Composite lithium electrode, battery, production system and electric device

Abstract

The utility model discloses a composite lithium electrode, a battery, a production system and an electric device, the composite lithium electrode comprises a composite lithium foil, and the composite lithium foil comprises a metal lithium or lithium alloy matrix and an MXene nanosheet; and the MXene nanosheets are of an oriented layered arrangement structure in the matrix. The composite lithium foil in the composite lithium electrode comprises the MXene nanosheet oriented layered arrangement structure, and the oriented layered arrangement structure can effectively prevent corrosives (such as air and electrolyte) from corroding lithium metal and shows excellent air stability.

Description

Technical Field

[0001] The utility model belongs to the field of batteries, in particular to a composite lithium electrode, a battery, a production system and an electricity-using device. Background Art

[0002] In the current battery market, lithium-ion batteries are widely used in electronic devices, unmanned vehicles, electric vehicles and other fields due to their stable cycle performance. However, since the theoretical capacity of the graphite negative electrode of lithium-ion batteries is relatively low and the current actual capacity is close to the theoretical capacity of the graphite negative electrode, the capacity of lithium-ion batteries is difficult to meet the long-range requirements of electric vehicles or drones. Metallic lithium has the highest theoretical capacity (3860 mAh / g), the lowest electrochemical potential (-3.040V vs. SHE) and the lowest density (0.53 g / cm 3 ) advantages, making it an ideal anode material for next-generation lithium batteries. However, the current lithium metal battery anode to cathode capacity ratio (N / P) far exceeds 1.05. Excessive lithium metal anode reacts with the electrolyte to produce a larger solid electrolyte interface (SEI), resulting in a decrease in the initial coulombic efficiency. Lithium's high chemical activity leads to the release of large amounts of heat during injection, which also poses a safety hazard. Furthermore, excess lithium inevitably reduces the battery's mass energy density and increases the cost of battery manufacturing. Therefore, one technical solution is to manufacture ultra-thin lithium (thickness ≤ 20 μm) that can match the cathode capacity.

[0003] However, there are currently two main difficulties in the preparation of ultra-thin lithium: First, the mechanical properties of metallic lithium itself are extremely poor and its texture is very soft. Therefore, when metallic lithium is mechanically rolled to a thickness of less than 50 μm, the metallic lithium strip is prone to breakage; when rolled to a thickness of 20 μm or even less, the metallic lithium will adhere to the polymer substrate material due to the pressure exerted by the roller and cannot be separated from the substrate to obtain a continuous ultra-thin lithium strip. At the same time, because metallic lithium has a low hardness and is easily deformed during rolling, the precision requirements of the rolling equipment for preparing ultra-thin lithium are extremely high, which invisibly increases the cost of preparing ultra-thin lithium. Second, when using the melting method to prepare ultra-thin lithium, the liquid lithium metal will be incompatible with most substrates due to the large tension, and will appear as spherical droplets on the substrate, which is not conducive to the spreading and deep processing of metallic lithium on the substrate, and it is difficult to obtain an ultra-thin lithium strip with uniform thickness. In addition to the difficulty in preparing ultra-thin lithium itself, the high chemical activity of metallic lithium also causes ultra-thin lithium electrodes to be easily oxidized during production, storage and transportation, which not only causes capacity loss but also is not conducive to the long-cycle performance of the battery. Utility Model Content

[0004] The utility model provides a first aspect of a composite lithium electrode, which includes a composite lithium foil. The composite lithium foil includes a matrix of metallic lithium or a lithium alloy and MXene nanosheets; the MXene nanosheets are arranged in a directional layered structure in the matrix.

[0005] In some embodiments, the thickness of the composite lithium foil is ≤100 μm; preferably, the thickness is ≤50 μm; more preferably, the thickness is ≤20 μm; more preferably, the thickness is ≤10 μm.

[0006] In some embodiments, the chemical formula of the MXene is: n+1 X n T x , wherein M represents a transition metal element wherein M represents one or more transition metal elements Ti, V, Mo, Nb, Ta, W, Zr, Y, X represents one or more carbon, nitrogen or boron elements, T x Represents the presence of functional groups; 1≤ n ≤4.

[0007] In some embodiments, the functional groups of the MXene contain fluorine.

[0008] In some embodiments, M in the above MXene is Ti, X is carbon, and T x Contains fluorine element.

[0009] In some embodiments, the lithium alloy is a lithium aluminum alloy or a lithium magnesium alloy.

[0010] In some embodiments, the composite lithium foil forms the oriented layered structure by the following method: mixing molten metallic lithium or lithium alloy with MXene nanosheets to obtain a composite lithium slurry; cooling and solidifying the composite lithium slurry to obtain a composite lithium ingot; and forming the composite lithium ingot into a composite lithium foil by extrusion and / or rolling.

[0011] In some embodiments, the method for forming the oriented layered arrangement structure includes: first extruding the composite lithium ingot into a composite lithium sheet, and then rolling the composite lithium sheet several times to reduce the thickness to obtain a composite lithium foil.

[0012] In some embodiments, the directional layered structure is characterized by scanning electron microscopy. Preferably, the metallic lithium in the composite lithium foil is stripped before performing scanning electron microscopy.

[0013] In some embodiments, the surface of the composite lithium foil is covered with two-dimensional nanosheets, which can be characterized by scanning electron microscopy and found to be MXene nanosheets.

[0014] In some embodiments, the X-ray diffraction test (XRD) characterization of the composite lithium foil shows the (002) diffraction peak of MXene, and the diffraction peaks of the (110) crystal plane and the (200) crystal plane of metallic lithium; and the intensity ratio of the diffraction peaks of the (110) crystal plane and the (200) crystal plane of metallic lithium is greater than 2.6.

[0015] In some embodiments, the ratio of the diffraction peak intensities of the metallic lithium (110) crystal plane and the (200) crystal plane is greater than 4.2.

[0016] In some embodiments, the ratio of the diffraction peak intensities of the metallic lithium (110) crystal plane and the (200) crystal plane is greater than 5.2.

[0017] In some embodiments, the ratio of the diffraction peak intensities of the metallic lithium (110) crystal plane and the (200) crystal plane is greater than 7.6.

[0018] In some embodiments, the composite lithium electrode comprises: the composite lithium foil described above; and a current collector layer in surface contact with the composite lithium foil.

