Large‐Area Smooth Conductive Films Enabled by Scalable Slot‐Die Coating of Ti₃C₂T_x MXene Aqueous Inks

Abstract

Large‐area flexible transparent conductive electrodes (TCEs) featuring excellent optoelectronic properties (low sheet resistance, Rs, at high transparency, T) are vital for integration in transparent wearable electronics (i.e., antennas, sensors, supercapacitors, etc.). Solution processing (i.e., printing and coating) of conductive inks yields highly uniform TCEs at low cost, holding great promise for commercially manufacturing of transparent electronics. However, to formulate such conductive inks as well as to realize continuous conductive films in the absence of percolation issue are quite challenging. Herein, the scalable slot‐die coating of Ti3C2Tx MXene aqueous inks is reported for the first time to yield large‐area uniform TCEs with outstanding optoelectronic performance, that is, average DC conductivity of 13 000 ± 500 S cm−1. The conductive MXene nanosheets are forced to orientate horizontally as the inks are passing through the moving slot, leading to the rapid manufacturing of highly aligned MXene TCEs without notorious percolation problems. Moreover, through tuning the ink formulations, such conductive MXene films can be easily adjusted from transparent to opaque as required, demonstrating very low surface roughness and even mirror effects. These high‐quality, slot‐die‐coated MXene TCEs also demonstrate excellent electrochemical charge storage properties when assembled into supercapacitors.

Roll‐To‐Roll Fabricating MXene Membranes with Ordered Interlayer Distances For Molecule And Ion Separation

“…The G'/G'' ratio of MXene dispersions shows concentration-dependency, reaching a range of 1 to 10 from 0.1 to 10 rad s −1 , indicating the membrane morphology will be maintained after the removal of the shear force. [19,21] Besides dispersion fluidics, the processing parameters, such as coating speed and groove depths of the Meyer rods, must be optimized to allow a high degree of flat and integrality control of the coated Ti 3 C 2 T x MXene membranes. Therefore, control experiments were conducted to figure out the impacts of dispersion concentration, Meyer rod groove depths, and coating speeds on the fabrication of MXene membranes.…”

“…The G’/G’’ ratio of MXene dispersions shows concentration‐dependency, reaching a range of 1 to 10 from 0.1 to 10 rad s −1 , indicating the membrane morphology will be maintained after the removal of the shear force. [ 19,21 ]…”

“…Various alternative methods, such as spray coating, drop-casting, and slot-die coating, have been proposed to fabricate large-area MXene membranes. [18,19] Spray coating uses a spray gun to deposit nanoflakes, featuring fast drying and easy scale-up. However, the spray method is hard to fabricate well-ordered laminar structures.…”

“…[12] The membranes made by drop-casting underwent natural sedimentation, producing thick membranes in several tens micrometers with no mirror effect due to the lack of shear force and less uniform deposit. [12,19] Slot-die coating is superior in the production of smooth and thin MXene membranes, showing promising potential in the large-scale fabrication of highly conductive membranes and nanofiltration. [18,19,21] However, most of the existing methods for fabricating MXene membranes are batch processes rather than continuous ones.…”

Single-to-Trilayer MXenes Enabling Kinetically Enhanced High-Energy-Density Li-Ion Capacitors

“…As a novel promising anode, MXenes with high electrical conductivity (25 000 S cm –1 ), , a low Li + -ion diffusion barrier (0.07 eV), , and a two-dimensional (2D) open structure , can probably solve the above-discussed issues. However, similar to other 2D materials, van der Waals force makes MXenes prone to restack.…”