A method for preparing a laser-induced micro-supercapacitor with dimensional transformation

Abstract

The present invention specifically relates to a method for preparing a laser-induced micro-supercapacitor with dimensional transformation, and belongs to the field of micro energy storage devices. The present invention uses a simple laser reduction method to use laser waste heat to prepare a MXene-rGO-based micro-composite thin film electrode with a three-dimensional structure in one step during the shaping process of the micro-supercapacitor. The laser reduction process of graphene oxide generates a large amount of enthalpy change to trigger a multi-stage reaction, causing the electrode material layer to "explode", and realize the transformation of the thin film electrode from a two-dimensional structure to a three-dimensional structure. At the same time, there is a heterogeneous film bonding effect between MXene and the graphene sheet, which effectively prevents the electrode material from destroying the three-dimensional structure during the dimensional transformation process. The MXene-rGO film obtained by laser reduction provides a fast ion transmission channel and sufficient energy storage active sites, so that the performance of the MXene-rGO micro-supercapacitor is effectively improved. The method is simple to operate, has good repeatability and high precision. Any form of integration can be achieved to achieve different voltage and current outputs.

Description

Technical Field

[0001] The present invention specifically relates to a method for preparing a laser-induced micro-supercapacitor with dimensional transformation, and belongs to the field of micro-energy storage devices. Background Art

[0002] The popularization and application of miniaturized and intelligent electronic products has stimulated the rapid development of micro energy storage devices with electrochemical reliability and flexibility. Among them, micro supercapacitors have attracted much attention from the scientific community for their ultra-high power density, long cycle life, strong flexibility, high safety and high efficiency. However, the relatively low energy density of micro supercapacitors limits their further commercial application. Compared with in-plane micro supercapacitors, three-dimensional micro supercapacitors effectively increase the loading amount of active electrode materials per unit area and maintain a large ion-accessible specific surface area. The introduction of three-dimensional structure increases the diffusion rate of electrolyte ions, changes the ion diffusion pathway, and can also effectively improve the space utilization of electronic devices, thereby achieving higher specific energy and specific power. The construction of three-dimensional micro supercapacitors has become a general trend. Summary of the invention

[0003] In order to break through the energy bottleneck of existing micro-supercapacitors, the electrode structure of micro-supercapacitors is transformed from two-dimensional to three-dimensional. The present invention provides a method of preparing a MXene-reduced graphene oxide (MXene-rGO) micro-composite thin film electrode with a three-dimensional structure in one step by using the residual heat of the laser during the shaping process of the micro-supercapacitor with the help of a simple laser reduction method. The large amount of enthalpy change generated during the laser reduction process is used to trigger a multi-stage reaction, and the rapid release of a large amount of gas generated by the shedding of functional groups on the graphene oxide causes the "explosion" of the electrode material layer, thereby realizing the transformation of the thin film electrode from a two-dimensional structure to a three-dimensional structure. At the same time, there is a heterogeneous film bonding effect between MXene and the graphene sheet, which overlaps the loose and disordered reduced graphene oxide nanosheets during the reduction process, effectively preventing the electrode material from being damaged in the dimensional transformation process. The three-dimensional structure is obtained, and a three-dimensional MXene-rGO micro-electrode with a certain mechanical strength is obtained; in addition, the introduction of MXene with pseudocapacitive properties effectively improves the capacitance performance of the MXene-rGO micro-supercapacitor. The MXene-rGO film obtained by laser reduction provides a channel for rapid ion transmission and sufficient active sites, which effectively improves the performance of the MXene-rGO micro-supercapacitor. This method is simple to operate, fast to process, high in precision, and easy to integrate.

[0004] The present invention is achieved through the following technical solutions.

[0005] A method for preparing a laser-induced micro-supercapacitor with dimensional transition, the method comprising the following steps:

[0006] Step 1. Prepare graphene oxide dispersion using the reported Hummers method, and prepare MXene dispersion using the hydrofluoric acid etching method. Ultrasonicate and stir the mixed solution of MXene and graphene oxide to mix evenly. Then vacuum filtration is used to obtain the MXene-GO composite film. In order to ensure the quality of the membrane obtained after filtration, the concentration of the overall mixed solution is determined before filtration, and the volume of the filtration solution added is strictly controlled.