[0019] In some embodiments, the composite lithium electrode comprises: the composite lithium foil; an electrochemically active material layer in surface contact with the composite lithium foil; and a current collector layer in surface contact with the electrochemically active material layer.

[0020] In some embodiments, the current collector layer is a metal foil, preferably a copper foil, a stainless steel foil, a nickel foil or a titanium foil.

[0021] A second aspect of the present invention provides a battery, which includes the above-mentioned composite lithium electrode.

[0022] The third aspect of the present invention provides a production system for the above-mentioned composite lithium electrode, characterized in that it includes: an inert gas system, a melting device, a cooling and solidifying device, an extrusion device and / or a rolling device, and a slitting device; the inert gas system includes an inert gas environment chamber, and the melting device and the cooling and solidifying device are arranged in the inert gas environment chamber; the melting device includes a heater, a container and a stirring device, which is used to heat and melt metallic lithium or lithium alloy, mix it with MXene powder, and obtain a mixed lithium liquid; the cooling and solidifying device includes a mold, which is used to cool and solidify the mixed lithium liquid to obtain a composite lithium ingot; the extrusion device is used to extrude the composite lithium ingot into a composite lithium sheet or a composite lithium foil; the rolling device is used to roll the composite lithium ingot into a composite lithium foil; or, the extruded composite lithium sheet is roll-formed into a composite lithium foil; the slitting device is used to cut the composite lithium sheet or the composite lithium foil into a predetermined shape.

[0023] A fourth aspect of the present invention provides an electrical device, comprising the composite lithium electrode; or the battery.

[0024] Compared to the prior art, the present invention's advantageous technology lies in: the MXene nanosheets in the composite lithium electrode of the present invention exhibit a directional layered structure within the composite lithium foil. This directional layered structure effectively prevents corrosive agents (such as air and electrolyte) from corroding lithium metal (preventing the surface lithium metal from reacting with the corrosive agents). This is due to the inherent corrosion resistance of the MXene nanosheets. In addition, the layered arrangement of the MXene nanosheets acts as a physical barrier, increasing the structural tortuosity within the composite lithium foil, extending the path that corrosive agents need to traverse to attack the lithium metal, thereby effectively extending the time it takes for the lithium metal to oxidize, or in other words, preventing the majority of the lithium metal from being oxidized. In other words, the composite lithium foil of the present invention exhibits excellent air stability. When used in industrial production, it can be placed stably in an air environment for a long time, solving the problem of strict environmental requirements during the manufacturing process due to the easy oxidation and flammability of lithium metal. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a schematic diagram of the processing method of the present invention. Under the action of shear force, the disorderly dispersed MXene nanosheets in the composite lithium ingot form a directional layered arrangement structure.

[0026] Figure 2 This is a thickness test photo of the ultra-thin composite lithium foil obtained in Example 2 of the present invention. The result shows that the thickness is 13 μm.

[0027] Figure 3 This is a surface SEM photograph of the ultrathin composite lithium foil obtained in Example 2 of the present invention.

[0028] Figure 4 These are cross-sectional SEM photos at different magnifications of the composite lithium foil obtained in Example 2 of the present invention after stripping metallic lithium.

[0029] Figure 5 This is a cross-sectional SEM photograph of the ultra-thin composite lithium foil with a thickness of 9 microns obtained in Example 2 of the present invention.

[0030] Figure 6 To test the air stability of the metal lithium sheet, the comparative lithium foil, and the composite lithium foil of the present invention in Example 2 of the present invention, the test discs were placed in the air and the changes in surface properties at different times were observed.

[0031] Figure 7 This is a comparison chart of the XRD spectra of the metal lithium sheet, the comparative lithium foil and the composite lithium foil of the present invention in Example 2 of the present invention.

[0032] Figure 8 This is a comparison chart of the XRD spectra of composite lithium foils of different thicknesses in Example 2 of the present invention.

[0033] Figure 9 These are the hardness test results of the metal lithium sheet, composite lithium foil, and comparison lithium foil in Example 2 of the present invention.

[0034] Figure 10 These are the tensile test results of composite lithium foils with different MXene contents, comparative lithium foils, and metallic lithium foils in Example 3 of the present invention.

[0035] Figure 11 These are the electrochemical performance test results of the composite lithium electrode placed in air for 24 hours in Example 4 of the present utility model.

[0036] Figure 12 This is a schematic diagram of a production system for a composite electrode sheet in Example 5 of the present utility model.

[0037] Figure 13 This is a schematic diagram of another production system for composite electrode sheets in Example 6 of the present invention.

[0038] Figure 14 This is a schematic structural diagram of a battery in Example 9 of the present utility model.

[0039] Figure 15 This is a schematic structural diagram of a battery according to another embodiment of Example 9 of the present invention.

[0040] Figure 16 This is a schematic structural diagram of the composite lithium electrode in Example 11 of the present utility model.

[0041] Main reference numerals:

[0042] 10 - Inert gas system, 11 - Inert gas atmosphere chamber; 20 - Melting device, 21 - Heater, 22 - Container, 23 - Stirring device; 30 - Cooling and curing device, 31 - Mold; 40 - Extrusion device; 50 - Rolling device; 60 - Slitting device; 70 - Laminating device; 80 - Demolding device; 90 - Winding device;

[0043] 100-mixed lithium solution; 200-composite lithium sheet; 300-composite lithium foil; 400-film; 500-film-lithium foil-film composite layer;

[0044] A10-positive electrode sheet, A11-positive electrode current collector, A12-positive electrode material layer; A20-negative electrode sheet, A21-negative electrode current collector, A22-composite lithium foil; A30-diaphragm;

[0045] A40 - composite lithium electrode, A41 - composite lithium foil, A42 - electrochemically active material layer, A43 - current collector layer. DETAILED DESCRIPTION

[0046] The technical solution of the present invention is described below through specific embodiments. It should be understood that one or more steps mentioned in the present invention do not exclude the existence of other methods and steps before and after the combination step, or other methods and steps may be inserted between these explicitly mentioned steps. It should also be understood that these examples are only used to illustrate the present invention and are not used to limit the scope of the present invention. Unless otherwise specified, the numbering of each method step is only for the purpose of identifying each method step, and does not limit the order of arrangement of each method or limit the scope of implementation of the present invention. Changes or adjustments in their relative relationships can also be regarded as the scope of implementation of the present invention without substantial changes in the technical content.

