Method of in-situ growth of coating on aluminum surface, aluminum foil, aluminum-based current collector, electrode, and battery

Abstract

The application discloses a method for growing a coating on an aluminum surface in situ, aluminum foil, an aluminum-based current collector, an electrode and a battery, wherein the method comprises: covering the surface of metal aluminum or an aluminum alloy with a MXene material, and then performing a heating treatment at a predetermined temperature; the functional groups of the MXene material contain one or more of F, Cl, Br or I. The method provided by the application can form a coating containing a MAX phase material on the surface of aluminum or an aluminum alloy in situ, the MAX phase material is a kind of ceramic, has the advantages of high conductivity and corrosion resistance, and the formed coating improves the corrosion resistance of the surface of aluminum or the aluminum alloy.

Description

Technical Field

[0001] This invention belongs to the field of secondary batteries, specifically relating to a method for in-situ growth of a coating on an aluminum surface, an aluminum foil, an aluminum-based current collector, an electrode, and a battery. Background Technology

[0002] Secondary batteries can convert electrical energy and chemical energy into each other, making them ideal energy storage devices. Among them, lithium-ion and sodium-ion batteries have seen significant development in recent years due to their high energy density, high output power, and environmental friendliness. Lithium-ion batteries are now commercialized, particularly as power batteries in electric vehicles. Furthermore, sodium-ion batteries have also achieved breakthrough developments, and their commercial application is imminent.

[0003] With the commercialization of lithium-ion and sodium-ion batteries, many technical problems have emerged. Among them, a significant one is the degradation of energy density, which leads to a decrease in stored and released electrical energy, and in severe cases, directly causes battery failure. Currently, both lithium-ion and sodium-ion batteries use aluminum-based current collectors (aluminum foil) as the positive electrode. However, because these current collectors are easily corroded by fluorine-containing electrolytes and the HF produced by their decomposition within the battery, this will lead to a decrease in battery performance or even failure.

[0004] To address the issue of aluminum-based current collectors being easily corroded by HF, a carbon coating is typically applied to their surface (carbon coating), resulting in carbon-coated aluminum foil. The carbon materials in the coating mainly include carbon black, graphite flakes, and graphene. The carbon material powder is mixed with a film-forming agent, solvent, and additives to form a slurry, which is then coated onto the aluminum foil surface and dried to form a dense carbon coating layer. Compared to blank aluminum foil, carbon-coated aluminum foil increases the adhesion between the positive electrode material and the current collector, thus improving the conductivity of the positive electrode and reducing the battery's internal resistance. However, since the bonding force between the carbon coating and the aluminum foil is mainly achieved through the adhesive effect of the binder in the slurry, and the binder is a non-conductive material, adding the binder will reduce the conductivity of the aluminum foil to some extent. Furthermore, due to the weak bonding force between the carbon coating and the aluminum foil, the carbon coating may peel off, leading to the exposure of the aluminum foil surface for corrosion and affecting the battery's cycle performance. Summary of the Invention

[0005] This invention addresses the technical problem of easy corrosion of aluminum-based current collectors in lithium-ion and sodium-ion batteries by providing a new coating and its preparation method.

[0006] The first aspect of the present invention provides a method for in-situ growth of a coating on an aluminum surface, the method comprising the steps of: covering the surface of metallic aluminum or aluminum alloy with MXene material, and then performing heat treatment at a predetermined temperature; wherein the functional groups of the MXene material contain one or more of F, Cl, Br or I.

[0007] In some embodiments, the functional groups of the above-mentioned MXene material contain one or more of Cl, Br, or I.

[0008] In some embodiments, the method of coating the surface of aluminum or aluminum alloy with MXene material more specifically includes: spraying and / or coating the surface of the aluminum or aluminum alloy with MXene dispersion, followed by drying.

[0009] In some embodiments, the method of coating the surface of aluminum or aluminum alloy with MXene material more specifically includes: immersing the aluminum or aluminum alloy in an MXene dispersion, lifting it several times, and then drying it.

[0010] In some embodiments, the method of coating the surface of aluminum or aluminum alloy with MXene material more specifically includes: coating the surface of the aluminum or aluminum alloy with MXene powder.

[0011] In some embodiments, the concentration of the MXene dispersion is between 0.1 mg / ml and 500 mg / ml.

[0012] In some embodiments, the MXene dispersion described above comprises MXene material and solvent.

[0013] In some embodiments, the MXene dispersion described above is composed of MXene material and solvent.

[0014] In some embodiments, the solvent in the MXene dispersion described above is water and / or an alcohol.

[0015] In some embodiments, the chemical formula of the above-mentioned MXene material is represented as M n+1 X n T x , where 1≤n≤4, where M is selected from one or more transition metal elements; T represents a functional group element, and X is selected from one or more carbon, nitrogen, and boron elements.

[0016] In some embodiments, the aluminum or aluminum alloy described above is in the form of foil or sheet.

[0017] In some embodiments, the temperature of the above-described heat treatment is between 178°C and 660°C; more preferably, between 200°C and 600°C; and even more preferably, between 400°C and 600°C.