[0007] The concentration of the MXene dispersion used is 10 mg / mL to 20 mg / mL, and the concentration of graphene oxide is also 10 mg / mL to 20 mg / mL. The thickness of the obtained MXene-GO composite film is 10 μm to 20 μm.

[0008] Step 2. Prepare interdigitated micropoles with a three-dimensional framework structure using laser reduction.

[0009] After the MXene-GO composite film obtained in step 1 is naturally dried, it is peeled off from the cellulose filter membrane and fixed to a substrate. Then, with the help of laser marking in an argon atmosphere, the graphene oxide in the composite film can be reduced to reduced graphene oxide by using the energy of the laser, and a three-dimensional framework structure of interdigitated microelectrodes is obtained. The interdigitated microelectrode with a three-dimensional structure is formed by two interdigitated electrodes arranged crosswise, each interdigitated electrode has 3 to 6 interdigits, each interdigit has a width of 400 μm to 700 μm, and each interdigit has a length of 5 mm to 10 mm. The width of the interval between two adjacent interdigits in the electrode pattern with an interdigitated structure is 100 μm to 400 μm.

[0010] The degree of reduction of the obtained MXene-rGO composite film is different due to the different marking parameters and powers used in laser reduction. During the construction of the electrode, the influence of different laser parameter settings on the degree of reduction of the electrode material was studied in depth. The laser parameters are set as: speed 100-300 mm / s, frequency 20-40 KHz, Q pulse width 10-20 μs. Through red light positioning, focusing, and marking 1-5 times, a fully reduced interdigitated MXene-rGO composite film electrode (defined as MXene-rGO-J composite film electrode) can be obtained in one step.

[0011] When constructing an interdigitated microelectrode with a three-dimensional framework structure by laser reduction, it is necessary to introduce an inert protective gas into the working area of ​​the laser to protect the electrode material and prevent oxidation of the electrode material.

[0012] The thickness of the MXene-rGO composite thin film electrode structure obtained after laser reduction is 100μm to 400μm.

[0013] Step 3. The obtained interdigitated microelectrode with a three-dimensional framework structure is transferred to a polyimide tape, and copper foil is used as a lead wire at the pole ear. The conductive silver glue is used as a binder between the electrode material and the wire, and the pole ear is sealed after UV curing with green oil. Then, electrolyte is dripped on the constructed interdigitated electrode and covered with a layer of solid electrolyte film, and it is encapsulated with a plastic film to obtain a laser-induced three-dimensional micro supercapacitor with dimensional transformation.

[0014] The laser-induced three-dimensional micro-supercapacitor with dimensional transformation can realize the construction of electrodes of any shape and the integration of any number within a limited range. Under the protection of inert gas, the laser parameters are reasonably set, and the red light is positioned and marked to construct an electrode structure with a transformation from two-dimensional to three-dimensional. Lead out the wires, seal with green oil curing, drip electrolyte, cover with solid electrolyte membrane, and plastic seal. The structure of the micro-supercapacitor electrode in any combination and the packaging method are consistent.

[0015] Beneficial Effects

[0016] (1) The laser-induced construction of a three-dimensional high-energy-density micro-supercapacitor described in the present invention uses laser direct writing technology to reduce graphene oxide in one step and construct interdigitated microelectrodes. The laser thermal effect causes the interlayer spacing of the graphene sheet to "stretch" while reducing the graphene oxide, realizing the transformation of the electrode material from two-dimensional to three-dimensional. The electrode material provides a channel for rapid transmission of ions and sufficient electrochemical active sites, thereby improving the electrochemical performance of the micro-supercapacitor.

[0017] (2) In the laser-induced three-dimensional high-energy-density micro-supercapacitor described in the present invention, during the laser reduction process of the MXene-GO film, MXene plays a lap joint in the middle of the reduced graphene oxide sheet, which "grabs" and connects the loose and disordered reduced graphene oxide sheets together to form a complete MXene-rGO composite film electrode with a certain mechanical strength.

[0018] (3) The present invention uses the laser reduction method to first transfer and fix the MXene-GO composite film to a substrate, ensuring that the spacing between two adjacent interdigits on two different electrodes is consistent; the interdigital structure has a clear outline, and the device is not prone to short circuit and open circuit during the entire device preparation process, which can achieve large-scale integrated preparation. It lays a good foundation for the application and development of micro energy storage devices.