[0047] The raw materials and instruments used in the examples are not particularly limited in their sources and can be purchased from the market or prepared according to conventional methods known to those skilled in the art. The MXene nanosheets used in this utility model are MXene Ti3C2T produced by Jinan Sanchuan New Material Technology Co., Ltd. x Powder products.

[0048] The test method for tensile strength of the present invention is a tensile test of a metal strip. The tensile test is carried out in accordance with the national standard GB / T3076-1982 "Metal Sheet (Strip) Tensile Test Method". The size of the tensile sample is prepared in accordance with the national standard GB / T6397-1986 "Metal Tensile Test Specimen". The thickness of the tensile sample is 50 μm.

[0049] The hardness test method is static nanoindentation based on atomic force microscopy.

[0050] Extrusion in the present invention refers to the deformation of metal through a die mouth under the action of strong force, usually using an extruder, and the strong power source can be hydraulic, compressed air or mechanical pressure; rolling refers to the deformation of metal under the action of pressure and shear force when it passes through rotating rollers, which can also be called rolling, rolling or calendering.

[0051] The utility model provides a preparation method of a composite lithium electrode, wherein the composite lithium electrode includes a composite lithium foil. The preparation method of the composite lithium foil comprises the following steps: (1) melting and mixing, mixing molten metal lithium or lithium alloy with MXene to obtain a composite lithium slurry; (2) a solidification step, cooling and solidifying the composite lithium slurry to obtain a composite lithium ingot; (3) a forming step, providing shear force (Shear Force) to the composite lithium ingot by extrusion and / or roll forming, and forming the composite lithium ingot to obtain a composite lithium sheet or composite lithium foil, which can be used as the negative electrode of a lithium metal battery. Figure 1As shown, during the melt mixing step, MXene is dispersed in the molten lithium metal or lithium alloy, and MXene is uniformly and disorderly dispersed in the composite lithium slurry and composite lithium ingot. We unexpectedly discovered that the shear force generated by the extrusion and / or rolling processing method in the forming step can cause the disordered MXene nanosheets in the composite lithium ingot to form a directional layered structure in the lithium metal or lithium alloy matrix.

[0052] The present invention also discovered that the shear force generated by the extrusion and / or rolling process in the forming step can also induce the metallic lithium in the composite lithium ingot to expose more lithium Li (110) crystal planes. For lithium metal negative electrodes, since the migration barrier of Li atoms on the Li (110) crystal plane is lower than that on the Li (200) crystal plane, it is easier for them to diffuse and migrate laterally on the Li (110) surface, resulting in planar, dendrite-free lithium deposition. Therefore, it is generally believed that the Li (110) crystal plane is less likely to grow dendrites than other crystal planes. Therefore, the present invention also provides a method for inducing the production of metallic lithium with a high Li (110) crystal plane.

[0053] The present invention discovers that MXene nanosheets arranged in a directional layer can become the intrinsic reinforcement phase of the composite lithium foil, thereby improving the mechanical properties of the composite lithium foil, including hardness and tensile strength, and solving the technical problem that metallic lithium is easy to break and deform during extrusion or rolling due to its soft texture and low hardness, and is difficult to process; in particular, through the preparation method of the present invention, ultra-thin metallic lithium with a continuous thickness of ≤20 microns, uniform thickness and self-supporting properties can be prepared.

[0054] We also discovered that the extruded / rolled composite lithium foil exhibits excellent air stability. This stems from the inherent corrosion resistance of the MXene nanosheets. Furthermore, the oriented, layered arrangement of the MXene nanosheets within the metallic lithium or lithium alloy effectively prevents corrosive agents (such as air and electrolyte) from corroding the lithium metal (i.e., preventing the surface lithium metal from reacting with the corrosive agents). The layered MXene nanosheets act as a physical barrier, increasing the structural tortuosity within the composite lithium foil and extending the path that the corrosive agents must traverse to attack the metallic lithium. This effectively prolongs the oxidation time of the metallic lithium, or in other words, prevents most of the metallic lithium from being oxidized. This means that the composite lithium electrode of the present invention exhibits excellent air stability, resolving the environmental challenges faced by lithium metal batteries during manufacturing, which are often challenging due to the flammability and explosiveness of metallic lithium due to its susceptibility to oxidation. The composite lithium electrode of the present invention also exhibits resistance to electrolyte corrosion, preventing the release of large amounts of heat during injection and improving safety during the production process.

[0055] Due to MXene's excellent lithiophilicity, MXene can be uniformly mixed with molten lithium or lithium alloys. By adjusting the MXene content, the metallic lithium content in the composite lithium electrode of the utility model can also be controlled, thereby obtaining a composite lithium anode that matches the energy density of the positive electrode, avoiding the presence of excessive metallic lithium in the battery, which leads to low initial coulombic efficiency, high cost, and safety issues. The following specific examples illustrate the technical features of the utility model.

[0056] Example 1

[0057] This embodiment provides a composite lithium electrode and a preparation method thereof, wherein the composite lithium foil preparation method comprises the following steps:

[0058] 1) Melt mixing: In a glove box under argon atmosphere, place a metallic lithium block or metallic lithium alloy in a crucible and heat to melt it into a liquid state; add a certain amount of MXene to the liquid metallic lithium and stir to mix evenly. Due to the lithiophilicity of MXene, the composite lithium slurry after the addition of MXene transforms into a viscous gel state; preferably, the mass ratio of the added MXene to the metallic lithium or lithium and lithium alloy is between (0.1-30):100;

[0059] 2) Cooling and solidifying step: naturally cooling the composite lithium slurry in step 1 to room temperature and solidifying to obtain a composite lithium ingot; in the embodiment of the present invention, the composite lithium ingot is cylindrical (the internal shape of the container crucible);

[0060] In other embodiments, in order to facilitate subsequent processing and molding, the composite lithium slurry is filled into molds of other shapes (such as blocks or sheets) to obtain composite lithium ingots of different shapes;

[0061] 3) Processing and Forming: In a dry room environment, the composite lithium ingot obtained in step 2 is placed in an extrusion and / or rolling device to extrude and / or roll the composite metal lithium pillars into a sheet or foil. The extrusion or rolling process provides a significant shear force that produces directional deformation of the composite lithium ingot.

