MXenes is an emerging two-dimensional material with high conductivity, hydrophilicity and specific capacitance. It has broad application prospects in the fields of optoelectronics, biology and energy. Their unique structure and surface functional groups make them have many excellent properties, but similar to other two-dimensional materials, their stacking and agglomeration problems greatly limit the performance of MXenes. The negatively charged MXene sheet is coated on the surface of the melamine formaldehyde resin (MF) by the intermolecular electrostatic adsorption force, and finally the nitrogen-doped porous MXene (MXene-N) is obtained by calcination, which can not only reduce the stacking of the MXene sheet. Moreover, the nitrogen-doped porous structure design is also beneficial to improve the electrochemical performance of the material. At the same time, by using direct printing technology (such as: screen printing, extrusion printing, etc.) in the construction of flexible wearable devices, personalized custom devices and other advantages, and regulate the viscosity of MXene-N based ink for 2D and 3D respectively Printing technology, an electrochemical energy storage device with high capacity printing was prepared.

[Introduction]

Recently, Professor Sun Jingyu from the School of Energy, Energy and Materials Innovation Institute of Suzhou University and Dr. Shao Yuanlong (co-communication author) of King Abdullah University of Science and Technology (KAUST) used electrostatic adsorption to bring negatively charged MXene and positively charged The MF combination, in which MF is used as a template and provides a nitrogen source, results in a porous MXene-N material. The co-first author of the thesis is Yu Lianghao, a doctoral student of the research group, and Fan Zhaodi, a master student. The inks with different viscosities of LA132 and GO were applied to 2D and 3D printing respectively. The effects of the ratio of different ink components on their rheological properties were studied and constructed into different energy storage devices. The relatively low/high viscosity MXene-N inks were prepared separately. The area capacity of the energy storage devices obtained by screen printing and extrusion printing was 70.1 mF cm−2 and 8.2 F cm−2, respectively. This electrode device, which is designed for materials and adjusts the ink concentration to suit different printing methods, provides the basis for next-generation customized energy storage applications. The related results are published in Advanced Energy Materials under the title "Versatile N-doped MXene Ink for Printed Electrochemical Energy Storage Application".

[Graphic introduction]

Figure 1: MXene-N synthesis process and its ink combined with different printing technologies



The left is a schematic diagram of the preparation process of porous MXene-N; the right is the schematic diagram of different printing techniques by adjusting the ink of MXene-N of different viscosity.

Figure 2: Structural characterization of the prepared porous MXene-N



(a, b) SEM images of MXene-N;

(c, d) TEM image of MXene-N;

(e) HRTEM images of MXene-N sheet characterization layer spacing;

(f) the HAADF image of MXene-N and the element distribution of the corresponding area;

(g) MXene XRD patterns of Etched, Exfoliated and Crumpled;

(h, i) XPS N 1s and Ti 2p spectra of MXene-N.

Figure 3: Screen-printed 2D energy storage device



(a) a process flow chart for constructing an energy storage device by screen printing;

(b) an SEM cross-section of the MXene-N electrode and an elemental distribution of Ti, C, and N;

(c-e) rheological property test of MXene-N ink;

(f, g) Print MXene-N interdigital electrodes and their corresponding different bending states on different substrates.

Figure 4: Electrochemical performance of screen-printed 2D energy storage devices



(a) Schematic diagram of a quasi-solid microcapacitor;

(b) CV curves of energy storage devices constructed by MXene-N at different sweep speeds;

(c) Comparing the area ratio capacitance of the energy storage devices constructed by MXene-N and pure MXene at different sweep speeds;

(d) MXene-N constructed energy storage device cycle capacity retention rate, the inset is the GCD curve for different cycle times;

(e, f) different bending states of the printed MXene-N device and their corresponding CV curves on the PI substrate;

(g, h) The GCD and CV curves for single, series, parallel energy storage devices were tested separately.

(i) Comparing the area capacity of other energy storage devices constructed by printing based on 2D materials.

Figure 5: 3D printed MXene-N based supercapacitor and its electrochemical performance



(a, b) preparing 3D printed ink and its printed different shapes;

(c) the rheological properties of the inks with AC/M-N and AC as the main body, and the inset is the stability test of the ink;

(d) printing electrode width statistics of different line widths by controlling the inner diameter of the needle;

(e, f) printing SEM images of different layer electrodes and element distributions of corresponding regions;

(g) controlling the area capacity of the energy storage device by printing different electrode layers, the inset is a three-electrode test physical map;

(h, i) Contrast the area capacity and area energy density of the energy storage device by 3D and 2D printing, respectively.

【summary】

This article provides an ink that can be adjusted for different viscosities and is suitable for 2D and 3D printing. By designing a nitrogen-doped porous MXene material, not only the problem of two-dimensional material sheet stacking is improved for the electrode material, but also the porous and nitrogen doping characteristics contribute to the improvement of electrochemical performance. A low-viscosity MXene-N ink was prepared and a flexible micro-superior was obtained by 2D screen printing with an area capacity of 70.1 mF cm−2. The viscosity of the slurry is further adjusted by graphene oxide and is suitable for 3D printing, and the highest area and volume energy density is 0.42 mWh cm−2, 0.83 mWh cm−3. This work provides a reasonable solution for printing multi-dimensional electrode structures and constructing high-energy-density electrochemical energy storage systems.

Literature link: Versatile N-doped MXene Ink for Printed Electrochemical Energy Storage Application (Advanced Energy Materials, 2019, DOI: 10.1002/aenm.201901839).