[0019] (4) The method is simple to operate, quick, reproducible and accurate. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 Schematic diagram of the processing process of the MXene-GO composite thin film electrode with interdigitated structure prepared in Example 1.

[0021] Figure 2 This is an electronic image of the MXene-GO composite film prepared in Example 1

[0022] Figure 3 This is a cross-sectional scanning electron microscope (SEM) image of the MXene-GO composite film prepared in Example 1.

[0023] Figure 4 This is a cross-sectional scanning electron microscope (SEM) image of the laser-reduced MXene-rGO composite film prepared in Example 1.

[0024] Figure 5 Scanning electron microscope (SEM) image of the reduction range of the MXene-rGO composite film reduced by laser at a certain power in Example 1

[0025] Figure 6 This is a scanning electron microscope (SEM) comparison image of the laser-reduced MXene-rGO composite film and the rGO film interdigitated microelectrode prepared in Example 1.

[0026] Figure 7 These are high-magnification scanning electron microscope (SEM) images of the cross sections of the MXene-GO composite film prepared in Example 1, the laser-reduced MXene-rGO-J composite film electrode, and the solid-phase thermally reduced MXene-rGO-L composite film electrode.

[0027] Figure 8 XPS of the MXene-GO composite film prepared in Example 1 and the laser-reduced MXene-rGO-J composite film.

[0028] Fig. 9 This is a comparison chart of the BET specific surface areas of the MXene-GO composite film prepared in Example 1, the laser-reduced MXene-rGO composite film, and the solid-phase thermally reduced MXene-rGO composite film.

[0029] Fig.10 This is the constant current charge and discharge curve of a single MXene-rGO micro supercapacitor with a three-dimensional structure prepared in Example 1.

[0030] Fig.11 This is the constant current charge and discharge curve of two series-connected MXene-rGO micro supercapacitors with a three-dimensional structure prepared in Example 1.

[0031] Fig.12 This is the constant current charge and discharge curve of two parallel-connected MXene-rGO micro supercapacitors with a three-dimensional structure prepared in Example 1.

[0032] Fig.13 This is the constant current charge and discharge curve of the 2*2 series-parallel MXene-rGO micro supercapacitor with a three-dimensional structure prepared in Example 1.

[0033] Fig.14 This is an application demonstration diagram of the 2*2 series-parallel MXene-rGO micro supercapacitor with a three-dimensional structure prepared in Example 1. DETAILED DESCRIPTION

[0034] The present invention is further described below by specific examples. Unless otherwise specified, the technical means used in the present invention are methods known to those skilled in the art. In addition, the present invention includes but is not limited to the following examples, and any equivalent replacement or local improvement carried out under the spirit and principle of the present invention will be deemed to be within the protection scope of the present invention.

[0035] In the following embodiments:

[0036] Scanning electron microscopy (SEM) images were obtained using a JSM-7001F microscope (JEOL, Japan), and XPS data were recorded using an ESCALAB 250 photoelectron spectrometer (Themo Fisher Scientific, USA) with Al Kα (1486.6 eV). X-ray diffraction (XRD) was obtained using a D8 advanced X-ray diffractometer (Bruker AXS, Germany), and the specific surface area of ​​the material was determined using a BET specific surface area tester (3H-2000PM2, China).

[0037] Electrochemical performances were obtained using a CHI 760E (Shanghai Chenhua Instrument Co., Ltd., China).

[0038] Example 1

[0039] (1) Place 80 mL of HCl solution (9 mol / L) in a polytetrafluoroethylene beaker, then add 4 g of lithium fluoride and stir until it is completely dissolved. Slowly add 4 g of Ti over 0.5 h. 3 AlC 2(MAX). Move the polytetrafluoroethylene beaker into an oil bath, stir at 35°C for 30 hours, and add 100 mL of ultrapure water to terminate the reaction. Centrifuge the reaction solution at 3500 rpm for 5 minutes, pour out the supernatant, and leave the lower precipitate. Repeat the centrifugation and washing of the lower precipitate several times until the pH value of the solution is close to neutral (pH≈5 or 6); ultrasonicate at 70% power for 1 hour, and then centrifuge at 3500 rpm for 1 hour, collect the upper clear liquid, and obtain a single-layer or few-layer MXene dispersion.