[0062] In the processing method of the present invention, the melting and cooling solidification of metallic lithium and alloys are carried out in an inert gas environment, and the extrusion and rolling processes are carried out in a dry room environment to control the moisture in the environment; in a specific embodiment of the present invention, the melting and cooling solidification of metallic lithium and alloys are carried out in an argon environment, and the extrusion and rolling processes are carried out in a dry room environment with a dew point below -50°C, and other tests are carried out in a conventional air environment.

[0063] In one specific embodiment, a composite lithium ingot is placed in an extrusion machine and extruded to produce a composite lithium sheet with a thickness ranging from 100 microns to 1 mm. The resulting composite lithium sheet is then coated with a PET release film on both sides and rolled several times to produce composite lithium foil or ultrathin lithium metal with varying thicknesses (1 to 100 microns). Repeated rolling can optimize the oriented layered structure of the MXene and adjust the mechanical properties of the composite lithium foil or ultrathin lithium metal. In some preferred embodiments, the composite lithium foil or ultrathin lithium metal is heated and softened before rolling; in some embodiments, the heating and softening temperature is between 50°C and 120°C.

[0064] After removing the coating, the composite lithium sheet, composite lithium foil, or ultrathin lithium metal is reshaped, such as by shearing or stamping, to produce the composite lithium electrode of the present invention. In a specific embodiment of the present invention, a circular lithium metal electrode sheet (test disc) with a diameter of 16 mm is produced by stamping to assemble button-type batteries for electrochemical performance testing. In other embodiments, the composite lithium electrode can also be square, strip, or shaped, depending on the battery design requirements.

[0065] In practice, we found that the composite lithium foil of the present invention can be easily peeled from the PET film. This is because the oriented layered arrangement of MXene is parallel to the film surface, reducing the bonding force between the metal lithium and the film. This is very conducive to obtaining a continuous and uniformly thick composite lithium foil, especially suitable for industrial continuous production and large-scale composite lithium foil. In contrast, when preparing metal lithium foil by doctor blade coating a mixed lithium slurry on a substrate, there is a technical problem that is difficult to separate intactly due to the soft texture of the metal lithium and its high bonding force with the substrate. Therefore, it is difficult to obtain a continuous and uniformly thick metal lithium foil. This problem is particularly prominent when preparing large-scale metal lithium foil.

[0066] In the embodiment of the present invention, the coating is made of a PET release film with a thickness of 0.1 mm, which is used to assist in rolling and forming the film. Other materials or thicknesses may also be selected, such as polyimide (PI), polypropylene (PP) or polyethylene (PE).

[0067] In some embodiments, the coating layer can also be made of polymer and / or metal materials, and a metal composite film with a coating layer on one side or both sides is obtained during the rolling process; in a specific implementation, a metal lithium composite film with a metal copper foil on one side is obtained by rolling a composite lithium foil with a metal copper foil during the rolling process; preferably, the thickness of the composite lithium foil is between 1 and 100 microns; the thickness of the copper foil is between 1 and 10 microns; in a preferred embodiment, the thickness of the composite lithium foil is 10 to 20 microns, and the thickness of the copper foil is 3 to 5 microns. In other embodiments, the material of the coating layer provided on one or both sides of the composite lithium foil can also be a polymer material, such as PET, PI, PP, PE, etc.; or, other types of metal materials, such as aluminum foil, nickel foil, stainless steel foil, titanium foil, etc.; or, a composite foil of a polymer and a metal, such as a composite foil formed by PET and a metal copper foil.

[0068] It should be noted that extrusion processing has the advantage of rapid prototyping, but is limited by existing extrusion equipment and processes. In particular, compared with pure lithium, the mechanical properties and hardness of MXene composite lithium metal are enhanced after reinforcement, which greatly increases the pressure required during the extrusion process, and places higher requirements on the extrusion molding die and process. Therefore, it is difficult to extrude composite lithium foil with a thickness of ≤100μm in one go. In order to obtain thinner lithium foil, the extruded composite lithium sheet is rolled several times to further reduce the thickness. Therefore, a more preferred embodiment of the present invention is to first extrusion and then roll the process, which can obtain lithium foil with a thickness of ≤100μm (especially lithium foil with a thickness of ≤50μm, or even ≤20μm), and the production is also more efficient.

[0069] Example 2

[0070] This embodiment provides a specific composite lithium electrode and its processing method, wherein MXene is Ti3C2T containing fluorine functional groups. x Nanosheets, the processing method steps include:

[0071] In the argon atmosphere of the glove box, 10g of lithium metal was heated to 200℃ and the lithium metal was melted into liquid. 1g of Ti3C2T x The nanosheets are added to the liquid lithium and stirred continuously until Ti3C2T x The nanosheets are evenly dispersed in the liquid lithium to form a composite lithium slurry; after the composite lithium slurry is naturally cooled, a composite lithium ingot is obtained;

[0072] In a dry room (dew point below -50°C), the composite lithium ingot was placed in an extrusion device, and the extrusion head pressure and pushing speed were set to 50-150 tons and 1 mm / min respectively. After obtaining a composite lithium sheet with a thickness of 1 mm, the roller gap distance of the rolling device was adjusted to 50 μm under a pressure of 5 tons. The composite lithium sheet was then placed in the rolling device to obtain an ultra-thin composite lithium foil. The thickness of the foil was tested to be only 13 μm ( Figure 2 ), and the ultra-thin composite lithium foil exhibits obvious metallic luster and has good continuity and self-support.

[0073] The surface of the ultra-thin composite lithium foil was characterized by scanning electron microscopy (SEM). Figure 3 ), its surface can be seen to be covered with obvious flakes, which are MXene nanosheets. The ultra-thin composite lithium foil is immersed in anhydrous ethanol to remove the metallic lithium. The metallic lithium slowly reacts and dissolves with the ethanol, and the residue (MXene nanosheet) is characterized by cross-sectional SEM ( Figure 4 In (a) and (b), the oriented layered structure can be clearly observed, indicating that the MXene nanosheets transform from a disordered state to an ordered oriented layered arrangement during the extrusion process.

[0074] By adjusting the roller gap distance of the rolling equipment, composite lithium foils of different thicknesses (e.g., 1 μm to 1000 μm) can be obtained. In some specific embodiments of the present invention, composite lithium foils of different thicknesses of 9 μm, 13 μm, 20 μm, 50 μm, 100 μm, 200 μm, and 500 μm were obtained. Figure 5 A cross-sectional SEM photograph of an ultra-thin composite lithium foil with a thickness of only 9 μm obtained after rolling (without stripping of metallic lithium) is given. It can be seen that the ultra-thin composite lithium foil has a uniform thickness and a smooth surface.

