With the rapid advancement of technology, electronic devices are increasingly demanding lightweight, high-efficiency, and customizable energy-storage solutions. From smartwatches to drones, and from wearable devices to intelligent sensors, the “miniaturization” of energy storage has become a key focus in technological R&D. Among numerous emerging materials, MXene has emerged as a rising star thanks to its outstanding conductivity, high specific capacitance, and tunable properties. Nevertheless, effectively, stably, and precisely integrating MXene into micrometer-scale manufacturing processes remains a significant challenge.

A recent study published in Small Methods has pioneered a stable Ti₃C₂Tₓ MXene ink formulation and, by integrating aerosol jet printing (AJP), has enabled the fabrication of high-resolution, high-performance micro-supercapacitors, thereby opening up new possibilities for fields such as microelectronics and energy storage.

MXene

1. Basic Introduction to MXene

MXenes are a class of materials composed of two-dimensional transition-metal carbides, nitrides, or carbonitrides, featuring a layered structure, such as Ti₃C₂Tₓ.

Composition: Primarily composed of elements such as Ti and C, these materials are obtained by selectively removing “bulk” elements (e.g., Al) from MAX-phase compounds via a specialized chemical process, resulting in ultrathin two-dimensional layers.

Features:

High electrical conductivity: similar to metals, making it suitable for use as electrode materials.

High specific surface area: provides a large number of active sites.

Excellent mechanical flexibility: facilitates the preparation of thin films.

Tunable Surface Functional Groups (Tₓ): Influencing the Electrochemical Performance and Stability of Materials

2. Working Principle of MXene

Conduction mechanism: The metallic carbide layers in the layered structure exhibit extremely high electron mobility, enabling efficient current conduction.

Energy storage: In supercapacitors, surface functional groups on MXene—such as carboxyl and hydroxyl groups—can effectively store positive and negative ions during charge–discharge cycles, enabling rapid charge accumulation and release. This makes MXene an ideal electrode material, offering both high capacitance and high efficiency.

Why is a stable MXene ink necessary?

1. Sticky Problems and Stability Challenges

Highly Oxidizable: MXene materials are highly susceptible to oxidation in air, which can compromise their conductivity and energy-storage performance.

Poor rheological properties: Traditional MXene solutions exhibit unstable viscosity, making it difficult to meet the requirements of printing processes.

Storage challenges: Once oxidized or precipitated, the ink’s performance degrades sharply, making long-term storage difficult.

2. Limitations of the Current Solution

The use of complex additives or organic solvents (such as NMP and DMSO) can introduce toxicity and environmental concerns.

Drying at high temperatures may damage the structure of MXene, resulting in a loss of controllability at high resolution.

3. Breakthroughs of this work

Through meticulous formulation, the research team has developed an MXene ink with outstanding chemical and physical stability. While maintaining optimal rheological properties, this ink significantly extends its shelf life, minimizes oxidation, and ensures continuous, high-quality performance during aerosol jet printing.

Working Principle and Advantages of Aerosol Jet Printing (AJP)

1. Aerosol Jet Printing (AJP)

Brief process description: The ink is atomized into a fine aerosol and propelled onto the substrate surface by a carrier gas, forming precise lines and patterns.

Ultra-high resolution: down to the 1-micrometer level, meeting the requirements of modern microelectronic manufacturing.

Advantages:

Non-contact: does not damage the substrate

High precision: facilitates the fabrication of micrometer-scale structures.

Multi-layer application: can be sprayed multiple times to adjust the thickness.

Suitable for a wide range of rigid or flexible substrates.

2. Specific Work Process

Preparation of metal nanoparticles (such as gold) as a conductive underlayer

Curing the conductive layer through heat treatment.

Preparation of subsequent MXene inks

Aerosol jet printing is employed to achieve precise deposition onto the conductive underlayer, thereby forming the electrode.

Suspension and multilayer stacking to form a miniature supercapacitor.

3. Why choose aerosol jet printing (AJP)?

High-Resolution Manufacturing

Suitable for complex geometric structures in microelectronics

Precisely control the probability of the wet-dry interface to minimize material waste.

Can be prepared on a variety of substrates, such as ceramics and plastics.

Why Choose MXene + Aerosol Jet Printing (AJP) Technology?

High Performance: High Energy Capacity, Fast Charge/Discharge, Long Cycle Life

High-Resolution Manufacturing: Micron-Level Precision Control

Simple process: suitable for large-scale, low-cost production.

