A MXene flexible self-supporting membrane electrode based on microchannel regulation and its preparation method and application

Abstract

The present invention discloses a MXene flexible self-supporting membrane electrode based on microchannel regulation, and its preparation method and application. First, lithium fluoride and concentrated hydrochloric acid are used as selective etchants to selectively etch the aluminum layer of MAX phase precursor Ti3AlC2, and a single-layer or few-layer Ti3C2 dispersion is obtained through centrifugal ultrasound. At this time, a template is introduced to achieve regulation of the microenvironment of the two-dimensional Ti3C2 thin electrode. Then, this MXene flexible self-supporting membrane material with rich microchannel structure is used as an independent electrode of lithium-carbon dioxide battery. The obtained electrode can provide a shorter transmission path for ion transport and improve the accessibility of electrolyte. The Li-CO2 battery prepared using this electrode has a lower polarization voltage and better rate performance than the Li-CO2 battery prepared using the unregulated Ti3C2 self-supporting membrane electrode, and the cycle performance is also significantly enhanced.

Description

Technical Field

[0001] The present invention relates to a MXene flexible self-supporting membrane electrode based on microchannel regulation, a preparation method thereof, and an application thereof in a Li-CO2 battery, belonging to the technical field of metal-gas battery catalysts. Background Art

[0002] In modern society, with the rapid development of economy and technology, human demand for energy continues to grow. Mineral fuels and fossil energy are used in large quantities, and greenhouse gases represented by carbon dioxide are continuously released, exacerbating global warming. Lithium-carbon dioxide (Li-CO2) batteries, as a technology that converts the chemical energy of carbon dioxide gas into electrical energy at room temperature and stores it, have become an important secondary battery in the "post-lithium-ion era" due to their extremely high energy density and low-carbon green characteristics. Even among many metal-air batteries, Li-CO2 batteries still have high charge and discharge potential (≈ 2.8 V) and high theoretical specific capacity (1876 Wh kg -1 )’s typical advantages.

[0003] Li-CO2 batteries have made significant progress over the past decade. However, the wide bandgap of the discharge product, Li2CO3, leads to high overpotential, poor cycling performance, weak rate capability, and low discharge capacity, severely hindering their rapid development. Cathode catalysts are key factors in increasing electrode reaction rates and reducing overpotential during charge and discharge, and are the core of achieving efficient and reversible Li-CO2 batteries.

[0004] MXene (two-dimensional transition metal carbon / nitride) possesses a unique layered structure, offering significant advantages such as hydrophilicity, high conductivity, and tunable surface groups, making it a highly promising energy storage material. However, due to its own weight and the accumulation of charge and discharge products, pristine MXene is prone to stacking and collapse. Furthermore, the inert surface functional groups lack catalytic activity, resulting in low capacity and poor rate and cycle performance in Li-CO2 battery applications. Therefore, it is necessary to load or modify surface functional groups to create additional reaction sites, create a favorable electrochemical reaction microenvironment, and enhance the battery's specific capacity. Furthermore, its unique structure provides a shorter diffusion path for ions and electrons, improving ion diffusivity and conductivity, and thus enhancing battery rate and cycle performance. Summary of the Invention

[0005] The present invention aims to provide a MXene flexible self-supporting membrane electrode based on microchannel regulation, as well as a preparation method and application thereof. By using a MXene flexible self-supporting membrane material with a rich microchannel structure as an independent electrode for a lithium-carbon dioxide battery, the present invention can address the shortcomings of current catalysts such as poor conductivity and insufficient site exposure, and solve the problems of slow reaction kinetics, high overpotential, severe polarization, and poor reversibility of lithium-carbon dioxide batteries. At the same time, it meets the requirements of lithium-carbon dioxide battery systems for low overpotential and long cycle life. In addition, the use of self-supporting membrane materials as independent electrodes can reduce the weight of the battery itself and meet the battery's requirements for flexibility.

[0006] The present invention utilizes a hard template method to micro-regulate the MXene material using an MgO template, so that the MXene material has abundant microchannels, which is beneficial to the accessibility of the electrolyte. In addition, it can stabilize the layered structure of MXene and prevent the interlayer collapse of MXene to a certain extent. At the same time, it increases the specific surface area of the MXene material, provides more active sites, and does not destroy the flexibility of the membrane material.