[0040] (2) Grind 9g of graphite powder and 9g of sodium nitrate thoroughly and mix them evenly for later use. Take 240mL of concentrated sulfuric acid and put it into a 2L beaker; slowly add the ground graphite powder and sodium nitrate into the concentrated sulfuric acid under continuous stirring (in an ice-water bath), and stir for 1.5h. Note that the temperature of this process should be controlled below 8°C. Then slowly add 27g of potassium permanganate to the above mixed solution, control the system temperature below 5°C, and continue stirring for 2h. Then heat it to 36-40°C and stir for 90min to control the oxidation process. Add 400mL of ultrapure water (put it in the refrigerator in advance and freeze it into an ice-water mixture). During the addition of water, the system temperature is controlled at 70-80°C. Then heat it to 90°C and maintain it for 20-40min. At this time, the color of the system will gradually change until it becomes brown-yellow. Take it out, cool it to room temperature, add 1000mL of ultrapure water, and add 60mL of 30% hydrogen peroxide while stirring. After standing for a period of time, filter it. After the original mixed solution is completely filtered, 1000 mL of dilute hydrochloric acid solution is added for acid washing. After the filtration is completed, ultrapure water is added and allowed to stand for a week to wait for graphene intercalation. The sample with good reaction intercalation is ultrasonicated and centrifuged to remove the bottom impurities. Then dialyze to remove the excess impurities, and the graphene oxide product is obtained.

[0041] (3) The mixed solution of MXene and graphene oxide is ultrasonically and stirred to mix evenly. Then, the MXene-GO composite film is obtained by vacuum filtration. In order to ensure the quality of the membrane obtained after filtration, the concentration of the overall mixed solution is determined before filtration, and the volume of the filtration solution added is strictly controlled.

[0042] (4) After the obtained MXene-GO composite film is naturally dried, it is peeled off from the cellulose filter membrane and fixed to a substrate. Then, with the help of laser marking in an argon atmosphere, the graphene oxide in the composite film can be reduced to reduced graphene oxide by using the energy of the laser, and a three-dimensional framework structure of the interdigitated microelectrode is obtained. The interdigitated microelectrode with a three-dimensional structure is formed by two interdigitated electrodes arranged crosswise. Each interdigitated electrode has 4 interdigits, each interdigit is 560μm wide, and each interdigit is 8mm long. The width of the interval between two adjacent interdigits in the electrode pattern with the interdigitated structure is 300μm. The degree of reduction of the obtained MXene-rGO composite film is different when the marking parameters and power used in the laser reduction are different. In the process of electrode construction, the influence of different laser parameter settings on the degree of reduction of electrode materials was studied in depth. The laser parameters are set as: speed 200 mm / s, frequency 40 KHz, Q pulse width 20 μs. By red light positioning, focusing, and marking once, a completely reduced interdigitated MXene-rGO composite thin film electrode (defined as MXene-rGO-J composite thin film electrode) can be obtained in one step.

[0043] When constructing an interdigitated microelectrode with a three-dimensional framework structure by laser reduction, it is necessary to introduce an inert protective gas into the working area of ​​the laser to protect the electrode material and prevent oxidation of the electrode material.

[0044] (5) The obtained interdigitated microelectrode with a three-dimensional framework structure is transferred to a polyimide tape, and copper foil is used as a lead wire at the pole ear. The conductive silver glue is used as a binder between the electrode material and the wire, and the pole ear is sealed after UV curing with green oil. Then, an electrolyte is dripped on the constructed interdigitated electrode and covered with a layer of solid electrolyte film, which is encapsulated with a plastic film to obtain a laser-induced three-dimensional micro supercapacitor with dimensional transformation.

[0045] The entire preparation process of three-dimensional micro supercapacitors is as follows Figure 1 shown.