[0018] In some embodiments, the heating time is between 0.01 min and 48 h; preferably, between 1 min and 12 h; more preferably, between 1 min and 1 h.

[0019] A second aspect of the present invention provides a coating obtained by the above-described method.

[0020] In some embodiments, the thickness of the coating is between 0.3 nm and 10 μm; more preferably, between 1 nm and 5 μm; and even more preferably, between 1 nm and 1 μm.

[0021] In some embodiments, the coating contains a MAX phase material.

[0022] In some embodiments, the coating contains MAX phase material and MXene material.

[0023] In some embodiments, the X-ray diffraction (XRD) pattern of the coating contains the (002), (004), (104), and (110) crystal planes of the MAX phase material.

[0024] In some embodiments, the elemental analysis characterization results of the above coating show that it includes transition metal elements, aluminum, carbon and / or nitrogen.

[0025] A third aspect of the present invention provides an aluminum foil comprising an aluminum substrate and the coating described above.

[0026] A fourth aspect of the present invention provides an aluminum foil comprising an aluminum substrate and a coating comprising a MAX phase material.

[0027] In some embodiments, the X-ray diffraction (XRD) pattern of the coating contains the (002), (004), (104), and (110) crystal planes of the MAX phase material.

[0028] In some embodiments, the elemental analysis characterization results of the above coating show that it includes transition metal elements, aluminum, carbon and / or nitrogen.

[0029] In some embodiments, the coating is obtained by heat-treating the MXene material covering the surface of the aluminum substrate at a predetermined temperature; preferably, the heat treatment temperature is between 178°C and 660°C; more preferably, between 200°C and 600°C; and even more preferably, between 400°C and 600°C.

[0030] In some embodiments, the elemental analysis and characterization results of the aluminum foil above also include halogen elements; preferably, the halogen elements are Cl, Br, and I.

[0031] The fifth aspect of the present invention provides an aluminum-based current collector, wherein the aluminum-based current collector is coated by the above-described method; or, the above-described coating.

[0032] In some embodiments, the aluminum-based current collector is the aluminum foil described above.

[0033] A sixth aspect of the present invention provides an electrode comprising the aluminum-based current collector described above.

[0034] A seventh aspect of the present invention provides a battery comprising the electrodes described above, or the aluminum-based current collector described above.

[0035] The beneficial technical effects of this invention are as follows:

[0036] The method proposed in this invention can grow a coating containing MAX phase material in situ on the surface of aluminum or aluminum alloy. As a ceramic material, MAX phase material has the advantages of high conductivity and corrosion resistance. The coating formed improves the corrosion resistance of the aluminum or aluminum alloy surface. The method of this invention also has the advantages of convenient operation and simple process. It can be implemented with simple dispersion and heating equipment, which is conducive to industrial scale-up production and has practicality.

[0037] When the aluminum-based current collector provided by this invention is used as a current collector for lithium-ion and sodium-ion batteries, it can improve the problem of current collector corrosion by electrolyte in lithium-ion and sodium-ion batteries, so that the battery has more stable cycle performance and longer cycle life; it can also avoid the problem of battery swelling caused by hydrogen evolution due to corrosion, that is, it can suppress hydrogen evolution, prevent battery swelling, and improve the safety performance of the battery. Attached Figure Description

[0038] Figure 1 These are surface photographs of (a) the composite aluminum foil (MX / Al) and (b) the coated aluminum foil (MAX / Al) obtained after high-temperature heat treatment in Example 1 of the present invention. It can be seen that after high-temperature treatment, the MXene film changes from dark blue to gray.

[0039] Figure 2 This is the XRD pattern of the surface of the coated aluminum foil (MAX / Al) in Example 1 of the present invention.

[0040] Figure 3 The images shown are (a) and (b) SEM images of the cross-section of the coated aluminum foil (MAX / Al) in Embodiment 1 of the present invention, and are Al and Ti elemental analysis images at the marked locations.

[0041] Figure 4 The results of elemental scanning analysis of the cross-section of the coated aluminum foil (MAX / Al) in Example 1 of this invention are shown.

[0042] Figure 5 The results show the comparison of sheet resistance test results between the coated aluminum foil (MAX / Al) and the initial aluminum foil in Embodiment 1 of the present invention.

[0043] Figure 6 The images shown are: (a) a photograph of the MXene dispersion; (b) a photograph of the composite aluminum foil coated with the MXene film; and (c) a SEM photograph of the coating surface of the coated aluminum foil. The inset in the upper right corner is a cross-sectional SEM photograph of the coated aluminum foil.

[0044] Figure 7 The image shows the XRD pattern of the coated aluminum foil (MX-MAX / Al) surface in Embodiment 2 of the present invention.

[0045] Figure 8 This is a schematic diagram of the composite aluminum foil obtained by the impregnation method in Embodiment 3 of the present invention.