[0007] The present invention provides a method for microchannel control in a MXene flexible self-supporting membrane electrode. Using a simple synthesis process, a Ti3C2 flexible thin film material with a rich microchannel structure is synthesized through the manipulation of a template. The method involves selectively etching the aluminum layer of the MAX phase precursor Ti3AlC2 using lithium fluoride and concentrated hydrochloric acid as selective etchants. Centrifugal ultrasound is then used to obtain a single-layer or small-layer Ti3C2 dispersion. At this point, a template is introduced, and the type and amount of the template are controlled to achieve control of the microenvironment of the two-dimensional Ti3C2 thin electrode.

[0008] Hard templates offer high stability and excellent narrow confinement. Their use can modulate the interlayer spacing and intralayer pore size distribution of two-dimensional Ti3C2, stabilizing the interlayer structure and providing favorable reaction interfaces and transport pathways for lithium-carbon dioxide batteries. In this invention, nanoscale magnesium oxide is used as a hard template. Magnesium oxide exhibits excellent stability, is resistant to reaction with Ti3C2, and is easily removed by dilute acid, making it environmentally friendly. Nanoscale magnesium oxide particles (30-50 nm) create a unique microenvironment between Ti3C2 layers, imparting a certain degree of confinement to the two-dimensional layered structure of Ti3C2. This confines the size of discharge products and facilitates their decomposition. By using different ratios of magnesium oxide, the interlayer structure and pore size of Ti3C2 can be regulated, resulting in the preparation of Ti3C2 thin film electrodes with excellent catalytic activity and strong conductivity, endowing lithium-carbon dioxide batteries with low overpotential and excellent cycling stability. Furthermore, due to their excellent mechanical flexibility, the prepared thin film electrode can be used as a standalone positive electrode in the preparation of flexible lithium-carbon dioxide batteries, exhibiting excellent charge and discharge performance.

[0009] The present invention provides a method for preparing a MXene flexible self-supporting membrane electrode with abundant microchannels through microscopic regulation, comprising the following steps:

[0010] (1) Selective etching of precursor Ti3AlC2

[0011] Place 10-50 mL of 12 M HCl in a polytetrafluoroethylene liner, dissolve 0.8-4 g of LiF in the HCl, with a molar ratio of LiF to HCl of 1:4-1:40, and then heat and stir in a water bath to prepare a selective etchant for the Al layer.

[0012] Take 0.5-5 g Ti3AlC2 and slowly add it to the etchant. The molar ratio of Ti3AlC2 to LiF is 1:10~1:100. Then heat and stir in a water bath to fully react.

[0013] (2) Ti3C2 layering

[0014] Transfer the mixture from step (1) to a 50 mL centrifuge tube and wash it with 1 M HCl 2–3 times. Then wash it with water until the supernatant reaches neutrality, the precipitate begins to swell, and the supernatant turns dark green. Wash it with water again, then shake it well without pouring out the supernatant, and centrifuge it. After the mixture is shaken well, place it in an ice-water bath for sonication, and centrifuge it again to obtain the supernatant, which is the monolayer or few-layer Ti3C2 dispersion.

[0015] (3) Microscopic control of Ti3C2 using hard template method

[0016] Take a Ti3C2 dispersion (concentration of 10 mg / mL), add MgO to the Ti3C2 dispersion at a ratio of Ti3C2:MgO = 1:2~1:10 (mass ratio) and stir at room temperature for 24 h. Then, pickle it with 3 M glacial acetic acid, wash it with water, add ultrapure water, shake it evenly, and ultrasonicate it to obtain a micro-controlled Ti3C2 dispersion.

[0017] (4) Preparation of Ti3C2 self-supporting film

[0018] The micro-controlled Ti3C2 dispersion was filtered into a film using a vacuum filter and then dried in vacuum at 60 °C.

[0019] Application of the MXene flexible self-supporting film material obtained by the preparation method of the present invention in lithium-carbon dioxide batteries.

[0020] In the above application, the Li-CO2 button battery was assembled in a glove box with an Ar atmosphere. The electrolyte was configured with lithium bis(trifluoromethanesulfonyl)imide as the lithium salt dissolved in tetraethylene glycol dimethyl ether solvent. The battery negative electrode was a metal lithium sheet, and the diaphragm was glass fiber. The electrolyte was dripped on both sides of the diaphragm, with a total of 80-120 μl of electrolyte dripped. The MXene flexible self-supporting film was cut into discs with a diameter of 12 mm and directly used as the positive electrode. A porous metal shell was used as the positive electrode shell to facilitate the transport of CO2 gas. The assembled button battery was tested for its electrochemical performance in a high-purity CO2 atmosphere, and the test temperature was controlled at 30-35 °C.

