical reduction steps are commonly employed to decompose organic additives, but excessive temperatures may damage nanostructures. Post-processing also affects interfacial contact between active materials and current collectors, with poorly optimized treatments leading to increased charge-transfer resistance.

Applications of 3D-printed supercapacitor electrodes span wearable electronics and structural energy storage. In wearables, lightweight, flexible electrodes conform to curved surfaces, enabling integration into textiles or skin-mounted sensors. The combination of graphene and elastomeric binders yields stretchable conductors with maintained capacitance under strain. For structural applications, carbon-reinforced composites embed energy storage within load-bearing components, such as vehicle panels or building materials. Multifunctional designs leverage the high mechanical strength of CNT-based electrodes, achieving compressive strengths exceeding 10 MPa while retaining 80-90% of electrochemical performance after mechanical cycling.

Future advancements hinge on refining ink rheology for higher-resolution printing and developing multifunctional hybrid materials. Incorporating conductive polymers or 2D materials like MXenes could further enhance capacitance while maintaining printability. Scalability remains a hurdle, as batch processing of nanostructured inks must balance cost and performance for industrial adoption. Nevertheless, 3D printing of nanostructured electrodes represents a transformative approach to supercapacitor design, merging tailored electrochemistry with advanced manufacturing.