[0046] Figure 2 The MXene-GO composite film was prepared by vacuum filtration. Figure 3 This is a scanning electron microscope image of the cross section of the MXene-GO composite film, which intuitively shows the thickness of the MXene-GO composite film, which is about 16.6μm. After laser reduction of the MXene-GO composite film, the MXene-rGO-J composite film interdigitated electrode is obtained, and its thickness has changed across orders of magnitude. From the scanning electron microscope of the cross section of the MXene-rGO-J film electrode, it can be seen that the thickness of the MXene-rGO-J film is 250μm. From a dozen microns at the beginning to hundreds of microns, the cross-dimensional change of the thin film electrode from two-dimensional to three-dimensional has been achieved.

[0047] During the laser reduction process, the degree of reduction of the electrode material varies with the power. After continuous exploration of different laser parameter settings and adjustment of the laser power, we finally selected the marking parameters with a moderate reduction degree and a relatively uniform reduction range on both sides of the marking line. Figure 5 Under this parameter setting, the width of the electrode material film on both sides that is reduced is about 600 μm, which is sufficient to achieve complete reduction of the interdigitated microelectrode.

[0048] Under the same conditions, MXene-GO composite film and GO film were laser reduced for comparison. (The laser reduced GO film is defined as rGO-J). Figure 6 It can be seen that the MXene-rGO-J interdigital electrode has clear edges and a complete structure (Figure a), while the surface of the rGO-J interdigital electrode is chaotic and rough, and the electrode has multiple fractures, and there are many scattered and disordered reduced graphene oxides between the interdigital fingers (Figure b), which is caused by the instantaneous release of some gases formed by surface functional groups during the reduction of graphene oxide. This is in sharp contrast to the composite interdigital electrode containing MXene. This strongly illustrates that MXene provides adhesion of heterogeneous sheets between reduced graphene oxide sheets and plays a role in overlapping sheets. It "grabs" the loose graphene sheets after reduction tightly together, enhancing the mechanical strength of the MXene-rGO composite film electrode. In addition, the laser-constructed MXene-rGO-J micro-supercapacitor with an interdigital structure is composed of 8 micro interdigital fingers, each of which is 8 mm long, about 570 μm wide, 250 μm thick, and 250 μm apart. The spacing between two interdigits is 250 μm.

[0049] The cross-section of the laser-reduced electrode material shows obvious structural superiority to the solid-phase thermally reduced electrode. Figure 7 The cross-sectional SEM shows that the interlamellar spacing of the laser-reduced electrode material is relatively loose, the porosity is relatively developed, and it is not a simple opening of the lamellae, but a cross-linked overlapping structure in the middle, which is formed under the synergistic effect of graphene and MXene. This structure is far superior to the dense lamellae structure of solid-phase thermal reduction.

[0050] like Figure 8 As shown, the full XPS spectrum illustrates the presence of Ti, C, and O elements. Fig. 9 The N2 adsorption / desorption isotherm test showed that the specific surface areas of the three composite materials, MXene-GO film, MXene-rGO-L film and MXene-rGO-J film, were 6.11 m 2 / g, 53.41m 2 / g, 111.57m2 / g. The specific surface area of ​​the laser-reduced three-dimensional structure electrode is about twice that of the solid-phase thermal reduction electrode, which strongly proves that the laser-reduced MXene-rGO film provides a channel for fast ion transmission and abundant active sites, providing a strong basis for improving its electrochemical performance.

[0051] like Fig.10 The MXene-rGO-J micro supercapacitor was studied by constant current charge-discharge method at 0.9 mA / cm 2 ~1.7mA / cm 2 The charge and discharge performance of MXene-rGO-J micro supercapacitor at different current densities. 2 , 1.1mA / cm 2 , 1.3mA / cm 2 , 1.5mA / cm 2 , 1.7mA / cm 2 At a current density of , the area capacitance is 71.21mF / cm 2 、65.88mF / cm 2 、62.76mF / cm 2 、60.53mF / cm 2 、57.8mF / cm 2 , showing good electrochemical performance. Fig.11 , Fig.12 , Fig.13 The GCD curves are two series, two parallel, and two series and two parallel mixed. When two micro supercapacitors are connected in series, their voltage window expands by 2 times, and the discharge time is almost the same as that of a single micro supercapacitor. When two micro supercapacitors are connected in parallel, their discharge time is twice the discharge time of a single micro supercapacitor. When two micro supercapacitors are connected in series and two in parallel, their voltage window is doubled, and their discharge time is almost doubled. The application of two series and two parallel micro supercapacitors is demonstrated as follows Fig.14 , it can provide continuous power for decorative light bottles.