[0021] In the above application, the Li-CO2 flexible battery is assembled in a glove box with an Ar atmosphere. The electrolyte is configured with lithium bis(trifluoromethanesulfonyl)imide as the lithium salt dissolved in tetraethylene glycol dimethyl ether solvent. The battery negative electrode is lithium foil, and the diaphragm is glass fiber. The electrolyte is dripped on both sides of the diaphragm, and a total of 20-60 μL of electrolyte is dripped. The MXene flexible self-supporting film is cut into 1*3 cm strips to directly serve as the positive electrode. Copper wire is used as the conductor, and the resulting flexible strip battery is enclosed in a heat-shrinkable insulating sleeve. Several small holes are left on the positive electrode side to facilitate the transportation of CO2 gas. The assembled flexible strip battery is tested for its electrochemical performance in a high-purity CO2 atmosphere, and the test temperature is controlled at 30-35 °C.

[0022] The principle of the present invention is as follows: a certain proportion of selective etchant is prepared to perform in-situ etching of the Al layer to obtain a single layer or a few layers of Ti3C2, and then a hard template method is adopted to use MgO as a template to expand the Ti3C2 interlayer spacing, while regulating the microstructure of Ti3C2 so that Ti3C2 has a rich microchannel structure, which is convenient for ion transport during the reaction process, and at the same time makes the Ti3C2 layer wrinkled to increase the specific surface area, thereby suppressing the interlayer collapse of the Ti3C2 reaction process to a certain extent. At the same time, the easy film-forming property of Ti3C2 is utilized to obtain a flexible, thin Ti3C2 thin film material through vacuum-assisted filtration as an independent positive electrode of the Li-CO2 battery, so that the Li-CO2 battery has good cycle stability and lower overpotential.

[0023] Optionally, the raw materials required for the preparation of the selective etchant in step (1) are LiF and HCl.

[0024] Optionally, the method used for selectively etching the Al layer in step (1) is heating and stirring in a water bath at a temperature range of 30-60°C.

[0025] Optionally, in the step (2) of layering treatment of Ti3C2, the pickling reagent is 1 M HCl, and the pickling method is high-speed centrifugation.

[0026] Optionally, in the step (2), the washing method for the layered treatment of Ti3C2 is high-speed centrifugation, and the precipitate is shaken evenly without being poured out until the precipitate expands and the supernatant is neutral.

[0027] Optionally, the step (2) is to obtain a single layer or a few layers of Ti3C2 by ultrasonic treatment in an ice-water bath.

[0028] Optionally, the step (3) is to obtain Ti3C2 after micro-control, the method used is the MgO hard template method, and the mixing method is stirring at room temperature.

[0029] Optionally, the MgO template used in step (3) is nano-scale particles with a particle size of 30-50 nm.

[0030] Optionally, the step (3) is to remove the MgO template by pickling with 3 M glacial acetic acid.

[0031] Optionally, in step (3), in order to obtain a Ti3C2 self-supporting membrane material, a single layer or a few layers of Ti3C2 dispersion is subjected to vacuum-assisted filtration treatment, and then dried at 60°C under a vacuum environment to obtain a naturally formed membrane material.

[0032] Beneficial effects of the present invention:

[0033] (1) The Ti3C2 self-supporting membrane electrode with rich microchannel structure prepared by the present invention has a significantly increased specific surface area, an increased pore volume, a significant porous structure, and an increased interlayer spacing, which can provide a shorter transmission path for ion transport and improve the accessibility of the electrolyte.

[0034] (2) The Li-CO2 battery prepared by the Ti3C2 self-supporting membrane electrode with rich microchannel structure prepared by the present invention has a smaller polarization voltage and better rate performance than the Li-CO2 battery prepared by the unregulated Ti3C2 self-supporting membrane electrode; and the cycle performance is also significantly enhanced.