[0046] Figure 9 The following is a comparison of the charge-discharge performance of lithium-ion batteries using the coated aluminum foil, composite aluminum foil and initial aluminum foil of the present invention as current collectors in Example 6 of the present invention: (a) at a rate of 0.2C; (b) at a rate of 0.1 to 4C; (c) at a rate of 4C.

[0047] Explanation of key figure labels:

[0048] 10 Aluminum foil; 20 MXene film; 21 MXene nanosheets. Detailed Implementation

[0049] The technical solution of the present invention is illustrated below through specific embodiments. It should be understood that the one or more steps mentioned in the present invention do not preclude the existence of other methods and steps before or after the combined steps, or that other methods and steps may be inserted between these explicitly mentioned steps. It should also be understood that these examples are for illustrative purposes only and are not intended to limit the scope of the invention. Unless otherwise stated, the numbering of each method step is only for the purpose of identifying each method step, and not for limiting the order of each method or limiting the scope of the invention. Changes or adjustments to their relative relationships, without substantial changes to the technical content, can also be considered as within the scope of the invention. The raw materials and instruments used in the embodiments are not specified, and their sources are not specifically limited; they can be purchased from the market or prepared according to conventional methods well known to those skilled in the art.

[0050] The MXene powder and slurry containing halogen functional groups used in the embodiments of the present invention were purchased from Beijing Sanchuan Energ Technology Co., Ltd., wherein the MXene has a two-dimensional lamellar morphology.

[0051] The sheet resistance test method in this embodiment of the invention is as follows: the current versus voltage curve with a voltage range of -1 to 1V is measured using an electrochemical workstation (CHI660e, CHInstruments) at a scan rate of 10mV / s, and the sheet resistance is calculated.

[0052] MAX phase materials are a class of transition metal carbide / nitride ceramic materials, whose chemical formula can be represented as M n+1 AX nIn this MAX phase, M represents one or more transition metal elements, A is typically a group IIIA or IVA element, and X is carbon, nitrogen, and / or boron, where 1 ≤ n ≤ 4. The unique layered structure of MAX phase materials, possessing both covalent and metallic bonds, results in excellent electrical and thermal conductivity, corrosion resistance, and processability. Currently, MAX phase materials are widely used in the energy industry as electrode brush materials and corrosion-resistant materials. When A is a metal (such as Al or Sn), MAX phase materials are also used as precursors for preparing MXene materials because A is easily etched by acid.

[0053] MXene materials are a class of two-dimensional materials. Common preparation methods include etching the A component of the precursor MAX phase, which is represented by the chemical formula M. n+1 X n T x In this formula, M represents one or more transition metal elements, X is carbon, nitrogen, and / or boron, 1 ≤ n ≤ 4, T represents the surface functional group element of MXene, which usually contains halogen functional groups. The type of surface functional group element is related to the type of etchant and usually includes F, Cl, Br, I, O, and -OH. x is an indeterminate value, calculated theoretically, 0 ≤ x ≤ 2. In this field, T is commonly used in chemical formulas. x This indicates that MXene surfaces contain functional groups. MXene materials typically exhibit good electrical conductivity, hydrophilicity, and two-dimensional flexibility.

[0054] The technical concept of this invention lies in the in-situ heating treatment of MXene material containing halogen functional groups coated on the surface of aluminum foil. During the heating process, the halogen functional groups of the MXene material react with Al to remove them, generating aluminum halide. Al atoms bond with the MXene nanosheets to form a coating containing MAX phase material, resulting in an aluminum foil (or coated aluminum foil) covered with MAX phase material. In other words, this heating process forms a coating in situ on the surface of the aluminum foil, and this coating contains MAX phase material. Since the MAX phase itself is a corrosion-resistant ceramic material and also has the advantage of high conductivity, it can serve as a protective coating for aluminum current collectors. At the same time, due to the bonding force between the generated MAX phase and the aluminum foil, the coating also exhibits excellent adhesion, avoiding the problems of reduced conductivity and decreased adhesion over long-term use associated with carbon coatings that require binders.

[0055] Example 1

[0056] This embodiment provides a method for preparing a surface coating on aluminum foil (or aluminum-based current collector), and also a method for preparing an aluminum foil containing a coating, wherein the MXene material is Ti3C2Cl. xThe nanosheet (two-dimensional sheet morphology) powder, with an aluminum foil thickness of 20 μm, was coated with MXene slurry onto the aluminum foil surface using a blade coating process. More specific steps included:

[0057] 1) Prepare MXene dispersion (or MXene slurry). More specifically, the steps are as follows: Add 100 mg of MXene powder (Ti3C2Cl...) x Add the MXene to 10 ml of ethanol solvent and disperse it evenly by ultrasonic treatment, controlling the ultrasonic temperature to be less than 30℃, to obtain MXene dispersion (10 mg / ml);

[0058] 2) Lay the aluminum foil flat on the heating belt and heat it to 50°C;

[0059] 3) Pour the MXene slurry obtained in step 1 onto the aluminum foil surface and use a scraper with a thickness controlled at 200 micrometers to coat it until the aluminum foil surface is evenly covered with a layer of MXene slurry. Stop scraping and let it dry. After drying, a layer of dark blue Ti3C2Cl will be formed on the aluminum foil surface. x The membrane was used to obtain a composite aluminum foil (labeled MX / Al) coated with MXene.