Broad application potential: applicable across fields from microelectronics to flexible electronics.

Promising Future: Continuous Material Optimization and Equipment Upgrades Open Up Vast Prospects

Application Prospects

1.

Microelectronic devices: such as smart patches and wearable devices

Microsensors: Power Supplies for Temperature and Humidity, Gas, and Pressure Sensors

Smart Labels and IoT Devices: Enabling Thin, Integrated Energy Solutions

Flexible Electronics: Bendable and Rollable Energy Storage Devices

2.

Micro-scale Energy Storage: Advancing Toward Miniaturization, Complex Architectures, and Multifunctionality

Large-Scale Flexible Manufacturing: Integrating Roll-to-Roll Printing to Enable Large-Area, Low-Cost Production

Integrated Intelligent Systems: Achieving the Integration of Energy, Sensing, and Processing to Advance the Development of Smart Electronics

Research and Development of Novel MXene Materials: Optimizing Conductivity, Capacity, and Stability to Expand Application Frontiers

Environmental protection and sustainable development: non-toxic, easy to prepare, and aligned with the principles of green manufacturing.

Illustrated Guide

Figure 1. Schematic illustration of aerosol jet printing (AJP) of MXene supercapacitors on polyimide. 1) Gold nanoparticle ink was prepared based on our previous work. 2) The gold ink was aerosol jet printed onto a polyimide substrate. 3) The printed gold was annealed at 350°C. 4) Ti3C2Tx MXene ink was prepared. 5) The MXene ink was aerosol jet printed on top of the annealed gold current collector. 6) The SCs were annealed in an Ar/N2 atmosphere at 250°C for 2 hours.

Figure 2. Material and Ink Properties.

Figure 3. High-resolution printing and the electrical properties of printed MXene. a) Optical images of complex structures printed on a sapphire substrate, demonstrating the high-resolution printability of MXene ink and the capability of aerosol jet printing (AJP) to fabricate small-scale, intricate features. b and c) High-magnification micrographs of the same complex structures printed on a sapphire substrate, corresponding to the structures shown in (a). d) Optical images of MXene ink printed on an alumina tube with an inner diameter of 1 cm, highlighting the conformal printing capability of aerosol jet printing (AJP). e) Schematic illustration of the transmission-line measurement (TLM) method performed on a glass substrate, showing MXene ink printed at different numbers of layers (1, 2, and 3) and gold contact pads with lengths of 2 mm, 3 mm, 4 mm, 5 mm, and 6 mm. f) Cross-sectional scanning electron microscope images of MXene ink printed three times on a silicon substrate. g) Profile analysis of MXene ink printed once, twice, and three times on a glass substrate, illustrating the variation in film thickness. h) I–V curves for three-layer-printed MXene ink. i) Plot of resistance versus channel length for the printed TLM structure. j) Conductivity and resistivity as functions of the number of printing layers, demonstrating the impact of the number of printed layers on electrical performance.

Figure 4. Electrochemical performance of Ti3C2Tx supercapacitors printed in a NaClO4/PC organic electrolyte. a) Comparison of cyclic voltammetry (CV) curves for one-, two-, and three-layer printed electrodes at a scan rate of 100 mV s−1. The three-layer MXene supercapacitor exhibits a larger CV area. b) Comparison of galvanostatic charge–discharge (GCD) curves for one-, two-, and three-layer printed electrodes at a current of 150 μA. c) Area-specific capacitance calculated from the GCD curves of the single-, double-, and triple-layer three-electrode assemblies at various currents. d) Cyclic stability of the three-layer aerosol-jet-printed (AJP) MXene supercapacitor over 10,000 cycles at a current of 150 μA. The inset shows the GCD curves at different cycle numbers, illustrating the device’s capacitive behavior. e) Nyquist plots of the three-layer MXene supercapacitor before and after 10,000 GCD cycles at a current of 150 μA. f) CV curves of the three-layer MXene supercapacitor at a scan rate of 100 mV s−1 over a range of potential windows from 0.4 to 2 V, used to optimize the operating potential window. g) Area-specific capacitance values calculated from the CV curves obtained at different voltage windows. h) Cyclic voltammetry curves at a potential window of 1.6 V with scan rates of 5, 10, 20, 40, 50, 80, and 100 mV s−1. i) Galvanostatic charge–discharge curves at a potential window of 1.6 V and currents of 10, 20, 40, 60, 80, 100, and 150 μA, demonstrating how expanding the voltage window enhances supercapacitor performance.