[0035] (3) The Ti3C2 self-supporting membrane electrode with rich microchannel structure provided by the present invention has good flexibility and can meet the requirements of flexible batteries. In addition, the membrane electrode is light and thin, which effectively reduces the weight of the battery and has positive significance for the development of wearable devices.

[0036] (4) The experimental operation provided by the present invention is simple, low-cost, and environmentally friendly. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a scanning electron microscope (SEM) image of Ti3C2 prepared in Example 1 of the present invention;

[0038] Figure 2XRD diffraction patterns of Examples 1, 2, 3, and 4 of the present invention and Comparative Examples 1 and 4;

[0039] Figure 3 N2 adsorption and desorption curves of Examples 1, 2, 3 and Comparative Example 1 of the present invention;

[0040] Figure 4 The pore size distribution diagram of Examples 1, 2, 3 and Comparative Example 1 of the present invention is shown;

[0041] Figure 5 Graphs showing the charge and discharge performance of lithium-carbon dioxide batteries according to Examples 1, 2, 3, and 4 of the present invention and Comparative Examples 1 and 4;

[0042] Figure 6 Graphs showing the charge and discharge performance of lithium-carbon dioxide batteries according to Example 1 and Comparative Examples 1, 2, and 3 of the present invention;

[0043] Figure 7 Graph showing rate performance of lithium-carbon dioxide batteries according to Examples 1, 2, and 4 of the present invention and Comparative Example 1;

[0044] Figure 8 1 is a graph showing the cycle performance of the lithium-carbon dioxide battery of Example 1 and Comparative Example 1 of the present invention;

[0045] Figure 9 This is a graph showing the charge and discharge performance of the flexible ribbon-type lithium-carbon dioxide battery prepared in Example 1 of the present invention at a current of 20 μA. DETAILED DESCRIPTION

[0046] The present invention is further illustrated below by way of examples, but is not limited to the following examples. Example 1

[0047] S1: Place 10 ml of 12 M HCl in a polytetrafluoroethylene liner, dissolve 0.8 g of LiF in the HCl, and then heat and stir in a water bath at 45°C for 15 min to prepare a selective etchant for the Al layer.

[0048] S2: Take 0.5 g of Ti3AlC2 and slowly add the etchant, then heat and stir in a water bath at 45 °C for 24 h.

[0049] S3: Transfer the mixture prepared in S2 to a 50 ml centrifuge tube and wash it with 1M HCl 2-3 times, then wash it with water 3 times until the supernatant reaches neutrality, the precipitate begins to swell, and the supernatant turns dark green. Add 30 ml of ultrapure water again, shake well without pouring out the supernatant, and centrifuge it 3 times.

[0050] S4: After the mixture is shaken, it is placed in an ice-water bath for ultrasonication (temperature 0℃-4℃, ultrasonic frequency 80kHz) for 1 hour, and centrifuged again to obtain the supernatant to obtain a single-layer or few-layer Ti3C2 dispersion.

[0051] S5: Take 10 ml of Ti3C2 dispersion (concentration is 10 mg / ml), weigh 600 mg of MgO, add it to the Ti3C2 dispersion and stir at room temperature for 24 h.

[0052] S6: Then, the expanded Ti3C2 dispersion was obtained by acid washing with 3 M glacial acetic acid for three times and water washing for three times, adding 30 ml ultrapure water and shaking and ultrasonicating for 20 min.

[0053] S7: Use a vacuum filter to filter the Ti3C2 dispersion after MgO expansion to form a film, and vacuum dry it at 60 °C for 15 h.

[0054] In this example, LiF+HCl was used to prepare a selective etchant to selectively etch the Al layer to obtain Ti3C2. Excess etchant was then removed by pickling with dilute hydrochloric acid. Centrifugation and ultrasound were used for stratification to obtain a single-layer or few-layer Ti3C2 dispersion. The Ti3C2 interlayer spacing was expanded using the MgO hard template method, and a Ti3C2 self-supporting film was synthesized using a vacuum-assisted filtration method.

[0055] The expanded Ti3C2 self-supporting film was used as the air positive electrode, the lithium sheet was used as the negative electrode, and 80 μl of tetraethylene glycol dimethyl ether electrolyte containing lithium salt was added to form a Li-CO2 battery.