[0060] 4) The Ti3C2Cl coating obtained in step 3 x The aluminum foil with the film was placed in a tube furnace for heating treatment. Specifically, the heating temperature was 500℃, and the heating time was 1 hour. The atmosphere of the tube furnace was argon (continuously introduced during the heating process). After heating, it was allowed to cool naturally to obtain the target product, coated aluminum foil (labeled MAX / Al). During the heating process, Ti3C2Cl... x The surface contains abundant Cl functional groups. During heating, Cl reacts with Al to form aluminum chloride (AlCl3, boiling point 178℃), which vaporizes at high temperature and is discharged from the reaction system with the gas flow. Al reacts with MXene to form the MAX phase.

[0061] Figure 1 Image a shows a photograph of the MXene film surface of the composite aluminum foil (MX / Al), which appears dark blue. After the heat treatment in step 3, the surface turns gray. Figure 1 (b) This is because aluminum atoms in the aluminum foil penetrate into and react with the MXene layer covering the surface at high temperatures, generating a gray MAX phase in situ. The composition of the target product, the gray MAX / Al surface, was determined using X-ray diffraction (XRD), and the results are as follows: Figure 2As shown, characteristic peaks (inverted triangles) of metallic aluminum appear at 2θ angles of 38.5°, 44.7°, and 65.1°, while characteristic peaks (dots) of the MAX phase Ti3AlC2 appear at 2θ angles of 9.5°, 19.1°, 34.0°, 39.0°, 41.8°, 60.3°, 70.6°, and 74.1°, corresponding to the (002), (004), (100), (101), (104), (105), (110), (200), and (118) crystal planes of Ti3AlC2, respectively. This indicates that the reaction between aluminum foil and Ti3C2Cl... x In-situ high-temperature heating treatment was used to generate a MAX phase Ti3AlC2 coating on the surface of the aluminum foil, resulting in a coated aluminum foil (MAX / Al). In this embodiment, the characteristic peaks of MXene could not be characterized in the XRD pattern. Figure 3 Figure a shows a scanning electron microscope (SEM) image of the cross-section of the coated aluminum foil, which shows that the thickness of the MAX phase Ti3AlC2 layer is approximately 2.5 μm and it is tightly adhered to the surface of the aluminum foil. Figure 3 b provides elemental analysis images of aluminum (Al) and titanium (Ti) at the marked locations in the SEM images. Figure 3 The blue image above (b) shows the distribution of aluminum. As you can see, the aluminum signal is strong in the lower part of the image (aluminum foil location), while above the foil location, the aluminum is evenly distributed. This indicates that the high-temperature heat treatment allowed the aluminum to penetrate into the coating on the aluminum foil surface. This is consistent with the effect of Ti3C2Cl. x This is related to the formation of Ti3AlC2 by Al elements, and the signal of aluminum element distribution is more obvious in the coating near the aluminum foil. This may be due to the diffusion of aluminum elements at high temperature, which is beneficial to enhancing the bonding force between the MAX phase and the aluminum foil. Figure 3 The yellow image below b shows the distribution of titanium. It can be seen that titanium has no signal in the lower part (aluminum foil location), but is uniformly distributed above the aluminum foil location. The elemental scanning results of the coating cross-section were obtained using energy-dispersive electron microscopy (EDS). Figure 4 The presence of Ti, Al, C, and Cl elements is shown, with Ti, C, and Cl corresponding to unreacted MXene Ti3C2Cl in the coating. x The elements Ti, Al, and C correspond to the MAX phase Ti3AlC2 in the coating, and elemental analysis further confirmed the formation of the MAX phase in the coating.

[0062] Sheet resistance was tested on the obtained coated aluminum foil (MAX / Al) and the initial aluminum foil (uncoated), and the results are as follows: Figure 5As shown, the sheet resistances of the aluminum foil with the Ti3AlC2 coating and the original aluminum foil are 8.2 Ω / □ and 7.7 Ω / □, respectively, with a difference of only 0.5 Ω / □, indicating good conductivity. Therefore, the aluminum foil with the MAX phase Ti3AlC2 coating is suitable for use as a current collector in a battery.

[0063] The method of coating MXene material on the surface of aluminum foil according to the present invention can also be other methods, such as spraying MXene dispersion onto aluminum foil, immersing aluminum foil in MXene dispersion and then lifting it, or dispersing MXene powder on the surface of aluminum foil. The present invention does not limit the dispersion method of MXene material on the surface of aluminum foil. In order to disperse MXene efficiently, uniformly and controllably on aluminum foil, those skilled in the art can implement different dispersion methods as needed.

