Systematic review on 3D printed solid-state supercapacitors: Insights on printing techniques, materials, device performance, and architectures

The ongoing demand for miniaturized, portable, lightweight, wearable, and structural energy storage has annunciated solid-state supercapacitors as an integral technology, primarily based on their fast charge-discharge rates, high power densities, wide operating temperature range, and enduring cyclic stability. Solid-state or quasi-solid-state electrolytes have assisted in resolving typical drawbacks of aqueous and organic electrolytes (leakage, toxicity, etc.) and endowed desired mechanical properties (e.g., stiffness, flexibility, stretchability, durability) to supercapacitor devices, thus advancing the development of wearable consumer electronics and medical applications alike. These recent trends coupled with the emerging additive manufacturing technology (widely known as 3D printing) are steering the field of supercapacitor technology into new directions, enabling rapid prototyping and low-cost fabrication of supercapacitors with non-traditional form factors, utilizing various nanomaterials in composites (filaments, resins, and inks) and applying solid-state electrolytes with versatility. 3D printing techniques in device fabrication have included direct ink writing (DIW), fused filament deposition (FFF), stereolithography (SLA), and digital light processing (DLP). This systematic review summarizes the latest developments on 3D-printed solid-state supercapacitors, elaborating on the various additive technologies employed so far and highlighting their advantages and disadvantages. Special focus has been invested given on the limitations for each printing technique, employed materials for electrodes and electrolytes, device architectures and form factors, reported performance metrics, as well as proposed and possible applications.