[0056] The specific surface area of the Ti3C2 self-supporting film obtained by the above method is 69.81297 m 2 g -1 (See Table 1), the MgO template can expand the interlayer spacing of Ti3C2 and micro-regulate the Ti3C2 self-supporting film, so that Ti3C2 forms abundant microchannels and a unique porous structure. At the same time, it prevents interlayer collapse to a certain extent, which is conducive to the storage of discharge products. Its unique structure provides a shorter diffusion path for ions and electrons, thereby making the Li-CO2 battery have a lower charging voltage and a smaller overpotential.

[0057] The thin film positive electrode prepared in Example 1 has good mechanical flexibility and meets the basic conditions for being used as a flexible battery, and the prepared flexible battery weighs only 0.3 g. Example 2

[0058] The same as in Example 1, except that the amount of MgO added was 200 mg and other conditions remained unchanged, a Ti3C2 self-supporting film was obtained. The Ti3C2 self-supporting film was obtained by the above method. The ratio of MgO added in this example was not optimal, and the interlayer spacing was expanded (see Table 1), but the effective specific surface area was small (38.86750 m 2 g -1 ), the pore volume is small, the discharge product storage sites are few, and the rate performance of Li-CO2 batteries is as follows Figure 7 shown. Example 3

[0059] The same as in Example 1, the amount of MgO added was 400 mg, and other conditions remained unchanged to obtain a Ti3C2 self-supporting film. The Ti3C2 self-supporting film was obtained by the above method. The proportion of MgO added in this example is not the optimal ratio. The performance of the Li-CO2 battery is as follows Figure 5 shown. Example 4

[0060] The same as in Example 1, the amount of MgO added was 800 mg, and other conditions remained unchanged to obtain a Ti3C2 self-supporting film. The Ti3C2 self-supporting film was obtained by the above method. The proportion of MgO added in this example is not the optimal ratio. The performance of the Li-CO2 battery is as follows Figure 5 and 7 shown.

[0061] Comparative Example 1:

[0062] The same as Example 1, without adding MgO, and with other conditions unchanged, a Ti3C2 self-supporting film was obtained. The Ti3C2 self-supporting film was obtained by the above method. In this comparative example, since the MgO template was not used, the interlayer spacing of Ti3C2 was relatively small, the active sites were few, and the effective specific surface area was reduced by only 34.50731 m 2 g -1 , the electron transmission path is blocked and the catalytic performance is limited, resulting in the Li-CO2 battery not having an advantage in overpotential, rate, and cycle performance.

[0063] Comparative Example 2: Similar to Comparative Example 1, 2 ml of [BMIM][TFSI] ionic liquid was added as an intercalant. The resulting TiC powder was dissolved in ethanol and drop-coated onto a 12 mm diameter carbon paper sheet to serve as the positive electrode for a button cell. The resulting material, used as a Li-CO2 air cathode, performed no better than that of Example 1 and lacked mechanical flexibility, making it unsuitable for use in flexible batteries.

[0064] Comparative Example 3:

[0065] S1: Add 2 g of [Emim]PF6 to 30 mL of 9 M HCI aqueous solution and stir magnetically for 10 min.

[0066] S2: Slowly add 1 g of Ti3AlC2 powder and stir at 50°C for 36 h. The product is washed with deionized water until the pH is 6, and then the precipitate is dried in vacuum at 80°C for 12 h.

[0067] S3: The Ti3C2 powder obtained by etching with [Emim]PF6 was dissolved in an ethanol solution and drop-coated onto a 12 mm diameter carbon paper to serve as the positive electrode for a button cell. The material obtained by this method, while slightly superior to that of Comparative Example 1, performed poorly compared to Example 1 and lacked mechanical flexibility, making it unsuitable for use in flexible batteries.

[0068] Comparative Example 4:

[0069] S1: Same as S1-S4 in Example 1, to obtain a single-layer or few-layer Ti3C2 dispersion;

[0070] S2: Dissolve 0.4 g of CuSO4 and 0.15 g of sodium citrate in 100 ml of deionized water and stir for 15 min. Then add 1.25 M NaOH and 0.03 M vitamin C to obtain a Cu2O dispersion.

[0071] S3: 10 ml of a single-layer or few-layer Ti3C2 dispersion was added to the above Cu2O dispersion and allowed to stand at room temperature for 1 h, followed by washing with ethanol and deionized water, respectively;

[0072] S4: Use a vacuum filter to filter the mixed dispersion into a membrane, and then vacuum dry it at 60 °C for 15 h.