[0075] The composite lithium slurry is poured into a cylindrical mold, and after cooling and solidification, it is taken out of the mold and cut into a comparison lithium foil with a thickness of about 50 μm for comparative testing to illustrate the technical effect of extrusion or rolling.

[0076] In order to verify the air stability of the composite lithium foil of the present invention, the composite lithium foil (50 μm) and the comparison lithium foil were punched to obtain test discs and metal lithium sheets (thickness of about 500 μm, purchased from the market) were placed together in an air environment at room temperature (about 25°C) and the surface changes at different times were observed; the test results are as follows: Figure 6As shown, it can be seen that the metal lithium sheet initially has a silvery-white metallic luster. After 60 minutes of air exposure, the surface completely turns into black (lithium nitride). The metal lithium sheet is easily oxidized and nitrided in the air. In contrast, the lithium foil gradually changes from a silvery-white metallic luster to black after 15 minutes, and then gradually changes to grayish-white, indicating the nitridation and oxidation process of the metal lithium sheet. The composite lithium foil of the present invention still has a silvery-white metallic luster after being placed in the air for 360 minutes (6 hours), which shows that it has the best air stability.

[0077] Figure 7 A comparison of the XRD spectra of lithium metal sheets, comparative lithium foil, and the composite lithium foil (50 μm) of the present invention is given. It can be seen that the lithium metal sheet exhibits a sharp, high-intensity diffraction peak at the (200) crystal plane at around 52°, and a significantly low-intensity diffraction peak at the (110) crystal plane at around 36°, indicating that pure lithium metal exhibits a low (110) crystal plane and a high (200) crystal plane; while the composite lithium foil of the present invention is just the opposite, exhibiting a low-intensity diffraction peak at the (200) crystal plane and a high-intensity diffraction peak at the (110) crystal plane. In contrast, the intensities of the (200) and (110) crystal planes of the comparative lithium foil are intermediate. This indicates that the addition of MXene nanosheets and extrusion / rolling treatment can adjust the crystal plane orientation of lithium metal, thereby obtaining a lithium metal composite material with a high (110) crystal plane.

[0078] Because the migration barrier of lithium atoms on the lithium (110) crystal plane is lower than that on the lithium (200) plane, they easily diffuse and migrate laterally on the lithium (110) surface, resulting in planar, dendrite-free lithium deposition. Therefore, it is generally believed that the lithium (110) surface is less prone to dendrite growth than other crystal planes. Common knowledge suggests that controlling the crystallization of lithium with a preferred (110) crystal plane orientation is also an effective strategy for achieving highly reversible lithium metal batteries (LMBs), but there is a lack of simple control methods. (Please see the article: Directing (110) Oriented Lithium Deposition through High-flux Solid Electrolyte Interphase for Dendrite-free Lithium Metal Batteries, Angewandte Chemie International Edition, 2023(62)42, https: / / doi.org / 10.1002 / anie.202309622) [The title of the article is translated as: Directing (110) crystal surface lithium deposition through high-flux solid electrolyte interface to achieve dendrite-free lithium metal batteries, published in the journal "German Angewandte Chemie International Edition"]. In response to this technical problem, the present invention also provides a simple and easy method for regulating high (110) crystal surface metallic lithium, thereby obtaining a composite lithium foil with high (110) crystal surface for use in lithium metal battery electrode sheets, which is conducive to the production of planar dendrite-free lithium.

[0079] Composite lithium foils of different thicknesses can be obtained by adjusting the roller gap distance of the rolling equipment. Figure 8 The comparison of XRD spectra of composite lithium foils with thicknesses of 50, 100, 200, and 500 μm is given. It can be seen that as the thickness of the composite lithium foil becomes thinner, the intensity of the (110) crystal plane of metallic lithium gradually increases, and the intensity ratio of the (110) crystal plane to the (200) crystal plane of metallic lithium (I (110) :I (200) ) increases from 2.695 at 500μm to 7.646 at 50μm. This phenomenon can be explained by the fact that the huge shear force generated during the extrusion and rolling process promotes the directional layered arrangement of MXene. The thinner the composite lithium foil, the greater the shear force it is subjected to. At the same time, the horizontally arranged MXene induces the lithium exposed (110) crystal plane to slip under the action of pressure, resulting in a composite lithium foil with a high (110) crystal plane. The strength of the (002) crystal plane of MXene decreases with thickness.

[0080] In order to evaluate the effect of the method of the present invention on the mechanical properties of metallic lithium, hardness tests were conducted on metallic lithium sheets, composite lithium foils and comparative lithium foils. The results are as follows: Figure 9As shown in the figure, it can be seen that the hardness of the composite lithium foil of the present invention (342.3) is significantly higher than that of the metal lithium sheet (10.37) and the comparison lithium foil (29.7). This is also the reason why the composite lithium foil obtained by the method of the present invention exhibits excellent self-supporting properties.

[0081] Example 3

[0082] This example uses a method similar to that of Example 2 to adjust the MXene content and test the air stability of composite lithium foils with different MXene contents. The air stability is represented by the time the sample can maintain its metallic luster under normal temperature air environment. The longer the maintenance time, the better the air stability, as shown in Table 1 below:

[0083] Table 1. Air stability test results of composite lithium foils with different MXene contents in this invention

[0084]

[0085] It can be seen that air stability is related to the MXene content in the lithium metal. A higher MXene content forming a multilayer structure can provide more effective protection. Preferably, the mass ratio of MXene to lithium metal is greater than 1:10, more preferably greater than 1:20, and more preferably greater than 1:10. In some embodiments, the mass ratio of MXene to lithium metal is between (0.1-0.5):1.

[0086] Tensile tests were performed on composite lithium foils with different MXene contents, comparative lithium foils, and metallic lithium foils (pure lithium, 50 μm thick). The stress-strain curves are shown in Figure 2. Figure 10 As shown, Sample 3, with a MXene to lithium metal mass ratio of 1:10, exhibits the highest tensile strength (3.22 MPa), significantly outperforming both the control lithium foil (1.63 MPa) and the metal lithium foil (1.05 MPa). Samples 1 and 2, which incorporate a small amount of MXene, also exhibit significant increases in tensile strength. This indicates that the oriented layered structure of MXene formed after shear extrusion significantly enhances the mechanical properties of the composite lithium foil, resulting in improved tensile strength.