[0064] Example 2

[0065] This embodiment provides an implementation method for preparing an MXene film layer on the surface of aluminum foil using a spray coating method, and the more specific steps include:

[0066] 1) Lay the aluminum foil flat on the heating belt and heat it to 85 degrees Celsius;

[0067] 2) Add Ti3C2Cl by mass concentration x The ethanol dispersion of nanosheets (10 mg / ml) was poured into a spray gun and sprayed onto the surface of aluminum foil under a pressure of 0.4 MPa. The solvent ethanol evaporated rapidly, and a layer of MXene was uniformly covered on the surface of the aluminum foil. Spraying was stopped to obtain a composite aluminum foil coated with MXene (labeled as MX / Al).

[0068] 3) The composite aluminum foil MX / Al obtained in step 2 is placed in a tube furnace for heating treatment at a temperature of 500°C for 30 minutes. The atmosphere of the tube furnace is argon (argon is continuously introduced) to obtain the target product coated aluminum foil (marked as MX-MAX / Al).

[0069] The spraying method used in this embodiment sprays the MXene dispersion onto the surface of aluminum foil, which can improve the dispersion efficiency of MXene material, obtain large-size MXene films, and is more suitable for industrial production. Figure 6 Image a shows a photograph of the prepared MXene dispersion. Figure 6 Reference b shows a large-sized aluminum foil (20cm wide, 5m long) coated with an MXene layer, prepared by the applicant using a spraying method. The MXene film can be seen to be uniformly dispersed on the surface of the aluminum foil. By improving the spraying equipment, even larger MXene films can be obtained.

[0070] By controlling the conditions of high-temperature heating treatment, including temperature and time, the extent of the in-situ reaction between Al atoms and MXene materials can be controlled. In this embodiment, the heating time is 30 minutes, and the resulting coating consists of MAX phase Ti3AlC2 and MXeneTi3C2Cl. x Composite layer, Figure 6 The image shown in Figure c is a SEM image of the coating surface after high-temperature heat treatment, Ti3AlC2 / Ti3C2Cl. x The nanosheets are stacked in parallel and compact order, which can effectively protect the aluminum foil from corrosion. Figure 6 The inset in C is a cross-sectional SEM image, showing that the composite layer (coating) is tightly adhered to the aluminum foil surface. Figure 7 The XRD pattern of the coated aluminum foil obtained after the heating reaction shows characteristic peaks of metallic aluminum (inverted triangles) at 2θ angles of 38.5°, 44.7°, and 65.1°. Characteristic peaks of the MAX phase Ti3AlC2 (dots) appear at 2θ angles of 9.5°, 19.1°, 34.0°, 39.0°, 41.8°, 60.3°, 70.6°, and 74.1°, corresponding to the (002), (004), (100), (101), (104), (105), (110), (200), and (118) crystal planes of Ti3AlC2, respectively. Characteristic peaks of MXene (diamonds) appear at 8.0°, 16.0°, 24.1°, 40.7°, and 58.1°, corresponding to the Ti3C2Cl... x (002), (004), (006), (10l), and (110) illustrate the use of aluminum foil and Ti3C2Cl x In-situ high-temperature heating treatment generated Ti3C2Cl on the surface of the aluminum foil. x A composite coating of Ti3AlC2 was used to obtain coated aluminum foil (MX-MAX / Al).

[0071] In this invention, the solvent needs to be evaporated eventually. In some embodiments, the solvent in the MXene dispersion in Examples 1 and 2 can be replaced with other volatile solvents, such as water, propanol, isopropanol, NMP, or mixtures of multiple solvents, such as a mixture of water and ethanol. Since MXene materials have good hydrophilicity, aqueous solvents, such as water and / or alcohols, are preferred. In another preferred embodiment, the solvent for the MXene dispersion is water.

[0072] It should be noted that the MXene dispersions prepared in Examples 1 and 2 consist of MXene material and solvent, and do not contain binders. Therefore, the MXene film formed on the aluminum foil is composed only of MXene material, demonstrating that the coating of the present invention does not contain binder components. However, the present invention does not preclude the addition of functional additives to the MXene dispersion in other embodiments, depending on specific implementation needs.

[0073] Example 3

[0074] This embodiment provides an implementation method for coating MXene onto the surface of aluminum foil using an impregnation method, and the more specific steps include:

[0075] 1) Prepare a Ti3C2Cl solution with a mass concentration of 2 mg / ml. x Aqueous dispersion (solvent is water, no binder);

[0076] 2) Immerse a 20μm thick aluminum foil in Ti3C2Cl x After dispersing the Ti3C2Cl solution, slowly and uniformly lift the aluminum foil out of the water to allow the Ti3C2Cl solution to reach the surface. x Two-dimensional Ti3C2Cl in aqueous dispersion x The surface tension of the aqueous solution is applied to the surface of the aluminum foil. After the aluminum foil is pulled out and dried naturally, it is repeatedly pulled up and dried several times (5 times). Then it is placed in a vacuum oven and vacuum dried at 50°C for 4 hours to obtain a composite aluminum foil (marked as MX / Al) coated with MXene material.

[0077] 3) The dried composite aluminum foil MX / Al was placed in a tube furnace for heating treatment at a temperature of 500°C for 40 minutes. The atmosphere of the tube furnace was argon (argon was continuously introduced) to obtain the target product coated aluminum foil (marked as MAX / Al).