[0073] The above method was used to obtain a Ti3C2 self-supporting film. In this comparative example, Cu2O was used for intercalation, but Ti3C2 was not expanded. The Li-CO2 battery performance was inferior to that of Examples 1, 2, 3, and 4.

[0074] Table 1

[0075]

[0076] It can be seen from Table 1 that Example 1 has the largest specific surface area and the largest pore volume, indicating its obvious porous structure.

[0077] Figure 1 This is a scanning electron microscope (SEM) image of Ti3C2 prepared in Example 1 of the present invention. It can be seen from the figure that the cross-section of the electrode material prepared in Example 1 presents an accordion morphology and has a uniform and neat layered structure, which is convenient for ion transport.

[0078] Figure 2These are the XRD diffraction patterns of Examples 1, 2, 3, and 4 of the present invention and Comparative Examples 1 and 4. It can be seen from the figure that the peak of the (002) crystal plane of Example 1 shifts to a small angle, and the corresponding interplanar spacing increases, indicating that the two-dimensional interlayer spacing is effectively expanded.

[0079] Figure 3 The N2 adsorption / desorption curves for Examples 1, 2, and 3 of the present invention and Comparative Example 1 are shown. The sample prepared in Example 1 exhibits a Type IV isotherm, indicating the presence of mesopores ranging from 2 to 50 nm. A significant hysteresis loop is observed within the higher relative pressure range (0.6-1.0), indicating the presence of a rich mesoporous structure.

[0080] Figure 4 The pore size distribution diagram of Examples 1, 2, and 3 of the present invention and Comparative Example 1 is shown. It can be seen from the figure that the pore size of the sample prepared in Example 1 is relatively concentrated around 2-50 nm, indicating the presence of abundant mesoporous and macroporous structures.

[0081] Figure 5 The charge and discharge performance diagram of the lithium-carbon dioxide battery of Examples 1, 2, 3, 4 and Comparative Examples 1 and 4 of the present invention is shown in the figure. It can be seen from the figure that at 10 μA cm -2 At a current density of , the lithium-carbon dioxide battery using the sample prepared in Example 1 as the thin film positive electrode has a smaller polarization voltage of only 0.65V in the first cycle of charge and discharge compared with other examples.

[0082] Figure 6 The charge and discharge performance diagram of the lithium-carbon dioxide battery of Example 1 and Comparative Examples 1, 2, and 3 of the present invention is shown in the figure. As can be seen from the figure: at 10 μA cm -2 At a current density of , the Li-CO2 battery using the sample prepared in Example 1 as the thin film positive electrode has a smaller polarization voltage of only 0.65V in the first cycle of charge and discharge compared with other comparative examples.

[0083] Figure 7 The rate performance diagram of the lithium-carbon dioxide battery of Examples 1, 2, 4 and Comparative Example 1 of the present invention is shown in FIG. 1 . As can be seen from the figure, at 10-100 μA cm -2 Under different current densities, the lithium-carbon dioxide battery using the sample prepared in Example 1 as the thin film positive electrode has better rate performance than other examples, even after 100 μA cm -2 After the high current density, it returned to 10µA cm -2 Even at low current density, its performance remains stable.

[0084] Figure 8 The cycle performance diagram of the lithium-carbon dioxide battery of Example 1 of the present invention and Comparative Example 1 is shown in the figure. It can be seen from the figure that at 10 μA cm -2The current density is 100µAh cm -2 Under these conditions, the Li-CO2 battery using the sample prepared in Example 1 as the thin film positive electrode has better cycle performance than that of Comparative Example 1 and can be stably cycled for about 1800h.

[0085] Figure 9 This is a charge and discharge performance diagram of the flexible ribbon-type lithium-carbon dioxide battery prepared in Example 1 of the present invention at a current of 20µA. It can be seen from the figure that the flexible ribbon-type lithium-carbon dioxide battery prepared in Example 1 can be bent and folded at different angles and has stable charge and discharge performance at a current of 20μA.