[0087] Example 4

[0088] This example provides a lithium metal battery containing the composite lithium foil of the present invention. The composite lithium foil (approximately 20 microns thick) obtained by the method of Example 2 was exposed to ambient air for 24 hours before being assembled into a button-type lithium metal battery (CR2032). The battery's charge and discharge performance at various current densities was tested. A composite lithium foil not exposed to air was used as a control.

[0089] The battery assembly method involves placing a small, 16mm diameter, punched-out composite lithium foil as the negative electrode in a glove box with a water and oxygen content below 0.1 ppm. The negative electrode, separator, and positive electrode are then placed in that order. The electrolyte (LB-092) is then added and packaged. The positive electrode material is lithium iron phosphate. Following standard laboratory testing methods, the positive electrode material, binder, and conductive carbon black are mixed in an 8:1:1 ratio. The mixture is heated with the solvent NMP to form a slurry, which is then coated onto aluminum foil, dried, and then stamped. A comparison negative electrode battery was assembled using the same method.

[0090] The electrochemical performance test conditions are as follows: using a blue battery test instrument, the assembled full battery was subjected to a 2-3.8V charge and discharge cycle at room temperature in the order of 0.2C, 0.5C, 1C, 2C, 3C, 5C, and 2C. The electrochemical test results are as follows Figure 11 As shown, the electrochemical performance of the negative electrode sheet after 24 hours of exposure to air is very similar to that of the unexposed negative electrode sheet, indicating that the composite lithium electrode of the present invention has excellent air stability, greatly reducing the stringent requirements for environmental conditions in the production process of lithium metal batteries.

[0091] MXene is a family of two-dimensional materials with similar structures and properties. Its general chemical formula can be expressed as M n+1 X n T x , wherein M is selected from one or more of Ti, V, Cr, Nb, Ta, W, Zr, Sc, Y, and Hf; X is selected from one or more of carbon, nitrogen, and boron, and 1≤ n ≤4, T x The meaning is that the surface contains functional groups. In the specific embodiment of the present invention, MXene nanosheets composed of other elements can also be selected, such as Nb3C2T x 、V2CT x 、Ti2CT x 、Ti4C3T x 、Ti3CNT x 、VNbCT x 、Ta4C3T x These MXene nanosheets have similar two-dimensional layer structures and surface functional groups, and are used to produce the same or similar effects as the method of the present invention when combined with metallic lithium or lithium alloys, and are all included in the technical solution of the present invention. Considering the ease of raw material preparation and cost, the preferred MXene is Ti3C2T3 containing fluorine functional groups. x .

[0092] When the composite lithium sheet or lithium foil used in the present invention is used as a lithium battery negative electrode, MXene nanosheets containing fluorine (F) functional groups are preferred. The resulting composite lithium electrode also has a native LiF layer on its surface, resulting from the reaction between the F-containing functional groups on the MXene surface and metallic lithium. As a lithium metal battery electrode, this LiF can become part of the solid electrolyte interface on the lithium negative electrode surface during battery cycling, guiding and homogenizing the lithium ion flow, resulting in more uniform lithium metal deposition and mitigating the problem of lithium metal dendrite growth.

[0093] In some embodiments, the component of the composite lithium of the present invention can also be a composite of metallic lithium alloy and MXene, such as lithium-magnesium alloy, lithium-aluminum alloy, etc. Through the processing method of the present invention, the MXene nanosheets produce a directional layered arrangement structure in the lithium alloy, or obtain the same or similar technical effects as the present invention, which are all within the technical solution of the present invention.

[0094] Example 5

[0095] This embodiment provides a production system for a composite lithium electrode, such as Figure 12 As shown, it includes: an inert gas system 10, a melting device 20, a cooling and solidifying device 30, an extrusion device 40, a rolling device 50, and a slitting device 60; wherein, the inert gas system 10 includes an inert gas environment chamber 11, the melting device 20 and the cooling and solidifying device 30 are arranged in the inert gas environment chamber 11, and the inert gas environment chamber 11 is used to provide an inert gas environment (such as argon) and control the water and oxygen content to prevent the molten metal lithium or lithium alloy from reacting with water and oxygen; the melting device 20 includes a heater 21, a container 22 and a stirring device 23, which are used to heat and melt the metal lithium or lithium alloy and uniformly mix it with the MXene powder to obtain a mixed lithium liquid 100; the cooling and solidifying device 30 includes at least one mold 31, which is used to cool and solidify the mixed lithium liquid 100 to obtain a composite lithium ingot.

[0096] In this embodiment, a mixed lithium solution 100 is placed in a mold, cooled and solidified, and then demolded to produce a plurality of small composite lithium ingots. These composite lithium ingots are then placed in an extrusion device 40 for extrusion to form composite lithium sheets 200. Composite lithium sheets 200 then pass through a rolling device, where they undergo multiple rolling cycles to form composite lithium foil 300. The composite lithium foil is then formed into a predetermined shape by a slitting device 60 to produce a composite lithium electrode.

[0097] In another embodiment, the composite lithium sheet 200 obtained by extrusion molding directly enters the slitting device 60 to be formed into a predetermined shape to obtain a composite lithium electrode.

[0098] In another embodiment, the composite lithium ingot can also be directly rolled several times to form a composite lithium sheet or composite lithium foil, and then enter the slitting device 60 to form a predetermined shape to obtain a composite lithium electrode.

[0099] Example 6

[0100] This embodiment provides another production system for composite lithium electrodes. The inert gas system 10, melting device 20, and cooling and solidification device 30 are the same as those in embodiment 5. The difference is that Figure 13 As shown, the present invention also includes a coating device 70 for applying a coating layer to one or both sides of the composite lithium sheet 200 before rolling. In this embodiment, double-sided coating is applied to facilitate rolling to obtain a smooth composite lithium foil. After rolling, a coating-lithium foil-coating composite layer 500 is obtained. After the coating is removed by a demolding device 80, a composite lithium foil 300 is obtained. The composite lithium foil 300 is wound into a roll by a winding device 90. The coating is preferably a polymer material. In this embodiment, it is selected from PET film. The composite lithium foil of the present invention can be easily peeled from the PET film.