Figure 5. Electrochemical performance of the three-layer printed Ti3C2Tx supercapacitor in an aqueous H2SO4–PVA gel electrolyte. a) Cyclic voltammograms recorded at scan rates of 5, 10, 20, 40, 50, 80, and 100 mV s−1. b) Galvanostatic discharge curves recorded at different current densities (10, 20, 40, 60, 80, 100, and 150 μA). c) EIS results in the aqueous electrolyte. The inset shows an optical image of the MXene supercapacitor on a polyimide substrate. d) Cyclic stability of the aerosol-jet-printed MXene supercapacitor over 2000 cycles at a current of 150 μA. The inset displays the galvanostatic discharge curves, highlighting the capacitance retention at different cycle numbers. e) Nyquist plots recorded every 200 galvanostatic discharge cycles, from 200 to 1800 cycles, providing insights into the electrochemical performance in the aqueous electrolyte. f) Cyclic voltammograms recorded under different bending states: 0°, 45°, 60°, and 90°. The inset shows a photograph of the MXene supercapacitor on a polyimide substrate bent at 60°. g) Photograph of a 2×2 array of MXene supercapacitors (configured as 2S2P), comprising three printed MXene layers. h) Cyclic voltammograms measured at a scan rate of 100 mV s−1 for various configurations, including two devices in series (2S), two devices in parallel (2P), and a 2×2 device array (2S2P). i) GCD curves corresponding to the same configurations (2S, 2P, and 2S2P) at a current of 150 μA. Figure 6. a) An optical image of a high-resolution MXene (HR-MXene) ultrathin capacitor on a polyimide substrate. Magnified views of selected regions highlight uniform ink deposition and fine printing features. b) Profile measurement analysis along the fingers of the ultrathin capacitor shown in (a). The average thickness of the Au/MXene ultrathin capacitor is 1.75 μm, with the Au current collector layer measuring 0.5 μm and the average thickness of the MXene layer topping it being 1.25 μm. The thickness distribution of the Au current collector layer is shown in Figure S16 (Supporting Information). c) Variation in line width along the printed fingers, corresponding to (b). Line-width measurements were taken at a thickness of 0.5 μm, excluding the Au layer. d) Cyclic voltammograms of the HR-MXene ultrathin capacitor at different scan rates. e) Galvanostatic curves of the HR-MXene ultrathin capacitor at different current densities. f) Optical image of a high-resolution 22-array, with magnified views of selected regions. g) Comparison of areal capacitance with MXene39 printed by inkjet and extrusion in gel electrolyte in this study, demonstrating the superior performance of the aerosol-jet-printed MXene ultrathin capacitor. h) Comparison of the volumetric capacitance of this material in this study with that of MXene39 printed by inkjet (IJP) in gel electrolyte, confirming the higher C/V ratio of aerosol-jet-printed MXene. i) Comparison of the areal capacitance of aerosol-jet-printed MXene with previously reported supercapacitors (SC). j) Comparison of the volumetric capacitance of aerosol-jet-printed MXene with previously reported SCs. EP-MX: extrusion-printed MXene; IJP-MP/PH1000: inkjet-printed MXene/PH1000; IJP-MX: inkjet-printed MXene; IJP-G: inkjet-printed graphene; SM-G/MX: spray-masked graphene/MXene; SC-G/MX: spray-coated graphene/MXene; SC-G/PEDOT: spray-coated graphene/PEDOT; SCLCMX/rG: spray-coated and laser-cut-masked MXene/reduced graphene; IJP-EEG: inkjet-printed electrochemically exfoliated graphene; G-Q Dot: graphene quantum dots; SC-G: spray-coated graphene; SCLCMX: spray-coated and laser-cut-masked MXene; ScM-MX: scraped MXene; Transparent-MX: transparent MXene.

This study not only addresses the challenges of MXene ink stability and printability but also highlights the tremendous potential of aerosol jet printing (AJP) in the fabrication of micro-scale energy devices. As the technology continues to advance and its application scenarios expand, it is anticipated that, in the near future, micro-supercapacitors will play a pivotal role in portable electronic devices, sensor networks, and miniaturized energy-storage systems, thereby driving the lightweighting, high performance, and high integration of smart devices.