[0078] Compared to the coating method in Example 1 and the spraying method in Example 2, the dip-coating method in this embodiment can obtain a thinner MXene film. This is because during the dipping process, the surface tension of the liquid causes the two-dimensional MXene sheets in the MXene dispersion to be oriented and spread evenly on the surface of the aluminum foil, resulting in a thinner MXene film that completely covers the substrate surface. Figure 8 As shown in the schematic diagram, MXene nanosheets are laid flat and stacked on the surface of aluminum foil to form an ultrathin MXene film. The thickness of this MXene film can be as low as several layers of MXene nanosheets. Due to the flexibility of the MXene nanosheet layers, this ultrathin MXene film can adhere to the surface of the aluminum foil. After high-temperature heating treatment, a coated aluminum foil with an ultrathin MAX phase coating is obtained.

[0079] That is, the thickness of the aluminum foil coating (or aluminum product coating) can be controlled by different preparation methods. In some embodiments, the thickness of the aluminum foil coating is between 0.3 nm and 10 μm, more preferably between 1 nm and 5 μm; even more preferably between 1 nm and 1 μm.

[0080] In other embodiments, the high-temperature heating treatment temperature is preferably above 178°C, because the boiling point of AlCl3 generated during the reaction is 178°C, and a temperature above this is beneficial for the byproduct AlCl3 to be converted into a gaseous state and removed from the reaction system. Since the generated MAX phase is a ceramic material with excellent high-temperature resistance, the high-temperature heating treatment temperature can be selected from 178°C to 660°C (the melting point of aluminum), preferably from 200°C to 600°C, more preferably from 300°C to 600°C, and the heating treatment time can be selected from 1 min to 48 h; preferably, the heating treatment time is from 1 min to 12 h; more preferably, the heating treatment time is from 1 min to 5 h; even more preferably, the heating treatment time is from 1 min to 3 h; and even more preferably, the heating treatment time is from 1 min to 1 h.

[0081] Example 4

[0082] This embodiment provides an implementation of MXene with the functional group Br. The specific implementation is similar to that of Embodiment 1, except that the MXene is Ti3C2Br. x Since the boiling point of AlBr3 is 265°C, the preferred high-temperature heating treatment temperature is above 265°C, more preferably between 265°C and 660°C, even more preferably between 300°C and 600°C, and still more preferably between 400°C and 600°C. The heating treatment time can optionally be between 1 minute and 12 hours. In one specific embodiment, the heating treatment temperature is 600°C and the heating time is 2 hours.

[0083] This embodiment also provides an implementation of MXene with a functional group of I. The specific implementation is similar to that of Embodiment 1, except that the MXene is Ti3C2I. x Since AlI3 has a boiling point of 382°C, the preferred high-temperature heating treatment temperature is above 382°C, more preferably between 382°C and 660°C, and even more preferably between 400°C and 600°C. The heating treatment time can optionally be between 1 minute and 12 hours. In one specific embodiment, the heating treatment temperature is 600°C and the heating time is 3 hours.

[0084] Example 5

[0085] This embodiment provides an implementation of MXene containing fluorine (F) functional groups. The specific implementation method is similar to that of Example 1, except that the MXene is an F-functionalized MXene Ti3C2T prepared by hydrofluoric acid etching. x The heat treatment temperature is 500℃, and the heating time is 1 hour. However, since AlF3 has a boiling point of 1291℃, when using MXene materials with fluorine functional groups, a large amount of non-conductive AlF3 byproducts remain in the coating after high-temperature heat treatment, which is extremely difficult to remove and thus affects the coating performance. Therefore, this invention preferably uses MXene materials with functional groups containing Cl, Br, or I.

[0086] Example 6

[0087] To verify the application effect of the coated aluminum foil of the present invention as a battery current collector, this embodiment provides a positive electrode sheet and a battery containing the coated aluminum foil of the present invention, and uses the coated aluminum foil of the present invention as the positive electrode current collector of a lithium-ion battery. A more specific implementation method is as follows:

[0088] Preparation method of positive electrode sheet: Lithium iron phosphate (LiFePO4), conductive agent (Ketjen Black), and binder (polyvinylidene fluoride PVDF) are mixed in a mass ratio of 8:1:1, and an appropriate amount of N-methylpyrrolidone (NMP) is added to prepare a slurry; the coated aluminum foil (MAX / Al) prepared in Example 1 is used as the current collector, the slurry is coated on the coated aluminum foil, and it is placed in a vacuum oven to dry at 80°C for 12 hours;

[0089] Battery assembly method: The dried positive electrode sheet is stamped into a disc with a diameter of 14mm. Using lithium metal as the negative electrode, it is assembled into a CR2023 coin cell. The separator is made of PP material, and the electrolyte is a solution of 1M LiPF6 in EC, EMC, DEC (v:v:v=1:1:1) and 1% VC.

[0090] Using the same method, the coated aluminum foil was replaced with the initial aluminum foil and the composite aluminum foil obtained in step 3 of Example 1 (without high-temperature heating treatment), respectively, and the resulting battery was the control battery.