[0101] In another embodiment, the film stripping device 80 may not be provided, and the resulting product is a film-lithium foil-film composite layer 500, which is then slit or rolled. Because both sides are protected by the film layer, the film-lithium foil-film composite layer 500 can be adapted for long-term storage, thereby improving the safety of the composite lithium foil. When the composite lithium foil product is needed, the film can be removed by simply tearing off the film.

[0102] In another embodiment, the composite lithium foil 300 after demoulding enters the slitting device 60 to obtain a composite lithium electrode of a predetermined shape.

[0103] Because MXene materials are lithiophilic, they can be easily mixed and dispersed in molten lithium. When preparing a composite lithium alloy foil of lithium alloy and MXene, the lithium content of the alloy ranges from 0.1 to 99.9 wt.%. For lithium electrode applications, lithium alloys with a metallic lithium content greater than 50 wt.% are preferred, and more preferably, a metallic lithium content greater than 80 wt.%. The mass ratio of the MXene to the metallic lithium in the alloy ranges from 0.01 to 1:1, preferably from 0.1 to 0.5:1.

[0104] Example 7

[0105] This embodiment provides another composite lithium electrode and a preparation method thereof, specifically a composite lithium-magnesium alloy foil, which is similar to Example 2, except that, under an argon atmosphere, the molten lithium-magnesium alloy liquid is mixed with MXene nanosheets, cooled and solidified to form a composite lithium-magnesium alloy ingot, which is then extruded and / or rolled.

[0106] More specific implementation steps include: heating 10g of lithium metal block to 300℃ under argon atmosphere, melting the lithium metal block into liquid, and adding 1g of Ti3C2Tx The nanosheets are dispersed in molten lithium metal solution and stirred for 10 minutes using a metal stirrer to ensure uniform dispersion. 2g of small pieces of magnesium metal flakes are then added and the heating temperature is raised to 650°C to gradually melt the magnesium metal flakes to form a mixed lithium-magnesium slurry. The mixed magnesium-lithium slurry is then cooled and solidified into a composite lithium-magnesium ingot, which is then extruded and / or rolled into sheets or foils.

[0107] Similarly, in another embodiment, the metal magnesium sheet is replaced with a metal aluminum sheet to obtain a composite lithium aluminum alloy foil.

[0108] Similarly, in another embodiment, Ti3C2T x Nanosheets can also be replaced by other types of MXene, such as Nb2CT x , obtaining a composite lithium-magnesium alloy foil or a composite lithium-aluminum alloy foil.

[0109] Example 8

[0110] This embodiment provides a composite lithium-magnesium alloy foil of magnesium-lithium alloy and MXene and a preparation method thereof, which is similar to Example 2, except that, under an argon atmosphere, the molten magnesium-lithium alloy liquid is mixed with MXene nanosheets, cooled and solidified to form a composite lithium-magnesium alloy ingot, which is then extruded and / or rolled.

[0111] More specific implementation steps include: heating 10g of lithium metal block to 250℃ under argon atmosphere, melting the lithium metal block into liquid, and adding 1g of Ti3C2T x The nanosheets were dispersed in molten lithium metal solution and stirred with a metal stirrer for 10 minutes to make them uniformly dispersed, and then cooled to room temperature to obtain composite lithium metal.

[0112] The magnesium metal block is then heated to 650°C-680°C until it melts into a magnesium metal liquid. A predetermined amount of the composite lithium metal is added to the magnesium metal liquid and stirred to form a composite magnesium-lithium alloy liquid. The alloy is then cooled to room temperature to form a composite magnesium-lithium alloy. Preferably, the composite magnesium-lithium alloy contains 1% to 20% lithium metal by weight and 0.1% to 10% MXene by weight. The resulting composite magnesium-lithium alloy is then extruded and / or rolled to form a composite magnesium-lithium alloy foil.

[0113] In a specific embodiment, the composite magnesium-lithium alloy has a lithium metal content of 16% by mass, a MXene content of 8% by mass, and a magnesium metal content of 76% by mass.

[0114] Example 9

[0115] This embodiment provides a composite electrode sheet, specifically a negative electrode sheet A20, comprising a composite lithium foil A22 and a negative electrode current collector A21 (current collector layer). The composite lithium foil A22 is rolled and laminated with a metallic copper foil. In a specific embodiment, during the rolling step, a PET film is applied to one side of the composite lithium foil, and a metallic copper foil is applied to the other side to form a composite layer. The PET film is then removed to obtain a composite lithium electrode (negative electrode sheet) containing a copper foil current collector.

[0116] This embodiment also provides a battery, including a positive electrode sheet A10, a negative electrode sheet A20 and a separator A30, whose structure is as follows: Figure 14 As shown, the separator A30 is arranged between the positive electrode sheet A10 and the negative electrode sheet A20. The positive electrode sheet A10 includes a positive electrode collector A11 and a positive electrode material layer A12; the negative electrode sheet A20 includes a negative electrode collector A21 and a composite lithium foil A22 of the present invention.

[0117] In another embodiment, the positive electrode sheet A10 and the negative electrode sheet A20 can also be stacked by winding or laminating. Figure 15 As shown, in this embodiment, the positive electrode current collector A11 of the positive electrode sheet A10 has positive electrode material layers A12 on both sides, and the negative electrode current collector A21 of the negative electrode sheet A20 has composite lithium foil A22 of the present invention on both sides.

[0118] The positive electrode current collector A11 is typically a metal foil, such as aluminum foil or titanium foil. The positive electrode material layer A12 is a film layer containing a positive electrode material with an electrochemically active substance. Positive electrode materials include lithium iron phosphate, ternary materials, lithium cobalt oxide, lithium manganese oxide, and high-nickel ternary materials. This layer is formed by known preparation methods, including mixing the positive electrode material, a conductive agent, and a binder in predetermined proportions, adding a solvent to form a slurry, and then applying the slurry to the surface of the positive electrode current collector, followed by drying and rolling. The negative electrode current collector A21 is also typically a metal foil, such as copper foil. The composite lithium foil of the present invention can be directly used as the negative electrode material in lithium metal batteries.

[0119] Since the composite lithium foil of the present invention has good mechanical properties, in some embodiments, the composite lithium foil can be directly used as a negative electrode sheet without providing a negative electrode current collector, such as the button battery assembled in Example 4.