Claims

1. A method for preparing a laser-induced micro-supercapacitor with dimensional transition, It is characterized in that The method comprises the following steps: Step 1. Prepare graphene oxide and MXene dispersions by Hummers method and hydrofluoric acid etching method respectively; set aside, wherein the concentration of MXene dispersion is 15 mg / mL, and the concentration of graphene oxide is 5-15 mg / mL, The mass ratio of MXene to graphene oxide is 1:0.5-3; Firstly, graphene oxide and MXene are ultrasonically treated, stirred and mixed uniformly at low temperature, and a MXene-GO composite film of MXene and graphene oxide is obtained by vacuum filtration, and then the filtered MXene-GO composite film is naturally dried in an argon environment to obtain a MXene-GO composite film; wherein the power of the ultrasonic treatment of graphene oxide and MXene is controlled at 70% to 100%, the stirring time is 2 to 4 hours, and the temperature is controlled at 10 to 15°C; Step 2. Peel off the MXene-GO composite film from the water filter membrane and transfer it to a harder substrate. With the help of laser, the graphene oxide is reduced in one step to construct interdigitated microelectrodes: The reduction degree of the electrode material obtained by different laser setting parameters is different. The electrode material is placed in the laser working area for positioning, focusing and marking. The laser marking parameters are set to a speed of 100-300 mm / s and 500-800 mm / s, a frequency of 30-50 KHz, and a Q pulse width of 10-30 μs. The electrode material is marked 1-5 times in an argon atmosphere to obtain an interdigitated microelectrode with a three-dimensional structure. Step 3. Transfer the obtained interdigitated electrode to a polyimide substrate; drip an ionic liquid as an electrolyte, cover it with a solid electrolyte film, use copper foil as a lead wire, connect the electrode material and the copper foil with a conductive silver glue, and then use green oil to cure it. After plastic sealing, a laser-induced micro supercapacitor with a three-dimensional structure and high energy density is obtained; The interdigitated electrode obtained after laser reduction is composed of 4 to 10 interdigitated fingers, each of which has a width of 400 to 700 μm and a length of 5 to 10 mm; the spacing between the interdigitated fingers is 100 to 400 μm; after the interdigitated electrode is constructed, in order to control the spacing between each interdigitated finger to remain unchanged, a tape with a certain thickness is used for pasting and transfer; the tape used is a polyimide tape, and the thickness of the polyimide tape is 150 to 250 μm; the ionic liquid electrolyte is 1-ethyl-3-methylimidazole bistrifluoromethanesulfonyl imide salt; the solid electrolyte film is P(VDF-HFP)-IL; Among them, the micro-supercapacitor with a three-dimensional structure is integrated in any shape or form; the required designed circuit is drawn using the Ray Jam drawing software, and the restored interdigitated microelectrodes with a three-dimensional structure are obtained in one step by direct laser marking; the assembly methods of three-dimensional micro-supercapacitors of any shape and any integration are the same, and the microelectrodes and microelectrode arrays are transferred to a polyimide base, with copper foil as the lead-out wire, conductive silver glue as the adhesive between the electrode material and the copper foil, green oil is used for curing and sealing, electrolyte is supplemented, and plastic film is used for packaging.

2. The method for preparing a laser-induced micro-supercapacitor with dimensional transition according to claim 1, Features: The total mass of the MXene-GO film obtained by vacuum filtration is controlled at 30-60 mg; the pore size of the water filter membrane used in vacuum filtration is 220 nm.

3. The method for preparing a laser-induced micro-supercapacitor with dimensional transition according to claim 1, Features: The MXene-GO film obtained by vacuum filtration was dried in an argon-filled environment, and the bottom of the water filter membrane was laid with filter paper, a material with good water absorption.

4. The method for preparing a laser-induced micro-supercapacitor with dimensional transition according to claim 1, Features: The thickness of the MXene-GO film obtained by vacuum filtration is 10 to 20 μm. After laser reduction, the thickness of the film is 100 to 400 μm.

Images