[0091] The assembled battery was subjected to charge-discharge tests at voltages ranging from 0.1V to 4.2V. The results are as follows. Figure 9 As shown, Figure 9Figure a shows a comparison of the cycle performance of batteries using the coated aluminum foil of the present invention, composite aluminum foil (without high-temperature heat treatment), and the original aluminum foil at a rate of 0.2C. It shows that the battery using the coated aluminum foil of the present invention exhibits excellent cycle performance, with a capacity retention rate of 90% after 200 cycles. The capacity of the comparison battery 1 (composite aluminum foil) is relatively stable in the first 70 cycles, but then the capacity drops rapidly, with a capacity retention rate of 60% after 200 cycles. The capacity of the comparison battery 2 (original aluminum foil) decreases rapidly from the beginning, and the battery capacity is almost completely depleted after 150 cycles, and the capacity is only 9% of the initial capacity after 200 cycles. Figure 9 Figure b presents a performance comparison of three batteries at different rates. It can be seen that at high rates, the battery of the present invention exhibits superior rate performance compared to the other two comparative batteries. Figure 9 The figure shows that under 4C charge-discharge rate, the battery of the present invention has an initial discharge specific capacity of 135.7 mAh / g, and after 1000 cycles, the capacity retains 81% of the initial capacity, which is significantly better than the comparative battery.

[0092] In other embodiments, other lithium-ion cathode materials may be selected, such as lithium cobalt oxide, ternary materials, lithium manganese oxide, etc., and anode materials may be selected from carbon materials and silicon materials, such as graphite, expanded graphite, silicon carbon, etc.

[0093] Example 7

[0094] The coated aluminum foil of the present invention can also be used as a positive electrode current collector for sodium-ion batteries. This embodiment provides a sodium-ion battery positive electrode sheet and a sodium-ion battery. The preparation method of the sodium-ion positive electrode sheet and the sodium-ion battery is similar to that of Example 6, except that the positive electrode material is selected from sodium-ion battery positive electrode materials, such as transition metal layered oxides, polyanionic compounds, Prussian blue analogues; and the negative electrode material is a metallic sodium sheet.

[0095] In one specific embodiment, the positive electrode material of the sodium-ion battery is selected as P2 phase Na. 2 / 3 Ni 1 / 3 Mn 2 / 3 O2 cathode material.

[0096] The coated aluminum foil obtained by this invention, when used as a current collector in batteries, contributes to the excellent cycle performance of the batteries. This is due to the excellent corrosion resistance imparted to the aluminum foil by the coating containing the MAX phase, thus improving the service life of the aluminum foil. It should be noted that the aluminum foil of this invention can also be used for other purposes, such as as a corrosion-resistant packaging material.

[0097] It should be noted that the aluminum substrate in the aluminum foil or aluminum products of the present invention can be pure metallic aluminum or an aluminum alloy with metallic aluminum as the main component.

[0098] In this embodiment, an aluminum foil with a thickness of 20 μm is used as an aluminum base layer (or aluminum substrate). The thickness of the aluminum foil can also be adjusted according to actual needs. When the coated aluminum foil of the present invention is used as a battery current collector, the thickness of the aluminum foil is preferably 1 μm to 30 μm, more preferably 1 μm to 10 μm.

[0099] Example 8

[0100] Since MXene is a type of two-dimensional material, the transition metal element M commonly found in it is one or more of Ti, Nb, Ta, Cr, Zr, and V. Because MXene materials have similar material properties, MXene materials composed of these different elements can all be used to prepare the aluminum foil coating of this invention, producing the same or similar effects.

[0101] This embodiment provides a Nb2CCl x The embodiment for preparing the aluminum foil coating of the present invention is similar to that of Example 1, except that the heating temperature is 550°C and the heating time is 1 hour.

[0102] Example 9

[0103] This invention also provides a method for surface treatment of aluminum products, to form a corrosion-resistant coating on the surface of the aluminum products, wherein the aluminum products are made of aluminum or aluminum alloys. This embodiment also provides an aluminum product with a surface coating.

[0104] The preparation methods of the aluminum foil coating in Examples 1 to 8 are similar, except that the aluminum foil is jacquard with other shapes of aluminum material.

[0105] In some embodiments, an aluminum product is sprayed with an MXene dispersion, and after the solvent dries, it is placed in a high-temperature sintering furnace under inert gas protection and heated at a predetermined temperature. The heating temperature is optionally between 178°C and 660°C (the melting point of aluminum), preferably between 200°C and 600°C, more preferably between 300°C and 600°C, and the heating time is optionally between 1 min and 48 h; preferably between 1 min and 12 h; more preferably between 1 min and 5 h; even more preferably between 1 min and 3 h; and even more preferably between 1 min and 1 h.