[0120] The diaphragm A30 usually chooses polyolefin porous membranes, such as polypropylene (PP) or polyethylene (PE) porous membranes. In some batteries, glass fiber diaphragms, solid electrolyte diaphragms, etc. can also be selected.

[0121] In some embodiments, the battery of this embodiment further comprises a liquid electrolyte, resulting in a liquid lithium metal battery.

[0122] In some embodiments, the battery of this embodiment further comprises a semi-solid electrolyte, resulting in a semi-solid lithium metal battery.

[0123] In some embodiments, the separator A30 in the battery of this embodiment is a solid electrolyte separator, and the resulting battery is a lithium metal solid-state battery.

[0124] Example 10

[0125] This embodiment provides a lithium metal solid-state battery having a structure similar to that of Example 9, wherein the separator A30 is a solid electrolyte separator. The solid electrolyte separator materials include: polymer electrolytes, oxide electrolytes, or sulfide electrolytes. Polymer electrolytes are composed of a polymer matrix (such as polyester, polyenzyme, and polyamine) and a lithium salt (such as LiClO4, LiAsF4, LiPF6, and LiBF4). Oxide electrolytes include perovskite, NASICON, LISICON, and garnet types. Sulfide electrolytes include thiophosphates.

[0126] In a specific embodiment, the positive electrode material in the positive electrode sheet A10 of the solid-state battery is a high-nickel ternary material, the positive electrode current collector A12 is aluminum foil, the negative electrode current collector in the negative electrode sheet A20 is copper foil, and the composite lithium foil of the present invention is the negative electrode material; the solid electrolyte membrane is a perovskite-type oxide electrolyte.

[0127] Example 11

[0128] This embodiment provides a composite lithium electrode, specifically a positive electrode sheet A40, including a composite lithium foil A41 of the present invention, an electrochemically active material layer A42 and a current collector layer A43; Figure 16 As shown, the composite lithium foil A41 is in surface contact with the electrochemically active material layer A42, and the electrochemically active material layer A42 is in surface contact with the current collector layer A43.

[0129] As described in Example 8, the electrochemically active material contained in the electrochemically active material layer A42 is a positive electrode material or a negative electrode material; and the current collector layer A43 may be a positive electrode current collector or a negative electrode current collector.

[0130] In a specific embodiment, the composite lithium electrode in this embodiment is a composite lithium foil A41 provided on the surface of the positive electrode material layer A12 in the positive electrode sheet A10 in Example 8; preferably, the thickness of the composite lithium foil A41 is between 1 and 20 μm; more preferably, between 1 and 10 μm; in a specific embodiment, it is 5 μm.

[0131] In another embodiment, the electrochemically active material layer A42 in the composite lithium electrode A40 of this embodiment may also be a negative electrode material, such as graphite, silicon, silicon-carbon material, etc., and the current collector layer A43 is a negative electrode current collector, such as copper foil.

[0132] The foregoing descriptions of specific exemplary embodiments of the present invention are for purposes of illustration and description. These descriptions are not intended to limit the present invention to the precise forms disclosed, and it is apparent that many modifications and variations are possible in light of the foregoing teachings. The exemplary embodiments have been selected and described for the purpose of explaining the specific principles of the present invention and their practical application, thereby enabling those skilled in the art to realize and utilize a variety of exemplary embodiments of the present invention and various options and variations. The scope of the present invention is intended to be defined by the claims and their equivalents.

Claims

1. A composite lithium electrode, characterized in that The composite lithium electrode includes a composite lithium foil, which includes a matrix of metallic lithium or a lithium alloy and MXene nanosheets; the MXene nanosheets are arranged in a directional layered structure in the matrix.

2. The composite lithium electrode according to claim 1, wherein The thickness of the composite lithium foil is ≤100 μm.

3. The composite lithium electrode according to claim 2, wherein The thickness of the composite lithium foil is ≤50 μm.

4. The composite lithium electrode according to claim 2, wherein The thickness of the composite lithium foil is ≤20 μm.

5. The composite lithium electrode according to claim 2, wherein The thickness of the composite lithium foil is ≤10 μm.

6. The composite lithium electrode according to claim 1, wherein The lithium alloy is a lithium aluminum alloy or a lithium magnesium alloy.

7. The composite lithium electrode according to claim 1, wherein The composite lithium foil is formed into the oriented layered structure by extrusion or rolling.

8. The composite lithium electrode according to claim 1, wherein The surface of the composite lithium foil is covered with two-dimensional nanosheets.

9. A composite lithium electrode, characterized in that The composite lithium electrode comprises: a composite lithium foil according to any one of claims 1 to 8; and a current collector layer in surface contact with the composite lithium foil; Alternatively, the composite lithium electrode comprises: a composite lithium foil according to any one of claims 1 to 8; an electrochemically active material layer in surface contact with the composite lithium foil; and a current collector layer in surface contact with the electrochemically active material layer.

10. The composite lithium electrode according to claim 9, wherein The current collector layer is a metal foil.

11. The composite lithium electrode according to claim 10, wherein The metal foil is copper foil, stainless steel foil, nickel foil or titanium foil.

12. A battery, characterized in that: The method comprises the composite lithium electrode according to any one of claims 1 to 11.

13. A production system for producing the composite lithium electrode according to any one of claims 1 to 11, characterized in that: include: Inert gas system, melting device, cooling and solidification device, extrusion device and / or rolling device, slitting device; The inert gas system comprises an inert gas environment chamber, wherein the melting device and the cooling and solidifying device are arranged in the inert gas environment chamber; The melting device includes a heater, a container and a stirring device, which is used to heat and melt metallic lithium or lithium alloy and mix it with MXene powder to obtain a mixed lithium liquid; The cooling and solidifying device includes a mold for cooling and solidifying the mixed lithium liquid to obtain a composite lithium ingot; The extrusion device is used to extrude the composite lithium ingot into a composite lithium sheet or a composite lithium foil; The rolling device is used to roll the composite lithium ingot into a composite lithium foil; or to roll the extruded composite lithium sheet into a composite lithium foil; The slitting device is used to slit the composite lithium sheet or the composite lithium foil into predetermined shapes.

14. An electrical device, characterized in that: Comprising the composite lithium electrode according to any one of claims 1 to 11; or, the battery according to claim 12.

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