Free‐standing films that display high strength and high electrical conductivity are critical for flexible electronics, such as electromagnetic interference (EMI) shielding coatings and current collectors for batteries and supercapacitors. 2D Ti3C2Tx flakes are ideal candidates for making conductive films due to their high strength and metallic conductivity. It is, however, challenging to transfer those outstanding properties of single MXene flakes to macroscale films as a result of the small flake size and relatively poor flake alignment that occurs during solution‐based processing. Here, a scalable method is shown for the fabrication of strong and highly conducting pure MXene films containing highly aligned large MXene flakes. These films demonstrate record tensile strength up to ≈570 MPa for a 940 nm thick film and electrical conductivity of ≈15 100 S cm−1 for a 214 nm thick film, which are both the highest values compared to previously reported pure Ti3C2Tx films. These films also exhibit outstanding EMI shielding performance (≈50 dB for a 940 nm thick film) that exceeds other synthetic materials with comparable thickness. MXene films with aligned flakes provide an effective route for producing large‐area, high‐strength, and high‐electrical‐conductivity MXene‐based films for future electronic applications.

The discovery of liquid crystalline (LC) phases in dispersions of two-dimensional (2D) materials has enabled the development of macroscopically aligned three-dimensional (3D) macrostructures. Here, we report the first experimental observation of self-assembled LC phases in aqueous Ti 3 C 2 T x MXene inks without using LC additives, binders, or stabilizing agents. We show that the transition concentration from the isotropic to nematic phase is influenced by the aspect ratio of MXene flakes. The formation of the nematic LC phase makes it possible to produce fibers from MXenes using a wet-spinning method. By changing the Ti 3 C 2 T x flake size in the ink formulation, coagulation bath, and spinning parameters, we control the morphology of the MXene fibers. The wet-spun Ti 3 C 2 T x fibers show a high electrical conductivity of ∼7750 S cm −1 , surpassing existing nanomaterial-based fibers. A high volumetric capacitance of ∼1265 F cm −3 makes Ti 3 C 2 T x fibers promising for fiber-shaped supercapacitor devices. We also show that Ti 3 C 2 T x fibers can be used as heaters. Notably, the nematic LC phase can be achieved in other MXenes (Mo 2 Ti 2 C 3 T x and Ti 2 CT x ) and in various organic solvents, suggesting the widespread LC behavior of MXene inks.

applications because they can be integrated into textiles or be made elastic if the fiber electrodes are resilient to bending, stretching, and twisting. [7][8][9][10][11][12] To power electronics, FSCs require high electrical conductivity and high energy storage performance from the fiber electrodes. In hybrid fiber electrodes that comprise of at least one active material and a binder, these electrode properties are dependent upon the amount of active material (loading) and how well the two components are mixed. It is also important that the method of production can be made scalable and continuous. To date, however, a continuous and scalable production of fiber electrodes with high electrical conductivity and energy storage performance remains a challenge. One example of fiber fabrication is via a deposition technique that involves coating of active materials onto a conductive fiber substrate. [13][14][15][16][17][18] This method is simple and scalable to achieve FSC electrodes with active material loading of up to ≈30 wt%. [13,14] Another fiber fabrication example is biscrolling technique, which can trap active materials onto the helical corridors of carbon nanotube (CNT) sheets. [19][20][21][22][23][24][25] This method is suitable for making tens of centimeters long fiber electrodes with very high active material loadings (>90 wt%). Wet-spinning is an industrially viable approach to fiber production and has therefore attracted considerable attention for the fabrication of various FSC electrodes, such as graphene fibers, [26][27][28] CNT fibers, [29][30][31] and conducting polymer fibers. [32][33][34] In wet-spinning composite formulations containing an active material and a binder, the two components must be homogeneously dispersed to achieve "spinnablility" into long continuous fibers. Also, the two components must not limit the function of the other component particularly at high active material loading. The high conductivity and electrochemical performance of the active material must be maintained (for use as electrodes) and the binder must provide durability and flexibility (for continuous production).Ti 3 C 2 T x is one of the growing family of 2D early-transition metal carbides/carbonitrides (MXenes), which shows great promise for application in FSC electrodes. [14,35,36] Besides its high conductivity (up to 9880 S cm −1 ), [37] Ti 3 C 2 T x MXene has an exceptionally high capacitance (up to 1500 F cm −3 ) [38] that comes predominantly from the intercalation/deintercalation of H + and surface redox Fiber-shaped supercapacitors (FSCs) are promising energy storage solutions for powering miniaturized or wearable electronics. However, the scalable fabrication of fiber electrodes with high electrical conductivity and excellent energy storage performance for use in FSCs remains a challenge. Here, an easily scalable one-step wet-spinning approach is reported to fabricate highly conductive fibers using hybrid formulations of Ti 3 C 2 T x MXene nanosheets and poly(3,4-ethylenedioxythiophene):polystyrene sulfonate....

Yarn-shaped supercapacitors (YSCs) once integrated into fabrics provide promising energy storage solutions to the increasing demand of wearable and portable electronics. In such device format, however, it is a challenge to achieve outstanding electrochemical performance without compromising flexibility. Here, MXene-based YSCs that exhibit both flexibility and superior energy storage performance by employing a biscrolling approach to create flexible yarns from highly delaminated and pseudocapacitive MXene sheets that are trapped within helical yarn corridors are reported. With specific capacitance and energy and power densities values exceeding those reported for any YSCs, this work illustrates that biscrolled MXene yarns can potentially provide the conformal energy solution for powering electronics beyond just the form factor of flexible YSCs.

Textile devices have benefited from the discovery of new conductive materials and innovations in textile device design. These devices include textile-based supercapacitors (TSCs), encompassing fiber, yarn, and fabric supercapacitors, which have demonstrated practical value in powering wearable devices. Recent review articles have highlighted the limited energy density of TSCs as an important challenge, demanding new electrode materials with higher electronic conductivity and theoretical capacitance than present materials. Ti 3 C 2 T x , a member of the MXene family, is known for its metallic conductivity and high volumetric capacitance in acidic electrolytes due to its pseudocapacitive behavior. Driven by these excellent properties, recent literature has reported promising integration methods of Ti 3 C 2 T x into TSCs with significantly improved areal and volumetric capacitance compared with non-MXene-based TSCs. Furthermore, knitted MXene-based TSCs demonstrated practical application of wearable energy storage devices in textiles. Herein, the techniques used to produce MXene-based fibers, yarns, and fabrics and the progress in architecture design and performance metrics are highlighted. Challenges regarding the introduction of this new material into fiber/yarn/fabric architectures are discussed, which will inform the development of textile-based devices beyond energy storage applications. Opportunities surrounding the development of MXene-based fibers with tunable mechanical, electrical, and electrochemical properties are proposed, which will be the direction of future research efforts.