[0106] Example 10

[0107] This embodiment provides a method for preparing a coating by covering the surface of an aluminum product with MXene powder. The specific steps include: placing the aluminum product into a container filled with MXene powder, covering the aluminum product, and then placing it in a high-temperature sintering furnace under inert gas protection for heating treatment at a predetermined temperature. In one specific embodiment, the aluminum product is placed in a container filled with MXene Ti3C2Cl... x The powder was placed in a crucible, and the MXene powder was covered on the aluminum product. After the powder was compacted, it was placed in a tube sintering furnace under inert gas protection and sintered at 500°C for 1 hour. After cooling to room temperature, the aluminum product was removed and the excess powder on the surface was cleaned. After drying, a coating containing the MAX phase was obtained.

[0108] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A method for in-situ growth of a coating on an aluminum surface, characterized in that, The method steps include: The surface of aluminum or aluminum alloy is covered with MXene material, and then heat-treated at a predetermined temperature. The functional groups of the MXene material contain one or more of Cl, Br or I. During the heat treatment, the halogen functional groups of the MXene material react with aluminum to remove them, and a coating containing MAX phase material is formed in situ on the surface of the aluminum or aluminum alloy.

2. The method as described in claim 1, characterized in that, More specifically, the covering method includes: spraying and / or coating the MXene dispersion onto the surface of the aluminum or aluminum alloy, followed by drying; And / or, the covering method more specifically includes: immersing the metallic aluminum or aluminum alloy in MXene dispersion, lifting it several times, and then drying it; And / or, the covering method more specifically includes: covering the surface of the aluminum or aluminum alloy with MXene powder.

3. The method as described in claim 2, characterized in that, The concentration of the MXene dispersion is between 0.1 mg / mL and 500 mg / mL; And / or, the MXene dispersion comprises MXene material and solvent.

4. The method as described in claim 2, characterized in that, The MXene dispersion is composed of MXene material and solvent.

5. The method as described in claim 3, characterized in that, The solvent is water and / or an alcohol.

6. The method as described in claim 1, characterized in that, The chemical formula of MXene is M n+1 X n T x , where 1≤ n ≤4, where M is selected from one or more transition metal elements; T represents a functional group element; and X is selected from one or more carbon, nitrogen, and boron elements. And / or, the aluminum or aluminum alloy is in foil or sheet form.

7. The method according to any one of claims 1 to 6, characterized in that, The temperature of the heat treatment is between 178°C and 660°C; And / or, the heat treatment time is between 0.01 min and 48 h.

8. The method as described in claim 7, characterized in that, The temperature of the heat treatment is between 200°C and 600°C; And / or, the heat treatment time is between 1 minute and 12 hours.

9. The method as described in claim 8, characterized in that, The temperature of the heat treatment is between 400°C and 600°C; And / or, the heat treatment time is between 1 minute and 1 hour.

10. A coating obtained by the method according to any one of claims 1 to 9.

11. The coating as claimed in claim 10, characterized in that, The thickness of the coating is between 0.3 nm and 10 μm.

12. The coating as claimed in claim 10, characterized in that, The thickness of the coating is between 1 nm and 5 μm.

13. The coating as claimed in claim 10, characterized in that, The thickness of the coating is between 1 nm and 1 μm.

14. The coating as described in any one of claims 10 to 13, characterized in that, The coating contains MAX phase material; And / or, the X-ray diffraction (XRD) pattern of the coating contains the (002), (004), (104), and (110) crystal planes of the MAX phase material; And / or, the elemental analysis characterization results of the coating show that it includes: transition metal elements, aluminum, carbon and / or nitrogen.

15. The coating as described in any one of claims 10 to 13, characterized in that, The coating contains MAX phase material and MXene material.

16. An aluminum foil, characterized in that, It includes an aluminum base and a coating as described in any one of claims 10 to 15.

17. An aluminum foil comprising an aluminum substrate and a coating, characterized in that, The coating includes MAX phase material; And / or, the X-ray diffraction (XRD) pattern of the coating contains the (002), (004), (104), and (110) crystal planes of the MAX phase material; And / or, the elemental analysis characterization results of the coating show that it includes: transition metal elements, aluminum, carbon and / or nitrogen; And / or, the coating is obtained by heat-treating an MXene material covering the surface of the aluminum substrate at a predetermined temperature; the MXene material includes halogen elements; the halogen elements are Cl, Br, and I.

18. The aluminum foil as claimed in claim 17, characterized in that, The heat treatment temperature is between 178°C and 660°C.

19. The aluminum foil as claimed in claim 17, characterized in that, The heat treatment temperature is between 200°C and 600°C.

20. The aluminum foil as claimed in claim 17, characterized in that, The heat treatment temperature is between 400°C and 600°C.

21. An aluminum-based current collector, characterized in that, The aluminum-based current collector comprises a coating obtained by the method of any one of claims 1 to 9, or a coating of any one of claims 10 to 15; Alternatively, the aluminum-based current collector may be an aluminum foil as described in any one of claims 16 to 20.

22. An electrode, characterized in that, Includes the aluminum-based current collector as described in claim 21.

23. A battery, characterized in that, Includes the aluminum-based current collector as described in claim 21; or, the electrode as described in claim 22.

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