Claims

1. Application of a MXene flexible self-supporting membrane electrode in a lithium-carbon dioxide battery, characterized by: Cut the MXene flexible self-supporting film based on microchannel regulation to directly make the positive electrode; The microchannel control method of MXene flexible self-supporting membrane electrode is as follows: a Ti3C2 flexible thin film material with rich microchannel structure is synthesized through the control of template agent; The method includes using lithium fluoride and concentrated hydrochloric acid as selective etchants to selectively etch the aluminum layer of the MAX phase precursor Ti3AlC2, obtaining a single-layer or few-layer Ti3C2 dispersion through centrifugal ultrasound. At this point, a template agent is introduced, wherein the template agent is nano-magnesium oxide, and the amount of the template agent is controlled to a mass ratio of Ti3C2:MgO of 1:6, thereby achieving regulation of the microenvironment of the two-dimensional Ti3C2 thin electrode. The preparation method of MXene flexible self-supporting membrane electrode based on microchannel regulation includes the following steps: (1) Selective etching of precursor Ti3AlC2 Place 10-50 mL of 12 M HCl in a polytetrafluoroethylene-lined reactor, dissolve 0.8-4 g of LiF in the HCl, with a molar ratio of LiF to HCl of 1:4-1:40, and then heat and stir in a water bath to prepare a selective etchant for the Al layer. Take 0.5-5 g Ti3AlC2 and slowly add it to the etchant. The molar ratio of Ti3AlC2 to LiF is 1:10~1:

100. Then heat and stir in a water bath to fully react. (2) Ti3C2 layering Transfer the mixed solution in step (1) to a 50 mL centrifuge tube, acid-wash 2–3 times, then wash with water until the supernatant reaches neutrality, the precipitate begins to swell, and the supernatant turns black-green, wash with water again, then shake well without pouring out the supernatant, and centrifuge; after shaking well, place the mixed solution in an ice-water bath for ultrasonication, centrifuge again to obtain the supernatant, which is the monolayer or few-layer Ti3C2 dispersion; (3) Microscopic control of Ti3C2 using hard template method A Ti3C2 dispersion with a concentration of 10 mg / mL was added with MgO at a mass ratio of Ti3C2:MgO = 1:6 and stirred at room temperature for 24 h. The dispersion was then acid-washed with 3 M glacial acetic acid, washed with water, and then shaken and sonicated with ultrapure water to obtain a micro-controlled Ti3C2 dispersion. The MgO template was nanoparticles with a particle size of 30-50 nm. (4) Preparation of Ti3C2 self-supporting film The micro-controlled Ti3C2 dispersion was filtered into a film using a vacuum filter and then dried in vacuum at 60 °C.

2. The use according to claim 1, characterized in that: The temperature range of step (1) water bath heating is 30-60°C.

3. The use according to claim 1, characterized in that: In step (2), the pickling reagent is 1 M HCl, and the pickling method is high-speed centrifugation; the water washing method is high-speed centrifugation.

4. The use according to claim 1, characterized in that: The parameters of the ice-water bath ultrasonic treatment in step (2) are: temperature 0°C-4°C, ultrasonic frequency 60kHz-120kHz.

5. The use according to claim 1, characterized in that: Used for Li-CO2 button batteries; Li-CO2 button batteries are assembled in a glove box with an Ar atmosphere. The electrolyte is configured with lithium bis(trifluoromethanesulfonyl)imide as the lithium salt dissolved in tetraethylene glycol dimethyl ether solvent. The battery negative electrode is a metal lithium sheet, and the diaphragm is glass fiber. The electrolyte is dripped on both sides of the diaphragm, and a total of 80-120 μl of electrolyte is dripped. The MXene flexible self-supporting film is cut into discs with a diameter of 12 mm and directly used as the positive electrode. A porous metal shell is used as the positive electrode shell to facilitate CO2 gas transportation.

6. The use according to claim 1, characterized in that: Used for Li-CO2 flexible batteries; Li-CO2 flexible batteries are assembled in a glove box with an Ar atmosphere. The electrolyte is configured with lithium bis(trifluoromethanesulfonyl)imide as the lithium salt dissolved in tetraethylene glycol dimethyl ether solvent. The battery negative electrode is lithium foil, and the diaphragm is glass fiber. The electrolyte is dripped on both sides of the diaphragm, and a total of 20-60 μL of electrolyte is dripped. The MXene flexible self-supporting film is cut into 1*3 cm strips to directly serve as the positive electrode. Copper wire is used as the conductor, and the resulting flexible strip battery is enclosed in a heat-shrinkable insulating sleeve. Several small holes are left on the positive electrode side to facilitate the transport of CO2 gas.

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