3D Printing of Freestanding MXene Architectures for Current‐Collector‐Free Supercapacitors

Abstract

formulations that can maximize surface area accessibility and ion transport within electrodes while minimizing space and environmental impact. Consequently, Additive Manufacturing (AM) technologies, which are capable of printing 3D objects and complex structures, offer unique possibilities to bring novel electrode materials into highperformance EES devices. Among the AM technologies, continuous extrusion-based 3D printing (also called direct ink writing or robocasting) is a versatile and costeffective processing route where the formulation and properties of colloidal inks directly control the printability and architecture of printed parts. It further offers the ability to integrate functional materials of different surface chemistry and dimensionality into EES devices [1] such as Li-ion batteries, [2][3][4] micro-supercapacitors (MSCs), [5,6] and wearable electronics. [7,8] Recently, 2D transition metal carbides, called MXenes (M n+1 X n T x , with M representing an early transition metal, X representing C and/or N and, and T x representing the terminal functional groups), [9,10] have shown huge potential as electrode materials for supercapacitors. [11,12] Their combination of metallic conductivity, high density (3.8 ± 0.3 g cm −3 ), and redox active, negatively charged surfaces can lead to superior charge storage and transfer capabilities when compared to other 2D materials. Their surface functional groups (O, OH, and F) further render them hydrophilic allowing them to be easily dispersed into aqueous suspensions and inks for processing electrodes using different approaches such as vacuum filtration, [10,13] spin coating, [14,15] screen printing, [16,17] stamping, [18] and spraying. [19][20][21] While these approaches show the potential of MXene for water-based processing of EES devices, limitations remain with respect to architectural control, scalability, or cost-effectiveness that could be addressed by employing 3D printing technologies. Although MXene aqueous inks have been recently employed in commercial pens for direct writing functional films, [22] the development of 3D printable MXene inks and their integration into customized 3D device architectures is still unexplored. In order to realize this challenge, these materials need to be integrated into inks with very specific rheological properties that allow smooth flow through narrow nozzles while still enabling the extruded filaments to retain their shape even after multiple layers are Additive manufacturing (AM) technologies appear as a paradigm for scalable manufacture of electrochemical energy storage (EES) devices, where complex 3D architectures are typically required but are hard to achieve using conventional techniques. The combination of these technologies and innovative material formulations that maximize surface area accessibility and ion transport within electrodes while minimizing space are of growing interest. Herein, aqueous inks composed of atomically thin (1-3 nm) 2D Ti 3 C 2 T x with large lateral size of about 8 µm possessing ideal vis...

3D‐Printed Structure Boosts the Kinetics and Intrinsic Capacitance of Pseudocapacitive Graphene Aerogels

“…Direct ink writing (DIW) is one of the most commonly used 3D‐printing techniques. It offers great flexibility in the material (ink) selection and has been recently applied to prepare electrodes for electrochemical energy storage devices, including lithium‐ion batteries, sodium‐ion batteries, lithium–sulfur batteries, lithium metal batteries, and supercapacitors . In comparison to bulk electrodes, these 3D‐printed electrodes have shown improved electrolyte infiltration and ion diffusion …”

MXene-based 3D porous macrostructures for electrochemical energy storage

“…Although Akuzum et al study provides insights into the processability of MXenes, the development of printing procedures and ink formulations are still at the early stages; mostly producing flat re-stacked films or single printed layer arrays using techniques such as painting, writing [88], stamping [89], screen printing [90,91] and extrusion [92] and hence not fully utilizing the potentialities of printing in threedimensions. Only recently Yang et al demonstrated for the first time the possibility to print 3D MXene freestanding objects by designing inks composed solely of large, high aspect ratio MXene flakes (8 μm average lateral size and 1-3 layers) and water [93]. The inks were specifically formulated and characterised to probe their printability in 3D.…”

“…200 μm. Further, by assemblying MXenes into 3D structures with high effective porosity the specific surface area can be increased from 4 to 55 m 2 g −1 (typical of compact films made using traditional methods) to 177 m 2 g −1 (in 3D printed MXene) [93].…”

“…Porous Ti 3 C 2 T x assembled with bacterial cellulose (mass loading of 5 mg cm −2 ) showed high gravimetric and areal capacitances (416 F g −1 and 2.084 mF cm −2 , respectively at 3 mA cm −2 with 5 mg cm −2 mass loading) and excellent mechanical strength, even at high deformation [101]. Meanwhile, some promising reports have started to pave the way for MXene based 3D printed electrodes [91,93]. For example, freeze-dried extrusion printed Ti 3 C 2 T x electrodes (8.5 mg cm −2 mass loading) presented an areal capacitance of 2100 mF cm −2 with 242 F g −1 gravimetric capacitance at 1.7 mA cm −2 [93].…”

“…Meanwhile, some promising reports have started to pave the way for MXene based 3D printed electrodes [91,93]. For example, freeze-dried extrusion printed Ti 3 C 2 T x electrodes (8.5 mg cm −2 mass loading) presented an areal capacitance of 2100 mF cm −2 with 242 F g −1 gravimetric capacitance at 1.7 mA cm −2 [93].…”